NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

2013 Cost of Wind Energy 

Review

C. Moné, A. Smith, B. Maples, and M. Hand

National Renewable Energy Laboratory

Technical Report

NREL/TP-5000-63267

February 2015
NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

2013 Cost of Wind Energy 

Review 

C. Moné, A. Smith, B. Maples, and M. Hand

National Renewable Energy Laboratory

Prepared under Task No. WE15.CA03

Technical Report

NREL/TP-5000-63267

February 2015
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, 

express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of 

any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately 

owned rights. Reference herein to any specific commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, 

or favoring by the United States government or any agency thereof. The views and opinions of authors 

expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Available electronically at http://www.osti.gov/scitech

Available for a processing fee to U.S. Department of Energy

and its contractors, in paper, from:

U.S. Department of Energy

Office of Scientific and Technical Information

P.O. Box 62

Oak Ridge, TN 37831-0062

phone: 865.576.8401

fax: 865.576.5728

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from:

U.S. Department of Commerce

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

phone: 800.553.6847

fax: 703.605.6900

email: orders@ntis.fedworld.gov

online ordering: http://www.ntis.gov/help/ordermethods.aspx

Cover Photos: (left to right) photo by Pat Corkery, NREL 16416, photo from SunEdison, NREL 17423, photo by Pat Corkery, NREL 

16560, photo by Dennis Schroeder, NREL 17613, photo by Dean Armstrong, NREL 17436, photo by Pat Corkery, NREL 17721.

NREL prints on paper that contains recycled content. 
1

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Acknowledgments

This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-

08GO28308 with the National Renewable Energy Laboratory. Funding for the work was provided 

by the DOE Office of Energy Efficiency and Renewable Energy, Wind and Water Power 

Technologies Office. The authors would like to extend thanks to Mark Higgins from the DOE 

Wind and Water Power Technologies Office for supporting this research. Thanks also to Jose 

Zayas, Rich Tusing, and Dan Beals (DOE contractors) of the DOE Wind and Water Power 

Technologies Office as well as Karlynn Cory, David Mooney, and David Corbus of NREL for 

reviewing and providing strategic guidance in the development of this work. Thanks to Aaron Barr 

(MAKE Consulting), Aisma Vitina (Ea Energianalyse), Carsten Westergaard (Texas Tech 

University), and David Weir (Norwegian Water Resources and Energy Directorate) for reviewing 

earlier versions of this report. Any remaining errors or omissions are the sole responsibility of the 

authors.
2

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

List of Acronyms

AEP Annual energy production

AEP net Net annual energy production

AWEA American Wind Energy Association

BNEF Bloomberg New Energy Finance

BOEM Bureau of Ocean Energy Management

BOS Balance of system

CapEx Capital expenditures

CFnet Net capacity factor

Cp Coefficient of Power

CRF Capital recovery factor

DOE U.S. Department of Energy

DOI U.S. Department of the Interior

EIA U.S. Energy Information Administration

ENS Danish Ministry of Energy and Environment

EPRI Electric Power Research Institute

FCR Fixed charge rate

GWEC Global Wind Energy Council

JEDI Jobs and Economic Development Impact

kW Kilowatt

LCOE Levelized cost of energy

LLC Land lease cost

MACRS Modified Accelerated Cost Recovery System

MAIN Maintenance

MW Megawatt

MWh Megawatt-hour

NREL National Renewable Energy Laboratory

OPER Operation

OCS Outer Continental Shelf

OpEx Operational expenditures

PPA Power purchase agreement

PTC Production tax credit

PVdep Present value of depreciation

SCBS System cost breakdown structure

TSR Tip-speed ratio

WACC Weighted average cost of capital
3

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Executive Summary

This report uses representative commerical project types to estimate the levelized cost of energy 

(LCOE) for both land-based and offshore wind plants in the United States (U.S.) for 2013. 

Scheduled to be published on an annual basis, it relies on both market and modeled data to 

maintain an up-to-date understanding of wind generation cost trends and drivers. It is intended to

provide insight into current component-level costs and a basis for understanding variability in the 

LCOE across the industry. Data and tools developed from this analysis are used to inform wind 

technology cost projections, goals, and improvement opportunities. 

The primary elements of the 2013 report include:

• Estimated LCOE for a reference land-based wind project installed in the interior region of 

the U.S. in 2013 

• Estimated cost of energy for a reference fixed-bottom U.S. offshore wind project reflecting 

projects currently in late-stage development on the North Atlantic Coast

• Sensitivity analyses showing the range of effects that basic LCOE variables could have on 

the cost of wind energy for land-based and offshore wind power plants

• Historical trends in the LCOE for land-based and offshore wind plants.

The LCOE equation applied here is a standard methodology (Short et al. 1995, EPRI 2007) that 

includes four basic inputs: capital expenditures, operational expenditures, annual energy 

production, and the fixed charge rate (a coefficient that captures the cost of financing the 

construction of a wind project and the entirety of the planned plant’s operational life). Additional 

detail on the LCOE can be found in the 2010 Cost of Wind Energy Review (Tegen et al. 2012). 

The LCOE values reported within the reviews are expected to be greater than negotiated contract 

prices for wind power, as reflected by recent power purchase agreements. This increase is because 

recent power purchase agreements incorporate the value of the production tax credit (PTC), 

accelerated depreciation, other Renewable Energy Credits, or other applicable revenue streams.

Key Inputs and Results

Throughout this report, the representative land-based and offshore project types are referred to as 

“reference projects.” Tables ES1 and ES2 summarize the four basic LCOE inputs for the reference 

land-based and fixed-bottom offshore wind projects, with some additional detail around project 

capital expenditures and the respective turbine capacity factor associated with the net annual 

energy production estimate. These are the assumptions used to calculate LCOE for the 2013 

reference projects. In each table, the left-hand column shows the data source. “Model” refers to the 

techno-economic models used, such as the National Renewable Energy Laboratory’s (NREL’s)

Wind Turbine Design Cost and Scaling Model (Fingersh et al. 2006, Maples et al. 2010). “Market” 

indicates that NREL used current market data, with individual data sources listed in sections of this 

paper related to the specific cost components. 
4

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table ES1. Summary Description of the Land-Based Reference Project 

Using 1.91-MW Turbines

Data

Source

1.91-MW 

Land-Based

Turbine

$/kilowatt 

(kW)

1.91-MW

Land-Based

Turbine

$/Megawatthour (MWh)

Model Turbine capital cost 1,185 35

Model Balance of system 349 10

Model Financial costs 155 5

Market Market price adjustment* 39 1

Market CAPITAL EXPENDITURES 1,728 51

Market Operating expenditures ($/kW/yr) 50 15

Market Fixed charge rate (%) 10.2

Model Net annual energy production 

(MWh/MW/yr) 3,410

Model Net capacity factor (%) 38.5

Calculated TOTAL LCOE ($/MWh) 66

*The market price adjustment is the difference between the modeled cost and the market price paid for the typical 

project in 2013.

Table ES2. Summary Description of the Fixed-Bottom Offshore Reference Project 

Using 4.3-MW Turbines

Data 4.3-MW 4.3-MW

Source Offshore

Turbine

Offshore

Turbine

$/kW $/MWh

Model Turbine capital cost 1,660 56

Model Balance of system 2,697 91

Market Financial costs 830 28

Market CAPITAL EXPENDITURES 5,187 175

Market Operating expenditures ($/kW/yr) 136 39

Market Fixed charge rate (%) 11.7

Model Net annual energy production 

(MWh/MW/yr) 3,463

Model Net capacity factor (%) 39

Calculated TOTAL LCOE ($/MWh) 215
5

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Land-based wind project cost estimates were derived primarily from installed project data reported 

by Wiser and Bolinger (2014) and supplemented with outputs from NREL’s Wind Turbine Design 

Cost and Scaling Model. Because of the absence of installed or operating offshore wind projects in 

the United States, the offshore reference project data were estimated from proposed U.S. projects 

and market data from the existing international offshore wind industry. The assumed wind resource 

regime for the offshore reference plant is comparable to that of the U.S. North Atlantic Coast. The 

land-based reference project was assumed to have a moderate wind resource regime and location

within the interior region of the United States.

As domestic and global wind markets mature, information about component-level costs are

increasingly available. To manage and organize this component-level cost data, NREL has 

developed a system cost breakdown structure (SCBS) for land-based and offshore wind projects. A 

SCBS is able to break an entire wind project into smaller, more specific components (e.g., gearbox 

and generator). It provides a standardized approach to characterizing total lifetime expenditures for 

wind projects at the component level, including both physical (e.g., materials, labor, and 

equipment) and financial (e.g., insurance, profit, and carrying charges) costs. Each level of the 

SCBS hierarchy represents an increasingly detailed look at the project components. The new 

SCBS is further described in Section 2 and the associated appendices. More detailed breakdowns

of capital expenditures (CapEx) are shown in Figures ES1 and ES2. 

The three major component cost categories and many subcategories are represented in these 

figures including wind turbine (e.g., wind turbine components), balance of system (e.g.,

development, electrical infrastructure, assembly and installation), and financial costs (e.g., 

insurance and construction finance). From these data, it is clear that the breakdown of wind turbine 

component and installation costs varies greatly between land-based and offshore turbines. For 

example, the majority of the land-based project cost (68%) is in the turbine itself, whereas the 

turbine makes up only 32% of the offshore reference project cost.
6 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Figure ES1. Capital expenditures for the land-based wind plant reference project 

Source: NREL 

Figure ES2. Capital expenditures for the offshore wind plant reference project 

Source: NREL 
7 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Figures ES3 and ES4 define the LCOE associated with the land-based and offshore reference 

plants along with a range of sensitivity variables affecting cost and performance. Reference project 

values of $66/megawatt-hour (MWh) for land-based wind and $215/MWh for offshore wind rely 

on inputs summarized in Tables ES1 and ES2 (and are identified by the vertical white line in these 

figures). Figures ES3 and ES4 also show the observed industry ranges for LCOE inputs and the 

resulting LCOE. To provide more detail on the fixed charge rate, the authors divided it into two 

principal components: discount rate and economic operational life. Annual energy production 

(AEP) was converted to capacity factor to help convey the full range of performance reflected by 

2013 projects. As shown, the land-based net capacity factors from 2013 projects range from 25% 

to 50% (Wiser and Bolinger 2014), with an assumed 38.5% for the 2013 reference project. Clearly, 

the ranges for land-based and offshore wind LCOE inputs vary significantly (note the different 

axes in these figures). For example, offshore wind net capacity factor ranges from 30% to 50%, 

with an assumption of 39% for the reference project. Both figures show the effect capacity factor 

and CapEx have on the LCOE for both land-based and offshore wind projects. More detailed 

descriptions of the ranges and assumptions are included in the body of the report. 

Figure ES3. Land-based wind assumptions and ranges for key LCOE input parameters 

Source: NREL 

Note: The reference LCOE represents the estimated LCOE for the NREL reference project. 

Changes in LCOE for a single variable can be understood by moving to the left or right along a 

specific variable. Values on the X-axis indicate how the LCOE will change as a given variable is 

altered, and assuming that all others are constant. For example, as capacity factor decreases 

toward 25%, the LCOE shown on the X-axis will increase accordingly to more than $100/MWh. As 

the operational life for the reference project moves toward 30 years, the LCOE will decrease to 

nearly $58/MWh. 
8 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Figure ES4. Offshore wind assumptions and ranges for key LCOE input parameters 

Source: NREL 

Along with the reference LCOE estimates, NREL researchers created additional land-based wind 

project scenarios to demonstrate the impact of some project permutations: taller towers used on the 

project, larger rotors used to capture greater AEP, the combination of both a taller tower and larger 

rotor diameter, and higher average annual wind speed. Each of these scenarios resulted in a lower 

LCOE relative to the reference project, ranging from $63/MWh for a project with taller towers to 

$52/MWh combining all of the scenarios. The altered variables and their resulting LCOE are 

summarized in Table ES3. 

 
9

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table ES3. Land-Based LCOE Cost Reduction Scenarios

Reference Taller 

Tower

Larger 

Rotor

Tower & 

Rotor

Higher 

Wind 

Speed

All

Scenarios

Combined

Nameplate capacity (MW) 1.91 1.91 1.91 1.91 1.91 1.91

Rotor diameter (m) 96.9 96.9 110 110 96.9 110

Hub height (m) 82.7 100 82.7 100 82.7 100

Average wind speed at 50 m 

(Average wind speed at hub height)

7.25 

(7.79)

7.25 

(8.0)

7.25 

(7.79) 7.25 (8.0) 8.0 (8.6) 8.0 (8.8)

Net annual energy production 

(MWh/MW/yr) 3,410 3,536 3,796 3,918 3,866 4,345

LCOE ($/MWh) 66 63 59 57 58 52

From these results, researchers came to the following key conclusions:

• Final LCOE estimates continue to show a downward trend from the 2010 Cost of Wind 

Energy Review (Tegen et al. 2012) to 2013. Offshore turbine costs have shown similar cost 

reductions; however, the decrease in LCOE for the land-based projects can be attributed 

more to the turbine technology, and the offshore decreases to the balance-of-system costs.

• Although the reference project LCOE for land-based installations was observed to be 

$66/MWh, the full range of land-based estimates from the sensitivity analysis covers $50–

$103/MWh. 

• The reference project offshore estimate is $215/MWh, with a full range of $127–

$270/MWh. This dramatic range is mostly caused by the large variation in capital 

expenditures ($3,200–$6,000/kW) reported by project developers. 

• The sensitivity analysis shows that LCOE can vary widely based on changes in any one of 

several key factors; however, the variable with the most dramatic effect on LCOE is 

capacity factor—which is the case for both land-based and offshore projects.

Although LCOE calculations in this report do not include policy factors, it should be noted that the 

number of commissioned U.S. land-based wind projects was down significantly in 2013, partly

because of policy uncertainty around the PTC in 2012. The expiration of the PTC forced a 

substantial deceleration of wind development; so much that, even with the January 1, 2013, 

extension of the PTC, demand for new wind projects proved to be weak. The American Wind 

Energy Association (2012) reported that three past expirations of the PTC resulted in a drop of 

73%−93% for annual land-based wind installations in the year after expiration, and 2013 saw a 

92% drop in installations compared to 2012, with the PTC expiration. The extension in 2013 that 

allowed for projects to meet PTC requirements is expected to bolster the industry and show an 

increase in land-based installations in 2014 and 2015. Observations made by Wiser and Bolinger 

(2014) support these expectations, showing early indications from the first quarter of 2014 which 

suggest a dramatic increase in the number of land-based projects installed in 2014 compared to 

2013.
10

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table of Contents

Acknowledgments ...................................................................................................................................... 1

List of Acronyms......................................................................................................................................... 2

Executive Summary.................................................................................................................................... 3

Key Inputs and Results........................................................................................................................... 3

Table of Contents...................................................................................................................................... 10

List of Figures ........................................................................................................................................... 11

List of Tables ............................................................................................................................................. 11

1 Background......................................................................................................................................... 13

2 Approach............................................................................................................................................. 16

3 System Cost Breakdown Structure .................................................................................................. 18

3.1 SCBS Description ....................................................................................................................... 18

3.2 Benefits ....................................................................................................................................... 19

3.3 Approach and Limitations........................................................................................................... 19

4 Land-Based Wind ............................................................................................................................... 23

4.1 2012 Land-Based Cost of Wind Energy...................................................................................... 23

4.2 Comparison of Two Different Cost of Wind Energy Methodologies......................................... 24

4.3 2013 Land-Based Cost of Wind Energy...................................................................................... 24

4.4 Capital Expenditures for Land-Based Wind ............................................................................... 25

4.5 Operating Expenditures for Land-Based Wind ........................................................................... 28

4.6 Annual Energy Production and Capacity Factor for Land-Based Wind ..................................... 29

4.7 Land-Based Wind Reference Project Summary.......................................................................... 31

4.8 Land-Based Wind LCOE Calculation......................................................................................... 32

4.9 LCOE Sensitivities...................................................................................................................... 33

4.10 Cost Reduction Scenarios............................................................................................................ 34

5 Offshore Wind..................................................................................................................................... 37

5.1 2013 Market Developments........................................................................................................ 37

5.2 CapEx for Fixed-Bottom Offshore Wind Reference Project ...................................................... 38

5.3 Operating Expenditures for Offshore Wind ................................................................................ 41

5.4 Offshore Annual Energy Production and Capacity Factor.......................................................... 41

5.5 Financial Parameters for Offshore Wind..................................................................................... 43

5.6 Offshore Wind Reference Project Summary............................................................................... 43

5.7 Offshore Wind LCOE Calculation.............................................................................................. 44

5.8 Offshore Wind LCOE Sensitivities............................................................................................. 46

6 Historical Levelized Cost of Wind Energy ....................................................................................... 47

7 Conclusions ........................................................................................................................................ 48

8 Related and Future Work................................................................................................................... 49

References................................................................................................................................................. 50

Appendix A. Present Value of Depreciation Calculations .................................................................... 53

Land-Based Wind................................................................................................................................. 53

Offshore Wind...................................................................................................................................... 53

Appendix B. Summary of Assumptions for 2013 Reference Projects................................................. 54

Land-Based Wind Project Assumptions............................................................................................... 54

Offshore Wind Project Assumptions.................................................................................................... 55

Appendix C. Summary of Assumptions for 2012 Reference Projects................................................. 56

Land-Based Wind Project Assumptions............................................................................................... 56

Offshore Wind Project Assumptions.................................................................................................... 57

Appendix D. Summary of Historical Levelized Cost of Energy Using Reference Projects............... 58

Appendix E. Summary of Land-Based System Cost Breakdown Structure ....................................... 60

Appendix F. Summary of Offshore System Cost Breakdown Structure ............................................. 74
11

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

List of Figures

Figure ES1. Capital expenditures for the land-based wind plant reference project............................ 6

Figure ES2. Capital expenditures for the offshore wind plant reference project................................. 6

Figure ES3. Land-based wind assumptions and ranges for key LCOE input parameters.................. 7

Figure ES4. Offshore wind assumptions and ranges for key LCOE input parameters ....................... 8

Figure 1. Levels 1 and 2 of the SCBS...................................................................................................... 18

Figure 2. Wind system cost breakdown structure: CapEx levels 1 to 3.............................................. 21

Figure 3. Wind system cost breakdown structure: OpEx levels 1 to 3 ............................................... 22

Figure 4. Capital expenditures for the land-based wind reference project......................................... 26

Figure 5. Component level cost breakdown for the 2013 land-based wind reference project ......... 33

Figure 6. Sensitivity of land-based wind LCOE to key input parameters ...............................................

Figure 7. Reported capital costs for installed, under construction, contracted, and approved 

offshore wind projects in $2012 (2000 to 2016)............................................................................... 39

Figure 8. Capital expenditures for the 2013 offshore wind reference project ........................................

Figure 9. Cost breakdown for the 2013 offshore wind reference project............................................ 45

Figure 10. Sensitivity of offshore wind LCOE to key input parameters .............................................. 46

Figure D1. Historical land-based wind plant levelized cost of energy (LCOE) as calculated by 

NREL including the U.S. Department of Energy’s LCOE goals..................................................... 58

List of Tables

Table ES1. Summary Description of the Land-Based Reference Project Using 1.91-MW 

Turbines................................................................................................................................................. 4

Table ES2. Summary Description of the Fixed-Bottom Offshore Reference Project Using 

4.3-MW Turbines................................................................................................................................... 4

Table ES3. Land-Based LCOE Cost Reduction Scenarios ..................................................................... 9

Table 1. Resources Referenced Prior to Developing the SCBS........................................................... 20

Table 2. Summary of Inputs and Reference Project 2012 LCOE for Land-Based Installations........ 23

Table 3. Comparison of Market-Based Cost of Wind Energy, 2013 Projects to Combined 

2013-2014 Projects ............................................................................................................................. 24

Table 4. Summary of Inputs and Reference Project LCOE for 2013 Land-Based Installations........ 25

Table 5. Land-Based LCOE and CapEx Breakdown.............................................................................. 27

Table 6. Land-Based Wind Reference Project OpEx ............................................................................. 29

Table 7. Reference Land-Based AEP Input Assumptions .................................................................... 29

Table 8. Land-Based Wind Turbine AEP and Capacity Factor Summary ........................................... 30

Table 9. Land-Based Reference Project Assumptions Summary........................................................ 31

Table 10. Land-Based Wind Reference Project LCOE Cost Breakdown............................................. 32

Table 11. Example of Land-Based LCOE Reduction Scenarios........................................................... 36

Table 12. Summary of Inputs and Results for the Fixed-Bottom Offshore Wind Project.................. 37

Table 13. Fixed-Bottom Offshore LCOE Component Cost Breakdown............................................... 41

Table 14. Fixed-Bottom Reference Offshore AEP Input Assumptions................................................ 42

Table 15. Offshore Wind Turbine AEP and Capacity Factor Summary ............................................... 43

Table 16. Fixed-Bottom Offshore Reference Project Assumptions Summary ................................... 44

Table 17. Fixed-Bottom Offshore Wind LCOE and Reference Project Cost Breakdown................... 45

Table 18. Historical Land-Based LCOE in Nominal Dollars.................................................................. 47

Table 19. Historical Offshore LCOE in Nominal Dollars ....................................................................... 47

Table 20. Ranges of LCOE and Elements for U.S. Land-Based and Offshore Wind in 2013 ............ 48

Table A1. Present Value of Depreciation Calculation for Land-Based Wind Reference 

(d = 8.8%)............................................................................................................................................. 53

Table A2. Present Value of Depreciation Calculation for Offshore Wind Reference (d = 10.5%) ..... 53

Table B1. Comprehensive List of Assumptions for 2013 Land-Based Reference Project 

Cost of Energy .................................................................................................................................... 54
12

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table B2. Comprehensive List of Assumptions for 2013 Offshore Reference Project Cost 

of Energy ............................................................................................................................................. 55

Table C1. Comprehensive List of Assumptions for 2012 Land-Based Reference Project Cost 

of Energy ............................................................................................................................................. 56

Table C2. Comprehensive List of Assumptions for 2012 Offshore Reference Project Cost of 

Energy.................................................................................................................................................. 57

Table D1. Historical Land-Based Wind Plant Levelized Cost of Energy as Calculated by NREL..... 58

Table D2. Historical Land-Based Average Wind Plant Turbine Specifications .................................. 58

Table D3. Historical Offshore Wind Plant Levelized Cost of Energy as Calculated by NREL .......... 59

Table D4. Department of Energy’s Cost Goals for Land-Based and Offshore Wind Power ............. 59

Table E1. Land-Based Wind System Cost Breakdown Structure Terms and Definitions ................. 60

Table F1. Offshore Wind System Cost Breakdown Structure Terms and Definitions ....................... 74
13

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

1 Background

This report evaluates the levelized cost of energy (LCOE) for land-based and offshore wind 

projects in the United States. LCOE is a metric used to assess the cost of electricity generation and 

the total plant-level impact from technology design changes. LCOE can be used to compare costs 

of all electricity generator types, as long as the same formula and calculations are used for each 

type. Different methodologies have been developed to calculate LCOE; the one used for this 

analysis is fully described in A Manual for the Economic Evaluation of Energy Efficiency and 

Renewable Energy Technologies (Short et al. 1995).1 Use of LCOE is especially important for 

technologies, where there is a constant tradeoff between maintaining or reducing capital 

investment and increasing energy capture, like wind and solar power.

There are four basic inputs into the LCOE equation. The first three—capital expenditures (CapEx), 

operational expenditures (OpEx), and annual energy production (AEP)—enable this equation to 

capture system-level impacts from design changes (e.g., taller wind turbine towers). The total costs 

of financing are represented by the fourth basic input—a fixed charge rate (FCR)—that represents

the amount of revenue required to pay the carrying charges2 on an investment during the expected 

project life per year.

3 For this analysis, the life of a wind project is assumed to be 20 years. All 

analysis and LCOE results will be in constant $2013 throughout the report unless otherwise noted. 

This report provides an update to the 2010 Cost of Wind Energy Review (Tegen et al. 2012) and an 

abbreviated look at the 2013 wind LCOE, turbine costs, financing, and market. Four specific areas 

are addressed:

• Estimate the LCOE for the reference land-based wind project located in a midwestern or 

“interior” site in the United States (U.S.) in 2013

• Estimate the LCOE for the reference fixed-bottom U.S. offshore wind project reflecting 

projects currently in late-stage development on the North Atlantic Coast

• Conduct sensitivity analyses showing the range of effects basic LCOE variables could have 

on the levelized cost of wind energy for land-based and offshore wind power plants

• Represent the National Renewable Energy Laboratory’s (NREL’s) calculated historical 

LCOE for land-based and offshore wind plants.

Despite addressing a number of assumptions and cost variables, this report does not capture the 

full spectrum of drivers that affect wind energy prices. For example, it does not consider policy 

incentives (such as the production tax credit, or PTC), factors from underlying economic 

conditions (such as an economic recession), the cost of building long-haul interstate transmission, 

or potential integration costs. These important variables can significantly impact wind power costs

by reducing total costs, adding expenditures, delaying projects, or halting projects altogether. 

Nevertheless, their exclusion is consistent with past economic analysis conducted by NREL 

(Tegen et al. 2012, Lantz et al. 2012) and others (Bloomberg New Energy Finance 2012, Lazard 

 1 For an overview of cost-of-energy calculators and models, see Gifford et al. (2011). 2 Carrying charges include the return on debt, return on equity, taxes, depreciation, and insurance. 3 The fixed charge rate does not allow for detailed analysis of specific financing structures; however, these structures

can be represented through the use of a weighted average cost of capital as the discount rate input. 
14

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

2008), as LCOE is not traditionally defined as a measure of all societal costs and benefits 

associated with power generation resources. 

The following equation is used to calculate LCOE:

LCOE = (CapEx × FCR) + OpEx

(AEPnet/1,000)

Where:

LCOE = levelized cost of energy [$/megawatt-hour (MWh)]

FCR = fixed charge rate (%)

=

CapEx = Capital expenditures ($/kilowatt [kW])

AEPnet = net annual energy production (MWh/MW/yr)

=

OpEx = Operational expenditures ($/kW/yr)

=

d = discount rate [Weighted average cost of capital (WACC)] (%)

n = operational life (years)

T = effective tax rate (%)

PVdep = present value of depreciation (%)

CFnet = net capacity factor (%)

LLC = land lease cost ($/kW/yr)

OPER = pretax levelized operation cost (O&M) ($/kW/yr)

MAIN = pretax levelized maintenance cost (O&M) ($/kW/yr)

The following sections of this report define the approach to calculating the LCOE and introduce

the new system cost breakdown structures (SCBS) to organize data and provide a common 

terminology across varying technologies. The report describes each component of the LCOE 

equation CapEx, OpEx, AEP, and FCR market context, and range of data for typical U.S. 

wind projects in the year 2013. In this 2013 Cost of Wind Energy Review, the authors first define

the 2013 LCOE components for a land-based reference project using an installed weighted average 

( )

( )

( )

( T )

T PVdep

d

d d

n

n

−

− ×

×

+ −

+

1

1

1 1

1

LLC + OPER + MAIN

MW x 8760 x CF net
15

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

turbine sized at 1.91-megawatts (MW), which was the average nameplate capacity installed in the 

United States in 2013. Next, the authors describe the 2013 LCOE components for an offshore wind 

reference project using 4.3-MW offshore turbines, which is the average nameplate capacity 

installed globally in 2013.
16

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

2 Approach

The 2013 Cost of Wind Energy Review applies the same approach as the 2010 and 2011 reports

(Tegen et al. 2012, Tegen et al. 2013). The authors used a number of data sources and models in 

NREL’s estimation of the cost of wind energy. For land-based wind technology calculations, the 

United States had over 61,000 MW of capacity installed and operating at the end of 2013.4 The

available data from these wind projects provided a large sample of empirical data on plant costs 

and performance. By contrast, no commercial offshore wind technology was deployed in the 

United States at the time of this study, and the market data supporting offshore cost of wind energy 

estimates are limited to international projects and proposed U.S. projects.

In addition to historical market data, the authors employed models to estimate disaggregated plantlevel cost components. Therefore, detailed data are provided on the individual components that 

make up capital expenditures, operating expenditures, and estimated annual energy production for 

the reference projects defined here. Given the market and model data available, the general 

approach for estimating the levelized cost of wind energy includes:

1. Evaluating market conditions and data for projects that have been installed in the United 

States in a given year, to understand total installed project cost, AEP, operating costs, and 

representative turbine technology. The primary source for these data is DOE’s Annual 

Wind Technologies Market Report (Wiser and Bolinger 2014). Accordingly, LCOE 

estimates reflect market conditions to the extent possible. Because of the small sample size 

of the 2013 commissioned projects, the projects were combined with others that were 

currently under construction in early 2014, with anticipated completion in 2014 per Wiser 

and Bolinger. The capacity-weighted averages of the U.S. installed projects were combined 

to yield 27 total projects, offering a larger sample size.

2. Evaluating market conditions and data for projects that have been installed in Europe and 

Asia when considering offshore wind technology in a given year, because no United States 

projects have been installed to date, to understand total installed project cost expenditures, 

AEP, operating expenditures, and representative turbine technology. The primary source 

for these data is NREL’s internal Wind Database and DOE’s Offshore Wind Market and 

Economic Analysis (Hamilton et al. 2014).

3. Supplementing available market data with modeled data based on a representative or 

reference project that reflects technology and project parameters for a given 

year. Principally, NREL’s Wind Turbine Design Cost and Scaling Model (Fingersh et al. 

2006, Maples et al. 2010) is used to estimate the capital cost and AEP of a project based on 

turbine rated capacity, rotor diameter, hub height, and a representative wind resource. This 

model uses scaling relationships at the component level (e.g., blade, hub, generator, and 

tower) developed with curve-fit industry data, published scaling models, and turbine 

models developed through the WindPACT studies (e.g., Malcolm and Hansen 2006) that 

reflect component-specific and often nonlinear relationships between size and cost (see 

Appendix C in Tegen et al. 2012). The use of this model provides additional componentlevel details for turbines (with user-defined parameters) and plants. 

 4 Note that data for all of these projects is not publicly available. 
17

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

4. Combining the market data and modeled data described above to estimate the primary 

elements necessary to calculate LCOE (i.e., CapEx, OpEx, AEP, and FCR) and provide 

details about wind technology costs and performance that are aligned with market data but 

reported at a more detailed resolution.

This approach is useful in that the reference project is described with a level of detail that is based 

on technology specifications, whereas market conditions are preserved; however, reliance on 

modeled data for disaggregated component-level and energy production estimates also introduces a 

degree of uncertainty in some LCOE input variables. Model uncertainty is introduced principally 

in two areas:

• Modeled installed capital cost tends to underestimate market data that are influenced by 

factors not captured by the model (e.g., the relative value of the U.S. dollar, industry profit 

margins, foreign labor costs, underlying market conditions, and changes in warranty terms 

or servicing agreements that are wrapped into turbine supply agreements) that are included 

in the market-based CapEx that would be included in a commercial wind project.

• The modeled AEPnet estimate relies on estimated total losses across the reference project;

however, production losses are, in reality, site- and technology-dependent, and 

measurements for individual projects are not available.

To address these two sources of uncertainty, model estimates for capital expenditures and capacity 

factor are adjusted to reflect market data by applying two terms: a “market price adjustment” factor 

and a generic “losses” term. These terms apply global adjustment factors (coefficients) to cost and 

production estimates that account for the myriad of factors that are not explicitly modeled, but that 

can have a significant cumulative effect. Continued efforts to improve the fidelity of NREL’s

bottom-up models are expected to result in greater confidence associated with individual 

component estimates and plant-level production; however, it is unlikely that differences between 

market and modeled data will ever be fully resolved. 
18 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

3 System Cost Breakdown Structure

As domestic and global wind markets mature, data for component-level costs are increasingly

available. To manage and organize this component-level cost data, NREL has developed a system 

cost breakdown structure (SCBS) for land-based and offshore wind projects. An SCBS provides 

the ability to view the components of a wind plant at varying degrees of cost detail. From the top 

down, a broad overview of plant costs is shown. From the bottom up, one can see how individual 

component costs are grouped into systems, and how their costs roll up to higher-level costs until 

reaching the plant level. The SCBS deconstructs the total expenditures of a wind project down to 

six levels and includes more than 300 components. 

3.1 SCBS Description

The wind SCBS provides structured and consistent breakdowns of a wind project into smaller, 

more specific components.5 It provides a standardized approach to characterizing total lifetime 

expenditures for wind projects at the component level, including both physical (e.g., materials, 

labor, and equipment) and financial (e.g., insurance during construction, profit, and carrying 

charges) costs. Each descending level of the SCBS hierarchy represents an increasingly detailed 

look at the project components. For example, total lifetime expenditures can be deconstructed into 

two “level 1” components: CapEx and OpEx. CapEx can be further deconstructed into three “level 

2” components: turbine, balance-of-system (BOS), and financial costs (see Figure 1). The sum of 

the costs across all components at a given level should equal the cost of the components in the 

level above them provided that all fields have data. For example, the sum of turbine costs, BOS 

costs, and financial costs (level 2), should equal the CapEx for a given project (level 1). 

Figure 1. Levels 1 and 2 of the SCBS

Source: NREL

 

5

Although the SCBS is similar to a work breakdown structure, they serve different purposes. A work breakdown 

structure is typically process or product oriented, whereas the SCBS is cost oriented with a focus on representing the 

components of a project that contribute to the capital and operational expenditures. 
19

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

The wind SCBS is hierarchical and defines both the position of a component within the system and 

its relationship to other components. In this way, the SCBS effectively defines the bounds for the 

categories of data, reduces the chance of double counting or making inappropriate comparisons,

and standardizes terminology to improve communication.

To be applicable and useful across a broad range of wind projects, an SCBS is designed to 

represent a generic project with line items to capture many possible technology configurations. 

Despite best efforts to define a generic SCBS, there are several reasons to expect it will not apply 

perfectly to any single project in the real world:

• Projects have different components depending on technical specification (e.g., a directdrive wind turbine will not have a gearbox)

• There are many permutations of possible contractual relationships for a project, ranging 

from a single Engineering, Procurement, and Construction (EPC) contract to a full multicontract approach, where a sponsor might manage all contracts internally

• Based on previous experience in collecting data from industry, various entities use different 

approaches for tracking the expenditures involved in a given wind project. The SCBS 

provides a consistent approach to organize the industry data and eliminate variations in 

how the industry groups its subcomponent data.

3.2 Benefits

The wind SCBS specifies well-defined categories to organize wind project expenditures and define 

hierarchical relationships between those categories. In this way, the SCBS provides a natural 

foundation for the design of the NREL wind plant database and provides several secondary 

benefits as well. The SCBS will simplify the collection, organization, and analysis of componentlevel data for projects because it:

• Offers a standard template that can be used for data collection

• Accommodates data required for both top-down and bottom-up analysis

• Enables accurate comparisons across different data sources

• Facilitates the definition of a standard approach for reporting analysis results.

The wind SCBS is also expected to enable improved analytical consistency across DOE’s Wind 

and Water Power Technologies Office portfolio by identifying the full range of system costs for a 

technology and highlighting elements that might be common across similar technologies.

3.3 Approach and Limitations

The first step in developing the SCBS was to review literature describing databases, taxonomies, 

and models related to land-based and offshore wind projects (Table 1). The guiding documents for 

the definition of SCBS elements related to the wind turbine included the ReliaWind Wind Turbine 

Reliability Taxonomy (Tavner 2010) and the Sandia National Laboratory Reliability Database (Hill 

et al. 2009). The guiding documents for the definition of SCBS elements related to the BOS

included BVG Associates’ Guide to an Offshore Wind Farm, NREL’s Offshore Wind BOS Model, 

NREL’s Land-Based BOS Model, and NREL’s Wind Deployment Barriers Project. The guiding 
20

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

documents for the definition of SCBS elements related to OpEx included Netherlands Energy 

Research Foundation Offshore O&M Tool and NREL’s Land-Based O&M Project.

Table 1. Resources Referenced Prior to Developing the SCBS

Land-Based Wind Offshore Wind

Capital Expenditures Capital Expenditures

Wind Turbine Reliability Taxonomy Guide to an Offshore Wind Farm 

 (Tavner 2010) (BVG Associates 2010)

Reliability Database (Hill et al. 2009) Cost Reduction Pathways Study 

 (Crown Estate 2012)

Land-Based BOS Model (NREL) Offshore BOS Model (NREL)

Wind Turbine Design Cost and Scaling Model 

 (Fingersh et al. 2006) Offshore JEDI Model (NREL)

Wind Deployment Barriers Project (NREL) Operational Expenditures

Operational Expenditures Offshore O&M Tool 

Land-Based O&M data collection (Rademaker et al. 2009)

 ([DNV GL Report] Internal Only)

Wind Turbine Design Cost and Scaling Model

 (Fingersh et al. 2006)

In addition to the information provided in the literature review, the following set of basic 

requirements and criteria were developed to guide the development of the SCBS:

• Components in the SCBS are first grouped based on contractual relationship, then 

function/process, then proximity. It is clear, however, that a variety of contractual 

arrangements are used in the industry and the wind SCBS cannot capture them all (e.g., 

turbine supply agreements can include delivery of the turbine either with or without 

installation)

• The SCBS reflects wind project components from the perspective of the project sponsor6

for level 3 categories, and from the perspective of original equipment manufacturers 

(OEMs) or EPC contractors at lower, more detailed levels of the hierarchy

• The SCBS includes wind project components through level 5; additional detail may be 

captured through the description of level 5 components 

• The wind SCBS is flexible enough to describe projects that use many possible technology 

configurations (e.g., a high-voltage alternating current [HVAC] or high-voltage direct 

current [HVDC] export system). A consequence of this variation is that a given project will 

not have all possible components listed in the SCBS—nor would this be expected.

 6 To ensure that the SCBS is a relatively generic structure that can be applied broadly across all wind projects, NREL 

has to account for the different ownership scenarios that are possible during the project lifetime. The project could be 

developed, owned, or operated by the same entity, or ownership could be transferred at any point in the lifecycle.
21

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

An SCBS deconstructs the total expenditures of a wind project down to five levels and includes

more than 300 components. Figure 2 and Figure 3 depict the structure of the hierarchy to level 3 

for capital and operational expenditures, respectively. The full wind SCBS, including descriptions 

of each component category, is included in Appendix E for land-based wind plants and Appendix 

F for offshore wind plants.

Figure 2. Wind system cost breakdown structure: CapEx levels 1 to 3

Source: NREL
22

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Figure 3. Wind system cost breakdown structure: OpEx levels 1 to 3

Source: NREL

Although there are many possible methods for organizing the hundreds of cost elements that make 

up a wind project, this structure strives to be consistent with the way that a project developer and 

operator might see or incur costs. That is, the authors prioritize the contractual relationships of cost 

elements above process or functional relationships. For example, wind turbine tower modules are 

often grouped with substructures and foundations as these three elements provide the same 

functionality. Together, they provide structural support for the wind turbine. Wind turbine supply 

agreements, however, have historically included the tower (the turbine manufacturer supplies both 

the turbine elements and the tower), making it difficult to distinguish the price of the individual 

components. Aligning the organizational structure of the SCBS with the way that project sponsors 

incur costs is expected to greatly simplify data collection and facilitate effective communication 

with commercial stakeholders.

The wind SCBS is not likely to perfectly capture the elements of a specific, real-world wind 

project. Invariably, at a very detailed level (i.e., level 4 or 5), wind projects may utilize different 

component breakdowns when compared to one another. Even at a less detailed level (i.e., level 3) 

the manner in which one sponsor tracks costs might differ from another. The guiding principle for 

the wind SCBS was to develop a systematic approach for organizing component information, with 

the flexibility to accommodate a wide variety of projects, and the specificity to clearly indicate the 

composition of each component line item. This approach removes uncertainty about where each 

component belongs and will minimize the possibility of counting components twice or making 

incorrect or inconsistent comparisons across different projects.

Upon completion of a preliminary wind SCBS, collaborators from NREL, DOE, and industry 

provided feedback on the structure to identify any gaps or redundancies and discussed suggestions 

for modifications and improvements.
23

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

4 Land-Based Wind

The land-based wind reference project was derived from representative characteristics of wind 

plants in DOE’s Wind Technology Market Reports and summarized in Table 6. Reference project 

wind turbine and component costs are based on the most common turbine design installed in the 

United States in 2013, which is a three-stage planetary/helical gearbox feeding a high-speed 

asynchronous generator and a standard spread-foot foundation design. Operating expenditures for 

this project, which are considered on an annual basis, reflect estimates from 94 projects built since 

2000 (Wiser and Bolinger 2014). The reference project wind regime is generally equivalent to a 

moderate wind resource site in the interior region of the United States, generally considered 

Minnesota to Oklahoma.

4.1 2012 Land-Based Cost of Wind Energy 

For the year 2012, no annual cost of wind energy review was published. However, according to the 

2013 Wind Technology Market Report (Wiser and Bolinger 2014), the United States installed a 

record amount of new capacity totalling 13.1 gigawatts (GW) with an average installed cost of 

$1,940/kW. Using the reported average nameplate capacity, rotor diameter, and tower heights for 

the interior project, NREL calculated an AEP of 3,284 MWh/MW/yr using a 200-MW project size. 

Given these inputs as well as the additional variables considered to reflect the reference project, 

details of which are located in Appendix C and summarized in Table 2, the resulting LCOE for 

2012 was $73/MWh.

Table 2. Summary of Inputs and Reference Project 2012 LCOE for Land-Based Installations

Data Source 1.94-MW 

Land-Based Turbine

$/kW

1.94-MW

Land-Based Turbine

$/MWh

Model Turbine capital cost 1,279 37

Model Balance of system 365 11

Model Financial costs7 162 3

Market Market price adjustment8 135 4

Market CAPITAL EXPENDITURES 1,940 56

Market Annual OpEx ($/kilowatt/yr) 55 17

Market Real fixed charge rate (%) 9.5

Model Net annual energy production 

(MWh/MW/yr) 3,284

Model Net capacity factor (%) 37.5

Calculated TOTAL LCOE ($/MWh) 73

 7 Financial costs are incurred before project commissioning, primarily related to the costs that are not part of construction.

8 The market price adjustment is the difference between the modeled cost and the price paid for the typical project in the 2013 

market.
24

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

4.2 Comparison of Two Different Cost of Wind Energy Methodologies

In 2013, the United States installed 1,087 MW of wind energy, a 92% drop from the previous year. 

As reported in the 2013 Wind Technologies Market Report (Wiser and Bolinger 2014), the 

capacity-weighted average cost for installation was $1,630/kW. The report also states that the 

average nameplate capacity was 1.87 MW, the average rotor diameter was 97 meters (m), and the 

average hub height was 80 m, resulting in an AEP of 3,424 MWh/MW/yr. The 2013 sample size 

was limited, with only 11 projects accounting for almost 60% of the installed projects, which could 

disproportionately influence the weighted averages and costs.

Early indications from a larger sample (16 projects totaling over 2 GW) at the time of writing this 

report that were currently under construction or anticipated completion in the first part of 2014 

suggest that the capacity-weighted average was closer to $1,750/kW (Wiser and Bolinger 2014). 

Because of the small 2013 completed project sample size, it was determined that to better represent 

the market, a capacity-weighted average of the 11 projects in 2013 and the 16 anticipated 

commissioned projects in 2014 would be combined to yield 27 projects for the land-based wind 

plant cost of energy analysis for the 2013 year review. Table 3 presents a side-by-side comparison 

of the LCOE analysis for 2013 and the combined 2013-2014 analysis.

Table 3. Comparison of Market-Based Cost of Wind Energy, 2013 Projects to Combined 2013-2014 

Projects

Parameters

(Capacity-weighted averages)

2013 

Projects

2013‒2014 

Projects

Nameplate capacity (MW) 1.87 1.91

Rotor diameter (m) 97 96.7

Hub height (m) 80 82

Modeled net capacity factor 38.5% 38.5%

CapEx ($/kW) 1,630 1,728

FCR (%) 10.2% 10.2%

OpEx ($/kW) 50 50

AEP (MWh/MW/yr) 3,425 3,386

Number of projects in sample 11 27

Total capacity (MW) in sample 650 1,919

TOTAL LCOE ($/MWh) 63 66

For the remainder of this report (and for greater clarity in presenting data) the 2013‒2014 

combined capacity-weighted averages will be labeled “2013,” providing the basis for the 2013 

reference project analysis and reporting.

4.3 2013 Land-Based Cost of Wind Energy

The land-based wind reference project was derived from representative characteristics of 2013 

wind projects consisting of 105 1.91-MW turbines (200 MW total installed capacity). The
25

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

capacity-weighted average of 2013 CapEx

9 costs was calculated to be $1,728/kW, with total 

pretax OpEx reported at $50/kW/yr. Accordingly, these values were ascribed to the land-based 

reference project. Given these inputs, as well as the additional variables considered to reflect the 

reference project and summarized in Table 4 below, the resulting LCOE is $66/MWh.

Table 4. Summary of Inputs and Reference Project LCOE for 2013 Land-Based Installations

Data

Source

1.91-MW 

Land-Based

Turbine

$/kW

1.91-MW

Land-Based

Turbine

$/MWh

Model Turbine capital cost 1,185 35

Model Balance of system 349 10

Model Financial costs10 155 5

Market Market price adjustment11 39 1

Market CAPITAL EXPENDITURES 1,728 51

Market Annual OpEx ($/kilowatt/yr) 50 15

Market Real FCR (%) 10.2

Model Net annual energy production

(MWh/MW/yr) 3,410

Model Net capacity factor (%) 38.5

Calculated TOTAL LCOE ($/MWh) 66

4.4 Capital Expenditures for Land-Based Wind

The weighted-average CapEx and OpEx data are published annually by DOE in the Wind 

Technologies Market Report (Wiser and Bolinger 2014). The analysis conducted here applies the 

NREL Wind Turbine Design Cost and Scaling Model to estimate component-level costs that were

calibrated to the market-based total cost estimates from Wiser and Bolinger (2014). This 

calibration was necessary because recent trends have been influenced by variables that are not 

captured in the current modeling approach of using national averages in a project-specific site 

analysis. NREL has developed a bottom-up model that associates physical parameters with cost 

estimates. Although this approach still under predicts the total cost, it can provide greater fidelity 

in component cost and relative component cost change with the size of the turbine.

 9 CapEx costs represent the cost of building a plant and do not include financing or escalation costs that can vary with 

risk perception, construction schedules, inflation expectations, and other factors. 10 Financial costs are non-construction costs incurred before project commissioning, primarily related to the cost of 

financing.

11 The market price adjustment is the difference between the modeled cost and the price paid for the average project in 

the 2013 market.
26

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Figure 4 illustrates the breakdown of CapEx for the NREL land-based reference project. In the 

figure, the CapEx component percentages highlighted in shades of green capture the turbine capital 

cost; percentages highlighted in blue capture the BOS share of capital costs; and components 

highlighted in purple capture the financial capital costs. For information on the assumptions and 

inclusions of the individual components, see Tegen et al. (2012), Maples et al. (2010), and

Fingersh et al. (2006).

Figure 4. Capital expenditures for the land-based wind reference project

Source: NREL

Table 5 summarizes the costs for individual components (including their contribution to LCOE) 

for average turbine characteristics used in the reference project, based on a project that uses 1.91-

MW turbines. Data sources for this table are described in Appendix B.
27

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 5. Land-Based LCOE and CapEx Breakdown

1.91-MW LandBased Turbine1.91-MW LandBased Turbine

$/kW $/MWh

Rotor Module 282 8

Blades 169 5

Pitch assembly 65 2

Hub assembly 48 1

Nacelle Module 695 21

Nacelle structural assembly 139 4

Drivetrain assembly 235 7

Nacelle electrical assembly 283 8

Yaw assembly 38 1

Tower Module 208 6

TURBINE CAPITAL COST 1,185 35

Development Cost 32 1

Engineering Management 19 1

Foundation 58 2

Site Access and Staging 48 1

Assembly and Installation 43 1

Electrical Infrastructure 150 4

BALANCE OF SYSTEM 349 10

Market Price Adjustment 39 1

Construction Financing Cost 50 2

Contingency Fund 105 3

FINANCIAL COSTS 194 6

TOTAL CAPITAL EXPENDITURES 1,728 51

Wind turbine costs for projects installed in 2013 ranged from $900/kW to $1,300/kW for utilityscale wind projects (Wiser and Bolinger 2014), with many factors driving these differences (such 

as terrain, site access, and regional labor costs). Because of CapEx variability, estimates for the

component costs were established using the NREL Wind Turbine Design Cost and Scaling Model,

and a market price adjustment was added to bring the CapEx cost in line with the industry average. 

The market price adjustment accounts for fluctuations in component costs, profit margins, foreign 

exchange rates, supply chain constraints, and other market conditions. This analysis does not 

attempt to predict which capital cost components are influenced by the market price adjustment, as 

these impacts can vary from project to project. 
28

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

BOS costs were estimated using new scaling relationships and costs from detailed data obtained 

through a major EPC firm active in the wind industry. These new relationships provided a basis for 

understanding the underlying impacts of turbine component designs on the BOS costs as well as 

the impacts of innovative BOS concepts. This additional cost information enabled a more detailed 

breakdown of BOS categories than was available in previous years. Construction financing was

estimated at 3% of hard costs, which is consistent with industry reporting.

4.5 Operating Expenditures for Land-Based Wind

OpEx typically include land lease costs (LLC), operations wages and materials (OPER), and 

maintenance (MAIN). OpEx costs are generally expressed in two categories: fixed operations, 

which includes discrete, known operations costs (e.g., scheduled maintenance, rent, land leasing, 

taxes, utilities, and insurance payments) and typically does not change depending on how much 

electricity is generated (called OPER in this report), and variable OpEx, which includes unplanned 

maintenance and other costs that may vary throughout the project life depending on how much 

electricity is generated (called MAIN in this report). For simplicity, annual OpEx can be converted 

to a single term and expressed as either dollars per kilowatt per year ($/kW/yr) or dollars per 

megawatt-hour ($/MWh). This analysis uses the $/kW/yr convention.

Annual MAIN estimates are calculated from recent estimates of operating costs for projects built 

since 2000. Wiser and Bolinger (2014) reported a pretax average MAIN value of $28/kW/yr that 

generally incorporates the costs of wages and materials associated with maintaining the turbines of 

a facility, but likely excludes other elements such as general operations, insurance, taxes, or 

depreciation.12

The OpEx values reported here include the average estimated property tax payments from NREL’s 

Jobs and Economic Development Impact (JEDI) model and the MAIN for major turbine 

components from Cohen et al. (2008), which are referred to as levelized replacement costs (LRC). 

Property tax costs and MAIN bring the total pretax OpEx to $50/kW/yr and are summarized in 

Table 6. It should be noted that, given the scarcity and unpredictable quality of the data, OpEx can 

vary substantially among projects (Wiser and Bolinger 2014), and the data presented here may not 

fully represent the challenges that operating expenditures present to the wind power industry. In 

addition, researchers across NREL and other laboratories in the wind industry have worked 

together over the past year to validate the $50/kW/yr calculation and support these pricing levels.

 12Alternatively, if expressed in $/kWh terms, O&M estimates in 2013 ranged from $5 to $20/MWh (based on plants 

with a commercial operation date of 2010), with the 2013 O&M baseline estimate of $9/MWh (Wiser and Bolinger 

2014).
29 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 6. Land-Based Wind Reference Project OpEx

1.91-MW

Land-Based 

Turbine

1.91-MW

Land-Based 

Turbine

Operations (OPER) $14/kW/yr $4/MWh

Maintenance (MAIN) $28/kW/yr $9/MWh

Land lease cost $8/kW/yr $2/MWh

OPERATIONAL EXPENDITURES $50/kW/yr $15/MWh

4.6 Annual Energy Production and Capacity Factor for Land-Based 

Wind

Annual energy production (AEP) for this analysis is computed using the NREL wind turbine 

design cost and scaling model. The model computes annual energy capture and other related 

factors, such as capacity factor, for a wind project that is specified by generic input parameters, 

presented in Table 7. These input parameters have been chosen as default values to be held 

constant for the annual LCOE calculations, allowing the differences in turbines and financing to 

influence the results and not project variability. The input parameters can be grouped into three 

general categories: turbine parameters, wind resource characteristics, and losses. 

Table 7. Reference Land-Based AEP Input Assumptions

Turbine Parameters

Turbine rated power (MW) 1.91

Turbine rotor diameter (m) 96.7

Turbine hub height (m) 82.5

Maximum rotor tip speed (meters per second [m/s]) 80

Tip-speed ratio at maximum coefficient of power (Cp) 8 

Drivetrain design Geared

Rotor peak power coefficient (Cp) 0.47

Wind Resource Characteristics

Annual average wind speed at 50-m height (m/s) 7.25

Weibull K 2 

Shear exponent 0.143

Elevation (above sea level [m]) 450

Losses

Losses (i.e., array, energy conversion, and line) 15%

Availability 98%

4.6.1 Turbine Parameters

Turbine parameters are characteristics that are specific to the turbine and independent of the wind 

characteristics. These parameters consist not only of turbine size (such as rated power, rotor 
30

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

diameter, and hub height), but also of turbine operating characteristics such as coefficient of power 

[Cp], maximum tip speed, maximum tip-speed ratio (TSR), and drivetrain design). Because the 

geared drivetrain topology dominates the U.S. market, a geared drivetrain was selected for the 

baseline turbines used in this analysis. For specific approaches used regarding additional turbine 

parameters (e.g., power curves), see the 2010 Cost of Wind Energy Review.

4.6.2 Wind Resource

The annual average wind speed chosen for the reference project analysis was 7.25 meters per 

second (m/s) at 50 m above ground level (7.75 m/s at hub height of 80 m). This wind speed is 

representative of a Class 4 wind resource (7−7.5 m/s) and is intended to be generally indicative of 

the wind regime for projects installed in moderate quality sites in the “interior” region of the 

United States (Minnesota to Oklahoma). An elevation above sea level of 450 m was used based on 

the representative “interior” site. The elevation above sea level coupled with a hub height of 80 m 

results in an average air density of 1.163 kg/m3.

4.6.3 Losses

Although some losses can be affected by turbine design or wind characteristics, losses are treated 

as independent of any other input in this simplified analysis. Types of losses accounted for in this 

analysis include array wake losses, electric collection and transmission losses (from the substation 

to the point of interconnection), and blade soiling losses, totaling 15%. An availability of 98% was 

used, indicating that the wind farm is ready to produce power between wind turbine cut-in and cutout wind speeds 98% of the time. Net annual energy production (AEPnet) is calculated by applying 

all losses to the gross AEP. Table 8 shows the AEP, capacity factors, losses, and availability for 

the land-based reference turbine operating in 2013.

Table 8. Land-Based Wind Turbine AEP and Capacity Factor Summary

1.91-MW Land-Based Turbine

Gross AEP (MWh/MW/yr) 4,094

Gross capacity factor (%) 46.1

Losses and availability (%) 17

AEPnet (MWh/MW/yr) 3,410

Net capacity factor (%) 38.5

4.6.4 Land-Based Wind Finance

Throughout the majority of 2013, the financing environment was not conducive for installing landbased wind projects. The 92% drop in projects completed in 2013 compared to 2012 can be 

directly attributed to the expiration of the production tax credit (PTC), which required projects to 

be completed by December 31, 2012. The PTC, under the American Taxpayer Relief Act of 2012, 

was reinstated in January 2013. This reinstatement allows projects to be eligible as long as they 

meet the Internal Revenue Service’s designation of “Physical Works” and “under construction”

before January 1, 2014; however, the delay in the PTC enactment had already negatively affected

financing and discouraged projects from being completed in 2013.
31

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

The cost of capital for both term debt and tax equity investment in 2013 departed slightly from 

2010 and 2011 levels as the benchmark interest rates in the United States rose. The 20-year 

treasuries that closely approximated the lifetime of a modeled wind project rose from 2.67% in 

December 2011 to 3.63% in December 2013. Similarly, 30-year treasuries rose from 2.98% in 

December 2011 to 3.89% in December 2013. With a rise in benchmark interest rates, the authors

would expect to see higher debt interest rates for wind energy projects generally as well as the 

associated required rate of return.

In 2013, both the tax equity and term debt yields were relatively steady with tax equity on an after 

tax, unlevered basis of 8%, whereas the 15-year CapEx, pretax basis, debt interest rates held below 

6% (Wiser and Bolinger 2014). For this analysis, the discount rate was calculated as the after-tax 

weighted average cost of capital (WACC) for land-based wind energy projects. The base-case 

assumptions used in estimating the WACC include a debt ratio of 50%, an after tax, levered tax 

equity yield of 11.5%, a pretax debt interest rate of 6.5%, and an effective marginal corporate tax 

rate of 38.9%. Under these assumptions, the nominal, after tax WACC for land-based wind energy 

projects in 2013 was estimated at approximately 8.8% (nominal). Assuming a 2.2% rate of 

inflation in 2013, the real after tax discount rate was estimated at 6.5%.13

4.7 Land-Based Wind Reference Project Summary

Table 9 captures the full array of variables that reflect the land-based reference project as well as 

the values (for each variable) that underlay the basic LCOE inputs. The CapEx for the project was 

assumed to be nearly $345 million, or $1,728/kW. A $20.9 million contingency fund was assumed 

to cover any possible increases in capital costs, and OpEx was estimated at $15/MWh. A 20-year 

project operational economic life was assumed, with a nominal discount rate of 8.8%.

Table 9. Land-Based Reference Project Assumptions Summary

General Assumptions

Project capacity (MW) 200

Number of turbines 105

Turbine capacity (MW) 1.91

Site 

Location U.S. Interior

Elevation (meters above sea level) 450

Layout Grid

Wind speed (m/s at 50-m height above ground) 7.25

Wind speed (m/s at 80-m height above ground) 7.75

Net capacity factor 38.9%

Technology

Rotor diameter (m) 96.7

Hub height (m) 82.5

Gearbox Three stage 

Generator Asynchronous

Foundation Spread foot

 13 Converted using the standard Fisher equation. The 2.2% rate of inflation is based on the 2014 Annual Energy 

Outlook by the Energy Information Administration (EIA 2014). 
32

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Cost

Capital cost (millions) $345

Contingency (6%) (millions) $20.9

OpEx ($/MWh) $15

Discount rate (real) 6.5%

Discount rate (nominal) 8.8%

Economic operating life (years) 20

FCR (real) 10.2%

Note: The nominal discount rate may be generally equated with the weighted average cost of 

capital and is distinguished from the real discount rate in that it includes an inflation factor. The 

discount rate constitutes a principal input into the FCR, which allows for the estimation of capital 

recovery on an annualized basis.

4.8 Land-Based Wind LCOE Calculation

Based on the NREL land-based baseline project inputsCapEx, AEP, OpEx, and FCRand using 

the LCOE equation, a land-based wind LCOE is computed to reflect the 2013 reference wind plant 

described above. Table 10 summarizes the costs for the primary components (including their 

contribution to LCOE). Data sources for this table are located in Appendix B. Figure 5 provides a 

graphical representation of the land-based reference project LCOE by line item.

Table 10. Land-Based Wind Reference Project LCOE Cost Breakdown

1.91-MW

Land-Based 

Turbine

1.91-MW

Land-Based Turbine

CAPITAL EXPENDITURES $1,728/kW $51/MWh

OPERATIONAL EXPENDITURES $50/kW/yr $15/MWh

Net 7.25 m/s AEP (MWh/MW/yr) 3,410

Net capacity factor 38.5%

FCR (real, after tax) 10.2%

LEVELIZED COST OF ENERGY ($/MWh) $66
33 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

 

Figure 5. Component level cost breakdown for the 2013 land-based wind reference project 

Source: NREL 

4.9 LCOE Sensitivities 

The input parameters described above reflect the land-based reference wind project; however, 

input parameters for a near-term, land-based wind project are subject to considerable uncertainty. 

As a result, it is beneficial to investigate how this variability may impact LCOE. The sensitivity 

analysis shown in Figure 3 focuses on the basic LCOE inputs: 1) CapEx, 2) OpEx, 3) capacity 

factor (a surrogate for AEP), and 4) FCR, although in Figure 6, FCR is broken into its principal 

elements⎯discount rate and economic operational lifetime. Sensitivities to these variables are 

tested across the ranges of market data reported in previous sections. 
34 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Figure 6. Sensitivity of land-based wind LCOE to key input parameters 

Source: NREL 

Note: The reference LCOE reflects a representative industry LCOE. Changes in LCOE for a single 

variable can be understood by moving to the left or right along a specific variable. Values on the 

X-axis indicate how the LCOE will change as a given variable is altered and all others are 

assumed constant (i.e., remain reflective of the reference project).

Sensitivity analyses were conducted by holding all reference project assumptions constant and 

altering only the variable in question. Sensitivity ranges were selected to represent the highs and 

lows observed in the industry. This selection of ranges provides insight into how real-world ranges 

influence LCOE. The sensitivity analysis yields ranges in LCOE from a low of $50/MWh to a high 

of $103/MWh—a low-to-high increase of nearly double the lower bound. Within the ranges 

shown, CapEx and capacity factor are the two factors that appear to have the greatest impact on 

LCOE; however, the capacity factor and discount rate appear to have the greatest influence with 

respect to decreasing the LCOE relative to the reference project. 

Although the ranges provided here for the selected variables are grounded in actual 2013 plant 

costs and performance data; the high and low LCOE ranges should not be taken as absolute. These 

variables are generally not independent, and it is unlikely for changes to occur only in a single 

variable. Moreover, each individual wind project has a unique set of characteristics. Accordingly, 

the sensitivities shown here are not universal. 

4.10 Cost Reduction Scenarios 

For the 2013 reference project installations, additional scenarios were modeled: 1) increasing the 

hub height, 2) increasing the rotor diameter, 3) combining the technology changes of taller towers 
35

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

and larger rotors, 4) increasing annual average wind speed, and 5) combining all three independent 

scenarios. Although there is a link between changes in cost and energy production, this analysis 

was performed by holding all reference project assumptions constant and changing only the 

necessary variables to demonstrate the relative impacts of isolated changes for illustrative 

purposes.

4.10.1 Increasing Turbine Characteristics

Wiser and Bolinger (2014) noted that average wind turbine characteristics, nameplate capacity, 

rotor diameter, and hub height, have been increasing. The industry is trending toward taller towers, 

with many geographic areas preferring 100-m-tall towers to increase AEP. Assuming the CapEx 

remains constant, the reference project LCOE with a 100-m-tall tower would be expected to 

decrease to $64/MWh (Table 9). In addition, the increase in rotor diameter has outpaced all other 

technological advancements, increasing up to 103% in size since 1998‒1999 (Wiser and Bolinger 

2014). Similar to the findings for taller towers, if the project costs remain constant, the 11% 

increase in AEP resulting from the increased rotor diameter would amount to an LCOE of 

$60/MWh.

Both of these advancements impact the capacity factor and AEP of projects. By combining both 

technology changes—increasing the hub height and rotor diameter—the LCOE would decrease to 

$58/MWh for the reference project (assuming constant capital costs).

4.10.2 Increasing Annual Average Wind Speed

A number of factors, such as policy influences, siting impacts, and technology changes, have led to 

the recent trend in siting wind projects in areas with lower wind resource quality (Wiser and 

Bolinger 2014). There is still a surplus of high-quality wind resource project sites that are 

undeveloped in the United States and an effort to place more projects in these areas could lower 

the project LCOE. Table 11 presents the change in LCOE that is a direct result of switching from a 

Class 4 wind resource (annual average hub-height wind speed of 7.79 m/s) to a Class 5 wind 

resource (annual average hub-height wind speed of 8.6 m/s), thereby decreasing the LCOE to 

$59/MWh. It is important to note that the decrease in LCOE resulting from the better wind 

resource is approximately equivalent to the LCOE reductions achieved with a taller tower or a 

larger rotor for the same turbine power rating ($59/MWh versus $58/MWh, respectively). If both 

of these technological advances can be implemented without a concurrent increase in either CapEx

or OpEx (using advanced controls or design innovations), in combination with a higher average 

wind speed, the net effect would be to reduce the LCOE to $52/MWh in the reference project 

scenarios. 
36

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 11. Example of Land-Based LCOE Reduction Scenarios

Parameters Reference 

Project

Taller 

Tower

Larger 

Rotor

Taller 

Tower and

Larger 

Rotor

Higher 

Wind 

Speed

Scenario

Combination

Nameplate (MW) 1.91 1.91 1.91 1.91 1.91 1.91

Rotor diameter (m) 96.9 96.9 110 110 96.9 110

Hub height (HH) (m) 82.7 100 82.7 100 82.7 100

Avg. speed at 50 m

(Avg. speed at HH) (m/s)

7.25 

(7.79)

7.25 

(8.0)

7.25 

(7.79) 7.25 (8.0) 8.0 (8.6) 8.0 (8.8)

AEP (MWh/MW/yr) 3,410 3,536 3,796 3,918 3,866 4,345

Net capacity factor 38.5% 40.4% 43.3% 44.7% 44.1% 49.6%

CapEx ($/kW) 1,728 1,728 1,728 1,728 1,728 1,728

OpEx ($/MW/yr) 50 50 50 50 50 50

Tax rate (%) 39 39 39 39 39 39

FCR (real, after tax) 10.2% 10.2% 10.2% 10.2% 10.2% 10.2%

LCOE ($/MWh) 66 64 60 58 59 52
37

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

5 Offshore Wind

Although there is much enthusiasm about the potential of offshore wind development in the United

States, no projects have been installed to date. The lack of domestic experience with offshore wind 

technology has contributed to considerable uncertainty in estimates of the potential cost of 

domestic offshore wind energy. The 2010 Cost of Wind Energy Review (Tegen et al. 2012) offers a 

detailed analysis of offshore wind cost trends in Europe as well as projections for the United States 

to develop input assumptions for a reference project based on commercial-scale, fixed-bottom 

offshore wind technology.

This report provides an update to the 2010 report including trends in capital costs observed outside 

of the country as well as recent market conditions; however, as no major differences from the 2010 

report have been observed in offshore costs for projects under development in the United States,

the cost estimates utilized in this report are a result of the annual Offshore Wind Market and 

Economic Analysis (Hamilton et al. 2014) completed by Navigant Consulting, Inc. (Table 12). The 

offshore wind reference project uses the average global turbine characteristics from the Navigant

report including 4.3 MW of capacity, a rotor diameter of 119.4 m, and an 89.5-m-tall tower. 

Although information on floating offshore wind projects is not included here, it is planned to be 

covered in future iterations of this report.

Table 12. Summary of Inputs and Results for the Fixed-Bottom Offshore Wind Project 

Data

Source

4.3 MW

Offshore Turbine

$/kW

4.3 MW

Offshore Turbine

$/MWh

Model Turbine capital cost 1,660 56

Model Balance-of-system costs 2,697 91

Model Financial costs 830 28

Market CAPITAL EXPENDITURES 5,187 175

Market OpEx ($/kW/yr) 136 39

Market FCR (%) 11.7

Model AEPnet (MWh/MW/yr) 3,406

Model Capacity factor (%) 39.0

Calculated TOTAL LCOE ($/MWh) 215

5.1 2013 Market Developments

In 2013, 1,567 MW of offshore wind capacity were installed worldwide (GWEC 2014). To date, 

offshore wind development has been highly concentrated geographically, with over 93% of 

cumulative capacity installed in Europe and 56% located in the United Kingdom (GWEC 2014). 

Installations in Asia are starting to accelerate, with two commercial-scale projects installed in 
38

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

China and three demonstration projects installed in South Korea and Japan. Global markets are 

poised for growth with aggressive goals in both Europe and Asia; however, deployments have 

been affected by uncertainty in the form and value of incentives (United Kingdom), delays in grid 

development (Germany), and local and national government concerns (China). In the United 

States, the three principle hurdles are:

• An uncertain timeline for permitting. The Bureau of Ocean Energy Management 

(BOEM) has made considerable progress in leasing and permitting projects since the 

‘Smart from the Start’ initiative was announced in 2010. BOEM has awarded commercial 

leases in three wind energy areas and is moving forward with an additional four, as well as 

two unsolicited lease request areas. Despite this progress, the duration of the timeline for 

permitting still remains to be seen.

• The scheduled expiration of federal tax credit incentives. The PTC and investment tax 

credit (ITC), the principle federal incentives for wind energy generation, expired at the end 

of 2013.14 Uncertainty over the availability of these incentive programs creates significant 

market risk and makes investors hesitant to commit capital for essential activities in the 

development phase. Furthermore, this uncertainty is likely to slow the development of the 

offshore wind industry because the multiyear development horizons for projects tend to 

exceed the typical periods when the PTC/ITC are active.

• The lack of a defined market for offshore wind power. The biggest near-term challenge 

for the offshore wind energy industry is the lack of a defined market. Federal incentives are 

generally not sufficient enough to attract investment in offshore wind projects by 

themselves given the current cost structure, and there is significant ambiguity as to the 

continued availability of these incentives. Developers are therefore working through state

representatives to augment the federal incentives and achieve financial viability; either 

through offshore wind-specific revenue streams (Offshore Renewable Energy Credits) or 

by negotiating long-term power purchase agreements. Although this approach is allowing a 

number of projects to move forward, it is very complicated and resource intensive for 

developers.

5.2 CapEx for Fixed-Bottom Offshore Wind Reference Project

For the 2011 Cost of Wind Energy Review (Tegen el al. 2013), NREL developed the offshore 

CapEx estimate by conducting several parallel assessments: 1) analyzing global market data, 2) 

reviewing published literature, and 3) interviewing active offshore wind developers in the United 

States. This multipronged approach yielded an average capital cost of $5,120/kW across the 

industry (for operational and proposed plants worldwide), and resulted in a U.S. reference cost 

estimate of $5,600/kW (consistent with the expected CapEx reported by the proposed Cape Wind 

offshore project located off Cape Cod in Nantucket Sound). The 2011 reported range of installed 

capital costs (again for operational and proposed projects) varied from $2,500/kW to $6,500/kW.15

 14 Offshore wind projects that started construction before the expiration of the tax credits—the 468-MW Cape Wind 

project and the 30-MW Block Island wind farm—have announced that they have met the ‘safe harbor’ criteria defined 

by the U.S. Internal Revenue Service and expect to qualify for the investment tax credit (Broehl and Ernst 2014). 15 Offshore wind capital costs may vary widely as a result of water depth, distance from shore, turbine size, and 

other factors.
39

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

In 2012, a DOE analysis of LCOE for offshore wind plant technology used the average global 

installed cost from the Offshore Wind Market and Economic Analysis report, which was 

$5,384/kW (Hamilton et al. 2014). For the LCOE analysis, the same technology was used in the 

2012 analysis as in the 2010 and 2011 cost of wind energy reviews. Details on the 2012 analysis 

are located in Appendix C and resulted in an LCOE of $225/MWh.

According to the 2013 Offshore Wind Market and Economic Analysis report (Hamilton et al.

2014), the global offshore CapEx may be stabilizing; however, there is little data on projects to be 

installed after 2016. Figure 7 shows the capital cost trends since 1994 inflated to 2012 currency 

and converted to U.S. dollars using 2012 average exchange rates. Globally, projects commissioned 

in 2013 had a capacity-weighted average capital cost of $5,187/kW, almost $200/kW lower than 

the average cost of a project installed in 2012.

Figure 7. Reported capital costs for installed, under construction, contracted, and approved 

offshore wind projects in $2012 (2000 to 2016)

Source: Hamilton et al. 2014

Figure 8 shows the percentage contribution of each component to total capital cost for the 

reference offshore wind project. Percentage estimates were based on the NREL Wind Turbine 

Design Cost and Scaling Model (Fingersh et al. 2006, Maples et al. 2010); several recent 

publications (Douglas-Westwood 2010, BVG Associates 2011, Deloitte 2011); and conversations 

with U.S. offshore wind project developers. In Figure 8, the segment in green represents the 

turbine cost, shades of blue represent BOS costs, and shades of purple represent financial costs.
40 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Figure 8. Capital expenditures for the 2013 offshore wind reference project 

Source: NREL 

The percentage estimates in Figure 8 were applied to the global industry average CapEx estimate 

of $5,187/kW to generate individual component costs in dollars per kilowatt for the 2013 reference 

project. This dollar-value component cost breakdown is shown in Table 13. As stated, there is a 

notable difference between the cost components that make up the land-based and offshore projects. 

In the land-based project, 68% of the cost is related to the turbine, whereas the turbine makes up 

only 32% of the CapEx for the offshore project. 

 
41

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 13. Fixed-Bottom Offshore LCOE Component Cost Breakdown

4.3 MW Offshore 

Turbine

$/kW

4.3 MW Offshore 

Turbine

$/MWh

TURBINE CAPITAL COST 1,600 56

 Development Cost 149 5

Engineering Management 90 3

Substructure and Foundation 730 25

Site Access, Staging, and Port 128 4

 Electrical Infrastructure 546 18

 Assembly and Installation 1,053 36

BALANCE OF SYSTEM 2,697 91

 Insurance 87 3

 Decommissioning (surety bond) 115 5

 Construction Financing Cost 156 5

 Contingency 432 15

FINANCIAL COSTS 830 28

CAPITAL EXPENDITURES 5,187 175

5.3 Operating Expenditures for Offshore Wind

There has been no indication that expected operating expenditures for offshore wind projects have 

shifted between 2010 and 2013. The OpEx baseline for 2013 was assumed to be $40/MWh,

equivalent to $136/kW/yr, with a range extending from $20/MWh to $70/MWh. The equivalent 

range on a $/kW/yr basis extends from $68/kW/yr to $239/kW/yr. Operating costs are broken 

down into MAIN, OPER cost,16 and the Outer Continental Shelf (OCS) lease payments.

17

5.4 Offshore Annual Energy Production and Capacity Factor

Hamilton et al. (2014) reported that installed European offshore wind projects typically achieve 

capacity factors between 35% and 50%. Rødsand II, a Danish project installed in 2010, reported a 

capacity factor of 55% in its first year of operation. U.S. developers have announced capacity 

factor expectations for nine project sites currently under development. Data collected by NREL 

suggests that net capacity factors at these projects may range from 32% to 50%, with a capacityweighted average of 38% (NREL 2013).

 16 O&M cost for offshore wind projects is assumed to include labor, vessels, equipment, scheduled maintenance, 

unscheduled maintenance, land-based support, and project administration. 17 Lease payments are expected to range between 2% and 7% of operational revenue. Cape Wind will pay 2% of 

operational revenue in years 1 to 15. The lease payment increases to 7% of operational revenue from year 16 until the 

plant is decommissioned (BOEMRE 2010).
42

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Because net AEP and the corresponding net capacity factor will vary with the wind resource and 

project design, the authors assumed specific site characteristics that are common to the North 

Atlantic Coast for the reference offshore wind project. AEP for this analysis was calculated using 

the NREL Wind Turbine Design Cost and Scaling Model and a Class 6 wind resource. Table 14

shows the assumptions used to calculate the net AEP for the reference project.

Table 14. Fixed-Bottom Reference Offshore AEP Input Assumptions

Turbine Parameters

Turbine rated power (MW) 4.3

Turbine rotor diameter (m) 119.4

Turbine hub height (m) 90

Maximum rotor tip speed (m/s) 90

Tip-speed ratio at peak coefficient of power (Cp) 8

Drivetrain design Geared

Rotor peak power coefficient Cp 0.47

Wind Resource Characteristics

Annual average wind speed at 50 m (m/s) 8.4

Weibull K 2.1

Shear exponent 0.1

Losses

Losses (array, energy conversion, line) 15%

Availability 96%

For this report, the authors assumed that offshore wind projects will experience losses from array 

wake impacts, availability, and inefficiencies in power collection and transmission. Assuming 19% 

total losses, AEPnet was estimated for offshore wind projects using commercially available 

technology and the NREL wind turbine design cost and scaling model. Table 15 shows the impact 

of losses on AEP and capacity factor.
43

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 15. Offshore Wind Turbine AEP and Capacity Factor Summary

4.3-MW Offshore Turbine

Gross AEP (MWh/MW/yr) 4,241

Gross capacity factor (%) 45

Losses and availability (%) 19

Net AEP (MWh/MW/yr) 3,463

Net capacity factor (%) 39.5

These data show that the 2013 baseline project will deliver 3,463 MWh/MW of installed capacity 

annually, which is equivalent to a net capacity factor of 39.5%. The range of AEP estimates around

this baseline extends from 2,600 to 4,820 MWh/MW/year, which corresponds to the range of 

capacity factors (30%–50%) observed in Europe and for planned projects in the United States.

5.5 Financial Parameters for Offshore Wind

There has been no indication that financial parameters for domestic offshore wind projects have 

changed between 2010 and 2013. The reference project discount rate for 2013 is assumed to be 

10.5%, with a range extending from 8% to 15%, based on data reported by Tegen et al. (2012). 

5.6 Offshore Wind Reference Project Summary

The databases and analysis described above informed the creation of the reference project shown 

in Table 16. The 2013 reference project is defined with 116 turbines on monopile foundations and

an average water depth of 15 m. Reference project costs for 2013 were based on estimates for a 

site located 20 km from shore. In addition, turbines rated at 4.3 MW, with a 119-m rotor diameter 

and a 90-m hub height were assumed. The average wind speed at the project site was assumed to 

be 8.4 m/s at 50 m and 8.9 m/s at the 90-m hub height (Class 6 wind regime).18 In the reference

project layout, the turbines are spaced in a grid formation at 8 rotor diameters apart and connected 

to the substation using a radial 33-kilovolt (kV) collection system design. 

The capital expenditures of the project were assumed to be $2.6 billion, or about $5,187/kW, 

including a contingency estimated at 10% of hard costs. After tax, annual operational expenditures

are equivalent to $39/MWh, or $577,600 per turbine per year. 

The weighted average cost of capital (WACC), or discount rate, used to finance the project was 

estimated to be 10.5% nominal (equivalent to 8.3% real). Although this discount rate could 

represent a number of different financial structures, the specific financial structures were not 

examined in this analysis. The reference project was assumed to have an operating life of 20 years 

from the date of commissioning; the FCR under these assumptions is 11.7%. 

 18Average wind speed based on a Weibull (k = 2.1) probability distribution.
44

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 16. Fixed-Bottom Offshore Reference Project Assumptions Summary

General Assumptions

Project capacity (MW) 500

Number of turbines 116

Turbine capacity (MW) 4.3

Site

Location North Atlantic Coast (U.S.)

Depth (m) 15

Distance from shore (km) 20

Wind speed (m/s at a 50 meters above mean sea level [MASML]) 8.4

Wind speed (m/s at a 90 MASML) 8.9

Net capacity factor 39.5%

Technology

Rotor diameter (m) 119

Tower height (m) 90

Gearbox Three-stage

Generator Asynchronous

Foundation Monopile

Cost

Capital cost (millions) $2,600 

Contingency [6.5% of hard costs](millions) $217

OpEx ($/MWh) $39

Discount rate (real) 8.3%

Discount rate (nominal) 10.5%

Operating life (years) 20

Fixed charge rate (real) 11.7%

5.7 Offshore Wind LCOE Calculation

Table 17 summarizes the offshore wind technology reference project by providing the component 

cost categories for the 4.3-MW turbines in the project as well as the LCOE calculation results. A

comprehensive summary of assumptions can be found in Appendix B. Estimates of the percentage 

contribution of individual project components to total capital costs were developed for each 

component based on the aforementioned publications and conversations. These estimates were

applied to the total capital expenditure estimate to generate individual component costs. NREL 

plans to continue to collect market data and develop bottom-up cost models in 2014. These data 

and models will enable the development of an improved understanding of scaling relationships and 

opportunities for technology improvement, and reflect current market data in 2014.
45 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 

Table 17. Fixed-Bottom Offshore Wind LCOE and Reference Project Cost Breakdown 

4.3-MW Offshore 

Turbine 

4.3-MW Offshore 

Turbine 

CAPITAL EXPENDITURES $5,187/kW $175/MWh 

Operations (OPER) $45/kW/yr $13/MWh 

Maintenance (MAIN) $85/kW/yr $24/MWh 

OCS lease cost $6/kW/yr $2/MWh 

OPERATING EXPENDITURES $136/kW/yr $39/MWh 

Net 8.0 m/s AEP (MWh/MW/yr) 3,463 

Net capacity factor 39.5% 

FCR (real, after tax) 11.7% 

LEVELIZED COST OF ENERGY ($/MWh) 215 

The 2013 NREL reference offshore wind project has an LCOE of $215/MWh. Figure 9 shows the 

cost breakdown for the project. 

Figure 9. Cost breakdown for the 2013 offshore wind reference project 

Source: NREL 
46 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

5.8 Offshore Wind LCOE Sensitivities

Although the input parameters used for the LCOE calculation in the reference project represent 

reasonable estimates for the costs and operational parameters of a near-term offshore wind project, 

as was the case for land-based projects, these inputs are subject to considerable uncertainty. The 

sensitivity analysis shown in Figure 10 focuses on the basic LCOE inputs: 1) capital expenditures, 

2) operating expenditures, 3) capacity factor (a surrogate for AEP), and 4) FCR, although in Figure 

10, discount rate and operational lifetime represent FCR. Sensitivities were tested using the 

observed ranges described above and by holding all other variables constant. In Figure 10, the 

reference estimate for each parameter is represented by the vertical white line within each bar, and 

specific high and low values are shown within each colored bar. 

Figure 10. Sensitivity of offshore wind LCOE to key input parameters

Source: NREL

Note: The reference LCOE provides a representative estimate of the offshore wind LCOE, 

assuming commercial-scale fixed-bottom technology. Changes in LCOE for a single variable can 

be understood by moving to the left or right along a specific variable. Values on the X-axis 

indicate how the LCOE will change as a given variable is altered and assuming that all others are 

constant (i.e., the variables remain reflective of the reference project).

During the analysis, sensitivity ranges were selected to represent the highs and lows seen in the 

industry. This selection of ranges provides insight into how real-world ranges influence LCOE. 

Figure 10 shows a very wide range of LCOE outcomes, extending from $147 to $282/MWh; 

however, as noted above in the discussion of land-based sensitivities, the high and low LCOE 

ranges should not be taken as absolute because these variables are not typically independent. For 

offshore wind projects, cost of energy is most sensitive to capital expenditures, capacity factors, 

and discount rate, and appears to be less sensitive to operating life and operating expenditures. 
47

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

6 Historical Levelized Cost of Wind Energy

DOE set goals in 2010 for LCOE for 2020 and 2030. NREL has been assessing the LCOE since 

that time. Table 18 and Table 19 summarize the trends of land-based LCOE and offshore LCOE, 

respectively, in nominal dollars, over time and include the primary LCOE inputs driving these 

results.

In Table 18, LCOE results in 2010 and 2011 differ from the official reports for the given years

because of the changes in methodology for OpEx. In the previous cost of wind energy reviews, the 

authors used an after-tax operational expenditure that affected the labor, equipment, and facilities 

portion of the OpEx. The methodology of using only a pretax value was established in 2012 

because rules and regulations differ based on the specific project location. To compare the 

historical LCOE values and represent the trends, the 2010 and 2011 OpEx were modified to align 

with the current methodology. Appendix D provides additional detail on the historical LCOE, 

DOE’s LCOE goals in 2010 dollars, and a graph showing the historical land-based LCOE in 

constant 2010 dollars with the DOE goals.

Table 18. Historical Land-Based LCOE in Nominal Dollars

Parameters 2010 COE 2011 COE 2012 COE 2013 COE

Nameplate capacity (MW) 1.5 1.5 1.94 1.9

Rotor diameter (m) 82.5 82.5 93.5 96.9

Hub height (m) 80 80 80 82.7

Modeled net capacity factor 38.0% 37.0% 37.5% 38.5%

CapEx ($/kW) 2,155 2,098 1,940 1,728

FCR (%) 9.5% 9.5% 9.5% 10.2%

OpEx ($/kW) 55 55 55 50

AEP (MWh/MW/yr) 3,345 3,263 3,284 3,410

LCOE ($/MWh) 78 78 73 66

Table 19. Historical Offshore LCOE in Nominal Dollars

Parameters 2010 COE 2011 COE 2012 COE 2013 COE

Nameplate capacity (MW) 3.6 3.6 3.6 4.3

Rotor diameter (m) 107 107 107 119.4

Hub height (m) 90 90 90 89.5

Modeled net capacity factor 39.0% 39.0% 39.0% 39.0%

CapEx ($/kW) 5,600 5,600 5,384 5,187

FCR (%) 11.7% 11.7% 11.7% 11.7%

OpEx ($/kW) 136 136 136 136

AEP (MWh/MW/yr) 3,406 3,406 3,406 3,463

LCOE ($/MWh) 232 232 225 215
48

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

7 Conclusions

The results and analysis in this technical report lead to the following conclusions:

• Final LCOE estimates continue to show a downward trend from the 2010 Cost of Wind 

Energy Review to 2013. Offshore turbine costs have shown similar cost reductions; 

however, the decrease in LCOE for the land-based projects can be attributed more to the 

turbine technology, and the offshore decreases to the balance-of-system costs.

• Although the reference project LCOE for land-based installations was observed to be 

$66/MWh, the full range of land-based estimates covers $50–$103/MWh. 

• The reference project offshore estimate is $215/MWh, with a full range of $147–

$282/MWh. This dramatic range is mostly caused by the large variation in capital 

expenditures ($3,200–$6,000/kW) reported by project developers. 

• The sensitivity analysis shows that LCOE can vary widely based on changes in any one of 

several key factors; however, the variable with the most dramatic effect on LCOE is 

capacity factor—which is the case for both land-based and offshore projects.

This analysis presents a picture of the levelized cost of land-based and offshore wind energy using 

real and modeled data that represents 2013 market conditions. Scenario planning and modeling 

activities often focus on one number (or cost) for land-based LCOE and one for offshore LCOE. In 

reality, the cost of land-based wind energy varies greatly across the United States and offshore 

wind LCOE varies significantly across Europe and Asia (Table 20).

The LCOE analysis presented in this report is only one way to measure the cost of wind energy

and it does not include other costs and price issues that influence a given wind project’s viability,

such as transmission, environmental impacts, military constraints, or other areas of consideration 

(e.g., public policy, consumer costs, energy prices, or public acceptance). In addition, these LCOE 

estimates do not reflect the value of electricity, incentives, or other policy mechanisms (such as 

production tax credits or investment tax credits) that affect the sales price of electricity produced 

from wind projects.

Table 20. Ranges of LCOE and Elements for U.S. Land-Based and Offshore Wind in 2013

Land-Based Wind Projects Offshore Wind Projects

Capital expenditures $1,447–$3,000/kW $3,200–$6,000/kW

Operational expenditures $4–$30/MWh $20–$59/MWh

Capacity factor 25%–50% 30%–50%

Discount rate 6%–11% 8%–15%

Operational life 20–30 years 20–30 years

Range of LCOE <$50−>$103/MWh <$147−>$282/MWh
49

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

8 Related and Future Work

NREL continues to work to gain a better understanding of costs associated with many components 

of land-based wind turbines and systems. Ongoing collaboration with industry could lead to better 

data, enhanced modeling capabilities, and increased awareness of current and future wind power 

system component costs. For offshore wind, this analysis provides a best estimate for potential 

domestic wind power projects.

NREL intends to update this review of wind energy costs on an annual basis. These updates are 

intended to help maintain a perspective on costs that is grounded in real-time market changes as 

well as offer greater insight into the costs and performance of individual components related to the 

wind generation system. In addition, these reports are intended to provide greater clarity regarding

wind energy costs and the effects of changes in specific variables on the LCOE. The data and tools 

developed from this work will be used to help inform projections, goals, and improvement 

opportunities. As the industry evolves and matures, NREL will continue to publish current 

representative project data and LCOE estimates for scenario planning, modeling, and goal setting.

Future work entails three primary objectives: 1) continue to enhance data representing marketbased costs, performance, and technology trends to reflect actual wind industry experience, 2) 

enhance the fidelity of bottom-up cost and performance estimation for individual wind plant 

components, and 3) understand sensitivities to factors such as regional differences, site 

characteristics, and technology choices. In 2015 and going forward, NREL will continue to work 

with industry and national laboratory partners to obtain project-specific data to validate and 

improve models. NREL’s ongoing wind analysis efforts include:

• Creating a model to better represent offshore non-turbine project costs, such as

foundations, electrical cabling, and installation, across a range of turbine and project sizes

• Developing a wind energy systems engineering model to conduct enhanced analysis of new 

innovation impacts on turbine cost and performance.

In addition, NREL plans to:

• Update the NREL cost and scaling model with improved, turbine-specific data

• Estimate the effect on LCOE from anticipated improvements to O&M in both land-based 

and offshore wind projects

• Continue work on computational fluid dynamics models to determine the magnitude and 

impact of wake losses

• Quantify the effect of potential technology pathways on system LCOE for land-based and 

offshore wind technology

• Collect data and examine key issues involved in wind power deployment, such as 

transmission, radar, wildlife issues, and public acceptance, to better understand their 

impacts on the cost of wind energy and potentially developable land

• Investigate and estimate the cost of offshore wind energy on floating platforms and 

compare to fixed-bottom foundation substructures.
50

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

References

American Wind Energy Association (AWEA). (2012). Federal Production Tax Credit for Wind 

Energy. Washington. http://www.awea.org/issues/federal_policy/upload/PTC-Fact-Sheet.pdf. 

Accessed August 2012.

Bloomberg New Energy Finance BNEF. (2012b). Levelized Cost of Electricity Update: Q3 2012. 

Energy – Research Note. July 18, 2012.

Bureau of Ocean Energy Management (BOEM). (2011). Renewable Energy Program State 

Activities Web Resources. Washington, DC: U.S. Department of the Interior (DOI) BOEM. 

http://www.boem.gov/Renewable-Energy-Program/State-Activities/Index.aspx. Accessed August 

2012.

BVG Associates. (2011). Guide to an offshore wind farm. The Crown Estate. 

http://www.thecrownestate.co.uk/media/211144/guide_to_offshore_windfarm.pdf. Accessed 

August 2013.

Cohen, J.; Schweizer, T.; Laxson, A.; Butterfield, S.; Schreck, S.; Fingersh, L.; Veers, P.; Ashwill, 

T. (2008). Technology Improvement Opportunities for Low Wind Speed Turbines and Implications 

for Cost of Energy Reduction. NREL/TP-500-41036. Golden, CO: National Renewable Energy 

Laboratory.

Deloitte. (2011). Analysis on the Furthering of Competition in Relation to the Establishment of 

Large Offshore Wind Farms in Denmark. The Danish Ministry of Climate and Energy (ENS). 

http://www.ens.dk/daDK/UndergrundOgForsyning/VedvarendeEnergi/Vindkraft/Havvindmoeller/Fremtidens%20havm

oelleparker/Documents/Deloitte%20Background%20report%202%20-

%20Analysis%20of%20competitive%20conditions%20within%20the%20offshore%20wind%20se

ctor.pdf. Accessed August 2012.

Douglas-Westwood. (2010). Offshore Wind Assessment for Norway. The Research Council of 

Norway.

http://www.nve.no/Global/Energi/Havvind/Vedlegg/Annet/Offshore%20Wind%20Asessment%20

For%20Norway%20-%20Final%20Report%20-%20190510%20with%20dc.pdf. Accessed August 

2012.

Electric Power Research Institute (EPRI). (2007). Renewable Energy Technical Assessment 

Guide—TAG-RE: 2006.

Energy Information Administration (EIA). (2011). Assumptions to the 2011 Annual Energy 

Outlook. ftp://ftp.eia.doe.gov/forecasting/0554(2011).pdf. Accessed February 2013.

Fingersh, L.; Hand, M.; Laxson, A. (2006). Wind Turbine Design Cost and Scaling Model.

NREL/TP-500-40566. Golden, CO: National Renewable Energy Laboratory. 

http://www.nrel.gov/docs/fy07osti/40566.pdf. Accessed August 2012.
51

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Gifford, Jason S.; Grace, R.; Rickerson, W. (2011). Renewable Energy Cost Modeling: A Toolkit 

for Establishing Cost-Based Incentives in the United States March 2010 — March 2011, 

NREL/SR-6A20-51093. Golden, CO: National Renewable Energy Laboratory.

http://www.nrel.gov/docs/fy11osti/51093.pdf. Accessed August 2012.

Global Wind Energy Council (GWEC). (2012). Global Wind Report: Annual Market Update 2013. 

Brussels. http://www.gwec.net/wp-content/uploads/2014/04/GWEC-Global-Wind-Report_9-April2014.pdf. Accessed June 2014.

Hamilton, B.; Bielecki, M.; Bloch, C.; Decker, T.; Frantzis, L.; Midura, K.; Paidipati, J.; Zhao, F. 

(2014). Offshore Wind Market and Economic Analysis 2014 Annual Market Assessment. 

Burlington, MA. 

http://energy.gov/sites/prod/files/2014/09/f18/2014%20Navigant%20Offshore%20Wind%20Mark

et%20%26%20Economic%20Analysis.pdf. Accessed August 2014.

Lantz, E.; Wiser, R.; Hand, M. (2012). The Past and Future Cost of Wind Energy. National 

Renewable Energy Laboratory. NREL/TP-6A20-53510. Golden, CO. 

http://www.nrel.gov/docs/fy12osti/53510.pdf. Accessed February 2013.

Lazard. (2008). Levelized Cost of Energy Analysis – Version 2.0. Lazard Ltd. June 2008.

Malcom, D.; Hansen, A. (2006). “WindPACT Turbine Rotor Design Study.” NREL/SR-500-

32495. Golden, CO: National Renewable Energy Laboratory.

http://www.nrel.gov/docs/fy06osti/32495.pdf. Accessed February 2013.

Maples, B.; Hand, M.; Musial, W. (2010). Comparative Assessment of Direct Drive High 

Temperature Superconducting Generators in Multi-Megawatt Class Wind Turbines. 40 pp.; NREL 

Report No. TP-5000-49086.

National Renewable Energy Laboratory (NREL). (2013). Internal Offshore Wind Project 

Database. The National Renewable Energy Laboratory. Unpublished.

Short, W.; Packey, D.J.; Holt, T. (1995). A Manual for the Economic Evaluation of Energy 

Efficiency and Renewable Energy Technologies. Golden, CO, National Renewable Energy 

Laboratory. March 1995. http://www.nrel.gov/docs/legosti/old/5173.pdf. Accessed February 2013.

Tegen, S.; Hand, M.; Maples, B.; Lantz, E.; Schwabe, P.; Smith, A. (2012); 2010 Cost of Wind 

Energy Review. National Renewable Energy Laboratory. April 2012. 

http://www.nrel.gov/docs/fy12osti/52920.pdf. Accessed February 2013.

Tegen, S.; Hand, M.; Maples, B.; Lantz, E.; Schwabe, P.; Smith, A. (2013); 2011 Cost of Wind 

Energy Review. National Renewable Energy Laboratory. Mach 2013. 

http://www.nrel.gov/docs/fy12osti/56266.pdf. Accessed March 2014.

Wiser, R.; Bolinger, M. (2014). 2013 Wind Technologies Market Report. U.S. Department of 

Energy, Office of Energy Efficiency and Renewable Energy, August 2014. 

http://emp.lbl.gov/sites/all/files/2013_Wind_Technologies_Market_Report_Final3.pdf. Accessed

August 2014.
52

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Wiser, R.; Bolinger, M. (2012). 2011 Wind Technologies Market Report. U.S. Department of 

Energy, Office of Energy Efficiency and Renewable Energy, August 2012.

http://eetd.lbl.gov/ea/emp/reports/lbnl-5559e.pdf. Accessed September 2012.

Wiser, R.; Yang, Z.; Hand, M.; Hohmeyer, O.; Infield, D.; Jensen, P.H.; Nikolaev, V.; O’Malley,

M.; Sinden, G.; Zervos, A. (2011). Wind Energy. In IPCC Special Report on Renewable Energy 

Sources and Climate Change Mitigation [O. Edenhofer, R. Pichs‐Madruga, Y. Sokona, K. 

Seyboth, P. Matschoss, S. Kadner, T. Zwickel, P. Eickemeier, G. Hansen, S. Schlömer, C. von 

Stechow (eds)]. Cambridge, UK, and New York, NY, USA: Cambridge University Press.
53

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Appendix A. Present Value of Depreciation Calculations

Land-Based Wind 

Table A1. Present Value of Depreciation Calculation for Land-Based Wind Reference (d = 8.8%) 

Year Net Book 

Value

5-Year 

MACRS

Depreciation 

Schedule

Depreciation

Present 

Value 

Depreciation

Accumulated 

Present 

Value 

Depreciation

1 100 20.00% 20 18.4 18.4

2 80 32.00% 32 27.0 45.4

3 48 19.20% 19.2 14.9 60.3

4 28.8 11.52% 11.52 8.2 68.5

5 17.28 11.52% 11.52 7.6 76.1

6 5.76 5.76% 5.76 3.5 79.6

MACRS: Modified Accelerated Cost Recovery System

Offshore Wind 

Table A2. Present Value of Depreciation Calculation for Offshore Wind Reference (d = 10.5%)

Year Net Book 

Value

5-Year 

MACRS

Depreciation 

Schedule

Depreciation Present Value 

Depreciation

Accumulated 

Present Value 

Depreciation

1 100 20.00% 20 18.1 18.1

2 80 32.00% 32 26.2 44.3

3 48 19.20% 19.2 14.2 58.5

4 28.8 11.52% 11.52 7.7 66.3

5 17.28 11.52% 11.52 7 73.3

6 5.76 5.76% 5.76 3.2 76.4

MACRS: Modified Accelerated Cost Recovery System
54

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Appendix B. Summary of Assumptions for 2013 Reference

Projects

Land-Based Wind Project Assumptions

Table B1. Comprehensive List of Assumptions for 2013 Land-Based Reference Project Cost of Energy

Assumption Units Value Notes

Project Information

Capacity megawatts 

(MW) 200 Calculation

Number of turbines # 105 Representative of commercial-scale projects

Turbine capacity MW 1.91 Average turbine size installed in United States

Net capacity factor % 38.6 Class 4 wind resource [7.25 meters per second (m/s) at 50 

m], assumed losses (17%)

Rotor diameter meters (m) 96.7 Average rotor size installed in United States

Tower height m 82.5 Average hub height installed in United States

Operational life years 20 Standard business case assumption

Capital Expenditures (CapEx)

CapEx (million) $ 344.7 Calculation

Capital expenditures $/kilowatt 

(kW) 1,728 Average CapEx of 2013 U.S. projects

Market price adjustment $/kW 39 Calculated to bring CapEx in line with market conditions

Hard costs Estimated based on the National Renewable Energy 

Laboratory’s (NREL’s) Wind Turbine Design Cost and 

Scaling Model (Fingersh et al. 2006, Maples et al. 2010), 

NREL’s new balance-of-system model, and NREL’s 

conversations with developers of land-based wind 

projects in the United States

 Turbine $/kW 1,185

 Balance of system $/kW 349

 Soft costs

Construction finance $/kW 50

Contingency $/kW 105

Operating Expenditures (OpEx)

OpEx costs $/megawatthour (MWh) 15

Representative of published literature and NREL’s 

conversations with U.S. land-based wind developers

OpEx costs (pretax) $/kW/yr 50

Operation (OPER) $/kW/yr 14

Maintenance (MAIN) $/kW/yr 28

Land lease $/kW/yr 8

Financing Costs [d, Fixed Charge Rate (FCR)]

Inflation rate % 2.2 Assumption in the Annual Energy Outlook 2013

(Energy Information Administration [EIA] 2013)

Discount rate (nominal) % 8.8

2013 land-based weighted average cost of capital averages Discount rate (real) % 6.5

FCR (nominal) % 12.2

Calculation FCR (real) % 10.2

Cost recovery factor (CRF) (nominal) % 10.8

CRF (real) % 9.0

Taxes (T)

Effective % 38.9 Calculation

Federal % 35 Standard federal corporate tax rate

State % 6 Representative state tax rate

Present Value Depreciation (PVDep)

Depreciable basis % 100 Simplified depreciation schedule

Depreciation schedule 5-yr Modified Accelerated Cost Recovery 

System (MACRS) Standard for choice for renewable energy projects

PVDep % 79.6 Calculation

Levelized cost of energy $/MWh 66 Calculation
55

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Offshore Wind Project Assumptions

Table B2. Comprehensive List of Assumptions for 2013 Offshore Reference Project Cost of Energy

Assumption Units Value Notes

Project Information

Capacity megawatts 

(MW) 500 Representative of commercial-scale projects

Number of turbines # 116 Calculation

Turbine capacity MW 4.3 Average turbine size installed globally

Depth meters (m) 15 Representative of proposed U.S. projects

Distance from shore (kilometers (km) 20 Representative of proposed U.S. projects

Net capacity factor % 39 Class 6 wind resource (8.4 m/s at 50 m), assumed losses 

(18%)

Rotor diameter m 119.4 Average rotor size installed globally

Tower height m 89.5 Average hub height size installed globally

Operational life years 20 Standard business case assumption

Capital Expenditures (CapEx)

CapEx ($) $ millions 2,587.3 Calculation

CapEx $/kilowatt (kW) 5,187 Average global installed capital expenditures (Hamilton et 

al. 2014)

Hard Costs

Values estimated based on the NREL Wind Turbine Design 

Cost and Scaling Model (Fingersh et al. 2006, Maples et al. 

2010), new balance-of-system model, several recent 

publications (Douglas-Westwood 2010, BVG Associates

2011, Hamilton et al. 2014), and NREL’s conversations with 

developers of offshore wind projects in the United States; 

percentage estimates applied to CapEx estimate to obtain 

dollar-per-kilowatt values

Turbine $/kW 1,660

Development $/kW 149

Engineer and management $/kW 90

Substructure and foundation $/kW 730

Port and staging $/kW 128

Electrical infrastructure $/kW 546

Transportation and installation $/kW 1,053

Soft Costs

Insurance during construction $/kW 87

Decommissioning bond $/kW 155

Construction finance $/kW 156

Contingency $/kW 432

Operating Expenditures (OpEx)

OpEx $/megawatthour (MWh) 39 Representative of published literature and NREL’s 

conversations with U.S. offshore wind developers OpEx costs (pretax) $/kW/yr 136

OPER (pretax) $/kW/yr 40 Representative of published literature and NREL’s 

MAIN $/kW/yr 75 conversations with U.S. offshore wind developers

Outer Continental Shelf (OCS) Lease $/kW/yr 21 Cape Wind OCS lease2% operational revenue in years 1–

15, 7% of operational revenue in years 15–20

Financing Costs (d, FCR)

Inflation rate % 2.2 Assumption in Annual Energy Outlook 2010 (EIA 2010)

Discount rate (nominal) % 10.5 Approximate weighted average cost of capital for Cape 

Discount rate (real) % 8.1 Wind and Block Island wind projects

FCR (nominal) % 13.9

Calculation FCR (real) % 11.7

Cost Recovery Factor (CRF)/nominal % 12.2

CRF (real) % 10.3

Taxes

Effective % 38.9 Calculation

Federal % 35 Standard federal corporate tax rate

State % 6 Representative state tax rate

Present Value Depreciation (PVDep)

Depreciable basis % 100 Simplified depreciation schedule

Depreciation schedule 5-yr Modified Accelerated Cost Recovery 

System Standard choice for renewable energy projects

PVDep % 76.4 Calculation

Levelized cost of energy $/MWh 215 Calculation
56

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Appendix C. Summary of Assumptions for 2012 Reference 

Projects

Land-Based Wind Project Assumptions

Table C1. Comprehensive List of Assumptions for 2012 Land-Based Reference Project Cost of Energy

Assumption Units Value Notes

Project Information

Capacity megawatts 

(MW) 200 Calculation

Number of turbines # 103 Representative of commercial-scale projects

Turbine capacity MW 1.94 Most common turbine size in the United States

Net capacity factor % 37.5 Class 4 wind resource [7.25 meters per second (m/s) at 50 

m], assumed losses (17%)

Rotor diameter meters (m) 93.5 Most common rotor size of GE-1.5

Tower height m 83.8 Average U.S. hub height

Operational life years 20 Standard business case assumption

Capital Expenditures (CapEx)

CapEx (million) $ 387.7 Calculation

CapEx $/kilowatt 

(kW) 1,940 Average CapEx of 2012 U.S. projects

Market price adjustment $/kW 195 Calculated to bring CapEx in line with market conditions

Hard costs

Estimated based on the NREL Wind Turbine Design Cost 

and Scaling Model (Fingersh et al. 2006, Maples et al. 

2010), NREL’s new balance-of-system model, and NREL’s 

conversations with developers of land-based wind 

projects in the United States

Turbine $/kW 1,279

Balance of system $/kW 365

Soft costs

Construction finance $/kW 54

Contingency $/kW 108

Operating Expenditures (OpEx)

OpEx costs $/megawatthour (MWh) 17

Representative of published literature and NREL’s 

conversations with U.S. land-based wind developers

OpEx costs (pretax) $/kW/yr 55

OPER (pretax) $/kW/yr 14

MAIN $/kW/yr 33

Land lease $/kW/yr 8

Financing Costs [d, Fixed Charge Rate (FCR)]

Inflation rate % 2.2 Assumption in the Annual Energy Outlook 2012

(EIA 2012)

Discount rate (nominal) % 8 2010 land-based weighted average cost of capital averages Discount rate (real) % 5.7

FCR (nominal) % 11.4

Calculation FCR (real) % 9.5

Cost recovery factor (CRF) (nominal) % 10.2

CRF (real) % 8.5

Taxes (T)

Effective % 38.9 Calculation

Federal % 35 Standard federal corporate tax rate

State % 6 Representative state tax rate

Present Value Depreciation (PVDep)

Depreciable basis % 100 Simplified depreciation schedule

Depreciation schedule 5-yr Modified Accelerated Cost Recovery 

System

Standard for choice for renewable energy projects

PVDep % 81.1 Calculation

Levelized cost of energy $/MWh 73 Calculation
57

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Offshore Wind Project Assumptions

Table C2. Comprehensive List of Assumptions for 2012 Offshore Reference Project Cost of Energy

Assumption Units Value Notes

Project Information

Capacity megawatts 

(MW) 500 Representative of commercial-scale projects

Number of turbines # 139 Calculation

Turbine capacity MW 3.6 Representative of turbine size planned for Cape Wind

Depth Meters (m) 15 Representative of proposed U.S. projects

Distance from shore kilometers (km) 20 Representative of proposed U.S. projects

Net capacity factor % 39 Class 6 wind resource (8.4 meters per second at 50 m), 

assumed losses (18%)

Rotor diameter m 107 Representative of turbine size planned for Cape Wind

Tower height m 90 Representative of turbine size planned for Cape Wind

Operational life years 20 Standard business case assumption

Capital Expenditures (CapEx)

CapEx ($) $ millions 2,694.2 Calculation

CapEx $/kW 5,384 Average global installed capital expenditures (Hamilton 

2013)

Hard Costs

Values estimated based on the NREL Wind Turbine Design 

Cost and Scaling Model (Fingersh et al. 2006, Maples et al. 

2010), several recent publications (Douglas-Westwood

2010, BVG Associates 2011, Deloitte 2011, Hamilton 

2013), and NREL’s conversations with developers of 

offshore wind projects in the United States; percentage 

estimates applied to the total CapEx estimate to obtain 

dollar-per-kilowatt values

Turbine $/kW 1,723

Development $/kW 155

Engineer and management $/kW 94

Substructure and foundation $/kW 758

Port and staging $/kW 133

Electrical infrastructure $/kW 566

Transportation and installation $/kW 1,093

Soft Costs

Insurance during construction $/kW 90

Decommissioning bond $/kW 161

Construction finance $/kW 162

Contingency $/kW 448

Operating Expenditures (OpEx)

OpEx $/MWh 39 Representative of published literature and NREL’s 

OpEx costs (pretax) $/kW/yr 136 conversations with U.S. offshore wind developers

MAIN $/kW/yr 40 Representative of published literature and NREL’s 

OPER (pretax) $/kW/yr 75 conversations with U.S. offshore wind developers

Outer Continental Shelf (OCS) Lease $/kW/yr 21 Cape Wind OCS lease2% operational revenue in years 

1–15, 7% of operational revenue in years 15–20

Financing Costs (d, FCR)

Inflation rate % 2.2 Assumption in Annual Energy Outlook 2010 (EIA 2010)

Discount rate (nominal) % 10.5 Approximate weighted average cost of capital for Cape 

Discount rate (real) % 8.1 Wind and Block Island wind projects

FCR (nominal) % 13.9

Calculation FCR (real) % 11.7

Cost recovery factor (CRF)/ nominal % 12.2

CRF (real) % 10.3

Taxes (T)

Effective % 38.9 Calculation

Federal % 35 Standard federal corporate tax rate

State % 6 Representative state tax rate

Present Value Depreciation (PVDep)

Depreciable basis % 100 Simplified depreciation schedule

Depreciation schedule 5-yr Modified Accelerated Cost Recovery 

System Standard choice for renewable energy projects

PVDep % 76.4 Calculation

Levelized cost of energy $/MWh 225 Calculation
58

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Appendix D. Summary of Historical Levelized Cost of Energy 

Using Reference Projects

Table D1. Historical Land-Based Wind Plant Levelized Cost of Energy as Calculated by NREL

Parameters 2010 COE 2011 COE 2012 COE 2013 COE

Nameplate capacity (megawatts [MW]) 1.5 1.5 1.94 1.91

Rotor diameter (meters [m]) 82.5 82.5 93.5 96.9

Hub height (m) 80 80 80 82.7

Modeled net capacity factor 38.0% 37.0% 37.5% 38.5%

Capital expenditures ($/kilowatt [kW]) 2,155 2,098 1,940 1,728

Fixed charge rate (%) 9.5% 9.5% 9.5% 10.2%

Operational expenditures ($/kW) 55 55 55 50

Annual energy production (megawatthour (MWh)/MW/yr) 3,345 3,263 3,284 3,410

Levelized cost of energy ($/MWh) 78 78 73 66

Table D2. Historical Land-Based Average Wind Plant Turbine Specifications

Respective Market Turbine Parameter Averages 2010 2011 2012 2013

Nameplate Capacity (MW) 1.79 1.97 1.94 1.91

Rotor Diameter (m) 79.8 89 93.5 96.9

Hub Height (m) 84.3 81 83.8 82.7

Figure D1. Historical land-based wind plant levelized cost of energy (LCOE) as calculated by NREL including the 

U.S. Department of Energy’s LCOE goals
59

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table D3. Historical Offshore Wind Plant Levelized Cost of Energy as Calculated by NREL

Parameters 2010 COE 2011 COE 2012 COE 2013 COE

Nameplate capacity (megawatts [MW]) 3.6 3.6 3.6 4.3

Rotor diameter (meters [m]) 107 107 107 119.4

Hub height (m) 90 90 90 89.5

Modeled net capacity factor 39.0% 39.0% 39.0% 39.0%

CapEx ($/kilowatt [kW]) 5,600 5,600 5,384 5,187

FCR (%) 11.7% 11.7% 11.7% 11.7%

OpEx ($/kW) 136 136 136 136

Annual energy production

(MWh/MW/yr) 3,406 3,406 3,406 3,463

Levelized cost of energy ($/MWh) 232 232 225 215

Table D4. Department of Energy’s Cost Goals for Land-Based and Offshore Wind Power

DOE Goals 2020 2030

Land-Based LCOE ($/MWh) 57 42

Offshore LCOE ($/MWh) 167 136
60

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Appendix E. Summary of Land-Based System Cost Breakdown 

Structure

Table E1. Land-Based Wind System Cost Breakdown Structure Terms and Definitions

Level Term Definition

1 Capital expenditures (CapEx) Includes all installed costs incurred prior to the commercial operations date (COD). 

CapEx components include turbine, balance-of-station (BOS), and soft costs.

2 Wind turbine Converts kinetic energy from wind into three-phase AC electrical energy

3 Nacelle module

Provides structural interface between tower module, drivetrain module, and rotor 

module; provides housing for sensitive electrical and mechanical components and 

equipment; enables access by maintenance personnel 

4 Nacelle structural assembly Provides the structure interface between the tower, drivetrain, and rotor and 

shelters sensitive equipment 

5 Enclosure Includes the fiberglass shell, hatches, latches, anchors, and venting

5 Drivetrain and generator support 

structures

Contains the bedplate, framing, flooring, and anchors, including welded steel and 

fasteners

5 Coatings Provides coatings to protect from weather

4 Drivetrain assembly 

Includes the main power conversion system in the wind turbine, where energy 

captured by the rotor is transferred to drive the generator via the main shaft 

system, with or without a gearbox 

5 Gearbox Provides speed and torque conversion between the rotor (low speed) and the 

generator (high speed); only applicable for geared designs

6 Gears Include the planet carrier, planet gear, ring gear, sun gear, spur gear, and hollow 

shaft

6 Bearings Include the planet bearing, carrier bearing, and shaft bearing

6 Housing Contains the bushing, case, mounting, and torque arm system

6 Sensors Include debris sensors, oil level sensors, pressure 1 and pressure 2 sensors, and 

temperature sensors

6 Lube system Contains the primary filter, secondary filter, primary motor, primary pump, 

hose/fitting, seal, and reservoir

6 Cooling system Consists of the pump, radiator, and hoses

5 Low-speed shaft and main 

bearing system

Transfers torque from the rotor to the gearbox (if applicable) or generator (if direct 

drive)

6 Low-speed shaft Contains the low-speed shaft, compression coupling, rotor lock, connector plate, 

and slip ring assembly

6 Main bearing Consists of the main bearing upwind, main bearing downwind, and main bearing 

seals 

6 Sensors Include the main bearing temperature sensors, low-speed shaft rpm, and position 

sensors

5 High-speed shaft and braking 

system

Contains the high-speed shaft, coupling, rotor lock, and transmission shaft
61

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

6 High-speed shaft Includes the high-speed shaft, coupling, rotor lock, and transmission shaft

6 Braking system Consists of the brake disc, brake calipers, brake pads, and transmission lock

6 Sensors Include high-speed shaft rpm sensors and position sensors

4 Nacelle electrical assembly Contains the power off-take system elements located in the nacelle

5 Generator Converts mechanical energy to electrical energy (based on the gearbox-generator 

system)

6 Cooling system Includes hoses, the filter, cooling fan, motor, pump, and radiator

6 Lubrication system Consists of the pump, pump motor, and the reservoir

6 Rotor Includes the commentator, exciter, resistance controller, rotor lamination, rotor 

winding, slip ring, rotor magnets, and brush

6 Sensors Include core temperature sensors, encoders, and watt meters

6 Stator Contains stator magnets, stator lamination, and stator windings

6 Structural and mechanical Includes the front bearing, rear bearing, silent block, housing, and shaft

5 Frequency converter

Converts variable frequency from an asynchronous generator to grid-compliant 

power of the right ‘quality.’ and with a stable frequency of either 50 hertz (Hz) or 60 

Hz

6 Converter auxiliaries 

Include the power supply, cabinet, heating system, cabinet sensor, communication 

and interface unit, control board, generator side fan, grid side fan, measurement 

unit, power supply, power supply (24 volts [V]), tachometer adapter, and 

thermostat

6 Converter power bus

Contains the branching unit, capacitors, contactors, generator side converter, 

generator side power module, grid side converter, grid side power module, 

inductor, load switch, and precharge unit

6 Power conditioning Includes the common mode filter, crowbar system, DC chopper, generator side 

filter, line filter assembly, and voltage limit unit

5 Power electrical system Converts generator voltage to array cable system voltage for collection

6 Power circuit

Includes the insulated-gate bipolar transistor (IGBT) module, rectifier bridge, 

crowbar system, driver/control board, cables, machine contractor, 

Mbusbar/isolator/circuit breaker, M switchgear/disconnect, motor contractor, soft 

starter, and grounding system

6 Main transformer (nacelle) Main transformer when located in the nacelle (also located on the ground outside 

tower)

6 Measurements Equipment to measure the function of the power electric system

6 Switchgear Located in the base of a tower (transformer up tower) or as part of a ground-based 

transformer external to the tower

5

Control and communication 

system (supervisory control and 

data acquisition [SCADA])

Connects the wind turbines with the operations center and utility off taker; provides 

the wind project operator with information about the status of wind turbine 

systems; and allows remote control of some functions

6 Wind turbine controller Includes the rotor controller, nacelle controller, tower controller (all comprised of 

numerous level 6 components)
62

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

6 Communication system 

Contains the analog I/O unit, digital I/O unit, Ethernet module, field bus master, 

field bus slave, frequency unit, and the controller internal communication system

6 Condition monitoring system Comprises sensors, cables, data logger, and the protocol adapter card for the data 

logger

6 Ancillary equipment Includes cables, connectors, and the contactor/circuit breaker fuses

6 Wind plant control equipment

Includes any advanced wind plant control equipment installed on the turbines (e.g., 

nacelle-mounted lidar) or distributed throughout a wind plant (e.g., groundmounted lidar)

5 Auxiliary nacelle electrical system Other equipment necessary for the function of the nacelle electrical system

6 Nacelle electrical services

Include a 24-DC feeder, the auxiliary transformer, breaker, cabinet, fan, fuse, grid 

protection relay, light, mechanical switch, power point/supply, protection cabinet, 

push button, relay, space heater, surge arrester, thermal protection, and 

Uninterruptible Power Supply (UPS)

6 Nacelle lightning protection 

system 

Contains air termination, the bonding element, earth connector and termination, 

sliding contact, spark gap system, and the surge arrester

4 Yaw assembly Provides the structure interface between the tower, drivetrain, and rotor and 

shelters sensitive equipment

5 Brake Comprises yaw brake calipers, the disc, path, and hoses

5 Drives and bearings Include the motor, gear, pinion, bearing, and damper

5 Hydraulics Contain the accumulator, pump, hoses, valves, and motor

5 Yaw sensors Include the wind-up counter, yaw encoder, and position sensor

4 Nacelle auxiliaries Consist of the other equipment within the nacelle necessary for the necessary for 

the function of the wind turbine 

5 Nacelle sensors Includes the anemometer, wind vane, and temperature sensors

5 Internal environment Consists of high-voltage alternating current (HVAC), nacelle vent, and nacelle 

lighting

5 Federal Aviation Administration 

(FAA) lighting Comprises navigational lights (requirements set by FAA in the United States)

5 Walking/climbing infrastructure Includes cat walks, cables, ladders, people hatch, crane hatch, and anchors

5 Safety system

Consists of the tie-off system, firefighting system, fall arrester, down conductor, 

service crate, beacon, nacelle cover metallic mesh, and lighting protection

5 Lightning protection system

Protects the turbine from damage resulting from lightning strikes by passing 

currents to the ground and includes air termination, the bonding element, earth 

connector and termination, sliding contact, spark gap system, and surge arrester

5 External maintenance crane

Lifts small components (<2 mT) from the ground into the nacelle or vice versa and

includes tools, supplies, and replacement equipment

4 Nacelle transportation Includes the costs of transporting the nacelle components from the manufacturing 

facility to the staging area
63

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

3 Tower module

Provides a support structure element that connects the nacelle, drivetrain and rotor

modules with the substructure and foundation, and has the ability to house 

electrical conversion equipment and provide emergency shelter

4 Tower system Provides the primary structural component

5 Tower structure

Includes tower sections that generally consist of rolled steel sections (though other 

options are being considered)

5 Fasteners Connect individual tower elements (e.g., bolts) to other tower elements, the nacelle 

module, and substructure

5 Coatings Protect from corrosion

4 Tower electrical assembly Consists of the electrical system, from the nacelle to the switchgear/transformer 

connection to the array

5 Drop cables

Off-take power from the drivetrain (or main transformer, if located up tower) and 

transport it down tower to the main transformer (if located at the tower base) or 

switchgear

5 Frequency converter

Converts variable frequency from thee asynchronous generator to grid-compliant 

power of the right ‘quality’ and with a stable frequency of either 50 or 60 Hz

6 Converter auxiliaries 

Include the power supply, cabinet, heating system, cabinet sensor, communication 

and interface unit, control board, generator side fan, grid side fan, measurement 

unit, power supply, power supply (24 V), tachometer adapter, and thermostat

6 Converter power bus

Includes the branching unit, capacitors, contactors, generator side converter, 

generator side power module, grid side converter, grid side power module, 

inductor, load switch, and precharge unit

6 Power conditioning Consists of the common mode filter, crowbar system, DC chopper, generator side 

filter, line filter assembly, and voltage limit unit

5 Power electrical system Converts generator voltage to array cable system voltage for collection

6 Power circuit

Comprises the IGBT module, rectifier bridge, crowbar system, driver/control board, 

cables, machine contractor, M Busbar/Isolator/Circuit Breaker, M 

Switchgear/Disconnect, motor contractor, soft starter, and grounding system

6 Main transformer (tower) Main transformer when located in the tower base (can also be mounted in the 

nacelle)

6 Measurements Includes equipment that measures the function of the power electric system

5 Auxiliary tower electrical system

Includes other equipment necessary for the function of the nacelle’s electrical 

system

6 Tower electrical services

Include the 24-DC feeder, auxiliary transformer, breaker, cabinet, fan, fuse, grid 

protection relay, light, mechanical switch, power point/supply, protection cabinet, 

push button, relay, space heater, surge arrester, thermal protection, and UPS
64

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

6 Tower lightning protection 

system 

Consists of air termination, the bonding element, earth connector and termination, 

sliding contact, spark gap system, and surge arrester

4 Ancillary equipment Includes other equipment within the tower necessary for the function of the wind 

turbine

5 Personnel access and survival 

equipment Includes climb assist, elevators, hatches, ladders, landings, lighting, and doors

5 Electrical system Comprises wiring to support tower auxiliaries

5 Tower internal lighting Provides a safe working environment

5 Equipment support Includes other equipment necessary for the function of the wind turbine

5 Aerodynamic accessories Consist of passive accessories on the tower to improve energy capture (likely 

applicable for downwind designs only)

5 Tower-mounted damping system Reduces the transfer of unwanted torque from the nacelle through the tower

5 Internal hoist/lifting 

device/elevator

Consists of a hoisting system (e.g., hoist, other lifting device, and internal 

elevator/lift system) within the tower used to lift tools and supplies during 

maintenance activities

4 Tower transportation Includes the costs of transporting the tower components from the manufacturing 

facility to the staging area

3 Rotor module Captures wind energy and transfers it to the drivetrain (through the low-speed 

shaft) 

4 Blade Captures the kinetic energy in the wind and transfers the torque and other 

unwanted loads to the drivetrain module and rest of the turbine

5 Root structure 

Provides the interface between the main composite section of the blade and the 

blade bearing

5 Sandwich core Consists of the low-density core material between laminates

5 Spar/spar box Includes the spar cap and spar web

5 Bond Provides the bonds for leading edge and trailing edge

5 Fasteners Include the T-bolt/root insert and others

5 Laminates Consist of internal structural laminates and skin laminates

5 Paint and coatings Protect the outside of the turbine and its components from erosion

5 Lightening protection Includes termination and down-conductor

5 De-icing system Consists of sensors, heaters, wiring, and thermal conductors

5 Ballast Adjusts the center of gravity and weight of the blades to make matching sets for a 

wind turbine

5 Aerodynamic accessories Include active and passive blade accessories such as aileron, tip brakes, and so on

4 Pitch assembly

Adjusts the pitch angle of the blades to control power output from the turbine, 

minimize loads, and start/stop turbine as needed; blades are attached to the hub 

through the pitch systems 
65

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

5 Pitch drive

Includes the motor, motor cooling fan, pitch bearing, motor brake, pitch gear, gear 

reducer, pinion, power electronics/drive, cabling, contractor/circuit breaker fuse, 

encoder, power supply, heater, accumulator, and pump

5 Pitch cabinet Consists of the switchboard/limit switch, battery, battery charger, heater, position 

controller, and load controller

5 Sensors Include the temperature sensor, voltmeter, and position sensor

5 Miscellaneous Includes seals, auto lube system, pitch cylinder linkage, bushing, proportional valve, 

and hose/fitting

Hub assembly Connects the blades and pitch system to the low-speed shaft within the drivetrain 

module

5 Hub Connects the blades and pitch system to the low-speed shaft within the drivetrain 

module

5 Nose cone Consists of a protective cap fitted on the hub, largely aesthetic

5 Exit hatch Provides access to and exit from the hub system

4 Rotor transportation Includes the costs of transporting the rotor components from the manufacturing 

facility to the staging area

2 Balance of station Consists of the balance of equipment, labor, and material costs (other than wind 

turbine) incurred prior to COD

3 Development

Includes all activities from project inception to financial close (where financial close 

is the date in which project and financing agreements have been signed and all 

required conditions have been met)

4 Permitting and leasing Consists of acquisition of permits and leases required for site assessment,

construction, and operation at the project site

5 Permit acquisition activities Include the activities necessary to obtain permits from relevant authorities 

5 Lease acquisition activities Include the activities necessary to obtain a commercial or research lease to operate 

the project from relevant authorities

5 Public outreach Consists of stakeholder education, marketing, and other efforts to facilitate public 

acceptance of a project

4 Professional advisory services Include legal support, external consultants, accounting, and so on during 

development

4 Engineering Includes engineering studies to specify the design of the project (e.g., technology

and layout) and better understand economics and risks associated with the design

5 PreFront End Engineering Design 

(FEED)

Includes preliminary engineering design studies to develop the general design of 

project, identify a short list of technologies for further evaluation, and identify fatal 

flaws 

5 FEED

Consists of engineering activities to develop final design specification, address areas 

of risk/uncertainty, determine technical and economic feasibility, and develop 

necessary specifications to begin the procurement process

5 Engineering certification Consists of a review by a third party, independent verification agent to assess the 

feasibility of the design basis, resulting in a certification report
66

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

4 Site characterization

Includes the equipment, material and labor costs required for collecting/analyzing a

wind resource, ocean conditions, and geological data at a project site; defines 

parameters for engineering assessments as data becomes available

5 Siting and scoping

Consists of the initial desktop-level studies to select a project location, develop a 

conceptual design, identify regulatory requirements, and create a preliminary 

business case

5 Studies and surveys

Include the climatic, environmental, and social surveys/studies required by 

regulators or that are otherwise necessary for the project

5 Meteorological (met) station and 

installation

Consists of the met tower, instrumentation, data acquisition system, and associated 

equipment rental and installation

5 Wind resource analysis 

Includes the collection, cleaning, and analysis of data to develop a wind resource 

profile and power production estimates for a selection of turbine types at a project 

site; might include array layout optimization surveys

5 Geotechnical and geophysical 

surveys Perform surveys for project site and each turbine location

4 Interconnection and power 

marketing

Includes activities that are intended to gain access to the transmission grid and 

negotiate contracts to sell or otherwise market power 

5 Interconnection studies and fees

Include the activities required to obtain a Large Generator Interconnection 

Agreement from the Federal Energy Regulatory Commission (FERC), prepared in 

coordination with the transmission system operator. Studies cover the technical 

considerations of an interconnecting project with the grid while maintaining system 

balance and will operate within grid operating limits

5 Transmission rights of way

Includes the costs of obtaining or expanding transmission rights of way for any landbased electric infrastructure (e.g., overhead transmission lines), as well as any costs 

to permit land-based transmission

5 Power marketing Includes efforts to develop power marketing strategies and forecast pricing and 

negotiate power purchase agreements

4 Project management during 

development

Consists of managing the project from the start of the development phase to the

financial close

5 Procurement Consists of the preparation of tenders for each work package, evaluation of bids,

and negotiation with suppliers

5 Salaries

Include salaries for management and support staff on the developer’s payroll; some 

overlap with the categories above is expected, depending on the amount of work 

that is completed internally versus through a contract

5 Sales, general, and administrative Include the overhead for the project company including administrative salaries and 

benefits, rent, utilities, depreciation, insurance, and so on

5 Profit (if private developer)

Consists of any margin earned by the developer upon the sale of the project at 

financial close; does not include the cost to a new owner of any stake that a 

developer might retain in the project
67

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

4 Financing and incentives Consists of fees, closing costs, and staff and consultant efforts to arrange and secure 

equity, debt financing, and government incentives

5 Due diligence 

Includes activities performed by potential investors to investigate the technical and 

economic aspects of the project and estimate its value prior to executing a financial 

commitment (typically conducted by third party technical consultant[s] hired by 

investor[s])

5 Incentives Include efforts performed by the developer to secure and demonstrate qualification 

for local, state, and federal incentives

5 Closing costs

Consist of administrative costs incurred by investors (debt and equity) during the 

evaluation of the investment

5 Legal support Consists of legal support provided to developers during financial negotiations 

3 Engineering management Includes management activities from the financial close to the COD

4 Detailed design and construction 

engineering

Includes costs related to detailed design and construction engineering activities for 

the project

4 Procurement management Includes bid management, purchasing, negotiations, and contract management

4 Construction management Includes quality control and assurance

5 Salaries Include salaries for management and support staff on the project owner’s and/or 

construction manager’s payroll

5 Sales: general and administrative

Consist of overhead for the project company and/or construction manager including 

administrative salaries and benefits, rent, utilities, depreciation, insurance, and so 

on

5 Profit Includes any margin earned by an independent construction management firm

4 Project certification

Consists of review by a third party, independent verification agent to assure that a 

project is in compliance with the design basis as well as technical standards and 

regulatory requirements, resulting in a project certificate

4 Health, safety, and environmental 

monitoring

Includes coordination and monitoring activities to ensure compliance with health, 

safety, and environment (HSE) requirements during construction

5 Health and safety monitoring Includes coordination and monitoring activities to ensure compliance with health 

and safety requirements during construction

5 Environmental monitoring Includes coordination and monitoring activities to ensure compliance with 

environmental requirements during construction

3 Electrical infrastructure Includes equipment and system installation to extract power from turbines via the 

array and transfers that power to the substation and then to the grid

4 Array cable system Collects power generated by the turbines and transports it to the substation

5 Medium Voltage (MV) power 

cables Provide the MV collection system that is buried within the project boundaries

5

Grounding transformer

Includes the supply, Dissolved Gas Analysis (DGA) testing, and installation of the 

grounding transformer at the substation
68

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

5

Pad mount transformer

Includes the supply, DGA testing, installation, and River Interference Voltage (RIV)

testing of the transformer at the turbine (if applicable)

5 Switchgear Provides the termination point between the collection system and the turbine

5 Low Voltage (LV) cables Provide the LV collection system buried within the project boundaries

5 Backfill Includes the engineered backfill to cover up the collection system and 

communication cabling system

5 Ground system Includes the lightening protection and grounding system supplied by the original 

equipment manufacturer (OEM) to be installed with the foundation 

5 Ancillary equipment Includes other elements that provide necessary functions to the export cable system 

6 Termination kit Consists of the necessary components to connect the cable to substation and 

electric infrastructure for communication, LV, and MV systems

6 Connectors Connect individual sections of cable together, in the event of long cable runs or 

damage

5 Array cable system 

commissioning

Assures that all array cable systems and components are operational through a 

predefined series of tests and checks

5 Array cable system transportation Includes the costs of transporting the array cable components from the 

manufacturing facility to the staging area

4 Ancillary systems Include other optional elements that provide functions to a project 

5 Diesel generator back up Provide power to the substation if the grid connection is lost

5 Fuel tanks Consist of the fuel tanks and pumping equipment for the generator 

5 Safety and security systems

Include access control, to safeguard personnel from hazards arising from the 

installation, maintenance, or operation of substation equipment

5 Spare parts Include spares for the substation

4 Transmission infrastructure Connects the onsite substation to the utility substation

5 Land leases/Right-of-Way Consist of the land lease or right-of-way payments for the transmission corridor

5 Transmission lines and poles Include the overhead transmission lines

5 Switchyard Interconnect switchyard at the utility substation

5 Land-based transmission 

infrastructure transportation

Includes the costs of transporting the land-based transmission infrastructure 

components from the manufacturing facility to the staging area

4 Underground cable system

Include any underground cables required for connecting export cables to the landbased substation

5 Underground cables Connect export cables to the land-based substation directly or via overhead lines

5 Ancillary equipment Includes the equipment required for the underground cable system including ducts 

4 Substations House the electric conversion equipment to transform or convert power from the 

export voltage to the grid voltage
69

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

5 Buildings/facilities Consist of climate-controlled structures that house electric conversion equipment

5 Civil infrastructure Provides improvements to a construction site (e.g., roads) necessary for substation 

construction and operation

5 Electric conversion equipment 

Transforms generated power from the export cable voltage to the interconnection 

voltage and/or converts that power from DC to AC (e.g., AC transformers, 

switchgears, shunt reactors, and DC converters)

5 Ancillary systems

Consist of other elements that provide necessary functions to the substation during 

operations (e.g., metering equipment, safety and security systems, fire protection, 

and gas detection )

5 AC transformers Consist of power convertors that step up generated power from the array cable 

voltage to the export voltage

5 High-voltage switchgear Controls, protects, and disconnects the high-voltage connection

5 Medium-voltage switchgear Controls, protects, and disconnects the medium-voltage connection

5 Shunt reactors Consist of onboard reactive compensation equipment

5 DC converter

Converts power from high-voltage AC (HVAC) to high-voltage DC (HVDC) for export 

to shore

5 Filtering system Uses filters to address harmonics generated by HVDC converters

5 Substation Integration, Assembly, 

Test and Checkout (IATC)

Consists of activities performed by the turbine manufacturer to integrate, assemble, 

test, and verify the substation substructure and foundation before delivering to the 

customer (does not include commissioning activities)

5 Substation transportation Includes costs of transporting the substation components from the manufacturing 

facility to the staging area

3 Plant commissioning Includes the cost incurred by the owner or prime contractor to test and commission 

the integrated power plant

3 Site access, ports, and staging

Includes the activities and physical aspects of a staging area; elements needed to 

support the delivery, installation, storage, handling, and deployment of wind plant

components

4 Facilities Consist of temporary facilities (trailers) supplied by subcontractors for supporting 

the construction of a wind plant; area needs to be leveled and compacted

5 Laydown area

Includes the space at the staging area used to store turbine components and 

conduct any pre-assembly work on the ground; also stores other subcontractor 

components prior to delivering to the pad

5 Utilities Include the temporary power, restrooms, and water located at a facility to be used 

by subcontractors during the construction phase

3 Assembly and installation

Include assembly and installation activities conducted at the project site; assume 

that financial costs related to warranties, contractor insurance, SG&A, profit margin, 

and so on are loaded in rates for labor and equipment
70

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

4 Roads

Includes modifying public roads as required, creating site entrances, and 

constructing site roads per the layout, OEM transportation guidelines, and 

engineering drawings

4 Erection Includes costs of equipment and labor to assemble wind turbines on individual pads

5 Cranage

Includes cranage fees to use and operate crawler cranes, topping cranes, and 

stabilizing cranes used for the assembly of a wind turbine; includes the number of 

cranes, day rates, mobilization and demobilization on site, and breakdowns as 

required for relocating crawler cranes over long distances

5 Fasteners Provides hardware to secure connections between the foundation structure, tower 

components, nacelle, and rotor elements

5 Grout, grout lines, and seals Consist of grout and ancillary equipment to secure connections between foundation 

elements 

4 Commissioning

Process of testing the mechanical components of a turbine and commissioning it for 

energy production; complete when 100 kilowatts per turbine are supplied to the 

grid

3 Foundation Provides the structural foundation for a wind turbine

4 Excavation Creating wind turbine pads and locating the structural foundation

4 Primary structure Consists of rebar and concrete (spread foot, P&H, or modified P&H)

4 Batch plant Provides a temporary onsite facility to create concrete for a project

4 Foundation transportation Involves the transportation of foundation materials to the staging area

3 Operations and maintenance

(O&M) infrastructure

Includes the capital investment in facilities, equipment, and other assets required 

for O&M

4 Permanent facilities

Include O&M facilities, offices, warehouse, parking, the SCADA server, restrooms, 

and so on

4 O&M equipment purchases

Include other purchases necessary for operating the wind project after COD;

examples include: safety equipment (e.g., harnesses), equipment to store 

replacement parts (e.g., climate control for spare electric cables), and vehicles to 

support operations (e.g., fork trucks)

2 Financial costs

Consist of financial expenditures for which the project owner is responsible prior 

to COD, related to either payments for financial products, carrying charges on 

loans, or setting up financial instruments 

3 Project contingency budget

Provides a liquid financial instrument set up to respond to "known unknown" costs 

that arise during construction; does not include contingences set by manufacturers 

and contractors as part of supply contract pricing
71

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

3 Insurance during construction 

(IDC)

Consists of insurance policies held by the owner during the construction period, 

which may include construction all risk, cargo, commercial general liability, workers 

compensation, environmental site liability, pollution liability, and so on; does not 

include insurance held by contractors

3

Carrying charges during 

construction (construction 

financing costs)

Include carrying charges of expenditures on equipment and services incurred before 

COD

3

Reserve accounts (maintenance 

expenditures [MRAs], debt 

service expenditures [DSRAs])

Provide financial arrangements in which payments (before commissioning) are 

deposited into reserve accounts; generally required by either financiers or 

regulators

4 Maintenance reserve accounts Include payments (before commissioning) into reserve accounts set up to cover 

major MRAs, often required by debt service providers

4 Debt service reserve accounts Include payments (before commissioning) into reserve accounts set up to cover 

DSRAs, often required by debt service providers

4 Decommissioning reserve 

account

Include payments (before commissioning) into reserve accounts to fund project 

decommissioning obligations (e.g., surety bonds) 

1 Operational expenditures Consist of expenditures required to operate the project and maintain availability, 

generally annualized

2 Operations Include nonequipment costs of operations for a project

3 Environmental, health, and safety Includes coordination and monitoring activities to ensure compliance with HSE 

requirements during construction

4 Health and safety monitoring Includes coordination and monitoring activities to ensure compliance with health 

and safety requirements during operations

4 Environmental monitoring Includes coordination and monitoring activities to ensure compliance with 

environmental requirements during operations

3 Business-related annual leases, 

fees, and costs

Consist of payments for permission to operate at a project site, terms defined within

a lease, any payments to transmission system operators for rights to transport 

generated power, any payments to infrastructure owners for the right to operate 

power facilities, and

4 Land leases Consist of payments to land owners for rights to operate transmission lines, the

substation, or other facilities

4 Transmission charges/rights Include any payments to transmission system operators or transmission asset 

owners for rights to transport generated power

4 FERC fees Include fees paid to FERC during operations

3 Insurance

Consist of insurance policies held by the project company or operations manager 

during the operational period

3 Operation, management, and 

general administration

Consist of activities necessary to determine, dispatch, sell, and manage the plant’s 

power production; includes staff and equipment both on and off site
72

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

4 Generation planning and 

integration

Includes efforts spent on forecasting, selling, and dispatching the power generated 

by the facility

4 Operating facilities Include co-located offices, parts store, maintenance sheds, and so on

4 Operating equipment Includes lease payments for operating equipment held by the project to support 

operations (e.g., cranes and fork trucks)

4 Sales: general, and administrative

Includes financial reporting, public relations, procurement, parts and stock 

management, HSE management, training, subcontracts, and general administration

of project site

4 Turbine power consumption Consists of charges for power drawn from the grid by the wind project (e.g., turbine

and substation) during operation

4 Weather forecasting Provides a daily 96-hour forecast of wind conditions that is used to plan 

maintenance visits and project power production

4 Operations management

Includes coordination of equipment and personnel to carry out maintenance and 

inspections of generation and transmission equipment

4 Condition monitoring Consists of monitoring SCADA data from wind turbine components to optimize 

performance and identify component faults

4 Operating margin Includes any margin earned by an independent operations management company

4 Professional advisory services Consist of legal support, external consultants, accounting, and so on during 

operation

2 Maintenance Includes labor and equipment costs of operations for the project

3 Long-term service agreement

Consists of the annualized cost of a contract between the project owner and a third 

party to maintain the project at a guaranteed level of availability for a defined 

period; will likely replace scheduled and unscheduled maintenance categories below 

for the duration of the contract

3 Scheduled maintenance

Consists of planned, routine activities to ensure that equipment, systems, and 

structures are operating correctly and at optimal efficiency, and to minimize 

unscheduled breakdowns/ downtime; includes cost of labor, equipment, spare 

parts, and consumables

4 Wind turbine scheduled 

maintenance Consists of planned maintenance activities for turbine systems

5 Nacelle module Includes planned maintenance related to the drivetrain modules

5 Rotor module Includes planned maintenance related to the rotor modules

5 Tower module Includes planned maintenance related to the tower modules

4 BOS scheduled maintenance Includes planned maintenance activities for BOS

5 Electrical transforming 

equipment inspection Consists of inspecting the switchgears, transformers, and back-up power supply

5 DC converter inspection Consists of inspecting the DC converter equipment and filtering equipment 

5 Land-based electric infrastructure Includes inspections of the switchgear, transformers, and any connections

3 Unscheduled maintenance

Involves interventions and other activities to respond to random failures; costs 

include equipment, labor, replacement parts, and consumables (also known as 

corrective maintenance)
73

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition

4 Wind turbine unscheduled 

maintenance Consists of performing unscheduled maintenance for turbine systems

5 Nacelle module Includes corrective maintenance related to the drivetrain modules

5 Rotor module Includes corrective maintenance related to the rotor modules

5 Tower module Includes corrective maintenance related to the tower modules

4 BOS unscheduled maintenance Includes unscheduled maintenance for BOS

5 Foundation Includes corrective maintenance related to the substructure and foundations

5 Electrical infrastructure Includes the corrective maintenance related to the electric infrastructure

5 Other infrastructure Includes the corrective maintenance related to other infrastructure

5 Electric infrastructure Includes servicing and repairs to the switchgear, transformers, and any connections 

(infrequent)

4 Unscheduled maintenance 

contingency

Consists of a liquid financial instrument set up to respond to ‟known unknown”

costs that arise during maintenance
74

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Appendix F. Summary of Offshore System Cost Breakdown 

Structure

Table F1. Offshore Wind System Cost Breakdown Structure Terms and Definitions

Level Term Definition 

1 Capital expenditures (CapEx) Consist of all installed costs incurred prior to the COD; CapEx components 

include the turbine, BOS, and soft costs

2 Wind turbine Converts kinetic energy from wind into three-phase AC electrical energy

3 Nacelle module

Provides a structural interface between the tower module, drivetrain module, 

and rotor module; Also provides housing for sensitive electrical and mechanical 

components and equipment, and enables access by maintenance personnel

4 Nacelle structural assembly Provides the structural interface between the tower, drivetrain, and rotor, and 

shelters sensitive equipment

5 Enclosure Includes the structure, exit hatch, hatch, latches, and helicopter landing pad

5 Drivetrain and generator support 

structures

Include the bedplate and generator frame (can be a single unit), including welded 

steel and fasteners

5 Coatings Protect the outside of the wind turbine from corrosion in a marine environment

4 Drivetrain assembly 

Consists of the main power conversion system in the wind turbine, where energy 

that is captured by the rotor is transferred and drives the generator via the main 

shaft system, with or without a gearbox 

5 Gearbox Provides speed and torque conversion between the rotor and the generator 

(only applicable for geared designs)

6 Gears Include the planet carrier, planet gear, ring gear, sun gear, spur gear, and hollow 

shaft

6 Bearings Include the planet bearing, carrier bearing, and shaft bearing

6 Housing Consists of the bushing, case, mounting, and torque arm system

6 Sensors Include the debris sensors, oil level sensors, pressure 1 and pressure 2 sensors, 

and temperature sensor

6 Lube system Consists of the primary filter, secondary filter, primary motor, primary pump, 

hose/fitting, seal, and reservoir

6 Cooling system Includes the pump, radiator, and hoses

5 Low-speed shaft and main bearing 

system

Transfers torque from the rotor to the gearbox (if applicable) or generator if 

direct drive

6 Low-speed shaft Includes the low-speed shaft, compression coupling, rotor lock, connector plate, 

and slip ring assembly

6 Main bearing Includes the main bearing upwind, main bearing downwind, and main bearing 

seals 

6 Sensors Include the main bearing temperature sensor, low-speed shaft rpm, and position 

sensor

5 High-speed shaft and braking 

system

Consists of the high-speed shaft, coupling, rotor lock, and transmission shaft

6 High-speed shaft Includes the high-speed shaft, coupling, rotor lock, and transmission shaft
75

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

6 Braking system Consists of the brake disc, brake calipers, brake pads, and transmission lock

6 Sensors Include the high-speed shaft rpm sensor and position sensor

4 Nacelle electrical assembly Consists of the power off-take system elements located in the nacelle

5 Generator Converts mechanical energy to electrical energy

6 Cooling system Includes the hoses, filter, cooling fan, motor, and radiator

6 Lubrication system Includes the pump, pump motor, and reservoir

6 Rotor Consists of the commentator, exciter, resistance controller, rotor lamination, 

rotor winding, slip ring, rotor magnets, and brush

6 Sensors Include the core temperature sensor, encoder, and watt meter

6 Stator Include stator magnets, stator lamination, and stator windings

6 Structural and mechanical Consist of the front bearing, rear bearing, silent block, housing, and shaft

5 Frequency converter

Converts the variable frequency from the asynchronous generator to gridcompliant power of the right ‘quality’ and with a stable frequency of either 50 or 

60 Hz

6 Converter auxiliaries 

Consist of the power supply, cabinet, heating system, cabinet sensor, 

communication and interface unit, control board, generator side fan, grid side 

fan, measurement unit, power supply, power supply (24 V), tachometer adapter, 

and thermostat

6 Converter power bus

Includes the branching unit, capacitors, contactors, generator side converter, 

generator side power module, grid side converter, grid side power module, 

inductor, load switch, and precharge unit

6 Power conditioning System Consists of the common mode filter, crowbar system, DC chopper, generator side 

filter, line filter assembly, and voltage limit unit

5 Power electrical system Converts the generator voltage to the array cable system voltage for collection

6 Power circuit

Consists of the IGBT module, rectifier bridge, crowbar system, driver/control 

board, cables, machine contractor, M busbar/isolator/circuit breaker, M 

switchgear/disconnect, motor contractor, soft starter, and grounding system

6 Main transformer (nacelle) Consists of the main transformer when located in the nacelle (can also be 

mounted in the tower)

6 Measurements Use equipment to measure the function of the power electric system

6 Switchgear

Provides the termination point between the collection system and the turbine. It 

is either located in the base of the tower (transformer up tower) or

or as part of a ground-based transformer that is external to the tower

5 Control and communication 

system (SCADA)

Connects wind turbines with a land-based operations center, providing wind 

project operators with information about the status of wind turbine systems and 

allowing for the remote control of some functions

6 Wind turbine controller Consists of the rotor controller, nacelle controller, and tower controller (all 

comprised of numerous level 6 components)

6 Communication system 

Consists of the analog I/O unit, digital I/O unit, Ethernet module, field bus 

master, field bus slave, frequency unit, and controller internal communication 

system

6 Condition monitoring system Includes sensors, cables, a data logger, and protocol adapter card for the data 
76

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

logger

6 Ancillary equipment Consists of cables, connectors, and the contactor/circuit breaker fuse

6 Wind plant control equipment

Includes any advanced wind plant control equipment installed on the turbines 

(e.g., nacelle-mounted lidar) or distributed throughout the plant (e.g., groundmounted lidar)

5 Auxiliary nacelle electrical system

Includes the other equipment necessary for the function of the nacelle electrical 

system

6 Nacelle electrical services

Consist of the 24-DC feeder, auxiliary transformer, breaker, cabinet, fan, fuse, 

grid protection relay, light, mechanical switch, power point/supply, protection 

cabinet, push button, relay, space heater, surge arrester, thermal protection, and

UPS

6 Nacelle lightning protection system 

Consists of air termination, bonding element, earth connector and termination, 

sliding contact, spark gap system, and surge arrester

4 Yaw assembly Provides the structure that interfaces between the tower, drivetrain, and rotor,

and shelters sensitive equipment

5 Brake Includes the yaw brake calipers, disc, path, and hoses

5 Drives and bearings Consist of the motor, gear, pinion, bearing, and damper

5 Hydraulics Include the accumulator, pump, hoses and valves, and motor

5 Yaw sensors Include the wind-up counter, yaw encoder, and position sensor

4 Nacelle auxiliaries Consist of the other equipment within the nacelle necessary for the function of 

the wind turbine 

5 Nacelle sensors Include the anemometer, wind vane, and temperature sensors

5 Internal environment Consists of the HVAC, nacelle vent, and nacelle lighting

5 FAA lighting Consists of the navigational lighting lights (requirements set by the FAA in the

United States)

5 Walking/climbing infrastructure Consists of the cat walks, cables, ladders, landing, people hatch, crane hatch, and 

anchors within the turbine tower

5 Safety system

Consists of the tie-off system, firefighting system, fall arrester, down conductor, 

service crate, beacon, metallic mesh nacelle cover, and lighting protection

5 Lightning protection system

Protects the turbine from damage caused by lightning strikes by passing currents 

to the ground; includes the air termination, bonding element, earth connector 

and termination, sliding contact, spark gap system, and surge arrester

5 External maintenance crane (Davit) Lifts small components (e.g., <2 metric Tons (mT)) from the support structure or 

maintenance vessel into the nacelle

4 Nacelle transportation Includes the costs of transporting the nacelle components from the 

manufacturing facility to the staging area

3 Tower module

Consists of a support structure element that connects the nacelle with the 

substructure and foundation, and can house electrical conversion equipment 

and provide emergency shelter

4 Tower system Consists of the primary structural component
77

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

5 Tower structure

Includes the tower sections, generally consisting of rolled steel sections (though 

other options are being considered)

5 Fasteners Consist of bolts the connect individual tower elements to other tower elements, 

the nacelle module, and the substructure

5 Coating Protect from corrosion in the marine environment

4 Tower electrical assembly

5 Drop cables

Consist of cables to off-take power from the drivetrain (or main transformer, if 

located up tower) and transport down tower to the main transformer (if located 

at tower base) or the array cable interface

5 Frequency converter

Converts variable frequency from the asynchronous generator to grid-compliant 

power of the right ‘quality’ and with a stable frequency of either 50 or 60 Hz

6 Converter auxiliaries 

Consist of the power supply, cabinet, heating system, cabinet sensor, 

communication and interface unit, control board, generator side fan, grid side 

fan, measurement unit, power supply, power supply (24 V), tachometer adapter, 

and thermostat

6 Converter power bus

Includes the branching unit, capacitors, contactors, generator side converter, 

generator side power module, grid side converter, grid side power module, 

inductor, load switch, and precharge unit

6 Power conditioning system

Consists of the common mode filter, crowbar system, DC chopper, generator side 

filter, line filter assembly, and voltage limit unit

5 Power electrical system Converts the generator voltage to the array cable system voltage for collection

6 Power circuit

Includes the IGBT module, rectifier bridge, crowbar system, driver/control board, 

cables, machine contractor, M busbar/isolator/circuit breaker, M 

switchgear/disconnect, motor contractor, soft starter, and grounding system

6 Main transformer (tower) Consists of the main transformer when located in the tower base (can also be 

mounted in the nacelle)

6 Measurements Use equipment to measure the function of the power electric system

5 Auxiliary tower electrical system

Includes other equipment necessary for the function of the nacelle’s electrical 

system

6 Tower electrical services

Include the 24-DC feeder, auxiliary transformer, breaker, cabinet, fan, fuse, grid 

protection relay, light, mechanical switch, power point/supply, protection 

cabinet, push button, relay, space heater, surge arrester, thermal protection, and

UPS

6 Tower lightning protection system 

Consists of the air termination, bonding element, earth connector and

termination, sliding contact, spark gap system, and surge arrester

4 Ancillary equipment Other equipment within the tower necessary for the function of the wind turbine

5 Personnel access and survival 

equipment

Includes the climb assist, elevators, hatches, ladders, landings, lighting, doors, 

food and fresh water storage

5 Electrical system Consists of the wiring needed to support tower auxiliaries

5 Tower internal lighting Consists of the lighting within the tower to provide a safe working environment
78

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

5 Equipment support Includes the other equipment necessary for the function of the wind turbine

5 Aerodynamic accessories Include the passive accessories on the tower to improve energy capture (likely 

applicable only for downwind deigns)

5 Damping system (tower mounted) Reduces the transfer of unwanted torque from the nacelle through the tower

5 Internal hoist/lifting 

device/elevator

Consists of the hoisting system (e.g., the hoist, other lifting device, and internal 

elevator/lift system) within the tower used to lift tools and supplies during 

maintenance activities

4 Tower transportation Includes the costs of transporting the tower components from the manufacturing 

facility to the staging area

3 Rotor module Captures wind energy and transfers it to the drivetrain (through the low-speed 

shaft) 

4 Blade Captures the kinetic energy in the wind and transfers torque and other unwanted 

loads to the drivetrain module and rest of the turbine

5 Root structure 

Provides the interface between the main composite section of the blade and the 

blade bearing

5 Sandwich core Consists of the low-density core material between laminates

5 Spar/spar box Includes the spar cap and spar web

5 Bond Provides the bond for the leading edge and trailing edge

5 Fasteners Includes the T-bolt/root insert and others

5 Laminates Include the internal structural laminates and skin laminates

5 Paint and coatings Protect the outside of the turbine and its components from erosion

5 Lightening protection Consists of termination and the down conductor

5 De-icing system Includes sensors, heaters, wiring, and thermal conductors

5 Ballast Adjusts the center of gravity and weight of the blades to make matching sets for 

a wind turbine

5 Aerodynamic accessories Include active and passive blade accessories such as aileron, tip brakes, and so on

4 Pitch assembly

Adjusts the pitch angle of the blades to control power output from the turbine, 

minimize loads, and start/stop the turbine as needed; blades are attached to the 

hub through the pitch systems 

5 Pitch drive

Includes the motor, motor cooling fan, pitch bearing, motor brake, pitch gear, 

gear reducer, pinion, power electronics/drive, cabling, contractor/circuit breaker 

fuse, encoder, power supply, heater, accumulator, and pump

5 Pitch cabinet Consists of the switchboard/limit switch, battery, battery charger, heater, 

position controller, and load controller

5 Sensors Includes the temperature sensor, voltmeter, and position sensor

5 Miscellaneous Include the seals, auto lube system, pitch cylinder linkage, bushing, proportional 

valve, and hose/fitting

4 Hub assembly Connects the blades and pitch system to the low-speed shaft within the 

drivetrain module
79

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

5 Hub Connects the blades and pitch system to the low-speed shaft within the 

drivetrain module

5 Nose cone Consists of a protective cap fitted on the hub that is largely aesthetic

5 Exit hatch Provides access to and from the hub system

4 Rotor transportation Includes the costs of transporting the rotor components from the manufacturing

facility to the staging area

2 Balance of system

Consists of the balance of equipment, labor, and material costs (other than the 

wind turbine) incurred prior to COD

3 Development

Includes all activities from project inception to financial close (financial close is 

the date in which the project and financing agreements have been signed and 

all the required conditions have been met)

4 Permitting and leasing Involves the acquisition of permits and leases required for site assessment, 

construction, and operation at the project site

5 Permit acquisition activities Includes the activities necessary to obtain permits from relevant authorities 

5 Lease acquisition activities Include the activities necessary to obtain a commercial or research lease (from 

relevant authorities) to operate the project

5 Public outreach Includes stakeholder education, marketing, and other efforts to facilitate public 

acceptance of a project

4 Professional advisory services Consist of legal support, external consultants, accounting, and so on during 

project development

4 Initial engineering

Consist of engineering studies to specify the design of the project (e.g., 

technology and layout) and understand the economics and risks associated with 

the design

5 Pre-FEED

Consist of preliminary engineering design studies to develop the general design 

of a project, identify a short list of technologies for further evaluation, and 

identify fatal flaws 

5 FEED

Include engineering activities to develop final design specification, address areas 

of risk/uncertainty, determine technical and economic feasibility, and develop 

the necessary specifications to begin the procurement process (20% to 30% 

design level); additional engineering activities (e.g., preliminary, detailed, and

final) are covered in engineering and management

5 Engineering certification Includes the review by a third-party, independent verification agent to assess the 

feasibility of design basis, resulting in a certification report

4 Site characterization

Consists of the equipment, material, and labor costs required for the

collecting/analysis of wind resource, ocean conditions, and geological data at a

project site; defines parameters for engineering assessments as data becomes 

available

5 Siting and scoping

Consist of the initial desktop-level studies to select the project location, develop 

a conceptual design, identify regulatory requirements, and create the preliminary 

business case

5 Studies and surveys

Include the environmental and social surveys/studies required by regulators or

that are otherwise necessary for the project
80

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

5 Met and ocean monitoring stations 

Includes the meteorological tower and the substructure (fixed or floating), buoys, 

benthic node, acoustic Doppler current profilers, instrumentation 

(meteorological and oceanographic), and data acquisition systems

5 Met and ocean monitoring 

installation 

Includes the vessels, labor, and equipment required to install the met station, 

instrumentation, and data acquisition system

5 Wind resource analysis 

Involves the collection, cleaning, and analysis of data to develop the wind 

resource profile and power production estimates for a selection of turbine types 

at a project site; might include array layout optimization surveys

5 Geotechnical and geophysical 

surveys

Include the vessels, labor, and equipment required to establish bathymetry, 

seabed features, water depth, stratigraphy, and identify hazards on the seafloor;

performed for the project site and potential cable routes to interconnection

4 Interconnection and power 

marketing

Consist of activities performed to gain access to the transmission grid and 

negotiate contracts to sell or otherwise market power 

5 Interconnection studies and fees

Include activities required to obtain a Large Generator Interconnection 

Agreement from FERC, prepared in coordination with the transmission system 

operator; studies cover technical considerations of the interconnecting project 

with the grid while maintaining system balance and grid operation within 

specified limits

5 Transmission rights of way

Include costs of obtaining or expanding the transmission rights of way for any 

land-based electric infrastructure (e.g., overhead transmission lines); includes 

any costs to permit transmission on land

5 Power marketing Includes efforts to develop a power marketing strategy, forecast pricing, and 

negotiate power purchase agreements

4 Project management during 

development

Managing the project from the start of the development phase to the financial 

close

5 Procurement Preparing tenders for each work package, evaluation of bids, and negotiations 

with suppliers

5 Salaries

Include salaries for management and support staff on the project developer’s 

payroll; some overlap with categories above is expected, depending on the 

amount of work that is completed internally versus contracted

5 Sales: general and administrative Consists of overhead for the project company including administrative salaries 

and benefits, rent, utilities, depreciation, insurance, etc.

5 Profit (if private developer)

Includes any margin earned by the developer upon sale of the project at financial 

close; does not include the cost to a new owner of any stake that a developer 

might retain in the project

4 Financing and incentives Include fees, closing costs, and staff and consultant efforts to arrange and secure 

equity, debt financing, and government incentives

5 Due diligence 

Involves activities performed by potential investors to investigate the technical 

and economic aspects of the project and estimate its value prior to executing a 

financial commitment; typically conducted by third-party technical consultant(s) 

hired by investor(s)

5 Incentives Consist of efforts performed by the developer to secure and demonstrate 

qualification for local, state, and federal incentives
81

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

5 Closing costs

Include administrative costs incurred by investors (debt and equity) during the 

evaluation of the investment

5 Legal support Consists of developer's legal support during negotiations to arrange financing

3 Engineering and management Consists of management activities performed from financial close through COD

4 Detailed design and construction 

engineering Include the detailed design and construction engineering costs

4 Procurement management

Consists of bid management, purchasing, negotiations, and contract 

management

4 Construction management Includes quality control and assurance

5 Salaries Consist of salaries for management and support staff on of the project owner’s

and/or construction manager’s payroll

5 Sales: general and administrative

Consists of the overhead for the project company and/or construction manager 

including administrative salaries and benefits, rent, utilities, depreciation, and 

insurance

5 Profit Includes any margin earned by an independent construction management firm

4 Project certification

Consists of review by a third party, independent verification agent to assure that 

the project is in compliance with the design basis as well as technical standards 

and regulatory requirements; results in a project certificate

4 Health, safety, and environmental 

monitoring

Consists of coordination and monitoring to ensure compliance with HSE 

requirements during construction

5 Health and safety monitoring Consists of coordination and monitoring to ensure compliance with health and 

safety requirements during construction

5 Environmental monitoring Includes coordination and monitoring to ensure compliance with environmental 

requirements during construction

3 Electrical infrastructure Consists of all electrical infrastructure to collect power from the generators and 

deliver to the grid

4 Array cable system Collects power generated by the turbines and transports it to the offshore 

substation

5 Array cables (high or medium 

voltage) Connect turbines with the offshore substation or export turbine

5 Protection Consists of equipment and materials used to protect cables from damage (e.g., 

strikes, overbending, and so on)

6 Scour protection Includes rock fill, sand bags, or concrete mattresses to protect from scouring;

used where burial is not possible

6 Seabed protection mats

Consist of concrete, sand bags, and polyurethane mats to route cables over 

existing electric/telecommunications cables

6 Ducting system

Provides a protective sheath that can be fitted around cables where burial is not 

an option
82

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

6 J-tube seals Provide a seal to the ends of the J-tube to keep sea water out; can be active or 

passive

6 Bend restrictors Prevents the overbending of static cables during installation and operation

6 Bend stiffeners Limit bending stresses and maintain an acceptable curvature for dynamic cables 

at the hang-off point and touch down

5 Ancillary equipment Include other elements that provide necessary functions to the array cable 

system

6 Termination kit Consists of the necessary components to connect the array cable to each turbine 

transformer

6 Connectors Connect individual sections of cable together, in the event of long cable runs or 

damage

6 Buoyancy modules Manage buoyancy in some dynamic cable configurations and control load

transfer

6 Anchorage Maintains the station of dynamic cable at the touchdown point

6 Messenger lines and buoys

Include the ancillary equipment used during the installation of static and dynamic 

cable systems

6 Portable diesel generators

Provide power to turbines if the grid connection is not established before 

commissioning, including generators, fuel tanks, fuel, fueling, and maintenance 

during deployment

6 Array cable system commissioning Assures that all array cable systems and components are operational through a 

predefined series of tests and checks

5 Array cable system transportation Includes costs of transporting the array cable components from the 

manufacturing facility to the staging area

4 Export cable system

Connect turbines or offshore substations with the land-based electric 

infrastructure or offshore converter station (if DC); includes IATC

5 Export cables (High or medium 

voltage)

Connect turbines or offshore substations with the land-based electric 

infrastructure or offshore converter station (if DC); includes IATC

5 Protection Includes the equipment and materials used to protect the cable from damage 

(e.g., strikes and overbending)

6 Scour protection Includes the rock fill, sand bags, or concrete mattresses to protect from scouring;

used where burial is not possible

6 Seabed protection mats

Include the concrete, sand bags, and polyurethane mats to route cables over 

existing electric/telecommunication cables

6 Ducting system

Provides a protective sheath that can be fitted around cables in which burial is 

not an option

6 J-tube seals Seal the ends of the J-tube and keep sea water out; can be active or passive
83

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

6 Bend restrictors Prevents the overbending of static cables during installation and operation

6 Bend stiffeners Limit bending stresses and maintain an acceptable curvature for dynamic cables 

at the hang-off point and touch down

5 Ancillary equipment Includes other elements that provide necessary functions to the export cable 

system 

6 Termination kit Consist of necessary components for connecting the cable to the substation and 

to land-based electric infrastructure

6 Connectors Connect individual sections of cable together, in the event of long cable runs or 

damage

6 Buoyancy modules Manage buoyancy in some dynamic cable configurations and control load 

transfer

6 Anchorage Maintains the station of dynamic cable at the touch down point

6 Messenger lines and buoys

Consist of the ancillary equipment used during the installation of static and 

dynamic cable systems

5 Export cable system transportation Includes the costs of transporting the export cable components from the 

manufacturing facility to the staging area

4 Offshore substation(s) 

Includes the electric conversion equipment required to step up or convert power 

for export to the land-based grid and support structure; also includes onboard 

work platforms, accommodation, equipment storage, and helicopter access

5 Topside 

Provides support and climate-controlled housing for the electrical conversion 

equipment; can also provide work platforms, accommodation, equipment 

storage, and helicopter access

6 Structure Includes material, equipment, and labor costs of fabricating structural steel or 

concrete structure

6 Helicopter deck Provides the onboard helicopter landing platform

6 Accommodations Include the refuge, temporary, or permanent accommodations for project 

personnel

6 Outfitting steel Includes additional nonstructural elements attached to the primary structure

6 Topside marine systems Consist of the ancillary systems required for marine operations

6 Substation topside and foundation 

IATC

Consists of activities performed by the manufacturer to integrate, assemble, test, 

and verify the substation topside before delivering to the customer (does not 

include commissioning activities)

6 Substation topside transportation Includes costs to transport the substation topside from the manufacturer to the 

staging port

5 Substructure and foundation Includes all elements of the offshore substation below the point of connection

with the topside

6 Foundation Consists of the main structural interface that transfers the loads into the seabed

6 Substructure Connects the foundation to the substation topside
84

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

6 Substructure marine systems

Consist of ancillary systems for marine operations; the major element is the 

ballast system for floating offshore substations

6 Scour protection Includes rock fill or concrete mattresses to protect substructures from scouring 

at the point of connection to the seafloor

6 Substation substructure and

foundation IATC

Consists of activities performed by the manufacturer to integrate, assemble, test, 

and check out the substation substructure and foundation before delivering to

the customer (does not include commissioning activities)

6 Substation substructure and

foundation transportation

Includes costs to transport the substation substructure and foundation from the 

manufacturer to the staging port

5 Electrical conversion equipment

Steps up power from the array cable voltage to the export voltage and/or 

converts power to DC 

6 AC transformers Step-up generated power from the array cable voltage to the export voltage

6 High-voltage switchgear Controls, protects, and disconnects the high-voltage connection

6 Medium-voltage switchgear Controls, protects, and disconnects the medium-voltage connection

6 Shunt reactors Consist of the onboard reactive compensation equipment

6 DC converter Converts power from HVAC to HVDC for export to shore

6 Filtering system Filters to address harmonics generated by HVDC converters

6 Substation electrical conversion 

equipment IATC

Includes activities performed by the manufacturer to integrate, assemble, test, 

and check out the substation electrical conversion equipment before delivering

to the customer (does not include commissioning activities)

6 Substation electrical conversion 

equipment transportation

Includes costs to transport the substation electrical conversion equipment from 

the manufacturer to the staging port

5 Ancillary systems

Consist of other elements that provide necessary functions to the offshore 

substation during operations

6 Diesel generator back up Provides power to the substation if the grid connection is lost

6 Fire protection system Includes fire alarms and fire response equipment

6 Water tanks Include fresh water tanks and pumping equipment

6 Fuel tanks Consist of fuel tanks and pumping equipment For the generator and possibly 

emergency fueling of service/crew transfer vessels

6 Control and communication 

system 

Connects the substation with an operations center on land; provides the project 

operator with information about the status of substation systems; and allows 

remote control of some functions

6 Safety and security systems

Include access control to safeguard personnel from hazards arising from the 

installation, maintenance, or operation of substation equipment

4 Land-based transmission 

infrastructure 

Include any land-based transmission or conversion equipment required to 

connect a project to the grid
85

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

5 Land leases

Consist of land lease or right-of-way payments for the transmission corridor prior 

to COD

5 Underground cable system

Includes any underground cables required for connecting export cables to the 

substation on land

6 Underground cables Connect export cables to the land-based substation directly or via overhead lines

6 Ancillary equipment Consists of the ancillary equipment required for the underground cable system 

including ducts 

5 Self-supporting towers with 

insulators

Support any overhead lines required for connecting export cables to the landbased substation

6 Foundations Include support tower structures, typically reinforced concrete

6 Transmission towers Support overhead transmission lines

6 Insulators Attach overhead transmission lines to the towers

5 Overhead lines Transmit power and enable communications with the offshore wind project

6 Conductors Transmit power between the export cable and land-based substation (threephase system)

6 Communications

Consist of the fiber optic wire routed to the control center that transmits 

information from the data acquisition system (DAS) and Conditioning Monitoring 

System (CMS), and allows land-based control of project systems

6 Shield wire Provides a grounded conductor to protect phase conductors from surges 

(lightning)

5 Onshore substations House electric conversion equipment to transform or convert power from the 

export voltage to the land-based grid voltage

6 Buildings/facilities House electric conversion equipment (climate controlled)

6 Civil infrastructure Provide necessary improvements to the construction site (e.g., roads) for 

substation construction and operation

6 Electric conversion equipment 

Transforms generated power from the export cable voltage to the 

interconnection voltage and/or converts power from DC to AC (e.g., AC 

transformers, switchgears, shunt reactors, and DC converters)

6 Ancillary systems

Include other elements that provide necessary functions to the substation during 

operations (e.g., metering equipment, safety and security systems, fire 

protection, and gas detection)

5 Land-based transmission 

infrastructure transportation

Includes the costs of transporting the land-based transmission infrastructure 

components from the manufacturing facility to the staging area

3 Plant commissioning Includes the cost incurred by the owner or prime contractor to test and 

commission the integrated power plant

3 Site Access, port, and staging

Consist of activities and physical aspects of a staging port; elements needed to 

support the delivery, storage, handling, and deployment of offshore wind plant

components
86

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

4 Facilities Include port facilities or space leased to support the installation of a project

5 Laydown area

Consists of the leased space at the staging port to store turbine components and 

foundations

5 Assembly areas

Consist of the leased space at the staging port with a high load bearing capacity 

to perform land-based assembly activities

5 Utilities Include temporary power, restrooms, and water located at facilities to be used 

by subcontractors during the construction phase

5 Fabrication facilities Support fabrication, construction, or assembly of components

4 Cranage

Includes cranage fees to use and operate crawler cranes, tower cranes, harbor 

cranes, and self-propelled modular transporters for the land-based assembly of 

components and loading onto installation vessels

4 Port improvements

Consist of any improvement to the existing port infrastructure that is paid for by 

the project owner (e.g., quayside reinforcement)

4 Port fees Include fees for vessel access, docking, and loading/unloading

5 Entrance/exit fees

Consist of charges levied upon entry of vessels into the port, generally calculated 

using a standard formula basis upon gross registered ton

5 Quayside docking fees

Include charges levied for the use of a berth either occupied by a vessel or by 

preassembly activities

5 Wharfage fees

Include charges for loading or unloading cargo from vessels, generally calculated 

by tonnage and equipment requirements for loading/unloading the cargo

3 Assembly and installation

Consists of assembly and installation activities conducted at the staging port 

and at the project site; assume that financial costs related to warranties, 

contractor insurance, SG&A, profit margin, and so on, are loaded in day rates 

for vessels, labor, and equipment

4 Substructures and foundations Include vessel, labor, and equipment costs to complete installation of 

foundations and substructures

5 Foundation Includes vessel, labor, and equipment costs to complete installation of the 

foundation

5 Substructure Includes vessel, labor, and equipment costs to complete installation of the 

substructure

5 Scour protection Includes vessel, labor, and equipment costs to complete installation of scour 

protection

4 Turbines Include vessel, labor, and equipment costs to complete turbine installation for 

the entire project

5 Towers Include vessel, labor, and equipment costs to complete tower installation 

5 Nacelle Includes vessel, labor, and equipment costs to complete nacelle installation

5 Blades Include vessel, labor, and equipment costs to complete blade installation

4 Electrical infrastructure Includes vessel, labor, and equipment costs to install electrical infrastructure

5 Array cables Include installation of the subsea array cable system
87

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

6 Laying Includes vessel, labor, and equipment costs to lay array cables

6 Trenching Includes vessel, labor, and equipment costs to bury array cables

6 Protection Includes vessel, labor, and equipment costs to protect array cables

6 Terminations Include vessel, labor, and equipment costs to pull array cables through J-tubes 

and connect to transformers

5 Export cables installation of subsea export power cable system from offshore substation to 

land-based substation 

6 Laying/trenching Includes vessel, labor, and equipment costs to lay and bury export cables

6 Protection Includes vessel, labor, and equipment costs to protect export cables

6 Terminations Includes vessel, labor, and equipment costs to pull export cables through J-tubes 

and connect to transformers

6 Landfall operations Include vessel, labor, and equipment costs to transition export cable from the

subsea trench to the land-based jointing pit 

5 Offshore substation(s) Include costs of installing offshore substations at a project site

6 Substructure Includes vessel, labor, and equipment costs to install substation substructure(s)

6 Topside Includes vessel, labor, and equipment costs to install substation topside(s)

5 Offshore accommodations 

platform(s) Include costs of installing offshore accommodations platforms at a project site

6 Substructure Includes vessel, labor, and equipment costs to install offshore accommodations 

platform substructure(s)

6 Topside Includes vessel, labor, and equipment costs to install offshore accommodations 

platform topside(s)

5 Land-based electric infrastructure Includes costs of installing land-based electric infrastructure

6 Underground cable system Includes labor and equipment costs to install underground cables on land

6 Overhead transmission lines Include labor equipment costs to install overhead transmission lines

6 Land-based substation Includes labor and equipment costs to install land-based substation

3 Other infrastructure Includes other capital investments made by the project company prior to COD

4 Offshore accommodations 

platform(s) House project personnel during operations

4 Dedicated O&M vessel(s) Includes new-build vessels owned by the project company that will be used 

exclusively to support operations at a project site

4 Land-based O&M facilities Consist of facilities on land, owned by the project company, to support the 

operation of the project

4 O&M equipment purchases

Include other purchases necessary for the operation of the wind project after 

COD; examples include safety equipment (e.g., harnesses and floatation devices), 

equipment to store replacement parts (e.g., climate control for spare electric 

cables), and vehicles to support operations (e.g., fork trucks)

3 Substructure and foundation Includes all elements of the offshore wind turbine support structure below the 

point of connection with the tower 
88

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

4 Substructure Connects the foundation to the tower

5 Primary structure

Consists of structural steel or concrete (e.g., jacket, tripod, floating platform, and 

gravity base)

5 Transition piece Provides the main structural interface between the primary structure and point 

of connection with the tower

5 Fasteners Secure connections between the substructure and foundation elements 

5 Grout, grout lines, and seals Secure connections between the substructure and foundation elements 

5 Marine coatings Provide anti-corrosion protection for substructure elements

4 Foundation Provides the main structural interface that transfers loads into the seabed 

5 Bedding stones

Provide a stable and level surface on which to place gravity-based structures or 

anchors

5 Piles Consist of steel pipes driven into the seabed to provide support and transfer 

loads acting on the structure into seabed

5 Anchors Transfer loads from floating platforms into the seabed (installed below the 

mudline)

5 Mooring lines Include chain, wire, or synthetic fiber ropes to connect floating platforms with 

anchors on the seabed

5 Mooring tendons Consist of synthetic fiber ropes or welded steel pipers to connect floating 

tension-leg platforms with anchors on the seabed

5 Connecting hardware (required) Attach the mooring lines/tendons to anchors and to the platform 

5 Messenger lines and buoys Provide the ancillary equipment used to install the mooring system

4 Outfitting steel Includes additional nonstructural elements attached to substructure elements

5 Vessel landing Provides the interface between the maintenance vessels and the substructure to 

enable safe access for personnel

5 Service platforms and decks Provide access to the inside of the turbine and a work platform for maintenance 

activities

5 J-tube Routes array cable from the trench to the point of connection with the turbine

and protects the cable from dynamic loads

5 Ladders Provide access from the vessel landing to the deck

5 Railings Enclose the deck to provide a safe working environment for personnel

5 Marine coatings Provide anti-corrosion protection to any outfitting steel elements

4 Marine systems Consist of ancillary systems for marine operations

5 On-board crane

Consists of a Davit crane installed on deck to lift small components; used for 

maintenance

5 Cathodic protection system

Consists of an active (impressed current) or passive (anodes) cathodic protection 

system 
89

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

5 Personnel access system

Consists of equipment installed on the vessel landing, ladders, and deck to 

facilitate safe access to the turbine

5 Ballast system

Controls draft/stability of floating systems; can be fixed or variable (active or 

passive)

5 Condition monitoring system Monitors and controls substructure systems (e.g., variable ballast)

4 Scour protection Consists of rock fill or concrete mattresses to protect substructures from 

scouring caused by currents

4 Substructure and foundation IATC

Include activities performed by the manufacturer to integrate, assemble, test, 

and check out the substructure and foundation before delivering to the customer 

(does not include commissioning activities)

4 Substructure and foundation 

transportation

Includes costs of transporting other substructure and foundation components 

from the manufacturing facility to the staging area

2 Financial costs

Consist of financial expenditures for which the project owner is responsible 

prior to the COD, related to either payments for financial products, carrying 

charges on loans, or setting up financial instruments 

3 Project contingency budget

Consists of a liquid financial instrument set up to respond to "known unknown" 

costs that arise during construction; does not include contingencies set by 

manufacturers and contractors as part of supply contract pricing

3 Insurance during construction

Consist of insurance policies held by the owner during the construction period, 

can include construction all risk, marine cargo, commercial general liability, 

workers compensation, environmental site liability, pollution liability, and so on;

does not include insurance held by contractors

3

Carrying charges during 

construction (construction 

financing costs)

Include carrying charges of expenditures on equipment and services incurred 

before COD

3 Reserve accounts Involve payments (before commissioning) into reserve accounts; generally 

required by financiers or regulators

4 Maintenance reserve accounts Involve payments (before commissioning) into reserve accounts set up to cover 

major MRAs, often required by debt service providers

4 Debt service reserve accounts Involve payments (before commissioning) into reserve accounts set up to cover 

DSRAs, often required by debt service providers

4 Decommissioning reserve account Involve payments (before commissioning) into reserve accounts to fund project 

decommissioning obligations (e.g., surety bonds) 

1 Operational expenditures (OpEx) Consist of expenditures required to operate the project and maintain 

availability, generally annualized

2 Operations Include nonequipment costs of operations for the project

3 Environmental, health, and safety 

monitoring

Consist of coordination and monitoring to ensure compliance with HSE 

requirements during construction

4 Health and safety monitoring Consist of coordination and monitoring to ensure compliance with health and 

safety requirements during operations

4 Environmental monitoring Consist of coordination and monitoring to ensure compliance with 

environmental requirement during operations; includes postconstruction survey 
90

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

activities

3 Annual leases, fees, and other 

costs of doing business

Consist of ongoing payments, including but not limited to: payments to a 

regulatory body for permission to operate at a project site (terms defined within 

lease); payments to transmissions systems operators or transmission asset 

owners for rights to transport generated power

4 Submerged land-lease Involve payments to the state or federal regulatory authorities for rights to 

operate an offshore wind project on a publicly owned seabed or lakebed

4 Onshore land-lease Involve payments to land owners for rights to operate transmission lines, a landbased substation, or other facilities

4 Transmission charges/rights Consist of any payments to transmissions systems operators or transmission 

asset owners for rights to transport generated power

4 FERC fees Consist of fees paid to FERC during operations

3 Insurance Consists of insurance policies held by the project company or operations 

manager during the operational period

3 Operation, management, and 

general administration

Consist of the activities necessary to forecast, dispatch, sell, and manage the 

production of power from the plant; includes both on-site and off-site personnel,

software, and equipment to coordinate high-voltage equipment, switching, port 

activities, marine activities, and weather forecasting

4 Generation planning and 

integration Include efforts to forecast, sell, and dispatch power generated by the facility

4 Operating facilities Consist of co-located offices, parts store and quayside facility, helicopter 

facilities, and so on

4 Operating equipment Include lease payments for operating equipment held by the project to support 

operations (e.g., cranes and fork trucks)

4 Sales: general and administrative

Includes financial reporting, public relations, procurement, parts and stock 

management, HSE management, training, subcontracts, and general 

administration

4 Turbine power consumption Include charges for power drawn from the grid by the wind project (e.g., turbine, 

foundation, and substation) during operation

4 Weather forecasting Provides a daily 96-hour forecast of metocean conditions used to plan 

maintenance visits and project plant power production

4 Marine management

Involves the coordination of port equipment, vessels, and personnel to carry out 

maintenance and inspections of generation and transmission equipment

4 Condition monitoring Involves monitoring of SCADA data from wind turbine components to optimize 

performance and identify component faults

4 Operating margin Includes any margin earned by an independent operations management 

company

4 Professional advisory services Include legal support, external consultants, accounting, and so on during 

operation

2 Maintenance Includes vessel, labor, and equipment costs of operations for the project
91

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Level Term Definition 

3 Long-term service agreement

Includes the annualized cost of a contract, generally between the owner and 

turbine OEM or third party, to maintain the offshore wind project at a 

guaranteed level of availability for a defined period; will likely replace scheduled 

and unscheduled maintenance categories below for duration of contract

3 Scheduled maintenance

Includes planned and routine activities to ensure that turbines, substructures, 

and all related systems are operating correctly and at optimal efficiency, and to 

minimize unscheduled breakdowns/ downtime; includes cost of vessels, labor, 

equipment, spare parts, and consumables (sometimes referred to as 

preventative maintenance)

4 Wind turbine scheduled 

maintenance Includes planned maintenance activities for turbine systems

5 Nacelle module Involves planned maintenance related to drivetrain modules

5 Rotor module Involves planned maintenance related to rotor modules

5 Tower module Involves planned maintenance related to tower modules

4 BOS scheduled maintenance Involves planned maintenance activities for BOS

5 Regular cable surveys Involves conducting surveys of array and export cable routes to ensure coverage 

and determine cable burial depth 

5 Foundation inspections

Consist of inspections that cover above- and under-water aspects of the 

substructure and foundation as well as the integrity of the cathodic protection 

system maintenance 

5 Electrical transforming equipment 

inspection Involves inspections of switchgears, transformers, and the back-up power supply

5 DC converter inspection Includes inspection of DC converter equipment and filtering equipment 

5 Land-based electric infrastructure Includes inspections of switchgear, transformers, and any connections

3 Unscheduled maintenance

Includes interventions and other activities needed to respond to random failures;

costs include equipment and vessels, labor, replacement parts, and consumables;

also known as corrective maintenance

4 Wind turbine unscheduled 

maintenance Involves unscheduled maintenance for turbine systems

5 Nacelle module Involves corrective maintenance related to drivetrain modules

5 Rotor module Involves corrective maintenance related to rotor modules

5 Tower module Involves corrective maintenance related to tower modules

4 BOS unscheduled maintenance Involves unscheduled maintenance for BOS

5 Substructure and foundation Involves corrective maintenance related to the substructure and foundations

5 Electrical infrastructure Involves the corrective maintenance related to the electric infrastructure

5 Other infrastructure Involves the corrective maintenance related to other infrastructure

5 Land-based electric infrastructure Involves servicing and repairs to the switchgear, transformers, and any 

connections (infrequent)

4 Unscheduled maintenance 

contingency

Consists of a liquid financial instrument set up to respond to "known unknown" 

costs that arise during maintenance