Wind power in the United States
Wind power in the United States is a branch of the energy industry that has expanded quickly over the latest several years. From January through December of 2019, 300.1 terawatt-hours were generated by wind power, or 7.29% of all generated electrical energy in the United States. That same year, wind power surpassed hydroelectric power as the largest renewable energy source generated in the U.S.
As of January 2020, the total installed wind power nameplate generating capacity in the United States was 105,583 megawatts.
This capacity is exceeded only by China and the European Union. 1,821 MW were further installed by the end of the first quarter of 2020, increasing the total capacity to 107,443 MW.
Thus far, wind power's largest growth in capacity was in 2012, when 11,895 MW of wind power was installed, representing 26.5% of new power capacity.
By September of 2019, 19 states had over 1,000 MW of installed capacity with 5 states generating over half of all wind energy in the nation. Texas, with 28,843 MW of capacity, about 16.8% of the state's electricity usage, had the most installed wind power capacity of any U.S. state at the end of 2019.
Texas also had more under construction than any other state currently has installed.
The state generating the highest percentage of energy from wind power is Iowa at 42% of total energy production, while North Dakota has the most per capita wind generation.
The Alta Wind Energy Center in California is the largest wind farm in the United States with a capacity of 1,548 MW.
GE Power is the largest domestic wind turbine manufacturer.
History
The first municipal use of multiple wind-electric turbines in the USA may have been a five turbine system in Pettibone, North Dakota in 1940. These were commercial Wincharger units on guyed towers.In 1980 the world's first wind farm, consisting of twenty 30 kW wind turbines was installed at Crotched Mountain, in New Hampshire.
From 1974 through the mid-1980s the United States government worked with industry to advance the technology and enable large commercial wind turbines. A series of NASA wind turbines were developed under a program to create a utility-scale wind turbine industry in the U.S., with funding from the National Science Foundation and later the United States Department of Energy. A total of 13 experimental wind turbines were put into operation, in four major wind turbine designs. This research and development program pioneered many of the multi-megawatt turbine technologies in use today, including: steel tube towers, variable-speed generators, composite blade materials, partial-span pitch control, as well as aerodynamic, structural, and acoustic engineering design capabilities.
Later, in the 1980s, California provided tax rebates for wind power. These rebates funded the first major use of wind power for utility electric power. These machines, gathered in large wind parks such as at Altamont Pass would be considered small and un-economic by modern wind power development standards. In 1985 half of the world's wind energy was generated at Altamont Pass. By the end of 1986 about 6,700 wind turbines, mostly less than 100 kW, had been installed at Altamont, at a cost of about $1 billion, and generated about 550 GWh/year.
Largest wind farms
Ten of the largest wind farms in the United States are:| Project | Capacity | State |
| Alta Wind Energy Center | 1548 | California |
| Shepherds Flat Wind Farm | 845 | Oregon |
| Meadow Lake Wind Farm | 801 | Indiana |
| Roscoe Wind Farm | 781 | Texas |
| Horse Hollow Wind Energy Center | 736 | Texas |
| Tehachapi Pass Wind Farm | 705 | California |
| Capricorn Ridge Wind Farm | 662 | Texas |
| San Gorgonio Pass Wind Farm | 619 | California |
| Limon Wind Energy Center | 601 | Colorado |
| Fowler Ridge Wind Farm | 600 | Indiana |
Economics
A 2012 report by a clean energy consulting group concluded that new wind farms can produce electric power in the 5-8 cents per kWh range, making wind power cost-competitive with fossil fuels in many areas. As of 2013, the US Energy Information Administration estimates the "levelized cost" of wind energy from new installations as 7 to 10 cents per kWh, depending on the geographic area, but cautioned that levelized costs of non-dispatchable sources such as wind should be compared to the avoided energy cost rather than the levelized cost of dispatchable sources such as natural gas, or baseload sources such as coal or geothermal. In 2015, a Koch-funded institute of Utah State University stated that the cost of wind energy is higher than most cost estimates calculate. Renewable portfolio standards require renewable energy to exist, but at the expense of utilities and consumers.The production tax credit makes wind power cheaper for utilities and consumers, but at the expense of taxpayers. The American Wind Energy Association has criticized the study of lacking comparison with pollution and subsidies incurred by other electric power sources, and for counting transmission as a cost rather than a benefit.
National trends
Production
| Wind generation by year in the United States | Wind generation capacity by year in the United States |
ImageSize = width:290 height:auto barincrement:20 PlotArea = left:48 bottom:21 top:10 right:10 AlignBars = justify Period = from:0 till:310000 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:50000 start:0 PlotData= color:coral width:20 bar:2000 from:start till:5593 text:5,593 bar:2001 from:start till:6737 text:6,737 bar:2002 from:start till:10354 text:10,354 bar:2003 from:start till:11187 text:11,187 bar:2004 from:start till:14144 text:14,144 bar:2005 from:start till:17811 text:17,811 bar:2006 from:start till:26589 text:26,589 bar:2007 from:start till:34450 text:34,450 bar:2008 from:start till:55363 text:55,363 bar:2009 from:start till:73886 text:73,886 bar:2010 from:start till:94652 text:94,652 bar:2011 from:start till:120177 text:120,177 bar:2012 from:start till:140822 text:140,822 bar:2013 from:start till:167840 text:167,840 bar:2014 from:start till:181791 text:181,655 bar:2015 from:start till:190927 text:190,927 bar:2016 from:start till:226993 text:226,993 bar:2017 from:start till:254303 text:254,303 bar:2018 from:start till:274952 text:274,952 bar:2019 from:start till:300071 text:300,071 | ImageSize = width:290 height:auto barincrement:20 PlotArea = left:48 bottom:21 top:10 right:10 AlignBars = justify Period = from:0 till:125000 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:15000 start:0 PlotData= color:skyblue width:20 bar:2000 from:start till:2539 text:2,539 bar:2001 from:start till:4232 text:4,232 bar:2002 from:start till:4687 text:4,687 bar:2003 from:start till:6350 text:6,350 bar:2004 from:start till:6723 text:6,723 bar:2005 from:start till:9147 text:9,147 bar:2006 from:start till:11575 text:11,575 bar:2007 from:start till:16907 text:16,907 bar:2008 from:start till:25410 text:25,410 bar:2009 from:start till:34863 text:34,863 bar:2010 from:start till:40180 text:40,180 bar:2011 from:start till:46919 text:46,919 bar:2012 from:start till:60007 text:60,007 bar:2013 from:start till:61087 text:61,108 bar:2014 from:start till:65877 text:65,877 bar:2015 from:start till:74472 text:74,472 bar:2016 from:start till:82183 text:82,183 bar:2017 from:start till:88973 text:88,973 bar:2018 from:start till:94295 text:94,295 bar:2019 from:start till:105583 text:105,583 bar:2020* from:start till:124983 text:124,983 |
| Power from wind generated annually since 2000 | Installed wind power generating capacity since 2000 This is a forecast accounting for economic impacts of the COVID-19 pandemic. |
As of 2019, the United States has over 105 GW of installed wind power capacity. Wind power has increased dramatically over the past years. In 2010, however, newly installed generating capacity was about half of the previous year due to various factors, including the financial crisis, and recession. In 2013 there was a 92% reduction in newly installed generating capacity compared to 2012, due to the late extension of the PTC. The graph at left shows the growth in installed wind generation capacity in the United States based on data from the Office of Energy Efficiency and Renewable Energy. In 2008, installed capacity in the U.S. increased by 50% over the prior year. The world average growth rate that year was 28.8%.
By 2014, the wind industry in the USA was able to produce more power at lower cost by using taller wind turbines with longer blades, capturing the faster winds at higher elevations. This opened up new opportunities and in Indiana, Michigan, and Ohio, the price of power from wind turbines above the ground competed with conventional fossil fuels like coal. Prices had fallen to about 4 cents per kilowatt-hour in some cases and utilities had been increasing the amount of wind energy in their portfolio, saying it is their cheapest option. For power contracts made in the year 2014, the average price of wind power fell to 2.5¢/kWh.
The capacity factor is the ratio of power actually produced divided by the nameplate capacity of the turbines. The overall average capacity factor for wind generation in the US increased from 31.7% in 2008, to 32.3% in 2013.
Wind generation potential
According to the National Renewable Energy Laboratory, the contiguous United States has the potential for10,459 GW of onshore wind power. The capacity could generate 37 petawatt-hours annually, an amount nine times larger than current total U.S. electricity consumption. The U.S. also has large wind resources in Alaska, and Hawaii.
In addition to the large onshore wind resources, the U.S. has large offshore wind power potential, with another NREL report released in September 2010 showing that the U.S. has 4,150 GW of potential offshore wind power nameplate capacity, an amount 4 times that of the country's 2008 installed capacity from all sources, of 1,010 GW. Some experts estimate that the entire East Coast could be powered by offshore wind farms.
The U.S. Department of Energy’s 2008 report 20% Wind Energy by 2030 envisioned that wind power could supply 20% of all U.S. electric power, which included a contribution of 4% to the nation’s total electric power from offshore wind power. In order to achieve this, however, significant advances in cost, performance and reliability are needed, based on a 2011 report from a coalition of researchers from universities, industry, and government, supported by the Atkinson Center for a Sustainable Future. Obtaining 20% from wind requires about 305 GW of wind turbines, an increase of 16 GW/year after 2018, or an average increase of 14.6%/year, and transmission line improvements. Analysts estimate around 25 GW of added US wind power in 2016-18, depending on the Clean Power Plan and PTC extensions. After the current PTC phase-out in 2021, additional wind power capacity is expected to be around 5 GW per year.
Wind power by state
In 2019, electric power generation from wind power was 10 percent or more in fourteen U.S. states: Colorado, Idaho, Iowa, Kansas, Maine, Minnesota, North Dakota, Oklahoma, Oregon, South Dakota, Vermont, Nebraska, New Mexico, and Texas.Iowa, South Dakota, North Dakota, Oklahoma, and Kansas each had more than 20 percent of their electric power generation come from wind. Twenty states now have more than five percent of their generation coming from wind. Iowa become the first state in the nation to generate 40% of its electricity from wind power in late 2019, as predicted in 2015.
The five states with the most wind capacity installed at the end of 2019 were:
- Texas
- Iowa
- Oklahoma
- Kansas
- California
The top five states according to percentage of generation by wind in 2019 were:
- Iowa
- Kansas
- Oklahoma
- North Dakota
- South Dakota
Texas
In July 2008, Texas approved a $4.93 billion expansion of the state's electric grid to bring wind energy to its major cities from western areas of the state. Transmission companies will recoup the cost of constructing the new power lines, expected to be completed in 2013, from fees estimated at $4 per month for residential customers. A lack of transmission capacity forced wind turbines to be shut down at times and reduced wind power generation in Texas by 17% in 2009.
The Roscoe Wind Farm in Roscoe, Texas, Texas's largest wind farm with 627 wind turbines and a total installed capacity of 781.5 MW, surpassed the nearby 735.5 MW Horse Hollow Wind Energy Center. It is located about 200 miles west of Fort Worth and the wind farm area spans parts of four Texas counties.
| Wind farm | Installed capacity | Turbine manufacturer | County |
| Buffalo Gap Wind Farm | 523 | Vestas | Taylor / Nolan |
| Capricorn Ridge Wind Farm | 662 | GE Energy / Siemens | Sterling / Coke |
| Horse Hollow Wind Energy Center | 735 | GE Energy / Siemens | Taylor / Nolan |
| Lone Star Wind Farm | 400 | Gamesa | Shackelford / Callahan |
| Panther Creek Wind Farm | 458 | GE Energy | Howard / … |
| Papalote Creek Wind Farm | 380 | Siemens | San Patricio |
| Peñascal Wind Farm | 404 | Mitsubishi | Kenedy |
| Roscoe Wind Farm | 781 | Mitsubishi | Nolan |
| Sweetwater Wind Farm | 585 | GE Energy / Siemens / Mitsubishi | Nolan |
Iowa
More than 42 percent of the electric power generated in Iowa now comes from wind power as of April 2020. Iowa had over 10,200 megawatts of generation capacity at the end of 2019, with over 1,500 megawatts planned to come online in the near future. Electrical energy generated in Iowa by wind in 2019 amounted to over 21 million Megawatt-hours. Since Iowa adopted a renewable energy standard in 1983, the wind power industry has generated over $19 billion in investment. The second concrete wind turbine tower to be built in the U.S., and also the country's tallest at the time built, is in Adams county. The tower was completed in the spring of 2016.In 2018, Invenergy announced it plans to develop a pair of wind farms in Iowa. Each farm will be capable of generating 200 MW. Construction is planned to begin in early 2019.
Oklahoma
Oklahoma has one of the best resources in the United States. Bergey Windpower, a leading manufacturer of small wind turbines is located in Oklahoma. Programs leading to careers in the wind power industry are provided at tech schools, community colleges and universities in Oklahoma. The Oklahoma Wind Power Initiative supports the development of wind power in the state.Kansas
In 2012, Kansas saw a large number of wind projects completed making it among the largest and fastest-growing wind energy markets. At the end of 2014 the total capacity sits at 2,967 MW.Kansas has high potential capacity for wind power, second behind Texas. The most recent estimates are that Kansas has a potential for 950 GW of wind power capacity. Kansas could generate 3,900 TW·h of electric power each year, which represents more than all the electric power generated from coal, natural gas and nuclear combined in the United States in 2011.
California
Wind power in California has doubled in capacity since 2002. With a total of nearly 4,000 megawatts installed, as of the end of 2011, wind energy supplied about 5% of California’s total electric power needs, or enough to power more than 400,000 households. The amount varies greatly from day to day. In 2011, 921.3 megawatts were installed. Most of that activity occurred in the Tehachapi area of Kern County, with some big projects in Solano, Contra Costa and Riverside counties as well. After 2014, California ranked second nationwide in terms of capacity, behind Texas with a capacity of 5,917 MW.Large portions of California's wind output, are located in three primary regions: Altamont Pass Wind Farm ; Tehachapi Pass Wind Farm, and San Gorgonio Pass Wind Farm. The giant new Alta Wind Energy Center, is also located within the Tehachapi Pass region.
| Name | Location | Capacity | |
| Altamont Pass Wind Farm | Alameda County | 576 | |
| Alta Wind Energy Center | Kern County | 1548 | |
| San Gorgonio Pass Wind Farm | Riverside County | 615 | |
| Tehachapi Pass Wind Farm | Kern County | 705 |
Illinois
Wind power has been supported by a renewable portfolio standard, passed in 2007, and strengthened in 2009, which requires 10% renewable energy from electric companies by 2010 and 25% by 2025. Illinois has the potential for installing up to an estimated 249,882 MW of wind generation capacity at a hub height of 80 meters.Commercialization of wind power
Industry trends
Since 2005 many turbine manufacturing leaders have opened U.S. facilities; of the top 10 global manufacturers in 2007, seven – Vestas, GE Energy, Gamesa, Suzlon, Siemens, Acciona, and Nordex – have an American manufacturing presence. REpower is another manufacturer with notable usage in the United States.Plans for 30 new manufacturing facilities were announced in 2008, and the wind industry expects to see a continued shift towards domestic manufacturing in the coming years. In total, 70 manufacturing facilities have begun production, been expanded, or announced since January 2007.
As of April 2009, over 100 companies are producing components for wind turbines, employing thousands of workers in the manufacture of parts as varied as towers, composite blades, bearings and gears. Many existing companies in traditional manufacturing states have retooled to enter the wind industry. Their manufacturing facilities are spread across 40 states, employing workers from the Southeast to the Steel Belt, to the Great Plains and on to the Pacific Northwest.
The U.S. Department of Energy is working with six leading wind turbine manufacturers towards achieving 20% wind power in the United States by 2030. The DOE announced the Memorandum of Understanding with GE Energy, Siemens Power Generation, Vestas Wind Systems, Clipper Windpower, Suzlon Energy, and Gamesa Corporation. Under the MOU, the DOE and the six manufacturers will collaborate to gather and exchange information relating to five major areas: research and development related to turbine reliability and operability; siting strategies for wind power facilities; standards development for turbine certification and universal interconnection of wind turbines; manufacturing advances in design, process automation, and fabrication techniques; and workforce development.
In 2014, GE had 60%, Siemens had 26%, and Vestas had 12% of US market share. Combined, they had 98%. Most new turbines were designed for low wind. The turbine manufacturers compete with each other and cause decreasing turbine prices.
Other government involvement
The DOE's National Renewable Energy Laboratory has announced a number of wind technology projects, including a new state-of-the-art wind turbine blade test facility to be built in Ingleside, Texas. The Texas-NREL Large Blade Research and Test Facility will be capable of testing blades as long as 70 meters. It will be built and operated through a partnership among NREL, DOE, and a state consortium led by University of Houston, with the university owning and operating the facility's buildings, DOE funding up to $2 million in capital costs, and NREL providing technical and operational assistance. The blade test facility is estimated to cost between $12 million and $15 million and should be completed by 2010. Located on the Gulf Coast, the Texas facility will complement a similar facility that is being built on the coast of Massachusetts.NREL has also recently signed agreements with Siemens Power Generation and First Wind, a wind power developer. Siemens is launching a new research and development facility in nearby Boulder, Colorado, and has agreed to locate and test a commercial-scale wind turbine at NREL's National Wind Technology Center. First Wind owns and operates the 30-megawatt Kaheawa Wind Power farm in West Maui, Hawaii, and has agreed to let the NWTC establish a Remote Research Affiliate Partner Site at the facility. The Maui satellite of NWTC will collaborate with First Wind on studies to develop advanced wind energy technologies, including energy storage and integration of renewable electric power into Maui's electrical grid.
In 2010, the DOE awarded $60 million for a study of transmission requirements. Beginning in 2006, the DOE is required to provide a transmission congestion report once every three years.
Recent U.S. policy has generally been to provide an inflation-adjusted federal production tax credit of $15 per MW·h generated for the first ten years of operation for wind energy sold. As of 2015, the credit was $23 per MW·h. Renewable portfolio standards mandating a certain percentage of electric power sales come from renewable energy sources, which are in place in about half of the states, also have boosted the development of the wind industry.
Each time Congress has allowed the production tax credit to expire, wind power development has slowed as investors wait for the credit to be restored. Each year it is renewed, development has expanded. The tax credit expired at the end of 2012, bringing wind power development activity to a near halt. A short term, one-year policy was enacted at the beginning of 2013 which provides a tax credit to projects under construction by the end of 2013 and completed before the end of 2014. The PTC was first introduced in 1992. When it was allowed to expire, development dropped 93%, 73%, and 77% the following year.
The Energy Information Administration has reported that wind power received the largest share of direct federal subsidies and support in fiscal year 2013, accounting for 37% of total electric power-related subsidies. Almost three-quarters of wind energy subsidies in that year were direct expenditures and largely resulted from the ARRA programs. These figures do not include subsidies and supports from other levels of government.
The development of wind power in the United States has been supported primarily through a production tax credit, which pays producers on the amount of electric power produced. On January 1, 2013 the production tax credit was extended for another year.
In late 2015 authorities provided an extension of the Production Tax Credit. The extension phases out the credit over a period of five years. The 30 percent wind and solar tax credit will extend through 2019 and then taper to 10 percent in 2022.
The average price of Power purchase agreements was $23.5/MWh in 2014. Operating expenses were estimated to $10/MWh.
Siting considerations
There is competition for wind farms among farmers in places like Iowa or ranchers in Colorado. Farmers, with no investment on their part, typically receive $3,000–5,000 per year in royalties from the local utility for siting a single, large, advanced-design wind turbine.Landscape and ecological issues may be significant for some wind farm proposals, and environmental issues are a consideration in site selection.
Worldwide experience has shown that community consultation and direct involvement of the general public in wind farm projects has helped to increase community approval, and some wind farms overseas have become tourist attractions, like the Ten Mile Lagoon wind farm.
Offshore wind power
Offshore development is hindered by relatively high cost compared to onshore facilities. Several projects are under development with some at advanced stages of development. The United States, though, has very large offshore wind energy resources due to strong, consistent winds off the long U.S. coastline.The 2011 NREL report, Large-Scale Offshore Wind Power in the United States, analyzes the current state of the offshore wind energy industry. According to the report, offshore wind resource development would help the country to achieve 20% of its electric power from wind by 2030 and to revitalize the manufacturing sector. Offshore wind could supply 54 gigawatts of capacity to the nation's electrical grid, thereby increasing energy security. It could also generate an estimated $200 billion in new economic activity and create thousands of permanent jobs. NREL’s report concludes that "the development of the nation’s offshore wind resources can provide many potential benefits, and that offshore wind energy could play a vital role in future U.S. energy markets".
Coastal residents have opposed offshore wind farms because of fears about impacts on marine life, the environment, electric power rates, aesthetics, and recreation such as fishing and boating. However, residents also cite improved electric power rates, air quality, and job creation as positive impacts they would expect from wind farms. Because the bases of offshore turbines function as artificial reefs, studies have shown that after the initial disturbance of construction, local fish and shellfish are positively affected. Because wind turbines can be positioned at some distance from shore, impacts to recreation and fishing can be managed by careful planning of wind farm locations.
Five exploratory leases for wind power production on the Outer Continental Shelf offshore from New Jersey and Delaware were issued in June 2009 by the Secretary of the Interior. The leases authorize data gathering activities, allowing for the construction of meteorological towers on the Outer Continental Shelf from six to offshore. Four areas are being considered. On February 7, 2011, Salazar and Steven Chu announced a national strategy to have offshore wind power of 10 GW in 2020, and 54 GW in 2030.
Projects are under development in areas of the East Coast, Great Lakes, and Gulf coast.
New England
Rhode Island and Massachusetts state officials picked Deepwater Wind to build a $1.5-billion, 385-megawatt wind farm in federal waters off Block Island. The 100-turbine project could provide 1.3 terawatt-hours of electric power per year – 15 percent of all electric power used in the state of Rhode Island. In 2009, Deepwater signed an agreement with National Grid to sell the power from a $200-million, 30-MW wind farm off Block Island, at an initial price of 24.4 ¢/kW·h. Construction of the Block Island Wind Farm, a five turbine project began in April 2015.Cape Wind started development around 2002, but faced opposition and eventually ceased before being realized. The floating VolturnUS operated in Penobscot Bay near Castine from June 2013 to November 2014. Maine Aqua Ventus intends to have two floating 6 MW turbines in operation off the coast of Monhegan Island by the end of 2020. Each turbine will be supported on a VolturnUS floating concrete hull.
Mid Atlantic
To promote wind power in New Jersey, in 2007 the state awarded a $4.4 million contract to conduct an 18-month Ocean/Wind Power Ecological Baseline Study, becoming the first state to sponsor an ocean and wind power study before allowing renewable energy developers to study and build off its shores. The study focused on a designated area off the coast to determine the current distribution, abundance and migratory patterns of avian species, fish, marine resources and sea turtle use of the existing ecological resources. The results of the study were released in June 2010. The study concluded that the effects of developing offshore windfarms would be negligible.In 2008, new federal rules greatly expanded the territory offshore wind parks can be built. Previously, projects were only allowed in shallow state waters within of shore. The edge of U.S. territory is about out. Increased distance from the coast diminishes their visibility. Waters off the coast of the United States are deeper than in Europe, requiring different designs.
Atlantic Wind Connection is a proposed electrical transmission backbone to be built off the Atlantic Coast of the United States to serve offshore wind farms. The transmission line, proposed by Trans-Elect Development Company, would deliver power ashore in southern Virginia, Delaware, southern New Jersey and northern New Jersey. As a first of its kind project, it poses significant risks of encountering unexpected technological challenges and cost overruns. Such an offshore backbone is an element in the national electric power strategy.
Bechtel has been selected as the EPC contractor and Alstom as technical advisor for the first phase of the development for the project. Google and Good Energies, an investment firm, are the major investors in the $5 billion project.
Ocean Wind is a proposed utility-scale offshore wind farm with a capacity of 1100MW to be located on the Outer Continental Shelf approximately off the coast of Atlantic City, New Jersey. If built it will be the largest in the U.S.
Wind energy meteorology
Winds in the Central Plains region of the U.S. are variable on both short and long time scales. Variations in wind speed result in variations in power output from wind farms, which poses difficulties incorporating wind power into an integrated power system. Wind turbines are driven by boundary layer winds, those that occur near the surface of the earth, at around 300 feet. Boundary layer winds are controlled by wind in the higher free atmosphere and have turbulence due to interaction with surface features such as trees, hills, and buildings. Short term or high frequency variations are due to this turbulence in the boundary layer.Long term variations are due to the passage of transient waves in the atmosphere, with a characteristic time scale of several days. The transient waves that influence wind in the Central U.S. are large scale and this results in the power output from wind farms in the region being somewhat correlated and not entirely independent. Large scale distribution of wind farms significantly reduce short term variability, limiting the relative standard deviation of the capacity factor to about 45%. The correlation is highest in summer and lowest in winter.
Environmental Impacts and Regulations
Bird protection
The US federal government has jurisdiction to prevent bird and bat deaths by wind turbines, under the Endangered Species Act, the Migratory Bird Treaty Act, and the Bald and Golden Eagle Protection Act. Under the 2009 Bald and Golden Eagle Protection Act, the Interior Department could issue permits to allow "non-purposeful take" for activities where eagle deaths were considered unavoidable; however, as of December 2013, no take permits had been issued to wind energy developers.The United States Fish and Wildlife Service has published voluntary guidelines for design and siting of wind turbines to minimize bird and bat deaths.
In 2013, the Obama administration was accused of having a double standard to protect the wind industry from Bald and Golden Eagle Protection Act prosecutions, while vigorously pursuing violations by oil companies and owners of power lines. The administration refused to divulge the number of raptor deaths reported to it by wind companies, saying that to do so would reveal trade secrets. The government also ordered federal law enforcement field agents not to pursue bird-death prosecutions against wind companies without prior approval from Washington. The policy was said to be an environmental trade-off to promote renewable energy.
In November 2013, the federal government obtained its first criminal conviction of a wind power operator for killing protected birds in violation of the 1918 Migratory Bird Treaty Act. Duke Energy plead guilty, and was fined $1 million, for the deaths of 160 birds, including 14 golden eagles, at two wind farms in Wyoming. The Justice Department charged that Duke had designed and sited the turbines knowing that they would kill birds; Duke noted that it had self-reported the bird deaths, and that US Fish and Wildlife Service guidelines for reducing bird deaths by wind turbines had not been issued when the turbines were built. After they were charged, Duke implemented a radar detection system, at a cost of $600,000 per year, designed to turn off turbines when approached by large birds; the company noted that the system was working, as no golden eagle deaths had been observed in more than a year of operation since the radar was installed.
In December 2013 the US Fish and Wildlife Service announced that it would issue 30-year permits to wind energy projects to allow for eagle deaths; previously, permits had been available for only 5 years, but none were issued to wind projects. Under the 30-year permits, wind power developers would be required to report eagle deaths, and the permits would be reviewed every 5 years. The measure was intended to remove what was seen as legal uncertainty discouraging wind energy investments. The government said that an environmental review was not needed for the change, because it was only an administrative change. The new regulation was welcomed by the American Wind Energy Association, which said that wind power caused less than two percent of human-caused eagle fatalities, and pointed out that the rules would require extensive mitigation and monitoring of eagle deaths. The extension of eagle taking permits from 5 to 30 years was opposed by a number of conservation groups, including the American Bird Conservancy, the Nature Conservancy, the Sierra Club, the Audubon Society, and the Humane Society of the United States.
More than 30,000 wind turbine locations are within federally protected bird habitats, out of which almost 24,000 lie in the migratory corridor of the whooping crane and almost 3000 in the breeding grounds of the endangered greater sage-grouse.
According to Dr. Michael Hutchins, the director of the American Bird Conservancy's Bird Smart Wind Energy Campaign, wind turbines present a threat to the nation's birds, and that the present permitting process is ineffective in addressing the issue. Concern about the bird deaths prompted the American Bird Conservancy and 70 other conservation organizations, to lobby the U.S. Department of Interior to develop a National Programmatic Wind Environmental Impact Statement which would identify appropriate areas for wind energy development, as well as areas where development should be avoided, but these lobbying efforts failed. Tom Vinson, the American Wind Energy Association vice president for regulatory affairs noted the ambiguity in estimation and extrapolation of various data and also questioned the credibility of the assumptions of organizations such as American Bird Conservancy in estimating future bird deaths.
Collision risks are primarily influenced by the height of the turbines and tower type. The average death count of birds increases as turbine heights reach 475 to 639 feet. Danger to birds increases because blades at higher altitudes overlap with the average flight height of nocturnally migrating birds.
Offshore wind
The harassment of any marine mammal species in U.S. waters is a violation of the Marine Mammal Protection Act of 1972.Offshore wind developers are required to apply for a letter of authorization or Incidental Harassment Authorization with all the pertinent details of the species under potential threat from their offshore activities, the mitigation measures, and monitoring and reporting obligations. Offshore wind projects must also comply with all regulatory obligations contained in the Federally approved State coastal management plan, under the Coastal Zone Management Act of 1972, to keep in check their effect on coastal resources.