Conference Paper 

NREL/CP-500-43412 

October 2008 

The Future of Wind Energy 

Technology in the United States 

R. Thresher and M. Robinson 

National Renewable Energy Laboratory 

P. Veers 

Sandia National Laboratories

Presented at the 2008 World Renewable Energy Congress 

Glasgow, Scotland, UK 

July 19–25, 2008 
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The Future of Wind Energy Technology in the United States 

Robert Thresher1, Michael Robinson2, and Paul Veers3

1

 Wind Energy Research Fellow, National Renewable Energy Laboratory, Golden Colorado, USA; 

Telephone: 01-303-384-6922; e-mail: Robert_Thresher@nrel.gov. This work has been authored by an 

employee or employees of the Midwest Research Institute under Contract No. DE-AC36-99GO10337 

with the U.S. Department of Energy. The United States Government retains and the publisher, by 

accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this 

work, or allow others to do so, for United States Government purposes. 

2

 Deputy Director of the National Wind Technology Center, National Renewable Energy Laboratory, 

Golden Colorado, USA; Telephone: 01-303-384-6947; e-mail: Mike_Robinson@nrel.gov. 

3

 Distinguished Member Technical Staff, Sandia National Laboratories is a multiprogram laboratory 

operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of 

Energy under Contract DE-AC04-94AL85000. 

1 Introduction 

Wind energy is one of the fastest growing 

electrical energy sources in the United States. 

The United States installed over 5,300 

megawatts (MW) in 2007, and experts are 

forecasting as much to be 

installed in 2008. The United States 

cumulative installed capacity as of December 

31, 2007, was 16,904 MW. The state 

distribution of wind capacity is illustrated in 

Figure 1. 

FIGURE 1. Installed Wind Capacity in the United States as of December 31, 2007. 

1 
FIGURE 2. The Wind Resource Potential at 50m on Land and Offshore. 

Wind capacity in the United States and in 

Europe has grown at a rate of 20% to 30% per 

year over the past decade. Despite this rapid 

growth, wind only provides for about 1% of 

total electricity consumption in the United 

States. 

The United States is blessed with an 

abundance of wind energy potential. The landbased and offshore wind resource has been 

estimated to be sufficient to supply the 

electrical energy needs of the entire country 

several times over. The Midwest region, from 

Texas to North Dakota, is particularly rich in 

wind energy resources, as illustrated in Figure 

2. 

2 The Current Status of Wind Energy 

Technology in the United States

During the past 20 years, average wind turbine 

ratings have grown almost linearly, as shown 

in Figure 3. Current commercial machines are 

rated at 1.5 MW to 2.5 MW. 

Each group of wind turbine designers 

predicted that their machines were as large as 

they will ever be. However, with each new 

generation of wind turbines, the size has 

increased along the linear curve and has 

achieved reductions in life-cycle cost of 

nergy. 

al, it costs more to build a larger 

rbine. 

e

The long-term drive to develop larger turbines 

stems from a desire to take advantage of wind 

shear by placing rotors in the higher, much 

more energetic winds at a greater elevation 

above ground (wind speed increases with 

height above the ground). This is a major 

reason that the capacity factor of wind turbines 

installed in the United States has increased 

over time, as documented by Wiser and 

Bolinger1

, and shown in Figure 4. However, 

there are constraints to this continued growth; 

in gener

tu

2 
FIGURE 3. The Development Path and Size Growth of Wind Turbines. 

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

2006 Capacity Factor

 Capacity-Weighted Average 2006 Capacity Factor, by COD

 Individual Project 2006 Capacity Factor, by COD

COD:

# Projects:

# MW:

 Pre-1998 1998-99 2000-01 2002-03 2004-05

 20 20 25 25 25

 936 875 1,741 1,911 2,455

Source: Berkeley Lab database

Figure 4. 2006 Project Capacity Factors by Commercial Operation Date (1). 

The primary argument for a size limit for wind 

turbines is based on the “square-cube law.” 

Roughly stated, it says that “as a wind turbine 

rotor increases in size, its energy output 

increases as the rotor-swept area (the diameter 

squared), while the volume of material, and 

therefore its mass and cost, increases as the 

cube of the diameter.” In other words, at some 

size the cost for a larger turbine will grow 

faster than the resulting energy output revenue, 

making scaling a losing economic game. 

Engineers have successfully skirted this law by 

changing the design rules with increasing size 

3 
FIGURE 5. WindPACT (2) Study Results Indicating the Lowering of Growth in Blade Weight 

Due to the Introduction of New Technology

and removing material or by using material 

more efficiently to trim weight and cost. 

Studies have shown that in recent years, blade 

mass has been scaling at roughly an exponent 

of 2.3 instead of the expected 3, as shown by 

the WindPACT blade scaling study2

. This 

WindPACT study shows how successive 

generations of blade design have moved off the 

cubic weight growth 

curve to keep weight down as illustrated in 

Figure 5. If advanced research and 

development were to provide even better 

design methods, as well as new materials and 

manufacturing methods that allowed the entire 

turbine to scale as the diameter squared, then it 

would be possible to continue to innovate 

around this limit to size. 

Land transportation constraints can also pose 

limiting factors to wind turbine growth for 

turbines installed on land. Cost-effective 

transportation can only be achieved by 

remaining within standard over-the-road trailer 

dimensions of 4.1 m high by 2.6 m wide. Rail 

transportation is even more dimensionally 

limited. 

3 The Cost of Wind-Generated 

Electricity in the United States 

The cost of wind-generated electricity has 

dropped dramatically since 1980, when the 

first commercial wind plants began operation 

in California. Figure 6 depicts price data for 

some more recent wind energy projects from 

public records. This chart shows that in 2006, 

the price paid for electricity generated in large 

wind plants was between 3 and 6.5 cents per 

kilowatt-hour (kWh) with an average near 5 

cents per kWh (1cent/kWh = 10$/MWh). 

These figures represent the electricity price as 

sold by a wind plant owner to the utility. The 

price includes the benefit of the federal 

production tax credit and any state incentives, 

as well as revenue from the sale of any 

renewable energy credits. Thus the true cost of 

the delivered electricity would be higher by 

approximately 1.9 cents per kWh, which is the 

value of the federal tax credit. Accounting for 

the tax credit, the unsubsidized cost for windgenerated electricity for projects completed in 

2006 ranges from about 5 to 81⁄2 cents per 

kWh. 

4 
0

10

20

30

40

50

60

70

80

90

 Capacity-Weighted Average 2006 Wind Pow er Price, by COD

 Individual Project 2006 Wind Pow er Price, by COD

2006 W ind Pow er Pric e (2006 $/M W h)

 1998-99 2000-01 2002-03 2004-05 2006 

 11 14 21 17 9

 591 857 1,765 1,666 723

COD:

# Projects:

# MW:

Source: Berkeley Lab database

Figure 6 Wind Energy Price by Commercial Operation Date Using 2006 Data (1).

The reasons generally offered for the 

increasing price of wind-generated electricity 

after the long downward price trend of the past 

25 years include: 

 Turbine and component shortages due to 

the dramatic recent growth of the wind 

industry in the United States and Europe 

 The weakening U.S. dollar relative to the 

Euro (because many major turbine 

components are imported from Europe) 

and relatively few wind turbine 

component manufacturers in the United 

States 

 A significant rise in material costs such 

as steel and copper, as well as 

transportation fuels, over the past 3 years 

 The on-again and off-again cycle of the 

wind energy production tax credit, which 

hinders investment in new turbine 

production facilities and encourages 

hurried and expensive production, 

transportation, and installation of 

projects when the tax credit is available. 

Decreasing wind energy costs to below the 

2003 level will require further research and 

development efforts and will be considered 

later. 

4 Potential Growth of Wind Energy in 

the United States

The vision of the wind industry in the United 

States and in Europe is to increase wind’s 

fraction of the electrical energy mix to more 

than 20% within the next two decades. 

Recently, the U.S. Department of Energy in 

conjunction with American Wind Energy 

Association (AWEA), the National Renewable 

Energy Laboratory (NREL), Sandia National 

Laboratories, and Black & Veatch, undertook a 

study4

 to explore the possibility of producing 

20% of the nation’s electricity using wind 

energy. This investigation attempts to estimate 

all aspects of this scenario, including the wind 

resource assessment, materials and 

manufacturing resources, environmental and 

siting issues, transmission and system 

integration, and public policy. It should be 

noted that several states have Renewable 

Electricity Standards that mandate comparable 

levels of renewable energy be deployed within 

the next 20 years. 

The Wind Energy Deployment System model3

developed at NREL was used to estimate the 

consequences of producing 20% of the 

nation’s electricity from wind technology by 

2030. This generation capacity expansion 

model selects from electricity generation 

5 
technologies that include pulverized coal 

plants, combined cycle natural gas plants, 

combustion turbine natural gas plants, nuclear 

plants, and wind technology to meet projected 

demand in future years. Technology cost and 

performance projections, as well as 

transmission operation and expansion costs, 

are assumed. This study demonstrates that 

producing 20% of the nation’s projected 

electricity demand in 2030 from wind 

technology is technically feasible, not costprohibitive, and provides benefits in the forms 

of carbon emission reductions, natural gas 

price reductions, and water savings. 

The United States possesses more than 8,000 

gigawatts (GW) of wind resources that could 

be harnessed to produce electricity at 

reasonable cost if transmission expenditures 

are excluded. Considering some elements of 

the transmission required to access these 

resources, a supply curve that shows the 

relationship between wind power class and 

cost is shown in Figure 7, taken from reference 

(4). It includes the cost of accessing the current 

transmission system and shows that more than 

600 GW of potential wind capacity is available 

for $60 to $100/MWh. The relatively flat 

supply curve for wind energy clearly shows an 

abundance of modestly priced wind energy is 

available in the United States, even with 

limited transmission access. 

FIGURE 7. Wind Energy Supply Curve for the 20% Wind Scenario Modeling 

6 
0%

5%

10%

15%

20%

2000

2006

2012

2018

2024

2030

Annual Generation (%) 

0

5

10

15

20

Annual Installed Capacity (GW)

Annual Generation (left scale)

Annual Capacity (right scale)

Figure 8. Prescribed annual wind generation and capacity additions 

Figure 8 shows the wind capacity expansion 

necessary to reach 20% electricity generation 

by 2030. This trajectory was designed to 

produce an aggressive annual growth rate that 

reached a sustainable level of manufacturing 

by accounting for both demand growth and the 

repowering of aging wind plants. Based on the 

assumptions used in this study, the wind 

industry would need to grow from an annual 

installation rate of 5 GW/year in 2007 to a 

sustained rate of about 15 GW/year by 2018, 

which is a threefold growth over the next 

decade. 

The scenario assumes a modest improvement 

of wind technology over the 20-year modeling 

period. Wind turbine costs are assumed to 

decrease by 10% to 12% between 2010 and 

2020, and wind turbine performance, or 

capacity factor, is assumed to increase by 15 % 

from today’s capacity factors of 35% by the 

year 2030. Although these increases do not 

appear to be particularly aggressive, they 

represent a significant technical challenge 

given the present situation where turbine costs 

are increasing with time not decreasing. 

5 Offshore Wind Energy Potential 

U.S. offshore wind energy resources are 

abundant, indigenous, and broadly dispersed 

among the most expensive and highly 

constrained electric load centers. The DOE 

Energy Information Administration shows that 

28 of the 48 contiguous states with coastal 

boundaries use 78% of the nation’s electricity. 

In the United States, approximately 10 

offshore projects are being considered. 

Proposed locations span both state and federal 

waters and total more than 2,400 MW. 

Offshore turbines being considered for 

deployment range from 3 MW to 5 MW in size 

and typically have three-bladed horizontal-axis 

upwind rotors that are nominally 80 m to 

126 m in diameter. Tower heights offshore are 

lower than land-based turbines because wind 

shear profiles are less steep, tempering the 

energy capture gains sought with increased 

elevation. The foundations for offshore wind 

turbines differ substantially from land-based 

turbines. Current estimates indicate that the 

cost of energy from these offshore wind plants 

is more than 10 cents/kWh and that the 

operation and maintenance costs are also 

higher than for land-based turbines due to the 

difficulty of accessing turbines during storm 

conditions. 

7 
Footnote: Since the 2002 baseline, there has already been a sizeable improvement in capacity factor, from just over 30% to 

almost 35%, while capital costs have increased due to large increases in commodity costs in conjunction with a drop in the 

value of the dollar (Ref. 1). Therefore, working from a 2006 baseline, we can expect a more modest increase in capacity 

factor, but the 10% capital cost reduction is still possible, although beginning from a higher 2007 starting point, because 

commodity prices are unlikely to drop back to 2002 levels. 

The high cost of offshore wind energy and the 

need to develop a new regulatory process for 

permitting this unique technology has greatly 

slowed offshore wind development. Currently, 

there are no operating offshore wind plants in 

the United States. It is expected that during 

the next 5 years, one or more offshore wind 

farms will be deployed in the United States. 

They will be installed in shallow water and 

will supply electricity to nearby onshore 

utilities that serve large population centers. If 

they are successful, the technology will 

develop more rapidly. The much deeper water 

along the coastlines of the United States will 

not longer be able to use the concepts currently 

being installed in very shallow water.. 

However, the path toward deepwater floating 

systems must be supported by an extensive 

R&D program for at least a decade. For more 

information on the viability of offshore wind 

energy see reference (5). 

6 Potential Future Turbine Technology 

Improvements 

The DOE Wind Energy Program has 

conducted cost studies under the WindPACT 

Project that identified a number of areas where 

technology advances would result in changes 

to the capital cost, annual energy production, 

reliability, operations and maintenance, and 

balance of station. Many of these potential 

improvements, summarized in Table 1, would 

have significant impacts on annual energy 

production and capital cost. Table 1 also 

includes the manufacturing learning-curve 

effect generated by several doublings of 

turbine manufacturing output over the coming 

years. The learning-curve effect on capital cost 

reduction is assumed to range from zero in a 

worst case scenario to the historic level in a 

best-case scenario, with the most likely 

outcome halfway in between. The probable 

scenario is a sizeable increase in capacity 

Table 1: Areas of Potential Technology Improvement 

Technical Area Potential Advances 

Cost Increments 

(Best/Expected/Least, Percent) 

Annual Energy 

Production Turbine Capital Cost 

Advanced Tower Concepts 

* Taller towers in difficult locations 

* New materials and/or processes 

* Advanced structures/foundations 

* Self-erecting, initial or for service 

+11/+11/+11 +8/+12/+20 

Advanced (Enlarged) Rotors 

* Advanced materials 

* Improved structural-aero design 

* Active controls 

* Passive controls 

* Higher tip speed/lower acoustics 

+35/+25/+10 -6/-3/+3 

Reduced Energy Losses and 

Improved Availability 

* Reduced blade soiling losses 

* Damage tolerant sensors 

* Robust control systems 

* Prognostic maintenance 

+7/+5/0 0/0/0 

Drivetrain 

(Gearboxes and Generators 

and Power Electronics) 

* Fewer gear stages or direct drive 

* Medium/low speed generators 

* Distributed gearbox topologies 

* Permanent-magnet generators 

* Medium-voltage equipment 

* Advanced gear tooth profiles 

* New circuit topologies 

* New semiconductor devices 

* New materials (GaAs, SiC) 

+8/+4/0 -11/-6/+1 

Manufacturing and Learning 

Curve 

* Sustained, incremental design and 

process improvements 

* Large-scale manufacturing 

* Reduced design loads 

0/0/0 -27/-13/-3 

Totals +61/+45/+21 -36/-10/+21 

8 
factor with a modest drop in capital cost from 

the 2002 levels. 

7 SUMMARY 

Power production from wind technology has 

evolved very rapidly over the past decade. 

Capital costs have plummeted, reliability has 

improved, and efficiency has dramatically 

increased, resulting in robust commercial 

market product that is competitive with 

conventional power generation. Investments in 

R&D as well as the development of robust 

standard design criteria have helped to mitigate 

technology risk and attract market capital for 

development and deployment of large 

commercial wind plants. High-quality products 

are provided by every major turbine 

manufacturer, and complete wind generation 

plants are now being engineered to seamlessly 

interconnect with the grid infrastructure to 

provide utilities with dependable energy 

supply, free of the risks of future fuel price 

escalation inherent in conventional generation. 

The cost-of-energy metric remains the 

principal technology indicator, incorporating 

the key elements of capital cost, efficiency, 

reliability, and durability. The unsubsidized 

cost of wind-generated electricity ranges from 

about 5 to 8.5 cents/kWh for projects 

completed in 2006 (1). No major technical 

breakthroughs in land-based technology are 

needed for a broad geographic penetration of 

wind power on the electric grid. Advancement 

requires a systems development and 

integration approach, reflecting the high level 

of engineering already incorporated into 

modern machines. No single component 

improvement in cost or efficiency can achieve 

significant cost reductions or dramatically 

improved performance. Capacity factor can be 

increased over time using enlarged rotors on 

taller towers. Market incentives are necessary 

to sustain near-term industry growth, but in the 

longer term, subsidies can probably be 

eliminated. In addition, with continued R&D, 

offshore wind energy has great potential to 

allow the United States to greatly expand its 

electrical energy supply. 

8 References 

1. Wiser, R.; Bolinger, M. (2007). Annual 

Report on U.S. Wind Power Installation, 

Cost, and Performance Trends: 2006, May 

2007. National Renewable Energy 

Laboratory, Golden, CO. NREL Report 

No. TP-500-41435; DOE/GO-102007-

2433. Available at www.osti.gov/bridge. 

2. Griffin, D. A. (2001). WindPACT Turbine 

Design Scaling Studies Technical Area 1 -- 

Composite Blades for 80- to 120-Meter 

Rotor. 44 pp.; National Renewable Energy 

Laboratory, Golden, CO. NREL Report 

No. SR-500-29492. Available at 

www.nrel.gov/publications/

3. Short, W.; Blair, N.; Heimiller, D.; and 

Singh, V. (2003). Modeling the Long-Term 

Market Penetration of Wind in the United 

States, National Renewable Energy 

Laboratory, Golden, CO, NREL/CP-620-

34469, 2003. Available at 

www.nrel.gov/publications/

4. U.S. Department of Energy (2008). 20% 

Wind Energy by 2030: Increasing Wind 

Energy’s Contribution to the U.S. 

Electricity Supply. National Renewable 

Energy Laboratory, Golden, CO. NREL 

Report No. NREL/SR-500-41869;

DOE/GO-102008-2567. Available at 

www.eere.energy.gov/windandhydro 

5. Musial, W.; Offshore Wind Electricity: A 

Viable Energy Option for Coastal USA, 

Marine Technology Society Journal, 

Volume 41(3), Fall 2007; pp. 32-43; 

National Renewable Energy Laboratory, 

Golden, CO. NREL Report NO. 

NREL/JA-500-41338. Available at 

www.nrel.gov/publications/

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This paper describes the status of wind energy in the United States as of 2007, its cost, the potential for growth, 

offshore wind energy development, and the potential future wind energy technology improvements. 

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