Large-Scale 

Offshore 

Wind Power 

in the United 

States

ASSESSMENT OF

OPPORTUNITIES

AND BARRIERS

September 2010
NOTICE

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Large-Scale 

Offshore 

Wind Power 

in the United 

States

ASSESSMENT OF

OPPORTUNITIES

AND BARRIERS

September 2010

NREL/TP-500-40745

Authors:

Walter Musial, NREL

Bonnie Ram, Energetics
Acknowledgements

The National Renewable Energy Laboratory (NREL) would like to acknowledge the experts in the wind community, too numerous to 

mention, that have played an important role in the publication of this report. NREL also thanks the U.S. Department of Energy, Energy 

Efficiency and Renewable Energy, Office of Wind and Water Power Technologies for their financial and technical support for the research 

and production of this report.

Major chapter contributors in alphabetical order include: Karen Bushaw-Newton,1 Sandy Butterfield,2 Dennis Elliot,2 Fort Felker,2 Maureen Hand,2

 Steve Haymes,2 Donna Heimiller,2 Alan Laxson,2 Nora Phillips,1 Russell Raymond,1 Amy Robertson,2 Marc Schwartz,2 Walter 

Short,2 Aaron Smith,3 Wendy Wallace.1

Peer Reviewers in Alphabetical Order: Maureen Bornholdt,4 Fort Felker,2 Jeremy Firestone,5 Patrick Gilman,6 Maureen Hand,2 Mary Hallisey-Hunt,7

 Laurie Jodziewicz,8 Jason Jonkman,2 Willett Kempton,9 Andrew Levitt,9 Jim Manwell,10 Bonnie McCay,11 Rachel Pachtner,12

Aaron Smith,3 Laura Smith Morton,6 Tim Redding,4 Amy Robertson,2 John Rodgers,13 Heidi Souder.2

Report Editors and Production Coordinator: Kathleen O’Dell2 and Rene Howard.14

Graphic Images and Figures: NREL and Energetics Incorporated.

 Energetics Incorporated, Washington, D.C.

 National Renewable Energy Laboratory, Golden, Colorado

 Sustainable Power Consulting

 Bureau of Ocean Energy Management, Regulation and Enforcement

 University of Delaware

 U.S. Department of Energy

 Georgia Institute of Technology

 NRG Bluewater Wind

 University of Delaware

 University of Massachusetts

 Rutgers University

 Cape Wind Associates

 Union of Concerned Scientists

 WordProse, Inc.

1

2

3

4

5

6

7

8

9

10

11

12

13

14
iii

Table of Contents

List of Figures.............................................................................................................................. vii

List of Tables................................................................................................................................ ix

Acronyms and Abbreviations...................................................................................................... x

1.0 Executive Summary................................................................................................................ 1

1.1 Opportunities in Offshore Wind Power................................................................................ 1

1.2 Status of the Offshore Wind Industry ................................................................................... 2

1.3 A Powerful U.S. Resource.................................................................................................... 3

1.4 Technology Status and Trends.............................................................................................. 4

1.5 Economics of Offshore Wind Power.................................................................................... 6

1.6 Regulatory Pathways for Siting and Permitting.................................................................... 7

1.7 Environmental and Socioeconomic Risks ............................................................................ 8

1.8 Findings and Conclusions..................................................................................................... 9

2.0 Rationale for Offshore Wind ............................................................................................... 10

2.1 Energy Supply..................................................................................................................... 10

2.2 The Environment ................................................................................................................ 10

2.3 The Economy...................................................................................................................... 12

2.4 The Contribution of Offshore Wind ................................................................................... 12

2.5 Findings and Conclusions................................................................................................... 17

2.6 References........................................................................................................................... 18

3.0 Industry Overview and U.S Activities............................................................................... 22

3.1 Historical Context............................................................................................................... 22

3.2 Current Offshore Wind Activity ......................................................................................... 22

3.3 Worldwide Offshore Wind Projections .............................................................................. 26

3.3.1 Europe.......................................................................................................... 26

3.3.2 Other Parts of the World.............................................................................. 27

3.4 U.S. Offshore Wind Project Overview ............................................................................... 28

3.5 U.S. Policy Overview ......................................................................................................... 33

3.5.1 National and Regional Organizations.......................................................... 34

3.5.2 State Initiatives............................................................................................. 34

3.6 Description of Offshore Wind Supply Chain...................................................................... 41

3.6.1 Turbine Suppliers......................................................................................... 41

3.6.2 Key Components.......................................................................................... 42

3.6.3 Balance of Station........................................................................................ 42

3.6.4 Vessels, Harbors, and Local Economic Activity ......................................... 42

3.7 Findings and Conclusions................................................................................................... 43

3.8 References........................................................................................................................... 44

4.0 Offshore Wind Energy Resources in the United States..................................................... 53

4.1 Wind Resource Methodology ............................................................................................. 53

4.1.1 Mesoscale Modeling .................................................................................... 53

4.1.2 Wind Turbine Array Density ....................................................................... 56

4.1.3 Wind Speed Gradients ................................................................................. 56

4.2 Offshore Wind Regions ...................................................................................................... 56

4.2.1 East Coast: New England............................................................................. 56
iv

4.2.2 East Coast: Mid-Atlantic States................................................................... 57

4.2.3 East Coast: The South Atlantic Bight.......................................................... 57

4.2.4 West Coast: California................................................................................. 57

4.2.5 West Coast: The Pacific Northwest ............................................................. 57

4.2.6 Great Lakes Region...................................................................................... 57

4.2.7 Gulf of Mexico............................................................................................. 58

4.2.8 Hawaii.......................................................................................................... 58

4.2.9 Alaska .......................................................................................................... 58

4.3 Offshore Wind Resource Potential ..................................................................................... 59

4.3.1 Coastal State Boundaries and Distance from Shore .................................... 63

4.3.2 Wind Resource Information......................................................................... 64

4.3.3 Bathymetry................................................................................................... 64

4.4 Wind Resource Research Trends........................................................................................ 64

4.4.1 Resource Mapping and Quantification ........................................................ 65

4.4.2 Metocean Validation................................................................................... 65

4.4.3 Remote Sensing ........................................................................................... 65

4.5 Findings and Conclusions................................................................................................... 66

4.6 References........................................................................................................................... 67

5.0 Offshore Wind Energy Technology—Status and Trends ................................................. 69

5.1 Offshore Wind Technology Status...................................................................................... 69

5.2 Offshore Wind Technology Barriers .................................................................................. 72

5.2.1 High Cost ..................................................................................................... 72

5.2.2 Technology Immaturity ............................................................................... 72

5.2.3 Limited Resource Area ................................................................................ 72

5.2.4 High Risk and Uncertainty........................................................................... 73

5.3 Technology Trends ............................................................................................................. 73

5.3.1 Wind Turbine Technology........................................................................... 73

5.3.1.1 Optimized Offshore Wind Turbine Systems............................................. 73

5.3.1.2 Advanced Rotors and Towers................................................................... 75

5.3.1.3 Drivetrains................................................................................................. 76

5.3.1.4 Reliability.................................................................................................. 77

5.3.1.5 Controls and Condition Monitoring.......................................................... 77

5.3.2 Offshore Wind Substructure Technology .................................................... 78

5.3.2.1 Substructure Technology Overview ......................................................... 78

5.3.2.2 Shallow-Water Substructures.................................................................... 80

5.3.2.3 Transitional Technology ........................................................................... 82

5.3.3 Floating Wind Turbine Technology............................................................. 85

5.3.4 Dynamic Computer Simulation Modeling................................................... 90

5.3.5 Grid and Electrical Distribution Systems .................................................... 90

5.3.6 Arrays and Array Effects............................................................................. 91

5.3.7 Regional Issues............................................................................................ 92

5.3.7.1 Ice Load Resistance .................................................................................. 92

5.3.7.2 Hurricane Resiliency................................................................................. 93

5.3.8 Logistics and Infrastructure ......................................................................... 93

5.3.9 Research Facilities for Field Testing ........................................................... 94

5.3.10 Certification and Standards........................................................................ 95
v

5.3.11 Metocean Characterization ........................................................................ 95

5.4 Synergies with Other Offshore Industries........................................................................... 96

5.5 Findings and Conclusions................................................................................................... 97

5.6 References........................................................................................................................... 98

6.0 Offshore Wind Economics ................................................................................................. 108

6.1 Offshore Wind Capital Cost.............................................................................................. 109

6.1.1 Market Studies........................................................................................... 109

6.1.2 Capital Cost Breakdown ............................................................................ 114

6.2 Offshore Wind Cost of Energy ......................................................................................... 116

6.3 Projected U.S. Offshore Wind Deployment ..................................................................... 119

6.3.1 Regional Energy Deployment System....................................................... 120

6.3.2 Offshore Generation Capacity Expansion Modeling................................. 121

6.3.3 Offshore Penetration for the 20% Wind by 2030 Scenario ....................... 121

6.3.4 Restricted Coastal Grid and High Gas Pricing .......................................... 123

6.4 Findings and Conclusions................................................................................................. 127

6.5 References......................................................................................................................... 128

7.0 Federal and State Regulatory Pathways for Siting and Permitting Offshore Wind 

Facilities..................................................................................................................................... 133

7.1 Introduction....................................................................................................................... 133

7.2 Ocean Policies and Jurisdictions....................................................................................... 133

7.2.1 Jurisdiction................................................................................................. 133

7.2.2 Ocean Policies......................................................................................... 136

7.3.1 MMS Regulatory Paradigm....................................................................... 138

7.3.2 Leasing Process.......................................................................................... 141

7.3.2.1 Commercial Lease .................................................................................. 141

7.3.2.2 Limited Lease.......................................................................................... 145

7.4 NEPA Compliance and the BOEM Program.................................................................... 147

7.4.1 The PEIS.................................................................................................... 148

7.4.2 Federal Regulatory Nexus and NEPA Compliance ................................... 148

7.4.3 Cape Wind History: Challenges and Lessons Learned.............................. 150

7.5 State Permitting Challenges.............................................................................................. 153

7.5.1 Great Lakes................................................................................................ 154

7.6 Structural Safety Certification .......................................................................................... 155

7.6.1 BOEM Infrastructure Authority.............................................................. 155

7.6.2 Offshore Codes and Standards................................................................... 155

7.6.3 Type versus Project Certification............................................................... 157

7.6.4 Structural Safety Compliance .................................................................... 158

7.7 Findings and Conclusions................................................................................................. 160

7.8 References......................................................................................................................... 162

8.0 Environmental and Socioeconomic Risks of..................................................................... 169

Offshore Wind Projects............................................................................................................ 169

8.1 Introduction....................................................................................................................... 169

8.2 Comparing Analytical Frameworks.................................................................................. 170

8.2.1 NEPA-Related Approaches ....................................................................... 170

8.2.2 An Integrated Risk Framework.................................................................. 173

8.2.2.1 Tier 1: Sector Risk Analysis................................................................... 174
vi

8.2.2.2 Tier 2: Extended Risk Analysis .............................................................. 175

8.2.2.3 Life-Cycle Risk....................................................................................... 175

8.2.2.4 Cumulative Risks.................................................................................... 177

8.2.2.5 Public Concerns...................................................................................... 178

8.2.2.6 Climate Change....................................................................................... 179

8.2.2.7 Comparative Analysis and Determining Risk Tolerability..................... 179

8.2.2.8 Tier 3: Management Options and Strategy ............................................. 179

8.2.2.9 Siting Strategies...................................................................................... 180

8.2.2.10 Adaptive Management and Monitoring Programs............................... 181

8.3 Sectoral Risks: Considering the European Experience..................................................... 181

8.4 Avian Risks....................................................................................................................... 185

8.5 Other Flying Animals ....................................................................................................... 190

8.6 Fish and Benthos Risks..................................................................................................... 191

8.7 Marine Mammals.............................................................................................................. 194

8.8 Turbine Fluid Leakage and Containment ......................................................................... 195

8.9 Ship and Air Collisions..................................................................................................... 195

8.10 Socioeconomic Risks...................................................................................................... 196

8.11 Visual Effects and Aesthetics ......................................................................................... 198

8.12 Findings and Conclusions............................................................................................... 200

8.13 References....................................................................................................................... 202

Appendix A: Interagency Coordination ................................................................................. 211

Appendix B: Summary of Studies Conducted on Resource Areas as Part of the Cape Wind 

Environmental Impact Statement ........................................................................................... 215
vii

List of Figures

Figure 1-1. Nameplate generating capacity of offshore wind projects (1991–2010) ..................... 2

Figure 1-2. United States offshore wind resource by region and depth for annual average wind 

speed sites above 7.0 m/s.................................................................................................... 3

Figure 1-3. Status of offshore wind energy technology.................................................................. 5

Figure 2-1. Concentrations of important long-lived greenhouse gases in the atmosphere 

(given in ppm and ppb)..................................................................................................... 11

Figure 2-2. Global CO2 emissions for 1940 to 2000 and emissions ranges for categories of 

stabilization scenarios from 2000 to 2100 are shown in the left panel. The relationship 

between the stabilization target and global average temperature increase above 

preindustrial levels is shown in the right panel................................................................. 11

Figure 2-3. Coastal versus inland state electric rates (2008) ........................................................ 15

Figure 3-1. Nameplate generating capacity of offshore wind projects (1991–2010) ................... 24

Figure 3-2. Installed offshore wind capacity by country (January 2010)..................................... 24

Figure 3-3. Offshore projects showing capacity, water depth, and distance to shore................... 25

Figure 3-4. Middelgrunden Wind Plant (HC Sorensen, Middelgrunden Wind Turbine 

Cooperative, NREL/Pix 17855)........................................................................................ 25

Figure 3-5. Proposed U.S. offshore wind projects and capacity showing projects with significant 

progress............................................................................................................................. 29

Figure 4-1. U.S. land-based and offshore wind resource estimates at 50-m height (wind classes 

3–7) ................................................................................................................................... 54

Figure 4-2. U.S. offshore wind speed estimates at 90-m height................................................... 55

Figure 4-3. Massachusetts offshore wind speed estimates at 90-m elevation .............................. 55

Figure 5-1. Estimated life-cycle cost breakdown for a typical baseline offshore wind project.... 71

Figure 5-2. Why larger turbines might lower overall cost............................................................ 74

Figure 5-3. Substructure technology classes for offshore wind turbines...................................... 78

Figure 5-4. Cost of offshore wind turbine substructures with water depth .................................. 79

Figure 5-5. Shallow-water foundation technology ....................................................................... 81

Figure 5-6. Transitional substructure technology ......................................................................... 83

Figure 5-7. Repower 5-MW turbine installed on jacket substructure (left, Talisman Energy, 

NREL/PIX 17883) and load-out to Beatrice Field (right, Talisman Energy, NREL/PIX 

17884) ............................................................................................................................... 84

Figure 5-8. Transitional substructure technology under development: BARD 1 foundation 

structures awaiting loadout with 5-MW AREVA and REpower test turbines in 

background (Gary Norton, DOE NREL/PIX 17889); submerged four-pile jacket with 

transition to tube tower on Talisman Energy project with Repower 5-MW turbine (right, 

Talisman Energy, NREL/PIX 17885) (MacAskill 2005) ................................................. 85

Figure 5-9. First operating deepwater floating wind turbine: Statoil Hywind 2.3-MW prototype 

during load-out (left) and installed on station (right) (Photos courtesy of Statoil)........... 86

Figure 5-10. Stability triangle for classifying floating substructures according to method of 

achieving static stability.................................................................................................... 87
viii

Figure 5-11. Floating deepwater platform concepts: (1) semisubmersible Dutch tri-floater 

(Bulder et al. 2002); (2) spar buoy with two tiers of guy wires (Lee 2005); (3) three-arm 

mono-hull tension-leg platform (TLP) by Glosten Associates (2010); (4) concrete TLP 

with gravity anchor (Fulton, Malcolm, and Moroz 2006); (5) deepwater spar 

(Sway 2010)...................................................................................................................... 88

Figure 5-12. Expertise and experience for offshore wind development....................................... 96

Figure 6-1. Offshore wind plant capital cost per kilowatt .......................................................... 109

Figure 6-2. Effect of water depth on capital cost per kilowatt.................................................... 111

Figure 6-3. Effect of distance from shore on capital cost per kilowatt....................................... 112

Figure 6-4. Effect of project size on capital cost per kilowatt.................................................... 113

Figure 6-5. Capital cost breakdowns for offshore wind plants in shallow water ....................... 115

Figure 6-6. Life-cycle cost breakdowns for offshore wind plants in shallow water................... 117

Figure 6-7. LCOE sensitivity with respect to capital cost, discount rate, and wind speed......... 118

Figure 6-8. Cumulative wind generation capacity associated with 20% wind by 2030............. 122

Figure 6-9. Comparison of U.S. average natural gas price increase from Annual Energy Outlook 

2006 with 3% annual increase ........................................................................................ 124

Figure 6-10. 2030 capacity in a gas price and siting restriction comparison.............................. 125

Figure 6-11. 2030 offshore wind capacity under a high gas price, siting-restricted scenario .... 126

Figure 7-1. Schematic of state, federal, and international ocean jurisdictions........................... 135

Figure 7-2. MMS timeline of rule development activities.......................................................... 139

Figure 7-3. OCS renewable energy process................................................................................ 143

Figure 7-4. OCS interim policy limited lease areas.................................................................... 146

Figure 7-5. Cape Wind history and timeline............................................................................... 151

Figure 7-6. Relationships among the USACE Section 10 permit, CZMA consistency 

determination, and the NEPA EIS process (timelines are approximations)................... 154

Figure 8-1. Offshore wind farm activity and socioeconomically relevant interactions.............. 172

Figure 8-2. A framework for integrated risk analysis of gigawatt-scale wind energy 

deployments.................................................................................................................... 176

Figure 8-3. Potential effects of offshore wind farms on birds.................................................... 186

Figure 8-4. Biological flyways through the continental United States....................................... 187

Figure 8-5. Eider distribution at Horns Rev................................................................................ 188

Figure 8-6. Previsualization of the Horns Rev I wind farm from Blåvands Huk (top) and actual 

post-construction photograph from Blåvands Huk (bottom).......................................... 199
ix

List of Tables

Table 1-1. Summary of Key Project, Resource, and Technology Attributes ................................. 6

Table 2-1. Energy Production by Wind Power Class................................................................... 13

Table 3-1. Summary of Current Offshore Projects Installed as of the Second Quarter of 2010 .. 23

Table 3-2. Offshore Development in Permitting and Under Construction................................... 26

Table 3-3. Selected Offshore Wind Energy Projects (Federal and State Waters) ........................ 30

Table 3-4. Electric Energy Use and Offshore Wind Energy State Activity ................................. 35

Table 3-5. Commercial Offshore Wind Turbines......................................................................... 41

Table 4-1. Offshore Wind Resource Potential by Region and Water Depth for Areas with Annual 

Average Wind Speeds 8.0 m/s or Greater at 90-m Elevation........................................... 59

Table 4-2. Offshore Wind Resource Potential by Region and Water Depth for Areas with Annual 

Average Wind Speeds 7.0 m/s or Greater at 90-m Elevation........................................... 59

Table 4-3. State Offshore Wind Resource Potential (in Gigawatts) by Wind Speed, Water Depth, 

and Distance from Shore................................................................................................... 60

Table 4-3 (continued). Offshore Wind Resource Potential (in Gigawatts) by Wind Speed, State, 

Water Depth, and Distance from Shore ............................................................................ 61

Table 4-3 (continued). Offshore Wind Resource Potential (in Gigawatts) by Wind Speed, State, 

Water Depth, and Distance from Shore ............................................................................ 62

Table 4-3 (concluded). Offshore Wind Resource Potential (in Gigawatts) by Wind Speed, State, 

Water Depth, and Distance from Shore ............................................................................ 63

Table 5-1. Wind Turbines Rated Above 5 MW, Planned or Under Development....................... 75

Table 6-1. Estimation Methodologies for Future Offshore Wind Project Costs (US$2008)...... 110

Table 6-2. Descriptions of Cost Breakdown Categories............................................................. 114

Table 6-3. Announced PPA Prices for U.S. Projects under Development ................................. 119

Table 7-1. Major Provisions in the Final Renewable Energy Framework ................................. 140

Table 7-2. Selected Relevant Laws............................................................................................. 152

Table 8-1. Classification of Impacts in a NEPA Document ....................................................... 173

Table 8-2. Summary of European Large-Scale, Multidisciplinary Studies of the Environmental 

Effects of Offshore Wind Farms..................................................................................... 184

Table 8-3. Intensities of Different Anthropogenic Sounds......................................................... 192

Table A-1. Applicable Laws and Responsible Agencies Related to Renewable Energy 

Development on the Outer Continental Shelf................................................................. 211

Table B-1. Cape Wind Project Studies....................................................................................... 215
x

Acronyms and Abbreviations

ANSI American National Standards Institute

AOWEC Atlantic Offshore Wind Energy Consortium

API American Petroleum Institute

AWEA American Wind Energy Association

BACI Before and After Construction Impact

BOEM Bureau of Ocean Energy Management, Regulation and Enforcement

BOS balance of station

CAD Canadian dollar

CA-OWEE Concerted Action on Offshore Wind Energy in Europe

CEQ Council on Environmental Quality

C-MAN Coastal-Marine Automated Network

CESA Clean Energy States Alliance

CMSP coastal and marine spatial planning

CO2 carbon dioxide

COD Concerted Action for Offshore Wind Energy Deployment

COE cost of energy

CVA certified verification agent

CWA Clean Water Act

CZMA Coastal Zone Management Act

DKK Danish krone (currency)

DNV Det Norske Veritas

DOE U.S. Department of Energy

DOI U.S. Department of the Interior

EA environmental assessment

EEZ exclusive economic zone

EIA Energy Information Administration

EIS environmental impact statement

EMFs electromagnetic fields

EPA U.S. Environmental Protection Agency

EPAct Energy Policy Act of 2005

ESP electric service platform

EU European Union

EWEA European Wind Energy Association

FDR Facility Design Report

FEIS Final Environmental Impact Statement 

FERC Federal Energy Regulatory Commission

FIR Fabrication and Installation Report

FIT feed-in tariff
xi

FLOWW Fisheries Liaison with Offshore Wind and Wet Renewables

FONSI Finding of No Significant Impact

FWS U.S. Fish & Wildlife Service

GAP General Activities Plan

GDP gross domestic product

GHGs greenhouse gases

GIS geographic information system

GL Germanischer Lloyd

GLWC Great Lakes Wind Collaborative

GLO General Land Office (Texas)

GW gigawatts

GWEC Global Wind Energy Council

Hg mercury

IEA International Energy Agency

IEC International Electrotechnical Commission

IHAs Incidental Harassment Authorizations

IPCC Intergovernmental Panel on Climate Change

ISO International Standards Organization

JWGL JW Great Lakes Wind, LLC

km kilometer

km2 square kilometer

kV kilovolt

kW kilowatt

kWh kilowatt-hour

LCOE levelized cost of energy

LEEDCo Lake Erie Energy Development Corporation

LOS Convention United Nations Convention on the Law of the Sea

m meter

MASSCEC Massachusetts Clean Energy Center

MBTA Migratory Bird Treaty Act

met meteorological

MIT Massachusetts Institute of Technology

MLLW mean lower low water 

mm millimeter

MMPA Marine Mammal Protection Act

MMS Minerals Management Service

MOU memorandum of understanding

MTC Massachusetts Technology Collaborative
xii

NAERC North American Electric Reliability Council

NAS National Academies of Science

NEMS National Energy Modeling System

NEPA National Environmental Policy Act

NERI National Environmental Research Institute

NGOs nongovernmental organizations

NHPA National Historic Preservation Act

NIST National Institute of Standards and Technology

NJCEP New Jersey Commerce, Economic Growth, and Tourism Commission

NJDEP New Jersey Department of Environmental Protection

nm nautical mile

NMFS National Marine Fisheries Service (also NOAA Fisheries)

NRC National Research Council

NREL National Renewable Energy Laboratory

NOAA National Oceanic and Atmospheric Administration

NOK Norwegian krone (currency)

NOx nitrogen oxides

NWS National Weather Service

NYPA New York Power Authority

O&M operations and maintenance

OCS Outer Continental Shelf

OCSLA Outer Continental Shelf Lands Act

OECD Organisation for Economic Co-operation

OEM original equipment manufacturer

OffshoreWindDC Offshore Wind Development Coalition

OVC other variable costs

OWWG Offshore Wind Working Group

PPA power purchase agreement

PEIS Programmatic Environmental Impact Statement

PINCS inspection procedures

ppb parts per billion

ppm parts per million

PSC Public Service Commission

R&D research and development

RECs renewable energy credits

RECOFF Requirements for Offshore Wind Turbines

ReEDS Regional Energy Deployment System

REF Renewable Energy Futures

RFI request for information

RFP request for proposals

RGGI Regional Greenhouse Gas Initiative

RIPUC Rhode Island Public Utilities Commission

Risø DTU Risø DTU National Laboratory for Sustainable Energy
xiii

ROD Record of Decision

rpm revolutions per minute

RPS renewable portfolio standard

s second

sap Site Assessment Plan

SAMP Special Area Management Plan

SCADA supervisory control and data acquisition

SEPAs State Environmental Policy Acts

SO2 sulfur dioxide

SRES Special Report on Emission Scenarios (IPCC) 

TC88 Technical Committee 88

TLP tension-leg platform

TRB Transportation Research Board

TWh terawatt-hour 

UNC University of North Carolina

UNESCO United Nations Educational, Scientific, and Cultural Organization

USACE U.S. Army Corps of Engineers

USOWC U.S. Offshore Wind Collaborative

V volt

VLA vertical-load anchors

WinDS Wind Deployment System or 

WWPP Wind &Water Power Program (DOE)
xiv

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1 

1.0 Executive Summary

Offshore wind power is poised to deliver an essential 

contribution to a clean, robust, and diversified U.S. 

energy portfolio. Capturing and using this large and 

inexhaustible resource has the potential to mitigate 

climate change, improve the environment, increase 

energy security, and stimulate the U.S. economy. 

The United States is now deliberating an energy 

policy that will have a powerful impact on the nation’s 

energy and economic health for decades to come. This 

report provides a broad understanding of today’s wind industry and the offshore resource, as well 

as the associated technology challenges, economics, permitting procedures, and potential risks 

and benefits. An appreciation for all sides of these issues will help to build an informed national 

dialog and shape effective national policies.

1.1 Opportunities in Offshore Wind Power

In common with other clean, renewable, domestic 

sources of energy, offshore wind power can help to 

build a diversified and geographically distributed 

U.S. energy mix, offering security against many 

energy supply emergencies—whether natural or 

man-made. Wind power also emits no carbon 

dioxide (CO2) or other harmful emissions that 

contribute to climate change, ground-level pollution, 

or public health issues. 

The United States’ offshore wind energy resources 

can significantly increase the wind industry’s 

contribution to the nation’s clean energy portfolio. 

The United States is fortunate to possess a large and accessible offshore wind energy resource. 

Wind speeds tend to increase significantly with distance from land, so offshore wind resources 

can generate more electricity than wind resources at adjacent land-based sites. The National 

Renewable Energy Laboratory (NREL) estimates that U.S. offshore winds have a gross potential 

generating capacity four times greater than the nation’s present electric capacity. While this 

estimate does not consider siting constraints and stakeholder inputs, it clearly indicates that the 

U.S. offshore wind capacity is not limited by the magnitude of the resource. 

Developing the offshore wind resource along U.S. coastlines and in the Great Lakes would help 

the nation to:

• Achieve 20% of its electricity from wind by 2030. In assessing the potential for supplying 

20% of U.S. electricity from wind energy by 2030, NREL’s least-cost optimization model 

found that 54 gigawatts (GW)1

 

1 1 gigawatt = 1,000 megawatts

 of added wind capacity could come from offshore wind. 

"Wind power isn't the silver bullet that 

will solve all our energy challenges—

there isn't one. But it is a key part of a 

comprehensive strategy to move us 

from an economy that runs on fossil 

fuels to one that relies on more 

homegrown fuels and clean energy."

President Barack Obama,

April 2010

Under conservative assumptions 

about transmission, fossil fuel supply, 

and supply chain availability, the 

United States could feasibly build 54 

GW of offshore wind power by 2030.

20% Wind Energy by 2030,

U.S. Department of Energy, 

July 2008

*Based on the model scenario optimizing total delivered 

cost for conventional and wind resources. For other 

assumptions, see www.nrel.gov/docs/fy08osti/41869.pdf

 
2

Achieving 20% wind would provide significant benefits to the nation, such as increased 

energy security, reduced air and water pollution, and the stimulation of the domestic 

economy. 

• Revitalize its manufacturing sector. Building 54 GW of offshore wind energy facilities 

would generate an estimated $200 billion in new economic activity and create more than 

43,000 permanent, well-paid technical jobs in manufacturing, construction, engineering, 

operations and maintenance. Extrapolating from European studies, NREL estimates that 

offshore wind will create more than 20 direct jobs for every megawatt produced in the 

United States.

• Provide clean power to its coastal demand centers. High winds abound just off the coasts 

of 26 states. More specifically, suitable wind resources exist near large urban areas where 

power demand is steadily growing, electric rates are high, and space for new, land-based 

generation and transmission facilities is severely limited. These characteristics provide 

favorable market opportunities for offshore wind to compete effectively in coastal regions.

1.2 Status of the Offshore Wind Industry

The United States leads the world in installed, 

land-based wind energy capacity, yet has no 

offshore wind generating capacity to date. Since 

Denmark’s first offshore project in 1991, Europe 

has held the lead in offshore wind, having 

installed more than 830 turbines with grid 

connections to nine European countries (see 

Figure 1-1). Almost all of the 2,300 megawatts 

(MW) of installed capacity has been built in 

shallow waters (less than 30 meters deep). The 

market is continuing to expand, with Europe 

planning to add another 1,000 MW in 2010. An 

additional 50,000 MW is being planned or is 

under development for 2011 and beyond. Interest 

in offshore wind is now spreading to Canada, 

China, and the United States. 

Although the United States has built no 

offshore wind projects so far, about 20 

projects representing more than 2,000 MW of 

capacity are in the planning and permitting process. Most of these activities are in the Northeast 

and Mid-Atlantic regions, although projects are being considered along the Great Lakes, the Gulf 

of Mexico, and the Pacific Coast. The deep waters off the West Coast, however, pose a 

technology challenge for the near term.

Untested regulatory and permitting requirements in federal waters (outside the three-nauticalmile state boundary) have posed major hurdles to development, but recent progress is clarifying 

these processes. Most notably, after 9 years in the permitting process, the Cape Wind project off 

of Massachusetts was offered the first commercial lease by the Department of Interior in April 

2010.The U.S. Department of the Interior bears responsibility for reducing the uncertainties and 

Figure 1-1. Nameplate generating 

capacity of offshore wind projects 

(1991–2010)
3

potential risks to the marine environment and making the federal permitting process more 

predictable under the Bureau of Ocean Energy Management (In June 2010, the Minerals and 

Management Service [MMS] was reorganized and renamed Bureau of Ocean Energy 

Management, Regulation and Enforcement [BOEM]). Some states have been proactive in 

promoting offshore wind demonstration projects in their own waters close to shore, which may 

provide a more efficient regulatory path to meet their renewable energy obligations, while jumpstarting a new locally grown industry. 

1.3 A Powerful U.S. Resource

Offshore winds tend to blow harder and more uniformly than on land, providing the potential for 

increased electricity generation and smoother, steadier operation than land-based wind power 

systems. The availability of these high offshore winds close to major U.S. coastal cities 

significantly reduces power transmission issues. 

The offshore wind resource in the United States has been sufficiently documented at a gross 

level to suggest an abundance of potential offshore wind sites as shown in Figure 1-2. 

Figure 1-2. United States offshore wind resource by region and depth for 

annual average wind speed sites above 7.0 m/s.

The gross resource has been quantified by state, water depth, distance from shore, and wind class 

throughout a band extending out to 50 nautical miles from the U.S. coastline. This total gross 
4

wind resource is estimated at more than 4,000 GW, or roughly four times the generating capacity 

currently carried on the U.S. electric grid. This estimate assumes that one 5-MW wind turbine 

could be placed on every square kilometer of water with an annual average wind speed above 7.0 

meters per second (m/s). As shown in Figure 1-2, this gross resource is distributed across three 

main depth categories, increasing from 1,071 GW over shallow water (30 meters), to 628 GW 

over transitional waters (between 30 and 60 meters in depth), and to 2,451 GW over deep water 

(deeper than 60 meters). However, this wind mapping effort does not currently account for a 

range of siting restrictions and public concerns. These gross resource values will likely shrink by 

60% or more after all environmental and socioeconomic constraints have been taken into 

account. Further study is also required to determine optimal spacing of turbines based on array 

effects, which could reduce the density of the potential offshore wind development.

For now, this complex process of identifying suitable sites is left up to state and local authorities, 

which are working with federal entities to develop a marine spatial planning framework. In spite 

of the resource potential and benefits to the nation, the development of offshore wind as an 

energy source for the United States faces several significant challenges and barriers that stem 

from technology limitations, high cost, regulatory and institutional uncertainties, and potential 

environmental and social risks. A sustained, nationally focused research and development 

initiative is needed to address these challenges and inform decision makers and public policies.

1.4 Technology Status and Trends

Although Europe now has a decade of experience with offshore wind projects in shallow water, 

the technology essentially evolved from land-based wind energy systems. Significant 

opportunities remain for tailoring the technology to better address key differences in the offshore 

environment. These opportunities are multiplied when deepwater floating system technology is 

considered, which is now in the very early stages of development.

The opportunities for advancing offshore wind technologies are accompanied by significant 

challenges. Turbine blades can be much larger without land-based transportation and 

construction constraints; however, enabling technology is needed to allow the construction of a 

blade greater than 70-meters in length. The blades may also be allowed to rotate faster offshore,

as blade noise is less likely to disturb human habitations. Faster rotors operate at lower torque, 

which means lighter, less costly drivetrain components. Challenges unique to the offshore 

environment include resistance to corrosive salt waters, resilience to tropical and extra-tropical 

storms and waves, and coexistence with marine life and activities. Greater distances from shore 

create challenges from increased water depth, exposure to more extreme open ocean conditions, 

long distance electrical transmission on high-voltage submarine cables, turbine maintenance at 

sea, and accommodation of maintenance personnel.

A primary challenge for offshore wind energy is cost reduction. Developing the necessary 

support infrastructure implies one-time costs for customized vessels, port and harbor upgrades, 

new manufacturing facilities, and workforce training. In general, capital costs are twice as high 

as land-based, but this may be partially offset by potentially higher energy yields—as much as 

30% or more. As was experienced with land-based wind systems over the past two decades, 

offshore wind costs are expected to drop with greater experience, increased deployment, and 

improved technology. To make offshore wind energy more cost effective, some manufacturers 

are designing larger wind turbines capable of generating more electricity per turbine. Several 
5

manufacturers are considering 10-MW turbine designs, and programs, such as UpWind in the 

European Union, are developing the tools to allow these larger machines to emerge.

Figure 1-3 provides a brief overview of the technology status in each depth category and some 

representative design options.

Figure 1-3. Status of offshore wind energy technology

In shallow water, the substructure extends to the sea floor and includes monopoles, gravity bases, 

and suction buckets. In the transitional depth, new technologies are being created, or adapted 

from the oil and gas industry, including jacket substructures and multi-pile foundations, which 

also extend to the sea floor. At some depth it is no longer economically feasible to have a rigid 

structure fixed to the sea floor, and floating platforms may be required. Three idealized concepts 

have arisen for floating platform designs, including the semisubmersible, the spar buoy, and the 

tension-leg platform, each of which use a different method for achieving static stability. 

Although it is not yet known which of these designs will deliver the best system performance, 

designers seek platforms that are easy to install and minimize overall turbine loads. To determine 

this optimized design point, advanced computer simulation models need to be developed and 

validated. As shown in the figure, most of the projects now reside in shallow water, and only two 
6

projects to date use transitional structures. One Norwegian demonstration project, Hywind 

(launched in 2009), uses a deepwater floating design.

Table 1-1 summarizes the key attributes of the resource and technology needed for large-scale 

offshore wind development in the United States.

Table 1-1. Summary of Key Project, Resource, and Technology Attributes 

1.5 Economics of Offshore Wind Power

Offshore wind projects are analyzed in terms of their initial installed capital cost (ICC) as well as 

their life-cycle costs, also known as the levelized cost of energy (LCOE). Cost projections of 

either type for the U.S. market are difficult because of the many regulatory and technical 

uncertainties and the lack of U.S. market experience. Although the European market is based on 

a more developed supporting infrastructure and substantially different regulatory, policy, and 

physical environments, preliminary analyses of that experience provide some potentially useful 

insight.

As in the case of land-based projects, the ICC for offshore wind power has been increasing over 

time. Costs jumped approximately 55% between 2005 and 2007, leading to an estimated average 

capital investment of $4,250 per kW for an offshore wind project in 2010. The wind turbine itself 

contributes 44% of this total. In general, capital costs are expected to increase with distance from 

land and water depth, and decrease as the size of a project increases, as a result of economies of 

scale. As the technology matures, prices are expected to decline.

The LCOE calculations, or the cost of energy produced over the anticipated 20-year life of a 

project, are based on a range of factors, many of which are currently unknown and must be 

Technology 

Depth Class Depth

Number of 

Projects 

Worldwide

U.S. Gross 

Offshore 

Wind 

Resource 

above 7.0 

m/s (GW)

U.S. Gross 

Offshore 

Wind 

Resource 

above 8.0 

m/s (GW)

Technology Description

Shallow 

Water 0 – 30m 42 1,071 457

Uses fixed-bottom monopile and gravitybase substructures with proven turbine 

technology adapted from land-based 

systems. 

Transitional 

Depth

30m –

60m 2 628 549

Uses fixed-bottom jacket (lattice) or multipile substructures to provide stiffer base 

for turbines; similar to shallow water. 

New vessels for deeper deployments may 

be needed. 

Deepwater >60m 1 2,451 1,951

Floating substructures decouple from the 

bottom and allow site independence,

which may allow greater degree of mass 

production and less work at sea. Typical 

substructures under consideration include 

semi-submersibles, spar buoys, and 

tension-leg platforms. New optimized 

turbines will be developed.
7

projected. In addition to the ICC, these include operations and maintenance (O&M) costs, the 

cost of financing, amount of energy to be generated, long-term system reliability, and 

decommissioning costs. 

Operation and maintenance costs are higher for offshore wind turbines than for land-based 

turbines, primarily because of access issues. It is simply more difficult to perform work at sea. 

Although more research is needed to determine the range of these offshore O&M costs, some 

reports estimate they are two to three times higher than on land and can reach 20% to 30% of the 

LCOE.

The LCOE for offshore wind is heavily influenced by the relatively high ICC and the cost of 

financing. A significant part of the financing cost is based on the perception of financial risk and 

project uncertainties. These risk perceptions could potentially be lowered through research on 

virtually all of the factors that make up the LCOE for offshore wind, but the larger impacts will 

come from confidence built on deployment experience.

Under reasonable economic assumptions, offshore wind can be expected to penetrate the U.S. 

market on a large scale without introducing substantial new technology—such as large-scale grid 

storage or smart grid load management. Although these analyses are still preliminary, NREL’s 

Regional Energy Deployment System (ReEDS) model (formerly called the Wind Deployment 

System [WinDS] model) shows offshore wind penetration of between 54 GW and 89 GW by 

2030 when economic scenarios favoring offshore wind are applied. These cases used 

combinations of cost reductions (resulting from technology improvements and experience), 

rising natural gas prices (3% annually), heavy constraints on conventional power and new 

transmission development in congested coastal regions, and national incentive policies. 

Furthermore, analyses indicate that if wind energy is to supply 20% of the nation’s electricity by 

2030, offshore wind will be an essential component.

1.6 Regulatory Pathways for Siting and Permitting

Although the United States has a long history of managing energy-related extractive industries 

(e.g., oil and gas) on federal lands and in federal waters, there is no institutional knowledge about 

offshore wind energy facilities. Offshore wind power is a relatively new energy industry with 

about a 20-year demonstration history in European seas and less than a 10-year operational 

history for utility-scale projects. As such, the regulatory and institutional structures for offshore 

wind energy are just now emerging in the United States. 

BOEM was assigned jurisdiction over leasing of federal waters (greater than 3 nautical miles 

from shore in all but Texas and the west coast of Florida) for ocean energy technologies under 

the Energy Policy Act of 2005. Secretary Salazar issued the final rule governing easements and 

rights of way for offshore wind on the outer continental shelf in April 2009. Several projects are 

now in early permitting stages under BOEM regulations and developer’s estimate that approvals

may take as long as 7 to 10 years – longer than permitting approvals for most other types of 

energy facilities

States desiring offshore wind supplies to meet their renewable energy goals and project 

developers seeking economic development opportunities have identified potential sites in state 

waters. State projects are typically near shore and have marginally lower wind resources, but 

there is a perception that state institutions and regulations provide an accelerated approval

process. Regardless of these perceptions, state waters will not be able to provide enough sites for 
8

large-scale offshore wind power in the United States. To accelerate the deployment of offshore 

wind energy, the federal government needs to partner strategically with states where offshore 

wind development is planned or underway. The formation of several BOEM state task forces and 

the Atlantic Offshore Wind Energy Consortium, involving 10 governors, are steps taken in 2010

that proactively engage interested and affected parties and could help mature the regulatory and 

stakeholder engagement processes.

1.7 Environmental and Socioeconomic Risks

Risks associated with offshore wind energy are not as serious or potentially catastrophic 

compared with other energy supply technologies. Also wind turbines can be deployed relatively 

quickly to reduce greenhouse gases, reduce other air emissions and help conserve water 

resources. Potential risks in deploying offshore wind projects can typically be reduced through 

development and use of best management practices, mitigation strategies, and adaptive 

management principles. Although risks are site-specific, research at European installed projects 

and U.S. baseline studies are building the knowledge base and helping to inform decision makers 

and the public.

Primary stakeholder concerns regarding offshore wind power facilities include: 

Marine animal populations: Although European studies conducted to date suggest that the 

impacts of offshore wind facilities on marine animal populations are minimal, U.S. studies 

will be required to gain a better understanding of the potential risks and to mitigate any 

harmful effects.

Visual effects: Coastal residents in view of an offshore wind farm may voice concerns about 

visual impacts. More research is needed to better understand coastal communities and their 

ability to accept changes to the seascape. 

Property values: Studies conducted on land-based wind projects show minimal to no impact on 

real estate prices and property values as a result of the presence of wind turbines; however, 

extensive studies have not been conducted on coastal communities.

Noise: Based on European studies and experiences to date, the most significant environmental 

impact stems from the noise associated with pile driving during the construction phase. 

Mitigation strategies may be effective in reducing this risk. Alternative technology can also 

be implemented if appropriate to avoid some of the pile driving activity.

Tourism: Impacts on tourism may be a concern to some communities that are dependent on 

beach vacationers and the resulting local revenues and tax base, but the evidence is 

ambiguous and actual effects appear to be minimal.

Marine safety: The possibility of a ship colliding with a turbine poses a potentially significant 

risk to the marine environment from fuel leaks from a disabled ship or to human safety 

should the turbine collapse. No reported incidents have occurred to date.

Research is also needed to fill gaps in the knowledge base and prioritize risks based on analysis 

of uncertainties and potential impacts. Several important gaps and uncertainties include visual 

effects, public perception of deployment risks, endangered and migrating species, conflicting use 

of military and recreational spaces, and construction impacts. BOEM and other federal and state 

agencies are beginning to fill these gaps with baseline surveys and studies. Sector-by-sector 
9

impact analyses, however, as required with NEPA documentation, are limited in revealing the 

true risks to the ocean or lake ecologies. Applying an integrated risk framework that compares 

costs and benefits of deploying offshore wind as opposed to another energy option is needed to 

inform decisions about the actual risks. Developing prudent siting policies will likely avoid 

coastal areas with intense competing uses and sensitive habitats and will reflect the sensitivities 

of multiple stakeholder groups. Siting strategies are needed that go beyond narrow technical 

appraisals of sites to include collaborative approaches with potential host states and 

communities. Well-developed risk communication and stakeholder involvement strategies need 

exploration and are essential to the successful development of offshore wind projects.

1.8 Findings and Conclusions

Overall, the opportunities for offshore wind are abundant, yet the barriers and challenges are also 

significant. In the context of the greater energy, environmental, and economic concerns the 

nation faces, accelerating the deployment of offshore wind could have tremendous benefits to the 

United States. Technological needs are generally focused on making offshore wind technology 

economically feasible and reliable and expanding the resource area to accommodate more 

regional diversity for future U.S. offshore projects. Prudent siting strategies that involve 

stakeholders at the site would reduce potential risks. Removing deployment barriers can help 

support the first projects in the competitive energy supply market, with the objective of reducing 

long-term uncertainties. In the short term, reducing risk will stimulate economic growth, 

accelerate permitting time frames, and help address important aspects of climate change 

mitigation. Although offshore wind alone cannot solve the nation’s energy problems, this report 

concludes that with effective research, policies, and commitment, it can play a significant and 

vital role in future U.S. energy markets. As a result, it should be considered a necessary part of a 

diverse sustainable energy portfolio along with energy conservation and efficiencies.
10

2.0 Rationale for Offshore Wind

The world and the nation face an unprecedented convergence of three interwoven dilemmas: 

energy supply shortages resulting from depletion of global fossil energy supplies; environmental 

consequences of fossil fuel emissions; and a worldwide economic crisis that threatens the 

livelihood of millions.

2.1 Energy Supply

The United States remains dependent on fossil fuels that are decreasing in supply and are 

increasingly imported from unstable and unreliable nations. The Energy Information 

Administration (EIA) forecasts that global energy consumption will rise 49% from 2007 levels 

by 2035, with the majority of the increase in non-OECD (Organisation for Economic Cooperation) countries (EIA 2010a). Energy consumption at such elevated levels will likely test 

the resource extraction and distribution capabilities of the global fossil fuels market. Strains on 

supply are likely to increase the prices of fossil fuel resources and leave the U.S. economy 

exposed to international market volatility. Reliance on foreign energy resources has significant 

implications for the national security situation, transferring wealth to several despotic regimes 

and leaving our economy vulnerable to the decisions of these governments (House Select 

Committee on Energy Independence and Global Warming 2010).

2.2 The Environment

Fossil power generation technologies have significant impacts on both public health and on our 

environment. Fossil fuel generation plants emit 39% of carbon dioxide (CO2) emissions, 22% of 

nitrogen oxide (NOx) emissions, 69% of sulfur dioxide (SO2) emissions, and 40% of mercury

(Hg) emissions in the United States (Jacobson and High 2008). A report by the National 

Academy of Sciences found that burning fossil fuels for transportation and for electricity 

generation costs the United States $120 billion a year, primarily in health damages. The 

nonclimate damages caused by coal-fired power plants are estimated at $62 billion per year or 

about 3.2 cents per generated kWh (National Research Council of the National Academies 

2010). 

A more widely publicized externality of fossil fuel generation is the emission of greenhouse 

gases (GHGs) that are linked to global climate change. Concentrations of CO2 in the atmosphere 

are rising steadily, primarily because of human consumption of fossil fuels (see Figure 2-1). The 

Intergovernmental Panel on Climate Change (IPCC) suggests that mitigation measures be taken 

to stabilize CO2 at 550 ppm (which implies an 80% reduction in fossil fuel emissions) by 2050 

(approximately double preindustrial levels). Even with these mitigation measures, another IPCC

report posits the likelihood of a global temperature rise somewhere between 2°C and 4°C by 

2050 (see Figure 2-2). 
11 

Source: Solomon et al. (2007a).

Figure 2-1. Concentrations of important long-lived greenhouse gases 

in the atmosphere (given in ppm and ppb)

Furthermore, the IPCC’s Summary for Policy Makers (IPCC Core Writing Team 2007) states 

that “Warming of the climate system is unequivocal, as is now evident from observations of 

increases in global average air and ocean temperatures, widespread melting of snow and ice and 

rising global average sea level.”

Source: Adapted from IPCC Core Writing Team. (2007).Notes: SRES = Special Report on Emission Scenarios (IPCC) 

Figure 2-2. Global CO2 emissions for 1940 to 2000 and emissions ranges for categories of 

stabilization scenarios from 2000 to 2100 are shown in the left panel. The relationship between the 

stabilization target and global average temperature increase above preindustrial levels is shown 

in the right panel. 
12

Although there is no panacea for the predicament posed by global climate change, a major part 

of the solution must include the reduction of carbon emissions into the atmosphere. Increasing 

the use of renewable energy will help to reduce these emissions.

2.3 The Economy

The nation is also recovering from the most significant economic downturn since the Great 

Depression. Economists are raising concerns about a return to economic slowdown (gross 

domestic product [GDP] growth fell from 3.7% in the first quarter of 2010 to 2.4% in the second 

quarter of 2010) and the prospect of a jobless recovery (as of this writing, the unemployment rate 

is at 9.5%, down just 0.6 percentage points from its high of 10.1% in October 2009; see Bureau 

of Economic Analysis 2010; Bureau of Labor Statistics 2010). In addition, the U.S. 

manufacturing sector, traditionally a source of economic strength, has been buffeted by the 

outsourcing of production operations overseas and, more recently, the recession. Data from the 

Bureau of Labor Statistics show that the manufacturing industry as a whole lost more than 4.1 

million jobs between 1998 and 2008 and suggest that the sector will lose an additional 1.2 

million jobs by 2018 (Bureau of Labor Statistics 2009). A continued decline in manufacturing 

activity will likely increase our nation’s trade deficit; eliminate stable, high-wage jobs for skilled 

domestic workers; and generally reduce the potential for robust economic growth. 

2.4 The Contribution of Offshore Wind

Offshore wind has the potential to address all three issues: the energy supply, the environment, 

and the economy. Offshore wind uses the vast renewable wind resources adjacent to the ocean 

perimeter of the United States, which are domestic, indigenous, inexhaustible energy supplies in 

close proximity to our urban energy load centers. Offshore wind turbines can convert the strong 

ocean winds into clean, renewable power with no harmful emissions. Offshore wind has the 

potential to contribute significantly to the revitalization of the U.S. manufacturing sector, which 

will help strengthen both the economies of coastal states and the U.S. economy as a whole. 

Recognizing these issues, the Obama administration has strengthened the nation’s commitment 

to renewable energy and clarified some of the actions needed to reduce our dependence on fossil 

fuels and bring emission levels in line with IPCC recommendations. The administration has set 

forth the following specific clean energy actions for the United States (White House 2009):

• Double this nation’s supply of renewable energy in the next 3 years.

• Invest $15 billion per year to develop technologies like wind power and solar power,

advanced biofuels, clean coal, and more fuel-efficient cars and trucks.

• Cut our carbon pollution by about 80% by 2050, and create millions of new jobs.

• Lease federal waters for projects to generate electricity from wind, as well as from ocean 

currents and other renewable sources.

• Put the nation on the path to generating 20% or more of our energy from renewable sources 

by 2020.

As a contributor to the overall solutions, the offshore wind resource in the United States has the 

potential to deliver substantial amounts of clean electricity to U.S. consumers. The National 

Renewable Energy Laboratory (NREL) estimates that the gross U.S. offshore wind resource over 
13

all water depths, in regions with annual average wind speeds greater than 8.0 m/s, is 2,957 GW

(1 GW = 1,000 MW).

2 If average winds of 7.0 m/s are included, the estimated wind resource 

grows to 4,150 GW (Heimiller et al. 2010; see also Section 4). This is approximately four times 

the electricity generating capacity of the U.S. electric grid. Although these numbers provide only 

an upper bound, they demonstrate that for 54-GW offshore wind scenarios like those defined in 

the U.S. Department of Energy’s (DOE) 20% Wind Energy by 2030: Increasing Wind Energy’s 

Contribution to U.S. Electricity Supply (the “20% report” or the “20% scenario), the offshore 

wind resource supply is not the primary issue determining deployment (DOE 2008).

3

Wind speeds generally increase significantly with distance from the coast, resulting in a higher 

annual energy production than a similar turbine sited on land. Table 2-1 shows how sites with 

higher wind speeds—such as those found offshore—translate into high energy production. The 

table illustrates that an increase of two wind power classes (the difference that can be reasonably 

expected between a typical “Class 4” land-based site and a typical “Class 6” offshore site) would 

result in a gain of about 29% in annual average energy production for an NREL reference wind 

turbine (Jonkman et al. 2009).

Table 2-1. Energy Production by Wind Power Class

Average Annual Wind 

Speed (m/s)

Wind Power Class Change in Energy

Production Relative 

to Class 4 Sitea (%)

5.6–6.4 2 –34

6.4–7.0 3 –15

7.0–7.5 4 0

7.5–8.0 5 +13

8.0–8.8 6 +29

8.8–9.5 7 +45

Source: Elliott et al. 1987.

a The relative change in energy production was computed using NREL’s 5-MW reference wind turbine parameters, varying only 

the annual average wind speed. Actual turbine performance could be optimized for site-specific design conditions.

In addition to being plentiful, the offshore wind resource of the United States is broadly 

distributed. Thirty U.S. states border an ocean or Great Lake. The offshore wind resource exists 

within reasonable distances from major urban load centers, reducing the need for long-distance 

power transmission. These urban areas are home to much of the U.S. population; have the 

highest electricity prices in the nation; and currently depend heavily on a high-carbon, volatile 

supply of imported fossil fuels. According to the EIA (2007), the 28 coastal states in the lower 

48 states4 generate 75% of the nation’s electricity (3,108 TWh of 4,157 TWh generated 

nationally in 2007).

5

 2 This estimate is based on wind speeds at a 90-m elevation (hub height of the reference wind turbine) and includes all regions 

out to 50 nm. The estimate assumes that 5 MW (or about 1 turbine) of installed capacity would be installed in every square 

kilometer. This estimate includes the coastal regions for all of the lower 48 contiguous states with no exclusions.

The electricity generated in the U.S. coastal states represents 16.6% of the 

3 These resource estimates do not assume any exclusion areas where wind development would not be allowed. Judging from

land-based experience, exclusion zones would result in at least a 60% reduction of the available resource. 4 Alaska and Hawaii, although remote, have abundant offshore resources and could become electrically self-sufficient using 

offshore wind in conjunction with other renewables, along with smart grid and storage technologies. These states are treated 

separately, though, because they are isolated and cannot distribute power to other states. 

5 Electric energy generation figures published by the EIA can provide a rough estimate of the energy consumed by the same state. 

In some cases generation is transmitted across state boundaries or generation can take place behind the meter, as in large 
14

world’s total electricity (world electric energy generation was approximately 18.77 TWh in 

2007; EIA 2010a). As such, the electricity consumption of U.S. coastal states has a large impact 

on the world’s carbon emissions. These states could significantly reduce global GHG emissions 

if they choose to adopt renewable energy solutions such as offshore wind. 

In coastal areas of the United States, offshore resources tend to dwarf the land-based wind 

component. Most coastal states do not have optimal land-based wind energy resources with the 

exception of a few: California, Oregon, Texas, Washington, and Maine. If offshore and landbased wind resources are counted together, coastal states would have sufficient wind resources to 

make wind energy a significant part of their electricity profiles (see sections 3 and 4). For many 

of these states, offshore wind is the most abundant indigenous energy source and the only 

commercial option for renewable power generation. This is especially true in some southern 

states where land-based resources become scarcer with decreasing latitude. Most other 

alternatives involve importing energy across state lines, which would require building up 

interstate transmission corridors or depending even more on fossil-fueled electricity generation.

U.S. wind energy generated offshore has the potential to compete economically in highly 

populated coastal energy markets where land-based wind energy is less available. Figure 2-3 

shows that the offshore resource tends to be geographically located near states with high electric 

utility rates (EIA 2007). Figure 2-3, which is based on retail energy prices obtained from the 

EIA, also shows that the Mid-Atlantic and northeastern states have significantly higher 

electricity prices than the national average of $0.099/kWh.

6 These prices are higher than inland 

and southern retail electricity prices, where energy prices are generally lower because of a fuel 

mix that relies heavily on imported coal and nuclear generation. The Pacific Northwest also has 

low electricity prices resulting from abundant hydropower resources (UCS 2010).

 industrial facilities. Electric energy generation exceeds the energy consumption based on EIA retail sales. Generation is a better

metric for stating total U.S. electricity demand.

6 Ideally, the cost of offshore wind should be compared to wholesale electricity price data, not retail price data, though these 

metrics are expected to follow the same trends. This analysis does not address the fact that many external costs (e.g., public 

health, emissions, and nuclear waste disposal) are not included in the market price of energy 
15 

Source: EIA 2007.

Figure 2-3. Coastal versus inland state electric rates (2008)

Regionally high electricity costs in congested offshore areas, more energetic wind regimes, and 

closer proximity to grid interconnects might allow offshore wind to compete, even at higher 

initial costs, in many coastal areas. Although capital costs for offshore wind energy will remain 

higher than those of land-based wind energy systems, unique regional market conditions and 

enhanced offshore turbine performance will, at least partially, offset the difference. 

Increasing the percentage of renewable energy generation in our nation’s fuel mix has the 

potential to significantly reduce harmful emissions. Although offshore wind projects have high 

capital costs, they have no fuel costs and low operating costs. These characteristics allow the 

turbines to produce energy at a much lower marginal cost than fossil-fuel power plants. As a 

result, offshore wind turbines displace power that otherwise would have been generated by the 

fossil-fuel plants and avoid any emissions that would have resulted from the combustion of the 

fuel. The specific type of displaced generation will vary by region and is dependent on the mix of 

generation in the area (Jacobson and High 2008). 

DOE’s Wind and Water Power Program has led a number of initiatives to drive down the cost of 

wind energy through sustained technology innovations (NWTC 2006a, 2006b). These targeted 

cost reduction programs are partially responsible for the dramatic reduction in the cost of landbased wind energy and subsequent acceleration in deployment. During the past two decades, 

land-based wind energy has seen a tenfold reduction in cost and is now competitive with fossil-
16

fuel and nuclear power generation. Over the same time period, deployment has increased from 

1,800 MW in 1990 to 35,603 MW at the end of 2009 (AWEA 2010).

Although cost-competitiveness remains an important driver for wind energy deployment, the 

industry faces new challenges that must be overcome if current wind energy growth rates are to 

be sustained and projections of 20% wind energy by 2030 are to be met (see DOE 2008). The 

availability of electric transmission, the firm delivery of generated wind capacity, the long-term 

cost and reliability of the turbine equipment, and the availability of critical supply chain growth 

all challenge the nation’s ability to meet these projections. 

Fifty-four gigawatts of offshore wind will be required to achieve the 20% scenario. But other

recent studies present detailed and compelling analyses indicating that 20% or 30% wind 

electricity cannot be realized in the United States without developing both land-based and 

offshore wind resources (see, for example, EnerNex 2010). Offshore resources must be 

developed in high wind-energy penetration scenarios mainly because of transmission constraints 

and load balancing concerns. 

Offshore wind projects offer a number of cost reduction opportunities and advantages that are 

unique when compared to land-based projects. These opportunities include fewer restraints on 

turbine size, reduced transmission requirements, and the ability to site projects farther from 

human use areas. 

The generation cost of offshore wind could be lowered by taking advantage of larger turbines

than those typically employed for land-based wind energy. Most wind turbine manufacturers are 

preparing 5-MW offshore machines for large-scale commercial deployment and several 

manufacturers have designs in the range of 8 to 10 MW on the drawing board. The shipping and 

lifting capacities of marine equipment and vessels still far exceed the installation requirements 

for the current generation of multimegawatt offshore wind turbines. In contrast, the size of landbased turbines is restricted by the capacity limits of the existing transportation and erection 

equipment. The capacity limits of the existing equipment is causing the growth of land-based 

wind turbines to level off. This is a significant advantage for offshore wind because larger 

machines could significantly lower the installation and balance-of-station (BOS) costs, per 

kilowatt, for offshore wind projects. The challenges of building larger machines, however, have 

not been fully explored (see Section 5).

The 20% scenario estimates that 305 GW of installed wind power (land-based and offshore 

combined) would avoid 825 million metric tons of CO2 in 2030 for a cumulative total of 7,600 

million tons of CO2 from 2010 to 2030. For comparison, the U.S. electric sector currently emits 

about 2,500 million metric tons of CO2 per year (EIA 2010b). 

Developing a domestic wind industry offers a viable way to revitalize our domestic 

manufacturing sector and create high-paying, stable jobs while increasing the nation’s 

competitiveness in twenty-first century energy technologies. In the 20% scenario, 54 GW of 

offshore wind would create more than $200 billion in new economic activity with a high 

percentage of that revenue remaining in the local economies. This offshore wind power 

development would create many benefits beyond the $200 billion in revenues because the power 

generated would have no fuel price variability, no emissions, and no significant use of water 

resources. Finally, offshore wind development would reduce dependence on foreign energy 

resources (DOE 2008).
17

Most of the labor for offshore wind will draw from local and regional sources that cannot be 

easily outsourced overseas. Analysis done at NREL, extrapolated from European studies (EWEA 

2009), estimates that offshore wind will create approximately 20.7 direct jobs per annual 

megawatt in the United States. In addition, approximately 0.8 jobs would be created for every 

cumulative megawatt of offshore wind in operation. If 54 GW were installed under the 20% 

scenario, more than 43,000 permanent operations and maintenance (O&M) jobs and more than 

1.1 million job-years would be required to manufacture and install the turbines (GWEC et al. 

2008; Musial 2007).

Land-based wind resources are generally located far from population centers and require 

significant transmission capacity to deliver electricity to load centers. Recent evidence shows 

that the development of high-quality land-based wind sites is being constrained by limited access 

to transmission and that the output of operational wind farms is increasingly being curtailed by 

system operators as a way of reducing congestion (Piwko et al. 2005; Fink et al. 2009). These 

examples suggest that transmission will be a primary near-term barrier to large-scale 

development of land-based wind projects in the United States. Although the nation needs to 

develop both land-based and offshore resources, offshore wind is less likely to be affected by 

congestion in the transmission system. Offshore wind resources are located close to coastal urban 

load centers. attribute that could be very valuable to utilities in helping to alleviate transmission 

constraints. 

Both land-based and offshore wind projects face issues associated with their visible impact.

Aesthetic concerns may continue to be an issue whenever turbines can be seen from populated 

areas but offshore wind projects have the advantage of being located farther from inhabited areas 

than most land-based projects. With the development of new technology for deeper waters, 

offshore wind turbines could eventually be sited far enough from shore to virtually eliminate 

visual impacts. Offshore wind turbines also have the potential to eliminate human objections to

sounds from turbines because most projects would be sited beyond the threshold of sound 

propagation. Public concerns about other factors such as the effects on local tourism, rights to 

private use of the public commons, and possible avian collisions with turbines suggest that 

further studies on these impacts will be necessary (Kempton et al. 2005). Wide-ranging

environmental and social issues have been investigated in existing European wind farms for 

more than 10 years, and no significant environmental impacts have been identified (see Section 

8; see also Nielsen 2003; DONG Energy 2006). As a result, public concerns about offshore wind

can be expected to wane as consumers gain comfort with this technology. Studies have shown 

that when the public is faced with an energy choice between offshore wind and other forms of 

electricity generation, offshore wind energy is considered preferable (Firestone, Kempton, and 

Krueger 2009).

2.5 Findings and Conclusions

Looking toward the future, offshore wind appears to be a leading contender to provide a 

substantial portion of a low-carbon energy supply. In 2007, the European Union (EU) and the 

European Wind Energy Association (EWEA) established aggressive targets to install 40 GW of 

offshore wind by 2020 and 150 GW by 2030. In the United States, there are no offshore wind 

projects yet but interest is growing with greater than 2,000 MW of offshore wind in the detailed 

planning, site development, and approval process (see Section 3). Based on the U.S. experience 

to date, regulatory and permitting issues will have a large effect on the pace at which offshore 
18

development can progress. The Minerals Management Service (MMS; renamed the Bureau of 

Ocean Energy Management, Regulation and Enforcement (BOEM) in June 2010) has 

traditionally taken a cautious approach to permitting and certification for offshore wind projects. 

The MMS published the final rules for wind energy development on the Outer Continental Shelf 

in April 2009 (MMS 2010). Multiple agencies and industry members are now looking at the 

implications of this rule with respect to the total regulatory process time frame and further 

clarifications are expected as experience with the process is gained. 

Although offshore wind development is sure to benefit from continued innovation associated 

with land-based growth, experience has shown that offshore wind cannot be simply extrapolated 

from land-based experience alone. Establishing a competitive, mature offshore wind industry in 

the United States will require dedicated investment in technology research specific to offshore

conditions. European countries have already installed more than 2,000 MW of offshore capacity 

and the experiences gained from these initial deployments are supporting new technology 

developments that have the potential to lower costs (see sections 5 and 6). Offshore wind faces 

many near-term technical and regulatory challenges that must be addressed before the 

technology can compete broadly in U.S. energy markets. The remainder of this report focuses on 

these challenges.

2.6 References

AWEA (American Wind Energy Association). (2010). U.S. Wind Energy Projects. 

http://www.awea.org/projects/. Accessed June 7, 2010.

Bureau of Economic Analysis. (July 2010). GDP Growth Slows in the Second Quarter. U.S. 

Department of Commerce. 

http://www.bea.gov/newsreleases/national/gdp/gdphighlights.pdf. Accessed August 8, 

2010.

Bureau of Labor Statistics. (December 2009). Table 2.1 Employment by Major Industry Sector, 

1998, 2008, Projected 2018. U.S. Department of Labor.

http://www.bls.gov/emp/ep_table_201.htm. Accessed August 9, 2010.

Bureau of Labor Statistics. (July 2010). Table A-3: Employment Status of the Civilian 

Noninstitutional Population by Sex and Age, Seasonally Adjusted. U.S. Department of 

Labor. http://www.bls.gov/web/empsit/cpseea3.pdf. Accessed August 9, 2010.

DOE (U.S. Department of Energy). (July 2008). 20% Wind Energy by 2030: Increasing Wind 

Energy’s Contribution to U.S. Electricity Supply. DOE/GO-102008-2567. Golden, CO: 

National Renewable Energy Laboratory (NREL).

http://www.nrel.gov/docs/fy08osti/41869.pdf, Accessed August 30, 2010.

DONG Energy, Vattenfall, Danish Energy Authority, Danish Forest and Nature Agency. 

(November 2006). Danish Offshore Wind – Key Environmental Issues. 

http://193.88.185.141/Graphics/Publikationer/Havvindmoeller/havvindmoellebog_nov_2

006_skrm.pdf. Accessed August 22, 2010.
19

EIA (Energy Information Administration). (2007). State Electric Profiles Web page. 

http://www.eia.doe.gov/electricity/st_profiles/e_profiles_sum.html. Accessed June 7, 

2010. 

EIA. (2010a). International Energy Outlook 2010. DOE/EIA-0484(2010). 

http://www.eia.doe.gov/oiaf/ieo/index.html. Accessed August 15, 2010.

EIA. (2010b). U.S. Carbon Dioxide Emissions by Sector and Fuel for 2007 Actual and 2030 

Projected. http://www.eia.doe.gov/environment.html. Accessed August 15, 2010.

EnerNex Corporation. (January 2010). Eastern Wind Integration and Transmission Study.

NREL/SR-550-47078. Golden, CO: NREL. 

http://www.nrel.gov/wind/systemsintegration/pdfs/2010/ewits_final_report.pdf. Accessed 

August 15, 2010.

EWEA (European Wind Energy Association). (January 2009). Wind at Work: Wind Energy and 

Job Creation in the EU. 

http://www.ewea.org/fileadmin/ewea_documents/documents/publications/Wind_at_work

_FINAL.pdf. Accessed August 28, 2010.

Elliott, D.; Holliday, C.; Barchet, W.; Foote, H.; Sandusky, W. (1987). Wind Energy Resource 

Atlas of the United States. DOE/CH 10093-4, Golden, CO: Solar Energy Research 

Institute. 

Fink, S.; Mudd, C.; Porter, K.;Morgenstern, B. (October 2009). Wind Energy Curtailment Case 

Studies: May 2008 – May 2009. NREL/SR-550-46716. 

http://www.nrel.gov/docs/fy10osti/46716.pdf. Accessed August 15, 2010.

Firestone, J.; Kempton, W.; Krueger, A. (2009). “Public Acceptance of Offshore Wind Power 

Projects in the United States.” WE-08-0057.R628. Wind Energy (12:2); pp. 183–202.

GWEC (Global Wind Energy Council). (2010). Renewable Energy House; Greenpeace 

International. (2008). Global Wind Outlook 2008. Brussels: GWEC. 

http://www.gwec.net/fileadmin/images/Logos/Corporate/GWEO_A4_2008_lowres.pdf.

Accessed August 9, 2010.

House Select Committee on Energy Independence and Global Warming. (2010). Energy 

Independence Web Page. U.S. House of Representatives. 

http://globalwarming.house.gov/issues/energyindependence?id=0002. Accessed August 

9, 2010.

IPCC Core Writing Team. (2007). “Summary for Policy Makers, Figure SPM.11” in Climate 

Change 2007: The Synthesis Report. Contribution of Working Groups I, II and III to the 

Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Pachauri, 

R.K.; Reisinger, A., eds. Geneva: IPCC. 

http://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_s

ynthesis_report.htm. Accessed August 15, 2010.
20

Jacobson, D.; High, C. (February 2008). Wind Energy and Air Emission Reduction Benefits: A 

Primer. NREL/SR-500-42616. Golden, CO: NREL. 

http://www.windpoweringamerica.gov/pdfs/policy/wind_air_emissions.pdf. Accessed 

August 15, 2010.

Jonkman, J.; Butterfield, C.P.; Musial, W.; Scott, G. (2009). Definition of a 5-MW Reference 

Wind Turbine for Offshore System Development. NREL/TP-500-38060. Golden, CO:

NREL.

Kempton, W.; Firestone, J.; Lilley, J.; Rouleau, T.; Whitaker, P. (2005). “The Offshore 

Windpower Debate: Views from Cape Cod.” Coastal Management Journal (33:2); pp. 

119–149.

National Research Council of the National Academies. (2010). Hidden Costs of Energy: 

Unpriced Consequences of Energy Production and Use. Washington, DC: The National 

Academies Press.

Nielsen, P. (June 2003). Offshore Wind Energy Projects Feasibility Study Guidelines. 

SEAWIND ALTENER PROJECT 4.1030/Z/01-103/2001, Ver. 3.0. Aalborg, Denmark: 

EMD International A/S. 

http://www.emd.dk/Projects/Projekter/Seawind/OTHER%20RELEVANT%20DOCUME

NTS/Feasibility%20Study%20Guidelines.pdf. Accessed August 15, 2010.

NWTC (National Wind Technology Center). Web page, Publications, Low-Wind-Speed 

Technologies. http://www.nrel.gov/wind/pubs_technologies.html#low. Accessed 

September 14, 2010.

MMS (Minerals Management Service). (2010). “Renewable Energy and Alternate Uses 

ofExisting Facilities on the Outer Continental Shelf; Final Rule.” Federal Register, 30 

CFR, Parts 250, 285, and 290.

http://www.mms.gov/offshore/RenewableEnergy/PDF/FinalRenewableEnergyRule.pdf. 

Accessed June 7, 2010.

Musial, W. (2007). “Offshore Wind: Viable Option for Coastal Regions of the United States.” 

Marine Technology Society Journal. (41:3).

Piwko, R.; Osborn, D.; Gramlich, R.; Jordan, G.; Hawkins, D.; Porter, K. (2005). “Wind Energy 

Delivery Issues: Transmission and Competitive Electricity Market Operation.” IEEE 

Power and Generation Magazine. (3:6); pp. 47–56.

Schwartz, M.; Heimiller, D.; Haymes, S.; Musial, W. (June 2010). Assessment of Offshore Wind 

Energy Resources for the United States. NREL/TP-500-45889.Golden, CO: NREL. 

www.nrel.gov/docs/fy10osti/45889.pdf. Accessed August 15, 2010.

Solomon , S.; Qin, D.; Manning, M.; Marquis, M.; Averyt, K.; Tignor, M.M.B.; Miller, H.L. Jr.; 

Chen, Z., eds. (2007a). Chapter 2, FAQ 2.1, Figure 1 in Climate Change 2007: The 

Physical Science Basis. Contribution of Working Group I to the Fourth Assessment 

Report of the IPCC (Intergovernmental Panel on Climate Change). New York: 
21

Cambridge University Press; 

http://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_

wg1_report_the_physical_science_basis.htm. Accessed August 15, 2010.

UCS (Union of Concerned Scientists). (May 2010). “Burning Coal, Burning Cash: Ranking the 

States That Import the Most Coal.” 

http://www.ucsusa.org/clean_energy/technology_and_impacts/impacts/burning-coalburning-cash.html. Accessed August 23, 2010.

White House. (August 10, 2009). North American Leaders’ Declaration on Climate Change and 

Clean Energy. Press release.

http://www.whitehouse.gov/search/site/North%20American%20Leaders%20Declaration. 

Accessed August 24, 2010.
22

3.0 Industry Overview and U.S Activities

3.1 Historical Context 

The first documented offshore wind energy generation concept was proposed by Hermann 

Honnef in 1932 (Honnef 1932). The first detailed study was done by Ismael Dambolena.

Dambolena did his Ph.D. dissertation at the University of Massachusetts at Amherst in 1972, 

where he studied under Professor William E. Heronemus (Dambolena 1972). Heronemus is 

largely credited with having the vision for large-scale offshore wind turbines for bulk power 

generation just before the rebirth of the modern wind turbine (Heronemous 1972). In the 1970s 

Heronemus foresaw thousands of floating “windships” off the eastern coast of the United States, 

but it was not until the early 1990s, after the land-based wind industry had achieved some 

commercial success, that the mainstream research community began to investigate offshore wind 

energy again. While the first offshore pilot projects were being installed in the 1990s, some 

researchers continued to pursue floating-technology concepts in the laboratory (Henderson and 

Patel 2003; Heronemus and Stoddard 2003; Jamieson 2003; Halfpenny 2000;).

Not surprisingly, the first full-scale applications of offshore wind turbines used fixed-bottom 

substructures in the shallow waters of the North and Baltic seas. Initial development of the 

offshore resource was driven largely by the commercial aspirations of the European wind 

industry, whose proponents saw the oceans as an obvious solution to the shortage of land-based 

sites (GWEC and Greenpeace International 2005). To date, all large-scale projects have used 

shallow-water technology, but deepwater technology is moving closer to commercialization. 

More than 2,000 MW of offshore wind projects are proposed in the United States, indicating 

substantial private sector interest. As in Europe, U.S. developers are aiming to site projects in 

shallow water, building from the European experience. 

3.2 Current Offshore Wind Activity 

The first offshore wind farm was installed in Vindeby, Denmark in 1991. Since then, the industry 

has slowly grown in northwest Europe as developers and operators gained experience with 

offshore wind turbine implementation and operational requirements. As shown in Table 3-1, 

approximately 42 projects have been installed and most are still operating. The total installed 

capacity is estimated at 2,377 MW (4C Offshore Ltd 2010; Alpha Ventus 2010; C-Power NV 

2010; Centrica Energy 2010; DONG Energy 2010a, 2010b; Japan for Sustainability 2010; 

NoordzeeWind 2010; Offshore Center Denmark 2010; Prinses Amalia Windpark 2010; Statoil 

ASA 2010; Vindpark Vänern 2010; Blue H. USA 2009; E-ON UK 2009; EWEA 2009a; Invest 

in Denmark 2009; RWE Npower Renewables 2009; OWE 2008). Most installations have been 

in water depths of less than 30 m.

Figure 3-1 shows the installed capacity of each significant project by the year in which the 

project was completed. Figure 3-2 shows the installed capacity of offshore wind by country. 

Figure 3-3 is a bubble plot of each project showing capacity, water depth, and distance from 

shore, along with the year the project was installed. Note that most projects are located close to 

shore and in shallow water below 30 m in depth. New technologies being developed to extend 

this design space are discussed in Section 5.
23

Table 3-1. Summary of Current Offshore Projects Installed as of the Second Quarter of 2010

Country Project

Rated 

Capacity

(MW)

Average 

Water 

Depth

(m)

Average 

Distance 

Offshore 

(km)

Number of 

Turbines

Turbine 

Capacity 

(MW)

Turbine 

Manufacturer

Year 

Online

Belgium Thornton Bank 30 20 29 6 5 Repower 2008

China Donghai Bridge 102 10 10.5 34 3 Sinovel 2010

Denmark

Vindeby 5 4 3 11 0.45 Bonus 1991

Tunø Knob 5 3 6 10 0.5 Vestas 1995

Middelgrunden 40 8 3 20 2 Bonus 2000

Horns Rev 160 10 16 80 2 Vestas 2002

Samsø 23 20 3.5 10 2.3 Bonus 2002

Frederickshavn 10.6 3 1 4 2.65 Vestas/Bonus/ 

Nordex 2003

Nysted 165.6 8 8 72 2.3 Bonus 2003

Ronland 17.2 Unknown Unknown 8 2.3 /2 Bonus/Vestas 2003

Horns Rev 2 209 13 30 91 2.3 Siemens 2009

Sprogø 21 11 1 7 3 Vestas 2009

Avedøre 7.2 2 0.1 2 3.6 Siemens 2009

Finland Kemi Ajos I + II 30 0 1 10 3 WinWinD 2008

Germany

Ems-Emdem 4.5 3 0.1 1 4.5 Enercon 2004

Breitling 2.3 2 0.5 1 2.3 Nordex 2006

Hooksiel 5 5 0.5 1 5 Enercon 2008

Alpha Ventus 60 30 45 12 5 Repower 2009

Ireland Arklow Bank 25.2 15 10 7 3.6 GE 2004

Italy Brindisi 0.08 108 20 1 0.08 Blue H 2008

Japan Setana 1.32 10 0.2 2 0.66 Vestas 2004

Netherlands

Lely 2 7.5 0.8 4 0.5 Nedwind 1994

Irene Vorrink 16.8 2 0.1 28 0.6 Nordtank 1996

Egmond aan Zee 108 20 10 36 3 Vestas 2006

Prinses Amalia 120 22 23 60 2 Vestas 2008

Norway Hywind 2.3 100 10 1 2.3 Siemens 2009

Sweden

Bockstigen 2.8 7 3 6 0.3 Windworld 1998

Utgrunden 10.5 7 7 7 1.425 Enron/GE Wind 

Energy 2000

Yttre Stengrund 10 10 4 10 2 NEG-Micon 2001

Lillgrund 110 6 10 48 2.3 Siemens 2007

Vanern 30 7 4 10 3 WinWind 2010

United Kingdom

Blyth 4 6 1 2 2 Vestas 2000

North Hoyle 60 9 8 30 2 Vestas 2003

Scroby Sands 60 6 3 30 2 Vestas 2003

Kentish Flats 90 5 9 30 3 Vestas 2005

Barrow-in-Furness 90 15 7 30 3 Vestas 2006

Beatrice 10 45 25 2 5 Repower 2007

Burbo 90 10 5 25 3.6 Siemens 2007

Lynn/Inner Dowsing 194.4 10 5 54 3.6 Siemens 2009

Rhyl Flats 90 8 8 25 3.6 Siemens 2009

Robin Rigg 180 5 9.5 30 3 Vestas 2009

Gunfleet Sands 173 8 7 48 3.6 Siemens 2010
24

Figure 3-1. Nameplate generating capacity of offshore wind projects (1991–2010)

Figure 3-2. Installed offshore wind capacity by country (January 2010)
25

Note: Does not include experimental deepwater projects (e.g., Hywind)

Figure 3-3. Offshore projects showing capacity, water depth, and distance to shore

Middelgrunden is a 40-MW demonstration project that 

was installed just 3 km east of the center of Copenhagen 

in 2001. At the time, it was the largest offshore wind 

farm in the world. It led the way for two larger 160-MW 

projects, Horns Rev I in 2002 and Nysted in 2003. 

Figure 3-4 shows photos of Horns Rev I and 

Middelgrunden. 

These projects experienced some cost overruns and 

higher than expected failure rates resulting from wind 

and wave exposure that proved more severe than 

anticipated, along with an immature basis for planning 

and executing the projects. These issues displaced some 

of the initial enthusiasm for offshore wind energy 

development. As a result, 2005 was a slow year for 

offshore wind with only one offshore wind project 

installed. Manufacturers and developers placed 

considerable effort on understanding and correcting the 

problems associated with this first phase of projects. 

The growth of offshore wind remained slow through 

Figure 3-4. Middelgrunden Wind Plant 

(HC Sorensen, Middelgrunden Wind Turbine 

Cooperative, NREL/Pix 17855)
26

2008, but eight new projects were installed in 2009 (see Figure 3-1), indicating a rejuvenation of 

offshore development. Note also that the first Asian project was installed recently in China.

3.3 Worldwide Offshore Wind Projections

The use of energy from offshore wind resources has shown inconsistent growth throughout the 

world, but there are indications that the growth trend may begin to smooth out and accelerate 

(Table 3-2). European nations connected 584 MW of offshore wind capacity to the electrical grid 

in 2009, an increase of 56% over the previous year. European nations have a long history of 

harnessing wind energy, and Europe has been the leader in offshore wind. Several other 

countries, though, have begun looking toward offshore wind to meet their energy needs, 

including Canada, China, and the United States. 

3.3.1 Europe

Recently, the need to decrease carbon emissions; stabilize energy costs; and increase the use of 

indigenous, reliable energy sources has created an urgency in Europe that is resulting in a 

concerted effort to generate more energy from the wind. With almost 2,300 MW of installed 

capacity, Europe leads the world in offshore wind energy production (Table 3-2). After the first 

offshore wind project was installed off the coast of Denmark in 1991, more than 830 turbines 

have been installed and connected to the grid in nine European countries (EWEA 2010a). The 

market is continuing to expand with at least 1,000 MW expected to be installed during 2010. Of 

the hundreds of projects that are currently navigating some layer of the permitting process, at 

least 52 have been given consent and at least 16 are under construction. As seen in Table 3-2, 

Germany and the United Kingdom are expected to lead this growth. According to the European

Wind Energy Association (EWEA), 50 GW of offshore wind energy projects are in some stage 

of permitting and construction and at least 100,000 MW of projects are in some stage of planning

and development (EWEA 2009b). If 100 GW of capacity were installed, 8.7% to 11% of the 

European Union’s (EU) electricity demand would be met by offshore wind, and 202 million 

metric tons of carbon dioxide (CO2) per year would be eliminated (EWEA 2010a). For the long 

term, the EU has set goals for offshore wind installations to reach 40 GW by 2020 and 150 GW 

by 2030. 

Table 3-2. Offshore Development in Permitting and Under Construction

Country

Permitting, Approved, 

or Under Construction 

(MW)

In Operation 

(MW)

Belgium 1,194 30

Canada 1,826 0

China 201 102

Denmark 653 664

Estonia 1,000 0

Finland 1,306 30

France 1,455 0

Germany 25,411 72

Greece 1,101 0

Ireland 1,530 25
27

Italy 2,526 0

Japan 0 1

Maldives 75 0

Netherlands 3,969 247

Norway 565 2

Romania 500 0

Spain 70 0

Sweden 3,346 163

United Kingdom 6,085 1,041

United States ~2,000 0

Total 54,813 2,377

Source: 4C Offshore Ltd. 2010.

3.3.2 Other Parts of the World

Other than European nations, only a few countries have offshore wind projects in operation 

and/or development (Table 3-2). In Asia, China and Japan have operating offshore projects.

China has several projects in development and one project has been approved in the Maldives. 

Other Asian countries, including South Korea and Taiwan, are still in the planning stages. In 

North America, Canada and the United States have several projects in development. The 

following subsections summarize efforts in other countries, and Section 3.4 covers the status of 

offshore wind in the United States.

China: China deployed its first offshore wind turbine in 2007 and recently completed 

construction on its first offshore wind farm, the 102-MW Donghai Bridge project. By 2020, the 

Chinese government plans to increase the use of alternatives to fossil fuels to generate 15% of 

the nation’s total energy consumption (GOV.cn 2010). Offshore wind energy has the potential to 

generate more than 750 GW of China’s energy, which is almost three times the wind energy 

potential on land (see http://english.gov.cn/). In January 2010, China’s National Energy Bureau 

and the State Oceanic Administration enacted an interim measure on the management of offshore 

wind farm development. Highlights of this measure include the following:

• Offshore wind must be developed through public tender.

• Chinese-funded enterprises must be the developers or have majority ownership.

• Developers must start construction within two years of winning the tender.

Japan: Japan has put a strong policy framework in place for renewable energy development, 

including a renewable portfolio standard (RPS), power purchase agreements (PPAs), and 

subsidies for field testing and business. But extreme weather, economic downturns, a volatile 

legal system, and grid issues have decreased investment in both land-based and offshore wind 

energy. Recently, however, there have been indications that interest in offshore wind has been 

renewed (GWEC 2010). 

The Republic of Maldives: The Republic of Maldives, a group of islands in the Indian Ocean,

relies heavily on fossil fuel imports to meet its energy needs. The government has set a goal of 

becoming carbon neutral within the next decade. The production of energy from offshore wind 

farms is expected to supply 40% of the nation’s energy needs by 2013 (Miadhu 2010).
28

Canada: As a signatory to the Kyoto Protocol, Canada is committed to reducing its carbon 

emissions to below 1990 levels, and the country has been steadily increasing its energy 

production from land-based wind resources. Now, several offshore wind energy projects are in 

phases of development in the Great Lakes region as well as in coastal areas. For the last few 

years, the Canadian government has encouraged wind energy through the ecoENERGY for 

Renewable Power program. This program provides production incentives of 1 cent/kWh for the 

first 10 years of production (GWEC 2010). In addition, most provinces have set targets for wind 

energy development. Several provinces are also in the process of signing PPAs (GWEC 2010).

The Province of Ontario launched a feed-in tariff program in late 2009 as an incentive to 

developers and to meet its goal of phasing out coal plants by 2014 (Wood 2010). The program 

provides inflation adjusted payments of 19 cents/kWh for offshore wind over a 20 year period 

(Ontario Power Authority 2010). The provincial government of Ontario has also set distinct rules 

for the offshore wind industry. In Ontario, the construction permitting process is limited to 6 

months, and the government offers projects priority connection rights to the grid (Wood 2010). 

In turn, the provincial government envisions that the 20 GW of proposed projects (in different 

stages of development) in the Great Lakes area will create $253.5 billion in gross economic 

activity and more than 65,000 jobs, but the expected time frame could not be verified (Wood 

2010).

3.4 U.S. Offshore Wind Project Overview

Figure 3-5 shows the13 projects that have advanced significantly in the U.S. permitting process 

at press time for this report. As the map indicates, most of the initial activity is concentrated in 

the Northeast and Mid-Atlantic regions. Despite this, offshore wind is being considered in most 

U.S. coastal regions including the Great Lakes, the Gulf of Mexico, and the West Coast. The 

depth of the water on the West Coast, however, will preclude near-term development in spite of a 

very good wind resource because deepwater wind turbine designs are not currently commercially

available.
29

Figure 3-5. Proposed U.S. offshore wind projects and capacity showing projects with significant 

progress

Proposed U.S. offshore wind projects can be divided into two regulatory groups; those in federal 

waters (i.e., outside the 3-nm state boundary) and those under state jurisdiction (see Section 7 for 

ocean jurisdictions). This distinction dominates the current and near-term market today because 

of the perceived differences in regulatory uncertainty and timing. State projects are typically near 

shore and have marginally lower wind resources, but some developers are willing to accept these 

disadvantages to avoid the perceived regulatory delays associated with the federal process 

through the BOEM. For large-scale offshore wind development, there are not enough viable sites 

in state waters to achieve the 54 GW of offshore wind described by the U.S. Department of 

Energy’s (DOE) 20% by 2030 wind scenario (DOE 2008). In the short term, it remains to be 

seen if states will pave an accelerated path to regulatory approval. Long-term solutions lie with

the U.S. Department of the Interior (DOI), which is responsible for reducing the uncertainties 

associated with potential risks to the marine environment, and making the Bureau of Ocean 

Energy Management, Regulation and Enforcement’s (BOEM; formerly the Minerals 

Management Service [MMS]) permitting process more predictable (see Section 8).

Two projects in federal waters were granted special status under the Energy Policy Act of 2005 

(EPAct), which was initiated in part to address the need for offshore wind energy regulations and 

establish a federal program. Currently, Cape Wind (off Cape Cod, Massachusetts) is the only 

project that still holds that status; however, the project was in the approval process for 9 years. 

On April 29, 2010, Secretary of the Interior Ken Salazar, granted Cape Wind a commercial lease 

in federal waters (McConville 2010). Because the project was proposed before federal rules 

emerged, Cape Wind had to comply with the original ad hoc rules of the U.S. Army Corps of 

Engineers (USACE) as well as the new BOEM rules (see Section 7). The exact permitting and 

agency consultation timelines for offshore projects that proceed along a normal course in the 
30

federal BOEM process are currently unknown because no project has gone through it. The 

apparent timeline is much longer than the siting of other energy facilities on the Outer 

Continental Shelf. 

Table 3-3 describes most of the U.S. offshore wind development projects. Although many more 

proposals have been made, the projects listed in the table are more advanced, meeting one or 

more of the following criteria: they have been approved by their state, received an interim lease 

from BOEM (2010), or granted a BOEM lease. 

Table 3-3. Selected Offshore Wind Energy Projects (Federal and State Waters)

Developer 

and Location

Nameplate 

Capacity 

(MW)

Estimate 

Number of 

Turbines

Distance 

from 

Shore

(mi)

Project Status

(as of June 2010)

Projects with BOEM Lease (Federal)

Cape Wind 

Associates, 

Nantucket

Sound, MA

468 130 5.2–13.8

In 2001, the permitting process began under 

the USACE. In 2005, MMS gained regulatory 

authority and issued a final environmental 

impact statement (EIS) in 2009. Also in 2009,

the state and local permitting process was 

finalized and a long-term PPA was negotiated

with National Grid. In April 2010 the project 

was approved and a commercial lease offered. 

For further information, see Section 7.

NRG 

Bluewater 

Wind, 

Atlantic City, 

NJ

350 TBD 15–18

In June 2009, MMS awarded NRG Bluewater 

Wind an interim limited lease.

a It has also 

received a meteorological (met) tower rebate 

from the state, and has since begun baseline 

surveys (NRG Bluewater Wind 2010a).

Garden State 

Offshore 

Energy 

(GSOE),

Avalon, NJ

350 96 16 

GSOE is a subsidiary of the Public Service 

Enterprise Group and Deepwater Wind. GSOE 

won a competitive solicitation by the New 

Jersey Board of Public Utilities in the fall of 

2008 and received a met tower rebate from the 

state. MMS awarded an interim limited lease 

in June 2009, and the developers began 

conducting baseline surveys shortly thereafter

(GSOE 2008).
31

Developer 

and Location

Nameplate 

Capacity 

(MW)

Estimate 

Number of 

Turbines

Distance 

from 

Shore

(mi)

Project Status

(as of June 2010)

Fishermen's 

Energy,

Atlantic City, 

NJ

330 66 8 

MMS awarded an interim limited lease in June 

2009. Fishermen’s Energy received a met 

tower rebate from the state and began 

baseline surveys in August 2009. Fishermen’s 

proposes to develop the projects in two 

phases (Fishermen’s Energy 2007).

NRG 

Bluewater 

Wind,

Rehoboth 

Beach, DE 

450 60–200 11.5

In 2008, NRG Bluewater Wind and Delmarva 

Power negotiated a PPA for 200 MW. In 2009, 

MMS awarded an interim limited lease and 

NRG Bluewater Wind began conducting 

geophysical studies for a met tower 

installation. The project is anticipated to be 

450 MW; 293 MW has been initially contracted

(NRG Bluewater Wind 2010b).

Southern 

Company,

Savannah, GA

10 3–5 TBD

In 2007, a 2-year collaborative study with the 

Georgia Institute of Technology concluded that 

conditions were favorable but costs and the 

regulatory environment were preclusive. In 

2008, Southern Company was offered an 

interim limited lease that has not yet been 

executed (Georgia Institute for Technology 

and Southern Company 2005).

Projects in State Waters

Hull Municipal

Light Plant 

(HMLP), Hull, 

MA

12–20 4 1.5 

In 2007, Hull received funding from the 

Massachusetts Technology Collaborative to 

support permitting and siting analyses for a 

community project. In 2009, Hull received 

roughly $1.5 million in funding through 

Congressionally Directed Projects in 2009 

(Manwell 2007).
32

Developer 

and Location

Nameplate 

Capacity 

(MW)

Estimate 

Number of 

Turbines

Distance 

from 

Shore

(mi)

Project Status

(as of June 2010)

Deepwater 

Wind,

Block Island,

RI

29 8 3

In 2008 Deepwater awarded a competitive 

solicitation for a project. In 2009, Deepwater 

began studies for demonstration project in 

state waters. National Grid has agreed to a 20-

year PPA (Deepwater Wind 2010).

Fishermen's 

Energy,

Atlantic City, 

NJ

20 6 3

Fishermen’s Atlantic City Offshore Wind Farm 

is the first phase of a two-phase project (see 

federal project described previously). The wind 

farm is located in the New Jersey Ecological 

Baseline Study area. State permits are under 

review (Fishermen’s Energy 2007).

University of 

North Carolina 

(UNC), Chapel 

Hill/Duke 

Energy,

Pamlico 

Sound, NC

3-9 3 5–10 

In June 2009, UNC completed a study for the 

North Carolina General Assembly on offshore 

wind. In October 2009, Duke Energy signed a 

contract with UNC Chapel Hill to install 

turbines in the Pamlico Sound (Duke Energy 

2010). Three turbine demonstration projects

were cancelled in August 2010. It is not clear 

how this will be resolved. 

Coastal Point 

Energy 

(formerly 

W.E.S.T.), 

Galveston, TX

300 63 9

Coastal Point signed its first lease with Texas 

General Land Office (GLO) in 2005. Texas 

GLO awarded four competitively leased areas 

in 2007. A met tower was installed and began 

collecting data in 2007. The developer plans to 

begin construction on a project in 2010 

(Baryonyx Corporation 2009).

Lake Erie 

Energy 

Development 

Corporation

(LEEDCo), 

Cuyahoga 

County, Lake 

Erie, OH

20 3–7 3

The Great Lakes Energy Development Task 

Force spearheaded research on a 

demonstration project in Lake Erie. JW Great 

Lakes Wind released a final feasibility study for 

the Great Lakes Wind Energy Center in April 

2009. The task force established LEEDCo, 

which recently completed an agreement to 

purchase five 4.0-MW turbines from General 

Electric (Cuyahoga County Department of 

Development 2010).
33

Developer 

and Location

Nameplate 

Capacity 

(MW)

Estimate 

Number of 

Turbines

Distance 

from 

Shore

(mi)

Project Status

(as of June 2010)

New York 

Power 

Authority 

(NYPA),

Lake Erie or 

Lake Ontario

At least 

120 40–166 TBD

In 2009, NYPA selected five firms to perform 

technical studies. In December 2009, NYPA 

issued a request for proposals (RFP) to select 

developers for projects of at least 120 MW 

(and up to 500 MW) in the state waters of Lake 

Erie or Ontario. They received five responses 

to the RFP (NYPA 2010).

Source: Energetics Incorporated. Offshore Wind Energy Database. Unpublished. a

An interim limited lease term is 5 years. It does not allow for turbine construction and does not guarantee that a commercial

lease will be granted. 

3.5 U.S. Policy Overview 

For both federal and state offshore wind projects, a primary impetus for offshore wind 

development appears to stem from the desire to develop a zero-emissions generation technology 

that will increase energy security, attract economic development, and improve environmental 

quality. These factors are driving policies at both the state and federal level. Federal production 

tax incentives and government loan guarantees have helped stimulate interest for both land-based 

and offshore wind energy. Some states are beginning to develop climate change legislation that 

will price CO2 emissions and, in some cases, require utilities to transition from fossil fuels to 

clean renewable energy options. Many states with near-term potential for offshore wind have

enacted an RPS, mandating that utilities obtain a certain percentage their retail electricity sales 

from renewable energy or renewable energy credits (DSIRE 2010). Studies estimate that an 

additional 61 GW of renewable capacity will be needed to fulfill current state RPS requirements 

(see, for example, Wiser and Barbose 2008). States in New England and the Mid-Atlantic region 

currently meet the majority of their RPS goals with wind, biomass, and solar (Wiser and Barbose 

2009). For many states in the Northeast, offshore wind may be the only cost- effective utilityscale resource available to meet RPS goals (NREL 2010). New Jersey is the first state to pass a 

renewable energy certificate specifically for offshore wind and has proposed potential goals of

1,000 MW of by 2012 and 3,000 MW by 2020 (NJPBU 2009). Maine is facilitating the 

development of the next generation of deepwater floating turbines and foundations, and has 

announced goals “to install at least 2,000 megawatts of wind capacity by 2015 and at least 3,000 

megawatts by 2020, 300 of which could be located in coastal waters” (Maine Wind Energy Act 

2003).

One of the major barriers to efficiently deploying large-scale offshore wind is the long-term 

planning process of traditional utility markets and the lack of incentives to make a transition to 

low-carbon fuels. A recent study by ISO New England, Inc. (2009) found that focusing 

investment on offshore wind could be the most cost-effective use of new and existing 

transmission. Additionally, as described in Section 2, high regional electric costs make offshore 

wind attractive (Dhanju and Firestone 2009;EIA 2009 ). In the Northeast, ten coastal states are 

involved in the Regional Greenhouse Gas Initiative (RGGI), a “cap-and-trade” system to 
34

regulate CO2 emissions in the electricity sector. Auction revenues from such a system are often 

used to offer financial incentives to renewable energy projects (Clarke et al. 2009).

3.5.1 National and Regional Organizations

Several groups aimed at coordinating stakeholder efforts have formed to overcome the technical, 

economic, regulatory, environmental, and public perception barriers to offshore wind power 

development in the United States. These organizations help to connect state governments, 

industry representatives, academics, and clean energy advocates and allow these stakeholders to 

pool their resources and expertise. Selected groups are described in more detail in the list that 

follows:

U.S. Offshore Wind Collaborative: The USOWC was originally formed by three partners—the 

Massachusetts Technology Collaborative (MTC), GE Wind Energy, and DOE—to tackle 

offshore stakeholder concerns that arose in response to the issues surrounding the development 

of Cape Wind. USOWC is an interdisciplinary nonprofit organization directed at facilitating the 

development and growth of a U.S. offshore wind industry (USOWC 2010).

American Wind Energy Association Offshore Wind Working Group: AWEA formed a 

subcommittee called the Offshore Wind Working Group (OWWG), which primarily coordinates 

information exchange among offshore wind stakeholders.

Offshore Wind Development Coalition: OffshoreWind DC was founded in July 2010 in 

cooperation with AWEA and a group of seven U.S. offshore wind developers to promote 

offshore wind energy through advocacy and education (AWEA 2010). 

Atlantic Offshore Wind Energy Consortium: The AOWEC was formed by the governors of 

10 eastern costal states to facilitate cooperation between federal (DOI) and state governments on 

issues related to developing offshore wind on the Atlantic Outer Continental Shelf. Maine, New 

Hampshire, Massachusetts, Rhode Island, New York, New Jersey, Delaware, Maryland, 

Virginia, and North Carolina are currently AOWEC members (Vickery and Bullin 2010).

Great Lakes Wind Collaborative: GLWC is a regional organization working to facilitate the 

development of offshore wind projects in the Great Lakes. The group is staffed by the Great 

Lakes Commission and includes a broad coalition of stakeholders who are examining the 

technical, environmental, regulatory, educational, and financial issues related to the deployment 

of both land-based and offshore wind. The GLWC Offshore Wind Workgroup has produced 

siting principles for offshore wind in the Great Lakes (The Great Lakes Commission 2010).

3.5.2 State Initiatives

Thirty U.S. states border an ocean or Great Lake, and each has a unique demand for energy and a 

unique resource potential. As a result, each has responded differently to offshore wind at this 

early stage of development. Table 3-4 gives an overview of some of the state activities that are

under way in several coastal states. The table is not, however, an exhaustive list for all states 

because the number of organizations continues to grow at a rapid rate. One of the ways to 

compare the states to each other is by looking at their energy use and comparing it to the 

available offshore resource. Column 2 of Table 3-4 gives figures for the total generation of 

electricity for each coastal state in 2008 (EIA 2008). Column 3 presents the ratio of the gross 
35

wind resource potential for offshore wind7

The table also presents some policy information by state. Of 29 U.S. states that have adopted an 

RPS, 22 border an ocean or Great Lake. Column 4 in Table 3-4 shows the RPS parameters for 

these states (DSIRE 2010).

in each state as a percentage of the total generation of 

electricity in that state. This ratio gives a rough indication of how much of the state’s electric 

energy needs could be met by offshore wind and should only be used for qualitative evaluations.

For example, in states with extensive high wind resources, such as California, Massachusetts, 

and Maine, the percentages of resource potential from offshore wind exceed the total generation 

for those states. As a result, we could expect a higher dependence on offshore wind in these 

states than in low wind states, such as Florida, Alabama, and Mississippi, which show virtually 

no potential. In future analyses, offshore wind sites with wind speeds below 8.0 m/s could be 

considered, which would greatly improve this picture for some southern states. 

Table 3-4. Electric Energy Use and Offshore Wind Energy State Activity 

State

Total State

Generation

(MWh)

Resource 

Potential as a 

Percentage of 

Total Electric 

Generation

Renewable 

Portfolio 

Standards

(percentage; 

year)a

State Offshore Wind Studies and 

Planning Initiatives

Alabama 145,869,895 NAd

Alaska 6,774,834 NAd

California 207,984,263 634 33; 2020

Connecticut 30,409,473 2 27; 2020

Delaware 7,523,839 430 20; 2020

Integrated Resource Plan results in RFP 

from Delmarva Power;

Planning/deployment memorandum of 

understanding (MOU) with Virginia and 

Maryland;

MMS EA on Delaware Interim Lease;

MMS RFI for Competitive Leasing

Florida 219,636,818 NAd

Georgia 136,173,395 6

Georgia Tech/Southern Company resource 

and feasibility study

State Funded Marine Mapping Report

Hawaii 11,376,385 9,452 40; 2030 Interisland Cable Project

Illinois 199,475,178 32 25; 2025

Indiana 129,510,294 4

Louisiana 92,453,141 0

Maine 17,094,919 2,776 40; 2017

Ocean Energy Task Force;

Gulf of Maine Offshore Wind Energy 

Development Initiative;

Governor’s Task Force on Wind Power 

Development;

Report of Governor’s Task Force;

 7 Resource potential from offshore wind is based on winds above 8.0 m/s and a net capacity factor of 0.37. The 

figures include all windy waters without taking territorial exclusions into account. 
36

Legislative Directive (L.D.) 1465 directs 

Department of Conservation in choosing 

testing sites

Maryland 47,360,953 227 20; 2022

Request for Expressions of Interest and 

Information;

Planning/deployment MOU with Delaware 

and Virginia;

Maryland’s Offshore Wind Power Potential

Massachusetts 42,505,478 1,498

22.1; 2020

New renewable 

energy

percentages: 15

in 2020 + 1 

annually 

thereafter

Ocean Management Plan;

Ocean Management Initiative

Michigan 114,989,806 1,045 10; 2015 + 1,100 

MWa

Great Lakes Wind Council;

Report of the Michigan Great Lakes Wind 

Council;

Planning for Offshore Wind Developments 

in Michigan’s Great Lakes;

Grand Valley State University—West 

Michigan Wind Assessment

Minnesota 54,763,360 0 25; 2025

Xcel: 30; 2020

Mississippi 48,205,711 0

New 

Hampshire 22,876,992 43 25; 2025

New Jersey 63,674,789 456 22.5; 2021

Blue Ribbon Panel;

Ocean/Wind Power Ecological Baseline 

Studies;

New Jersey Offshore Wind Energy 

Feasibility Study;

MMS EA on New Jersey Interim Lease

New York 140,322,100 277 29; 2015

Long Island-New York City Offshore Wind 

project;

NYPA Ongoing Project Studies

North Carolina 125,239,063 693

Investor-owned 

utilities: 12.5; 

2021

Cooperatives 

and 

municipalities:

10; 2018 

UNC Coastal Wind Study (commissioned 

by General Assembly);

Governor’s Scientific Advisory Panel on 

Offshore Energy

Ohio 153,412,251 62 12; 2024

The Great Lakes Energy Development 

Task Force;

Cuyahoga County Feasibility Study

Oregon 58,718,438 1,160

Large utilities:

25; 2025b

Small utilities: 5–

10; 2025 

Pennsylvania 222,350,925 12 ~18; 2021c

Rhode Island 7,387,266 1,048 16; 2019

The Rhode Island Ocean Special Area 

Management Plan (SAMP);

RI WINDS siting study;
37

Offshore Wind Stakeholders Final Report

South Carolina 100,978,005 263

SC Offshore Wind Collaborative;

Palmetto Wind Research Project;

Ocean and Coastal Resource Management 

Plan;

Wind Energy Production Farms Feasibility 

Study Committee;

Regulatory Task Force for Coastal Clean 

Energy

Texas 404,787,781 115

5,880 MW; 2015

10,000 MW; 

2025

Lease process with Texas GLO

Virginia 72,678,531 320 15; 2025b

Planning/deployment MOU with Delaware 

and Maryland;

Virginia Coastal Energy Research 

Consortium Final Report of Offshore Wind

Energy and Economic Potential for 

Offshore Wind in Virginia;

Mapping and GIS Analysis in support of 

Clean Energy Development Offshore in 

Virginia

Washington 110,828,451 267 15; 2020b

Wisconsin 63,479,555 413 10; 2015 PSC Feasibility Study

a RPS includes a goal for a percentage of renewable energy and the year it must be achieved unless otherwise noted. b Extra credit for solar or customer-sited renewables c Includes nonrenewable alternative sources

d

not analyzed

Notes: EA = environmental assessment; RFI = request for information; GIS = geographic information system; PSC = Public 

Service Commission

Many of the states where interest in offshore development is building have begun various 

planning processes to integrate wind, and some governors have explicitly funded and approved 

offshore wind plans, studies, and projects (Table 3-4, column 5). Links given in the table indicate 

that several states have instituted panels or task forces to make recommendations on offshore 

wind, undertaken feasibility studies to estimate wind resource areas in the sea, and/or undertaken 

initiatives in ocean management planning. 

Several states such as Delaware, Rhode Island, and New York are incorporating PPAs into their 

competitive solicitations. Other states (e.g., Maine and Rhode Island) are requiring utilities to 

buy more clean energy. This movement toward binding contracts and PPAs is important for 

creating sustained demand, utility commitments, and financial incentives. Selected state 

activities are described in more detail in the paragraphs that follow.

New Jersey: New Jersey became involved in offshore wind in part because several private 

developer proposals received media and community attention around 2004. In response, the 

governor imposed an 18-month moratorium on offshore wind. During that time, a blue-ribbon 

panel was formed to identify and weigh the economic and environmental costs and benefits of 

wind compared with other energy sources (State of New Jersey 2006). The panel’s findings led 

to recommendations for further baseline studies and the development of a demonstration project

of up to 350 MW. In July 2010, the New Jersey Department of Environmental Protection 

(NJDEP) released the final ecological baseline study, intended to fill major data gaps for birds, 

sea turtles, marine mammals, and other natural resources and their environments in the 

designated study area (Geo-Marine 2010; NJDEP 2010). In addition, the New Jersey Commerce, 
38

Economic Growth, and Tourism Commission (NJCEP; 2009) conducted public opinion studies 

of offshore wind. In 2008, New Jersey issued an RFP seeking interested developers to begin the 

first demonstration project. Several proposals were received and three developers were 

considered competitive. All three developers have now secured MMS interim limited leases to 

install met towers. The current goal of New Jersey’s Energy Master Plan is to install 1,000 MW 

of offshore wind capacity by 2012 and 3,000 MW of capacity by 2020 to help meet the state’s 

RPS goals. New Jersey currently has developer proposals for 1,050 MW of offshore wind. The 

state has also passed the Offshore Wind Economic Development Act, which creates an offshore 

wind renewable energy certificate program and will provide financial assistance and tax credits 

for the development of key renewable energy infrastructure (North American Wind Power 

2010).

Rhode Island: Rhode Island wants to explore the integration of offshore wind into its electricity 

portfolio. The state has used ocean spatial planning to identify the best areas for offshore wind 

development. Technical wind resource data and water depths were coupled with information on 

financial feasibility, environmental risks, and public acceptance to identify the ten best areas for 

offshore wind. The Rhode Island Coastal Resources Management Council (2009) is developing 

an ocean special area management plan (SAMP) that will be an important component in siting 

offshore wind projects. In April 2008, Rhode Island’s Office of Energy Resources issued an RFP 

to develop a demonstration project in state waters off the coast near Block Island (State of Rhode 

Island, Office of the Governor 2009). In January 2009, Deepwater Wind signed a joint 

development agreement with the state. In December 2009, the developer negotiated a 20-year 

PPA with National Grid. In March 2010, the Rhode Island Public Utilities Commission (RIPUC) 

rejected this agreement because of cost concerns. Demonstrating political support for offshore 

wind, the Rhode Island legislature subsequently passed H 8083A and S 2819A, which required 

Deepwater and National Grid to file a new PPA with the RIPUC (Isensee 2009; Kuffner 2009).

The commission approved the revised PPA on August 12, 2010. Rhode Island has proposals for 

installing 428 MW of offshore wind energy, which represents approximately 15% of its electric 

energy needs.

Massachusetts: Cape Wind was the first offshore wind project proposed in the United States.

Despite opinion polls showing that state residents overwhelmingly support the project, the 

project has been met with significant opposition. After 9 years of regulatory review, Cape Wind 

finally received federal permits in April 2010 and signed a PPA with National Grid in May 2010. 

Though the project is likely to face further legal challenges from opponents, the developers aim 

to start construction in 2011 and complete the project by the end of 2012.

Another significant Massachusetts initiative was initiated by DOE’s Wind and Water Power 

Program (WWPP), which competitively selected the MTC to develop a Wind Blade Technology 

Testing Center in partnership with the National Renewable Energy Laboratory (NREL). MTC 

was awarded $25 million in funding from the American Recovery and Reinvestment Act of 2009 

to accelerate development (EERE 2009).

Massachusetts has also developed an ocean management plan that establishes three categories of 

management area: prohibited, regional energy, and multiuse. The plan allows for commercialscale wind projects only in specified areas (Massachusetts Office of Energy and Environmental 

Affairs 2009). In June 2009, the governor’s office set a goal of developing 2,000 MW of wind by 

2020 (Sullivan et al. 2009). Massachusetts has proposals for installing up to 688 MW of offshore 

wind.
39

Delaware: Delaware initiated legislation and policies to encourage offshore wind which resulted 

in a PPA between Delmarva Power and NRG Bluewater Wind. The state legislature passed

several laws, including HR-6, which amended the Electric Utility Retail Customer Supply Act of 

2006. This required utilities to consider energy efficiency, renewable energy, price stability, and

environmental impact ahead of fossil-fuel sources (Firestone and Kempton 2006). The PPA 

guarantees financial returns and certainty for novel resource development and is seen as a path to 

move offshore wind energy forward (Dhanju and Firestone 2009). Throughout the process of 

allocating a PPA, NRG Bluewater Wind partnered with the University of Delaware to create a 

stakeholder dialogue process that engaged the community on the prospect of offshore wind 

power, which ultimately aided in the final award to NRG Bluewater Wind (Kempton 2009). In 

addition to supporting the NRG Bluewater Wind project, the energy plan calls for developing 

business and research related to wind energy, and supporting a center of excellence in offshore 

wind at the University of Delaware. Delaware has proposals for installing 450 MW of offshore 

wind. An important milestone was the issuance of a Request for Interest for an area off Delaware 

that begins the commercial wind leasing process (MMS 2010).

Maine: Maine is facilitating the development of deepwater floating turbines and substructures. 

In June 2009, the state legislature passed a legislative directive (LD 1465) recommended by the 

Ocean Energy Task Force, which was established by Governor Baldacci in 2008. The legislation 

called for the identification of ocean energy testing areas in coastal state waters for the 

development of a Maine Offshore Wind Energy Research Center in concert with the University 

of Maine. As directed by the legislation, the state Department of Conservation selected sites 

through the University of Maine’s Offshore Wind Energy Geographic Information System and 

solicited stakeholder input (Maine Ocean Energy Task Force 2009). Under a comprehensive, 

multiphase initiative known as DeepCwind, the University of Maine has plans to develop one of

the test sites in state waters. At the site, a one-third-scale deepwater floating offshore turbine 

prototype will be built for the purpose of developing the design tools needed for full-scale 

commercial development. The new state legislation calls for a speedy permitting process and for 

applicants to submit site plans, fish and wildlife monitoring plans, and navigation plans. The 

University of Maine has received federal funding of approximately $12 million from DOE, 

Congress, and the National Institute of Standards and Technology (NIST) for this project 

(Dagher 2010). On June 8, 2010, voters in Maine approved an additional $11 million for the 

DeepCwind project. 

The Great Lakes: To date, no offshore wind turbines have been sited in freshwater, particularly 

a potable water source such as the Great Lakes. Developing the offshore resource in the Great 

Lakes will pose engineering challenges like ice floes that will impose substantial forces on 

turbine bases, floats, and mooring lines (Public Service Commission of Wisconsin 2009a).

Additionally, large vessel access to the Great Lakes is more restricted than at ocean sites, which 

creates supply and logistical challenges. Specifically, the lock system that allows access to the 

Great Lakes limits the breadth of vessels to 24.4 m (Steward 2010). Many turbine installation 

vessels exceed this limitation, complicating the logistics of offshore wind project development

(A2SEA 2010).

Despite the challenges, state leaders and renewable energy advocates perceive tremendous 

benefits from siting wind on the lakes—including greater energy potential than land-based 

options, proximity to load centers, balancing heavy dependence on fossil fuels for current supply, 

and the potential for creating jobs and manufacturing supply chains to support a new industry. A 
40

number of stakeholder organizations are exploring offshore wind in the region and tackling the 

permitting and siting issues. Individual states and municipalities, such as Michigan and 

Cuyahoga County, Ohio, have also formed stakeholder groups addressing area-specific offshore 

wind energy development. The Michigan Great Lakes Wind Council, created by Governor 

Granholm in early 2009, produced a report about developing offshore wind in Michigan waters. 

The report estimates the local wind resource potential and the regulatory changes needed to 

facilitate permitting, leasing, construction, and monitoring of offshore wind projects. The 

governor has extended the council’s charter through December 31, 2010 (Michigan Great Lakes 

Wind Council 2010). In Ohio, the Great Lakes Wind Energy Task Force was formed in 

Cuyahoga County to advise the county on the development of wind projects in Lake Erie, the 

shallowest of the Great Lakes (Cuyahoga County Department of Development 2010). In 2007,

the Cuyahoga Task Force recommended the creation of a Great Lakes Wind Research Center, 

which would include a demonstration project of several turbines and produce 5 to 20 MW of 

power. In 2008, the Cuyahoga County Board of County Commissioners approved a contract for 

more than $1 million with JW Great Lakes Wind, LLC (JWGL) to examine the legal, technical, 

environmental, economic, and financial aspects of developing a Great Lakes Wind Energy 

Center. JWGL issued its report in 2009 (JWGL 2009). In addition, the PSC of Wisconsin 

commissioned a feasibility study that identifies options for meeting major challenges to offshore

wind (PSC of Wisconsin 2009b). At this stage, many uncertainties exist along the path forward 

for the eight states along the Great Lakes, and many of the needs and requirements of the 

stakeholders in federal waters will be the same along these coasts. 

One significant development for Canadian prospects is the new Ontario feed-in tariff or FIT 

program. This is North America’s first comprehensive guaranteed pricing structure for renewable 

electricity production. It offers stable prices under long-term contracts for energy generated from 

renewable sources, including offshore wind. It provides a guaranteed price of CAD$190/MWh 

over 20 years (subject to consumer price index inflation; see Ontario Power Authority 2010).

These types of financial incentives are intended to spur development and establish a predictable 

financial pathway for offshore wind deployments. Development on the Canadian side could have 

a synergistic impact on progress attained by U.S. developers in the Great Lakes region.

Texas: Texas has the most land-based wind installed of any state, with almost 10,000 MW in 

operation (Wiser and Bollinger 2009). Texas is the only state that has a regulatory framework for 

leasing renewable energy resources in its state waters, which extend out to 9 nm from shore. In 

2001, the Texas GLO began evaluating state lands, including offshore areas, for the development 

of wind using detailed GIS layered data (Texas GLO 2007). The Texas GLO has initiated leases

for the rights to develop offshore wind (noncompetitive; see Dhanju and Firestone 2009) and 

conducted a competitive leasing program as well. Leases were awarded to Coastal Point Energy 

(formerly Wind Energy Systems Technology, W.E.S.T.) on four tracts of land (Snyder and 

Kaiser 2009; Texas GLO 2009). In July 2009, the Texas GLO held another lease sale, and two 

offshore tracts were awarded to Baryonyx Corporation for development (Baryonyx 2009). The 

Texas GLO has predicted that Texas will have the first operational offshore turbine in the United 

States (Beniwal 2010). Texas has proposals for installing more than 300 MW of near-term 

offshore wind energy projects and both Costal Point Energy and Baryonyx have indicated that 

their projects will be larger than 1 GW when all phases are fully operational.
41

3.6 Description of Offshore Wind Supply Chain

The United States could benefit from new manufacturing and employment opportunities that an 

expanding offshore wind industry could potentially drive and sustain along our coastlines and 

lakeshores. Although densely populated areas near high load centers limit the land use options 

for alternative energy supplies, offshore wind can promote jobs and economic activity from 

domestic supply chains, which is a prime motivation for state leaders to advocate for offshore 

deployments in and adjacent to their waters. 

3.6.1 Turbine Suppliers 

Only two major turbine manufacturers, Siemens and Vestas, contributed substantially to new 

offshore wind capacity in 2008 (EWEA 2010b), but several new offshore turbines are now 

nearing commercial viability. Both Repower Systems AG (majority ownership by Suzlon) and 

Multibrid (majority ownership by Areva) installed commercial 5-MW turbines with the Alpha 

Ventus project in Germany.8

Table 3-5. Commercial Offshore Wind Turbines 

Sinovel also entered the market in 2009 with the SL3000, the first 

offshore wind turbine made in China. Most recently, General Electric reentered the offshore 

wind market with the announcement of its 4.0-MW direct drive turbine, which is still under 

development in Europe (GE Power & Water, Renewable Energy 2010). Table 3-5 lists the 

current manufacturers of offshore wind turbines. 

Turbine 

Manufacturer

Turbine Model and

Rated Power (in MW)

Date 

Available Offshore Operating Status

Siemens SWT2.0—2.0 2000 Commercially inactive

Vestas V80—2.0 2000 Commercially inactive

General Electric GE 3.6 —3.6- 2003 Commercially inactive

Siemens SWT2.3—2.3 2003 Commercial

Vestas V90—3.0 2004 Commercial

Siemens SWT3.6—3.6 2005 Commercial

Repower 5M—5.0 2005 45-m Water Depth Demonstration

Commercial at Alpha Ventus, Thornton Bank

Multibrid M5000— 5.0 2005 Onshore 2005

Commercial at Alpha Ventus 2009

Sinovel SL3000—3.0 2009 First Chinese Offshore Project—102 MW 

installed

BARD BARD—5.0 2010 Installations at BARD Offshore 1 project 

began in March 2010

General Electric GE 4.0/110—4.0 2012 Commercial sales announced, no prototype 

experience

Most of the offshore wind turbines in operation are marinized versions of proven land-based 

turbine designs with upgraded electrical systems and corrosion systems, which are placed on 

free-standing concrete gravity bases or steel monopile foundations. Offshore turbine designs are 

likely to increasingly decouple from land-based technology as original equipment manufacturers 

 8 Note that Repower had previously demonstrated its 5-MW wind turbine in the Beatrice Fields in the Talisman 

Energy DOWNVInD project, which was installed in 45 m of water in 2006. 
42

(OEMs) explore the possibilities of larger turbines and optimize the technology for offshore 

application (see Section 5). 

3.6.2 Key Components

Offshore wind turbines are generally larger than land-based machines. As a result, a large portion 

of the project costs results from transporting very large parts from component manufacturers to 

the OEM assembly plant and then to the installation site. This is especially true for some key 

components, such as blades and tower sections, which tend to limit land-based turbine size. 

In addition, offshore wind turbine components can be expensive to fabricate in existing facilities 

that are designed to manufacture land-based machines. Building new, specialized manufacturing 

facilities presents a significant opportunity to reduce the costs of manufacturing blades, towers, 

and other components.

These factors are likely to drive OEMs to build new manufacturing facilities. In Europe, OEMs 

have already begun to cluster manufacturing plants in cities that are well situated to support the 

logistics and fabrication requirements for offshore deployment (Williams 2010). In addition to 

improving the turbine supply chain and positioning manufacturers to achieve cost improvements, 

construction of these new, specialized manufacturing facilities is bringing valuable 

manufacturing jobs to European coastal communities. This experience is likely to be repeated in 

the United States as the offshore wind industry grows because high transportation costs favor 

local production. To maximize the benefits, manufacturers will probably construct facilities in 

locations with access to ports suitable for offshore logistics and a high concentration of 

underutilized skilled labor. These locations will likely be centrally located in the proposed 

development regions. 

3.6.3 Balance of Station

More than half of the installed capital cost of an offshore wind project goes to the balance of 

station (BOS). Included under the BOS umbrella are the turbine substructure, the electrical 

distribution, substation, and grid connection; logistics and installation; and geotechnical, 

regulatory, and permitting activities (see Section 6). These parts and services are generally 

sourced from the local supply chain that comprises traditional construction and fabrication labor.

Because BOS represents such a large part of project costs, considerable effort will be directed at 

attempting to reduce these costs through the homogeny of foundation design and mass 

production.

3.6.4 Vessels, Harbors, and Local Economic Activity

The lack of suitable vessels for moving, constructing, installing, and maintaining offshore wind 

turbines may present a short-term barrier to development (AWEA 2009). Currently oil and gas 

vessels are the most applicable for use in the offshore wind industry because they have some of

the critical attributes needed for the construction and installation phases. Most of these vessels 

are located in the Gulf of Mexico, would require at least some modifications or upgrades to 

perform as needed, and may not be available to the wind industry because the demand for 

offshore oil exploration and development is high. Potential near-term construction of new, 

specialized vessels dedicated to offshore wind will likely be restricted by the cost of building 

such a vessel (capital outlay estimated at more than $100 million). Such a high initial investment 

makes it unclear who will build these first ships considering the current levels of uncertainty 

about the future offshore wind build-out. Europeans built their first dedicated offshore heavy-lift 
43

wind construction ships after their offshore wind project installations ramped up in the early part 

of the last decade. 

It is highly unlikely that these ships would be available to construct projects in the United States 

given the high demand in Europe (~50 GW in the permitting pipeline). Even if these vessels 

were available, they could not operate in the United States because of the Jones Act. This act, 

also known as the Merchant Marine Act of 1920, requires that all goods transported between 

U.S. ports be carried in U.S.-flagged ships that were built domestically, owned by U.S. citizens, 

and crewed by personnel authorized to work in the United States. The purpose of the law is to 

support the U.S. merchant marine industry and to sustain national security preparedness. The 

effect for offshore wind development is that only vessels qualified under the Jones Act will be 

able to transport, construct, install, and maintain offshore wind turbines (Online Lawyer Source 

2010).

Although the Jones Act provisions might represent a short-term barrier to offshore wind 

development, the act also creates a substantial opportunity for domestic shipbuilders. The 

construction of the initial dedicated offshore wind vessel might require either a large-scale wind 

project with sufficient capital investment to offset the upfront costs for a specialized vessel or 

evidence of a large, probable U.S. development pipeline. 

Effective development of offshore wind projects requires the use of ports that meet specific 

requirements. Port facilities must have quaysides 200 to 300 m long that can accommodate 

vessels up to 140 m in length with a 45-m beam and a draft of 6 m. Quayside infrastructure must 

be capable of offloading rotors, nacelles, towers, and foundations. Port facilities must also have 

significant lay-down acreage; experience suggests that each turbine requires between threequarters and one acre of land per turbine for lay-down and preassembly (BVG Associates 2009; 

AWS Truewind 2009).

3.7 Findings and Conclusions

The development of offshore wind resources is seen by many nations—including the United 

Kingdom and Germany—as an integral component of decreasing their carbon emissions while 

meeting their energy needs. Globally, 2,377 MW of offshore wind is in operation with another 

gigawatt to be added by the end of 2010. In Europe alone, more than 50 GW of capacity is in 

some phase of development. Several Asian countries including China, Japan, and the Maldives 

are also developing their offshore resources. In North America, several provinces in Canada are 

actively pursuing offshore wind development. 

In the United States, more than 2,000 MW of offshore wind projects are in the permitting process 

but none have yet been installed. Uncertainty and projections of lengthy timelines have 

motivated states to encourage offshore wind development in their near-shore waters. By doing 

this, state governments hope to lock in early manufacturing investments, which would 

strategically position them to capture the economic benefits of the future offshore wind buildout. In many instances, state-sponsored projects appear to be moving ahead of projects under

federal agency jurisdiction. Projects in state waters face a unique set of challenges including a 

patchwork of rules and permits, along with gaps in leasing, zoning, and fee structures for using

the seabed. Siting projects in state waters could accelerate the deployment of offshore wind 

energy, but this must be done carefully to avoid problems related to regulatory uncertainties, 
44

aesthetic issues (arising from the close proximity to the coast),

9

A positive trend is the coalescence of regional entities directing efforts to assuage public and 

regulatory concerns and minimize siting conflicts arising from offshore wind development. 

Several groups, such as the USOWC, AWEA’s OWWG, the AOWEC, OffshoreWindDC, the 

Clean Energy States Alliance (CESA), and the GLWC are building stakeholder relationships.

Maryland, Virginia, and Delaware have also signed an MOU to collaborate on offshore wind 

issues. Many groups have identified a need to coordinate offshore issues among the states, but

they will need federal leadership, technical guidance, and financial resources. 

and other public concerns about 

uses of the coastal waters (see Section 7).

The global offshore wind supply chain has expanded substantially with the buildup of installed 

capacity in Europe and the huge amount of projects in the global development pipeline. A 

number of OEMs are in the process of releasing new models of offshore turbines for commercial 

operation, giving project developers more options. These new turbine models generally have 

greater capacity than the current generation of turbines and represent a shift away from adapting

land-based turbine designs to handle the environmental stresses of offshore deployment. Even 

though the United States has not yet developed an offshore wind project, the logistical 

requirements of transporting offshore machines would encourage OEMs to build up U.S. 

manufacturing operations as soon as a long-term pipeline of likely project emerges. The nation’s 

economy would benefit from the new manufacturing and employment opportunities that an 

expanding offshore wind industry could deliver to our coastlines and lakeshores.

Despite short-term uncertainty, the long-term prospects for offshore wind appear to be solid. 

Large offshore resources exist in close proximity to the varied coastal regions of the United 

States (see Section 4) and the technology to harvest these wind resources is commercially 

available (see Section 5). As a result, the United States could feasibly build 54 GW of offshore 

wind by 2030 under conservative assumptions about transmission, fossil-fuel supplies, and 

supply chain availability. 

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Sullivan, K.; Duesser, B.; Haberlin, K. (January 13, 2009). “Governor Patrick Sets New Goals 

for Wind Power.” Press release. 

http://www.mass.gov/?pageID=gov3pressrelease&L=1&L0=Home&sid=Agov3&b=pres

srelease&f=090113_Goals_Wind_Power&csid=Agov3. Accessed July 31, 2010.

Texas GLO (General Lands Office). (October 2, 2007). “Texas Awards First Competitive Wind 

Leases in the United States.” Press release. 

http://www.glo.state.tx.us/news/archive/2007/events/windlease_100207.html. Accessed 

December 30, 2009.
52

Texas GLO. (2009). Mapping and Monitoring Sustainable Energy. 

http://www.glo.state.tx.us/energy/sustain/mapping.html. Accessed December 30, 2009.

The Great Lakes Commission. (2010). “The Great Lakes Wind Collaborative.”

http://www.glc.org/energy/wind/pdf/GLWC%20Overview_709.pdf. Accessed January 5, 

2010.

U.S. Offshore Wind Collaborative. Web site. http://www.usowc.org/index.html. Accessed 

August 16, 2010.

Vickery, H.; Bullin, L. (June 8, 2010). Salazar Signs Agreement with 10 East Coast Governors 

to Establish Atlantic Offshore Wind Energy Consortium. U.S. Department of the Interior.

http://www.doi.gov/news/pressreleases/Salazar-Signs-Agreement-with-10-East-CoastGovernors-to-Establish-Atlantic-Offshore-Wind-Energy-Consortium.cfm. Accessed 

August 15, 2010. 

Vindpark Vänern. “Renewable Energy in Värmland.” Web site (in Swedish). 

http://www.vindparkvanern.se/. Accessed January 8, 2010.

Williams, A. (February 11, 2010.). “The Offshore Challenge: Installation Tactics.” Wind Energy 

Update. http://social.windenergyupdate.com/industry-insight/offshore-challengeinstallation-tactics. Accessed July 30, 2010.

Wiser, R.; Barbose, G. (2008). Renewable Portfolio Standards in the United States: A Status 

Report with Data through 2007. LBNL-154E. Berkeley, CA: Lawrence Berkeley 

National Laboratory. 

Wiser, R.; Barbose, G. (2009). “State of the States: Update on RPS Policies and Progress.”

Presented to the State-Federal RPS Collaborative National Summit on RPS, Chicago, IL,

November 18.

http://www.cleanenergystates.org/Meetings/RPS_Summit_09/WISER_RPS_Summit2009

.pdf. Accessed July 30, 2010.

Wiser, R.; Bolinger, M. (2009). 2008 Wind Technologies Market Report. Washington, DC: DOE.

http://eetd.lbl.gov/ea/ems/reports/2008-wind-technologies.pdf. Accessed July 31, 2010.

Wood, E. (2010). “Offshore Awakening: US Investment Flows to Offshore Wind.”

http://www.renewableenergyworld.com/rea/news/article/2010/03/offshore-awakening. 

Accessed April 15, 2010.
53

4.0 Offshore Wind Energy Resources in the United States

The National Renewable Energy Laboratory (NREL) first estimated the offshore wind resources 

of the United States in 2003. These data, which were reported in several technical papers (see, 

for example, Musial and Butterfield 2004, 2005), demonstrated that the U.S. offshore wind 

energy resources were very large, with an estimated potential gross resource nearly equal to the 

total generating capacity of the national grid. These data were conservative because they did not 

include key areas such as Hawaii, the southeastern coast, or the Gulf of Mexico. In addition, they 

contained generalized assumptions about wind energy exclusions areas that were not fully 

developed.

The data contained in this report have been updated and improved since the early studies. The 

resource potential reported in this section includes the wind resource in the lower 48 contiguous 

United States, except for Florida, Alabama, and Mississippi, which were not assessed in this 

version of the analysis. In addition, wherever possible, the offshore data were regenerated for a 

90-m height reference to more accurately reflect the resource at hub heights closer to those 

where offshore turbines will operate. This new resource estimate does not assess exclusion 

areas—areas where wind turbines cannot be built—which allow for competing uses of the ocean, 

lakes, and seabed and would be a substantial fraction of the gross resource. Exclusion areas 

should be defined in cooperation with state or regional stakeholders, and the authors felt that an 

attempt to estimate them here on a cursory level could be misleading. As a result, the resource 

numbers reported here are the gross resource estimates of all the windy water, and are therefore 

higher than what is actually extractable. These numbers form the foundation for computing the 

potential deployment on a state-by-state basis. It should also be noted that establishing and 

maintaining the most accurate estimate of the wind resource is a continuous process requiring 

refinements and updates as better models are developed and the techniques for estimating and 

measuring wind characteristics are improved. This analysis is likely to be updated in future 

reports as better data become available. 

4.1 Wind Resource Methodology

This section describes how the offshore U.S. wind resource maps were created and how the map 

data were converted to estimates of the wind potential. The offshore potential estimates are 

presented by region and individual state.

4.1.1 Mesoscale Modeling

The most comprehensive estimates of the wind energy resource potential in the United States 

come from wind resource maps generated from mesoscale wind models. Mesoscale weather 

prediction models are used to determine the wind resource potential over wide geographic areas

on the scale of 100 km or more. This methodology has been validated extensively for land-based 

applications in the United States against actual anemometer data. To a more limited extent, the 

methodology has been validated for coastal and offshore areas using data from weather buoys, 

U.S. Coast Guard stations, and satellite imagery. Although these models have not been fully 

validated in all climatological conditions, they are more accurate than the earlier boundary-layer 

prediction methods used in conjunction with measured data. The models continue to be updated 

and refined as new data become available. 
54

These models use inputs from synthesized historical weather databases to determine averages 

and frequency distributions for wind speed, direction, and wind power density at various 

elevations on annual, monthly, and daily time scales. The modeling results presented in this 

report are a composite of different regional model runs using the most current version of the 

model at the time the runs were made. Examining these offshore regions out to 50 nm shows an 

abundance of wind energy potential in the offshore regions over the continental shelf. Florida, 

Alabama, and Mississippi have not yet been included in the mesoscale modeling, and the lack of 

alternative tall tower wind measurements for this region precluded resource estimates at the 90-

m height for this analysis. The offshore wind resource for these states will be estimated in later 

studies but are not expected to make a large contribution to the national offshore wind resource. 

Figures 4-1 and 4-2 are two maps of the national offshore resource. Figure 4-1 shows the 

national distribution of the offshore and land-based wind resource by power class at 50 m above 

the surface (Elliott et al. 1987). For this map, NREL meteorologists empirically estimated the 

offshore resource for Florida, Alabama, and Mississippi. These are included to present a 

comparison of the land-based and offshore resource in this region. Figure 4-2 shows the national 

offshore wind speed at 90 m above the surface. Noticeable horizontal discontinuities of the wind 

speed at several state borders result from using different versions of the mesoscale models, both 

on land and offshore, over different time periods. Figure 4-3 is a 90-m wind speed map for 

Massachusetts that was recently developed using a mesoscale model. Here, it serves as an 

example of a state map (Schwartz et al. 2010). Schwartz and colleagues also developed and 

catalogued individual state maps for most of the other coastal states.

.

Source: Schwartz et al 2010

Figure 4-1. U.S. land-based and offshore wind resource estimates at 50-m height (wind classes 3–7)
55

Source: Schwartz et al. 2010.

Figure 4-2. U.S. offshore wind speed estimates at 90-m height

Source: Schwartz et al. 2010.

Figure 4-3. Massachusetts offshore wind speed estimates at 90-m elevation
56

4.1.2 Wind Turbine Array Density

The wind resource was quantified in 0.5 m/s wind speed intervals at 90 m, starting from an 

annual average value of 7.0 m/s and moving up. The mesoscale model maps describe the wind 

characteristics of geographical areas, but expressing these wind areas in terms of wind turbine 

nameplate potential is often desirable. A uniform factor of 5 MW/km2 was applied to calculate 

the total resource potential in terms of installed nameplate wind energy generating capacity. This 

number corresponds to approximately eight rotor diameter (8D) spacing between turbines, using 

the 5-MW NREL reference wind turbine (Jonkman et al. 2009). By comparison, spacing for the 

Horns Rev I wind array is 7D (Horns Rev Offshore Wind Farm 2010), but the research 

community is still determining the optimal spacing with no consensus yet. Although the 

modeling is not fully validated for all offshore conditions and new estimates of the U.S. wind 

resource are still being calculated, the Schwartz et al. study (2010) gives the best available 

estimates to date of offshore wind resources in the United States. The gross resource does not 

account for the wind energy that would be extracted by turbines over such a large area and the 

physical limitations imposed by upper level air on wind replenishment near the sea surface.

These array effects, which will diminish the available energy, should be considered to determine 

the practical spacing for entire wind farms in general. This is discussed briefly in Section 5.3.6.

4.1.3 Wind Speed Gradients

Typically, the models predict steep gradients in annual average wind speed in the coastal regions,

extending orthogonally from the shoreline to a few miles offshore. These gradients can represent 

increases of two or more wind power classes in just a few miles, although their exact nature and 

exactly how far off the shore they extend adds uncertainty to the estimates. Generally, the wind 

speed increases with distance from shore. The gradient diminishes with distance from shore and 

probably levels off from Class 6 to Class 8 depending on the latitude. Ocean surface temperature 

variations can modify these gradients. 

4.2 Offshore Wind Regions

NREL has completed a preliminary offshore study from the wind resource assessments of coastal 

states in five key geographic regions: the East Coast (including New England, the Mid-Atlantic 

states, and the South Atlantic Bight); the West Coast (California and the Pacific Northwest); the 

Great Lakes region; the Gulf of Mexico; and Hawaii. The new resource maps, compiled in 

Figures 4-1 and 4-2, indicate immense areas of Class 5, Class 6, and some Class 7 wind 

resources (wind speeds 7.5 m/s and higher) within 50 nm of shore. The physical characteristics 

of each of the five regions mapped are discussed in the subsections that follow.

4.2.1 East Coast: New England

The northeastern region comprises the Atlantic Ocean offshore areas of Maine, New Hampshire, 

Massachusetts, Rhode Island, Connecticut, and New York. Generally, the winds are Class 6 

throughout this region. The largest uncertainties concern the location of the near-shore windspeed gradients and the areas where the higher wind classes are achieved. Sea ice may be present 

in some areas but is not a primary design driver. Shallow-water sites are available in many 

locations, but the waters are generally deeper than those in the Mid- and South Atlantic, 

especially in Maine. Extreme conditions are driven by lower intensity hurricanes and more 

frequent and widespread winter “nor’easters,” which are usually within the design envelope 

prescribed by current wind turbine design standards.
57

4.2.2 East Coast: Mid-Atlantic States

The resource study of the Mid-Atlantic region comprises the offshore areas of New Jersey south 

to North Carolina.10 In the northern part of this region, offshore winds are quite good with 

classes 5 and 6. To the south, the speeds diminish slightly. The largest uncertainty is still with the 

location of the near-shore wind-speed gradients and the areas where the higher wind classes are 

achieved. Thermal changes caused by the Gulf Stream farther out, however, may influence farshore wind-speed prediction. Sea ice is not likely to be a design problem for wind turbines, but 

moderate hurricanes will likely dictate the extreme survival conditions.11

4.2.3 East Coast: The South Atlantic Bight

This region has the 

advantage of large areas of shallow water that are very well suited for near-term technology.

The South Atlantic Bight comprises the Atlantic Ocean offshore areas of South Carolina, 

Georgia, and Florida. As the coastline curves westward nearing the Georgia coast, the 

continental shelf widens, forming a large area of shallow-water resource farther from shore. This 

area is known as the South Atlantic Bight. Although the offshore winds in this region are thought 

to be comparatively lower than those of the northern Atlantic coast, the milder climate and 

shallow water may provide overriding benefits for offshore wind in this region (Stewart, Bulpitt, 

and Hunt 2006). A full mesoscale modeling assessment of the Georgia coastal area was 

completed in 2006, and this assessment has improved the accuracy of offshore resource estimates 

in this region. Hurricanes are a concern in this area, but each site must be evaluated with respect 

to its unique site-specific conditions because the track and intensity of hurricanes are highly 

dependent on coastal geography and latitude (Sheets and Williams 2001).

4.2.4 West Coast: California

The winds along the California coast are classes 6 and 7, increasing from the south northward. 

Some good wind resource areas exist near shore, but a very narrow continental shelf results in a 

minimal shallow-water resource. Deepwater technology development will be very important if 

offshore wind is to be developed off the Pacific coast. Sea ice is not an issue, and extreme 

conditions are storm driven, with little risk from hurricane weather events. The best near-term 

opportunities may be in shallow coastal regions. 

4.2.5 West Coast: The Pacific Northwest

The Pacific Northwest includes the coasts of Washington and Oregon, where solid Class 6 wind 

resources are found. These resources do diminish slightly off the coast of Washington. As with 

California, a very narrow continental shelf limits the shallow-water resource. Sea ice is not an 

issue, and extreme conditions are storm driven, with little risk from catastrophic weather events. 

High average sea-states may increase fatigue concerns on offshore wind turbine structures.

4.2.6 Great Lakes Region

This region includes the lake offshore areas of Minnesota, Wisconsin, Michigan, Indiana, Ohio, 

Pennsylvania, and New York. A recent comprehensive mapping project indicates that the Great 

 10 Note that the Mid-Atlantic region as defined by the Energy Information Administration (EIA) and the North 

American Electric Reliability Council (NAERC) includes only New Jersey to Pennsylvania. 11 Extreme wind conditions for wind turbines can generally be prescribed by International Electrotechnical 

Commission (IEC) TC-88 standards in accordance with specified wind classes (NWTC 2002). The overall structural 

requirements for certification and operation in the ocean will be determined by the Bureau of Ocean Energy 

Management, Regulation and Enforcement (BOEM; formerly the Minerals Management Service [MMS]). 
58

Lakes have wind resources ranging from Class 4 through Class 6. Each lake has its own unique 

characteristics in terms of bathymetry, as well as environmental and socioeconomic issues. Local 

and state governments will largely determine what they will allow in terms of offshore 

development. The Canadian government has adopted its own approach and Canada, especially 

Ontario, may offer good synergies for offshore wind development in the United States. The lakes 

contain freshwater, and surface ice floes will be a major design driver for any offshore turbines

(Barker and Timco 2006; Määttänen 2002). Wave heights are substantially lower than ocean 

areas, so hydrodynamic loading will also be lower.

4.2.7 Gulf of Mexico

This region includes the coastal areas stretching from Florida to Texas. Ninety-meter wind 

resource data for Alabama, Mississippi and Florida, however, are not available. A study 

performed at Stanford University suggests that the Gulf states have an excellent wind resource

because of better-than-predicted wind shears and higher wind speeds at 80 m (Archer and 

Jacobson 2003). This has prompted some interest, but claims have not been substantiated by 

mesoscale models or accurate meteorological measurements. A new comprehensive mesoscale 

modeling assessment was completed for the wind resource in the Gulf of Mexico for the Texas 

and Louisiana coastal areas and was incorporated into the larger national assessment (Schwartz 

et al 2010). The strongest wind potential was found in the western Gulf, from Corpus Christi to 

the Mexican border. Texas is in a unique position to capitalize on offshore wind resources 

because its state boundary waters extend 9 nm from shore, whereas other coastal state waters end 

at 3 nm (Renewable Energy World 2005). Any offshore wind development in the Gulf of Mexico 

will have to be evaluated in the context of extreme hurricanes that frequent the region. 

Hurricanes will not preclude installing offshore wind turbines in the Gulf, but this additional risk 

factor must be considered in the structural design of any turbines that are put in place. 

4.2.8 Hawaii

The resource study of Hawaii shows many excellent wind resource areas around each island and 

an abundance of offshore wind resource relative to the total load of the islands. The relatively 

high electricity rates in Hawaii make wind an attractive alternative. The resource is effectively 

stranded, however, because of its remoteness from the U.S. mainland. 

4.2.9 Alaska

Alaska is not included in the current estimates of the offshore wind resource for the United 

States. Alaska does, however, have excellent offshore wind resources and high electricity rates. 

Although Alaska is isolated from the lower 48 states, its offshore wind resources greatly exceed 

its electricity needs. If these resources were included in the national total, the additional resource 

capacity would inflate the available resource potential of the United States. Under current 

energy-use and grid-integration scenarios, exporting electricity generated by offshore wind to the 

lower 48 states would not be practical, which is why Alaskan wind resources are not included in 

current estimates. With its vast coastline and extensive regions of Class 7 and 8 winds, Alaska 

would dwarf any other state’s offshore resource. Because the Alaskan coastline is remote and its 

climate is severe, this study assumes that offshore Alaskan wind potential is stranded and will be 

unable to contribute to the national electric energy production beyond its own borders.
59

4.3 Offshore Wind Resource Potential

For this study, the offshore resource has been categorized within each state by average wind 

speed, bathymetry, and distance from shore. No exclusions (e.g., shipping lanes and 

environmentally sensitive areas) have been applied to the offshore wind resource estimates in 

order to arrive at an upper bound of the gross offshore resource potential. Further studies are 

needed to evaluate the impact of specific exclusions, such as unacceptable human 

encroachments, shipping lanes, and fisheries, among others. Similar studies produced by other 

organizations (e.g., in the United Kingdom, Germany, and Delaware) will serve as templates for 

developing similar exclusions for a U.S. study. Tables 4-1 and 4-2 summarize the estimated 

regional offshore resource based on bathymetry. Table 4-3 gives additional detail on the 

breakdown of resource potential by individual state and wind speed. Note that all resource 

figures are based on the nameplate capacity of the installed wind turbines, which have capacity 

factors between 0.35 and 0.5, depending on the average wind speed.

Table 4-1. Offshore Wind Resource Potential by Region and Water Depth for Areas with Annual 

Average Wind Speeds 8.0 m/s or Greater at 90-m Elevation

Region GW by Depth (m) Total

0–30 30–60 >60 (GW)

New England 73.5 132.2 250.1 455.8

Mid-Atlantic 209.4 179.0 92.5 480.9

South Atlantic Bight 39.1 48.8 7.7 95.6

California 0.9 6.9 521.2 529.0

Pacific Northwest 3.3 18.8 304.1 326.2

Great Lakes 74.6 72.2 388.8 535.6

Gulf of Mexico 55.5 89.3 57.6 202.4

Hawaii 1.2 1.7 328.6 331.5

Total 457.4 548.9 1,950.7 2,957.0

Source: Schwartz et al. 2010.

Table 4-2. Offshore Wind Resource Potential by Region and Water Depth for Areas with Annual 

Average Wind Speeds 7.0 m/s or Greater at 90-m Elevation

Source: Schwartz et al. 2010.

Region

GW by Depth (m)

0–30 30–60 >60 Total

New England 100.2 136.2 250.4 486.8

Mid-Atlantic 298.1 179.1 92.5 569.7

South Atlantic Bight 134.1 48.8 7.7 190.7

California 4.4 10.5 573.0 587.8

Pacific Northwest 15.1 21.3 305.3 341.7

Great Lakes 176.7 106.4 459.4 742.5

Gulf of Mexico 340.3 120.1 133.3 593.7

Hawaii 2.3 5.5 629.6 637.4

Total 1,071.2 628.0 2,451.1 4,150.3
60

Table 4-3. State Offshore Wind Resource Potential (in Gigawatts) by Wind Speed, Water Depth, 

and Distance from Shore

Wind Distance from Land

Total

Speed 0–3 nma 3–12 nm 12–50 nm

at 90 m Depth Category (m) Depth Category (m) Depth Category (m)

State (m/s) 0–30 30–60 >60 0-30 30–60 >60 0–30 30–60 >60

California 7.0–7.5 1.3 1.2 1.3 0.5 2.3 22.8 0.0 0.1 27.7 57.2

7.5–8.0 1.2 1.3 0.9 0.4 3.0 19.3 0.0 0.1 98.1 124.3

8.0–8.5 0.6 0.9 1.4 0.0 0.5 22.7 0.0 0.0 89.1 115.3

8.5–9.0 0.2 0.7 0.9 0.0 0.1 22.8 0.0 0.0 89.5 114.3

9.0–9.5 0.0 0.1 0.1 0.0 0.0 4.9 0.0 0.0 60.8 65.9

9.5–10.0 0.0 0.0 0.1 0.0 0.0 3.3 0.0 0.0 72.8 76.2

>10.0 0.0 0.0 0.0 0.0 0.0 1.4 0.0 0.0 33.2 34.6

Connecticut 7.0–7.5 2.5 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.7

7.5–8.0 3.1 0.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.5

8.0–8.5 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2

Delaware 7.0–7.5 1.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.1

7.5–8.0 3.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.6

8.0–8.5 0.7 0.1 0.0 3.2 0.0 0.0 1.2 0.0 0.0 5.3

8.5 - 9.0 0.0 0.0 0.0 0.0 0.0 0.0 1.3 3.4 0.0 4.7

Georgia 7.0–7.5 2.7 0.0 0.0 10.8 0.0 0.0 5.6 0.0 0.0 19.1

7.5–8.0 0.4 0.0 0.0 2.6 0.0 0.0 26.0 9.6 0.0 38.7

8.0–8.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.6 0.0 2.6

Hawaii 7.0–7.5 0.6 0.5 13.2 0.0 0.2 11.1 0.2 0.6 68.1 94.4

7.5–8.0 0.3 0.5 12.0 0.0 0.7 25.3 0.0 1.3 171.3 211.5

8.0–8.5 0.5 0.6 11.8 0.0 0.1 23.8 0.0 0.0 128.5 165.2

8.5–9.0 0.3 0.3 10.5 0.0 0.0 13.1 0.0 0.0 45.3 69.6

9.0–9.5 0.1 0.2 5.0 0.0 0.0 9.3 0.0 0.0 24.3 38.9

9.5–10.0 0.1 0.2 3.3 0.0 0.0 5.3 0.0 0.0 24.6 33.6

>10.0 0.1 0.4 6.7 0.0 0.0 10.1 0.0 0.0 6.9 24.3

Illinois 7.0–7.5 0.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5

7.5–8.0 0.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.8

8.0–8.5 1.2 0.1 0.0 4.1 2.6 0.7 0.0 2.1 8.4 19.2

8.5–9.0 0.0 0.0 0.0 0.1 0.4 0.0 0.0 0.0 0.0 0.4

Indiana 7.0–7.5 0.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4

7.5–8.0 0.8 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 1.1

8.0–8.5 0.5 0.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 1.4

Louisiana 7.0–7.5 39.8 0.1 0.0 39.1 3.2 7.3 55.8 27.4 68.4 240.2

7.5– 8.0 0.8 0.0 0.0 8.1 0.0 0.0 40.9 11.1 14.3 75.2
61

Table 4-3 (continued). Offshore Wind Resource Potential (in Gigawatts) by Wind Speed, State, 

Water Depth, and Distance from Shore

State

Wind

Speed

at 90 m

(m/s)

Distance from Land

Total

0–3 nm 3–12 nm 12–50 nm

Depth Category (m) Depth Category (m) Depth Category (m)

0–30 30–60 >60 0–30 30–60 >60 0–30 30–60 >60

Maine 7.0–7.5 3.9 0.5 0.1 0.0 0.0 0.0 0.0 0.0 0.0 4.5

7.5–8.0 4.0 1.4 0.1 0.0 0.1 0.1 0.0 0.0 0.0 5.7

8.0–8.5 3.9 2.2 0.4 0.3 1.9 1.2 0.0 0.0 0.0 9.9

8.5–9.0 2.6 3.1 0.8 0.1 1.1 7.0 0.0 0.0 2.0 16.7

9.0–9.5 0.7 2.0 1.5 0.1 2.3 17.5 0.0 0.3 17.7 42.1

9.5–10.0 0.0 0.1 0.2 0.0 0.2 7.3 0.0 0.0 69.5 77.4

>10.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.2

Maryland 7.0–7.5 10.9 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 11.0

7.5–8.0 9.6 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 9.7

8.0–8.5 0.8 0.0 0.0 4.6 0.0 0.0 2.2 0.1 0.0 7.7

8.5–9.0 0.0 0.0 0.0 0.0 0.0 0.0 2.7 16.1 6.7 25.4

Massachusetts 7.0– 7.5 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0

7.5–8.0 2.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.6

8.0–8.5 4.6 1.6 0.1 0.4 0.8 0.6 0.0 0.0 0.0 8.2

8.5–9.0 7.5 1.9 0.1 1.6 1.8 4.1 0.1 0.1 1.0 18.0

9.0–9.5 5.7 1.6 0.1 13.5 7.1 5.0 8.4 25.3 35.0 101.8

9.5–10.0 0.0 0.0 0.0 0.0 0.6 0.0 2.4 17.3 48.1 68.4

Michigan 7.0–7.5 17.1 1.7 1.2 0.7 0.2 1.3 0.0 0.0 0.1 22.3

7.5–8.0 23.2 6.3 3.2 15.3 14.6 15.0 0.1 0.5 12.2 90.4

8.0–8.5 12.9 6.3 3.8 13.9 29.4 47.1 0.2 4.4 37.5 155.4

8.5–9.0 0.7 0.8 2.0 0.7 2.8 42.9 0.6 6.9 114.2 171.5

9.0–9.5 0.0 0.0 0.0 0.0 0.0 0.3 0.6 1.2 41.4 43.6

Minnesota 7.0–7.5 0.0 0.2 1.4 0.0 0.1 8.6 0.0 0.0 5.2 15.5

7.5–8.0 0.0 0.0 0.1 0.0 0.0 0.3 0.0 0.0 4.6 5.0

New 7.0–7.5 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1

Hampshire 7.5–8.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2

8.0–8.5 0.2 0.1 0.0 0.0 0.4 0.1 0.0 0.0 0.0 0.9

8.5–9.0 0.0 0.1 0.0 0.0 0.1 1.3 0.0 0.0 0.2 1.7

9.0– 9.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.3 0.5

New Jersey 7.0–7.5 2.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.6

7.5–8.0 4.8 0.0 0.0 2.6 0.1 0.0 0.0 0.0 0.0 7.5

8.0–8.5 3.9 0.0 0.0 13.8 0.6 0.0 4.5 1.9 0.1 24.8

8.5–9.0 0.1 0.0 0.0 1.1 0.0 0.0 10.1 51.9 1.5 64.7
62

Table 4-3 (continued). Offshore Wind Resource Potential (in Gigawatts) by Wind Speed, State, 

Water Depth, and Distance from Shore

State

Wind Distance from Land

Speed 0–3 nm 3–12 nm 12–50 nm

at 90 m Depth Category (m) Depth Category (m) Depth Category (m)

(m/s) 0–30 30–60 >60 0–30 30–60 >60 0–30 30–60 >60 Total

New York 7.0–7.5 5.2 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 5.5

7.5–8.0 9.9 1.8 0.1 2.4 3.0 4.3 0.0 0.0 0.3 21.8

8.0–8.5 6.6 3.0 1.0 1.9 2.7 15.6 0.2 0.1 10.5 41.6

8.5–9.0 2.7 0.6 0.0 5.2 0.5 0.0 1.3 3.6 0.5 14.4

9.0–9.5 0.0 0.0 0.0 2.0 7.0 0.0 0.0 24.6 3.6 37.3

9.5–10.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 9.1 17.5 26.6

North 7.0–7.5 9.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 9.2

Carolina 7.5–8.0 15.0 0.0 0.0 5.5 0.0 0.0 0.0 0.0 0.0 20.5

8.0–8.5 19.6 0.0 0.0 23.3 0.0 0.0 20.2 3.7 1.5 68.3

8.5–9.0 0.5 0.0 0.0 14.8 1.3 0.0 31.9 72.6 78.2 199.4

Ohio 7.0–7.5 1.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.7

7.5–8.0 5.5 0.0 0.0 9.8 0.0 0.0 0.0 0.0 0.0 15.3

8.0–8.5 2.8 0.0 0.0 11.0 0.0 0.0 15.4 0.0 0.0 29.1

Oregon 7.0–7.5 1.8 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.9

7.5–8.0 2.6 1.6 0.2 0.2 1.2 1.7 0.0 0.0 0.0 7.5

8.0–8.5 1.0 1.4 0.0 0.1 3.0 12.8 0.0 0.0 24.9 43.2

8.5–9.0 0.3 0.5 0.0 0.0 0.5 9.8 0.0 0.2 58.2 69.6

9.0–9.5 0.3 0.3 0.2 0.0 0.2 3.0 0.0 0.0 33.0 36.7

9.5–10.0 0.2 0.4 0.1 0.0 0.2 3.2 0.0 0.0 26.3 30.3

>10.0 0.0 0.1 0.2 0.0 0.1 6.8 0.0 0.0 22.7 30.0

Pennsylvania 7.0–7.5 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2

7.5–8.0 0.6 0.0 0.0 0.3 0.2 0.0 0.0 0.0 0.0 1.1

8.0–8.5 1.4 0.0 0.0 3.6 1.8 0.0 1.1 0.4 0.0 8.4

Rhode Island 7.0–7.5 1.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.1

7.5–8.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6

8.0–8.5 0.7 0.2 0.0 0.2 0.3 0.0 0.0 0.0 0.0 1.4

8.5–9.0 0.6 0.5 0.0 0.9 1.4 0.0 0.0 0.0 0.0 3.4

9.0–9.5 0.3 0.1 0.0 0.9 3.9 0.0 0.0 2.2 0.0 7.3

9.5–10.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.8 6.9 11.8

South 7.0–7.5 4.2 0.0 0.0 3.0 0.0 0.0 0.0 0.0 0.0 7.3

Carolina 7.5–8.0 3.0 0.0 0.0 15.3 0.0 0.0 21.4 1.4 0.0 41.0

8.0–8.5 0.1 0.0 0.0 8.0 0.0 0.0 20.8 19.6 3.4 51.9

8.5–9.0 0.0 0.0 0.0 0.0 0.0 0.0 10.1 15.5 4.3 30.0
63 

Table 4-3 (concluded). Offshore Wind Resource Potential (in Gigawatts) by Wind Speed, State, 

Water Depth, and Distance from Shore

State

Wind Distance from Land

Total

Speed 0–3 nm 3–12 nm 12–50 nm

at 90 m Depth Category (m) Depth Category (m) Depth Category (m)

(m/s) 0–30 30–60 >60 0–30 30–60 >60 0–30 30–60 >60

Texasa 7.0–7.5 8.9 0.0 0.0 0.5 0.0 0.0 0.7 0.0 0.0 10.1

7.5–8.0 45.2 0.0 0.0 5.8 0.0 0.0 40.2 30.9 2.0 124.1

8.0–8.5 29.6 0.6 0.0 3.7 0.7 0.0 2.9 22.2 23.0 82.8

8.5–9.0 19.0 3.0 0.0 0.2 4.7 0.0 0.0 16.1 18.4 61.4

Virginia 7.0–7.5 4.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.4

7.5–8.0 18.0 0.1 0.0 0.2 0.0 0.0 0.0 0.0 0.0 18.3

8.0–8.5 5.7 0.0 0.0 14.9 0.0 0.0 11.8 0.3 0.0 32.7

8.5–9.0 0.0 0.0 0.0 0.1 0.0 0.0 10.2 24.2 4.5 39.0

Washington 7.0–7.5 3.1 0.7 0.3 1.2 1.8 0.9 0.0 0.0 0.0 7.9

7.5–8.0 1.9 0.0 0.0 1.0 4.2 5.7 0.0 0.0 10.2 23.1

8.0–8.5 0.3 0.0 0.0 1.1 4.9 2.4 0.0 0.1 82.6 91.3

Wisconsin 7.0–7.5 5.3 1.3 0.7 1.7 3.1 5.4 0.0 0.2 0.8 18.6

7.5–8.0 7.1 1.2 0.1 1.8 1.1 3.9 0.0 0.0 1.8 17.0

8.0–8.5 4.2 1.9 0.0 2.3 6.9 12.7 0.0 0.1 10.8 38.8

8.5–9.0 0.1 0.0 0.0 0.1 1.5 6.7 0.0 0.3 33.3 42.1

Source: Schwartz et al. 2010. a Federal waters begin at 3 nm with the exception of Texas, which begins at 9 nm. For Texas, the area reported is for 0–9 nm; 9–

12 nm; and 12–50 nm, respectively.

4.3.1 Coastal State Boundaries and Distance from Shore

The definition of offshore areas is complex, involving the interpretation of the physical 

characteristics of an area as affected by various treaties and international and domestic law. The 

BOEM and the National Oceanic and Atmospheric Administration (NOAA) are working to 

establish this information by defining a baseline of the mean lower low water (MLLW) line. 

These data can change rapidly, particularly as coastlines are reinterpreted because of storm 

events. Modifications to the MLLW might also be made to separate inland waters (i.e., bays). 

From the MLLW, the state and federal administrative zones are derived, extending to the 200-nm 

U.S. international boundary or another international boundary. These data are still under 

development, but published interim data—acquired from the BOEM Web portal 

(http://www.boemre.gov/offshore/mapping/)—were used in this study. These data depict the 

location of the federally administered offshore regions by state. The federal jurisdiction generally 

begins 3 nm from the MLLW line, except for Texas and the Gulf Coast of Florida, where federal 

jurisdiction begins at 9 nm from the baseline.

For purposes of this study, the resource areas are classified into the following: state waters (0–3 

nm), nearer shore (3–12 nm), and far shore (12–50 nm). These distances were chosen to separate 

federal and state management of offshore areas and to delineate some economic separation to 

depict the varying costs associated with delivering energy produced offshore. In addition, the 12-

nm boundary makes an appropriate division between far shore and nearer shore because it is 

already defined as the boundary for territorial waters. It is also convenient to use this distance as 
64

a subjective boundary where visual impacts are estimated to be minimal. Table 4-3 accounts for 

the additional state waters (0–9 nm) off the coast of Texas.

4.3.2 Wind Resource Information

Although a comprehensive U.S. offshore wind resource assessment is still under way, sufficient 

information already exists to determine a preliminary wind resource distribution, as shown in 

Figures 4-1 and 4-2. Where no updated offshore maps are available, the estimates are derived 

from near-shore resource data created during land-based wind resource assessment activities, 

supplemental products created by land-based wind mapping projects for areas farther from shore, 

and resource estimates inferred by examining other modeled and measured wind information. 

The exceptions to this are the 90-m estimates for Florida, Alabama, and Mississippi. The wind

resource information is sorted by average wind speed at 90 m above the water surface (near the 

turbine hub height). Annual average wind speeds of 7.0 m/s and 8.0 m/s were used to generate 

Tables 4-1 and 4-2 to allow the resource to be summarized in different ways, with 8.0 m/s and 

above being a more conservative estimate of the entire resource. 

4.3.3 Bathymetry

The assessment of the offshore wind resource with respect to water depth will have a significant

effect on the type of technology needed (Musial, Butterfield, and Boone 2003). Most offshore 

wind turbine technology uses either monopole or gravity-base foundations, employing a class of 

jack-up installation barges that are limited to a maximum water depth of 25 to 30 m. In general,

European installations are in water depths of less than 30 m (EWEA 2010). New technology has 

already been demonstrated, though, which allows fixed-bottom installations in water depths of 

up to 45 m (MacAskill 2005). Installations beyond these depths will call for even more 

innovation, such as floating platforms (see Section 5).

Detailed bathymetry data are available from the NOAA Coastal Relief Model

(http://www.ngdc.noaa.gov/mgg/coastal/startcrm.htm) for the majority of the study area, with the 

exception of Lake Superior. In Hawaii, the NOAA data did not extend the necessary distance 

from shore, so these data were supplemented by less detailed global bathymetry data. For this 

study, the bathymetry was classified into ranges corresponding to the technology available: 

shallow (0–30 m), transitional (30–60 m), and deep (>60 m).

4.4 Wind Resource Research Trends 

The scientific understanding of the environment in which offshore wind turbines operate and the 

characteristics of the wind, ocean waves, currents that affect offshore wind turbine structural 

safety and energy production is at an immature state. Validation measurements and 

computational analytical models must be evolved from other disciplines or developed to address 

this new specific area. The need to improve wind resource assessment capabilities is closely 

linked to the technology of offshore wind turbines themselves, which is covered in Section 5. 

The technology trends described in the following subsections relate to the characterization of the 

wind resource; Section 5 is more focused on the site-specific characteristics that can impinge on 

a wind turbine installation. Both categories are extremely important and should be addressed in 

future research initiatives. 
65

4.4.1 Resource Mapping and Quantification

The complete mapping of the entire U.S. coastal boundary has been under way for several years 

but is not yet complete. Completing this mapping and validating these offshore wind resources 

for the entire U.S. coastline could reduce many uncertainties in the planning of wind energy 

projects in their early stages and could assist states and federal governments as they plan longterm energy strategies. Today, much of the data is derived from land-based extrapolations that 

are incomplete and are patched together with some uncertainty. Mapping and validation efforts 

could include all remaining unmapped areas including the Atlantic coast from Rhode Island to 

South Carolina, the West Coast, and the coasts of Alaska, Florida, Hawaii, and the Gulf of 

Mexico. Updated assessments could be compiled and published regularly in an offshore resource 

catalogue and report (Schwartz et al. 2010).

The analytical mesoscale models described earlier have improved, but must be validated by 

accurate long-term measurements. Currently these models are limited to global resource 

characterization and are not very useful for micrositing or accurately predicting complex weather 

phenomena such as wind shear profiling, atmospheric stability, or seasonal variations. Models 

that can estimate these effects at specific offshore wind sites, without the need for the long-term 

installation of a meteorological (met) mast, are needed to managing risk during the site 

development of offshore projects, especially in deeper water (Jiminez 2007; Jǿrgensen 2005;).

4.4.2 Metocean Validation

The existing database of accurate anemometer-based offshore wind-speed measurements consists

of a sparsely distributed system of buoys and fixed Coastal-Marine Automated Network (CMAN) stations maintained and operated by the National Data Buoy Center. Buoy data are 

generally taken at an elevation of 5 m and are insufficient for confident wind-resource

validations or to fully characterize the wind regime at a particular site. The traditional land-based 

method of taking wind measurements from a met mast is expensive offshore, especially for a 

large number of sites, and particularly in deeper water.

All modeling estimates must be validated by long-term measurement records. Wind, sea-surface 

temperature, and other weather data available from numerous databases (NOAA, NASA, the 

National Weather Service [NWS], and other government agencies) can be compiled to 

supplement the characterization of coastal and offshore wind regimes (Hasager et al. 2005). The 

limitations and availability of existing offshore data collected for the purpose of weather 

observations and forecasting must be reassessed. It may be necessary to increase these 

measurement efforts to gather real-time data at sea for the purpose of understanding renewable 

energy production potential. In the future, advanced analytical modeling of the atmospheric 

boundary layer might be able to accurately determine site-specific wind characteristics. If 

validated, analytical techniques might allow developers to avoid expensive met measurements.

4.4.3 Remote Sensing

For a large number of sites, installing met masts may not be feasible because of cost or water 

depth. Alternative methods are needed to measure wind speed at multiple locations and to 

determine wind-shear profiles up to the elevations where wind turbines operate. This will require 

new systems based on, for example, sodar, lidar, and radar, combined with more stable buoy 

systems or fixed bases (Antoniou et al. 2006). Some systems are currently being developed, but 

experience thus far is limited (Zack 2006). To gain enough confidence for these systems to 

replace the conventional met mast, a large amount of experience with commercial projects at sea 
66

will be needed. This will require, in turn, close cooperation among private technology 

companies, offshore developers and operators, and government R&D programs at the U.S. 

Department of Energy (DOE) and BOEM, both in terms of taking the data and verifying the 

results. Once a reliable and proven track record has been established, the improved accuracy for 

wind and energy production measurements will remove a significant amount of risk from 

developers. An effective R&D approach might be to engage in international collaborative 

activities that support the development of these advanced meteorological solutions.

4.5 Findings and Conclusions

To derive state and regional estimates of offshore wind potential for the United States, the wind 

resource, bathymetry, distance from shore, and administrative jurisdiction information were

combined using geographic information system (GIS) technology. Tables 4-1 and 4-2 show the 

available regional resource for 8.0 m/s annual speeds and greater at 90 m and 7.0 m/s, 

respectively, by water depth. Table 4-3 categorizes the resource in more detail, by state, depth, 

and distance from shore. 

As shown in Table 4-1, significant quantities of potential resource areas 8.0 m/s or greater at 90 

m are available in each region in different depth categories. More than 450 GW of potential 

occurs in the shallow-depth category (0–30 m) drawn from all of the reported regions for the 

United States. Expanding this to include 60-m (transitional) depths increases the gross U.S. 

offshore resource to more than 1,000 GW. Adding deep water brings the gross resource to almost 

3,000 GW. Table 4-2 gives these same figures, with the addition of low wind sites (sites with 

average wind speeds of 7.0 m/s or greater). The gross total resource then exceeds 4,000 GW. 

The resource assessment database is based on extensive analysis conducted by NREL and AWS 

Truepower (formally AWS Truewind) spanning many years (Schwartz et al 2010). The results 

in some states are preliminary, but enough of the significant regions of the United States have 

been mapped and included in the database to conclude that the development of offshore wind in 

the United States is not resource-limited on a national scale. Some individual states fare better

than others in terms of their local resource potential. The database contains the necessary 

information to allow each state to make the decision about whether their resource can make a 

significant impact on their local energy needs. Regional and physical geographical differences 

may influence the technology required for each state. Some of these differences include 

distribution of the resource according to water depth, distribution of the resource with respect to 

the distance from shore, hurricane risk, and the possibility of ice floe loading (particularly when 

siting on the Great Lakes). 

Research trends show that analytical mesoscale models and atmospheric methods and models 

could help lower cost and uncertainty by reducing the need for expensive met towers. Similarly, 

remote sensing techniques that are still under development might someday be able to replace met 

towers for site characterization. 

This assessment of offshore wind resources shows that the United States has an abundance of 

offshore wind that could make a significant impact on its total energy needs. The resources 

required to meet the scenario presented in the DOE 20% report (see DOE 2008) are a small 

fraction of the gross potential offshore wind energy resource of the United States. 
67

4.6 References

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M. (2006). “Offshore Wind Profile Measurements from Remote Sensing Instruments.” 

Presented at the European Wind Energy Conference, EWEC06, Athens, February 27–

March 2.

Archer, C.L.; Jacobson, M.Z. (2003). “Spatial and Temporal Distributions of U.S. Winds and 

Wind Power at 80-m Derived from Measurements.” Journal of Geophysical Research 

(108: D9); 4289, DOI:10.1029/2002JD002076.

Barker, A.; Timco, G. (2006). “Ice Design Considerations for Wind Turbines in the Great 

Lakes.” Canadian Hydraulics Centre, National Research Council of Canada, Ottawa, CA. 

Presented at Great Lake Offshore Wind Gathering, April 4.

DOE (U.S. Department of Energy). (July 2008). 20% Wind Energy by 2030: Increasing Wind 

Energy’s Contribution to U.S. Electricity Supply. DOE/GO-102008-2567. 

http://www.nrel.gov/docs/fy08osti/41869.pdf. Accessed August 30, 2010.

Elliott, D.; Holliday, C.; Barchet, W.; Foote, H.; Sandusky, W. (1987). Wind Energy Resource 

Atlas of the United States. DOE/CH 10093-4. Golden, CO: Solar Energy Research 

Institute. 

EWEA (European Wind Energy Association). (January 2010). The European Offshore Wind 

Industry: Key Trends and Statistics 2009. 

http://www.ewea.org/fileadmin/emag/statistics/2009offshore/. Accessed August 23, 

2010.

Hasager, C.B.; Christiansen, M.B.; Nielsen, M.; Barthelmie R. (October 2005). “Using Satellite 

Data for Mapping Offshore Wind Resources and Wakes.” Presented at Copenhagen 

Offshore Wind, Copenhagen, DK, October 26–28. 

Horns Rev Offshore Wind Farm. (2010). Web site. 

http://www.hornsrev.dk/Engelsk/default_ie.htm. Accessed August 23, 2010.

Jimenez, B.; Durante, F.; Lange, B.; Kreutzer, T.; Claveri, L. (March/April 2007). “Offshore 

Wind Resource Assessment: Comparative Study between MM5 and WAsP.” Wind 

Energy (10:2); pp. 121–134.

Jonkman, J.; Butterfield, C.P.; Musial, W.; Scott, G. (February 2009). Definition of a 5-MW 

Reference Wind Turbine for Offshore System Development. NREL/TP-500-38060. 

Golden, CO: NREL.

Jørgensen, H.; Nielsen, M.; Barthelmie, R.J.; Mortensen N.G. (October 2005). “Modelling 

Offshore Wind Resources and Wind Conditions.” Presented at Copenhagen Offshore

Wind, Copenhagen, DK, October 26–28. 
68

NWTC (National Wind Technology Center). (2002). IEC Wind Turbine Standards. 

http://wind.nrel.gov/cert_stds/Certification/standards/iec_stds.html#Table%20I%20-

%20IEC%20Wind%20Energy%20Standards. Accessed August 31, 2010.

Määttänen, M. (September 2002). Numerical Simulation of Ice-Induced Vibrations in Offshore 

Structures. Department of Mechanical Engineering, Helsinki University of Technology. 

http://virtual.vtt.fi/virtual/proj6/arki/julkaisut/strice/Maattanen.pdf. Accessed August 23, 

2010.

MacAskill, A. (October 2005). “The Beatrice Wind Farm Demonstrator: Applying Oil and Gas 

Expertise to Renewables.” Presented at Copenhagen Offshore Wind, Copenhagen, DK, 

October 26–28.

Manwell, J.F.; Elkinton, C.; Rogers, A.; McGowan, J.G. (February 2007). “Review of Design 

Conditions Applicable to Offshore Wind Energy in the United States.” Renewable and 

Sustainable Energy Reviews (11:2); pp. 183–364.

Musial, W.D.; Butterfield, C.P. (June 2004). “Future for Offshore Wind Energy in the United 

States.” NREL/CP-500-36313. Golden, CO: National Renewable Energy Laboratory 

(NREL).

Musial, W.D.; Butterfield, C.P. (2005). “Deepwater Offshore Wind Technology Research 

Requirements.” Presented at Windpower 2005, Denver, CO, May 15–18.

Musial, W.D.; Butterfield, C.P.; Boone, A. (November 2003). Feasibility of Floating Platforms 

Systems for Wind Turbines. NREL/CP-500-34874. Golden, CO: NREL.

Schwartz, M.; Heimiller, D.; Haymes, S.; Musial, W. (April 2010). Assessment of Offshore 

Wind Energy Resources for the United States. NREL/TP-500-45889. Golden, CO: 

NREL.

Sheets, B.; Williams, J. (2001). Hurricane Watch: Forecasting the Deadliest Storms on Earth. 

New York: Random House.

Stewart, S.; Bulpitt, W.; Hunt, M. (2006). “Feasibility of Offshore Wind Power in the South 

Atlantic Bight.” Presented at 2006 Offshore Technology Conference, Houston, TX.

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World. http://www.renewableenergyworld.com/rea/news/article/2005/10/texas-bid-couldbe-first-u-s-offshore-wind-farm-38618. Accessed August 23, 2010.

Zack, J.W. (August 2006). DOE-NREL Low Wind Speed Technology Project – Conceptual 

Design Study: Development of Atmospheric Profiling and Modeling Techniques to 

Evaluate the Design and Operating Environment of Offshore Wind Turbines in the MidAtlantic and Lower Great Lakes. Unpublished draft.
69

5.0 Offshore Wind Energy Technology—Status and Trends

5.1 Offshore Wind Technology Status

Today’s offshore wind turbine design configurations are adapted from standard land-based 

designs with some significant subsystem upgrades to account for ocean conditions. These 

modifications include strengthening the tower to handle the added loading from waves, 

pressurized nacelles and environmental controls to keep corrosive sea spray away from critical 

drivetrain and electrical components, and personnel access platforms to facilitate maintenance 

and provide emergency shelter. Offshore turbines require corrosion protection systems at the sea 

interface and high-grade marine coatings on most exterior components. Turbine arrays can be 

equipped with aircraft warning lights, bright markers on tower bases, and fog signals to facilitate 

marine navigational safety. To reduce operational costs and yield better diagnostic information, 

offshore turbines are often equipped with condition-monitoring systems, automatic bearinglubrication systems, onboard service cranes, and oil-temperature-regulation systems, all of which

go beyond the standard equipment required for land-based turbines. Lightning protection is 

mandatory for both land-based and offshore systems. The major portion of the turbine’s blades, 

nacelle covers, and towers are painted light gray to minimize visual impacts. 

Offshore turbine power capacity is greater than standard land-based turbines, ranging from 

2 MW to 5 MW. The current generation of offshore wind turbines typically have three-bladed 

horizontal-axis, yaw-controlled, active blade-pitch-to-feather controlled, upwind rotors, which 

are nominally 80 m to 130 m in diameter. Offshore machines are generally larger because there 

are fewer constraints on component and erection equipment transportation, which limit landbased machine size. Blade-tip speeds of offshore turbines are typically higher (80 m/s or greater) 

than those of land-based turbines because of lower aerodynamic noise concerns in the near field. 

The basic drivetrain topology differs very little from land-based systems and is typically 

designed around a modular, fixed-ratio, three-stage, gearbox speed increaser with planetary

stages on the low-speed side and helical stages on the high-speed side. Nominal generator speeds 

are around 1,800 rpm, but turbine designs usually operate under variable-speed torque control. 

Offshore towers are shorter than land-based towers for the same output because wind shear (the 

change in wind velocity resulting from the change in elevation) is lower offshore, which reduces 

the energy capture potential of increasing tower height. 

The offshore substructure and foundation systems differ considerably from land-based 

foundations. The most common substructure type is the monopile—a large steel tube with a wall 

thickness of up to 60 mm and diameters of up to 6 m. Monopiles have been placed in water 

depths ranging from 5 m to 30 m. The embedment depth varies with soil type, but typical North 

Sea installations require pile embedment 25 m to 30 m below the mud line. A transition piece is 

grouted onto the part of the monopile that protrudes above the waterline, which provides a level 

flange to fasten to the tower. The monopile foundation requires special installation vessels and 

equipment for driving the pile into the seabed and lifting the turbine and tower into place. 

Approximately 20% of offshore wind projects use gravity-base foundations, which avoids the 

need to use a large pile-driving hammer. Gravity-base systems require a significant amount of 

bottom preparation before installation and are compatible only with firm soil substrates in 

relatively shallow waters. Multi-pile substructures such as tripods and jackets have been 

deployed in some projects, especially when the water depth starts to exceed the practical limit for 

monopiles. 
70

Infrastructure mobilization and logistical support for constructing a large offshore wind plant are 

major portions of the total system cost. The wind turbines are arranged in arrays that take 

advantage of the prevailing wind conditions at the site. Turbine spacing is chosen to minimize 

array losses and interior array turbulence, while balancing the cost of cabling between turbines,

which increases with turbine spacing. Varying water depth presents a siting obstacle that often 

requires a customized approach to individual substructure design to ensure that each turbine’s 

structural vibration modes are compatible with the turbine operating frequencies (Dolan et al. 

2009; Elkinton, Manwell, and McGowan 2008).

The wind plant electric power distribution system consists of the individual turbine’s power 

electronics, the turbine step-up transformer and distribution wires, the electric service platform 

(ESP), cables to shore, and the shore-based interconnection system. This system, which is 

counted as part of the overall offshore plant cost, extends beyond the typical costs for a landbased wind farm where the costs are counted only to the substation. Power is delivered from 

each turbine from the generator and the power electronics at voltages ranging from 480 V to 

690 V, and is then increased via the turbine transformers (which can be cooled with dry air or 

liquid) to a distribution voltage of about 34 kV. The distribution system collects the power from 

each turbine at the ESP, which serves as a common electrical collection point for all the turbines

and as a substation where the turbines outputs are combined and brought into phase. For smaller 

arrays, or projects closer to shore, the ESP can be eliminated and the power can be aggregated at 

an onshore substation. For larger projects, the voltage is stepped up at the offshore substation

(i.e., the ESP) to about 138 kV for transmission to a land-based substation where it connects to 

the onshore grid. Power is transmitted from the ESP through a number of buried high-voltage 

subsea cables that run to the shore-based interconnection point. The voltage may need to be 

increased again onshore to, nominally, 345 kV for offshore power plants larger than 500 MW 

(Green et al. 2007).

The ESP can also function as a central service facility for the wind plant, which may include a 

helicopter landing pad, a wind plant control room and supervisory control and data acquisition 

(SCADA) monitoring system, a crane, a rescue boat, and a communications station, along with 

firefighting equipment, emergency diesel backup generators, and staff and service facilities, 

including emergency temporary living quarters. Note that the exact requirements for offshore 

safety and service have not yet been established (Sheppard, Puskar, and Waldhart 2010).

Currently, installed capital costs for offshore projects are higher than those for land-based wind 

turbines. Factors that contribute to these additional costs include the upgrades required for 

operation at sea, higher reliability components, and particularly, higher balance-of-station (BOS) 

costs (e.g., expensive installation vessels, logistics of working at sea, longer power cables to 

shore). In addition, operations and maintenance (O&M) costs are two to three times higher than

those for land-based systems. This is partly because turbine accessibility is more complicated, 

external conditions are more severe and more difficult to measure and characterize, and extreme 

wind and wave loads add substantial uncertainty to the design methods used on the turbines and 

substructures. Figure 5-1 breaks down the costs of installing a typical offshore turbine. Capital 

expenditures for installed and planned projects are examined in greater detail in Section 6. 
71

Source: Ernst & Young 2009; Krohn, Morthorst, and Awerbuch 2009; Fingerish, Hand, and Laxson 2006; Junginger and Faaij 

2004; Morgan, Scott, and Snodin 2003)

Figure 5-1. Estimated life-cycle cost breakdown for a typical baseline offshore wind project 

The primary point that should be drawn from Figure 5-1 is that offshore project costs are largely 

determined by a range of elements that extend well beyond the turbine itself. Future efforts to 

lower cost should place a greater emphasis on other aspects of the system relative to previous 

land-based R&D efforts. 

One element that is not recognized in Figure 5-1 is the initial one-time costs associated with 

developing the necessary infrastructure to support an offshore industry, including the costs for 

fabricating numerous vessels, upgrading ports and harbors, establishing manufacturing facilities, 

and creating and administering workforce training programs. Early projects may have to bear 

some of these costs of the additional investments needed to get started.

Finally, the baseline shallow-water offshore wind technology described earlier gives the United 

States a gross technical resource potential of about 457 GW at sites with wind speeds of 8.0 m/s 

or greater (see Section 4). This gross potential does not take into account numerous siting 

limitations and exclusions, which will reduce the practical resource potential considerably. It also 

does not account for some technology solutions that are needed to break down the barriers to 

offshore wind to allow competitive costs in all shallow-water resource areas, with minimal 

conflicts with humans and the surrounding ecosystems. Such solutions include turbine designs 

to withstand hurricanes, especially in the south, and ice designs that would allow turbines to be 

placed in freshwater, such as the Great Lakes.

 
72

5.2 Offshore Wind Technology Barriers

Several barriers to offshore wind development—summarized in this section—are inhibiting the 

deployment and acceptance of offshore wind technology. 

5.2.1 High Cost

Currently, capital costs for offshore projects are nearly double those for land-based wind 

projects. These higher costs accrue from, for example, the offshore turbine support structures, 

offshore electrical infrastructure construction, the high cost of building at sea, O&M warranty 

risk adjustments, turbine cost premiums for marinization, and a decommissioning contingency. 

These costs can be partially offset by increased energy production. In comparison with landbased wind, however, offshore wind is also immature and its costs are higher because less 

deployment and experience has not allowed for full realization of the learning curve, by which 

product costs in new industries are known to decline as a function of production quantity. Further 

cost uncertainty and upward cost pressure may be introduced because of U.S. dollar/euro 

exchange rates. High cost is one of the primary deterrents for would-be developers of offshore 

wind. Current projects in the United States depend on policy incentives to offset some of the 

high costs, but there are no guarantees that the necessary incentives will be available when a 

project is approved and permitted. Developing innovative offshore wind technology, accelerating

U.S. offshore wind deployment, and implementing regulatory and operational supports to reduce 

the risks associated with offshore wind investments can all have a downward influence on the 

future costs of offshore wind. Section 6 covers offshore costs and economics in greater detail.

5.2.2 Technology Immaturity

The near-term technology is still immature, which is an obstacle to offshore wind development. 

High cost of wind energy can, in part, be addressed directly with technology innovations that 

increase reliability and energy output and lower system capital expenses. The current technology 

limits the domain for offshore machines to shallow-water sites at a cost premium that is 

reflective of the industry’s early state. New technology is needed to lower costs, increase 

reliability and energy production, solve regional deployment issues, expand the resource area, 

develop infrastructure and manufacturing facilities, and mitigate known environmental impacts. 

Because of the high up-front investment costs required to explore new technology innovation

and the long timeline that is usually required to reap the full benefits of high-risk game-changing 

innovations, many companies may not be motivated to invest in R&D for offshore wind 

technology solutions. 

5.2.3 Limited Resource Area

The current technology limits offshore development to shallow-water sites in the North and MidAtlantic regions with about 457 GW of gross technical potential. This includes sites in the Great 

Lakes region and the Gulf of Mexico, but risks associated with ice floes and hurricanes, 

respectively, have not been fully explored and could reduce the gross potential resource even 

further. Similarly, this resource includes near-shore sites, which might still trigger public 

engagement issues that could further reduce the offshore wind potential. Public opposition tends 

to decrease with distance from shore where waters are deeper but the technology is not yet 

available to deploy in these areas. Technology solutions that would allow for developing further 

offshore sites could expand the resource area of the United States by a factor of 6, from the 

457 GW in shallow water to nearly 2,900 GW (see Section 4 for the wind resource assumptions). 
73

5.2.4 High Risk and Uncertainty

High project risk has contributed to high discount rates for financing offshore wind projects and 

justifiably, a cautious investment climate. Project risk can be broken down into the uncertainty 

surrounding regulatory and permitting issues, the risks associated with construction and 

installation, and the operational risks that are associated with accurate energy production and 

long-term reliability. Risk and uncertainty may dissipate as the industry matures, but today the 

process remains immature. Risk reduction can have as big of an impact on the life-cycle cost of 

an offshore wind project as the reduction in capital expenses. As the project advances through 

the development process and key milestones are achieved, the overall risk to the project 

decreases. At the time the project developer seeks the financial backing for the major part of the 

project’s capital expenditure—the capital to procure the wind turbines and the BOS—the largest 

fraction of risk and uncertainty remaining is primarily associated with the construction, 

installation, operation, and decommissioning phases. As a result, the biggest opportunity for 

reducing the costs of offshore wind likely resides in mitigating these technology risk elements. 

5.3 Technology Trends

Offshore wind is relatively new in comparison with land-based systems, and there are numerous 

opportunities to improve on the technology in ways that will lead to lower cost, expanded access 

to wind resources, and improved performance. 

5.3.1 Wind Turbine Technology

Offshore wind turbine technology is significantly different from land-based wind turbine 

technology, although there are several similarities as well. The pace of technology innovation in 

offshore wind turbines is also different because the technology is less established and the growth 

is on an earlier part of the learning curve. 

5.3.1.1 Optimized Offshore Wind Turbine Systems

Offshore turbines were originally derived from land-based wind turbines, which have realized a 

basic level of commercial maturity over the past decade. The evolutionary path taken by landbased designs, though, is not optimum for offshore machines because of the following 

fundamental differences in the offshore environment, market, and infrastructure:

• Siting farther from human habitations 

• Corrosive seawater exposure 

• Less constrained shipping size limits

• Higher offshore construction costs

• Poorer accessibility

• Wave loading added to extreme wind and fatigue load combinations 

• Lower wind shear and turbulence

• Other external conditions requiring special attention (e.g., ice and hurricanes)

• Contrasting regulatory, construction, and operational risk profiles

• Subsea electrical distribution and land-based interconnections. 

Because of these differences, future trends may move toward significant divergences between 

offshore and land-based designs. Optimized offshore turbine designs may take advantage of 
74

innovations and design opportunities that were previously rejected for land-based turbines in 

order to meet strict noise requirements or to improve aesthetics. Most offshore turbines will be 

placed far enough from people that some noise sources, such as aerodynamic blade noise, may 

not propagate an appreciable distance outside the project perimeter. Low-frequency infrasonic 

noise should be treated separately but has not been an issue for modern upwind turbines, even 

when in relatively close proximity to residences.

Because of higher BOS and O&M costs, the cost of an offshore wind turbine (the tower plus the 

rotor nacelle assembly) is estimated to be less than one-half of the capital cost of the wind 

project (see Section 6). Because transportation and erection size limits are less constrained and 

BOS costs are higher offshore, the optimum turbine size may be greater than the current sizes 

that evolved for land, and growth should continue until overall system costs are minimized. The 

optimized system could even allow for turbines that cost more per megawatt as long as the lifecycle project costs for the offshore system decrease as turbine size increases. Figure 5-2 shows 

how offshore project economics favor large turbines. As shown, the nonturbine project elements 

trend toward lower cost on a dollar-per-megawatt basis as turbine size increases. Land-based 

systems have benefited from turbine growth in a similar way, but offshore systems will probably 

be larger because of three major factors: (1) greater fraction of cost devoted to the BOS; (2) 

larger transportation and installation capacity size limits; and (3) the mobilization and logistics of 

offshore equipment (which favor large structures and larger projects). These factors will enable 

cost reductions as the turbine and project scale grows. As shown in Figure 5-2, the cost per 

megawatt of wind turbine capacity decreases with turbine size for the substructure, installation, 

O&M, and the grid and electrical infrastructure. In addition, larger turbines can extract more 

total energy for a given project site area than smaller turbines. 

Figure 5-2. Why larger turbines might lower overall cost
75

There is no consensus on how large offshore wind turbines will become, although most agree 

that no physical limit prevents building 10-MW or larger turbines. But the technology to develop 

these ultralarge turbines has not yet been proven and several significant challenges and 

development risks may exist. Wind turbine growth on land has been an evolutionary process in 

which wind turbines have grown from 100 kW during the early 1980s to 1,500 kW by 2000. 

Today, land-based machine size growth may be slowing, and future wind turbine size growth 

may be paced by offshore development. In Germany, at least three manufacturers have 

commercial machines on the 5-MW scale, with most targeting the offshore commercial market. 

According to findings from the UpWind Project (funded by the European Union [EU] and led 

by the Risø DTU National Laboratory for Sustainable Energy [Risø DTU]), wind turbines will 

have rotor diameters of more than 150 m and capacities of 8–10 MW in the near future. The 

UpWind project has been funded at about 110 million Danish krones (DKK) and will develop 

design tools to optimize large wind turbine components such as rotor blades, gearboxes, and 

other systems that must perform in large offshore wind farms (Risø DTU 2005). Indeed, 

manufacturers across Europe and North America are now developing wind turbines of this size 

(Next Big Future 2010; Renewable Energy Focus 2010; Clipper Windpower 2009; deVries 

2009). Table 5-1 lists some of the large wind turbines under development.

Table 5-1. Wind Turbines Rated Above 5 MW, Planned or Under Development

Company Rating (MW) Turbine Description

Clipper Windpower 10 Britannia: design under development

American Superconductor 10 Sea Titan: design under development

Repower 6 6M, based on 5-MW 126-m rotor design: in 

production

Areva/SWAY (Norway) 10 Floating offshore design: planned

Enercon 6 E126: production; no announced offshore plans

The critical issue in developing ultralarge machines is that the physical scaling laws do not allow 

some components to be increased in size without a change in the fundamental technology. New 

size-enabling technologies will be required to extend the design space for offshore wind turbines 

beyond the current 5-MW size. Some of these technologies may include a variety of stiffer, 

lightweight composite materials and new composite manufacturing methods; lightweight, lowmaintenance drivetrains; lightweight, high-speed downwind rotors; direct-drive generators; and 

large gearbox and bearing technologies that can tolerate slower rotational speeds and larger 

scales.

5.3.1.2 Advanced Rotors and Towers

The rotor represents only a small fraction of the total cost of the offshore system, but transfers 

most of the aerodynamic loads and all of the energy; therefore, this is one of the best places to 

look for system cost improvements. New high-technology strategies may cause turbine costs to 

increase to benefit the overall life-cycle economics. Turbine rotors can be enlarged to increase 

the energy capture in ways that do not increase structural loads, costs, or the requirements of 
76

electrical power equipment. A significant amount of R&D has been devoted to this approach for 

reducing the costs of land-based turbines, and offshore turbines can benefit from the same 

strategy.

Concepts such as active variable diameter rotors, bend-twist coupled blades, two-bladed rotors, 

or active control surfaces could have a higher economic value offshore, as long as they can also 

contribute to higher reliability (Energy Unlimited 2006; TPI Composites 2003a; Griffin 2002).

Structural loads caused by turbulence can be reduced using both passive and active controls to 

allow for longer blades and greater swept area, which can benefit both land-based and offshore 

turbines. But as offshore blade designs grow beyond the length of current land-based turbines, 

designers will seek more advanced technologies that offer higher material performance while 

reducing total blade weight and minimizing tip deflections for the next class of 10-MW turbines 

fabricated specifically for offshore applications. In addition, blade designers must overcome 

unique challenges in the offshore environment, considering mitigation strategies for marine 

moisture, corrosion, and extreme weather. At higher latitudes, ice accretion on the blades and ice 

floes can add to these concerns.

The wider use of composites and concrete may also penetrate the machine material mix. Blades, 

hubs, towers, foundations, and drivetrains could all benefit from lightweight, low-cost solutions.

Lightweight carbon hybrids and advanced manufacturing techniques employed in blade 

fabrication may differ significantly from those of traditional land-based blades, which rely 

mostly on fiberglass-reinforced polymers. The effects of the marine environment on many wind 

turbine blade materials, especially with respect to fatigue and corrosion, are not well known. 

These must be determined, though, before designing and fabricating durable offshore wind 

structures (Rasmussen 2005). Because blades for offshore turbines are not subject to onshore 

transportation constraints, larger blades are simply more practical, and will challenge researchers 

to improve material properties, manufacturing processes, and testing methods, and to develop 

large-blade test facilities (Griffin and Ashwill 2003).

Finally, the heaviest component above the water is the tower, which is fabricated almost 

exclusively from low-cost steel. Alternative, lightweight materials (like composites that could 

also help resist corrosion) could lower tower weight. Concrete has also been proposed as a 

possible low-cost tower material for large offshore towers. 

5.3.1.3 Drivetrains

Higher rotational speeds could allow for smaller blade planform areas and lighter blades for the 

same energy output. Increasing the maximum design blade tip speed, which is normally 

constrained to about 75 m/s, could result in significantly lower nacelle weights because of lower 

input torque, lower gear ratios, and hence, smaller drive shafts and gearboxes (DUWind 2001).

Some trends in offshore drivetrain designs favor direct-drive generators, which could be smaller, 

lighter, and less expensive with higher rotational speeds. Some engineers believe that directdrive generators could be more reliable than modular gear-driven systems, but some of today’s 

direct-drive generators use wire wound-rotor generators that are heavier than the modular 

systems. Permanent-magnet generator designs promise weight reductions and improved 

efficiency (Poore and Lettenmaier 2002). Larger capacity turbines may allow the industry to

move into technologies such as lightweight, superconducting generators that become more cost

effective with size and show promise for substantial weight reductions that could be 

advantageous in large floating wind turbines (Jamieson 2003).
77

5.3.1.4 Reliability

One lesson learned from offshore oil and gas is that work at sea takes longer because it is more 

difficult to plan and predict and the conditions are harsher. Even simple tasks take more time. 

Complex logistics can add extra steps that are necessary to maintain safety but do not contribute 

to the end goal and require a more skilled, more highly paid local labor pool. Work at sea, 

however, is inherently more expensive. Reassessing current practices for an offshore wind 

project could reveal many opportunities to lower project costs by redistributing the balance 

between work done at quayside and that done at sea. For offshore systems, the current landbased turbine service and reliability records are unacceptable and have contributed to some 

notable operational misfortunes (Modern Power Systems 2005). In the long term, a new balance 

between initial capital investment and long-term operating costs could be established that might 

have a broad impact on the cost of energy. Because new offshore strategies must minimize work 

done at sea, a paradigm shift that accounts for all aspects of the project is needed. If the offshore 

wind industry is to be successful, new turbine designs must place a higher premium on reliable 

designs and low-cost in situ repair methods, from the preliminary concepts to the finished 

product. Likewise, new materials must be selected for durability and environmental tolerance. 

The design basis could be refined to minimize uncertainty and ensure that actual offshore loads 

will not exceed the design envelope. Emphasis should be placed on avoiding large maintenance 

events that require deploying expensive and specialized equipment. This could be done through 

integrated system designs and design tools, appropriate design redundancy, improved quality 

control and inspection, and a substantial increase in the level of validation testing at all stages of 

development.

Offshore prototype wind turbines should be proven on land or on sites close to shore before they 

are deployed offshore in large numbers. The industry could establish guidelines to determine 

when a new machine is ready for deployment at sea. This process of improving reliability begins 

by identifying the root causes of component failures and understanding the frequency and cost of 

each event. Reliability is then determined, and finally, appropriate design improvements are 

implemented (Stiesdal and Madsen 2005; Rademakers et al. 2003).

5.3.1.5 Controls and Condition Monitoring

One trend is to equip operators remotely with intelligent turbine-condition monitoring and selfdiagnostic systems to manage O&M, predict weather windows, minimize downtime, and reduce 

the equipment needed for up-tower repairs. Systems that monitor turbine operating conditions 

can be used to inform smart controllers of needed operational changes or parameter adjustments. 

They also alert operators to schedule maintenance at the most opportune times. A warning about 

an incipient failure can alert the operators to replace or repair a component before it causes 

significant damage to the system or leaves the machine inoperable for an extended period of time 

(WindRisk 2010). More accurate weather forecasting could also become a major contributor in 

optimizing service for low cost, and this research area has strong synergies with land-based 

systems (Ougaard 2005).

Because offshore turbines are larger, they offer new opportunities that are not as practical at

smaller sizes. The cost of the control system and health-monitoring sensors that diagnose turbine 

status will not increase substantially as turbine size increases because the hardware is 

independent of size. For the same cost fraction, larger offshore turbines will enable a much 

higher level of control, maintenance management, and condition-monitoring intelligence. The 

value of such condition-monitoring information is multiplied in offshore applications because 
78

their remote and relatively inaccessible siting makes service and status information more critical. 

Much of the controls research for land-based systems can also apply to offshore machines, 

including new algorithms to increase power production and decrease blade loading. Some unique 

offshore applications may offer opportunities for enhancing these solutions, especially for 

floating systems that can use the rotor to help manage overall system displacements and loads 

(Neville 2009).

5.3.2 Offshore Wind Substructure Technology

Substructures are one of the most critical aspects in the development and expansion of offshore 

wind energy. The following section is devoted to a discussion of the state of this technology and 

some of the opportunities for technology advancement.

5.3.2.1 Substructure Technology Overview

The substructure of the offshore wind turbine is defined as the supporting system that begins at 

the lower flange of the tower and extends to the structural elements that attach it to the seabed. 

Offshore wind substructure technology can be divided into three major technology classes based 

on water depth, such as those shown in Figure 5-3.

Figure 5-3. Substructure technology classes for offshore wind turbines
79

Shallow water is defined in this study as between 0 m and 30 m. This definition captures the 

water depth of most of the projects installed today, as well as the bulk of industry experience 

(refer back to Figure 3-3). Transitional depths range between 30 m and 60 m. Beyond 60 m in 

depth, several floating concepts derived from the oil and gas industry have been developed. 

As a caution, note that the above-water depth bands for shallow, transitional, and deep water are 

specific to offshore wind turbines and are not derived from the oil and gas vocabulary, where 

deep water can mean 2,000 m or more. In addition, these depth bands only approximate the 

break points for the three technologies, but not enough experience exists to know if they are 

chosen accurately. They serve as good guides, though, for estimating the resource and the need 

to develop new solutions.

As water depth increases, the cost of offshore substructures is likely to increase because of the 

added complexity of design, fabrication, and installation, as well as the additional materials

needed below the waterline.

12

Figure 5-4 gives a conceptual view of how the costs of different substructure technologies 

change with respect to water depth. The figure also illustrates the need for different designs to 

suit the exact site depth conditions. The actual trajectories of these foundation cost curves will 

vary depending on the detailed design, site-specific metocean characteristics, soil conditions, 

visual impact requirements, environmental constraints on seabed disturbance, and various other 

external conditions. The objective, however, is to develop designs that are the most economical 

and that meet the requirements for a given set of site conditions and water depths.

Rising costs resulting from water depth may appear in stages as 

technology limits are reached. Industry trends indicate that technology solutions might be able to 

mitigate these jumps for the specific site characteristics as the industry gains experience. 

Source: Adapted from Dolan 2004.

Figure 5-4. Cost of offshore wind turbine substructures with water depth

 12 In some cases very shallow waters can increase the cost of offshore wind because of the added difficulty in 

finding heavy-lift vessels that can navigate at these depths. 
80

In shallow water, the necessary substructures and installation vessels are more basic, and to a 

large degree, design and implementation methods have been extrapolated from current landbased experience. Although monopiles and gravity-base foundations are the most commonly 

used substructures, they tend to increase in size nonlinearly with depth. At transitional or 

intermediate water depths, tripods, jackets, and other multi-pile systems may become more costeffective than monopiles and gravity bases. Multi-pile offshore wind substructures are modified 

versions of proven oil and gas offshore designs. Because wind turbines have inherently lower 

environmental and safety risks and can expect higher production volumes demanded by offshore 

large modular wind power facilities, however, costs can be expected to be lower for wind energy. 

For transitional depths, the main challenge will be to minimize cost escalation with water depth. 

The development of floating technology will require substantial additional investment, 

validation, and verification not just in the substructure, but in the integrated turbine/system, with 

the payoff being a tripling of the usable U.S. resource area. Note that even though the cost of the 

substructure may increase with depth for floating substructures, the system cost has the potential 

to be lower or the same for floating systems. Floating wind turbines and substructures are treated 

together in Section 5.3.3 because an integrated approach is required for these technologies to 

succeed.

5.3.2.2 Shallow-Water Substructures

Figure 5-5 shows the most common shallow-water foundations being deployed today. They 

include monopiles, gravity-base, and suction-bucket substructures, with the latter in the 

experimental stage. There is no technical reason why some of the transitional substructures 

(discussed later) would not also perform well in shallow water, but a full analysis of all 

conditions has not yet been performed. 

Monopiles are used in shallow depths because they are simple and the design developments 

required to transition from land to sea are minimal. In addition, their footprint on the seabed is 

minimal. Monopiles are used in most offshore installations, including the 160-MW wind farm at 

Horns Rev I off the western coast of Denmark (DONG Energy 2010). Monopile designs are 

limited by resonance avoidance issues because they are slender and flexible. For the same pile 

diameter, the natural frequency of the turbine/support structure system decreases with water 

depth until it coalesces with rotor excitation sources that are typically focused on the one-perrevolution rotor speed and the blade-pass frequencies. To maintain adequate monopile stiffness, 

the monopile diameter and thickness must grow to accommodate greater depths. This requires a 

volumetric (cubic) increase in mass, and a concomitant increase in material costs. At the same 

time, installation equipment such as pile hammers and jack-up vessels also become more 

specialized and expensive to drive these increasingly large diameter piles. Eventually the 

required hammer capacities and jack-up water depths will not be practical and the monopile 

becomes much larger than required for structural strength. The practical depth limit is thought to 

be somewhere near 30 m (Ali 2004), but it is technically feasible to design a monopile to work at 

40 m. The tradeoff is that to meet the resonance avoidance criteria, the monopile will be larger 

and more expensive than necessary to meet its strength requirements at depths beyond 25 m to 

30 m. Other considerations include soil characteristics—relatively hard bottom conditions with 

no significant rock to obstruct the pile penetration are required. Monopiles generally have a 

larger projected area toward the wave front, which can increase the loading from waves in 

general. In some shallow-water sites (between 10 m and 15 m deep), where waves may only 

break when they reach extreme wave heights, the load contribution from extreme breaking waves 
81

can become a design driver for monopiles and must be given full attention in the design (Dolan 

et al. 2009). In shallower sites, the waves may break more frequently under storm conditions but 

the wave attenuation is significant enough to reduce the overall impact on the design. Because 

these conditions may still drive certain fatigue cases, they must be considered. 

Figure 5-5. Shallow-water foundation technology

The gravity-base substructure (also shown in Figure 5-5) is the most common alternative to the 

monopile. Gravity-base substructures have been deployed successfully at sites such as the 165.6-

MW Nysted project in southeastern Zeeland and at the 23-MW Samsø project in northeastern 

Jutland, both in Denmark, and more recently at the Thornton Bank project in Belgium. These 

substructures overcome the structural flexibility and pile-driving issues of monopiles, but are 

very sensitive to soil conditions at the surface. The cost of gravity-base foundations generally 

increases rapidly as the water deepens. Under some site conditions where rocky substrates exist 

or where pile-driving vessels are not available or are excluded for ecological reasons, gravitybase substructures can be the best alternative (Volund 2005). Extensive site-specific soil analysis 

is required for each gravity base to ensure homogeneous soil properties and compaction to 

minimize uneven settling. When bottom conditions are thoroughly understood, the seabed must 

be prepared so that foundations can be accurately leveled to within 20 mm in some cases

(Aarsleff July/August 2003). Heavy-lift cranes are used to set the unballasted gravity-base 

structure in the proper position and thousands of tons of dead weight (ballast) are added to the 

structure to stabilize it from high overturning moments.

Monopile

Gravity 

Base

Suction 

Bucket
82

The suction-bucket foundation has not yet been used commercially as a shallow-water 

foundation, but significant development research has been done. This new technology could

show promise for some shallow-water sites, especially in avoiding the limitation of the large pile 

drivers needed to install monopile-type foundations (Ibsen 2005). Suction buckets provide a 

wide base and are driven into the seabed by drawing a vacuum inside to allow the bucket to be 

seated by hydrostatic pressure. 

In shallow water with soft soils or extreme breaking waves (see Section 5.3.11), it could be 

necessary to use technology now being considered for transitional water depths. Under these 

unique conditions, technologies that depend on a central column at the mud line to resist 

overturning might not be the optimum substructure. A concept for a shallow-water multi-pile 

substructure is being proposed for a project off Galveston Bay in Texas (Coastal Point Energy 

2010).

5.3.2.3 Transitional Technology

Transitional substructure technologies are used to support offshore wind turbines in waters 

deeper than 30 m but shallower than 60 m. Transitional depths are often referred to as 

intermediate depths but are thought of in this report as “transitioning” from the current 

technology into deeper waters but still fixed to the bottom. This means that projects installed in 

transitional water depths will be deeper and farther from shore than projects in the current 

experience base. For water depths greater than 30 m, or at sites with softer soil compositions, a 

wider substructure base is needed to counteract overturning forces and to conform to turbine 

design requirements for stiffness. In most cases, transitional substructures will result in higher 

costs and add incremental technology challenges. Transitional substructures use multiple anchor 

points, using jackets or tripods. Deeper water means more structure placed below the waterline, 

and logistically, a more difficult installation process. A fleet of installation vessels will need to 

be adapted to perform the needed functions at these greater depths. New installation methods and 

quayside infrastructure would need to be developed to make this technology competitive with 

shallow-water wind. Figure 5-6 gives a range of conceptual transitional substructures. 
83

Figure 5-6. Transitional substructure technology

Not all of the concepts shown in Figure 5-6 have been developed yet, but the figure shows some 

possibilities. The tripod shown on the left and the Talisman energy project concept are discussed 

later in this report. The guyed steel tube concept provides a wider base in deeper water but has 

not yet been deployed in the field. The full height jacket or spaceframe design (third from the 

left) is a variation of designs that have been tried on land but were eliminated because they cost 

more and tended to attract birds.

Transitional-depth technology is an important step in the development of offshore wind. 

Resource assessments at 90-m elevation for the United States show that the transitional-depth 

wind energy resource exceeds 552.9 GW for 8.0 m/s or greater (see Section 4). In general, one 

advantage of this resource area is its location farther from shore where visual impacts are

lessened. In many cases, the wind farms would be entirely beyond the horizon. Another 

advantage is that breaking waves are not as likely to occur at transitional water depths as they are 

in some shallow-water sites, significantly reducing extreme wave loading.

Talisman Energy deployed the first offshore wind turbines with a transitional substructure in a 

demonstration project of two 5-MW wind turbines at 45-m depths in the North Sea (MacAskill 

2005). Figure 5-7 shows the load-out and lattice type substructure—known more commonly as a 

“jacket” substructure—for the Talisman wind turbine project.
84

Figure 5-7. Repower 5-MW turbine installed on jacket substructure (left, Talisman Energy,

NREL/PIX 17883) and load-out to Beatrice Field (right, Talisman Energy, NREL/PIX 17884)

The Alpha Ventus project in Germany, which was completed in November 2009, also uses a 

transitional substructure. Although the water depths are just above 30 m, the project comprises 

six 5-MW Repower turbines on jackets and six 5-MW Multibrid turbines on tripods, and is the 

largest project installed in transitional depths so far. In the United States, Deepwater Wind has 

adopted this four-pile jacket design and has proposed a long-term marketing strategy that focuses

on transitional technology. Deepwater Wind is now in the process of planning its first project 

sites in Rhode Island, New Jersey, and New York (Deepwater Wind 2010).

Figure 5-8 shows actual examples of transitional technology multi-pile foundation types. On the 

left is the Bard substructure concept (BARD GmbH 2010), which uses three vertical piles and a 

transition piece to a tube tower. This is still in the demonstration phase of development. The 

photo on the right in Figure 5-8 shows the jacket substructure with a transition to a tube tower. 

This concept was first deployed on the Talisman project using a Repower 5-MW turbine and has 

been replicated at the Alpha Ventus project on six units.
85

Figure 5-8. Transitional substructure technology under development: BARD 1 foundation structures 

awaiting loadout with 5-MW AREVA and REpower test turbines in background (Gary Norton, DOE NREL/PIX 

17889); submerged four-pile jacket with transition to tube tower on Talisman Energy project with 

Repower 5-MW turbine (right, Talisman Energy, NREL/PIX 17885) (MacAskill 2005)

5.3.3 Floating Wind Turbine Technology

At deeper water sites, it might be more economical to use floating substructures, but the 

technology is at a nascent stage of development. The development of floating wind technology 

will dictate a new set of wind turbine design specifications to handle the coupled 

hydrodynamic/aerodynamic forcing, as well as the added weight and buoyancy stability 

requirements. These new requirements will initially add a higher degree of technical risk but 

with a potentially high payoff in the long term. The major incentives to develop floating systems 

include the following:

• Potential for reducing costs through system design site independence and greater 

opportunities for mass production

• Greater potential for full-system assembly at quayside and reduced load-out cost

• Higher wind speeds and energy capture over deeper waters

• Reduced impacts on human activities and environmental ecosystems

• Tripling the U.S. resource potential past 60 m in depth. 

In this study, the total deep water wind energy resource potential for the United States at a 90-m 

elevation was calculated to be 1,978 GW for annual average wind speeds greater than 8 m/s and 

inside 50 nm from shore (see Section 4). This represents about two-thirds of the total offshore 

wind resource in the United States. 

For floating systems, the benefits derived from turbine weight reduction will increase and could 

spur a new class of novel, lightweight wind turbine technologies that might be economical only 

in the context of floating substructures. The marine industry has demonstrated that a large 

portion of the buoyancy structure is needed to support the mass above the waterline. In the case 

of wind energy, this is the tower and rotor-nacelle assembly. Further studies are needed to 

quantify the benefit of pursuing lighter weight wind turbine subsystems on integrated floating 

platform architectures that could support such turbines (Butterfield et al. 2007). Some examples
86

of novel concepts that have been previously rejected for land-based and fixed-bottom offshore 

substructures for economic reasons include lightweight composite towers, concrete aggregates 

that weigh 30% less than standard mixtures but can deliver the same strength (Holm and Ries 

2006); multi-rotor concepts (Heronemus and Stoddard 2003; Jamieson 2003); high tip-speed 

rotors, downwind rotors, two-bladed designs, superconducting generators, and vertical axis 

rotors (Vita et al 2009). Cost-saving opportunities with the mooring and anchor systems could 

also be significant (Liu 2004; Ruinen 2004).

As a caution to manage expectations, note that revolutionary innovations often promise lower 

costs and optimized system performance, but the benefits may take longer to realize if the 

concept is a significant departure from conventional practice. 

In June 2009, Statoil Hywind teamed with Siemens Wind Energy to install the world’s first fullscale floating wind turbine (Statoil 2009). Statoil will test the 2.3-MW Siemens wind turbine 

over a 2-year period. The project is a demonstration of the Hywind concept, which uses a 

ballasted spar type substructure. Statoil is investing around 400 million Norwegian krones 

(NOK) in the construction, testing, and R&D related to this wind turbine concept. This cost, 

which translates to approximately US$70 million 2009$, appears to make this technology look 

unreasonably expensive, but this project is the first of its kind and most of the costs are one-time 

investments associated with R&D and infrastructure to design the system, deploy it at sea, and 

monitor its behavior. Future cost projections by Statoil suggest that the mature commercial costs 

can be competitive with fixed-bottom offshore wind. Figure 5-9 shows two photos of the 

Hywind turbine project as it appeared during load-out and after installation. 

Figure 5-9. First operating deepwater floating wind turbine: Statoil Hywind 2.3-MW prototype 

during load-out (left) and installed on station (right) (Photos courtesy of Statoil)

Many of the issues governing the current knowledge about floating platforms for wind turbines 

can be described in terms of platform stability and system dynamics because it is logical that 

successful turbine platform systems will minimize the external loading introduced by the two 

equally important, simultaneously acting spectrums resulting from wind and waves, respectively. 
87

This design space is a considerable departure from standard oil and gas platform designs, which 

are driven primarily by wave loading and static vertical payload capacity. Many of the same 

issues that govern oil and gas platforms will also influence the design of wind platforms, but the 

importance of each variable will be weighted differently. 

A vast number of permutations of offshore wind turbine platform configurations are possible,

considering the variety of available anchors, moorings, floater geometry, and ballast options. To 

help simplify the design process, the National Renewable Energy Laboratory (NREL) has 

developed a framework for generically plotting the design space for most floating platform 

designs. The method is referred to as the “stability triangle,” which classifies floating wind 

turbine platforms according to their method of achieving static stability (see Figure 5-10). 

Figure 5-10. Stability triangle for classifying floating substructures according to method of 

achieving static stability

Three idealized structures were defined to plot the design space that corresponds to three 

methods for achieving static stability (Butterfield et al. 2007):

1. Buoyancy at the water plane (ideal barges)

2. Ballast (spars) 

3. Mooring line tension (tension-leg platforms). 

The optimum platform will probably be a balance between a platform that can deliver dynamic 

behavior to minimize loads and deflections while also minimizing the complexities of 

installation, load-out, logistics, maintenance, and overall work at sea. Some of the variables to be 

considered are identified in the following list (Butterfield et al. 2007):

• Additional control requirements to limit motion

• Buoyancy tank cost and complexity

• Tank material and fabrication options

• Manufacturing automation and assembly options for mass production

• Mooring system cost and deployment complexity
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• Load-out cost and complexity

• On-site installation requirements

• Decommissioning cost 

• Maintainability and personnel access

• Corrosion resistance and exposure 

• Degree of water depth independence

• Sensitivity to bottom conditions

• Required footprint (varies as a function of depth and mooring strategy)

• System weight and weight distribution (especially above the waterline)

• Degree of induced tower-top motions 

• Wave loading and exposure at the waterline

• Allowable heel angle.

Figure 5-11 shows some examples of floating offshore platform architectures that are being 

considered.

Figure 5-11. Floating deepwater platform concepts: (1) semisubmersible Dutch tri-floater (Bulder 

et al. 2002); (2) spar buoy with two tiers of guy wires (Lee 2005); (3) three-arm mono-hull tensionleg platform (TLP) by Glosten Associates (2010); (4) concrete TLP with gravity anchor (Fulton, 

Malcolm, and Moroz 2006); (5) deepwater spar (Sway 2010)

Most of the concepts shown in Figure 5-11 have not yet been demonstrated. The Dutch tri-floater 

concept (1) was developed in a design study in the Netherlands and uses buoyancy to achieve 

static stability, although mooring lines and heave plates add significant pitch and roll damping 

1 2 3 4 5 
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for dynamic motion control. The spar shown in (2) was analyzed under an independent study at 

the Massachusetts Institute of Technology (MIT) and features a two-tiered guy-wire system 

using both mooring lines and ballast. The concept in (3) features a conventional TLP design with 

a single center buoyancy tank stabilized by mooring lines similar to the concept proposed by 

Glosten Associates (2010). Studies at NREL indicate that TLPs can be very stable but the 

expensive vertical load anchors used by the oil and gas industry may limit their costeffectiveness. Alternative TLP concepts like the one shown in (4) may reduce the cost of these 

expensive vertical load anchors. Fulton and colleagues (2006) performed this analysis under a 

U.S. Department of Energy (DOE) study in 2005. The classical deep-draft spar buoy, much like 

the Hywind concept described earlier, is shown in (5). This concept was developed by another 

Norwegian company, SWAY, which is partially owned by Statoil. 

Floating platforms, mooring line systems, and anchor installation and deployment are all 

significant cost drivers. A new generation of drag embedment-type anchors or vertical-load 

anchors (VLA) should be developed to lower installation and deployment costs (Liu 2004; 

Ruinen 2004). Deployable gravity anchors show promise for all platform types because they can 

be manufactured from low-cost materials and can be incorporated into simple float-out 

installation systems. Concept Marine Associates analyzed a gravity-anchor concept for a TLP

using concrete buoyancy tanks and deployable anchors (Fulton, Malcolm, and Moroz 2006).

Because offshore wind farms could consist of hundreds of turbines, developers can take 

advantage of economies of scale to streamline repetitive installation procedures and look for 

innovative tooling that cannot be justified in single-unit installations such as offshore oil rigs.

All floating designs should be fully evaluated in terms of the key variables that will determine 

survivability under extreme conditions, fatigue loading, and life-cycle costs. This comparison

would allow the key issues that limit each platform type to be identified, guiding future study in 

this area. A floating substructure must have enough buoyancy to support the weight of the 

turbine and to restrain pitch, roll, and heave motions within acceptable limits. Although these 

limits have not yet been fully established, modeling results to date indicate that turbine loads and 

tower-top motions will probably be higher than those of conventional fixed-bottom turbines 

because of system-wide interactions. As one example, coupled turbine/platform dynamics add 

inertial loading, requiring turbines that are more dynamically tolerant. 

Floating wind turbines in deeper water would be naturally located farther from shore with 

increased technical risk and development that would tend to drive costs upward, so the costcompetitiveness of floating systems depends on other factors. Floating wind systems enable 

major departures from fixed-bottom systems in their ability to partially decouple from the 

seabed. This offers a new degree of site independence that fixed foundations do not have, along 

with the ability to mass produce the platform and automate the system assembly at quayside. 

Fabrication facilities could be strategically located near harbor facilities for mass production, 

onshore assembly, and rapid deployment with minimal dependence on large vessels and landbased transportation. Offshore floating systems could be loaded out fully assembled and installed 

with a reduced burden for large vessels and time spent at sea, which could significantly reduce 

project costs. Turbine/platform systems and offshore infrastructure could be designed to take 

advantage of this strategy. These new strategies could be integrated into the turbine design 

process at an early stage (Fulton, Malcolm, and Moroz 2006; Hansen 2005; Lindvig 2005; 

Poulsen and Skjærbæk 2005).
90

The development of floating wind turbines comprises multiple technology challenges that will 

require more time, rigorous engineering discipline, broader skill sets, and more complex 

infrastructure. As such, the commercial development of this technology will take longer than 

shallow-water and transitional-water technology, but with the benefits of mass production and 

site independence, could open up a large new resource area at costs similar to those of shallowwater offshore wind.

5.3.4 Dynamic Computer Simulation Modeling 

Researchers have used an integrated hydrodynamic/aerodynamic approach to understand the 

system loads and design requirements to develop offshore wind energy system concepts, 

especially floating systems. Following such an approach is strongly recommended before

hardware is constructed (Jonkman 2009; Nichols et al. 2009; Jonkman 2007; Jonkman and Buhl 

2007; Jonkman et al. 2007; Passen et al. 2007; Jonkman and Sclavounos 2006; Nielsen, Hanson, 

and Skaare 2006; Tarp-Johansen 2005). Creating computer codes capable of accurately 

predicting the dynamic forces and motions acting on offshore turbines is considered essential 

before floating turbines can be reliably evaluated, designed, and tested at sea. To a lesser degree 

of complexity, the same challenge exists for fixed offshore wind structures, which are also 

subjected to significant wave loading. These design codes need to address not just structural 

design, but also controls to enhance stability, energy production, and certification verification 

issues. The work to develop these codes is underway, but they are not complete and have not yet 

been verified to deliver results with the necessary accuracy. Land-based wind experience 

indicates that validating the codes will require substantial measured field data from 

demonstration projects such as the ongoing DOE-funded project at the University of Maine 

(Dagher 2010a; 2010b).

The complexity of the task to develop accurate offshore modeling tools increases with the degree 

of flexibility, movement, and coupling of the turbine and substructure system. Structural analysis 

must also account for the dynamic coupling between the translational (i.e., surge, sway, and 

heave) and rotational (i.e., roll, pitch, and yaw) platform motions and turbine motions, as well as 

the dynamic characterization of mooring lines. NREL is conducting some of this work and the 

European wind industry is performing other parts of the work in collaboration with the 

International Energy Agency (IEA; see Jonkman and Musial 2010). Usually, greater substructure 

flexibility results in greater responses and motions to wave and wind loading. As a result, 

predicting wave loads and dynamics for turbines on monopiles is less difficult than for turbines 

on floating platforms. A primary challenge for floating systems is to predict loads and resulting 

dynamic responses of the coupled wind turbine and support structure when subjected to 

combined stochastic wave and wind loading. The existing codes are becoming mature with 

respect to wind load modeling. In the new coupled models, though, a broad complement of 

hydrodynamic effects must be incorporated, including a representative combination of waveloading models in regular and irregular waves for the design envelope defined in the stability 

triangle. These results will yield better insights about optimization. Time-domain wave-loading 

theories, including free-surface memory effects, should be used to relate simulated ambient 

wave-elevation records to loads on the platform.

5.3.5 Grid and Electrical Distribution Systems

The rate of offshore wind deployment in the United States could be paced, as it is on land, by the 

available grid infrastructure. With 54 GW of new wind capacity expected according to the DOE 
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20% report (DOE 2008), the availability of suitable transmission injection points for offshore 

wind is one of the factors that might limit the nation’s ability to meet the target set in the study. 

Comprehensive grid integration analysis should be conducted to identify weaknesses in the 

current grid infrastructure and opportunities for future expansion that facilitates the growth of the 

offshore industry. DOE has begun conducting some of these studies, including the Eastern Wind 

Integration and Transmission Study, which was published in January 2010 (EnerNex 

Corporation 2010). Other studies have focused on regional offshore solutions to the problems

states would face in bringing offshore wind onto the main grid system. Several concepts are 

being explored, such as constructing a large-capacity offshore transmission backbone that 

multiple offshore projects could share. This would eliminate the need to bring the power from 

each project to shore individually (Tierney, Okie, and Carpenter 2010; Ackermann et al. 2005; 

Tambke et al. 2005). 

The offshore grid will have unique characteristics that warrant more in-depth studies and 

modeling, including grid-fault and stability analysis. As wind farms grow in size and move 

farther from shore, the behavior and modeling of offshore electrical transmission systems should 

be analyzed with respect to grid-system reliability, grid losses, and grid-architecture options 

(Tambke et al. 2005). Offshore wind meteorology and its impact on power fluctuations and wind 

forecasting will also be critical (Kempton et al. 2010). Offshore winds may correlate differently 

with load than typical land-based sites, but more information is needed to quantify these effects 

over multiple regions (Barthelmie et al. 2005a; Sørensen et al. 2005). New grid code and security 

standards should also be established. Control and communication systems for large offshore 

farms will also be needed for aggregating the behavior of hundreds of large turbines onto the grid 

under transient or high-penetration scenarios (Barthelmie et al. 2005b).

5.3.6 Arrays and Array Effects

If offshore wind capacity expansion follows the scenarios predicted by the Regional Energy 

Deployment System (ReEDS; formerly known as the Wind Deployment System or WinDS; see 

Section 6), dozens of large arrays spanning large areas will be required. The offshore wind 

regime introduces a unique set of atmospheric and turbine-to-turbine interactions that developers 

will have to take into account. The configuration and spacing of wind turbines within an array 

has a marked effect on power production from the aggregate wind plant, as well as for each 

turbine. Consequently, these uncertainties in power production could create a large economic 

risk factor for offshore development. Computer codes are needed to model regional project 

development to monitor and predict the impacts of future fleet expansion and to help ensure that 

thousands of offshore wind turbines are introduced in an orderly way, which minimizes conflict 

on the Outer Continental Shelf (OCS) and maximizes the benefits to the public. 

Experience has established that the performance of turbines operating within an array is 

negatively affected because adjacent turbines reduce the kinetic energy in the flow and generate 

additional turbulence that is difficult to predict. Empirical data show that computer models 

attempting to predict turbine array performance are inadequate in representing individual turbine 

output. Some codes have been successful in predicting aggregate array performance for 

rectangular arrays (Jensen and Høgedal 2005). These codes, however, cannot be relied on for 

detailed array layouts, nor do they capture the turbine-specific physical conditions that relate to 

specific energy production and reliability. Array losses of more than 10% for offshore wind 

farms have been documented, but improvements in array layout and optimization models could 
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enable more efficient array designs that could reduce these losses and make better use of the 

available submerged land. 

Offshore wind array performance is very sensitive to the stability of the atmospheric boundary

layer, which influences the degree of mixing in the wind. The stability tends to vary significantly 

at a given site as well as by region. This characteristic determines the degree of stratification as 

the wind moves over the water and the amount of mixing among the horizontal layers because of

thermal density differences. A stable, stratified boundary layer is less able to dissipate 

mechanically generated turbulence created by upstream turbines and cannot regenerate the 

kinetic energy in the wind as fast as an unstable boundary layer that is naturally mixing with the 

outer, more energetic layers. This mixing is necessary to regenerate the kinetic energy of the 

inflow for downstream turbines. Current array models represent these stability effects poorly. In 

addition, they lack the ability to accurately predict the impact of turbulence inside the wind plant, 

which increases greatly when stable boundary layers are present. Accurately characterizing the 

behavior of the atmospheric boundary layer, and developing more accurate wake models, will be 

essential for designing turbines that can withstand offshore wind plant turbulence (Mróz, 

Holnicki-Szulc, and Kärnä 2008; Noppenau 2005). Because turbulence causes wear and tear on 

the turbines, maximizing turbine reliability will require careful characterization of the degree of 

turbine-generated turbulence under a wide range of conditions. This can be done by developing 

tools to optimize the layout of an array to balance low turbulence with high energy production. 

The degree to which stable boundary layer conditions occur could be studied using climate 

models and empirical data taken in situ. 

Offshore, the impact of one wind plant on another is likely to be a larger problem than for landbased systems because the open ocean contains continuous tracks of unobstructed windy 

territory. Wind plants introduce downstream turbulence that regenerates over some distance

depending on the atmospheric stability and other variables, but analytical models to predict 

optimum spacing between arrays are immature. Nevertheless, wind plants installed upstream 

must be assessed in terms of their effect on downstream wind plants and the resulting impacts on 

energy capture and structural loads. Understanding and managing “wind rights” and setback 

requirements could require accurate flow models, new satellite measurement techniques, broader 

satellite data domains, and better weather prediction tools and methods (Gravesen et al. 2005). In 

Europe, some researchers have begun using satellite images to determine the extent of the wake 

behind operating offshore wind plants. Understanding this issue in the near term may prove 

essential because minimum spacing requirements could limit the total extractable resource 

potential. 

5.3.7 Regional Issues

Several potentially significant regional barriers to the development of offshore wind may limit its 

deployment in the United States. They include floating ice, water depth (already covered), and 

hurricanes. 

5.3.7.1 Ice Load Resistance

Additional offshore foundation loads arise from the impact of floating debris and ice. In the 

United States, this is most likely to be an issue in the freshwater of the Great Lakes but could 

present a problem in other specific areas (e.g., northern latitudes). Turbines designed for and 

placed in the Baltic Sea have already managed ice issues successfully but salt content there may 

decrease the impact. The issue of ice loading requires more in-depth study, which could be done 
93

in collaboration with cold-climate countries—such as Canada and Sweden—that are pursuing 

offshore wind (Online Lawyer Source 2010; AWEA 2009).

5.3.7.2 Hurricane Resiliency

In some cases and in certain locations in the United States, the current generation of wind 

turbines that are type-certified to the IEC 61400-03 code for offshore turbines may not be able to 

withstand the extreme loading caused by hurricanes (IEC 2005). Although the IEC standards 

require the designer to determine the extreme loads imposed by hurricane conditions and design 

the appropriate strength into the structure, most wind turbines are designed and type-certified 

long before the site location is known. In many locations in U. S. waters, the extreme wind 

conditions will exceed the IEC Class 1 specifications—the most stringent class—which assumes 

gusts no greater than 70 m/s. In many sites, the 50-year storms will be category 4 and 5 

hurricanes that can have gusts greater than 80 m/s. Even though it is possible to develop 

structurally adequate designs using the existing standards, the process may require a more 

integrated design approach in cooperation with the turbine manufacturers or a Class S turbine 

(hurricane resilient) that exceeds the Class 1 requirements. It is possible to implement turbine 

design modifications for existing turbine designs that would resist or reduce the extreme loads

resulting from these conditions. Such modifications could involve changes to blades and towers. 

Some of these changes may require compromises that might diminish the energy capture 

potential for a wind turbine installed at those sites to ensure survivability. For example, although 

the extreme winds are higher, hurricane sites have typically lower annual average wind speeds 

that would normally warrant a larger rotor. At hurricane sites, larger rotors may be prohibitive

due to requirements for resisting extreme hurricane gusts. This may dictate a new design 

strategy. Work on the next edition of 61400-3 is scheduled to begin in 2010 and will incorporate 

explicit guidance for hurricanes (IEC 2010).

Understanding of extreme loads on wind turbines generated by hurricanes is important for 

reducing the uncertainty about survivability of the primary structure. The methodology for 

determining the probability of a hurricane at a particular site and the magnitude of its winds is 

not fully established. Some methods do exist but further validation is needed (FPLPM 2010).

In shallow water, hurricane-generated breaking waves may also create an extreme load case that 

has not yet been properly evaluated, especially in the Atlantic (Dolan et al. 2009).

Hurricanes present unique external conditions that could require turbine design modifications. 

The turbine’s protection system may need specific upgrades to withstand hurricane conditions. 

This could include not only extreme winds that could impose high instantaneous loads, but also 

sustained wind speeds, high wind/wave frequency, rapid direction changes, impulsive gust 

loading, breaking and slamming wave loads, and multidirectional wind/wave spectra. 

5.3.8 Logistics and Infrastructure

Impeding the onset of the offshore wind industry in the United States are the one-time costs 

associated with establishing the necessary infrastructure, such as upgrades to ports, harbors, 

manufacturing facilities, and vessels. Small projects will have a difficult time absorbing these 

costs and as mentioned earlier, these costs may not show up on the balance sheet but are 

necessary for project development. 

According to the American Wind Energy Association (AWEA), not a single specialized vessel 

for constructing offshore wind energy projects has been built in the United States to date. U.S.-
94

built vessels currently serving the oil and gas industry are not available for offshore wind 

because they are in high demand in the oil and gas industry (TPI Composites 2003b). Even if 

they were available, they would need modifications to perform wind turbine installations. New 

special-use vessels are needed, as well as upgraded ports and harbors from which to build and 

deploy them. Strategies that are consistent with the Jones Act (see Section 3.6.4) should be 

developed (Snodin, Hassan, and Partners Ltd. 2004). A survey of other potential port facilities

might be needed to look for regional synergies, taking into account the siting and resource needs 

for vessel work, manufacturing, and deployment. 

Large-scale development of offshore wind farms would require a significant stream of resources 

(EWEA 2009; Tegen, Goldberg, and Milligan 2006, Ancona 2010). Unlike land-based 

installations, which are typically in remote areas far from production and assembly operations, 

offshore turbines and components could be constructed and assembled in or near seaport 

facilities. This could allow easier transportation from the production location to the installation

site and eliminate the need to ship large components over inland roadways (GWEC 2008). Under 

the 20% wind scenario (DOE 2008), assuming that reasonable cost reductions can be realized 

over the next 20 years, the offshore wind industry may invest more than $150 billion in 

constructing offshore projects. Offshore wind production facilities could deliver economic 

benefits to local communities by creating high-paying industrial jobs in regions aiming to expand 

the manufacturing sector. This was discussed in the SeaWind Europe Report and the EWEA 

report Wind at Work: Wind Energy and Job Creation in the EU, and similar outcomes for job 

creation could apply in the U.S. economy (Garrad Hassan 2004, EWEA 2009 ). Port staging 

areas could be upgraded to handle the logistics of the turbine assembly, substructure assembly, 

and load-out, allowing work at sea to be minimized.

5.3.9 Research Facilities for Field Testing

Offshore turbines will also require significant new test facilities and upgrades to accommodate 

larger component sizes and higher reliability requirements. In 2009, DOE directed $25 million in 

funding to support the Massachusetts Clean Energy Center (MASSCEC) in a partnership with 

NREL to build a large-blade testing facility capable of testing blades up to 80 m (Cotrell, Musial, 

and Hughes 2006). In addition, DOE awarded $45 million in matching funds to a South Carolina 

consortium that will develop a new large-scale drivetrain test facility for wind turbines up to 

10 MW in size (Hull 2010). 

These same needs exist for open-ocean test facilities. Shallow-water testing will be essential to 

verify standards, validate design tools, and test design assumptions. The first phase of offshore 

wind deployments could be used to establish offshore design requirements and to verify design 

assumptions through measurements made on actual wind turbines at sea (Palo 2003). It might be 

necessary to conduct multiple tests or deploy several test beds to examine technology at various 

depths and external conditions. These types of projects could validate the fundamental baseline 

turbine and foundation technology assumptions, allow the actual meteorological ocean 

environment to be measured, and verify assumptions relating to permitting and potential 

environmental impacts. The field data output could yield critical design methods and codes; 

uniform standards for structural reliability; design specification guidelines; industry-accepted 

safety margins; and valuable data to validate design models, codes, and assumptions (Sclavounos 

2004). As transitional and deepwater technologies are deployed and tested, more specialized 

testing facilities may be warranted. In 2009, the University of Maine was awarded more than $12
95

million in DOE grants to begin developing a deepwater wind energy test facility (University of 

Maine 2010), and in June 2010, voters approved a bond for $11 million of additional funding. 

5.3.10 Certification and Standards

The Bureau of Ocean Energy Management Regulation and Enforcement (BOEM; formerly the 

Mineral Management Service [MMS]) has been authorized to define the structural safety 

standards for offshore wind turbines on the OCS (see Section 7) (IEC 2010; MMS 2009). 

Technical research, analysis, and testing are needed to build confidence that safety is adequate 

and to prevent an excess of caution resulting from a lack of information. This will require a 

complete review of the existing offshore wind standards as well as the applicable offshore oil 

and gas standards (e.g., American Petroleum Institute [API]). A joint industry project, partially 

funded by DOE and BOEM, revealed that, as written, the existing IEC and API standards will 

deliver comparable levels of safety. Nevertheless, BOEM has not yet adopted any standards for 

use in the United States for wind turbines on the OCS (Dolan et al. 2009). The AWEA Standards 

Coordinating Committee has formed an expert industry-based working group that is tasked with 

developing a roadmap or guide that identifies the appropriate existing standards to use in the 

design, fabrication, installation, testing, operation, and inspection of offshore wind projects. 

Developers, turbine designers, manufacturers, regulators, and certification verification agents, 

among others, may use this guide. This joint project, supported by DOE and AWEA, is 

underway. Further development is also continuing to make sure that the existing IEC TC-88 

61400-03 standard for offshore wind is maintained and upgraded to account for innovations in 

the industry (IEC 2005). These innovations will include deepwater floating platforms, new 

offshore load cases, turbines larger than 5 MW, and hurricane survival criteria.

5.3.11 Metocean Characterization

The metocean characteristics at offshore sites, which include a range of wind, ocean waves, 

water current, and ice floe conditions, as well as their various combinations, are much more 

difficult to assess than the winds over land. 

Manwell and colleagues (2007) discuss external design conditions related to offshore wind and 

the topic is also covered in IEC 61400-03 where the external conditions and load cases are 

defined for wind turbines. One of the primary challenges is to assess and evaluate the statistical 

nature of wind and wave combinations as they affect the turbine substructures under a wide 

range of design conditions. The evaluation of extreme events that are determined through 

statistical analysis comprising the probabilistic occurrence of the 50-year extreme wind/wave 

conditions is the subject of substantial research. Assessments of fatigue conditions are also 

extremely important and can have a hand in driving the design. Directionality of waves and wind 

and their combinations may influence the assessment significantly. Experimental validation is 

required to verify design load assumptions and to assess stochastic turbine responses over a 

wider range of metocean conditions where the analysis might miss significant load cases. The 

response of the system is highly dependent on the type of substructure, the water depth, and the 

characteristics of the waves. Breaking waves can impart loads that have more than twice the 

magnitude of regular more sinusoidal wave structures, and can be a unique design driver that has 

not yet been fully validated (Dolan et al. 2009). The research done so far indicates that the 

impact of breaking waves can be much more severe on a monopile substructure than on a jackettype substructure because of the monopile’s larger profile. This impact has not yet been fully 

explored but may have significant economic consequences at some sites. 
96

Ice loading will be a factor in the Great Lakes where freshwater ice loading must be taken into 

account during the design. Ice loading can result in significant horizontal loading to the 

substructure during ice floes and through expansion cycles. Ice floes can also cause harmonic 

excitations to the tower base under certain conditions and ice fracture modes that can in turn 

result in possible resonance conditions that need to be assessed. Ice can also build up around the 

base at the water surface and change the dynamic characteristics of the turbine system by 

effectively stiffening the structure. This condition also needs thorough evaluation. Most field

work on ice loading has been conducted in the Baltic Sea and in the Great Lakes on bridge 

structures. Freshwater test facilities are needed to explore ice loading on wind turbine 

substructures in the Great Lakes. 

5.4 Synergies with Other Offshore Industries 

The development of offshore wind technology in the United States could take advantage of vast 

experience already obtained in both the oil and gas industry and the European wind energy 

industry. The oil and gas experience dates back over 50 years when the first oil wells were 

drilled in shallow water offshore. In Europe, more than 2 GW of offshore wind has already been 

installed with a track record approaching 20 years. These existing industries can be valuable 

alliances in the development of offshore wind in the United States, using experts already trained 

in the various offshore fields (see Figure 5-12).

Figure 5-12. Expertise and experience for offshore wind development

Many of the technologies for offshore wind development have already been proven in the oil and 

gas industry. Applying this experience to offshore wind, however, will require technology 

innovations and new methods for manufacturing, logistics, and maintenance that will be critical 

to lowering costs and expanding the resource areas where offshore wind is viable. 
97

The increased complexity of offshore construction, operation, and maintenance relative to landbased wind will require adaptations of technologies, methods, and experience derived from the 

marine and offshore oil and gas industry. The portion of the offshore turbine system below the 

waterline will largely be designed and implemented using experience developed over the past 4 

decades by the oil and gas industry but with several modifications to adapt to the offshore wind 

situation. Primarily, the installation of an offshore wind farm is a mass production event that 

requires repetitive steps not common to oil and gas. Most oil platforms, for example, are singleunit installations. The installation of a wind farm is a continuous operation that takes place over 

several months rather than several days. 

The design and installation of the electrical grid system, from placing interturbine cabling to 

running the cable to shore, will be performed by the existing submarine cable industry. Offshore 

wind projects will employ the established offshore industry to perform site assessments and 

geotechnical engineering. Turbines could be installed and maintained using existing, modified, 

or new offshore vessels and equipment, with designs based on the established practices of the 

offshore industry. Personnel access and service for turbines will use experienced offshore labor 

or new labor forces trained by the established marine industry. In the United States, where landbased wind development has been largely unregulated, offshore turbines will have to undergo 

extensive structural evaluation and certification with a BOEM approval process (MMS 2009).

This transfer of knowledge between offshore wind and offshore oil is already well underway in

Europe, where dozens of oil and gas and marine engineering and construction contractors are 

engaged in offshore wind energy. In addition, other technological advancements in computers, 

controls, materials, corrosion prevention, energy storage, and generation, among others, continue 

to increase the capabilities for offshore oil and gas development and will synergistically 

strengthen the technical viability of offshore wind. Ultimately the dependence of wind energy on 

offshore oil and gas experience will help to facilitate the transition from a fossil-based energy 

economy to a more sustainable energy economy based on renewable sources. 

5.5 Findings and Conclusions

So far, offshore wind energy has used technology similar to land-based wind energy but the 

opportunities for offshore technology improvement are significantly different. For offshore wind 

technologies, a much higher fraction of the capital cost must go toward BOS and construction. 

In addition, there is a greater need for high reliability because the inherent lack of turbine access 

at sea makes O&M more difficult. Offshore wind turbines are generally larger because many of 

the land-based transportation and erection constraints can be avoided. They also rotate faster than 

land-based machines because there are fewer near-field noise issues. Offshore turbines need to 

be strengthened to accommodate waves and storms, weatherized to guard against corrosion and 

the sea environment, and designed to accommodate unique offshore personnel facilities. 

Consequently, offshore wind energy tends to cost more per unit of energy capacity than landbased wind energy. Also, one-time costs are associated with developing the infrastructure to 

support the offshore industry, including vessels for installation, ports and harbor upgrades, 

manufacturing facility construction, and workforce training program development. 

The biggest design difference in offshore wind energy technology is in the substructure and 

foundation as it pertains to water depth. This presents a major barrier that could prevent the 

development of the largest resource areas located in waters with depths greater than 60 m, which 

in turn would prevent offshore wind energy from reaching its full potential as an energy supply. 
98

Offshore wind turbine substructure designs are mainly based on water depth, soil conditions, and 

vessel constraints. The technology break points fall into three depth categories: shallow (30 m or 

less), transitional (>30 m to 60 m), and deep water (>60 m). In shallow water, the substructure 

extends to the sea floor and includes monopoles, gravity bases, and suction buckets. In the 

transitional depth, new fixed-bottom technologies are being created or adapted from oil and gas, 

including jacket substructures and multi-pile foundations. At some depth, it is no longer 

economically feasible to affix a rigid structure to the sea floor, and floating platforms may be 

justified. 

Three idealized concepts have arisen for floating platform designs, including the 

semisubmersible, the spar-buoy, and the tension-leg platform. Each design uses a different 

method for achieving static stability. Although it is not yet known which configuration will 

deliver the optimum system performance, designers choose platforms that are easy to install and 

that minimize the increase in the overall turbine loads when compared to loads from a land-based 

reference turbine. 

Shallow-water projects dominate the current market. Work on transitional technologies is just 

beginning and only two have been installed to date. Transitional foundations may cost more 

because greater depths usually mean higher costs for fixed-bottom systems. There is currently 

one floating deepwater demonstration project, the Hywind, which was launched in 2009. One of 

the key conclusions is that future floating deepwater technology may not necessarily cost more 

than fixed-bottom systems because full wind turbine/substructure systems can be mass produced 

and fully assembled on land, avoiding expensive ocean-based construction costs. More research 

is needed to verify this supposition for low-cost floating wind turbines. New technology will be 

needed to address low-cost, easily deployable mooring systems for floating wind systems. In 

addition, there is more wind and therefore more energy over the deeper waters. The development 

of this technology is more complex and higher risk, but has a potential for high payoff. 

To minimize cost, new turbine designs must be optimized for the offshore environment. Some 

manufacturers are leaning toward designing larger offshore turbines, as evidenced by the current 

research being conducted on turbines in the 10-MW class. Improved efficiency may be obtained 

by employing new rotor and drivetrain designs, using new materials, developing better codes to 

analyze arrays and their effects, improving design standards, and gaining a better understanding 

of the external metocean conditions. 

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6.0 Offshore Wind Economics

In the last 20 years, more than 2,000 MW of offshore wind capacity have been installed in 

Europe (EWEA 2010; Fichaux and Wilkes 2009). Several industry and academic publications 

cite actual capital costs and projected levelized costs of energy (LCOE) for these installations. 

These sources, which are generally based on the actual experiences of developers, are the best 

publically available information on project costs. 

This section looks at offshore wind cost data in two ways: the capital cost to install the wind 

plant and the life-cycle cost, or LCOE. The LCOE is the cost of energy produced over the life of 

the project, generally considered to be 20 years. LCOE calculations are more uncertain than 

capital cost estimates because they include future projections of energy production, operational 

costs, decommissioning costs, and long-term reliability, in addition to the initial capital cost. 

This section begins by examining the observed capital cost trends of offshore wind projects and 

then discusses the levelized cost of offshore wind energy. Finally, it describes two capacity 

expansion scenarios that investigate plausible market conditions under which offshore wind 

could flourish in the U.S. energy market. 

Numerous economic and technology-specific factors can affect the capital cost of offshore wind 

projects—fluctuations in exchange rates, commodity prices, credit availability, manufacturing 

capacity, labor costs, and risk premiums. These variables are liable to change drastically from 

year to year, which makes it difficult to accurately predict future project costs. Uncertainty 

increases when attempting to forecast U.S. project costs by extrapolating European data because

the two markets differ substantially:

• The infrastructure or logistical support required for offshore wind projects is not yet 

developed in many areas of the United States. 

• Policy and regulatory environments are distinctly different.

• Risk perceptions associated with initial offshore wind projects differ because of contrasting 

policies and market motivation.

• The U.S. metocean and physical environment is different because of water depth and tropical 

storms.

Some of these differences could mean higher initial costs for U.S. offshore wind projects, but 

these costs should come down as the U.S. market matures.

National Renewable Energy Laboratory (NREL) projections of U.S. offshore wind deployment 

scenarios show tremendous sensitivity to assumptions about the regulatory, policy, and market 

conditions. Scenarios examined under the 20% report (DOE 2008)—which are based on 

assumptions that reflect plausible conditions of the current U.S. economic and political 

environment—postulate substantial deployments of offshore wind in the United States in the 

coming years.
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6.1 Offshore Wind Capital Cost

Offshore wind project cost cannot be fully evaluated by looking at the upfront capital 

investments, but because the industry is very new, life-cycle cost assessments are more 

uncertain. Therefore capital cost can provide a useful metric for evaluating the state of the 

industry. 

6.1.1 Market Studies 

Capital cost data for offshore projects are available for 2,263 MW of the total global installed 

offshore wind capacity of 2,387 MW (Alpha Ventus 2010; Offshore Wind Energy 2010a, 2010b, 

2010c, 2010d, 2010e, 2010f, 2010g, 2010h, 2010i; PowerTechnology.com 2010a, 2010b; RWE

npower renewables 2010; Vattenfall 2010; EWEA 2009; Ministry of Foreign Affairs of Denmark 

2009; National Wind Watch 2009; reNews 2009; Snyder and Kaiser 2009). Data for proposed 

projects in the United States and Europe were gathered from news articles and developer web 

sites (AWS Truewind 2010; Garden State Offshore Energy 2010; reNews 2009; Sokolic 2008; 

Williams 2008; Geoghegan 2007). Usually the project developer reported the data, which could 

be not be verified independently. Estimates of reported capital cost were converted to 2008 

dollars and then averaged to arrive at a normalized capital cost number for each project. Figure 

6-1 shows capital cost per kilowatt for the wind farms where data are available. 

Figure 6-1. Offshore wind plant capital cost per kilowatt 
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Figure 6-1 shows that capital costs of offshore wind plants commissioned between 1991 and 

2006 ranged between $1,300/kW and $2,800/kW (a capacity-weighted average of $2,273/kW). 

Beginning in 2007, installed project costs were considerably higher. Capital costs of projects 

commissioned between 2007 and 2009 ranged between $2,500/kW and $5,800/kW13

• Fluctuations in exchange rates

(a capacityweighted average of $3,544/kW). The 56% rise in capacity-weighted average project cost can be 

attributed to a number of factors:

14

• Increased demand for turbines 

• Increased supply-chain bottlenecks 

• Higher profit margins for turbine original equipment manufacturers (OEMs) and wind 

project developers

• Increased knowledge of technical risks gained from developing and operating offshore wind 

projects (e.g., logistics, reliability)

• Increased complexity in siting, engineering, and building offshore wind projects (larger 

capacity, increasing depth, increasing distance from shore)

• Higher raw material and commodity prices.

Analysis of the estimated cost of proposed projects shows increasing variability, and based on 

projections from developers, this wide range of capital cost is expected to persist at least in the 

near term (projected future project costs range from $2,000/kW to $6,390/kW with a capacityweighted average of $4,260/kW). Table 6-1 lists future project costs for several different 

subgroups. 

Table 6-1. Estimation Methodologies for Future Offshore Wind Project Costs (US$2008)

Metric for Calculation of Future Offshore Wind 

Project Cost

Arithmetic Mean 

(US$/kW)

Capacity-Weighted Average 

(US$/kW)

Installed 2009 projects 4,252 3,964

Proposed 2010 projects 3,965 3,905

Proposed U.S. project 2010–2015 4,191 3,921

Proposed European projects 2010–2015 4,411 4,431

Proposed projects 2010–2015 4,327 4,259

 13 The installed capital cost of $7,000/kW in 2007 represents the Talisman Energy demonstration project, which is installed in 

deeper waters than any commercial offshore wind project. 14 The variability of currency exchange rates has the potential to obscure cost trends when projects that are denominated in 

English pounds or euros are compared to projects denominated in U.S. dollars. This possibility was investigated by plotting data 

that had been converted to 2008 euros using official European Union (EU) inflation data. This study found that the data exhibit 

the same basic trend of increasing capital costs with time, which confirms that this is a real trend and not simply an artifact of 

exchange rate fluctuations.
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Table 6-1 gives a range of estimates of future offshore project capacity-weighted costs from 

$3,921/kW for near-term U.S. projects to $4,431/kW for near-term European projects. This 

range of estimates is consistent with the stated opinions of developers, who expect costs to 

stabilize or rise slightly from 2009 levels. Note that the cost projections of U.S. developers are 

about 13% lower than the cost projections of European developers for 2010 to 2015.

The capital costs of offshore wind can vary widely depending on technical aspects of the specific 

project. Figures 6-2 through 6-4 show the influence of water depth, distance from shore, and 

project size on the capital costs of offshore wind development thus far. Data from plants in 

operation are divided into two groups: plants brought online before 2007 and projects 

commissioned between 2007 and 2009. These data points are compared to data for proposed 

U.S. and European projects. 

Figure 6-2 plots the average water depth of each project site against capital cost per kilowatt. 

Engineering and economic modeling suggests that fixed-bottom projects sited in deeper water 

should have higher costs because they require increasingly heavier and more complex 

foundations and specialized installation vessels. This expected trend is not readily apparent, 

however, in either the data for commissioned projects or those for proposed projects. Of the 50 

installed and proposed projects in the data set, 48 are in shallow water (depths of 30 m or less) 

and the average depth is 12.9 m. The two projects installed in deeper water, Talisman Energy 

and Alpha Ventus, have significantly higher capital costs, but both are relatively small 

demonstration projects and may not adequately represent large-scale future projects. 

Figure 6-2. Effect of water depth on capital cost per kilowatt 
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Capital costs are also expected to increase when projects are sited farther from shore because of 

longer power cables and increasingly complex project logistics. Figure 6-3 shows distance from 

shore plotted against capital costs. The expected relationship between distance from shore and 

capital costs is not apparent for either installed projects or proposed projects. Of the 50 projects 

examined in this study, 49 are sited within 30 km of shore and the average distance is 13.5 km. 

Alpha Ventus is the only project sited outside this range, at 45 km from shore.

Figure 6-3. Effect of distance from shore on capital cost per kilowatt

Another factor that influences capital cost per installed kilowatt is the overall project size. It is 

generally expected that large offshore wind projects will benefit from economies of scale. Larger 

projects are expected to have lower capital costs per kilowatt because they can spread the fixed 

costs of project development (e.g., permitting, vessels, and grid connection) over a greater 

amount of total generating capacity. The data in Figure 6-4 demonstrate that project size does not 

yet show a clear effect on capital cost per kilowatt, but this could be caused by the lack of 

consistent data. If one looks at only the most recent project installations (2007 to 2009—blue 

diamond symbols), project size and cost appear to be correlated, but further analysis is needed. 
113

Figure 6-4. Effect of project size on capital cost per kilowatt

Projects in the data set range in size from 2 MW at the Lely Windpark in the Netherlands to 

209 MW at the Horns Rev II project in Denmark (installed in 2009). The average size for 

installed projects is 69 MW. Projects scheduled to come online between 2010 and 2015 will be 

significantly larger than existing offshore projects. Proposed projects range from the 10-MW 

North Carolina Coastal Wind demonstration project15

Possible reasons why the offshore wind project cost data do not reveal some of the expected 

trends associated with depth, distance from shore, and size/scale are related to the relative 

immaturity of the industry and differing market and policy environments that project developers 

face. These reasons include the following:

in the United States to the 630-MW 

London Array in the United Kingdom. The average capacity of the proposed projects in the data 

set is 267 MW.

• The few offshore wind projects built makes it difficult to extract statistically significant 

trends. 

 15 Duke Energy has not released an estimate of the North Carolina Coastal Wind demonstration project’s capital cost. As a result, 

the project cannot be included in NREL’s capital cost database, although these demonstration turbines could be among the first 

installed in U.S. coastal waters (Duke Energy 2010).
114

• The broad jump in project costs after 2006 appears to be market-related and overwhelms

more subtle trends in recent and projected costs. 

• Companies are still standardizing their approaches to project financing, transport, logistics, 

and installation. 

• Project costs vary depending on the extent to which the electrical grid and the 

interconnection are considered part of the overall project. In countries like Germany and 

Denmark, the government-managed utility is responsible for the grid infrastructure out to and 

including the offshore substation—this is not the case for the United States or the United 

Kingdom (EWEA 2009).

6.1.2 Capital Cost Breakdown

A literature survey was conducted to determine the installed capital cost breakdown for a typical 

offshore wind project. Several studies estimated the breakdown of capital costs for offshore 

turbines installed in shallow water by component. Generally, the authors segmented capital costs 

into the categories described in Table 6-2. The operational categories (operation and 

maintenance [O&M] and other variable costs [OVC]) do not contribute to capital cost, but are 

used here in the subsequent discussion of LCOE.

Table 6-2. Descriptions of Cost Breakdown Categories

Cost Category Description

Turbine • Rotor and blades

• Drivetrain nacelle

• Tower

• Control, safety system, condition monitoring

• System marinization

• Commissioning

• Surety bond (to cover decommissioning)

• Warranty (typically 5 years)

Electrical Infrastructure Internal grid between turbines

Export cables to shore 

Substation

• Transformers

• Grid connection/upgrades

Support Structure Turbine base (e.g., monopile, gravity base)

• Transition piece connecting base and tower

• Personnel access infrastructure 

• Scour protection

Logistics and 

Installation

Note: Some reports separate logistics and installation costs from the costs 

of the turbine, electrical infrastructure, and the support structure. This 

category includes costs for one or more of the following: 

Port and staging equipment

Component transportation

Turbine Installation

• Electrical infrastructure installation

• Support structure installation

Project Development 

and Permitting

Project development

Project engineering

Environmental studies

Permitting

Other Capital Costs Miscellaneous capital costs not included in categories listed 

O&M Regularly scheduled maintenance 
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Unscheduled maintenance

Service and spare parts

• Logistics and installation

OVC Lease payments

• Taxes

Insurance premiums

Transmission charges

• Operational administration

Figure 6-5 shows the capital cost breakdown results (Blanco 2009; Duke Energy 2009; Ernst & 

Young 2009; Krohn, Morthorst, and Awerbuch 2009; Carbon Trust 2008; Fingerish, Hand, and 

Laxson 2006; Junginger and Faajj 2004; Morgan, Scott, and Snodin 2003; DUWind 2001). The 

estimates for the turbine’s contribution to total capital cost range from 36% to 59%, with a mean 

of 44%. This is a lower percentage of the capital cost than for land-based turbines, where the 

turbine can comprise nearly 70% of total project costs (Blanco 2009). Some studies do not 

specifically treat logistics and installation as a separate category.

Figure 6-5. Capital cost breakdowns for offshore wind plants in shallow water
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6.2 Offshore Wind Cost of Energy

The overall economics of offshore turbines depend on project life-cycle costs, including the 

capital investment, O&M costs, cost of fuel (zero for wind projects), and cost of capital. Total 

project life-cycle costs are divided by total lifetime energy production to obtain an LCOE, which 

is the cost of generating power from a particular project (Fingerish, Hand, and Laxson 2006).

Offshore wind energy is roughly twice as expensive as land-based wind, which currently costs 

about 5–8¢/kWh. Significant cost reductions are possible, however, because offshore wind is a 

relatively new technology and has not yet realized many of the technology optimization and 

learning opportunities. The future cost of offshore wind energy will be closely tied to the state of 

the technology, the maturity of the industry, the level of deployment, and the experience gained 

through implementation.

Differences in the energy markets of the United States and Europe, especially how risk is 

allocated during project development and financing, could affect the cost of offshore wind in the 

United States. Different government policies and project support mechanisms between EU 

countries and the United States might influence both the required up-front capital investment and 

the cost of capital. Germany, for example, requires utilities cover the cost of grid connection out 

to and including the substation, which is located several kilometers out to sea for offshore wind, 

reducing the required investment cost to developers. Germany also offers feed-in tariffs that 

guarantee a price of 15 euro cents for every kilowatt-hour of electricity generated by an offshore 

wind project for the first 12 years of operation. By guaranteeing revenue, the German 

government reduces the risk of investing in projects, effectively reducing the cost of capital 

(GWEC 2010). The effects of different policies and support mechanisms are not fully analyzed 

in this report but contribute to some cost uncertainty in projecting the LCOE of initial offshore 

projects in the United States. 

Breakdowns of the elements of LCOE are given in the studies cited in Figure 6-5, and Figure 6-6 

summarizes those data. Because of differences in the way that each author cited life-cycle project 

costs, some assumptions were made to allow reasonable comparisons across the various datasets 

(see the footnotes to Figure 6-6).

Although the exact proportions of each cost category will vary with the specifics of each project, 

life-cycle cost of offshore wind energy is dominated by balance of station (BOS) and O&M. The 

electrical and grid infrastructure, foundations and support structures, offshore logistics and 

installation, and O&M represent the highest percentage of the total project cost, ranging from 

57% to 71%. Because project economics are dominated by BOS and operating costs, adopting

larger capacity turbines should result in significantly lower overall costs of energy for offshore 

projects. O&M costs are two to three times higher than those of land-based systems (Rademakers 

et al. 2003) and can reach 20% to 30% of the LCOE.
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Figure 6-6. Life-cycle cost breakdowns for offshore wind plants in shallow water

1

Ernst and Young [6-33] estimate that total operational costs for projects closing in 2009 ran to ₤79,000/MW/yr. This amount is 

divided into ₤60,000/MW/yr for O&M and ₤19,000/MW/yr for other operating costs (lease payments, transmission charges, grid 

maintenance costs, insurance premiums, and decommissioning provisions). With a 3% rate of escalation over 20 years of 

operation, life-cycle O&M was ~₤950,000/MW, and other operating costs ran to ~₤300,000/MW. 2

Blanco (2009) estimates that O&M costs are 50% of the variable costs of a turbine over a project’s lifetime, meaning that other 

operational costs (management, administration, land rental, insurance premiums) make up the other 50%.

3

The Carbon Trust (2008) does not estimate O&M costs or of other variable costs for offshore wind projects. Based on industry 

standards, an O&M cost assumption of £16/MWh was used to estimate the life-cycle cost of O&M. Assuming a 35% capacity 

factor, a 3% rate of escalation and a 20-year operational life, the total life-cycle O&M cost was £780,000/MW. 4

Khron, Morthorst, and Awerbuch (2009) state that offshore O&M costs typically run €16/MWh over the lifetime of the project. 

Assuming a 35% capacity factor, a 3% rate of escalation, and a 20-year operational life, the total life-cycle O&M cost was 

approximately €780,000/MW. Khron and colleagues (2009) estimate that O&M costs are 60% of the variable costs over a 

project’s lifetime, meaning that other operational costs (split equally between land, insurance, and overhead) make up the 

remaining 40%.

5

Junginger and Faaij’s article (2004) gives a range of estimates for cost components based on the literature. An average of the 

range for each component was normalized to create a usable cost breakdown estimate.

6

Morgan, Scott, and Snodin (2003) state that estimated variable costs are ₤70,000/year per turbine (includes O&M, overhead, and 

insurance) but do not define the size of the turbine. The turbine was assumed to have a rated capacity of 2 MW, based on the size 

of a typical offshore wind turbine available in 2003. Using Morgan and colleagues’ cost assumption (2003), O&M costs were 

assumed to be ₤35,000/yr/MW. With a 3% rate of escalation over 20 years of operation, total life-cycle O&M spending was 

approximately ₤556,000/MW.

The LCOE of offshore wind projects is highly sensitive to project-specific economic factors. To 

illustrate this, NREL developed a set of baseline assumptions for the current cost of energy and 

calculated the capital and operating costs for a hypothetical project using its cost and scaling 
118

model (Fingerish, Hand, and Laxson 2006). Researchers then calculated the LCOE of the project 

and its sensitivity to changes in the three key variables—capital costs, discount rates, and wind 

speeds. A financial model developed by Sam Baldwin of the DOE’s Office of Energy Efficiency 

and Renewable Energy was used to conduct the analysis (Baldwin 2010). Figure 6-7 illustrates 

how LCOE varies with wind speed and discount rate for two different capital cost scenarios; it 

also gives detailed explanations of the rationale for choosing capital cost and discount rate 

parameters in the figure’s footnotes.

Figure 6-7 shows estimates of LCOE for a project with a capital cost of $4,259/kW varying from 

$0.14/kWh with a low discount rate and high wind speed to $0.40/kWh with a high discount rate 

and low wind speed. The LCOE for a project with a capital cost of $3,194/kW (25% reduction 

from baseline) ranges from $0.11/kWh to $0.30/kWh. 

A reduction in the cost of capital from 16% to 8% for a project with a capital cost of $4,259/kW

and wind speed of 9 m/s will reduce LCOE from $0.23/kWh to $0.16/kWh ($0.07/kWh). For a 

project with the same characteristics but a 25% lower capital cost, LCOE is reduced from 

$0.23/kWh to $0.18/kWh ($0.05/kWh). This suggests that even with the higher capital costs 

expected to persist in the near future, offshore wind energy production costs could be reduced 

substantially if developers can obtain favorable financing terms for their projects.

Figure 6-7. LCOE sensitivity with respect to capital cost, discount rate, and wind speed

1 A capital cost of $4,259/kW is the baseline capital cost assumption. The value is the capacity-weighted average cost of all 

projects proposed for installation between 2010 and 2015 for which data are available (AWS Truewind 2010; Duke Energy 2010; 

Garden State Offshore Energy 2010; Blanco 2009; reNews 2009; Sokolic 2008; Williams 2008; Geoghegan 2007).

2 A capital cost of $3,194/kW is a 25% reduction in cost from the baseline capacity cost assumption of $4,259/kW. This value is 

tested to illustrate how capital cost improvements affect LCOE.

3 A 7% discount rate is commonly used by the U.S. Department of Energy (DOE) as reference for the comparison of renewable 

energy generation technologies. 4 The California Energy Commission (2003) uses a 16% discount rate as a standard assumption for merchant (nonutility) project

developers.

5 According to NREL conversations with private equity financiers, a 100% equity investment in renewable energy technologies 

with no operational history in the United States requires a return on equity between 25% and 35% (P. Schwabe, personal 

communication). A discount rate greater than 25% is likely to be cost-prohibitive. 
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To date, three U.S. offshore wind projects under development have signed power purchase 

agreements (PPAs) with utilities. Table 6-3 shows the prices and terms of these PPAs (National 

Grid 2010, 2009; Delmarva Power & Light 2008). The price of an individual PPA is very 

different from the cost of generation (LCOE) for an offshore wind project. Renewable energy 

projects receive subsidies from the federal government and include attributes such as renewable 

energy credits (RECs) and the value of capacity credits. These attributes produce additional 

revenue streams and allow project owners to sell output below the actual cost of generation. As 

an example, the PPA price for the Delaware Offshore Wind project is 9.99¢/kWh and depends 

on the assumption that the Delaware legislature would pass Senate Bill 328. This amendment 

increases the value of RECs generated by the wind project to 350% of the value of RECs from 

other renewable projects and allows Delmarva to pass the incurred costs of off-taking power 

from the project onto its entire ratepayer base. This measure was passed in June 2010 (Delaware 

State Senate 2010).

Table 6-3. Announced PPA Prices for U.S. Projects under Development

Project 

Name

Developer Power 

Purchaser

Capacity 

Contracted

(MW)

PPA 

Price

(¢/kWh)

PPA 

Base 

Year

Escalator 

(%)

Term

(years)

Cape Wind Cape 

Wind 

Associates 

National 

Grid

264 18.70 2013 3.5 15

Delaware 

Offshore 

Wind

NRG 

Bluewater

Wind

Delmarva 

Power & 

Light 

200 9.99 2007 2.5 25

Block Island 

Wind Farm 

Deepwater 

Wind

National 

Grid 

29 23.75 2007 3.5 20

The prices of these offshore wind PPAs range from 10¢/kWh to 24¢/kWh. It is important to be 

cautious when comparing the prices and terms of PPAs. These contracts are immensely 

complicated, and the purchase price depends on several factors other than the simple generating 

cost of the project, including differences in state policy, regulation, and the structure of the 

regional electric market. 

6.3 Projected U.S. Offshore Wind Deployment 

Today, offshore wind in the United States might be able to compete in coastal markets, assuming 

the availability of economic incentives. These could include a federal production energy tax 

credit, state renewable portfolio standards (RPSs), state-sponsored system benefits funds, high 

local energy prices, pollution-control incentives (e.g., a price on carbon emissions or stricter air 

quality controls), or certain state-sponsored incentives. This competitiveness is evidenced by the 

more than 2,000 MW of offshore wind projects currently proposed under varying economic 

schemes. It is not clear how many of these projects will actually be completed because they 

would need significant long-term cost reductions. Costs might be lowered, however, through the 
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initiation and success of a few early projects to first develop experience and intuition with the 

technical and regulatory issues. 

The key question examined in this section is whether offshore wind has the potential to make a 

significant, long-term impact in the energy mix. Part of the answer was given in Section 4, which 

showed ample wind resource near large load centers for offshore wind to become a major 

contributor. The critical question remaining is whether technology-driven cost reductions

combined with reasonable state and federal government incentives could create sufficiently 

favorable market conditions for offshore wind to be competitive with conventional generation. 

The answer will require a significant amount of analysis, along with some assumptions about 

current costs, engineering innovations, and future energy market trends. 

6.3.1 Regional Energy Deployment System

To conduct these analyses, NREL developed an economic computer model that examines the 

entire U.S. electric grid. The primary tool was the Wind Deployment Systems (WinDS) model 

(now called the ReEDS [Regional Energy Deployment System] model), developed by Short et 

al. (2003). ReEDS is a multiregional, multi-time-period, geographic information system (GIS) 

and linear-programming model of capacity expansion in the electric sector of the continental 

United States that can forecast out to 2050. ReEDS is designed to examine the principal market 

issues related to the penetration of wind energy technologies into the electric sector. These issues 

include access to and cost of transmission, along with the variability of wind power. As a linearoptimization model, ReEDS resembles the Electric Market Module of the National Energy 

Modeling System (NEMS) model maintained and developed by the Energy Information 

Administration (EIA). It varies significantly from NEMS as a whole—most obviously because it 

features greater geographic diversity and deals only with the electric generation sector (NREL 

2006).

Although the model does account for the cost of adding new transmission and the intermittency 

impacts at high penetration levels, it does not explore potential barriers related to transmission 

construction lead time or wind-farm permitting and site selection other than via typical resource 

exclusions. If the economics dictate, the model will build new electrical transmission links that 

become available at the time the capacity is needed. Also, it does not look beyond the 

geographical borders at Canada or Mexico to evaluate the effect of exporting or importing wind 

energy.

ReEDS models aggregate land-based and distributed wind technologies into one category 

because tools do not yet exist for handling distributed wind. It treats offshore wind separately, 

and specific cost models were developed to model these installations. Generally, the 

characteristics of the model’s offshore wind penetration predictions depend highly on system 

interactions with land-based wind energy as well as on interactions with other forms of electric 

energy conversion.

The model considers an average capital cost of installed wind, an average O&M cost, varying 

capacity factors for different wind-speed classes, estimated transmission-line availability, 

estimated cost of new transmission construction, and estimated future improvements in 

performance or reductions in cost, out to a target year of 2030. Finally, the model does not 

differentiate wind turbine size, even though offshore turbines are generally larger than landbased turbines and thus will have different economics.
121

6.3.2 Offshore Generation Capacity Expansion Modeling

The assessments made in this section are preliminary and are not a comprehensive study of the 

cost reduction potential for offshore wind. Instead, they attempt to build a reasonable case for 

offshore wind that demonstrates economic feasibility within a rational set of market assumptions. 

They also supply suitable justification to pursue offshore wind as part of a broader national 

energy agenda, which would include a more detailed study of the market potential.

Two assessments are presented here. The first is the study titled 20% Wind Energy by 2030: 

Increasing Wind Energy’s Contribution to U.S. Electricity Supply, which was conducted by the 

American Wind Energy Association (AWEA), DOE, NREL, and Black & Veatch. The 20% 

report, as it is commonly known, demonstrated a plausible scenario in which it is technically 

feasible to generate 20% of the nation’s electricity from wind energy by 2030, with a significant 

portion coming from offshore wind (DOE 2008).

The second assessment looks at specific input assumptions that correlate with high expansion 

rates of offshore wind energy generation (Short and Sullivan 2007).

6.3.3 Offshore Penetration for the 20% Wind by 2030 Scenario

The 20% wind study relied on the WinDS model (Short and Sullivan 2007) to simulate 

electricity generation capacity expansion through 2030. The wind energy contribution in each 

year was specified to approximate industry growth that expands rapidly in the next 8–10 years 

and reaches a relatively constant level of annual installations that could theoretically be 

maintained (including replacing retiring wind turbines) beyond 2030. Assumptions about the cost 

and performance of wind technology today through 2030 include capital cost reductions of 

12.5% for offshore wind technology (from $2,400/kW in 2006 U.S. dollars excluding 

construction financing, 10% for land-based wind technology from $1,650/kW in 2006 U.S. 

dollars excluding construction financing) and an average of 15% improvement in performance 

over all wind classes for both land-based and offshore wind technology. Conventional generation 

technology cost and performance projections were also assumed (Short and Sullivan 2007). 

These costs are low according to today’s market data but were accurate at the time the study was 

conducted. The marked increase in offshore wind costs in 2006 (see Figure 6-1) demonstrates the 

dynamic market for offshore wind and for wind power in general. Indeed, these upward cost 

trends are indicative of the entire energy marketplace. 

The study estimated regional variations in the cost of generation technology and new 

transmission lines. Wind technology capital costs were increased as a function of population 

density, with an additional 20% of the capital cost added for plants sited in the Northeast. These 

cost variations reflect the regional costs of actual wind projects installed in 2006 (Wiser and 

Bolinger 2006). Variations in regional transmission cost, developed by an AWEA expert panel, 

include an additional 40% in New England and New York; 30% in PJM East (New Jersey and 

Delaware); 20% in PJM West (Maryland, West Virginia, Pennsylvania, Ohio, part of Illinois, 

Indiana, and Virginia); and 20% in California. These regional costs were intended to reflect real 

effects resulting from population and the experience of public resistance to siting generation 

technology or transmission lines.

The scenario defined in the 20% report requires more than 300 GW of wind generation capacity 

by 2030 to produce more than 1,200 TWh/yr, which is 20% of the projected U.S. electricity 

demand (DOE 2008; Figure 6-8).
122

Figure 6-8. Cumulative wind generation capacity associated with 20% wind by 2030

Of this capacity, 54 GW, or 18%, would be from offshore wind resources, primarily off the coast 

of the states in the Northeast. In the latter years of the 20% wind scenario, though, offshore 

technology is installed off West Coast states and southeastern states. Because the energy 

generation from wind technology is prescribed in each simulation period to create this scenario, 

the cost-optimization features of the WinDS model have the land-based wind technology 

competing against the offshore wind technology to meet the specified target for annual energy 

generation.

Much of this analysis depends on significant declines in offshore wind capital costs, which have 

not been demonstrated through rigorous study of the elements of a typical project because of the 

relative infancy of offshore installations. Nevertheless, significant cost declines are plausible

based on the historical behavior of other new industries, including land-based wind. New 

industries typically show significant cost decreases simply by increased production volume (i.e., 

learning curve effects) and technology improvements (Short and Sullivan 2007). Using the 

learning curve theory, offshore capital costs can expect greater reductions in the future than the 

costs of more mature land-based wind energy systems, which have realized an 11% cost decline 

per doubling of installed capacity over the past three decades (Wiser and Bolinger 2009).

Although learning curve effects may be more conservative because some maturation has been 

passed over from land-based wind, the effect could be very important in stimulating cost 

reductions in offshore wind, especially if European markets meet their targets of 150 GW by 

2030.
123

6.3.4 Restricted Coastal Grid and High Gas Pricing

To assess the potential penetration of offshore wind in the United States, the WinDS model was 

run outside the 20% wind scenario under different technology development, cost, and policy 

scenarios (Short and Sullivan 2007). The method was to define a business-as-usual case, which is 

considered conservative with respect to the market conditions that may stimulate wind energy 

growth, and then adjust the scenario via three parameters:

1. Allow the fuel price of natural gas to rise 3% annually.

2. Restrict technologies that can be built to meet electric demand along highly populated coastal 

areas of the country.

3. Set a national requirement that 20% of generation must come from renewable sources by 

2030.

The WinDS model was run for eight scenarios (created by combinations of these three 

conditions) to determine the effect of each condition, or set of conditions, on the penetration of 

offshore wind. Because this analysis was performed in 2007, the scenario definitions and 

assumptions may not reflect recent changes in the energy market, which could be significant. 

Clearly, further analysis is needed. It also does not consider the large amount of land-based 

capacity installed in recent years (~18,000 MW installed in 2008 and 2009, bringing the total to 

~35,000 MW). The trends identified in this assessment are, however, expected to remain 

relevant—under the right policy and market conditions offshore, wind has the potential to 

generate a significant portion of our nation’s electricity. 

The business-as-usual case for this offshore comparison uses fuel prices and load forecasts from 

the reference case of the EIA’s Annual Energy Outlook 2006 (DOE and EIA 2006).

Conventional generation technology costs and wind data inputs came from the 20% wind 

scenario. Other parameters are input according to current conditions: no national RPS, but state 

RPSs are enforced if currently enacted (as of August 2005); the sulfur dioxide (SO2) cap follows 

current regulations; and no carbon cap or tax is applied. Corporate financing and the consequent 

debt-service coverage requirements are accounted for explicitly, as are federal tax credits and 

income tax deductions. An inflation-adjusted production tax credit of $18.50/MWh for wind 

power is assumed to expire in 2008 (DOE and EIA 2006).

In the business-as-usual scenario, WinDS projects that by 2030, wind will deliver 74 GW of 

electric capacity to the grid, with only 0.07 GW coming from offshore wind—and all of it in 

shallow water off the coasts of California and Massachusetts. Because the scenario does not 

penalize or restrict carbon or fossil fuels, the build-out of wind power is in large part attributable 

to the ability of land-based wind power to cost-effectively meet state RPS requirements as well 

as the increasing economic competitiveness of wind farms with conventional power plants. 

Natural gas costs do increase slightly with time (Annual Energy Outlook 2006 projections, 

shown as a solid line in Figure 6-9), and SO2 emissions caps restrict using older coal 

technologies. Offshore wind, as evidenced by the lack of installed capacity, simply remains too 

expensive to compete.

In the first scenario, natural gas prices are allowed to increase at a flat rate of 3% per year after 

2010 (shown as a dashed line in Figure 6-9).
124

Source: DOE-EIA (Annual Energy Outlook) 2006.

Figure 6-9. Comparison of U.S. average natural gas price increase from Annual Energy Outlook 

2006 with 3% annual increase

This increases the relative cost of all natural gas technologies compared to alternative options 

such as coal, wind, or nuclear (no carbon emission penalties). This increased gas price trajectory 

does not, however, have a large near-term effect. The present value of gas costs over a 20-year 

analysis period for a gas plant investment does not exceed that of a plant built in 2006 until after 

2020. All other parameters remain consistent with the base case in this scenario.

As expected, with higher natural gas prices the installed capacity of both combined-cycle and 

combustion-turbine natural gas technologies decreases markedly. The bulk of the lost capacity is 

replaced by new coal plants (almost all modern plants use pulverized coal; integrated gasification 

combined-cycle plants are still not built in significant numbers), although over the last few time 

periods in the model, some nuclear plants are built as coal-plant construction lags. Wind 

experiences modest increases to 114 GW total capacity, with 5 GW coming from shallow-water 

offshore plants. In this scenario, the bulk of the offshore capacity is shared between New York 

and Massachusetts, with Maine, New Jersey, Rhode Island, and California claiming the rest.

In the second scenario, a constraint is placed on the technologies that can be built in populated 

coastal regions to meet the regions’ load growth. The new restriction requires that all new 

demand in heavily populated coastal regions be met either by combined-cycle gas power plants 

or by offshore wind farms, and that there can be no new transmission into the designated regions. 

The rationale for this constraint is that congestion in these regions makes new major transmission 

capacity prohibitively expensive and that the populace would resist new construction of dirtier 

generation technologies (e.g., coal or nuclear facilities).
125

The selected regions include the entire Pacific Coast and the northern Atlantic Coast. The 

southern Atlantic Coast and the Gulf of Mexico are unrestricted, except for Houston. Similarly, 

only Chicago is restricted around the Great Lakes. Arguments could be made to include some 

Great Lakes or southern coastal cities, such as Milwaukee, Cleveland, Detroit, Savannah, or 

Miami, or to leave out some of the more sparsely populated Pacific Coast regions. The decisions 

were not made by any specific metric, but instead by a first-pass estimation of where population 

density was sufficiently high over a large portion of the WinDS region. Also taken into account 

were nonscientific considerations for the environmental tolerance of the region’s inhabitants, the 

quantity and quality of the available wind resource, and current regional electric prices.

Siting-restricted scenarios were run with both regular and high natural gas prices so that the two 

conditions could be cross compared. Figure 6-10 compares the 2030 capacity for selected 

technologies among the four scenarios. In the scenario with both high gas prices and the siting 

restriction in place, offshore wind exhibits a sharp increase over the other three scenarios. In this 

scenario, offshore wind needs to compete only with combined-cycle gas—when gas prices get 

too high, offshore wind becomes the more economical of the two. In this case, 78 GW of 

offshore wind is built in exactly the regions where the coastal restrictions, shown in Figure 6-11, 

were imposed. If the siting-restricted scenario were extended over the high-population regions of 

the Great Lakes region and Gulf of Mexico, the amount of offshore wind nationally would most 

likely increase. Future studies should be done to show these effects.

Figure 6-10. 2030 capacity in a gas price and siting restriction comparison
126

Figure 6-11. 2030 offshore wind capacity under a high gas price, siting-restricted scenario

The third parameter is the institution of a 20% national RPS for wind, which would require at 

least 20% of U.S. electrical load to be met by wind power by 2030. The requirement ramps 

linearly from zero in 2007 to 20% in 2030. The four previous scenarios (high and regular gas 

prices, with and without the coastal restriction) are evaluated again, but this time with the 20% 

RPS.
127

In all the RPS scenarios, WinDS predicts much more wind capacity than before—both land 

based and offshore. In all the RPS cases, more offshore wind is installed than in the non-RPS 

cases simply because some offshore sites are more cost-effective than the remaining land-based

wind options at these high levels of penetration. For example, with regular gas prices and 

without the siting restriction, 32 GW of offshore wind is built by 2030, which is a significant 

amount—especially when compared to the 0.07 GW constructed in the RPS-free counterpart. On 

the other hand, the difference between the two cases with and without the 20% RPS (with high 

gas prices and siting restrictions) increases only from 78 to 89 GW, which is a much less 

substantial difference.

6.4 Findings and Conclusions

Capital costs for offshore wind plants are analyzed using data from European deployments and 

projected costs for potential U.S. projects. The costs have been trending up over time, as have the 

costs for land-based installations. Although water depth is expected to have a significant effect 

on capital cost, and larger wind plant sizes should lead to lower overall capital costs, these 

effects have been overshadowed in the data by recent jumps in the cost of energy from all 

sources and other energy market dynamics. The wind turbine itself contributes approximately 

44% of the total capital cost. Capital cost trends are presented for year of installation, water 

depth, distance from shore, and project size. Year of installation is the most significant variable 

in the capital cost, with a sharp rise in price (56%) indicated between 2006 and 2008. Other 

trends such as decreasing cost with project size may show some correlation, but consistent data 

are not yet available to quantify this trend. 

The LCOE of offshore wind plants is about double that of comparable land-based plants using 

2009 market prices. This increase in the cost of energy can be attributed to higher O&M costs as 

well as the previously described higher capital costs. O&M costs can account for as much as 

30% of the total life-cycle cost for an offshore wind plant. Three offshore wind projects in the 

United States have now signed PPAs (see Table 6-3). The reader is cautioned about making 

direct comparisons between these PPAs because the terms are complicated and several factors 

may not be obvious under a casual analysis. 

The two studies using WinDS (ReEDS) give solid evidence that offshore wind could supply a 

substantial and economically viable electric energy source in the future, although a 

comprehensive assessment has not yet been completed. The 20% report showed that offshore 

wind could contribute 54 GW, or 18%, of the nation’s total wind energy (DOE 2008). Short and 

Sullivan (2007) supported this magnitude of offshore wind growth, with up to 89 GW coming 

from offshore wind. Recent economic and political developments increase the likelihood that the 

“transmission-constrained” scenario may evolve as a baseline case in the eastern United States, 

leading to large deployments of offshore wind.

These scenarios testify that offshore wind could be used to meet new loads in locations where 

siting restrictions on new land-based power plants and transmission are severe, such as coastal 

metropolitan areas. In these locations, offshore wind could be competitive with combined-cycle 

natural gas plants if gas prices increase significantly from EIA projections. If a 20% RPS is 

implemented, some offshore wind will be built simply because it is more cost-effective than the 

remaining land-based resource at these high levels of penetration. 
128

Several other scenarios that might affect the deployment of offshore wind installations have yet 

to be investigated. Primary among these would be a climate change policy scenario with either 

carbon taxes or caps. NREL is modifying the ReEDS model to be able to address such scenarios. 

In addition, NREL is planning and making general improvements to the ReEDS model that will 

allow it to better capture the potential of offshore wind. These improvements are expected to 

include an updated regional structure, an improved representation of transmission, siting 

considerations for fossil-fired power plants, and recent state restrictions on the siting of both new 

generating plants and transmission.

6.5 References 

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Commissioned.” Press release. http://www.alpha-ventus.de/index.php?id=80. Accessed 

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AWS Truewind. (January 2010). NY’s Offshore Wind Energy Development Potential in the 

Great Lakes. New York State Energy Research and Development Authority. 

http://www.nyserda.org/publications/10-04_offshore_wind.pdf. Accessed August 15, 

2010. 

Baldwin, S. LCOE Calculator Spreadsheet. DOE Office of Energy Efficiency and Renewable 

Energy. February 1, 2010

Blanco, M. (2009). “The Economics of Wind Energy.” Renewable and Sustainable Energy 

Reviews (13); pp. 1372–1382.

California Energy Commission. June 2003. Comparative Cost of California Central Station 

Electricity Generation Technologies. Document 100-03-001F. 

http://www.energy.ca.gov/reports/2003-06-06_100-03-001F.PDF. Accessed February 26, 

2010.

Carbon Trust. (October 14, 2008). Offshore Wind Power: Big Challenge, Big Opportunity.

CTC743.

http://www.carbontrust.co.uk/Publications/pages/publicationssearch.aspx?q=offshore+wi

nd+power&pn=0&ps=10. Accessed August 4, 2010.

Delaware State Senate. Senate Bill No. 328 An Act to Amend Title 26 of the Delaware Code 

Relating to Offshore Wind Power Installations. General Assembly of the State of 

Delaware. Enacted June 2010. Accessed August 17 2010 

http://legis.delaware.gov/LIS/lis144.nsf/vwLegislation/SB+328/$file/legis.html?open

Delmarva Power & Light. (June 23, 2008). Power Purchase Agreement with Bluewater Wind 

Delaware. http://www.delmarva.com/_res/documents/FinalexecutedDPLBWWPPA.pdf. 

Accessed June 30, 2010.

DOE (U.S. Department of Energy). (July 2008). 20% Wind Energy by 2030: Increasing Wind 

Energy’s Contribution to U.S. Electricity Supply. DOE/GO-102008-2567. Golden, CO: 
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National Renewable Energy Laboratory (NREL).

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DOE; EIA (Energy Information Administration). (February 2006). Annual Energy Outlook 2006 

with Projections to 2030. DOE/EIA-0383. Washington, DC: DOE, EIA.

Duke Energy. (2010). “Wind Energy.” Duke Energy Corporation. http:/www.dukeenergy.com/environment/wind.asp. Accessed April 23, 2010.

DUWind (Delft University Wind Energy Research Institute). (2001). Offshore Wind Energy: 

Ready to Power a Sustainable Europe, Final Report. DUWind 2001.006. Delft, 

Netherlands: DUWind. http://www.emu-consult.dk/includes/totalfinalreport.pdf. 

Accessed September 8, 2010.

EIA. 2006. Annual Energy Outlook 2006 with Projections to 2030. DOE/EIA-0383(2006). 

Washington, DC: EIA. 

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September 6, 2010.

Ernst & Young. (2009). Cost of and Support for Offshore Wind. URN 09D/534. London: 

Department of Energy and Climate Change.

EWEA (European Wind Energy Association). (January 2010). The European Offshore Wind 

Industry Key Trends and Statistic 2009. Brussels: EWEA. 

EWEA. (2009). The Economics of Wind Energy. Brussels: EWEA.

Fichaux, N.; Wilkes, J. (2009). Oceans of Opportunity, Harnessing Europe’s Largest Domestic 

Energy Source. Brussels: EWEA.

Fingerish, L.; Hand, M.; Laxson, A. (2006.) Wind Turbine Design Cost and Scaling Model.

NREL TP-500-40566. Golden, CO: NREL.

Garden State Offshore Energy. (2010). Fact sheet. 

http://www.gardenstatewind.com/pdf/factsheet.pdf. Accessed January 28, 2010.

Geoghegan, J. (February 2007). “Inherit the Wind.” Wired Magazine. 

http://www.wired.com/wired/archive/15.02/wind.html. Accessed January 26, 2010.

GWEC (Global Wind Energy Council). (2010). The Policy Environment for Wind Power in 

Germany. Web site. http://www.gwec.net/index.php?id=129. Accessed August 20, 2010.

Junginger, M.; Faaij, A. (2004). “Cost Reduction Prospects for the Offshore Wind Energy 

Sector.” Wind Engineering (28); pp. 97–118.
130

Krohn, S.; Morthorst, P.E.; Awerbuch, S. (2009). The Economics of Wind Energy. Brussels: 

EWEA.

Ministry of Foreign Affairs of Denmark. (July 13, 2009). “DONG Energy Soon to Inaugurate 

Horns Rev 2 Offshore Wind Farm.”

http://www.investindk.com/visNyhed.asp?artikelID=22253. Accessed January 26, 2010.

Morgan, C.; Scott, N.C.; Snodin, H.M. (2003). Economies of Scale, Engineering Resource and 

Load Factors. Doc # 3914/BR/01. London: UK Department of Trade and 

Industry/Carbon Trust.

National Grid. (May 10, 2010). Power Purchase Agreement between National Grid and Cape 

Wind Associates, LLC. http://www.env.state.ma.us/dpu/docs/electric/10-

54/51010ngcwnd.pdf. Accessed June 30, 2010.

National Grid. (December 2009). Power Purchase Agreement with Deepwater Wind

3. 

National Wind Watch. (December 3, 2009). “A Giant Wind Farm Is Planned off the North Wales 

Coast.” http://www.wind-watch.org/news/2009/12/03/a-giant-wind-farm-is-planned-offthe-north-wales-coast/. Accessed January 26, 2010.

NREL. (March 2006). Projected Benefits of Federal Energy Efficiency and Renewable Energy 

Programs FY 2007 Budget Request. NREL/TP-620-39684. Golden, CO: NREL.

http://www.nrel.gov/docs/fy06osti/39684.pdf. Accessed September 6, 2010.

Offshore Wind Energy. (2010a). Middelgrunden Windfarm. http://www.offshorewindenergy.org. 

Accessed January 26, 2010.

Offshore Wind Energy. (2010b). Yttre Stengrund Windfarm. 

http://www.offshorewindenergy.org. Accessed January 26, 2010.

Offshore Wind Energy. (2010c). Samsø Windfarm. http://www.offshorewindenergy.org. 

Accessed January 26, 2010.

Offshore Wind Energy. (2010d). Horns Rev Windfarm. http://www.offshorewindenergy.org. 

Accessed January 26, 2010.

Offshore Wind Energy. (2010e). Scroby Sands Windfarm. http://www.offshorewindenergy.org. 

Accessed January 26, 2010.

Offshore Wind Energy. (2010f). Ronland Windfarm. http://www.offshorewindenergy.org. 

Accessed January 26, 2010.

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Accessed January 26, 2010.
131

Offshore Wind Energy. (2010h). Barrow-in-Furness Windfarm. 

http://www.offshorewindenergy.org. Accessed January 26, 2010.

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Accessed January 26, 2010.

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http://www.power-technology.com/projects/lynnandinnerdowsing/ Accessed January 26, 

2010.

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“Assessment and Optimisation of Operation and Maintenance of Offshore Wind 

Turbines.” ECN Wind Energy, Delft University of Technology.

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reNews. (November 19, 2009). Offshore Special Report 2009. http://www.renews.biz/ (by 

subscription only). Accessed August 15, 2010.

RWE npower renewables. (2010). North Hoyle Offshore Windfarm Site Statistics. 

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Penetration of Wind in the United States. NREL/CP-620-34469. Golden, CO: NREL.

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Wind Energy.” Renewable Energy (34); pp. 1567–1578.

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Performance Trends: 2006. DOE/GO-102007-2433. Washington, DC: DOE.
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7.0 Federal and State Regulatory Pathways for Siting and 

Permitting Offshore Wind Facilities

7.1 Introduction

The United States is still establishing the regulatory pathways for offshore wind. Although the 

country has a long history of managing energy-related industries such as oil and gas on federal 

lands and in federal waters, no such institutional knowledge exists regarding offshore alternative 

energy facilities. Wind turbine technology and electric power distribution offshore have siting 

characteristics that significantly differ from the more mature extractive industries. Moreover, 

offshore wind power is a relatively new energy industry, with about a 20-year demonstration 

history in European seas and less than a 10-year operational history for utility-scale projects in 

Danish waters. Because of the absence of wind energy land management agency experience in 

the United States and the nascent state of the offshore wind industry, the regulatory and 

institutional pathways for offshore wind energy are just now emerging. The learning curve faced 

by the federal and state agencies when balancing the risks and benefits of using energy generated 

from offshore wind farms has been steep. Consideration of the myriad competing and 

complementary ocean uses has been complex and still lacks cohesion across many U.S. coastal 

regions. Accordingly, federal regulatory and technology development agencies working are 

working together to develop a regulatory pathway with due regard for scientifically credible data 

needs and standards of environmental quality that have been established historically under 

National Environmental Policy Act (NEPA) and other federal laws. 

This section is an overview of the regulatory pathway for offshore wind development in federal 

waters with respect to ocean policies and jurisdictions, regulatory roles of federal agencies, and 

compliance with key regulatory legislation such as NEPA. This section also describes the 

changing codes, standards, and certification processes for the regulation of the offshore wind 

industry.

7.2 Ocean Policies and Jurisdictions

Rights, restrictions, and responsibilities in the marine environment are contingent on designated 

ocean jurisdictions and administrative boundaries (MMS 2010a) as well as on multiple and 

overlapping use rights. This complex regulatory environment determines whether a state or 

federal agency is the lead for the approval process. Section 7.2.1 below outlines the laws 

regulating ocean jurisdictions and Section 7.2.2 discusses the emerging ocean policy of coastal 

and marine spatial planning. This policy could further define ocean space boundaries, but is 

currently in its infancy.

7.2.1 Jurisdiction

The federal government retains the power to regulate commerce, navigation, power generation, 

national defense, and international affairs throughout state waters. States, however, are given the 

authority to manage, develop, and lease resources throughout the water column and on and under 

the seafloor (MMS 2006). As explained in Figure 7-1, for most states, jurisdiction extends to 3 
134

nm from the shoreline, in accordance with the Submerged Lands Act (2002), and federal 

jurisdiction extends the breadth of the territorial sea (out to 12 nm) and then out to at least 200 

nm on the Outer Continental Shelf (OCS) or to the outer edge of the continental margin. The 

jurisdictions of the Great Lakes, on the other hand, fall under state agencies until they meet the 

international borders with Canadian provinces. Bays and sounds are likewise under state 

jurisdiction (see Section 7.5 for more details).
135

Source: Energetics, adapted from U.S. Commission on Ocean Policy 2003.

Figure 7-1. Schematic of state, federal, and international ocean jurisdictions
136

The Outer Continental Shelf Lands Act (OCSLA) was enacted in 1953 to manage federal 

offshore areas for the exploration of mineral resources. The OCS refers to submerged lands lying 

seaward and outside of the area of lands beneath navigable waters of each of the respective states 

subject to federal jurisdiction and control (MMS 2010a). Over the past 20 years, U.S. presidents 

have issued a series of proclamations changing the extent and nature of U.S. authority over the 

oceans and reflecting aspects of the United Nations Convention on the Law of the Sea (LOS 

Convention; 2010). The LOS Convention, in effect since 1994, has been ratified by 158 nations 

as of December 2009. Absent the determination by the Continental Shelf Commission that the 

U.S. Continental Shelf extends beyond 200 nm, rights beyond 200 nm are governed by 

international law and regulatory bodies. Although a signatory of LOS, the United States has not 

ratified the treaty because of several objections to specific provisions. The United States 

generally accepts, however, most provisions of the LOS Convention as binding under customary 

international law. Given current and foreseeable technology options for powering offshore wind 

generation plants, currently planned and future projects will most likely be located within the 

200-nm (370-km) exclusive economic zone (EEZ) boundaries. 

Changes to U.S. maritime law have created a territorial sea to 12 nm (22 km), a contiguous zone 

to 24 nm (44 km), and an EEZ (between 12 and 200 nm or 370 km), although they have not been 

comprehensively reflected in domestic laws. Many laws also use imprecise or inconsistent terms 

to refer to ocean areas, such as “navigable waters,” “coastal waters,” “ocean waters,” “territory 

and waters,” “waters of the United States,” and “waters subject to the jurisdiction of the United 

States.” These terms can mean different things in different statutes and are sometimes not 

defined at all. Figure 7-1 depicts the maritime “zones” based on domestic and international laws. 

The important boundaries regarding offshore wind energy projects relate to the baseline, state 

waters, and the OCS. Ownership of the seabed resource raises political and socioeconomic issues 

relating to who is paying for and who is receiving project royalties and profits (Firestone et al. 

2004). 

7.2.2 Ocean Policies

Our oceans, coasts, and Great Lakes are already heavily industrialized and used for tourism,

commercial and recreational fishing, and aquaculture as well as extraction of nonrenewable 

resources. Coastal ecosystems are critical habitat for migratory birds and mammals as well as 

fish species. Despite the critical importance of these areas, wide range of stresses and competing 

demands threaten these resources and communities (see Section 8). The challenges lie not only 

in ecosystems management but also in the hundreds of policies, laws, authorities, and 

governance structures intended to manage our use and conservation of ecosystems (White House 

Council on Environmental Quality [CEQ] 2010a). 

Various administrations have attempted to streamline and strengthen ocean policies and 

governance—the most recent initiative was on June 12, 2009, when President Obama issued a 

memorandum establishing an Interagency Ocean Policy Task Force, led by the CEQ. Two major 

interim policy reports have suggested a national ocean policy to strengthen stewardship, a 

framework for better coordination, and an implementation strategy (CEQ, 2009a, CEQ 

2009b).The second report, Interim Framework for Effective Coastal and Marine Spatial 

Planning, offers a comprehensive, ecosystem-based approach to planning and managing uses 

and activities offshore that addresses conservation, economic activity, conflicts of interest, and 

sustainable use (CEQ 2009c). About a year later, President Obama signed an Executive Order 

establishing a National Policy for the Stewardship of the Ocean, Coasts, and Great Lakes, 
137

adopting the Final Recommendations of the Interagency Ocean Policy Task Force, and creating

a National Ocean Council to strengthen ocean governance and coordination across the federal 

government (The White House 2010).

Because offshore wind farms will potentially compete with or complement existing uses of state 

and federal waters, interagency coordination could assist a region in more efficient siting of 

offshore wind. Because potential risks of wind projects are very site specific, marine spatial 

planning should be assessed in concert with stakeholder engagement to anticipate potential 

conflicts and compatibilities in the marine environment. It is important to note that state 

governments are also moving toward marine spatial planning and “zoning” developments within 

state waters (see sections 3 and 7.5 for details on the state permitting and planning process).

The CEQ initiatives will most likely affect the siting and management of the offshore renewable 

energy projects along our coasts and in the Great Lakes as the guiding principles for coastal and 

marine spatial planning (CMSP) get tested and developed. CMSP can be defined several ways: 

according to the United Nations Educational, Scientific, and Cultural Organization (UNESCO), 

marine spatial planning is a public process of analyzing and allocating the spatial and temporal 

distribution of human activities in marine areas to achieve ecological, economic, and social 

objectives that usually have been specified through a political process (UNESCO 2010).

The two guiding principles outlined by CEQ include:

• Ecosystem-based management (which integrates ecological, social, economic , commerce, 

health, and security goals and recognizes both that humans are key components of 

ecosystems and that ecosystems are essential to human welfare). 

• Adaptive management (which calls for routine reassessment of management actions to better 

inform and improve future decisions).

Both principles are central to sustainable renewable energy deployments on the OCS, and some 

states are moving in this direction (see Section 7.5). CMSP could support siting of offshore wind 

deployments by instituting both science-based and robust stakeholder processes for selecting and 

vetting candidate sites or zones for developments. 

The CEQ process involved holding 38 expert roundtable meetings, including one on renewable 

energy in September 2009 (CEQ 2010a). Some of the concerns of the offshore wind energy 

interests focused on whether a perceived cumbersome federal process would slow down the 

urgent need to deploy clean energy supplies. The reality is that CMSP is a cumbersome and often 

lengthy process because of the variety of stakeholders, “users,” and agencies involved in 

management. Under the framework proposed, CMSP would be regional in scope and would be 

developed cooperatively among federal, state, tribal, and local authorities with stakeholder input.

It is still uncertain how these frameworks would affect the deployment of offshore renewable 

energy, but CMSP is an essential building block of sustainable offshore wind energy 

deployments. There is clear evidence for this approach as several states have instituted marine 

spatial planning along their coasts (see Section 3 for more details).

Another aspect of CMSP is to support data collection that is based on science and relies on a risk 

framework so decision makers can identify deployment sites that are more compatible with 

habitats, species, and human activities as well as those that would present conflicts (see Section 8 

for risk framework). Per the Energy Policy Act of 2005 (EPAct 2005) direction, the National 

Oceanic and Atmospheric Administration (NOAA) and the Bureau of Ocean Energy 
138

Management, Regulation, and Enforcement (BOEM; formerly the Minerals Management Service 

([MMS]; see Section 7.3.1) are working on developing marine spatial planning tools and 

collecting data that will populate a Multipurpose Marine Cadastre, a mapping and permitting tool 

that identifies applicable jurisdictional boundaries, restricted areas, laws, critical habitat 

locations, and other important features (Digital Coast 2010, MMS 2006).

7.3 Current Regulatory Situation

On August 8, 2005, President Bush signed EPAct 2005 into law (PL 109-58) (42 USC 15801), 

granting the then-MMS new responsibilities over renewable energy and alternate uses of 

offshore federal lands. There are regulatory parallels between the compliance mechanisms and 

NEPA documentation already in place for the offshore oil and gas industry and the new 

requirements for a renewable energy program. 

7.3.1 MMS Regulatory Paradigm 

As stated in the Federal Register announcing the new regulatory program, “Section 388 of the 

Energy Policy Act of 2005 (EPAct) amended the OCSLA to grant the Secretary of the U.S. 

Department of the Interior (Secretary) the discretionary authority to issue leases, easements, or 

rights of way for activities on the OCS that produce or support production, transportation, or 

transmission of energy from sources other than oil and gas” (MMS 2008a). This authority covers 

renewable energy developments, including, but not limited to, commercial-scale and 

demonstration wind, wave, current, and solar power pilot projects. The authority does not 

supersede or modify existing authority of any other federal agency (Burton 2002). In July 2010, 

the MMS was reorganized under a new name; the Bureau of Ocean Energy Management, 

Regulation, and Enforcement (BOEM). The bureau will remain in the U.S. Department of the 

Interior (DOI) and will retain responsibility for managing the nation's natural gas, oil and other 

mineral resources on the OCS, including offshore wind. The BOEM was developed with greater 

provisions for oversight of managing the resources, collecting revenues, and guarding the public 

safety. 

Congress directed the Secretary of the Interior through EPAct 2005 to establish a regulatory 

paradigm for siting and managing offshore wind facilities within 270 days and made specific 

requirements for inclusion in the regulations. Key provisions mandated that the Secretary:

• Act as the lead agency for permitting offshore renewable energy projects

• Grant easements, leases, or rights-of-way for uses of the OCS on a competitive basis (unless 

it is determined that there is no competitive interest) 

• Ensure consultation with affected states and other stakeholders

• Coordinate with relevant federal agencies

• Ensure safety and environmental protection

• Prevent interference with other reasonable uses of the sea and seabed

• Protect national security interests

• Perform oversight, inspection, research, monitoring, and enforcement
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• Require financial surety to ensure that facilities constructed are properly removed at the end 

of their economic life (decommissioning) 

• Ensure a fair return to the nation. 

MMS finalized the regulatory rules when they were announced by President Obama on Earth 

Day in April 2009 and published in the Federal Register on April 29, 2009. The rules went into 

effect on June 29, 2009, and detailed guidelines were issued on August 3, 2009. Figure 7-2 charts 

significant milestones in the rule development process, including public hearings to support the 

rulemaking, publication of a Programmatic Environmental Impact Statement (PEIS; see Section 

7.4.1), and the issuance of an interim policy allowing the installation of met towers at a limited 

number of sites (see Section 7.3.2.2).

Source: MMS 2009a, 2009b, 2009c 2009d, , 2008b, 2007a. 

Figure 7-2. MMS timeline of rule development activities 
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The framework establishes a “cradle to grave” approach to regulate offshore renewable energy 

activity from the prelease stage through leasing, site assessment, construction and operations, 

and decommissioning. Key elements support safety, environmental protection, state and local 

coordination with affected agencies, financial assurance, fair return for use of submerged public 

lands, and equitable revenue sharing with the states (Cushing 2009; Bornholdt 2009). Table 7-1

outlines the major provisions in the program.

Table 7-1. Major Provisions in the Final Renewable Energy Framework

Major Sections of the Rule

General provisions and 

definitions

Subpart in Rule

(Subpart A)

Leasing process and issuance 

• Commercial and limited

• Competitive and 

Noncompetitive

• Research activities

(Subpart B)

Rights-of-way grants and rightsof-use and easement grants for 

renewable energy activities 

(Subpart C)

Lease and grant administration (Subpart D)

Payments and revenue sharing (Subpart E)

Plans

• Site assessment and 

construction and operations

• General activities

(Subpart F)

Facility design, fabrication, and 

installation 

(Subpart G)

Conduct of approved plan 

activities; environmental and 

safety monitoring and 

inspections

(Subpart H)

Source: MMS 2009b, 2009f.

Before EPAct 2005, no regulatory mechanism for authorization of offshore renewable energy 

activity existed except through Section 10 of the Rivers and Harbors Act, which is administered 

by the U.S. Army Corps of Engineers (USACE) and covers construction activities in navigable 

waters (the USACE is still the lead federal agency for the Great Lakes region; see Section 7.5.1 

for more details). Wind developers of two proposed projects, Cape Wind and Long Island 

Offshore Wind Park (the Long Island proposal was ultimately put on indefinite hold), had 

applications that were proceeding under the Rivers and Harbors Act when EPAct 2005 was 

enacted. These two initiatives were given special status by Section 388(d) of EPAct 2005 and 

were exempted from the site competition requirements. During the lengthy rulemaking process 

under EPAct 2005, MMS recognized that potential offshore wind developers needed to pursue 

site characterization and technology testing activities to support future leasing and development. 

In November 2007, MMS announced an interim policy authorizing such activities on the OCS 

under limited leases (see Section 7.3.2.2 on the interim policy) (MMS 2008b). A centerpiece of 
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the new MMS regulations was the establishment of a leasing process for prospective developers.

The next section outlines the provisions of the leasing process, including the competitive and 

noncompetitive options as outlined in the Final Rule (MMS 2009b).

7.3.2 Leasing Process

In developing a regulatory paradigm for the issuance of renewable energy leases, easements, and 

rights of way on the OCS, MMS had to consider how to ensure a fair return to the public for use 

of the sea and seabed while not putting an undue financial burden on new renewable energy 

companies. As noted in Subpart E of the rule, the regulatory framework prescribes a base rent of 

$3.00 per acre for leases and $5.00 per acre and $70 per statute mile for easements (right of use 

and easement) and right-of-way grants (see Subpart C). Leases that generate electricity also are 

subject to an annual operating fee based on a formula that includes nameplate capacity, hours per 

year, capacity factor, power price, and a fee rate. Limited leases pay the rental fee only because

they may authorize only de minimus generation of energy for commercial sale (see Section 

7.3.2.2.). In addition to these lease payments, a revenue-sharing provision through Section 388 

amended OSCLA 8 (p. 2). Coastal states are entitled to 27% of the revenue from offshore leases 

in federal waters within 3 miles of the state's seaward jurisdictional boundary. These revenues 

can start with bids for a competitive lease or acquisition fees for a noncompetitive lease. Where 

multiple states are involved, the revenues are calculated assuming states are within 15 nm (28 

km) of the geographic center of a project (for more details, see Subpart E of the MMS rule).

As explained in Subpart B, the framework establishes two leasing options—a commercial or a 

limited lease:

• A commercial lease allows full-scale project development and sale of power to the grid for 

30 years.

• A limited lease allows resource assessment and technology testing for 5 years. 

According to Snyder and Kaiser (2009), such a lease term is consistent with European policies 

that aim to limit speculation but allow enough time for fluctuations in the economic climate. 

The first OCS renewable energy leases issued by MMS came under the interim policy. Five 

limited leases for authorizing construction of meteorological towers or buoys were offered in 

June 2009, and four were executed and went into effect in November 2009. The first commercial 

wind lease was offered to Cape Wind Associates in July 2010, and the first commercial wind 

leasing process under the regulatory framework was initiated with the issuance of a Request for 

Interest for an area off Delaware in April 2010 (MMS 2008b, 2007a, and 2010c).

7.3.2.1 Commercial Lease

EPAct 2005 requires the issuance of competitive leases, although the rule allows for a 

noncompetitive process if no competitive interest exists in a particular area of the OCS after 

public notice (Figure 7-3). If competitive interest exists, BOEM will follow the competitive 

process outlined in the regulatory framework (§§ 210–225) and conduct an auction. If 

competitive interest does not exist, BOEM will move forward with the noncompetitive process 

outlined in the regulatory framework (§§ 226–231). BOEM begins the competitive process by 

issuing a “Call for Information and Nominations” to announce interest in leasing an area and to 

solicit relevant information. After this call, BOEM evaluates the nominations and information 

received, determines the leasing area to be analyzed under NEPA (and suitable alternatives), 
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issues a proposed sale notice to inform the public and request comments on lease terms and 

conditions, and ultimately issues a final sale notice announcing the details of the auction at which 

bids for leases will be accepted.

Some factors that BOEM will consider in determining competitive interest include (Bradley 

2009):

• Site locations

• Timing and type of proposed activities

• Infrastructure

• Anticipated power production and likely purchasers

• Environmental and resource data and information

• Qualifications to hold an OCS lease.

As shown in Figure 7-3, issuance of a commercial lease either competitively or noncompetitively 

requires NEPA review (see Section 7.4.2). It is likely that a lease sale Environmental Impact 

Statement (EIS) and associated consultations must be completed, which could take a minimum 

of 18–24 months. After acquiring a lease, the lessee must receive approval of required plans—a 

Site Assessment Plan (SAP) for construction of a data collection facility and associated activities 

and a Construction and Operations Plan (COP) for full build-out of the commercial generating 

facilities. In the final rule preamble, MMS assumed that geophysical and geotechnical surveys 

would be conducted either pre- or postlease under a permit from the USACE Nationwide Permit 

Program. MMS did nonetheless encourage developers to coordinate activities with MMS as well 

as USACE (§§ 285.605, 285.610, 285.625, 285.645), because this process has not been tested 

across the USACE Districts (MMS 2009e).

NEPA review is also required for these plans, calling for an Environmental Assessment (EA) or 

EIS for each, depending on the depth of analysis accomplished for each preceding step. For 

example, if a lease issuance EIS analysis is robust enough to cover the leasing scenario, as well 

as subsequent site assessment and construction and operations scenarios, the need for subsequent 

NEPA analysis when a plan is submitted could be minimized or fulfilled completely by the 

initial analysis. If initial analyses are not so robust, subsequent separate analyses will be needed 

for each plan, resulting in a longer, sequenced fulfillment of NEPA requirements. The regulatory 

framework is flexible enough to accommodate either approach, but the key to achieving 

efficiencies in review and approval of leases and plans is the availability of information for 

analysis. Thus, it is incumbent on the developers to develop and submit complete plan 

information as early as practicable to foster timely and efficient NEPA analysis in support of 

their projects.
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Source: BOEM June 2010

Figure 7-3. OCS renewable energy process
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Commercial leases have a site assessment term of 5 years in which to complete site 

characterization activities and prepare a COP for submission to MMS. The COP describes all 

activities and installed facilities to be used to gather, transport, transmit, generate, or distribute 

energy from the lease. If a project is deemed “complex or significant,” which is likely for all 

commercial-scale generating facilities, the lessee must submit two additional reports before 

construction and installation: a Facility Design Report (FDR) and a Fabrication and Installation 

Report (FIR), as described in Subpart G. Also, the lessee must submit a Safety Management 

System, as described in Subpart H (MMS 2009b). The results of surveys and studies undertaken 

prelease must be described in the plans that are subsequently submitted (Final Rule, Subpart F) 

(§§ 285.610(b), 285.626(a), 285.645(a)). As discussed previously, if the COP is submitted with 

the SAP, NEPA reviews could take place simultaneously (§ 285.601(d)), reducing review time 

within the approval process. Though not required by EPAct, BOEM will conduct scheduled and 

unscheduled inspections of the OCS facilities and any vessels engaged in authorized activities. 

The inspection procedures are detailed on the BOEM regulatory compliance Web site at 

http://www.boemre.gov/regcompliance/inspect.htm. As specified in Subpart I, the agency will 

also review applications for decommissioning plans.

MMS began the leasing process under the final framework by establishing state task forces 

before issuing Requests for Interest (RFI). An RFI is a formal invitation for submissions of 

interest in obtaining one or more commercial leases from MMS, and it serves as the first step in 

the leasing process (Bradley 2009). The task forces help MMS comply with the requirement of

EPAct 2005 calling for coordination and consultation and are a forum for MMS to share 

information about leasing activities with state and other government officials and for those 

officials to supply input on the implementation of the framework. MMS has named Delaware, 

New Jersey, and Rhode Island as priority states because those states made significant progress in 

preparing for OCS renewable energy development while the MMS regulatory framework was 

being developed. In addition to these three states, task forces are being pursued with North 

Carolina, Massachusetts, Virginia, Maine, New York, Maryland, and other states that have 

initiated offshore wind activities (MMS 2009f). As of December 2009, MMS had held task force 

meetings in Delaware, Rhode Island, Massachusetts, New Jersey, Virginia, and Maryland (MMS 

2009c). Further solidifying development of an offshore program at MMS, Interior Secretary 

Salazar established an Atlantic Renewable Energy Office to manage and implement the 

renewable energy program (Quimby 2009).

In April 2010, MMS released the first RFI for Commercial Leasing for Wind Power on the Outer 

Continental Shelf Offshore Delaware under the new renewable energy framework (MMS 2010c). 

The RFI invited developers to submit descriptions of their interest in obtaining a commercial

lease in the OCS lease areas off the coast of Delaware and asked other interested and affected 

parties to submit relevant comments and information. Several areas have been excluded because 

of NOAA fisheries concerns and potential conflicts with shipping lanes, among other reasons. 

The RFI detailed specific information that developers should submit. The Delaware RFI was 

developed in consultation with the state task force. The MMS announced that two entities 

responded to the RFI, and they are considering the responses before deciding the next steps 

concerning commercial wind leasing off Delaware. One of the entities, NRG Bluewater Wind,

currently holds an interim lease in Delaware, which allows them to hold the lease for 5 years and 

to build a meteorological (met) tower (MMS 2009f).
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BOEM asks interested and affected parties to submit the following information to indicate their 

interest in OCS leases:

• A description of the specific whole or partial OCS blocks or areas within the RFI area that 

are of interest for commercial development, including any required buffer area. Any 

indications of interest identifying areas greater than what would be reasonably necessary to 

develop a proposed commercial wind facility will not be considered as valid indications of 

interest. In addition, BOEM will not consider any areas outside of the RFI area in this 

process.

• A description of the objectives and the facilities necessary to achieve those objectives.

• A schedule of proposed activities, including those leading to commercial operations.

• Available and pertinent data and information concerning renewable energy and 

environmental conditions in the area of interest, including energy and resource data and 

information used to evaluate the area of interest.

• Documentation demonstrating that the applicant’s qualifications to hold a lease as set forth in 

30 CFR §285.107, including documentation demonstrating technical and financial 

capabilities of constructing, operating, maintaining, and decommissioning the facilities.

Financial qualification can include documentation of access to sufficient capital to complete

development. Examples of documentation of technical qualification can include evidence of 

international or domestic experience with renewable energy projects or other types of 

electric-energy-related projects.

7.3.2.2 Limited Lease

In November 2007, MMS announced the interim policy for regulating renewable energy on the 

OCS (72 FR 214, pp. 62673–62675). Although it did not allow offshore wind projects to 

proceed, the interim policy engaged developers in a leasing process that allowed meteorological 

or marine data collection for 5 years (MMS 2007a). From the original 16 lease areas selected, 

five project applications were submitted, and MMS subsequently prepared a multiproject EA in 

cooperation with the USACE (Pardi 2009; MMS 2008b). The EA examines the potential effects 

of wind resource data collection activities offshore of Delaware and New Jersey during the 5-

year life of the lease. Activities authorized by the leases include construction, operation, and 

decommissioning of seven meteorological towers with oceanographic data collection devices. 

The NEPA compliance path also included other environmental consultations with appropriate 

agencies, including examining endangered species and essential fish habitat. 

Following the completion of the EA, five limited leases were offered on five OCS blocks off the 

coasts of Delaware and New Jersey (Figure 7-4; Clark et al. 2009, Pardi 2009):

• NRG Bluewater Wind Delaware LLC 

• NRG Bluewater Wind New Jersey LLC

• Fisherman’s Energy of New Jersey LLC 

• Deepwater Wind LLC (two offerings).

As of November 2009, four of these leases had been executed (the exception was lease block 

area 6738—Deepwater Wind; MMS 2009d). The limited lease applies to operational rights for 
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activities that support alternative energy, such as installing a met tower. The leases may be 

renewed, but cannot be converted to a commercial lease without being subject to a separate 

commercial lease process (Portman et al. 2009, 72 FR 214, pp.62673–62675). At present, it is 

unclear what the disposition of these lease sites will be after the 5-year limited lease period.

Source: Pardi 2009 (permission granted from BOEM).

Figure 7-4. OCS interim policy limited lease areas

Implementing an actual project will be important to assessing how the regulation works in 

practice, because several uncertainties remain. One uncertainty is estimating the time it takes 

from the initial bidding process to securing a permit for constructing a project. As noted 

previously, sequential NEPA analyses will take significantly longer to complete than combined 

analyses. Also, regulatory steps such as combining the lease sale and site assessment activities 

into one review will reduce potential timelines (MMS 2009b). Another uncertainty remains in 

how current projects under development, especially those with a limited lease, will be able to 

convert their lease to a commercial lease, and how the data they gather, such as resource 

assessments, will be handled, because of privacy concerns. Additionally, states have begun to 

hold competitive bids to preselect preferred developers for offshore wind, and the relationship to 

the federal process is still unclear. Finally, questions remain as to how developers will fulfill the 

needs of various reporting requirements. Although most utility-scale developments will probably 

take place in federal waters in the long term, to expedite initiation of offshore wind and the 

benefits to local and regional economies, projects may be developed first in state waters (Dhanju 

and Firestone 2009). On the other hand, state projects will also face unexpected hurdles such as 

PPA approvals and legal gaps such as provisions for conveying state submerged lands. Examples 

include Deepwater Wind’s Block Island project, Fisherman’s Energy’s near-shore New Jersey 
147

project, and the LEEDCo project in Lake Erie adjacent to Cleveland, Ohio. Each of these state 

water projects are relatively small demonstration projects. In August 2010, Duke Energy’s 

Pamlico Sound project was cancelled citing the “lack of economies of scale” for the proposed 

three-turbine project, although the company will continue data collection and feasibility studies 

with the University of North Carolina (AWEA 2010).

The regulatory framework has continued issuance of limited leases to authorize data collection 

and technology testing activities. Although it is unlikely that developers will wish to compete for 

a limited lease with a 5-year term, all leases are subject to the competitive requirement in EPAct 

2005, so the framework describes both competitive and noncompetitive processes. Limited lease 

issuance also requires NEPA analysis, but it is likely that an EA would fulfill the requirement, 

because the leases do not authorize commercial generation and are for a term of only 5 years. 

Limited leases require a General Activities Plan (GAP) outlining the particular activities and 

operations to be undertaken. The GAP activities must undergo NEPA analysis, most likely 

documented by an EA. As with commercial leases, combined analysis of lease issuance and GAP 

activity scenarios could foster timely and efficient NEPA documentation.

7.4 NEPA Compliance and the BOEM Program

Any offshore wind power lease or permit issued by the federal government, or such a project 

undertaken by the federal government, would be subject to NEPA review (NEPA 1969). As the 

lead agency, BOEM is responsible for preparing the NEPA document and coordinating all 

federal, state, and local agency reviews as well as public comments. NEPA requires the 

consideration of potential environmental causes and effects of the proposed action (project) and a 

range of alternatives before an agency makes a decision to approve a project in federal waters. 

NEPA establishes requirements for preparing an EA or an Environmental Impact Statement 

(EIS). Under NEPA, an EIS is required for “major federal actions significantly affecting the 

quality of the human environment.” Although various public and other stakeholders can suggest 

divergent and conflicting concepts for the requisite scope of work, the lead agency—in this case, 

BOEM—determines the level of NEPA documentation needed in accordance with the current 

state of knowledge and the thresholds of proposed impacts and benefits.

All federal agencies have the authority to define certain types of actions or projects as 

“categorically excluded” if the project is expected to have minimal environmental effects that 

can be mitigated. Most federal agencies have designated “routine actions” in which categorical 

exclusions are issued without an EA or EIS. Some types of oil rig installations and operations in 

the Gulf of Mexico are considered routine actions that do not require any NEPA analyses (CEQ 

2010b). If the agency determines that some level of environmental analysis is needed, an EA 

may be prepared. Thereafter, the federal agency makes a “determination of significance” and 

either issues a Finding of No Significant Impact (FONSI) for the EA or determines that further 

assessment in the form of an EIS is required. An analysis must be made, and a FONSI issued or 

an EIS completed, before a federal agency can approve the construction and installation of a 

proposed action or project such as a wind generation plant. In some cases, the agency decides to 

prepare an EIS and skips the EA and FONSI determination. Who pays for the NEPA 

documentation and the studies needed to support the analyses could be changing. In the near 

future, the cost of NEPA document preparation and associated baseline studies might be borne 

by the government in some competitive cases. The Cape Wind pioneers, on the other hand, have 

been responsible for all the costs associated with the NEPA document, including ecological 
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studies to fill gaps in knowledge. Government-sponsored and peer-reviewed environmental 

studies would assist in building the knowledge base and closing some significant gaps (see 

Section 8).

The lead agency preparing an EIS follows various standard procedural steps to complete the 

NEPA process. The following steps are outlined in the federal regulation:

• Define the purpose and need for the project

• Scope the environmental issues

• Coordinate public scoping hearings

• Incorporate public comments into the draft document

• Analyze a set of reasonable alternatives

• Design and implement environmental surveys and investigations to assess the cause and 

effect of the proposed action/project (in some cases, the developer/lessee may be responsible 

conducting such surveys and investigations)

• Establish thresholds of potential impacts to understand the context and intensity of the 

impacts, including adverse and beneficial ecological impacts

• Identify mitigation and monitoring strategies

• Examine the impacts of decommissioning.

7.4.1 The PEIS

To comply with NEPA, MMS determined that establishing the Renewable Energy and Alternate 

Use Program was a major federal action requiring a PEIS. After a period of development and 

review, the final PEIS for the program was published in November 2007 (MMS 2007b) and the 

Record of Decision (ROD) was published in January 2008 (MMS 2007c).

The PEIS has two purposes. First, it discusses potential environmental consequences of 

establishing the program and alternatives to establishing the program. Second, it establishes a 

baseline framework to mitigate environmental consequences through policy development and 

best management practices. The PEIS is broad in scale and does not focus on site-specific issues. 

It is a general review of the technologies involved in harnessing offshore wind, waves, and ocean 

currents for energy production and associated potential environmental effects. Further, the PEIS 

focuses on those technologies that are expected to be economically viable by 2014. The PEIS 

does not analyze renewable energy activity on the OCS off Alaska or Hawaii because 

commercial deployment of these technologies is not expected to be feasible in those areas in this 

timeframe. Because any project proposed under the program must comply with NEPA, 

subsequent documentations of environmental reviews are expected to tier off and reference the 

PEIS (Section 1508.28). 

7.4.2 Federal Regulatory Nexus and NEPA Compliance

Although it is still determining the full extent of the NEPA review for OCS projects, BOEM is

likely to require EISs for the first several commercial-scale projects. During the NEPA document 

preparation, BOEM will solicit input from other federal agencies with regulatory authority over 

the marine resources and the coastal region. During these consultations, the gaps and overlap of 
149

institutional and regulatory authorities become more apparent (Adams 2002). Numerous federal 

agencies in addition to BOEM, Federal Energy Regulatory Commission (FERC), and the 

USACE have significant ocean roles and responsibilities that will involve them in offshore 

renewable energy and development processes. Appendix A lists federal agencies and their 

interests in renewable energy activity on the OCS—an abbreviated list is shown in Table 7-2 

below. In this section, the focus is on the maze of regulatory authorities governing specific 

activities at sea, including oversight of transmission lines, marine mammals and fisheries, and 

coastal zone management. State agencies also actively participate in this process under their own 

NEPA regulations, or State Environmental Policy Acts (SEPAs; see Section 7.5). Offshore 

developments must bury subsea transmission lines below state submerged lands (i.e., the first 3 

nm) to connect the transmission line to the coast; this also involves the state in the approval 

process for offshore energy projects in federal waters. 

The FERC maintains authority over interstate electricity transmission as well as the 

interconnection between the generator and the regional power network. Oversight of submarine 

power transmission line placement in federal waters, however, is shared between FERC and the 

USACE. Installing submarine cable systems, cable landfall transition structures, and the offshore 

wind park is subject to the regulatory permitting review and approval of USACE under Section 

10. 

Additionally, jurisdiction over the right of way of power transmission lines on the OCS was 

delegated to DOI under EPAct with the authority to grant a lease, easement, or right of way for 

renewable energy related uses of the OCS (Burton 2002). But FERC asserted additional authority 

over siting of ocean energy projects whose generator apparatus is physically located in the ocean 

(e.g., wave, ocean, tidal, and current power devices as opposed to offshore wind turbines) under 

the Federal Powers Act (Federal Power Act 1920). In one project, FERC won an administrative

legal case affirming its involvement in permitting wave power projects in navigable waters 

(FERC 2003). Potential oversight by MMS for offshore wind and FERC for hydrokinetic project 

licenses created some jurisdictional battles as well as consternation in the renewable energy 

industries. MMS and FERC, however, signed a Memorandum of Understanding (MOU) to 

clarify responsibilities related to hydrokinetic projects on the OCS, but their roles and 

responsibilities are still uncertain, including who manages the NEPA documentation (FERC and 

MMS 2009).

NOAA has jurisdiction in some areas based on its responsibilities to protect and manage marine 

sanctuaries, marine national monuments for which it has been assigned jurisdiction, and portions 

of some estuaries. Any projects in or around a marine sanctuary or any protected area will be 

subject to NOAA review and approval (National Ocean Service 2010). In addition, NOAA 

administers the Coastal Zone Management Act (CZMA), a voluntary federal-state partnership in 

which states and territories develop their own coastal management programs (CZMP 2010). 

After NOAA approves a state’s program, the state can review federal actions, licenses, or 

permits that could require land, water use, or natural recourse for “federal consistency,” ensuring 

that the project follows enforceable policies of the state’s coastal management program.

The U.S. Fish & Wildlife Service (FWS) and the National Marine Fisheries Service (NMFS, or 

NOAA Fisheries) also play an important consultation role in the NEPA process because they 

each have jurisdiction over some marine endangered species (including designating critical 

habitat) and marine mammals. NMFS also plays an important role in managing commercial 

fishing, including designating essential fish habitat. NOAA Fisheries is responsible for 
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implementing the Marine Mammal Protection Act (MMPA) of 1972 prohibiting, with limited 

exceptions, the take of marine mammals in U.S. waters, including species of whales, dolphins, 

porpoises, seals, and sea lions (MMPA 2007). The incidental take provisions require the 

applicant to mitigate the taking to the lowest level possible, and to monitor and report results to 

NOAA Fisheries (U.S. Department of Commerce 2000). Incidental Harassment Authorizations 

(IHAs) allow for taking of marine mammals by “harassment” for a specified lawful activity that 

takes place for no more than 5 years per authorization. IHA criteria for acoustic harassment, 

when they have been finalized by the NMFS (U.S. Department of Commerce 2010), will be of 

particular interest for offshore wind because marine mammals could be affected by pile driving 

during of wind farm construction.

Within DOI, the National Park Service and FWS are responsible for protection and conservation 

of natural resources, including national parks and wildlife refuges. To clarify potential competing 

interests between energy deployments and habitat and species protections, MMS and FWS 

recently signed an MOU on migratory birds. FWS has jurisdiction over migratory birds and 

eagles under the Migratory Bird Treaty Act and the Bald and Golden Eagle Act. The MOU 

clarified that MMS will protect and enhance habitat of migratory birds during energy extraction, 

from, in this case, offshore wind farms (FWS and MMS 2009).

7.4.3 Cape Wind History: Challenges and Lessons Learned

In 2001, Cape Wind Associates, LLC submitted an application to the USACE to develop a wind 

farm in Nantucket Sound, off Massachusetts. The project originally proposed 170 wind turbines 

in Horseshoe Shoal for 454 MW of maximum electrical output, 4.7 miles from the nearest point 

on land. At that time, no specific departmental jurisdiction or oversight existed for offshore wind 

projects in federal waters. Acting under Section 10 authority of the Rivers and Harbors Act of 

1899, USACE assumed the lead in the coordinating process. In 2002, Section 10 permit approval 

to install a meteorological tower was granted. About 17 different government agencies were 

involved in the Cape Wind NEPA document preparation and consultation processes. In 2004, the 

USACE released the Cape Wind draft EIS for public comment (Kaplan 2004). A year later, 

when MMS assumed expanded permitting authority under EPAct 2005, it requested that 

additional information be included in the DEIS to address all aspects of its “cradle to grave” 

jurisdiction. It took several more years of additional biological and ecological surveys, resource 

agency consultations, and public comment periods for the new NEPA process. In January 2009, 

MMS published the Final EIS (MMS 2009g and Cape Wind 2010).

One of the final agency challenges, before the issuance of the ROD, involved the National Park 

Service’s Keeper of National Register of Historic Places. The Service determined that Nantucket 

Sound is eligible for listing in the National Register of Historic Places. In January 2010, Interior 

Secretary Kenneth Salazar announced that “... it is now time to move the Cape Wind proposal to 

a final decision point” and that he was “prepared to take the steps necessary to bring the permit 

process to conclusion” (MMS 2010b). He announced the ROD in April 2010. The Cape Wind 

project illustrates important lessons about navigating the federal permitting process and 

negotiating with resource agencies regarding data gaps and uncertainties. As mentioned 

previously, the federal and state governments may in the future share in paying for the expenses 

to prepare the NEPA document and support studies that fill in knowledge gaps, but in this case, 

these financial and schedule commitments were borne by the developer. Certainly, different sites 

will have different community as well as agency concerns.
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Another lesson relates to the critical nature of early community and state involvement because 

that might stave off future citizen suits. The current BOEM leasing process involves a state task 

force and other stakeholders at the inception of the application process. Cape Wind Associates 

first proposed this site without any specific agency procedures for offshore wind. Given the 

contentious nature of this first utility-scale project proposed in the nation, the developers 

completed more than 500 public presentations over the last 9 years, and many of them took place 

outside the required public hearing process (Pachter 2010). The timeline in Figure 7-5 is a 

chronology of the Cape Wind project milestones. 

Source: Cape Wind Associates, LLC 2010; MMS 2009d; MMS 2009g.

Figure 7-5. Cape Wind history and timeline
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Table 7-2. Selected Relevant Laws
153

7.5 State Permitting Challenges 

As noted in Section 3, permitting processes vary from state to state, and the length of the 

approval process varies considerably (Kopf 2009). Even if a project is located in federal waters,

developers must receive state permission for transmission cables making landfall, for connecting 

with the grid (including building substations), and for shipping and dredging activities (Firestone 

et al. 2004).

The states can also review proposed renewable energy activities and their environmental effects 

for consistency with their federally approved coastal zone management programs pursuant to the 

CZMA (CZMP 2006), which strengthens the role of the state in OCS renewable energy leasing 

and development process and associated NEPA review. State agencies oversee the state coastal

management plans to determine whether a proposed activity is consistent with state policies. If 

the proposed activity is consistent with the state coastal zone plan, federal permits can be 

granted. If the review finds inconsistencies, the state can choose to negotiate conditions with the 

applicant or it can deny the permit and the applicant can ask the Secretary of Commerce to 

override the state decision (15 CFR 930). This CZMA process varies from state to state, and 

typically the states have 6 months to determine consistency. In addition, within 3 nm from the 

coast, the Great Lakes, and other inland water bodies, an applicant for a federal permit also must 

obtain a 401 Water Quality Certification under the Clean Water Act (CWA) to ensure that the 

project meets state water quality standards (i.e. thermal pollution, pollution, changes to water 

flow, and turbidity).

Figure 7-6 shows the USACE process that will govern offshore renewable energy development 

in state waters and the Great Lakes and its relationship to NEPA and CZMA reviews. USACE 

will most likely lead the federal permitting responsibilities along with the state natural resource

agencies in those states (see Section 3 for state project information and Section 7.5.1 for a Great 

Lakes overview). The USACE Section 10 permit relates to structures altering or obstructing 

navigable federal or state waters (e.g., a wind turbine), but it does not refer specifically to 

energy-related projects and it does not allow for ownership or leasing of the seabed by a 

developer (River and Harbors Act 1899). USACE’s authority to regulate potential obstructions to 

navigation extends to artificial islands, installations, and other devices located on the OCS 

seabed by Section 4(f) of OCSLA of 1953 (43 USC § 1333).Thus, the USACE Section 10 permit 

is issued for the approval of the design and construction of the turbine structures and 

transmission cable to shore without conveying property rights for the sea floor or providing for 

certification or periodic inspections (River and Harbors Act [USACE 1899]). In addition to 

Section 10, the USACE authority is grounded in Section 404 of the 1972 CWA, in which 

Congress broadened USACE’s mission to include restoring and protecting the nation’s water 

quality. Under the CWA, however, its jurisdiction extends only 3 nm from shore. A USACE 

Section 10 permit will be required for all renewable energy projects on the OCS, but BOEM will 

be the lead agency for such projects and the Section 10 permit process will be incorporated into 

the overall leasing and development processes under the BOEM regulatory framework.
154

Source: Adams 2002.

Figure 7-6. Relationships among the USACE Section 10 permit, CZMA consistency determination, 

and the NEPA EIS process (timelines are approximations) 

Under the Submerged Lands Act (2002), states are permitted to lease state-owned lands, but 

typically such a lease is not granted until all federal and state permits and approvals have been 

gained. Over the last several years, several states are developing new rules relating to leasing 

state submerged lands in relation to offshore wind (Michigan GLWC 2010; Texas GLO 2009), 

and other states such as Massachusetts, Rhode Island, and New Jersey are developing marine 

spatial planning policies. In some states (e.g., Virginia and Massachusetts), projects must receive 

local as well as state approval. States have jurisdiction over activities within state waters, but 

projects located within navigable waters may be in areas of federal jurisdiction, as discussed 

previously.

Some states also have their own NEPA regulations and public review process, but they can

collaborate with federal agencies to combine documents into one (as Massachusetts did with the 

Cape Wind EIS for MMS and the state environmental impact report). The NEPA process 

requires consultation with all relevant state agencies having jurisdiction over resources that may 

be affected by a proposed project, including historical properties, archaeological sites, and tribal 

resources. Also, local planning and zoning boards and tribal nations may have interests that 

would be affected. Some states agencies that regulate the generation of power will require that 

projects demonstrate “public convenience and necessity.” The necessity is sometimes discussed 

only as a need for power generation in a given area rather than as a need for renewable energy 

(Kimrey 2008; Renewable Energy Policy Project 2003). The Great Lakes are an example of a 

complex regulatory structure for bodies of water that overlap multiple state, tribal, and 

international boundaries.

7.5.1 Great Lakes

With eight states and two Canadian provinces claiming jurisdiction over the waters of the Great 

Lakes, numerous competing interests and activities relate to offshore wind energy. Considered 

state waters because the coastal states own the bottomlands (the land lying below the ordinary 
155

high water mark) of the lakes, the state agencies will play central roles in siting and permitting 

offshore wind projects. Each state issues Great Lakes bottomlands permits under the authority of 

Part 325, Great Lakes Submerged Lands (1955 PA 247) and the Natural Resources and 

Environmental Protection Act (1994 PA 451, as amended). This permit protects the waters of the 

Great Lakes and the Great Lakes bottomlands. In addition, a Section 10 permit from the USACE

is required for most activities that alter the Great Lakes coastal areas, including offshore wind 

projects. As mentioned previously, because BOEM does not have regulatory authority, it is likely 

that the USACE will serve as the lead federal permitting agency. In addition, the lakes border 

lands of Native American tribes and the Canadian provinces of Ontario and Quebec. These

create unique regulatory challenges, for example, where 35 tribal nations have rights in and 

around the shores of the Great Lakes.

7.6 Structural Safety Certification

The bulk of the U.S. effort in offshore wind industry development has been expended in 

permitting, site selection, site evaluation, and preconstruction studies aimed at obtaining 

regulatory approval. Once approval is obtained, however, which has happened so far only for 

Cape Wind and a very few state projects, the project developers will face a new set of regulatory 

hurdles to demonstrate that wind turbines are designed, manufactured, and installed to withstand 

the site-specific conditions. 

7.6.1 BOEM Infrastructure Authority

A major portion of the new BOEM domain will be to ensure the structural safety of offshore 

wind turbines by certifying and monitoring construction of the turbines, their substructures, and 

the associated infrastructure. Although no such process currently exists in the United States for 

land-based wind turbines, most European countries require turbine certification compliance with 

some recognized group of international standards to ensure structural integrity.

The BOEM is responsible for regulating the development of oil and gas reserves in the U.S. OCS 

waters. The bureau has significant experience with the design, fabrication, and installation of 

offshore structures, so it is appropriate that it assumes this role for wind energy projects as well. 

The authority granted to BOEM by EPAct 2005 to oversee offshore wind energy installations 

includes reviewing and approving plans for:

• Engineering design and structural safety

• Installation and construction

• Operation

• Ongoing maintenance throughout the life of the structure

• Decommissioning.

BOEM is also responsible for any inspections that may be needed to ensure compliance with the 

final approved plans and continued conformity with the original design as the project ages.

7.6.2 Offshore Codes and Standards

During the early 1990s, the wind energy industry—through the International Electrotechnical 

Commission (IEC)—began to establish international standards for land-based wind turbines. 

Technical Committee 88 (TC88) was established to develop and manage a suite of applicable 
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standards for wind turbines. The primary standard for structural design requirements is IEC 

61400-1 Edition 3 (IEC 2005). It defines design classes, external (environmental) conditions for 

each design class, design load cases, fault conditions that must be included in the design, 

procedures for assessing all static and dynamic loads, electrical requirements, and methods for 

assessing the site-specific suitability of the turbine. Perhaps the most important part of the 

standard is a detailed definition of the turbulent wind environment. Because the detailed 

characteristics of wind are so important to unsteady aerodynamic load distributions along the 

rotating blades, it is crucial that this part of the external conditions be defined consistent with 

analytical theory used for rotor load estimation.

In 2000, IEC/TC 88 began to develop an offshore wind turbine standard, Offshore Requirements 

for Wind Turbines, IEC 61400-3 (IEC 2010). It defers to IEC 61400-1 for the wind turbine 

aspects of the design requirements and relies on existing mature standards for setting general 

support-structure requirements. The IEC offshore committee surveyed structural guidelines for 

offshore oil and gas structures, including the American Petroleum Institute (API), International 

Standards Organization (ISO), Det Norske Veritas (DNV), and Germanischer Lloyd (GL) 

guidelines, and attempted to use them as the basis for the new IEC 61400-3 requirements. A 

European-funded project Requirements for Offshore Wind Turbines (RECOFF) included formal 

comparisons of these different standards and assessed the suitability for wind turbines (Frandsen 

et al. 2005). The RECOFF study concluded that for most “support structure” requirements, 

standards such as API and ISO could be used. The crucial deficiency, however, was the manner 

in which dynamic loads were estimated. Wind turbines are uniquely subjected to both wind and 

wave stochastic loading, and both loading sources are nearly equal in importance with respect to 

dynamic excitation of the wind turbine. IEC 61400-3 is the only international standard that 

specifically considers these offshore wind turbine issues. It is less mature than other international 

standards and guidelines, but because it is based on earlier standards, it represents an integrated 

version of all the work that preceded it. Also, because it is part of a series of international 

standards that consider the broader wind industry’s needs (such as verification testing for 

performance, structural design compliance, power quality, gearbox design requirements, and 

small turbines), it is the best available standard for the issues of structural safety for offshore 

wind turbines.

Codes such as the IEC 61400-3 and API RP 2A-LRFD (1997) have some overlapping design 

requirements for wave and current loading conditions. A direct comparison of the IEC and API 

standards shows, however, that other specific differences should be integrated. Examples of the 

differences include the following:

• The IEC uses a 50-year return period for defining extreme environmental design conditions, 

and API RP 2A-LRFD (1997) uses a 100-year return period for defining design conditions 

for high-consequence platforms. 

• API RP 2A-LRFD (1997) prescribes three levels of design wave height based on the platform 

type and its failure consequence—IEC requires that designs use the measured site waveheight statistics and wind environment and adjusts component safety factors based on the 

consequence of that component failing.

• API RP 2A-LRFD (1997) is a basis for the design of offshore structures subject to wave, 

wind, current, and earthquake loading conditions; it does not, however, consider the scope 

and range of all conditions required for designing wind turbine support structures. Similarly, 
157

IEC 61400-3 lacks some of the detailed provisions given by API RP 2A-LRFD with respect 

to some offshore engineering practices. 

These are some examples of the code differences, but the greatest challenge is to develop a full 

understanding of the conflicting requirements and the real differences in safety levels for these 

codes so that a guideline can be developed to clarify what BOEM will require from each 

developer. This comparison must also evaluate the similarities and differences in the failure 

consequence for the types of facilities. These consequence-of-failure issues should include 

human life safety, environmental impact, energy supply reliability, and economic factors. 

Ultimately, BOEM must determine the areas where existing standards are applicable and resolve 

any conflicts that may exist in establishing equivalent safety requirements for the design of 

offshore wind turbine systems. 

The best approach will most likely use IEC standards with API RP 2A-LRFD (1997) and other 

standards to fill critical gaps. MMI Engineering compared structural reliability (Dolan et al. 

2009) and concluded that the IEC offshore wind standard and the API RP 2A-LRFD (1997)

standard supplied similar levels of safety for offshore wind turbines in three reference sites in 

U.S. waters (Dolan et al. 2009). Although this study gave needed assurance that API and IEC 

could be combined to address both the offshore foundations and substructure (API 1997; API RP 

2A-LRFD) as well as the wind turbine itself (IEC 61400-3), it was not comprehensive enough to 

fully address tropical storms that frequent the Atlantic coastline and the need for specifications 

for turbines to withstand their impact. The need for this work has been recognized by IEC/TC-88 

and will be examined by a follow-on maintenance team that will revisit IEC 61400-3 begining in 

2010.

7.6.3 Type versus Project Certification

Very few legal requirements exist concerning structural safety in land-based U.S. wind energy 

installations and no single agency is responsible for those that do exist. The structures must meet 

local and state building codes, and the electrical systems must meet electrical standards. Both of 

these, however, are inadequate for defining wind turbine design requirements, and no 

overarching permitting process addresses structural safety. Instead, the process is commercially 

driven. Owners and operators choose to require type-certified wind turbines for their projects. 

The turbines are usually certified to IEC or other European standards. 

Recognizing that the offshore certification process is unique, IEC/TC 88 drafted a second edition 

of its wind turbine certification scheme IEC 61400-22 (IEC 2010), which passed the final voting 

stage and is being prepared for IEC executive approval. This new edition will rely on IEC 

61400-3 for technical requirements as well as define the certification process. Both IEC 61400-3 

and IEC 61400-22 assume that the turbine will be certified to a set of design classes specified in 

IEC 61400-1 Edition 3, and the support structure will be designed to site-specific conditions. The 

standard development process assumes that multiple parties will be responsible for different 

aspects of the project and offers guidance for each phase of the project. It allows for using other 

standards for the support structure, such as API RP 2A-LRFD (1997), ISO, DNV, and GL 

Windenergie Group specifications (though the last two specifications are heavily influenced by 

API for their offshore support structure guidance).

One primary technical difference in these design standards relates to the fact that wind turbines 

are mass-produced as opposed to the custom, single-unit design for each platform in the oil and 

gas industry. After final permitting of wind plants, many turbines of the same design type are 
158

installed (hence, the term “type certification” for a turbine that meets a generic design class 

rather than site-specific environmental conditions), and most likely the same design has operated 

in other sites, lending experience to the pitfalls of any new installation. Of course, the physical 

environmental conditions of each new site must be integrated into the engineering evaluation of 

site suitability, which may be problematic in some hurricane areas where extreme conditions can 

exceed the design loads of the type-certified turbine. The IEC recognizes that turbines will be 

designed and tested long before most projects are even conceived. Thus, the IEC standards 

require and give guidance to evaluating the suitability of a type-certified turbine for specific site 

conditions. This assessment to evaluate single-unit type certified wind turbines in the context of 

a multiple-turbine array should become part of new BOEM regulations. In accordance with IEC, 

this is called project certification, but BOEM has not yet adopted an approach in this regard.

Also, project certification follows the offshore wind facility through installation but does not 

include ongoing monitoring throughout the life of the project. With oil and gas installations, 

operations have a greater degree of inherent risk associated with human life safety and 

environmental safety, as exemplified by the Deepwater Horizon disaster in the Gulf of Mexico in 

April 2010, which leaked millions of gallons of oil for nearly 3 months and took the lives of 11 

men on board. Although the work on wind turbines cannot be considered risk-free, the lower 

consequences of failures must be taken into account when prescribing long-term inspection and 

operational measures to control unmanned wind projects, with consequences that are mostly 

economic and borne by the developer. The degree to which BOEM will require inspections of 

offshore wind turbines is yet to be determined. 

7.6.4 Structural Safety Compliance

BOEM’s basic requirements for oil and gas installations are similar to the quality system of IEC 

61400-22 wind turbine project certification. Many wind turbine manufacturers are familiar with 

these basic steps, especially the third-party engineering evaluation. Many differences exist, 

however, between offshore wind plants and oil and gas operations. The critical technological 

differences should be reflected in the standards. A significant part of the cost and economic 

viability of offshore wind plants will depend on the specific structural safety requirements 

chosen by BOEM.

As detailed previously, all commercial utility-grade wind turbines undergo extensive typecertification evaluations based on IEC or similar standards. Financial institutions are increasingly

requiring expert evaluations of land-based turbine designs and installations along with periodic 

operations surveillance. 

BOEM requires the following steps to comply with current oil and gas project permitting 

requirements for structural safety:

1. Approval of a plan for exploration drilling of certain sectors of OCS

2. A preliminary project plan to develop full production of that OCS sector (a prepermitting 

step to avoid gross misconceptions and agree on the fundamental steps required for project 

permitting)

3. Detailed engineering design documentation for all aspects of the project (generally defined 

by API RP 2A-LRFD [1997])

4. Third-party evaluation of the project plans and engineering documentation by a BOEMapproved engineering consultant experienced in offshore oil and gas installations
159

5. BOEM review of the third-party engineering evaluation and reconciliation of any 

discrepancies between BOEM requirements and the project documentation

6. Third-party oversight of all aspects of the project installation, commissioning, operations 

throughout the life of the structure, periodic inspections of structural health, and finally 

decommissioning.

This process, with its sector specification applicable to oil and gas, may not be effective in the 

near term for offshore wind. In this regard, the BOEM “does not want to limit the possibilities of 

development in federal waters by identifying locations” for development, but will seek industry 

proposals through a “call for interest” that is not limited to predetermined sectors (MMS 2007b). 

The final rule, CFR 285, released in April 2009, addresses, among other things, specific issues 

related to the design, installation, and safety of offshore wind facilities, but not a detailed scope 

of requirements. This phase of the project follows the process of obtaining a lease for the project 

site, which was covered earlier. Most offshore wind turbines will be delivered to U.S. projects 

from manufacturers with a type conformity certificate, but this will not guarantee that they are 

suitable for installation at a specific site. To address this, BOEM requires developers to submit 

design and installation documents for BOEM approval. These documents, outlined in Subparts 

F through J, are as follows:

• Facility Design Report

• Construction and Operating Plan

• Fabrication and Installation Report 

• Safety Management System

• Decommissioning Plan. 

The review and oversight of these documents can be carried out by a certified verification agent 

(CVA), a third-party evaluator hired by the developer to conduct a full evaluation of the project 

and assure BOEM that the project has been developed in accordance with best practices. The 

qualifications and selection process of CVAs are still being discussed. In June 2010, an 

independent committee, Offshore Wind Energy Turbine Structural and Operating Safety, was 

formed under the Transportation Research Board (TRB) of The National Academies to consider 

this issue and make recommendations to BOEM (The National Academies 2010). In addition, 

AWEA, under the direction of the American National Standards Institute (ANSI), formed a 

national group under their standards coordinating committee made up of experts from the wind 

industry, the oil and gas industry, government, certifying bodies, and classification societies to 

establish a recommended roadmap, or guideline, to advise and inform BOEM and the U.S. 

offshore wind industry on design methods and standards applicable to offshore wind. The 

combined efforts of these two groups will lead to a more comprehensive approach to offshore 

turbine development in the United States, and will give BOEM an opportunity to clarify the 

regulations governing offshore wind turbines while strengthening the rules to ensure uniform 

safety. 
160

7.7 Findings and Conclusions

The lack of U.S. wind energy policies and the evolving institutional and regulatory processes 

governing the planning, siting, and deployment of offshore wind projects present serious 

challenges. In June 2010, MMS was reorganized and renamed BOEM. These new activities and 

bureaucratic reorganizations have created significant regulatory uncertainties. The following 

conclusions describe findings based on the current evolutional rules and structures.

• A price placed on carbon emissions would accelerate the transition toward offshore wind. 

National policies specifically designed to accelerate deployment of offshore wind energy 

would influence greatly the direction of institutional and regulatory mechanisms on both state 

and federal levels. Recent steps taken by the Obama administration outline a national 

renewable energy strategy, though as yet specific standards, deployment goals, and long-term 

policy mechanisms for offshore wind are lacking. 

• The White House’s Executive Order 13547 and the formation of the National Ocean Council 

begin regional coastal and marine spatial plans that will involve frequent and robust 

engagement strategies under the leadership of CEQ (CEQ 2010a). This initiative, however, 

does not have a renewable energy or offshore wind focus. 

• The CEQ-led CMSP framework is now a building block for a more consistent ocean policy 

that will balance competing uses of the OCS such as offshore wind resources and an 

ecosystem-based vision for the nation’s coastal waters. Selecting candidate sites and 

analyzing potential cumulative effects will involve mapping compatible and conflicting areas 

of human use along with performing scientific assessments across the marine environment. 

This marine spatial planning process is essential for large-scale development of offshore 

wind.

• Several states are also moving toward marine spatial planning for state waters (e.g., 

Michigan, Massachusetts, Rhode Island, and New Jersey)—this will greatly assist the federal 

government in identifying potential sites for renewable energy. Federal leadership is critical 

for an efficient process that links marine spatial planning with candidate sites for offshore 

wind energy.

• As described in Section 6, national scenarios and modeling efforts have considered offshore 

wind, and these have been widely vetted and disseminated. Deployment scenarios include 54 

GW by 2030 based on the scenarios presented in the 20% report (DOE 2008a) and NREL’s 

Renewable Energy Futures (REF) study that projects a range of future deployment scenarios 

by 2050 (Pre-press 2010). How would the current regulatory structures evolve to support 

these developments in a sustainable manner? For example, if we consider the 54 GW 

scenario by 2030, it could involve more than one-hundred 500-MW facilities over 20 years 

or five utility-scale projects installed per year. The current paradigm for leasing and 

permitting and the potential rate of deployments would not only be slow but also probably be 

unrealistic to support the deployment of 54 GW by 2030. 

• The release of the MMS rule (now authorized under BOEM) in the second quarter of 2009 

was a clear step in establishing a regulatory pathway for siting offshore wind plants. The 

Cape Wind ROD and the issuance of the first commercial lease on the OCS in 2010, the 

release of the RFI for commercial leases in Delaware, and the formation of several state task 

forces demonstrate a forward movement in the federal agency. 
161

• Other signs of movement are visible on the federal level. In June 2010, DOE and DOI signed 

an MOU to spur cooperation in wind technology siting and permitting, resource 

characterization, technology standards, public engagement, and establishment of deployment 

goals (MOU 2010). This milestone forges an important federal working relationship to 

accelerate the offshore wind industry and overcome barriers. It is hoped that these activities 

will facilitate developments “by pursuing priority leasing and efficient regulatory processes 

for sites with high, commercial-scale offshore wind and water power development potential.”

• The nation’s regulatory structure should develop integrated national and state energy codes 

and standards for offshore wind. These will allow for efficient review and approval of project 

siting and safe and efficient permitting processes. This requires updating national laws and 

oversight agencies. The TRB of the National Academies is addressing this issue and will 

make recommendations to BOEM (The National Academies 2010). It is strongly 

recommended that BOEM adopt the TRB findings.

• The patchwork of federal regulations and fragmented institutions governing ocean uses, 

along with the MMS reorganization to BOEM, subjects developers and states to protracted 

processes for siting and permitting. Underlying concerns about this relatively new 

technology, gaps in the knowledge base, and new legal interpretations (e.g., Clean Air Act) 

are contributing to the delays in resource agency decision making. As we have seen in 

Europe, setting national offshore wind targets and government funding of priority 

environmental studies could help create more efficient decision timelines and fill in gaps in 

rules more effectively.

• Because the permitting and leasing processes are tied to NEPA compliance and the 

assessment of environmental and social effects of installations, building the knowledge base 

about the marine environment and the coastal communities at site-specific and regional 

locations is essential and must be done more rapidly to address gaps and uncertainties.

• The NEPA requirements need to be examined by high-level agency decision makers and the 

CEQ. The process needs to reflect the level of risk posed by offshore wind compared to other 

alternatives on the OCS and the life-cycle options for electricity supply (see Section 8 for 

more details on a risk framework).

• Possible opportunities for more efficient NEPA compliance procedures may involve defining 

new categorical exclusions for testing activities on the OCS; substituting requirements for 

shorter preconstruction studies with longer term, postconstruction monitoring programs, 

jointly funded with industry and government; and creating binding timeframes for agency 

consultations along with additional resources to assess permit applications more 

expeditiously. These ideas would also be relevant to state governments, many of which have 

their own NEPA statutes.

• The federal government must partner with state governments in coastal areas and the Great 

Lakes to create an offshore wind strategy. Activities in state waters could accelerate the 

offshore wind industry to help meet their RPS goals and to realize socioeconomic benefits. 

The states, however, must more rapidly develop their leasing structures and cooperate with 

their resource agencies. A strategic partnership between federal and state governments is 

essential for siting and permitting offshore wind in the United States.
162

• Stakeholder engagement through the NEPA process must also be examined. Although this is 

a valuable mechanism for involving the public, it is not sufficient in itself for building 

partnerships and community support for transitioning to a gigawatt-scale offshore wind 

industry. Long-term commitments to work with state and local communities undergoing 

transitions will help set the stage for accelerated market penetration (see Section 8). 

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169

8.0 Environmental and Socioeconomic Risks of 

Offshore Wind Projects 

8.1 Introduction

This section looks at the potential risks and uncertainties associated with siting, constructing, and 

operating offshore wind facilities within a gigawatt-scale deployment strategy. Balancing varied 

social interests (e.g., lower energy costs, quality of life, energy independence, and reduced power 

plant emissions and waste streams) with ecological considerations (e.g., habitat health, species 

and resource protections, and coastal management) will require a careful analysis of competing 

values to understand and optimize this interplay for the benefit of society. This section 

summarizes different sectors of risk, based on the available evidence from Europe (see Section 

8.5) and building on previous synthesis reports such as Worldwide Synthesis and Analysis of 

Existing Information Regarding Environmental Effects of Alternative Energy Uses on the Outer 

Continental Shelf (Michel et al. 2007), the Cape Wind Final Environmental Impact Statement 

(FEIS; MMS 2009a), and recent state-funded research. Several analytical constructs and themes 

frame environmental and social concerns related to offshore wind development:

• Applying coastal and marine spatial planning (CMSP)as national policy under the leadership 

of the Council on Environmental Quality (CEQ)-led National Ocean Council, as described in 

Section 7. The principles of ecosystem-based management and adaptive management to 

protect, restore, and improve stewardship of the ocean are related directly to siting of 

offshore wind on the Outer Continental Shelf (OCS) along with a robust stakeholder strategy 

to determine use conflicts and compatibilities (ERG 2010). 

• Comparing the potential risks to other threats in the coastal and marine environment, because 

marine systems are affected by multiple stressors (Crain, Kroeker, and Halpern 2008). In the 

environments where wind farms are proposed in the United States, there are already known 

stressors to both humans and the marine environment (Halpern et al. 2008). Reliance on the 

oceans has come at a cost (Millennium Ecosystem Assessment Report 2005).

• Ensuring that the length of time and depth of field surveys and research to fill data gaps 

reflects the proper level of risk posed by offshore wind as compared to other alternatives on 

the OCS and the life-cycle options for electricity supply (see Section 8.2).

• Focusing on individual sectors of scientific analyses (i.e., mammals, birds) at a particular site 

or region, driven by National Environmental Policy Act (NEPA) compliance and resource 

agency consultations. But sector-by-sector studies do not capture the sensitivities of the 

ecosystem and communities or cumulative effects. An alternative analytical framework—an 

integrated risk analysis—is proposed that includes environmental and social risks, but also is 

a more powerful analytical tool encompassing broader areas such as technology choices, 

transmission, public engagement, and siting strategies (see Section 8.2.2).

The need to transform our energy portfolio is underscored by climate change impacts that will 

dramatically affect the ecosystems as well as the economies of the United States (NRC 2010a, 

2010b; Karl, Melillo, and Peterson 2009; IPCC 2007). For example, the oceans are becoming 

more acidic, coastal ecosystems are seriously threatened by sea level rise, and freshwater 

resources and food security are also threatened. Offshore wind has the potential to be a 
170

significant, low carbon energy source that can help reduce the climate change threat and reduce 

conventional fuel impacts, but the current state of our oceans, coasts, and Great Lakes needs to 

be taken into account as offshore wind energy is added to the mix. 

Siting offshore wind farms can affect ecosystems and communities in a variety of ways. 

Understanding the potential risks and creating the means with which to anticipate and mitigate 

harmful effects will be important components in moving offshore wind to the forefront of the 

renewable energy field. The next section briefly discusses the state of the coasts and ocean in 

terms of multiple stressors. Section 8.3 outlines an analytical approach to assessing risks and 

benefits, Section 8.4 discusses in some detail how an integrated risk framework contributes to a 

better understanding of potential effects, and Section 8.5 reviews European studies assessing 

offshore wind projects. 

8.2 Comparing Analytical Frameworks

Risk frameworks are being developed to address environmental concerns of offshore wind 

installments (Ram 2009; Nunneri et al. 2008). One critical ecological concern, particularly of 

resource agencies and nongovernmental organizations (NGOs), is whether or not offshore wind 

turbines could entail a tipping point for fragile populations of marine animals and birds as well as 

ecosystems (NSF 2009). Several potential scenarios outline the additive role of stressors in 

altering the health of the ecosystem. Ecosystems, however, are complex. Eliminating one species 

could supply habitat for another competing species to occupy that niche. In turn, the ecosystem 

may still function as previously or change depending on that organism. In some areas, offshore 

wind farms have increased local biodiversity by acting as artificial reefs (Fayram and de Risi 

2007; Petersen and Malm 2006). Wilson and Elliott (2009) argue that building habitat and 

possibly increasing ecological carrying capacity could be a means for mitigation. Careful 

attention should be paid, however, to the actual physical and chemical make-up (e.g., gravel, 

rocky outcrop, seagrass beds) of the habitat lost. 

8.2.1 NEPA-Related Approaches

Physical, biological, and social areas of risk uncertainty have been identified with offshore wind 

energy development and have been the focus of well-established studies in Europe. Studies are 

also beginning in the United States, within both the Bureau of Ocean Energy Management, 

Regulation, and Enforcement (BOEM; formerly the Minerals Management Service [MMS]) and 

state governments. For example, the Cape Wind FEIS has volumes of original survey work that 

are good overviews of the potential physical and biological effects (MMS 2009a). The New 

Jersey Department of Environmental Protection (NJDEP) recently completed almost 2 years of 

avian, turtle, and mammal surveys in areas related to offshore wind, and a final report was 

released in the summer of 2010 (NJDEP 2010). 

As Section 7 explains, both the European and North American approaches to assessing offshore 

wind development risks are driven primarily by the requirements of permit applications and 

agency consultations, along with NEPA compliance. The expert community is learning that 

NEPA may require extensive data collection because of gaps in the knowledge base. Further, the 

data that do exist may not be sufficient to assess fully the risks or gain public acceptance, even 

though public hearings and comments are required as part of the process. More consistent 

engagement and analysis of stakeholder and decision maker views will have to complement the 

formal NEPA compliance requirements, as learned through the Cape Wind process and other 
171

energy technology siting. As summarized in Section 8.5, European experiences with strategic 

environmental assessments, analogous to the U.S. Programmatic Environmental Impact 

Statements (PEISs) and regional EISs, have already been important learning opportunities for 

North America. Extensive preconstruction surveys required to compensate for knowledge gaps 

and large uncertainties will be moderated or reduced as we better define the potential risks in 

comparison to other activities in the marine milieu.

Figure 8-1 demonstrates a sector-by-sector impact approach oriented to offshore wind farm 

activities, including siting, construction, operation, and maintenance. The critical first and final 

stage activities (i.e., planning, siting, and decommissioning) were added to the original graphic to 

show the life-cycle approach for any project. Although the two columns listing possible “effects” 

and “responses” is relevant for NEPA related analysis that focuses on sector specific impacts, 

(i.e., noise, ship traffic) some important factors are still missing due to the complexity. This 

limits the utility of this approach for understanding ecosystem-based or societal effects from 

offshore wind deployments. Figure 8-1 does not examine the probabilities of these effects 

occurring, quantification or magnitude of effects, and major uncertainties. These are the factors 

needed to capture the actual risks and benefits of wind. 

This figure as well as the NEPA-related approach for evaluating potential impacts of offshore 

wind energy facilities focus on sector-by-sector assessments of the proposed action, including an 

EIS or environmental assessment (refer to Section 7), or a permit application prepared by a 

government agency or a private developer or both. Perceptions of significant risks relate to 

important but narrow agency regulatory missions such as the Migratory Bird Treaty Act 

(MBTA), where even one bird collision is forbidden by statute. An integrated risk approach, by 

contrast, which integrates scientific knowledge and comparative data with risk assessment and 

management, gives a wide spectrum of decision makers and stakeholders the analyses needed for 

making decisions and mitigating potential risks that are relevant. Such an integrated knowledge 

base serves as a systematic overview of the major ecological, human health, and socioeconomic 

risks.
172

Source: Adapted from Gill 2005.

Figure 8-1. Offshore wind farm activity and socioeconomically relevant interactions

BOEM classified impacts related to NEPA analysis from negligible to major, as shown in Table 

8-1 and applied to the Cape Wind EIS (see Appendix B). This classification, however, also does 

not produce essential data about probability or uncertainty of the potential effects. This approach 

may also confuse severity and magnitude of the risk with irreversibility. In other words, although 

complying with the NEPA rules is central to responsible offshore wind deployment, both NEPArelated approaches do not address the fundamentals of whether the potential risk is one that is 

likely to occur and create a real concern to a receptor or whether it is an unavoidable trivial risk. 

These are the details that concern the resource agencies and the coastal communities, but could 

be addressed systematically and quantitatively by a risk analysis approach. Indeed, it is exactly 

for these considerations that the methods and analysis of risk assessment were created.
173

Table 8-1. Classification of Impacts in a NEPA 

Document

Classification Environmental Societal

Negligible Not measurable Not measurable

Minor Avoidable with 

proper mitigation; 

removal would 

allow complete 

recovery of 

affected source; 

potentially 

unavoidable

Avoidable with 

proper mitigation; not 

disruptive to routine 

functions of 

community; removal 

of impact would allow 

for complete reversal

Moderate Unavoidable; 

some permanent 

impacts; affected 

resource viable; 

potentially 

complete recovery

Unavoidable; 

impacts reduced via 

mitigation; 

adjustment by 

affected community; 

potentially complete 

reversal

Major Unavoidable;

affected resource’s 

viability 

threatened; 

incomplete 

recovery

Unavoidable; 

impacts reduced via 

mitigation; 

unacceptable 

disruptions; 

incomplete reversal

Source: MMS 2009a.

8.2.2 An Integrated Risk Framework

Ever since the 1983 publication of the National Research Council’s Risk Assessment in the 

Federal Government: Managing the Process, federal and state agencies as well as many global 

corporations have widely applied risk assessment and integrated risk frameworks to a range of 

environmental and health issues. A well-established set of tools and methods comprise an 

integrated analytical approach for assessing potential problems and making decisions related to 

technology deployments (NRC 1983). Risk assessments can also serve as a focal point for 

cooperation among local communities and state and federal government agencies. Further, they 

can build the knowledge base and approaches for determining how safe is “safe enough” and

identify the major trade-offs among different technology and policy choices. For offshore wind 

energy deployments, risk assessment can help determine the level of seascape impacts to marine 

habitats that might be considered tolerable and how wind energy risks could be balanced with 

climate change benefits and risks associated with conventional energy development. 

Well-executed risk assessments also can identify major divergences between public perceptions 

and expert judgments. A wealth of literature is available on risk paradigms (NRC 2005; Gregory 

2002; NRC 1996) and ecological risk assessments and their application to an array of health 

threats and environmental problems (NRC 2008b). A recent National Research Council (NRC 
174

2009c) review of risk assessment practices lists 53 U.S. Environmental Protection Agency (EPA)

reports on risk assessment and their regulatory programs. Risk analyses have been applied to 

numerous other industries, including nuclear power, chemical and heavy metals industries, food 

safety, and aviation. 

An integrated risk framework is, fundamentally, a logic structure that sets the stage for assessing 

a spectrum of potential areas of risk associated with deploying gigawatt-scale renewable energy 

supplies across the national landscape. Risk assessment informs decision making but does not 

serve as the sole basis for making decisions. Such decisions always involve a range of issues—

such as siting strategies, technology developments, and industry workforce needs—that may be 

important.

Beyond technical issues, the “values” placed on wildlife and habitats are complex and must be 

assessed across an array of stakeholders and communities and within the regulatory statute. This 

is not a step-by-step process, and it does not reflect a linear scientific process for solving a 

problem. An integrated risk framework is a set of interactive logical steps that allow for feedback 

loops. As a number of NRC reports, particularly Understanding Risk (NRC 1996), have 

described, the interactive nature of this framework shows that stakeholder involvement and 

public perception are critical at every stage of assessment, deliberation, decision making, and 

implementation. 

An integrated risk framework gives federal, state, and local decision makers and their 

stakeholders a common ground for analyzing and managing risks and devising policies and 

effective siting strategies. This approach is a “big picture” analysis of how the various scientific 

and analytical pieces fit together at any site or region—or indeed, at the national coastal and 

marine spatial planning level—and how the potential environmental and social effects in one 

area compare with those at other sites and with different technologies. By integrating fragmented 

research sectors, decision makers and stakeholders are better able to evaluate candidate sites that 

reflect the complex risk challenges. 

Figure 8-2 shows an example of an integrated risk framework that could be applied to the 

decision problem of evaluating how gigawatt-level offshore wind energy could be part of a 

national energy strategy and build a knowledge base to support this decision. Of course, no risk 

assessment would include a detailed analysis of every box in the diagram, but the diagram does 

show a systematic framework for the range of questions or potential concerns arising from siting 

decisions across the country. Defining the “decision problem” could be applied to large scale 

deployments or a choice between wind and another energy supplies or to a specific project or 

site.

8.2.2.1 Tier 1: Sector Risk Analysis

Sector risks (e.g., wildlife, habitats, oceans and land use) will, of course, vary depending on the 

specific technology deployed, the specific site considered, the scale of the deployment, and the 

stakeholder concerns at particular locations. The essential difference with the previous analytical 

approaches in Figure 8-1 and Table 8-1 is that the integrated risk framework summarizes for 

each sector risk quantitative data on the probability of occurrence, the magnitude of the 

consequences by sector, and major uncertainties. As demonstrated by European offshore 

projects, risk challenges are very site specific, and this makes it difficult to determine where and 

when potential problems may arise. A broader overview may ensure that significant risks or 

public perceptions will not be missed. Specific “tools” or metrics are applied to each sector risk 
175

(e.g., radar for avian risks and tracking migration patterns for habitat risks). The next step is “risk 

characterization and uncertainty analysis.” The sector risk characterization and uncertainty 

summary provides an overview of the risks and compares them across sectors to evaluate what 

might be the least or the most significant. Details about the current knowledge base of sectoral 

risks have been gained mostly in Europe and, accordingly, the evidence is presented in Section 

8.5.

8.2.2.2 Tier 2: Extended Risk Analysis

Moving down the Figure 8-2, the framework then supports an “extended risk analysis” by 

broadening the number of issues assessed, such as infrastructure issues (e.g., transmission) and 

life cycle risks. This is a proactive approach to the complex issues related to siting new energy 

technology options as well as transmission siting. It is beyond the scope of this technical 

assessment to address all of these important issues in detail, but three areas of the extended risk 

analysis are briefly described, as illustrations of the types of analysis eventually needed: lifecycle risks, cumulative risks, and public concerns.

8.2.2.3 Life-Cycle Risk

Every potential wind energy site has a unique set of potential risks and benefits, given the 

geographic diversity across coastal cities and states—navigation could be the principal problem 

at one offshore wind site and recreational use conflicts might be the principal concern at other 

locations. This is a challenge that all energy supply options face, and so analysis is needed across 

risks and sites to identify both the principal problem areas and the benefits.

The wind turbine life cycle (manufacturing, transportation, planning and construction, 

operations, monitoring, maintenance, and decommissioning) has fewer environmental risks than 

conventional energy generation because impacts are primarily temporal and localized. Life-cycle 

assessments show that the wind energy manufacturing and construction phase generates the 

largest risks owing to raw materials production and components assembly. This phase accounts 

for approximately 85% of emissions (NRC 2009). The operations and maintenance phases are 

not considered significant because electricity production from wind energy operations does not 

produce emissions. Further, these processes take place only once during a turbine’s life, and so 

their impacts have been estimated to be relatively small (Tester et al. 2005). Because of these 

one-time life-cycle effects, wind energy appears to hold substantial promise for reducing carbon 

dioxide (CO2) and other harmful emissions that pose ecological and health risks. A 2007 study 

by the National Academies of Science (NAS) estimated that wind energy would offset the 

amount of CO2 produced in national electricity generation by 4.5% by 2020 (NRC 2007), based 

on the U.S. Department of Energy (DOE) scenario of future wind energy installation (DOE 

2008a). 
176

Source: Ram 2009.

Figure 8-2. A framework for integrated risk analysis of gigawatt-scale wind energy deployments 

The impacts to the environment from fossil-fuel energy generation result from all phases of its 

life cycle—extraction, transportation, storage, combustion, and decommissioning. This life cycle 

also means human and biological impacts as well as ecological and financial effects associated 

with importing fossil fuels, stemming, in part, from acid precipitation, ozone pollution, mercury 

contamination, and oil spills. Likewise, the life cycle of nuclear power production, albeit not 

generating carbon emissions during operation, involves long-term, large-scale, known impacts 

associated with extraction, transportation, heating and cooling, and disposal of nuclear wastes, 

notwithstanding the potential for catastrophic risks from accidents and terrorism. Offshore wind
177

has a different and likely a more benign set of impacts. The reduced impacts of offshore wind 

should be weighed against these more significant potential life-cycle effects.

Uncertainty and risk need to be evaluated in the context of different energy facilities and 

considered comparatively if the nation moves into a gigawatt-scale deployment scenario. A 

sound evaluation of the merits of offshore wind power will involve comparative analyses and 

life-cycle effects of other alternative electricity-generating facilities as well as land-based wind 

energy facilities. Several energy life-cycle assessment reports support the idea that wind impacts, 

which may still have significance, are small compared to other generating sources (NRC 2009; 

ExternE 1995). The most recent NRC report concludes that even though life-cycle damages were 

not fully quantified (in aggregate for 2009), any potential damages associated with wind turbines 

are small.

8.2.2.4 Cumulative Risks

A cumulative effect refers to those impacts that result from the incremental impacts of an action 

when added to other past, present, and reasonably foreseeable future actions. For offshore wind, 

cumulative effects comprise the combination of, and interactions between, effects from offshore 

wind farms that accumulate over time—considering background conditions already existing at 

the site in addition to social, economic, and technological interactions. Assessing cumulative risk 

is challenging because such effects:

• Are highly site-specific

• Often have a significant time lapse between the environmental change and the onset of 

consequences

• May involve interactions between ongoing natural processes and human-induced changes 

as well as altered conditions resulting from past human activities

• Are synergistic within a natural/cultural resource base in which different types of 

potential changes may create unexpected effects.

Defining (or bounding) the extent of the problem is a first-order challenge that has to be analyzed 

within NEPA and by other environmental assessment research. In European waters, marine 

spatial planning is beginning to take hold to account for the potential cumulative effects of 

multiple projects. Bounding the extent of this uncertainty and the threshold—or assessing the 

point at which the effect becomes significant—is an important yet difficult task. Regulators face 

challenges in considering the cumulative effects that offshore farms may have within the context 

of other developments and uses of the ocean—such as bird migratory corridors, commercial 

fishing by-catches, recreational boating, electric power needs from renewable resources, and 

safety. As these assessments are made, they should take into account the current limitations in 

the United States in experience with and understanding of offshore wind energy. Such 

assessments need to be regularly updated as the risk research program evolves and additional 

monitoring results become available. Cumulative-effect research is in its infancy in Europe, 

although there have been attempts to develop assessment approaches. One suggested approach to 

assessing risk levels to species or natural resources is to compare risks at the “end of the 

pipeline” to the initial impacts on those species or resources.
178

8.2.2.5 Public Concerns

Wind turbines are simultaneously an old and a new technology. In general, people understand 

what windmills look like and how they work. The wind machines that generate power today, 

however, are substantially different from those of the past. The transformation of this technology 

along with a wider geographic diversity of sites has generated changing perceptions and 

reactions from communities across the nation. Various public entities see both benefits and risks 

associated with deploying offshore wind energy. The most careful analysis of this in the United 

States is the Cape Cod study Firestone and colleagues conducted in 2005 (Firestone and 

Kempton 2007; Firestone et al. 2005). The authors found that the majority of the sampled 

population expect negative impacts. The most frequently given factors influencing their position 

(beginning with the most frequently cited) were aesthetics and impacts on the local fishing 

industry, recreational boating, property values, environmental impacts, tourism, and electricity 

rates. Supporters of the then-proposed development are generally younger and have at least some 

college education, whereas those opposed are more likely to earn more than $200,000 per year 

and expect to see the turbines in their daily routine.

Scale may also be a relevant issue. The Firestone and Kempton study found a 32% increase in 

support for the Cape Wind project (including a 19% increase by opponents) if it becomes the 

first of 300 such offshore wind developments around the country (Firestone and Kempton 2007; 

Firestone et al. 2005). They also found that that 60% agreed that a larger deployment of offshore 

wind power would contribute to U.S. energy independence, but only 30% of respondents felt that 

it would help stabilize global climate change. From these findings, the authors call attention to 

the need for stakeholders to better recognize these substantial benefits from offshore wind 

development to overcome their concerns about potential, site-specific, adverse environmental 

effects. 

A well-documented pattern emerges: the core of opposition to wind energy development is the 

environmental community, and the primary issues of contention are potential environmental 

impacts (Pasqualetti 2004). Firestone and Kempton (2007) found that anticipated environmental 

effects were the most important drivers for both support and opposition of Cape Wind (MMS 

2009a; see Appendix B for more details). According to previous technological controversies, 

project acceptance in the end is not always an issue of majority support. A committed and wellconnected opposition has a strong ability to act as a veto group in society, regardless of the 

merits of a new project.

Early stakeholder involvement and better understanding of social effects are essential as more 

projects are proposed and sited along coastal communities. “The timing of risk communication 

entails a difficult tradeoff between the social imperative to inform without delay and the need for 

full scientific information and analyses” (Kasperson 1986). Beyond the public involvement 

procedures required under the NEPA regulations, a carefully conceived and ambitious public 

education program is essential. Wind power projects may bring a sense of town pride and energy 

independence, which would have significant qualitative benefits at the individual and community 

levels. It should also be recognized, however, that the issue may pit community residents against 

each other. For large-scale wind developments, nearby communities will serve as staging areas 

and be subjected to developmental activities. Commercial-scale wind projects may bring job 

benefits but, at the same time, alter the traditional character of the community and its relationship 

to marine activities. Thus, even where net regional benefits are realized because of wind energy 
179

development, self-perceived “winners” and “losers” may appear at the local level as a result of 

that development.

8.2.2.6 Climate Change

As noted previously, a 4.5% reduction in carbon would appear to have major implications that 

could reduce the ecological effects from climate change estimated by the four Intergovernmental 

Panel on Climate Change (IPCC) assessments and examined by the U.S. government and 

research institutions (NRC 2010a, 2010b; Karl, Melillo, and Peterson 2009). DOE estimated that 

the U.S. electricity sector could avoid 825 million tons of CO2 by integrating 20% wind energy 

(including 54 GW of offshore wind) into the U.S. electricity system by 2030 (DOE 2008a). 

Moreover, the adverse effects of global warming estimated by IPCC in its four assessments (e.g., 

IPCC 2007) involve ecological and social impacts that far outweigh the risks associated with 

wind energy. The benefits of wind energy in mitigating climate change and other energy issues 

need to be considered together with the negative impacts in estimating and comparing risks 

involved in different energy sources (NRC 2010).

8.2.2.7 Comparative Analysis and Determining Risk Tolerability

With the two tiers of risk assessment in place, including all the boxes from “sector risk analysis” 

and “extended risk analysis” in Figure 8-2, comparisons and risk tolerability decisions can now 

be made. This critical step places the estimate of risk from offshore wind energy in the context of 

other known risks and establishes priorities (Davies 1996). In general, the most appropriate 

comparative risk assessments of wind energy development come from analyzing risks associated 

with other energy generation sources. A recent U.S. study discusses the challenges of applying

comparative risk assessments to energy choices and notes the importance of this analytical 

framework for future decision making (NRC 2007). Beyond comparisons to the impacts from 

other energy sources, a valuable perspective on the scale of impacts can be gained from 

comparisons with other impacts. For birds, for example, it can be informative to examine bird

collisions with wind turbines within the national context of other stressors on various water 

birds, including by-catch from fishing and loss of habitat from coastal development (FWS 2002; 

Erickson et al. 2001). In this case, extrapolating bird fatality rates from existing land-based wind 

farms for a projected wide-scale national deployment plan—even using conservative numbers—

would give some sense of the potential magnitude of avian death risk. Of course, these 

estimations should be augmented by species-specific and localized effects as well as population 

impacts. In addition, given the significant uncertainties surrounding many environmental and 

health problems, comparing the risks helps prioritize which uncertainties require most urgent 

attention and resources and how scarce dollars to support needed research can best be allocated. 

Comparative analysis is at the heart of effective assessment and decision making. Integrated risk 

assessment gives capabilities not present in the required NEPA-related list making. 

8.2.2.8 Tier 3: Management Options and Strategy

Following the comparative analysis, the next tier in Figure 8-2 involves various “management 

options and strategy.” To provide some insight into these analyses, two areas will be addressed 

below, including “risk research prioritization,”“siting strategies, and “adaptive management.”

The various stages of deploying an offshore wind farm—planning, siting, installing, operating, 

and decommissioning—all have risks. But these risks need to be placed within a proper context. 

As stated previously, environmental risks can occur at any stage, but it is the construction phase 
180

that generates the largest temporal impacts. Because wind energy is not subject to catastrophic 

risks as are other fossil fuel and nuclear energy supply technologies, best management practices 

and mitigation strategies may be useful for managing current risks and uncertainties with wind 

energy.

Without an integrated approach, states and regions are susceptible to prioritization of risk 

impacts based on legal or regulatory drivers rather than actual impacts to communities or 

ecosystems. Some example drivers include the MBTA, the experience at the last site of 

deployment (e.g., radar interference), or the complexities of protecting endangered species (e.g., 

Indiana bats, whooping cranes). All of these issues trigger sensitivities within the communities 

that are responsible for managing these risks, but it is a commonly used reactive approach. This 

approach allocates resources to one issue at a time without assessing the actual level of 

ecological or human risks. The wind turbine studies conducted to date have substantially 

enlarged our knowledge base of some land-based sector risks (e.g., bird and bat collisions, radar 

interference, and property values) but have not made much progress measuring uncertainties 

analyses and developing comparative frameworks.

A major finding is that risk research prioritization can fill gaps in the knowledge base and define 

the uncertainties that surround the risk problems at stake. Important considerations are involved:

How much can the risk be reduced through further research and in what timeframe? How deep or 

removable are the uncertainties? Do uncertainties arise from data needs, modeling, or the lack of 

adequate scientific understanding of the risk phenomena? Most important, how do the 

uncertainties interact with the significance of the risk? Where will further research and 

assessment to reduce uncertainties most contribute to reducing overall risk and a more informed 

decision making process (Ram 2009)?

8.2.2.9 Siting Strategies

A robust siting policy is needed for industry decisions about the wind resources and costcompetitiveness. It would consider competing uses of the ocean and community concerns. A 

well-conceived siting policy would avoid coastal areas with intense competing uses and sensitive 

habitats. The CEQ-led national policy is to develop coastal and marine spatial planning 

guidelines to assist in the sustainable development of the U.S. oceans. Further, the National 

Oceanic and Atmospheric Administration (NOAA) and BOEM are developing a Multipurpose 

Marine Cadastre to produce maps and geographic information system (GIS) tools to support 

marine spatial planning and avoid use conflicts. A well-developed literature database exists on 

siting controversial facilities and should be taken into account in future wind energy siting 

decisions (Kunreuther, Susskind, and Aarts 1991). 

Regulations will need to allow for an efficient process for permits and approvals that allows 

timely reviews of applications and a reasonable level of flexibility to support this new industry. 

Moreover, siting policies will need to reflect the sensitivities of competing and complementary

uses of the ocean to multiple stakeholders. As yet, siting considerations in wind energy 

development have largely centered on relevant technical issues concerning the areas of 

substantial wind resource availability and the potential for connection to the energy grid. Moving 

from the current 1%–2% of the energy supply to 54 GW by 2030 requires a broader, more robust 

approach to wind plant siting. Siting strategies must go beyond narrow technical appraisals of 

sites to include collaborative approaches with potential host states and communities. Well-
181

developed risk communication and stakeholder involvement programs will be essential. In 

certain circumstances, a regional approach with federal policy support will be necessary.

8.2.2.10 Adaptive Management and Monitoring Programs

A prudent, yet flexible, deployment strategy will need to integrate monitoring with adaptive 

management approaches and risk mitigation strategies identified through the NEPA process 

(DOI 2008; Williams, Szaro, and Shapiro 2007). The research approach will need to be one of 

learning through experience—it must also flexible enough to easily accommodate and integrate

new information and improved risk knowledge as it becomes available. This approach can be 

designed to involve universities and NGOs that function as centers of excellence in various 

regions. The United States can learn from European Before and After Construction Impact 

(BACI) study methods applied to several offshore wind plants. Cumulative effects will need to 

be considered within the context of a comparative approach relative to other energy sources. An 

integrative approach is needed to allow current techniques and methods to be used in a context of 

uncertainty, with an understanding that the onset of a serious unanticipated impact may require 

significant modifications to a project’s site or design. 

Our experience tells us that “obvious” impacts of today at particular sites may not actually be, 

and often are not, the showstoppers of tomorrow. A more systematic assessment that 

incorporates principles of adaptive management would allow a better understanding of the 

probabilities of impacts or consequences at widely separated sites and diverse marine 

environments—from the Great Lakes fresh water to the warm waters of the Gulf and across to 

the Mid-Atlantic. Estimating probabilities of the risk occurring may be just as central as the 

possible magnitude of the impacts and consequences. It also is a systematic approach to 

comparing risks, assessing priorities, and formulating management strategies rather than reacting 

to the fear of uncertainty or what a special interest group finds resonates with their constituency.

8.3 Sectoral Risks: Considering the European Experience

After the European Union (EU) committed to the Kyoto Protocol and reducing greenhouse gas 

emissions in 2002 (UNFCCC 2010), several nations began comprehensive energy-planning 

exercises to evaluate how wind power could contribute to this new renewable energy pathway. 

Offshore wind projects have been deployed and are planned off the coasts of Denmark, Sweden, 

the United Kingdom, Netherlands, Germany, Finland, and Ireland. More deployments are 

anticipated off the coasts of Spain, France, and Belgium in the next few years (EWEA 2010; see 

also Section 3). 

The early experiences of these countries offer valuable lessons about offshore wind power

development (see Table 3-2). But they can only serve as guidelines rather than blueprints in the 

United States because of the differences between economic, political, biological, and 

geophysical conditions. Using mechanisms such as financial incentives, policy constructs, and 

streamlined permitting requirements, European nations are increasing their offshore wind

development. For offshore wind developments, the EU requires extensive environmental impact 

assessments similar to the EISs required for NEPA compliance for any U.S. major development. 

European planning for offshore wind energy has thus involved setting specific deployment

targets, devoting significant resources to preparing strategic environmental assessments, 

mapping specific development sites using GIS , performing multiyear field studies, and 

instituting BACI analyses for demonstration programs.
182

Scientifically rigorous BACI studies track changes in the marine environment and follow the 

project from conception to turbine installation to monitoring during operation and maintenance. 

The design includes pre- and postconstruction studies to examine changes in behavior and 

abundance of a target species, and other temporal and spatial ecological measures associated 

with an impact. 

Table 8-2 summarizes the offshore wind farm studies conducted in Europe. Important lessons

learned from these studies include:

• Methods and technologies to measure changes in marine resources from the effects of 

construction, operation, and maintenance

• Lessons about what worked and what did not work in pilot baseline investigations and 

monitoring programs

• Indicators of significant environmental and socioeconomic effects that can be used to

establish study priorities early on, ensuring limited resources are used cost-effectively

• Methods for determining cumulative effects of marine activities

• Analytical tools for strategic site assessments to help determine the amount of ocean 

space suitable for offshore wind developments and to screen for potential conflict of use

• Techniques for encouraging public involvement and accessing public response and 

acceptance.

Through these studies, Europe has accumulated a body of evidence regarding the potential 

environmental impacts from an offshore wind project, because wind farms have been operating 

in the waters of Europe since the early 1990s. Several early comprehensive studies were 

sponsored by the EU, including Concerted Action on Offshore Wind Energy in Europe (CAOWEE) and Concerted Action for Offshore Wind Energy Deployment (COD). In 2005, COD 

compiled the available studies in a searchable electronic database and summarized the findings 

in a final report, stating that “the COD work on the establishment of an environmental body of 

experience has brought an important overview of the present state of knowledge in this up to 

now unknown field” (COD 2005). Also, two Greenpeace International reports that summarize 

environmental impact assessment studies in Europe were prepared by Deutsches Windenergie 

Institute (Greenpeace International 2005) and Deutsche WindGuard GmbH (Greenpeace 

International 2000). The Danish government instituted another comprehensive study approach, 

along with their utility partners/developers, DONG Energy (formerly Elsam Engineering and 

ENERGI E2), for the offshore demonstration projects Horns Rev and Nysted; this approach used 

BACI methods as well as multiple scientific and stakeholder review committees (DONG Energy 

et al. 2006).

Since 2005, European nations have invested millions of dollars in research priorities targeted to 

areas with large deployment goals and projects installed. Many of these larger, national studies 

have been separated into individual sector analyses, which have gone through the peer-review 

process and have been published in scientific journals. Peer review of study design and results 

enhances the credibility of the study. In some cases, however, studies are prepared by the 

developer and do not undergo rigorous peer review. A rigorous process of gathering evidence 
183

builds public confidence in the research and assessments being conducted as well as in the 

results.

Since the passage of EPAct 2005 and the beginning of the offshore regulatory program, U.S. 

government agencies looked at the results of these European studies and initiated several sitespecific studies, particularly along the Atlantic coast. As the only completed EIS on offshore 

wind energy in the nation, the Cape Wind EIS establishes some precedent for assessing 

environmental and societal impacts, but this is an evolving area of development (see Appendix B 

for a detailed summary of the EIS findings). In the last several years, state governments have 

also begun to prepare baseline studies to support their planning processes and build a knowledge 

base (Table 3-4 in Section 3 summarizes these studies). Also, BOEM has supplemented its 

environmental studies program, historically focused on oil and gas in the Gulf region, to add 

regions with potential offshore wind deployments. A sampling of these projects includes the 

following, and a more complete list is available at 

http://www.gomr.mms.gov/homepg/regulate/environ/studiesprogram.html. As the list shows, 

social and community issues remain understudied: 

• Determining Night Time Distribution of Long-Tailed Ducks Using Radio Telemetry

• Effects of Pile Driving Sounds on Auditory and Non-Auditory Tissues of Fish

• Compendium of Avian Information and Comprehensive Geodatabase

• Energy Market and Infrastructure Information for Evaluating Alternative Energy Projects for 

OCS Atlantic and Pacific Regions

• Evaluation of Visual Impacts on Historic Properties

• Meteorological and Wave Measurements for Improving Meteorological and Air Quality 

Modeling

• Potential for Interactions between Endangered and Candidate Bird Species with Wind 

Facility Operations on the Atlantic OCS.
184

Table 8-2. Summary of European Large-Scale, Multidisciplinary Studies of the Environmental 

Effects of Offshore Wind Farms

Program Involvement Study Location Areas of Focus

Danish Monitoring 

Program

http://www2.dmu.dk/Atmosp

hericEnvironment/aq_besk/b

op.htm

Denmark—University, 

industry, government, 

and other stakeholders

North Sea Determine effects on 

marine environment,

including mammals, 

fish, birds, artificial 

reefs, 

socioeconomics, noise 

emissions, 

temperature gradients, 

benthic fauna, public 

issues, 

electromagnetic fields

Research at Alpha 

Ventus (RAVE)

http://rave.iset.unikassel.de/rave/pages/welco

me

Germany—Federal 

Ministry of Environment

North and Baltic 

seas

Assess effects on 

marine environment, 

evaluate standards for 

environmental impact 

assessments, study 

marine mammals, 

birds, fish, and 

benthos

BeoFINO Ecology of 

Benthic Organisms 

and electromagnetic 

fields (BeoFINO)

http://www.offshorewind.de/page/index.php?id=

11631&L=1 )

Germany—Federal 

Ministry of Environment

North and Baltic 

seas

Determine effects on 

marine environment 

and develop methods 

and criteria to analyze 

danger to life and 

habitats

FINO 3

http://www.fino3.de/joomla1

5/index.php?option=com_co

ntent&view=article&id=169&

Itemid=357

Germany—Federal 

Ministry of the 

Environment

North Sea Established three 

offshore research 

platforms, noise 

emissions

Mechanisms to Protect 

Nature and 

Environment

http://www.offshorewind.de/page/index.php?id=

11633&L=1

Germany—University of 

Berlin

North Sea Adapting Strategic 

Environmental 

Assessment (SEA), 

environmental impact 

assessments, and 

Habitats Directive to 

the offshore 

environment

Impact on Marine 

Endotherms (MINOS)

http://www.wattenmeernationalpark.de/themen/min

os/minos_en.html

Germany—Federal 

Ministry of Environment

North Sea Habitats, migratory 

routes, hearing, and 

sensitivity of 

porpoises, seals, and 

sea birds

Offshore Wind Energy 

and Environmental 

Protection Forum 

(FOWEUM)

http://www.offshorewind.de/page/index.php?id=

11640&L=1

Germany—Ministries, 

state governments, 

environmental groups

North Sea Support exchange of 

information and build 

consensus on 

environmental 

protection and nature 

conservation
185

European studies as well as the Cape Wind EIS have identified critical areas of potential impacts 

and areas where the potential outcomes are not well known. These are the priority topics for 

discussion in this section: 

• Avian impacts

• Acoustic impacts to marine mammals

• Impacts on fish and benthos communities

• Electromagnetic fields

• Visual effects

• Ship collisions

• Other socioeconomic effects.

As mentioned elsewhere, other risks that are not included here, such as noise impacts to workers, 

radar interference, military uses of the ocean space, and cultural resource impacts, need further 

examination.

8.4 Avian Risks

Figure 8-3 shows the potential effects of offshore wind farms on birds. The major risks from 

offshore wind turbines to sea birds and resting birds include:

• Collisions and mortality

• Physical habitat loss from displacement

We@Sea

http://www.we-at-sea.org/

Netherlands—Industry, 

environmental, and 

university

North Sea Siting and 

environmental issues, 

impact assessments

Far and Large 

Offshore Wind (FLOW)

http://www.flow-windpark.nl/

Netherlands—Industry, 

university, and other 

stakeholders

North Sea Environmental issues

Collaborative Offshore 

Wind Research Into 

the Environment 

(COWRIE)

http://data.offshorewind.co.u

k/

United Kingdom of Great 

Britain and Northern 

Ireland—Government, 

industry, university, and 

other stakeholders

Irish and North 

seas

Marine mammals, 

birds, cultural, 

soundscape, fish, 

shellfish, benthos, 

data, and radar 

Department for

Business, Enterprise, 

and Regulatory 

Reform (BERR) 

http://www.berr.gov.uk/ and 

Department of Energy 

and Climate Change 

(DECC)

http://www.decc.gov.uk/en/c

ontent/cms/what_we_do/uk_

supply/energy_mix/renewabl

e/policy/offshore/offshore.as

px

United Kingdom and 

Northern Ireland

Irish and North 

seas

Marine spatial 

planning, stakeholder 

dialogues, strategic 

environmental 

assessment, public 

perception surveys of 

awareness and 

attitudes
186

• Visual stimulus/avoidance response and barrier effects, including fragmentation of the 

ecological habitat network (e.g., migration pathways, breeding or feeding areas).

Source: Energetics, Fox et al. 2006

Figure 8-3. Potential effects of offshore wind farms on birds

Of these risks, assessments suggest that collisions and barrier effects (disturbance) could have 

the largest impacts on sea birds and resting birds (COD 2005). In most cases, bird collisions with 

offshore wind turbines are only a minor problem (Greenpeace International 2005). A key 

concern in the topic of avian risk, however, is the potential harm done to endangered species, 

where the loss of one individual could have a measurable impact. Quantitative risk estimates for 

collision, however, are difficult to calculate for several reasons:

• Results are highly site specific and therefore can often appear contradictory (Desholm 

and Kahlert 2005).

• Inadequate data exist on bird migration routes and flight behavior (Exo, Hüppop, and 

Garthe 2003).

• Impacts vary for different bird species.

• Measurements account only for bird carcasses that are found.

• The range of methods includes thermal imaging, microphone, and visual observations.
187

• There may not be a direct correlation between pre- and post-construction avian presence.

Several offshore facilities studies suggest minimal or no significant impacts on bird life from 

offshore wind farms (CA-OWEE 2001). Precautionary risk reduction and mitigation measures 

are available to reduce potential risks from wind turbines, including:

• Monitoring and understanding transient and resident bird behaviors

• Siting in areas with lower activities (e.g., avoiding high-density and migratory waterfowl 

areas, breeding areas, and migratory areas of species of concern) 

• Reducing the potential for cumulative effects through careful monitoring and siting.

In contrast, relatively high collision mortality rates have been recorded in isolated instances at a 

few poorly sited, land-based wind farms in areas with large concentrations of birds such as 

Altamont Pass in California and Tarifa in Spain (BirdLife International 2003). A recent 

presentation at the IEA Wind Task 28 meeting in October 2009 summarized the latest avian 

research from land-based wind studies (Strickland 2009). Individual projects affected individual 

birds rather than populations after informed siting and other impact reduction measures were 

taken. No studies documented detrimental effects to birds as a result of wind farm lighting. For 

offshore wind, a recent study of 1.5 million migrating seabirds from Swedish wind farms in 

Kalmarsund concluded that the fatality risk was only 1 in 100,000 passing seabirds (Pattersson 

2005). Offshore wind farms in the United States would most likely be placed along the eastern 

coast in the Atlantic, in the Great Lakes, and in the Gulf of Mexico, which are all part of major 

flyways for hundreds of thousands of migrating birds (Figure 8-4). The USFWS estimates that 7 

to 10 million birds use the Mid-Atlantic to North Atlantic shoals areas.

Source: http://www.fws.gov/migratorybirds/NewReportsPublications/flyways.html; Michael A. Johnson, North Dakota Game 

and Fish, photographer 

Figure 8-4. Biological flyways through the continental United States
188

A recently published study of sea birds at offshore wind farms near Blyth, England, found that 

numbers of Cormorants (Phalacrocorax carbo) decreased after construction, but numbers of 

Terns (Sterna sandvicensis) and Great Black-backed Gulls (Larus marinus) increased (Rothery, 

Newton, and Little 2009). Further, in 352 hours of observation, no collision mortality was 

observed and most seabirds flew below blade height. Hüppop et al. (2006) reported considerable 

variation in migration intensity for birds migrating over the North Sea and most collision 

mortalities as assessed by dead birds on the platforms (586 total from 2003–2006) were 

Thrushes. Nonsong birds represented 2% of the mortalities (Hüppop et al. 2006). This study also 

concluded that rain and wind gales probably increased the incidence of collisions. 

In Denmark, radar studies have shown that migrating birds largely avoid flying through the 

Nysted wind farm. These studies revealed that 35% of the birds flew through the area before 

construction, but only 9% flew through following construction, although individual behavior is 

somewhat species specific. Environmental monitoring at the Horns Rev I wind farm in Denmark

by DONG (Elsam Engineering and ENERGI E2 2005) following the first year of operation

found that most bird species also exhibit avoidance behavior, which may reduce the probability 

of collisions with the wind turbines (Figure 8-5).

 Source: DONG Energy et al. 2006.

Figure 8-5. Eider distribution at Horns Rev
189

Despite these relatively comprehensive studies, there are still questions about the length of time 

needed to assess bird activity before construction. Preconstruction avian studies should be 

balanced by comparable post-construction avian studies. For example, the avian studies at the 

offshore wind farms near Blyth, England, began 26 months before turbine construction, 

continued through construction, and lasted 32 months after construction (Rothery, Newton, and 

Little 2009). Further, a recent presentation by the FWS suggested that 3 years of studies for shoal 

areas may be required to adequately assess the resident and migratory bird populations.

The avoidance behavior of birds is highly site and species specific. Although avoidance can 

present other risks related to habitat loss and greater energy consumption of the species because 

of longer flight paths, this behavior could also reduce the probability of collision risks. A 

postconstruction survey conducted at Horns Rev I found that habitat loss for the common scoter 

caused no change in activity, and a second survey in 2006 observed large numbers of the 

common scoter in the wind farm. These observations illustrate that long-term monitoring is often 

necessary to fully track ecological shifts. Additionally, barrier effects at the Nysted wind farm, 

measured as additional energy expenditure caused by longer flight patterns around the periphery 

of a wind farm, were assessed in studies conducted from 1999 to 2005 (Masden et al. 2009; 

Petersen et al. 2006). For common eiders, the additional energy expenditure caused by avoidance 

behavior equated to about 0.5 km of extra flight distance, which is not significant compared with 

the 1,400-km migration episode.

Offshore wind plants may diminish foraging and resting opportunities for some bird species 

because of the ocean footprint. For example, Horns Rev I tower sections occupy only 

approximately 0.1% of the total wind area of the project. By comparison, land-based wind farms 

and their supporting infrastructure (such as substations and roads) generally occupy 1%–2% of 

the land (Elsam Engineering and ENERGI E2 2005). Even with the limited footprint of offshore 

wind farms, siting multiple wind farms in an area may diminish the attractiveness or suitability 

of an area to a particular species, and over time this could result in the cumulative effect of 

reducing the presence of this species in that area. Sea birds and resting birds appear to be less at 

risk of collision and habitat loss than migrating birds because they may adapt better to offshore 

wind farms because of their ability to habituate around the wind site (COD 2005).

Despite the lack of evidence to date that would suggest that offshore wind farms pose a major 

risk to individual birds or populations, this issue remains high in public and regulatory concern. 

Given the difficulty in assessing collisions at sea and the relatively large general variation in 

flocks from year to year at sites, biologists should be careful to apply BACI principles at their 

study sites and should use caution when formulating their conclusions. When designing BACI 

analysis, a great deal of effort goes into identifying suitable reference areas. Additionally, data 

must be collected on bird feeding behavior, including information on the abundance and 

distribution of prey. Precautionary measures and adaptive management principles are available to 

reduce and mitigate such risks as understood today. Some decision makers would argue that

carefully siting wind farms away from bird migratory paths, bird habitats, and large 

concentrations of higher risk species may be an effective way to minimize avian interactions 

with wind turbines. Mark Desholm, an ornithologist with the National Environmental Research 

Institute (NERI) at Arhaus University, suggests prioritizing migratory bird species for 

assessment. He states, “It will always be important to focus attention and direct the resources 

towards the most sensitive species to ensure cost-effective environmental assessments in the 

future . . .” (Desholm 2009).
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Indeed, initial reasons for excluding sites because of risk perceptions are not always the best 

reasons for site selection, as indicated by some notable case studies. For example, observations at 

the Nysted demonstration project, which is sited directly in an intensive eider migratory path, 

suggest that cautiously siting wind farms away from bird migratory pathways may not be a strict 

requirement (DONG Energy et al. 2006). Even though avian activity is abundant in the area, the 

wind farm has not posed an unreasonable risk. Another example is Horns Rev I, which is a 

habitat for harbor porpoises. If Danish developers had decided not to build Horns Rev I because 

of concerns about the harbor porpoises, they would not have explored the potential effects and 

found that the mammals still use the area as much as before the wind farm was established (C. 

Boeson, personal communication, May 31, 2007).

Nocturnal birds attracted to lighting on offshore oil platforms sometimes circle the platform for 

minutes or even hours, especially on overcast nights. One study of this behavior hypothesizes 

that birds become reluctant to leave the area of light, especially when they lack visual clues for 

orientation such as the moon and stars (Russell 2005). This nocturnal circling places birds at a

greater risk of colliding with the platform itself. Bird fatalities from collisions with oil and gas 

platforms are more common in the fall, when migrating birds fly past the facilities in hours of 

darkness. A single Gulf of Mexico platform is estimated to cause an annual average of 50 avian

deaths from collisions (Russell 2005). For offshore wind towers in the North Sea, lighting has 

been implicated as a potential cause of the increase in collision incidents during periods of fog, 

rain, or wind gales (Hüppop et al. 2006).

The Cape Wind EIS does not give definitive numbers of potential avian risk mortalities for all 

species observed during their monitoring studies because “calculating the risk of collision to 

species or groups of birds is difficult because of a paucity of information identifying exposure to 

collision” (MMS 2009a). A collision model for all bird species, however, estimated that 260 bird 

fatalities would occur annually (MMS 2009a). In addition, the FWS estimated that over the life 

of the project (~20 years), there would be 80 to 100 Roseate Tern fatalities and 10 Piping Plover 

fatalities (MMS 2009a). Both species are classified as threatened under the Endangered Species 

Act. Massachusetts Audubon (www.massaudubon.org) released their final position on the Cape 

Wind project on June 24, 2010: “Following nearly a decade of independent research and review, 

Mass Audubon has concluded that the Cape Wind Energy Project (Cape Wind) will not pose an 

ecologically significant threat to the birds and associated marine habitat of Horseshoe Shoal and 

Nantucket Sound. As an important component of our support for responsible development of 

clean, renewable energy and to reduce the worst effects of climate change, we support this 

project.”

8.5 Other Flying Animals

Bats and insect populations may also be affected by offshore wind farms. For land-based wind 

farms, bat fatalities can reach significant numbers and are a critical concern (Cryan and Barclay 

2009). As with land-based wind farms, the potential impacts to bats and insects at offshore wind 

farms include collisions as well as energy expenditures. Additionally, for insects, the wind farms 

may serve as a refuge area. Although there are no published studies on insects and offshore wind 

farms, there are some limited data on bats. It is well understood that bats migrate over water 

from landmass to landmass; however, it is not well known how they do this (Ahlén et al. 2007). 

Studies off the coast of Scandinavia found that bats were more exposed and at greater risk of 

collision when hunting insects near the upper parts of the turbines (Ahlén et al. 2007). Bats did 
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not avoid the turbines but hunted close to the turbines—they also rested on the platforms.

Hunting behavior was not influenced by blade movement, but insect hunting was observed more 

during calm weather (Ahlén, Baagøe, and Bach 2009; Ahlén et al. 2007). In general, migrating 

and foraging behaviors of bats offshore are not well understood, but as offshore wind farms are 

proposed along the coasts of the United States, there will be a need for better understanding. 

8.6 Fish and Benthos Risks

A few studies demonstrating a range of results have been published on the effects of offshore 

wind farms on the fish and benthic communities. Possible direct and indirect effects of a wind 

plant include:

• Temporary disturbance or long-term elimination of benthic communities from 

construction activities

• Changes in species composition and species numbers

• New habitat (e.g., artificial reefs, shellfish beds) serving as habitat for invasive species

• Hearing impairment in fish from low-frequency, hydrodynamic/acoustic fields from the 

wind turbines

• Changes in habitat conditions as a result of altered sedimentation and current

• Impacts to elasmobranchs and other marine species caused by electromagnetic fields 

from transmission lines. 

One study of the fish and benthic communities in a Swedish wind farm in the Baltic Sea found 

increased numbers of demersal fish and blue mussels around the turbines but lower 

concentrations of algae compared with other areas (Wilhelmsson, Malm, and Ohman 2006). 

Another study conducted on Swedish wind farms in the Baltic Sea found increases in the 

biomass of blue mussels and motile crustaceans but decreases in the biomass of algae compared 

with sites farther away from the turbines (Wilhelmsson and Malm 2008). Invasive species have 

also been documented on wind turbines in both Danish (DONG Energy et al. 2006) and Swedish 

offshore wind farms (Wilhelmsson, Malm, and Ohman 2006). 

Sounds transmitted through the water by wind farm construction, operation, and maintenance 

may also affect marine animals. A study conducted by the UK Department of Energy and 

Climate Change found that sounds generated by offshore wind turbines are in the same range of 

frequencies as those generated by existing shipping, fishing vessels, wind, and waves, and 

therefore would contribute only a relatively low background noise (during operation) to the 

preexisting noises (see Table 8-2 for a list of various anthropogenic sounds). During construction 

and decommissioning, placing and removing the monopile structures creates noise. During the 

operation phase, 20 years in most cases, offshore wind turbines produce sound through the 

movement of the rotor blades and gearbox and vibration of the structure, creating three paths for 

sound movement—through the air, water, and ground. 

Adverse effects to fish caused by noise include physiological stress such as an increase in 

cortisol, hearing impairment, and behavioral changes (Kikuchi 2009). Although a 2003 report 

from an offshore wind farm in Norgersund demonstrated no negative impacts on fish caused by 
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noise (ETNWE 2003), other studies demonstrate the opposite. Significant data gaps do, however, 

exist (Simmond and Dolman 2008). A recent laboratory study examined the swimming 

behaviors of two native species of fish (roach, three-spined stickleback) and their reactions to 

single-frequency sounds and noise generated by an offshore wind turbine in the Baltic Sea 

(Andersson et al. 2007a, Andersson et al. 2007b). The roach exhibited escape behavior and the 

three-spined sticklebacks exhibited twitching behavior (Andersson et al. 2007b). 

Table 8-3. Intensities of Different Anthropogenic Sounds 

Source Intensity

(dB re 1μPa at 1 m)

Threshold of human hearing 0

Threshold of human pain 140

Large tanker 177

Icebreaker 183

Military search sonar 230+

Ship siren at 30 m 130

Pile-driving at 30 m (Sweden) 140–>180

Pile-driving at 1 m (UK) 262

Pile-driving at 400 m (Germany) 180

Light traffic 50

Wind in trees 50

Rural nighttime background 20–40

Quiet bedroom 35

Land-based wind farm at 350 m 35–45

Car at 40 mph at 100 m 55

Jet aircraft at 250 m 105

 Source: Compiled from AWEA 2010; DOE 2008b.

The effects of electromagnetic fields (EMFs) emitted by electrical cables must also be assessed. 

These effects will be site specific and depend on the length of the cable and the method for 

burying the cable (such as with a plow or trenching). Potential effects from EMFs include

disorientation in fish, especially sharks and rays, as well as a slight increase in sediment 

temperature in the area of the transmission lines (COD 2005). Several studies conducted by 

Denmark, the United Kingdom, and Greenpeace found the effects of EMFs on the marine 

environment to be negligible (COWRIE 2007: Elsam Engineering and ENERGI E2 2006; 

Greenpeace International 2005). A recent report by Gill et al. (2009) for COWRIE, however, 

found that elasmobranchs (e.g., sharks and rays) in the benthos did respond to the presence of 

EMFs of the type and intensity associated with undersea cables. The response, however, 

appeared to be species or individual specific. Some species appeared to move less and others 

appeared to move more while the cable was transmitting. Given the ambiguity of their results, 

they suggest further monitoring of offshore wind sites as well as more experimental studies.

Transmission cable installation may also impact fish and benthic communities. These 

construction effects are certainly not unique to the offshore wind industry, because the 

telecommunications and other electric power sectors also bury cables. Methods that minimize 

seabed disturbance through cable trenching and burial are recommended for offshore wind 

construction. Several options minimizing the impacts on fish and the benthic communities from 

cable installation include using proven construction methods for reducing the effect of structures 
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and cables on existing fish stocks, food sources, and spawning activities; using antiscouring 

substrate at the foundation bases to mitigate erosion; and placing cables in a fishing exclusion 

zone. Considering potential impacts during structure foundation design could also minimize 

scouring, sediment redistribution, and current flow.

Fisheries are an important factor in the economies of all areas where offshore wind farms may 

potentially be sited. The British Department of Energy and Climate Change oversees the 

Fisheries Liaison with Offshore Wind and Wet Renewables (FLOWW) Group in the United 

Kingdom. Members of FLOWW include representatives from the fishing industry, renewable 

energy developers, and government regulators. FLOWW was organized to facilitate a dialogue 

between key energy and fishing stakeholders concerning issues between the two industries. 

These issues include the types of fishing permitted within a wind farm and best practice 

guidelines for coexistence. FLOWW meets four times a year and is developing a framework for 

assessing the value of fishing activities and disruptions or displacement caused by offshore wind 

farm development and negotiating commercial compensation (UK Department of Business, 

Enterprise, and Regulatory Reform 2010).

Overall, offshore wind farms have the potential to have a positive effect on fish and benthos 

through the creation of a restricted zone, of habitat, and of areas that could be used for 

mariculture. A 2005 environmental impact assessment conducted by DONG found that a wind 

farm would be a net gain for fish and benthic populations because trawling would be restricted 

around the wind farm under a 1992 Danish Executive Order (No. 939), which prohibits trawling 

within 200 m of sea cables (Elsam Engineering and ENERGI E2 2005). In the United States, 

Cape Wind Associates does not plan to restrict any recreational or commercial fishing activities 

in the Nantucket area (MMS 2009b). According to Fayram and de Risi (2007), wind turbines in 

the Adriatic Sea have the potential to act as “fish-aggregating devices” for bluefin tuna and other 

species, and they suggest designating the areas around wind farms as marine protection areas.

Offshore wind turbines may be new habitat for species. The monopile provides up to 2.5 times 

the amount of area lost through placement (Wilson and Elliott 2009). Although this new habitat 

is likely to be different than the habitat lost, it will be a refuge and food source for species. There 

is a long history of artificial reef complexes associated with offshore platforms throughout the 

world (Artificial Reefs 2010). To maximize the carrying capacity of the area around the 

monopiles and prevent scour, developers can use different substrates to simulate different 

environments and thus attract a variety of species. For example, gravel would simulate a gravel 

seabed, boulders would simulate a rocky outcrop, and synthetic fronds would simulate sea grass 

beds (Wilson and Elliott 2009). 

Offshore wind farms also represent an area that has the potential for multiple uses. Some 

European communities are pushing to integrate mariculture within the lattice work of the 

turbines in offshore wind farms. The turbines would be used as points of attachment, allowing 

economically viable and harvestable species such as blue mussels and algae to thrive (Buck et al. 

2008). This concept, however, is not without its opponents. In a recent survey of several different 

offshore wind farm user groups (i.e., environmental protection, public administration, maritime 

economies, tourism, offshore wind energy, fisheries, research, and policy), the fisheries group 

expressed predominantly negative attitudes toward the multiuse concept. A few reasons for the 

dissension include concern over the loss of other mussel fisheries, feasibility, loss of more 

fishing grounds, and safety risks (Michler-Cieluch and Kodeih 2008).
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8.7 Marine Mammals

The effects of offshore wind farms on marine mammals are not considered to be a priority risk 

area based on the evidence to date (CA-OWEE 2001). Several potential effects are possible,

though, including the following:

• Loss of habitat resulting from sound emissions

• Disruption of animal sonar systems through vibrations and low frequency sound 

emissions

• Fragmentation of migratory pathways

• Collision with underwater substructures.

The EU project COD concluded after an extensive review of Danish monitoring studies that the 

“offshore wind farm-induced effects are less severe than might have been anticipated.” 

Compared with other human activities in the marine zone, particularly fishery-related noise 

(DONG Energy et al. 2006) and ship traffic, risks from the sound emissions of single offshore 

wind facilities appear low (DONG Energy et al. 2006). A Greenpeace study found that “seals 

and grey seals are not significantly disturbed by the presence of offshore wind turbines”

(Greenpeace International 2000).

NERI, which is responsible for tagging seals, found a short-term impact to marine mammals 

during the construction phase as a result of the high sound levels caused by driving the piles into 

the seabed. To mitigate this potential effect on nearby mammals, deterrent devices such as 

“pingers” and a seal scare were used before construction to disperse the mammals and thereby 

reduce these temporal effects. Another study of harbor porpoises in the Baltic Sea found that the 

mammals left the area during construction at the Nysted wind farm (Carstensen, Henriksen, and 

Teilmann 2006). 

Many marine mammals move into different waters depending on their biological needs. The 

presence of offshore wind farms may create fragmentation of their habitats. Coupled with other 

stressors such as by-catch, prey depletion, and pollution, concern for the overall welfare of 

marine mammals is growing. Further, as more wind farms are erected in waters offshore, such as 

those of the North Sea, there will be greater competition for habitat. The seasonal distribution of 

harbor porpoises was followed for 4 years (2002–2006) in North Sea waters of the German 

exclusive economic zone (EEZ) (Gilles, Scheidat, and Siebert 2009). Hot spots (highly 

concentrated areas) for foraging were noted as well as times when the populations were at their 

lowest. It was estimated that up to 39% (worst-case scenario) of the harbor porpoise stock in 

German EEZ waters could be affected in some way by offshore wind farm production (Gilles, 

Scheidat, and Siebert 2009). 

Precautionary risk reduction and mitigation measures to reduce potential risks to marine 

mammals from sound emissions include:

• Avoiding areas with dense populations of marine mammals

• Avoiding construction operations such as pile driving during peak migration periods

• Applying noise-reduction measures or pingers or both, particularly before and during 

construction
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• Reducing or limiting boat traffic 

• Avoiding marine mammal protection areas.

8.8 Turbine Fluid Leakage and Containment 

Although they use no liquid fuel, wind turbines contain small amounts of various kinds of 

lubricating oils, liquid coolants, and greases necessary for the operation of the turbine’s 

gearboxes, pumps, fans, compressors, and other mechanical elements. If leaks occur during 

maintenance or operation, turbines have hermetically sealed decks to contain any fluid leakage. 

These sealed decks can hold the full amount of fluid until it can be safely recovered.

Concern has been raised over the potential for oil leakage from oil-cooled transformers in wind 

projects. Turbines to be used for typical wind development would use dry-type (air-cooled) stepup transformers to bring the wind electricity from nominal turbine voltages of 480–690 V up to a 

distribution range of about 32 kV. No danger of leaks would be possible from this type of

transformer. Each turbine would feed power to a common transformer electric service platform 

that serves as an electrical substation centrally located inside the wind plant. A substation to 

support a 400-MW wind farm would require four large transformers, each containing about

10,000 gallons of circulated dielectric cooling oil. To prevent this fluid from escaping into the 

environment in the event of a leak, each transformer would be mounted on a sealed compartment 

capable of holding 150% of the volume of transformer’s oil. In addition, each containment 

compartment is mounted to a secondary containment storage tank capable of capturing 100% of 

the oil should all four transformers leak. Possible leakage from each turbine’s emergency backup 

diesel generators is safeguarded by a 1,000-gallon diesel oil storage tank. Thus, the likelihood of 

even a small leak of fluid into the environment is remote.

New fluid technologies also mitigate the potential for environmental damage from transformer 

oil leakage. Alternative dielectric coolants produced from seed oils and food additives contain no 

petroleum, halogens, or silicones. In addition to being both nontoxic and biodegradable in soil 

and water, such coolants are markedly less flammable than oil coolants. Because of the stringent 

containment requirements and the expanded use of more environmentally friendly fluids in wind 

energy substation transformers, potential dangers posed by oil leakages from offshore wind 

energy projects constitute a very low risk. Regardless of this risk, EPA containment standards 

would apply.

8.9 Ship and Air Collisions

An offshore wind plant poses some potential risk of collisions between turbine systems and other 

sea users such as commercial and recreational vessels. Such collisions would pose not only 

safety risks but also the potential for environmental damage, including the release of pollutants 

in the form of fuel or oil. These risks are certainly a siting consideration, suggesting the need to 

avoid particularly busy maritime areas, shipping routes, traffic nodes, and fishing hot spots. On 

the other hand, some analysts classify turbines as aids to navigation that may serve to 

prominently indicate the navigational hazards associated with the shallow areas where projects 

are likely to be located in the foreseeable future. Measures will need to be taken to prevent

collisions (e.g., navigation exclusion zones, distance requirements for routes, mapping on 

navigation charts, and warning lights) or to respond rapidly to them (e.g., emergency response 

and rescue). Collision risks have been investigated at some length in the United Kingdom and 
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Germany, with a particular focus on risk reduction. A risk assessment for the proposed Horns 

Rev II wind farm concluded that the likelihood of ship-to-ship collision is “significantly higher” 

than the probability of a vessel colliding with a wind turbine (ENERGI E2 2006). At the Nysted 

offshore wind farm in Denmark, some 48,000 boats pass annually through the shipping lane 8 

km south of the wind farm and its was found to cause only “minimal hindrance” to commercial 

traffic (Elsam Engineering and ENERGI E2 2005).

Some assessments focused on possible collisions between land-based or offshore turbines and 

low-flying civil or military aircraft. Considerable attention has been paid to the effect of wind 

farms on the efficacy of radar systems and the potential for increased risk of aircraft collision or 

interference with defense systems. The United Kingdom conducted several years of study and 

initiated collaborations with military entities about potential effects on radar systems and 

mitigation strategies. These studies found that some level of the interference from wind turbines 

can be mitigated with improved radar hardware, filtering software, or gap-filling radar systems 

(BWEA 2010). Most recently, some land-based projects in the U.S. Midwest have experienced 

siting delays as the result of concerns regarding potential radar impacts to civilian aircraft or 

nearby military installations. Overall, collision risks are generally well understood and are 

unlikely to present a significant obstacle to offshore wind energy, provided these interactions and 

risks are considered carefully in the siting process and reasonable precautionary measures are 

taken to avoid the perceptions or realities of national security risks (COWRIE and BERR 2007).

8.10 Socioeconomic Risks

An offshore wind energy project could potentially produce diverse social and economic effects, 

particularly on nearby coastal communities, including the following:

• Positive and negative effects on other human activities (e.g., recreation, entertainment, 

tourism, and fishing)

• Valuation of the aesthetics of the natural landscape/seascape and its effect on real estate

• Interference or competition with key fishing grounds or other local land/sea uses

• Positive and negative impacts on communities, whether nearby or remote (such as 

nearness to staging areas for construction or decommissioning)

• Potential community conflict between project supporters and opponents

• Mostly positive effects on employment and economic stimulation from staging, 

construction, and operation and maintenance

• Improved electrical price stability

• Decreased dependence on foreign sources of fuel/energy.

Important in evaluating the full socioeconomic impact of a development, the “multiplier effects” 

of wind development on a local economy are threefold. These effects include direct effects from 

local manufacturing and construction activities as well as expenditures during operation, indirect 

effects from increased demand for local goods and services, and induced effects, which capture 
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the increase in wealth from the direct and indirect local spending by people involved in the wind 

farm development and operation (Tegen, Goldberg, and Milligan 2006).

Job generation and positive economic growth are two important factors for local communities. 

The effects on employment and local expenditures appear quite modest to date, although the 

renewable energy market has generated a significant employment base in Europe. For example, 

the Cape Wind EIS estimates an increase of 391 full-time workers during construction and 50 

full-time workers during permanent operation of the 130 wind turbines (MMS 2009a). At the 

Horns Rev wind site in Denmark, more than 1,700 man-years of local jobs were created during 

construction and 2,000 man-years will be created over the 20-year life of the project. About onefourth of these jobs were locally based.

Tourism is a complex issue with great uncertainty. In highly trafficked tourist areas with 

significant revenues going to local businesses, as well as to the state treasury, there are legitimate 

fears about any potential negative impacts to tourism. Although there is much to suggest that 

changes in tourism will be positive, the Cape Wind EIS anticipates that changes to the character 

of the area by the presence of wind turbines may deter people or change the type of activities in 

which they indulge (MMS 2009a; Landscape Institute and the Institute of Environmental 

Management and Assessment 2002). On the other hand, although some European projects faced 

initial reluctance from local communities because of these concerns, following construction, the 

communities saw a positive increase in tourism as people traveled to see operating offshore 

turbines (MORI Scotland 2002). In a survey conducted in July 2009 of coastal New Jersey 

communities, 89% of respondents (1,003 total) said that the presence of an offshore wind farm 

would not affect their plans to visit Atlantic City (Schulman 2009). Alternatively, in Germany, 

tourist operators fought vociferously to block offshore wind farm development in some 

communities (Gee 2010). As with potentially affected issues, the potential effects of offshore 

wind projects on tourism will be highly site specific, depending on the state of the local 

economy, compatibility of project siting with other uses of the ocean, and early stakeholder 

involvement. A sociological study conducted in communities near the Danish Horns Rev I and 

Nysted wind farms found that preconstruction apprehension, primarily concerning the visual 

impact, largely turned into acceptance once the wind farm began operation. The study suggested 

that this preconstruction antipathy resulted from an unrealistic perception of what would be the 

true aesthetic impacts, and that acceptance of the development spread as individuals became 

accustomed to the view (Elsam Engineering 2005).

Further, studies of public perception and tourism in communities near land-based wind farms in 

Scotland, Australia, and Germany found no noticeable decreases in tourism (MORI Scottish 

Renewables Forum 2002; N.I.T. GmbH 2001),and several studies reported that the wind farms 

boosted the tourism industry, with more curious sightseers coming to the area. A 2003 European 

Wind Energy Association (EWEA) public perception poll found that 81.3% of frequent tourists 

and 80.5% of occasional tourists felt “neutral to very positive” about near-shore wind farms 

(EWEA 2003).

Surveys of local residents along the North Sea coast found that attitudes toward offshore wind 

were seeded in three main aspects:

• The view of the sea as a natural space

• The local identity of an area linked to the local landscape
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• Perceptions of renewable energies in combination with attitudes toward climate change and 

sea level rise (Gee 2010).

Onshore, any potential effect to the tourism industry would come from the visual aesthetic. 

Temporary noise impacts on land would occur in a limited area only when the underground 

transmission cable was being installed. In fact, looking at case studies of land-based and offshore 

wind farms in Europe, Australia, and the United States, the Cape Wind EIS concludes that the 

Cape Wind development will most likely have a negligible impact on recreation and a positive 

impact on tourism in Cape Cod and on Nantucket and Martha’s Vineyard (MMS 2009a). Some 

aspects of tourism could be enhanced by the presence of a wind farm through local boat and 

aerial tours. Educational institutions could also take advantage of the wind farm to draw attention 

to energy issues and the environment.

8.11 Visual Effects and Aesthetics

The Cape Wind project shows that the perceived visual effects of an offshore wind development 

can be as significant to public acceptance of offshore wind farm siting as impacts to birds, 

mammals, and fish. Martin Pasqualetti, an expert in the public perception of energy and the 

aesthetic values of communities, described the situation of the Cape Wind project as one where 

“wind is colliding with the wishes of a prosperous and politically astute residential corps bent on 

protecting existing scenic and recreational qualities that it has come to cherish” (Pasqualetti 

2004). Visual impacts involve a host of considerations, including the following:

• Scale of the wind farm

• Prevailing weather conditions

• Change in landscape and seascape features, configurations, or general appearance

• Distance from sensitive receivers (people or animals)

• Intrusion of technology into natural landscapes or seascapes

• Presence of other developments in the foci area

• Effects on coastal recreation and tourism

• Effects on cultural communities.

It is already clear that the sensitivity of local coastal populations is highly site specific. Figure 8-

6 is a visual perspective of Horns Rev, one of the largest wind energy projects in the world, with 

80 turbines capable of producing 160 MW. A few European studies have examined changes in 

the visual landscape/seascape, focused primarily on methodological issues in analyzing public 

perceptions and values and developing approaches for landscape assessment (DONG Energy et 

al. 2006). In Denmark, the presence of offshore turbines did not affect the residents’ willingness 

for more turbines in the future, though the positive attitude could be jeopardized by too many 

wind farms (Ladenburg 2009a). 
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 Photos courtesy of DONG Energy.

Figure 8-6. Previsualization of the Horns Rev I wind farm from Blåvands Huk (top) and actual postconstruction photograph from Blåvands Huk (bottom)

Distance of the farm from shore and prevailing weather conditions that affect visibility can 

mitigate visual impacts. At Horns Rev I, a very limited sampling of the public revealed a strong 

preference for offshore wind farms to be located farther from the coast to preserve the 

impression that nature is unaffected by a human enterprise (Elsam Engineering and ENERGI E2 

2005). COD (2005) concluded that “the importance of a positive attitude toward wind energy 

must not be underestimated.” When these perceptions were analyzed with others from other sites 
200

in Denmark, it was clear that prior experience with offshore wind farms had an influence on the 

types of visual impacts people experienced and that positive perception of offshore wind farms 

was influenced by distance to the coast (Ladenburg 2009a). 

Beyond public sentiment, an additional area of legal concern is the potential for visual or other 

impacts to historic sites designated in the National Register. If there is the potential for a 

development to affect a recognized historic site, the regulatory process would require additional 

review and oversight of the proposed development as per Section 106 of the National Historic 

Preservation Act (NHPA) of 1966. In creating procedural obligations to study the impacts of 

federal actions, NHPA can be seen as a close analogue to NEPA, where NHPA does for historic 

sites what NEPA does for the environment (San Carlos Apache Tribe vs. United States 2005).

Before being permitted, the Cape Wind project was reviewed under Section 106 of NHPA 

because of the importance of the view of the seas in the cultural and religious rites of the 

Wampanoag tribe of Massachusetts. It was determined in part, however, that although the area 

has great historic and cultural significance, it is not untouched landscape with several cell phone 

towers, undersea cables, and other structures of modern life (DOI 2010). 

The impact of a visible wind farm on property values has also been an issue of concern. A 2003 

case study on the possible impact of 11 land-based U.S. wind farms on local property values 

found that property values within the “viewshed” did not perform any worse than those in a 

comparable region with no wind turbines. Additionally, a significant majority of projects studied 

revealed that property values within the wind power development’s viewshed grew at a faster 

rate than property values in a comparable region (Renewable Energy Policy Project 2003). More 

recently, Hoen et al. (2009) studied the sale of almost 7,500 homes within 10 miles of 24 existing 

wind farms in nine states and found no statistically significant evidence that wind farms lower 

property values. At present, it is not known how values of coastal residences in the United States 

will be affected by the presence of an offshore wind farm. 

8.12 Findings and Conclusions

A new paradigm is needed for thinking about the range of environmental and social risks of 

offshore wind developments, and it will need to be embodied in forward-looking state and 

federal energy policies. A diverse portfolio approach to energy development will include both 

land-based and offshore wind energy as important components in the energy mix. This new 

analytical paradigm is framed in the context of comparative sector risks with other energy 

technologies and is not limited to sector-by-sector risk analyses. 

An integrated and comparative risk framework can serve as a comprehensive assessment of the 

costs and benefits of deploying an offshore wind farm as opposed to proceeding with some other 

energy choice. Rather than the sector-by-sector approach, an integrated risk framework begins to 

give federal, state, and local decision makers and their stakeholders a common ground for 

analyzing and managing risks and devising public policies and effective siting strategies (Ram 

2009). Moreover, an integrated perspective helps build the knowledge base required for the 

national marine spatial planning initiative.

• Knowledge base—Known sectoral risks from the European studies include the following:

o Potential risks to specific species of bird and marine populations, changes to 

aesthetic values and viewsheds, effects on recreational uses of the sea and 
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tourism, competing use of the outer continental shelf, and human valuation (real 

estate) of seascape environments are the primary risk concerns for offshore wind 

power facilities, based on studies and experiences to date.

o Avian collisions resulting from wind turbine interactions may affect endangered 

species and species of concerns that already face a panoply of anthropogenic 

risks. To date, no installations in Europe have had significant impacts on bird or 

bat populations or habitats. 

o The largest risk found so far from studies at European wind plants stem from the 

noise generated during the construction phase. The impacts from pile driving were 

potentially significant in the short term, although recent experience suggests that 

these risks can be mitigated to some degree (see Section 5).

o Residents living near a wind site can have concerns about visual impacts, which 

can become a larger public concern. There are uncertainties relating to how 

coastal communities react or accept changes to the seascape when turbines are in 

their view. This area requires more research to better understand how visibility 

would affect public acceptance. 

o Effects on tourism could be an issue, but actual effects appear to be minimal. This 

can be a concern to some communities that depend on beach traffic and the 

resulting local revenues and tax base, but the evidence is ambiguous. 

o The possibility of a ship colliding with a turbine poses a potential significant risk 

because the result would affect safety and the marine environment should fuel or 

oil leak from a disabled ship or the turbine. No reported incidents have occurred, 

however, to date from existing wind projects, and so probabilities might be low.

o Studies of land-based wind projects show minimal to no effects on real estate 

prices and property values because of the presence of wind turbines, although 

studies have yet to been done on coastal communities. 

o Comparisons with other energy sources (such as fossil fuels and nuclear) indicate 

that the overall risks of offshore wind are relatively benign and not catastrophic 

(such as breached coal ash ponds, nuclear waste impacts). 

• Risk priorities—A finding of this analysis is that wind energy is not subject to catastrophic 

risks, as are other energy supply technologies. Best management practices and mitigation 

strategies are useful perspectives on managing current risks and uncertainties with wind 

energy. A major finding is that prioritizing risk research is needed to best fill gaps in the 

knowledge base and to understand more adequately the uncertainties that surround the risk 

problems at stake.

• Siting strategies—A prudent siting policy is sensitive to industry decisions about the wind 

resources and cost-competitiveness, considers competing uses of the ocean, and takes into 

account community concerns. Siting strategies must go beyond narrow technical appraisals 

of sites to include collaborative approaches with potential host states and communities. Welldeveloped risk communication and stakeholder involvement programs will be essential. In 

certain circumstances, a regional approach with federal policy support will be necessary.
202

• Adaptive management—A prudent, yet flexible, deployment strategy will need to integrate

monitoring with adaptive management approaches and risk mitigation strategies identified 

through the NEPA process (DOI 2008; Williams, Szaro, and Shaprio 2007). The research 

approach will need to be one of learning through experience, yet it must be flexible enough 

to easily accommodate and integrate new information and improved risk knowledge as they 

become available. 

• Stakeholder engagement—The benefits and costs of offshore wind to a community’s 

environmental, social, and economic factors will need to be discussed with stakeholders 

within the context of other sources of energy, sustainability, and anticipated impacts of 

climate change. A risk communication program must focus on risks, uncertainties, and local 

concerns and distinguish among the needs of different stakeholder groups. Current 

experiences indicate that leadership will be needed in these areas and that interested states 

and regional organizations will play a central role along with the federal agencies.

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Appendix A: Interagency Coordination

Table A-1. Applicable Laws and Responsible Agencies Related to Renewable Energy Development 

on the Outer Continental Shelf

Statute/Executive Order (E.O.) Responsible Federal

Agency/Agencies Summary of Pertinent Provisions

National Environmental Policy 

Act of 1969, as amended (NEPA) 

(42 U.S.C. 4321 et seq.)

Council on Environmental 

Quality (CEQ)

Requires federal agencies to prepare an 

Environmental Impact Statement (EIS) to 

evaluate the potential environmental 

impacts of any proposed major federal 

action that would significantly affect the 

quality of the human environment, and to 

consider alternatives to such proposed 

actions. 

Endangered Species Act of 

1973, as amended (16 U.S.C. 

1531 et seq.)

U.S. Fish and Wildlife 

Service (FWS); National 

Oceanic and Atmospheric 

Administration (NOAA) 

National Marine Fisheries 

Service (NMFS) 

Requires federal agencies to consult with 

the FWS and the NMFS to ensure that 

proposed Federal actions are not likely to 

jeopardize the continued existence of any 

species listed at the federal level as 

endangered or threatened, or result in the 

destruction or adverse modification of critical 

habitat designated for such species. 

Marine Mammal Protection Act of 

1972, as amended (16 U.S.C. 

1361-1407)

FWS (walruses, sea and 

marine otters, polar bears, 

manatees and dugongs); 

NMFS (seals, sea lions, 

whales, dolphins, and

porpoises) 

Prohibits, with certain exceptions, the take 

of marine mammals in U.S. waters by U.S. 

citizens on the high seas, and importation of 

marine mammals and marine mammal 

products into the United States.

Magnuson-Stevens Fishery 

Conservation and Management 

Act (also known as the Fishery 

Conservation and Management 

Act of 1976, as amended by the 

Sustainable Fisheries Act) (16 

U.S.C. 1801 et seq.)

NMFS Requires federal agencies to consult with 

the NMFS on proposed federal actions that 

may adversely affect essential fish habitats 

necessary for spawning, breeding, feeding, 

or growth to maturity of federally managed 

fisheries.

Marine Protection, Research, 

and Sanctuaries Act of 1972, as 

amended (33 U.S.C. 1401 et

seq.)

U.S. Environmental 

Protection Agency (EPA); 

U.S. Army Corps of 

Engineers (USACE); 

NOAA 

Prohibits, with certain exceptions, the 

dumping or transportation for dumping of 

materials including, but not limited to, 

dredged material, solid waste, garbage, 

sewage, sewage sludge, chemicals, 

biological and laboratory waste, wrecked or 

discarded equipment, rock, sand, 

excavation debris, and other waste into 

ocean waters without a permit from the 

EPA. For ocean dumping of dredged 

material, the USACE is given permitting 

authority. 

National Marine Sanctuaries Act 

(16 U.S.C. 1431 et seq.)

NOAA Prohibits the destruction, loss of, or injury to 

any sanctuary resource managed under the 
212

Statute/Executive Order (E.O.) Responsible Federal

Agency/Agencies Summary of Pertinent Provisions

law or permit, and requires federal agency 

consultation on federal agency actions, 

internal or external to national marine 

sanctuaries, that are likely to destroy, injure, 

or cause the loss of any sanctuary resource. 

E.O. 13186, Responsibilities of 

Federal Agencies to Protect 

Migratory Birds (January 10, 

2001)

FWS Requires that federal agencies taking 

actions likely to negatively affect migratory 

bird populations enter into Memoranda of 

Understanding with the FWS, which, among 

other things, ensure that environmental 

reviews mandated by NEPA evaluate the 

effects of agency actions on migratory birds, 

with emphasis on species of concern. 

CZMA of 1972, as amended (16 

U.S.C. 1451 et seq.)

NOAA Office of Ocean 

and Coastal Resource 

Management (OCRM) 

Specifies that coastal states may protect 

coastal resources and manage coastal 

development. A state with a coastal zone 

management program approved by NOAA 

OCRM can deny or restrict development off 

its coast if the reasonably foreseeable 

effects of such development would be 

inconsistent with the state’s coastal zone 

management program. 

Clean Air Act, as amended 

(CAA) (42 U.S.C. 7401 et seq.)

EPA; MMS Prohibits federal agencies from providing 

financial assistance for, or issuing a license 

or other approval to, any activity that does 

not conform to an applicable, approved 

implementation plan for achieving and 

maintaining the National Ambient Air Quality 

Standards (NAAQS).

Requires EPA (or an authorized state 

agency) to issue a permit before 

construction of any new major stationary 

source or major modification of a stationary

source of air pollution. The permit—called a 

Prevention of Significant Deterioration 

(PSD) Permit for stationary sources located 

in areas that comply with the NAAQS, and a 

Nonattainment Area Permit in areas that do 

not comply with the NAAQS—must control 

emissions in the manner prescribed by EPA 

regulations to either prevent significant 

deterioration of air quality (in attainment 

areas), or contribute to reducing ambient air 

pollution in accordance with an approved 

implementation plan (in nonattainment 

areas).

Requires the owner or operator of a 

stationary source that has more than a 

threshold quantity of a regulated substance 

in a process to submit a Risk Management 

Plan to EPA.

Clean Water Act (CWA), Section EPA; U.S. Coast Guard Prohibits discharges of oil or hazardous 
213

Statute/Executive Order (E.O.) Responsible Federal

Agency/Agencies Summary of Pertinent Provisions

311, as amended (33 U.S.C. 

1321); E.O. 12777,

Implementation of Section 311 of 

the Federal Water Pollution 

Control Act of October 18, 1972, 

as Amended, and the Oil 

Pollution Act of 1990

(USCG); MMS substances into or upon the navigable 

waters of the United States, adjoining 

shorelines, or into or upon the waters of the 

contiguous zone, or in connection with 

activities under the OCS Lands Act, or 

which may affect natural resources 

belonging to the United States.

Authorizes EPA and the USCG to establish 

programs for preventing and containing 

discharges of oil and hazardous substances 

from nontransportation-related facilities and 

transportation-related facilities, respectively.

Directs the Secretary of the Interior (MMS, 

now BOEM) to establish requirements for 

preventing and containing discharges of oil 

and hazardous substances from offshore 

facilities, including associated pipelines, 

other than deepwater ports. 

Marking of Obstructions (14 

U.S.C. 86)

USCG The Coast Guard may mark for the 

protection of navigation any sunken vessel 

or other obstruction existing on the 

navigable waters or waters above the 

continental shelf of the United States in such 

manner and for so long as the needs of 

maritime navigation require.

CWA, Sections 402 and 403, as 

amended (33 U.S.C. 1342 and 

1343)

EPA Requires a National Pollutant Discharge 

Elimination System (NPDES) Permit from 

EPA (or an authorized state) before 

discharging any pollutant into territorial 

waters, the contiguous zone, or the ocean 

from an industrial point source, a publicly 

owned treatment works, or a point source 

composed entirely of storm water.

CWA, Section 404, as amended 

(33 U.S.C. 1344)

USACE; EPA Requires a permit from the USACE before 

discharging dredged or fill material into 

waters of the United States, including 

wetlands.

Ports and Waterways Safety Act, 

as amended (33 U.S.C. 1221 et

seq.)

USCG Authorizes the USCG to implement, in 

waters subject to the jurisdiction of the 

United States, measures for controlling or 

supervising vessel traffic or for protecting 

navigation and the marine environment.

Such measures may include but are not 

limited to reporting and operating 

requirements, surveillance and 

communications systems, routing systems, 

and fairways. 

Rivers and Harbors Appropriation 

Act of 1899 (33 U.S.C. 401 et

seq.)

USACE Section 10 (33 U.S.C. 403) delegates to the 

USACE the authority to review and regulate 

certain structures and work that are located 

in or that affect navigable waters of the 

United States. The OCS Lands Act extends 
214

Statute/Executive Order (E.O.) Responsible Federal

Agency/Agencies Summary of Pertinent Provisions

the jurisdiction of the USACE, under Section 

10, to the seaward limit of federal 

jurisdiction. 

Resource Conservation and 

Recovery Act, as amended by 

the Hazardous and Solid Waste 

Amendments of 1984 (42 U.S.C. 

6901 et seq.)

EPA Requires waste generators to determine 

whether they generate hazardous waste 

and, if so, to determine how much 

hazardous waste they generate and notify 

the responsible regulatory agency.

Requires hazardous waste treatment, 

storage, and disposal facilities (TSDFs) to 

demonstrate in their permit applications that 

design and operating standards established 

by the EPA (or an authorized State) will be 

met. Requires hazardous waste TSDFs to 

obtain permits. 

National Historic Preservation 

Act of 1966, as amended (16 

U.S.C. 470-470t); Archaeological 

and Historical Preservation Act of 

1974 (16 U.S.C. 469-469c-2)

National Park Service 

(NPS); Advisory Council 

on Historic Preservation; 

State or Tribal Historic 

Preservation Officer 

Requires each federal agency to consult 

with the Advisory Council on Historic 

Preservation and the State or Tribal Historic 

Preservation Officer before allowing a 

federally licensed activity to proceed in an 

area where cultural or historic resources 

might be located; authorizes the Interior 

Secretary to undertake the salvage of 

archaeological data that may be lost 

because of a federal project.

American Indian Religious 

Freedom Act of 1978 (42 U.S.C. 

1996); E.O. 13007, Indian 

Sacred Sites (May 24, 1996)

NPS; Advisory Council on 

Historic Preservation; 

State or Tribal Historic 

Preservation Office

Requires federal agencies to facilitate 

Native American access to and ceremonial 

use of sacred sites on federal lands, to 

promote greater protection for the physical 

integrity of such sites, and to maintain the 

confidentiality of such sites, where 

appropriate.

Federal Aviation Act of 1958 (49 

U.S.C. 44718); 14 CFR part 77

Federal Aviation 

Administration (FAA)

Requires that, when construction, alteration, 

establishment, or expansion of a structure is 

proposed, adequate public notice be given 

to the FAA as necessary to promote safety 

in air commerce and the efficient use and 

preservation of the navigable airspace.

Federal Powers Act, 16 U.S.C 

792-823a 

Federal Energy 

Regulatory Commission 

(FERC)

BOEM will issue leases, easement and 

right-of-way for hydrokinetic projects located 

on the OCS. FERC will issue licenses for 

the construction and operation of 

hydrokinetic projects the OCS.
215

Appendix B: Summary of Studies Conducted on Resource Areas 

as Part of the Cape Wind Environmental Impact Statement 

Cape Wind is the first proposed offshore wind project in the United States that completed its 

Final Environmental Impact Statement (FEIS)16), in January 2009 (see timeline in Section 7 for 

more details). The Record of Decision (ROD), approving Cape Wind’s application for a lease, 

was announced in April 2010. The ROD modified the findings of the FEIS and is a snapshot of 

the outcomes and studies required for their permitting process as well as the potential 

environmental and socio-economic effects of the proposed Cape Wind Energy Project. As seen 

in Table B-1, although most areas were expected to experience negligible or minor impacts, the 

primary areas of concern from their analyses included effects to avifauna, cultural and historic 

resources, and aviation safety and navigation (indicated by gray shading in the table).

Table B-1. Cape Wind Project Studies

Resource Concern Studies Outcomes

PHYSICAL

Geology Characterization of the geology of 

the area using 

Geophysical/Hydrographic 

Surveys (yearly 2001–2005), 

geotechnical/sediment sampling, 

numerical modeling and 

engineering analysis and longterm data sets. 

Created seafloor profiles based on 

measurements of several factors, including 

sediments, seafloor morphology, and water 

depths. 

Delineated acoustic targets.

Modeled sediment transport.

Determined sand wave movement.

Concluded no salt or methane hydrate 

diapirs.

Noted little seismic activity.

Noise Characterization of above-water 

noise and underwater noise using 

the (24-h) equivalent sound level 

and the day-night sound level 

(above water: November–

December 2002, underwater: 

October 2002).

Demonstrated that ambient and 

underwater sound levels increased as wind 

speed increased.

Monitored above ground and underwater 

levels. 

Physical 

Oceanography

Characterization of currents, 

waves, salinity, temperature, 

sediment transport, and water 

depth/bathymetry using long-term 

data sets and local 

measurements (waves: May 

2003, September 2004).

Modeled flow of currents, wind-generated 

wave height, magnitude, and period for 

offshore area.

Summarized salinities and temperatures 

based on long-term data sets.

Modeled sediment transport under varying 

conditions using comprehensive twodimensional transport model.

Summarized bathymetric conditions.

Climate & 

Meteorology

Characterization of air 

temperature, wind conditions, 

precipitation and fog events, 

Summarized ambient temperatures, wind 

conditions, precipitation and fog events, 

presence of hurricanes, and mixing height.

 16 Minerals Management Service. (2009). Cape Wind Energy Project: Final Environmental Impact Statement. Herndon, VA: 

DOI. 
216

Resource Concern Studies Outcomes

hurricanes, and mixing height 

from long-term data (National 

Climate Data Center and local 

sources, e.g., wind buoys).

Air Quality Characterization of air quality 

based on long-term monitoring 

data National Ambient Air Quality 

Standards.

Summarized existing and regional air 

quality.

Noted that offshore monitoring is an 

unknown because there are no monitoring 

stations in Nantucket Sound.

Water Quality Characterization of the water 

quality of the coastal waters, 

onshore waters, wetlands from 

long-term data sets.

Chemical and physical analysis of 

sediment at proposed coffer dam 

site

Summarized existing information: including 

Lewis Bay and Nantucket Sound are Class 

SA coastal and marine water bodies and 

onshore waters are Class B.

Summarized locations of sites associated 

with releases/spills of petroleum products 

and hazardous substances in relation to 

land cable route.

Noted that land-based construction would 

be located within the Cape Cod Sole 

Source Aquifer.

Noted that proposed transmission cable 

system would not be prohibited by 

regulations of wetlands.

Analyzed sediments were within 

established guidelines.

Electrical & Magnetic 

Fields

Baseline determinations of power 

frequency magnetic flux densities 

of along proposed land-based 

transmission cable route coupled 

with computer modeling to 

produce worst-case conditions 

reflecting peak loads (June 5–6, 

2002).

Sources of EMFs include land-based 

existing overhead distribution lines; the 

Nantucket Cable, which runs underwater 

from Nantucket to Cape Cod; and the 

natural geomagnetic field of the earth.

BIOLOGICAL

Terrestrial Vegetation Characterization of salt marsh, 

freshwater wetland, and upland 

vegetation using review of 

existing studies, site 

investigations, and agency 

consultations.

Summarized the vegetation and defined 

the areas (e.g., upland, marsh, freshwater) 

along the proposed transmission cable 

route.

Coastal and Intertidal 

Vegetation

Characterization of vegetation 

using maps from the 

Massachusetts Department of 

Environmental Protection, 

geophysical studies, free diving,

and visual observations 

(geophysical sonar studies: 2002, 

2003, and 2005).

Summarized presence or absence of 

vegetation on adjacent beaches and 

described importance of shoreline in 

buffering storm damage.

Summarized brackish and saline wetlands 

including salt marshes, shellfish waters, 

and navigable waters intersected by 

transmission cable.

Determined presence/absence and 

composition of seagrass beds along 

proposed transmission cable route.
217

Resource Concern Studies Outcomes

Terrestrial and 

Coastal Faunas other 

than Birds

Characterization of mammals, 

reptilians, amphibians, freshwater 

fish, and invertebrates using data 

sets, published surveys and field 

surveys (2001–2002).

Summarized mammals known to inhabit 

the area based on historical surveys.

Summarized known bat species in the area 

and their associated habitats, ranges, 

hibernations, and feeding patterns.

Discussed need for information on the 

extent to which bats fly over coastal 

waterways.

Proposed that only a few bat species would 

be capable of crossing Nantucket Sound in 

spring and fall during migration.

Summarized reptile and amphibian species 

in the proposed area.

Unable to assess fish species in Thornton 

Brook where the proposed transmission 

cable would cross because of dry 

conditions.

Summarized invertebrates in the proposed 

area and highlighted the three state 

threatened and endangered species—

comet darner (Anax longipes), New 

England bluet (Enallagma laterale), and 

water-willow stem borer (Papaipema 

sulphurata).

Avifauna Characterization of birds in the 

proposed action area using 

existing data and aerial, boat, and 

radar surveys (March 2002–

September 2006: Massachusetts 

Audubon Society Surveys: 

August 2002–September 2004).

Summarized Nantucket Sound’s 

significance as part of Atlantic Flyway.

Summarized species found in the area and 

their protection under the Migratory Bird 

Act and additionally for some, the 

Endangered Species Act.

Conducted preliminary avian risk 

assessment.

Summarized species, their concentrations, 

distributions, seasonalities, and behaviors.

Subtidal Offshore 

Resources

Characterization of shellfish, 

meiofauna, and plankton 

resources based on review of 

existing data and scientific 

literature, site assessments and 

field surveys (2001–2005), and 

agency consultations.

Summarized hard/soft bottom benthic 

communities in proposed action area.

Noted new taxa, not found previously, on 

meteorological support pilings, but overall 

communities were similar to neighboring 

seafloor community.

Summarized distributions and numbers for 

several shellfish species, including conch, 

quahogs, scallops, and clams.

Identified proximity of proposed 

transmission cable route to commercial 

and recreational shellfish beds.

Little information known on meiofauna and 

plankton residing in Nantucket Sound and 

within proposed area.

Marine Mammals Characterization of marine 

mammals including acoustical 

impacts using scientific literature 

reviews and resource 

All marine mammals in proposed action 

area are protected under Marine Mammals 

Protection Act (MMPA) and some are 

protected under Endangered Species Act 
218

Resource Concern Studies Outcomes

management agencies 

consultation

(ESA).

Applicant will seek authorization with 

NOAA fisheries to allow for the accidental 

taking of marine mammals and 

acknowledges need to apply for Incidental 

Take Statement under ESA for MMPA 

authorization.

Summarized cetaceans, pinnipeds, and 

sea turtle species with emphasis on 

population sizes, sightings, strandings, 

seasonal distributions, food and feeding 

behaviors, known disturbances. mortality 

factors. and impacts of acoustical 

disturbance.

Fish and Fisheries Characterization demersal, 

pelagic fish and commercial and 

recreational fish and shellfish 

using data from NOAA fisheries 

and Massachusetts Department 

of Marine Fisheries (Mass DMF).

Conducted surveys and reviewed 

existing surveys (Survey of 

Commercial and Recreational 

Fishing Activities, 2005; 

Recreational Intercept Survey, 

August–November 2002).

Summarized demersal and pelagic fish,

commercial and recreational fish, and 

shellfish species with respect to population 

size, range, known migratory behavior, and 

catch size.

Reviewed Massachusetts Fisherman’s 

Partnership study (Weisma 2008), which 

focused on the impacts of wind turbine 

generator installations on the squid and 

fluke fisheries, which have major trawling 

grounds on Horseshoe Shoals and 

Nantucket Sound.

Reviewed Survey of Commercial and 

Recreational Fishing Activities (2005), 

NOAA Marine Recreational Fisheries 

Survey, and Recreational Intercept Survey,

looking at locations, types of fish caught, 

catch size, and economic data.

More than 70 vessels draft fish

commercially in Nantucket Sound, and 

local fishermen derive 50%–60% of 

livelihood from fishing in Nantucket Sound.

Essential Fish 

Habitat (EFH)

Performed Essential Fish Habitat 

assessment in compliance with 

Magnuson-Stevens Act using 

NOAA fisheries and Mass DMF 

data sets.

Summarized life histories and landings of 

demersal and pelagic fish and 

invertebrates.

Threatened and 

Endangered (T & E) 

Species

Characterization of endangered 

and threatened species in the 

proposed area through literature 

review, stock assessment 

reports, and consultation with 

agencies.

Biological Assessment initiated 

by MMS in compliance with 

NEPA and ESA.

Summarized known ESA species including 

marine mammals, turtles, birds, and 

insects with respect to life histories, 

populations, status, distributions, and 

threats that would be potentially affected by 

proposed action.
219

SOCIOECONOMIC RESOURCES AND LAND USE

Socioeconomic 

Analysis Area

Characterization of geographic 

scope of areas designated part of 

Region of Impact (ROI).

Described the potential impacts to ROI 

including potential increase in workforce, 

the building of infrastructure, and the use 

as a point of debarkment. 

Urban and Suburban 

Infrastructure

Characterization of housing, 

services, and industries present 

in ROI.

Summarized numbers of housing units, 

percent ownership, and percent rental.

Summarized industries and services 

including construction and manufacturing, 

educational, professional, scientific and 

technical, administration, support, waste 

management and remediation, 

accommodation, food, transit facilities, 

military activities, and energy.

Population and 

Economic 

Background

Characterization of demographic 

and economic data for ROI using 

current U.S. Census data.

Summarized population, age, race and 

ethnic composition, and education for 

Dukes, Barnstable, Nantucket, Bristol, and 

Washington counties using Census data 

Summarized current income levels, 

business activity by sector, employment, 

income and wealth, property values, and 

environmental justice considerations using 

local, state, and federal census data.

Performed Environmental Justice Analysis.

Visual Resources Characterization of visual 

resources associated with 

historic, religious, and 

recreational areas. Used 

assessments of simulation 

locations chosen with assistance 

from Massachusetts Historic 

Commission (MHC) and MEPA to 

represent worst-case visual 

impacts. Also employed field 

reconnaissance, background 

research, review of National 

Register of Historic Properties, 

and other MHC files.

Described 12 simulation locations and 

additional properties based on distance 

from proposed action, brief history of 

significance, whether or not it is registered 

with National Registry of Historic Places, 

photographs from different vantage points, 

and whether or not the proposed action 

would be viewable. 

Determined that wind turbines would most 

likely be viewable from some historic and 

recreational locations as well as large 

shoreline homes. Turbines would most 

likely be viewable from the waters around 

the island of Nantucket, Cape Cod, 

Martha’s Vineyard and those of Nantucket 

Sound.

Noted the concerns of the Wampanoag 

Tribe (“People of the First Light”), which

requires an unobstructed view of the first 

light on the horizon to carry out many 

religious and cultural beliefs and practices.

Description of recreational areas (e.g., 

beaches, marinas, simulation locations) 

that would potentially have a view of the 

proposed action.

Noted transmission cable would be buried 

underground or within existing easement 

not considered an issue.
220

Cultural Resources Defined Areas of Potential Effects 

(APEs) for land-based and 

offshore historical and prehistoric 

human cultural activities. 

Conducted archaeological 

surveys and marine sensitivity 

assessments, and compiled lists 

of historic structures within 

communities. 

Noted land-based historical archaeological 

sites would not be affected.

Identified 22 existing historic structures and 

districts within APE as well as Native 

American lands of the Mashpee 

Wampanoag Tribe.

Noted the Mashpee Wampanoag Tribe 

considers all of Nantucket Sound to be part 

of their tribal lands.

Summarized shipwrecks, potential Viking 

contact sites, and any sonar anomalies for 

the offshore site.

Recreation and 

Tourism

Characterization of recreational 

and tourism activities and 

assessment of potential impacts 

using Chamber of Commerce 

data, town surveys, and field 

observations.

Summarized potential impacts on various 

activities including birding, beach and 

shoreline activities, recreational boating 

and water sports, and recreational fishing.

NAVIGATION AND TRANSPORTATION

Overland 

Transportation 

Arteries

Characterization of major and 

minor roadways and assessment 

of potential impacts.

Summarized major and minor roadways 

with respect to volumes and access points 

in relationship to their use as routes for 

transporting materials and as staging and 

loading areas.

Summarized potential impacts to major and 

minor roadways from installation of the 

transmission cable.

Airport Facilities Characterization of airports in the 

area and assessment of potential 

impacts.

Excluded high altitude jetways from 

assessment because they were not 

considered a factor.

Documented that turbine array was not 

located in flight path where low-altitude 

instrument flight rules would apply.

Documented that general aviation traffic 

must maintain a minimum clearance of 500 

feet from any structure or vessel to be in 

compliance with federal regulations.

Port Facilities Characterization of Nantucket 

Sound and smaller surrounding 

ports with respect to navigation 

by recreational and commercial 

vessels.

Identified main ship channels and other 

private and federal channels and assessed 

usage by recreational vessels (e.g., sail 

boats, kayaks, canoes, small boats) and 

commercial vessels (e.g., fishing boats, 

ferries, cruise ships, scientific vessels) 

defining peak usage and potential impacts.

Summarized marinas and ports in the area 

that handle various traffic, though no deep 

draft traffic (e.g., container vessels).

Documented marine events that may be 

affected by proposed action.
221

COMMUNICATIONS

Communications: 

Radar, Television, 

Radio, Cellular, and 

Satellite Signals and 

Beacons

Characterization of main 

communications services 

(recreational, navigational and 

positioning, aviation and military 

surveillance radar) using FCC 

antenna structure databases.

Federal Aviation Administration

(FAA) study of the potential for 

turbines to interfere with 

communication instrumentation

Summarized AM, FM, and TV stations 

serving Cape Cod area.

Summarized location of airport control 

towers and military radar facilities in 

relation to proposed action.

FAA aeronautical study determined that the 

proposed turbines would not interfere with 

instrumentation needed for navigation or 

approach procedures.

Noted proposed use of glass reinforced 

plastic composition blades to ensure 

minimum effect on communication 

facilities.
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Large-Scale Offshore Wind Power in the United States: Assessment 

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This report provides a broad understanding of today's offshore wind industry, the offshore wind resource, and the 

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offshore wind energy; wind power; renewable energy

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