NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by 

U.S. Balance‐of‐Sta

Drivers and Sensi

AWEA OFFSHORE WINDPO

Ben MaplesOctober 10, 2012

NREL/PR‐5000‐56480
Acknowledgments

National Renewable Energy Laboratory 

Genevieve Saur

Maureen Hand

Walt Musial

Rebecca Meadows

Aaron Smith

GL Garrad Hassan

Chris Elkinton

Jules Clayton

Chris Garrett

Nestor Castillo

Ellen Crivella
Why We Are Here

• The U.S. Department of Energy has adopted a National

Offshore Wind Strategy to support the development of an

offshore wind industry in the United States

• The strategy sets goals for deployment and cost reduction

Deployment: 10 GW by 2020 and 54 GW by 2030

Levelized cost of energy (LCOE): $100/ megawatt‐hours (MWh) by 2020 and

$70/MWh by 2030

• Estimates show shallow (030 m)

and transitional depth (3060 m)

waters to have a net resource of

773 gigawatts (GW)

• If including deep waters that

would require floating sub‐

structures, the total net U.S.

offshore wind resource is

estimated to be well over 2,000

GW

http://www1.eere.energy.g

http://www.nrel.gov/wind/resource_assessment.html
Variability in LCOE

Source: Tegen, S.; Hand, M.; Maples, B.; Lantz, E.; Schwabe, P.; Smith, A. (2012). 2010 Cost of Wind Energy Review. 111 pp.; 

• Range of reported offshore wind project installed capital cost in

significant variability in LCOE

ICC = Installed Capital Cost AOE = Annual Operatin
Installed Capital Costs (ICC)

Source: Tegen, S.; Hand, M.; Maples, B.; Lantz, E.; Sch

Cost of Wind Energy Review. 111 pp.; NREL Report No

• Balance‐of‐station (BOS)

costs dominate ICC for

offshore wind projects

• There are three primary

BOS contributors:

Support structureElectrical infrastructure

Assembly, transport, and install

• Component contribution

can vary significantly from

one project to another
NREL BOS Model

• The BOS cost model is based 

GL Garrad Hassan America, In

• Data draws from GL GH’s acti

offshore wind projects in Euro

experience in the onshore wi

United States

• The model demonstrates how 

such as turbine size and vesse

BOS costs for offshore wind p

• Due to the high level of varia

parameters and uncertainty o

elements, results of the mode

as representative only
Parametric Sensitivity Analysis

Baseline project parametersProject Size (MW) 500

Turbine Rating (MW) 4.5

Rotor Diameter (m) 126

Hub Height (m) 90

Distance to Shore (km) 30

Water Depth (m) 15

Foundation MonopileArray Spacing (Rotor Diameters) 8x8

Array Voltage (kV) 33Transmission Voltage (kV) 220

IEC Wind Turbine Class II

• Baseline 

chosen to 

representproject in 

• To repres

altering a 

analyses 

project p

variable u

changed.
Sensitivity to Project Size

• Fixed costs such as vessel mobilization, export cable landfall oper

can dominate smaller project costs.

• Further reductions come from increased order sizes that reduce 

• The electrical costs represent a significant percentage of project c

project sizes. At larger project sizes, the support structure and ass

and install costs dominate.
Sensitivity to Turbine Size

• The total BOS cost is generally reduced as turbine size increases. 

structure costs increase as the turbine rating increases, but the co

outweighed by the reduction in electrical infrastructure and asse

and install costs.

• The step change increase in assembly, transport, and install cost i

a change to a larger class of vessels. This change is needed to han

monopile size required for the higher loads that are associated w
Sensitivity to Water Depth

• Water depth shows no impact to electrical costs. However, it doe

structure costs, which leads to increased total BOS cost.

• At shallow water depths, the assembly, transport, and install cost

by water depth. As the water depth increases, the monopile gets 

heavier, which triggers a step change in costs due to the need to 

more expensive class of installation vessels.
Sensitivity to Distance to Shore

• As distance to shore increases, BOS costs can rise significantly bec

costs of the long electrical cabling needed to connect the offshor

the land‐based grid.

• For projects sited farther from shore, the assembly, transport, an

increase as a result of transporting the turbines and foundations 

distances.
Sensitivity to Vessel Day Rates

• Variation of installation vessel day rates alone can substantially al

transport, and install costs as well as total BOS costs.

• Yet‐unverified U.S. installation vessel costs and the exceptionally 

history of European installation vessel costs lead to highly variabl

transport, and install costs.
Conclusions

• Electrical infrastructure, support structure, and a

transport, and install are the primary contributor

BOS costs.

• The largest uncertainty in near‐term offshore BO

vessel rates, which is the primary driver of the lar

cost: assembly, transport, and install.

• Choices made in the project planning phase (such 

location and turbine size) can play a large role in t

for the project.

• Development of new, innovative technologies tha

eliminate step changes in project costs can provid

cost savings.
Thank You

NREL PIX 17856