Wind Resource and Potential
Approximately 2% of the solar energy striking the Earth’s surface is converted to kinetic energy in wind.1 Wind turbines convert the wind’s kinetic energy to electricity without emissions. The distribution of wind energy is heterogeneous, both across the surface of the Earth and vertically through the atmosphere. Class 3 winds (average annual speed of 14.3 to 15.7 mph at 50m) are the minimum needed for a commercially viable project.3 Only 2% of U.S. electricity was derived from wind energy in 2015, but wind capacity is increasing rapidly.4
- Wind power is proportional to the cube of wind speed.
- Wind speeds are lower close to the Earth’s surface and more wind power is available at higher altitudes. The average hub height of most modern wind turbines is 82.7 meters off the ground.5
- Potentially, global onshore and offshore wind power at commercial turbine hub heights could provide 840,000 TWh of electricity each year, while total global electricity consumption from all sources in 2012 was about 19,710 TWh.6,7 Similarly, the U.S. annual wind potential of 68,000 TWh (lower 48 states) exceeds annual U.S. electricity consumption by about 3,700 TWh.4,6
- A 2015 study by the U.S. Department of Energy found wind could provide 20% of U.S. electricity by 2030 and 35% by 2050.8
- Wind’s variability increases the cost to operate the grid by less than 0.7¢/kWh of electricity (at 40% electricity from wind).5
U.S. Wind Resources, Onshore and Offshore2
(50 METER HEIGHT)
Wind Technology and Impacts
Horizontal Axis Wind Turbines
- Horizontal axis wind turbines (HAWT) are the predominant turbine design in use today. The HAWT rotor comprises blades (usually three) symmetrically mounted to a hub. The rotor is connected via a shaft to a gearbox, and the generator is housed within the nacelle. The nacelle is mounted atop a tower connected to a concrete foundation.9
- HAWT come in a variety of sizes, ranging from 2.5 meters in diameter and 1 kW for residential applications up to 100+ meters in diameter and over 3.5 MW for offshore applications.
- The theoretical maximum efficiency of a HAWT is ~59%, also known as the Betz Limit. Most HAWT extract about 50% of the energy from the wind that passes through the rotor area.8
- The capacity factor of a wind turbine is its average power output divided by its maximum power capability.8 On land, capacity factors range from 0.26 to 0.52.10 Offshore winds are generally stronger than on land, and capacity factors are higher on average, but offshore wind farms are more expensive to build and maintain.10 Offshore turbines are currently placed in depths up to 40-50m (about 131-164ft).11
Horizontal Axis Wind Turbine Diagram9,12
Installation, Manufacturing, and Cost
- More than 48,800 utility-scale wind turbines are installed in the U.S., with a cumulative capacity of 74.5 GW.13 U.S. wind capacity increased by 346% between 2007 and 2015, a 21% average annual increase.13 Global wind capacity increased by 21% annually, on average, from 2007 to 2015, reaching 433 GW in 2015.15
- U.S. average turbine size was 1.9 MW in 2014, up from 0.70 MW in 1999.5
- Average capacity factor has increased from 0.30 for projects installed through 2000 to around 0.33 for recent projects. Higher capacity factors tend to lower cost of energy.5
- On a capacity-weighted average basis, installed wind project costs declined by roughly $3,500/kW between the early 1980’s and 2014. In 2014, costs were $1,710/kW.5
- The installed cost of a small (<100 kW) turbine is approximately $6,230 per kW, on average.16
- Currently, commercial wind energy costs average 2.7¢/kWh wholesale.5 The 2015 average U.S. residential electricity price was 12.7¢/kWh.4
- Texas (17,711 MW), Iowa (6,364 MW), and California (5,662 MW) are the leading states in total installed wind capacity.13 Iowa generated over 31% of its electricity from wind, the highest percent in the U.S.17
- Wind turbines and components are manufactured at more than 560 U.S. facilities.18
- In 2015, an estimated 88,000 full-time workers were employed in the U.S. wind industry.19
- Large (>20 MW) wind projects require roughly 85 acres of land area per MW of installed capacity, but 1% or less of this total area is occupied by roads, turbine foundations, or other equipment; the remainder is available for other uses.8
- For farmers, annual lease payments provide a stable income of around $3,000/MW of turbine capacity, depending on the number of turbines on the property, the value of the energy generated, and lease terms.8 For a 250-acre farm, with income from wind at about $55 an acre, the annual income from a wind lease could be $14,000.20
U.S. Wind Capacity13,14
Global Wind Capacity, 201515
Energy Performance and Environmental Impacts
- Wind turbines can reduce the impacts associated with electricity generation. The current U.S. wind capacity of 61 GW annually avoids an estimated 96 million metric tons of CO2 emissions and reduces water use by about 37 billion gallons compared with conventional power plants.18
- According to a 2015 study, if 20% of U.S. electricity was wind-generated by 2030, electric sector GHG emissions would be reduced 16%, eliminating 380 billion kg of CO2 emissions annually, or 3.3 trillion kg cumulatively, and decreasing water use by 4%.8
- A 2005 study of two U.S. wind farms found life cycle net energy ratios (energy generated/energy invested) of 47 and 65.21
- Annual avian mortality from collisions with turbines is 200,000, with 130 million mortalities due to power lines and 300-1,000 million from buildings. The best way to minimize mortality is careful siting.8 Bat mortality due to wind turbines is less well studied, but research shows that a large percentage of bat collisions occur in summer and fall months when bats are most active.22 The wind industry has been testing methods that potentially reduce bat mortality by more than 50%.8
- Noise 350m from a typical wind farm is 35-45 dB(A). For comparison, a quiet bedroom is 35 dB(A) and a 40 mph car 100m away is 55 dB(A).23
- As of 2013, several studies have conclusively determined that sound generated by wind turbines has no impact on human health.8
Solutions and Sustainable Actions
Policies Promoting Renewables
Policies that support wind and other renewables can address externalities associated with conventional electricity, such as health effects from pollution, environmental damage from resource extraction, and long-term nuclear waste storage.
- A Renewable Portfolio Standard (RPS) requires electricity providers to obtain a minimum fraction of their energy from renewable resources.24
- Feed-in tariffs set a minimum price per kWh paid to renewable electricity generators by retail electricity distributors.24
- Net metering - offered in 41 states, D.C., and three U.S. territories - allows customers to sell excess electricity back to the grid.25
- Capacity rebates are one-time, up-front payments for building renewable energy projects, based on the capacity (in watts) installed.
- The federal production tax credit (PTC) provides a 2.3¢/kWh benefit for the first ten years of a wind energy facility’s operation, for projects started by the end of 2014. In 2015, the Consolidated Appropriations Act retroactively reinstated the tax credit for projects started by December 31, 2019.26 Small (<100 kW) wind installations can receive tax credits for up to 30% of the capital and installation cost.27
- Qualified Energy Conservation Bonds (QECBs) are interest-free financing options for state and local government renewable energy projects.28
- Section 9006 of the Farm Bill is the Rural Energy for America Program (REAP) that funds grants and loan guarantees for agricultural producers and rural small businesses to purchase and install renewable energy systems.29
- System benefits charges are paid by all utility customers to create a fund for low-income support, renewables, efficiency, and R&D projects that are unlikely to be provided by a competitive market.30
What You Can Do
- Make your lifestyle more efficient to reduce the amount of energy you use.
- Invest in non-fossil electricity generation infrastructure by purchasing “green power” from your utility.
- Buy Renewable Energy Certificates (RECs), also known as green tags or green energy certificates. RECs are sold by renewable energy producers in addition to the electricity they produce; for a few cents per kilowatt hour, customers can purchase RECs to “offset” their electricity usage and help renewable energy become more competitive.31
- Consider installing your own wind system, especially if you live in a state that provides financial incentives or has a net metering policy.
- Gustavson, M. (1979) Limits to Wind Power Utilization. Science, 204(4388): 13-17.
- U.S. Department of Energy (DOE), National Renewable Energy Lab (NREL) (2009) U.S. Wind Resource Map.
- U.S. DOE, NREL (2011) “Wind Data Details.”
- Energy Information Administration (EIA) (2016) Monthly Energy Review April 2016.
- U.S. DOE, Energy Efficiency and Renewable Energy (EERE) (2015) 2014 Wind Technologies Market Report.
- Lu, X., et al. (2009) Global potential for wind-generated electricity. Proceedings of National Academy of Sciences, 106(27).
- U.S. EIA (2015) “International Energy Statistics: Electricity Consumption.”
- U.S. DOE (2015) Wind Vision Report.
- U.S. DOE, EERE (2013) “The Inside of a Wind Turbine.”
- NREL (2015) “Transparent Cost Database: Capacity Factor” Open Energy Information.
- The European Wind Energy Association (2013) Deep Water: The Next Step for Offshore Wind Energy.
- California Energy Commission (2012) “Energy Quest: Wind Energy.”
- American Wind Energy Association (AWEA) (2016) U.S. Wind Industry First Quarter 2016 Market Report.
- AWEA (2012) Annual Market Report - Year Ending 2010.
- Global Wind Energy Council (GWEC) (2016) Global Wind Report 2015.
- U.S. DOE, American Wind Energy Association (2015) 2014 Distributed Wind Market Report.
- AWEA (2016) U.S. Wind Energy State Facts-Iowa Wind Energy.
- AWEA (2014) Annual Wind Industry Report - Year Ending 2013.
- AWEA (2016) “Wind Energy Facts at a Glance.”
- AWEA (2009) “Resources: Wind Energy and the Economy.”
- Spitzley, D. and G. Keoleian (2005) Life cycle environmental and economic assessment of willow biomass electricity. CSS04-05R.
- USGS Fort Collins Science Center (2016) “Bat Fatalities at Wind Turbines: Investigating the Causes and Consequences.”
- U.S. DOE, EERE (2008) 20% Wind Energy by 2030: Increasing Wind Energy’s Contribution to U.S. Electricity Supply.
- U.S. EPA (2016) “State Renewable Energy.”
- DSIRE (2016) USA Summary Maps: Net Metering.
- DSIRE (2016) “Renewable Electricity Production Tax Credit (PTC).”
- U.S. Department of Energy (2016) “Business Energy Investment Tax Credit (ITC).”
- DSIRE (2015) “Qualified Energy Conservation Bonds (QECBs).”
- DSIRE (2016) “USDA - Rural Energy for America Program (REAP) Grants.”
- DSIRE (2016) “Glossary.”
- US EPA (2014) “State and Local Climate and Energy Program: Renewable Energy.”