Wind Resource and Potential
Approximately 2% of the solar energy striking the Earth’s surface is converted to kinetic energy in wind. Wind turbines convert the wind’s kinetic energy to electricity without emissions.1 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 3% of U.S. electricity was derived from wind energy in 2017, but wind capacity is increasing rapidly.4
- High wind speeds yield more power because 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 83.0 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 2015 was about 21,153 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 64,318 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 54,000 utility-scale wind turbines are installed in the U.S., with a cumulative capacity of 89.4 GW.13 U.S. wind capacity increased by 431% between 2007 and 2017, a 18% average annual increase.13 Global wind capacity increased by 19% annually, on average, from 2007 to 2017, reaching 540 GW in 2017.14
- U.S. average turbine size was 2.15 MW in 2016, up from 1.94 MW between 2011 and 2015.5
- Average capacity factor has increased from 0.25 for projects installed from 1998 to 2001 to around 0.42 for projects built in 2014 and 2015.5
- On a capacity-weighted average basis, installed wind project costs declined by roughly $3,000/kW between the early 1980’s and 2016. In 2016, costs were $1,590/kW.5
- The installed cost of a small (<100 kW) turbine is approximately $5,900 per kW, on average.15
- In 2016, commercial wind energy cost approximately 2.5¢/kWh wholesale.5 The 2017 average U.S. residential electricity price was 12.9¢/kWh.4
- Texas (22,799 MW), Oklahoma (7,495 MW) and Iowa (7,312 MW) are the leading states in total installed wind capacity.13 Iowa generated over 37% of its electricity from wind, the highest percent in the U.S.16
- Wind turbines and components are manufactured at more than 500 U.S. facilities.18
- In 2017, 105,500 full-time workers were employed in the U.S. wind industry.16
- 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 $14,000.19
U.S. Wind Capacity13
Global Wind Capacity, 201714,17
Energy Performance and Environmental Impacts
- Wind turbines can reduce the impacts associated with electricity generation. The 2017 U.S. wind capacity of 89 GW annually avoids an estimated 189 million metric tons of CO2 emissions and reduces water use by about 95 billion gallons compared with conventional power plants.13,20
- According to a 2015 study, if 35% of U.S. electricity was wind-generated by 2050, electric sector GHG emissions would be reduced by 23%, eliminating 510 billion kg of CO2 emissions annually, or 12.3 trillion kg cumulatively from 2013, and decreasing water use by 15%.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 0.2 million, compared 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 38 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) (2018) Monthly Energy Review April 2018.
- U.S. DOE, Energy Efficiency and Renewable Energy (EERE) (2017) 2016 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 (2018) International Energy Statistics: Total Electricity Net 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) (2018) U.S. Wind Industry First Quarter 2018 Market Report.
- Global Wind Energy Council (GWEC) (2017) Global Wind Statistics 2017.
- GWEC (2017) Global Wind Report 2016.
- U.S. DOE, AWEA (2016) 2015 Distributed Wind Market Report.
- AWEA (2018) Wind Energy in the United States.
- AWEA (2016) Annual Wind Industry Report - Year Ending 2015.
- AWEA (2017) “Wind Energy Facts at a Glance.”
- AWEA (2018) U.S. Wind Industry Annual Market Report 2017 Executive Summary.
- Spitzley, D. and G. Keoleian (2005) “Life cycle environmental and economic assessment of willow biomass electricity.” CSS04-05R.
- U.S. Geological Survey, 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.”
- Database of State Incentives for Renewables and Efficiency (DSIRE) (2017) USA Summary Maps: Net Metering.
- DSIRE (2016) “Renewable Electricity Production Tax Credit (PTC).”
- U.S. DOE (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.”
- U.S. EPA (2014) “State and Local Climate and Energy Program: Renewable Energy.”