Sensitivities

LAND-BASED WIND PLANT BALANCE-OF-SYSTEM

COST DRIVERS AND SENSITIVITIES

C. Moné, B. Maples, M. Hand • National Renewable Energy Laboratory • Golden, Colorado

AWEA WINDPOWER 2014 • Las Vegas, Nevada • May 5-8, 2014

NREL/PO-6A20-61546 

• Balance-of-system (BOS) and soft costs for land-based wind plants are almost onethird of the total project investment cost; as such, there is a need to identify and test 

sensitivities to BOS cost drivers to ascertain the best strategies for reducing 

levelized cost of energy.

• The National Renewable Energy Laboratory (NREL) has developed a new landbased wind plant BOS cost model based on developer-provided data to explore 

these drivers and sensitivities. The data was generated from multiple cost methods 

including historical, commodity, indices, and projections.

• This model demonstrates how various factors such as turbine size and project size 

can affect BOS costs for land-based wind projects using the NREL Cost and 

Scaling Model to estimate top tower mass (nacelle and rotor) for various turbines.

• Results of these analyses are based on typical value ranges for projects built in the 

central United States using complex turbine layouts.

• All analyses use common baseline project parameters (see Table 1) while each 

variable under investigation is changed in turn.

• Because of the high level of variability in project parameters and uncertainty of sitespecific elements, the results of these sensitivity analyses should be taken as 

representative only.

Introduction

Conclusions

•Total land-based BOS costs are reduced with larger project size. 

• This effect is largely associated with fixed costs (e.g., crane mobilization and 

facilities) being distributed over many megawatts (MW). 

• Further reductions come from increased order sizes that reduce per-item costs. 

• The electrical costs represent a significant percentage of project costs at small 

project sizes. At larger project sizes, the foundation and erection costs dominate.

•The total BOS cost on a per-kilowatt (kW) basis is generally reduced as turbine size 

increases. Larger MW turbines require fewer foundations for the same project size, 

lowering the overall cost, even considering the additional electrical system costs.

•The combined mass of the nacelle and rotor assembly directly impacts the foundation 

costs caused by the additional mass of the components, the tower, local structural 

codes, and the requirements of the original equipment manufacturer for structural 

stability.

•The combined mass of the nacelle and rotor assembly has a larger effect on BOS costs 

than the hub height, up to 140 m, at which point the tower steel for the additional height 

has a greater effect on the foundation, assuming an all-steel tower.

•Development and project management costs are estimated as a percentage because 

they vary greatly due to sunk costs, length of time until a project begins construction, 

weather delays, risks, and project contingencies.

•Transmission and interconnection costs decrease more quickly for larger projects than 

distance to the substation (e.g., 50-mi T-line on a 200-MW project has less impact than 

the 10-mi T-line on a 50-MW project).

•Additional conclusions from our analysis not depicted above.

• Permanent operation and maintenance facilities are a very minor cost (less than 2%) 

compared to the project contingencies, margins, and other soft costs in the total 

BOS costs.

• Initial engineering costs and metrological masts are very minor costs (less than 

2.5%) in the total BOS budget that have long term benefits

1. Sensitivity to Project Size

4. Sensitivity to Hub Height

2. Sensitivity to Turbine Size 3. Sensitivity to Top Tower Mass

5. Breakdown of BOS & Soft Costs*

Source: Tegen, S.; Hand, M.; Maples, B.; Lantz, E.; Schwabe, P.; Smith, A. (2012). 2010 Cost of Wind Energy Review. 111 pp.; NREL Report No. TP-5000-52920.

Table 1. Common baseline project parameters

Project Size (MW) 150

Turbine Rating (MW) 2.0

Hub Height (m) 80

Interconnect Voltage (kV) 137

Distance to Interconnect (mi) 10

Site Terrain Flat/Rolling

Turbine Layout Complex

Pad Mount Transformer Required (Y/N) Yes

New Switchyard Required (Y/N) Yes

Rock Trenching Required (% of collection cable length) 10%

Contingency (%) 3%

Warranty Management (%) 0.02%

Overhead (%) 5%

Profit Margin (%) 5%

$0

$50

$100

$150

$200

$250

$300

$350

$400

$450

$500

100 140 180 220 260 300 340

BOS Cost per kW

Top Tower Mass (Tonnes)

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.

 Development, Project Management, & Soft Costs

 Transmission & Interconnection Cost

 Electrical Interface System 

 Temporary & Permanent Facilities

 Foundation, Installation, Roads, & Remainder of Civil Work

 Baseline Project