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 2020, 337.5 terawatt-hours were generated by wind power, or 8.42% of all generated electrical energy in the United States. In 2019, wind power surpassed hydroelectric power as the largest renewable energy source generated in the U.S.
As of January 2021, the total installed wind power nameplate generating capacity in the United States was 122,478 megawatts (MW).
This capacity is exceeded only by China and the European Union. Thus far, wind power's largest growth in capacity was in 2020, when 16,913 MW of wind power was installed. Following behind it was 2012, which saw the addition of 11,895 MW, representing 26.5% of the new power capacity installed during that year.
By September 2019, 19 states had over 1,000 MW of installed capacity with 5 states (Texas, Iowa, Oklahoma, Kansas, and California) 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 over 57% 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 (DOE). 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.
Currently, the ten largest wind farms in the United States are:
The Traverse Wind Energy Center, located in Oklahoma and with a capacity of 999 MW, will surpass Los Vientos as the second-largest wind farm upon coming online in 2021.
Economics.
The 2020 report on energy costs by Lazard found that the unsubsidized levelized cost of energy (LCOE) for onshore wind is 2.6 to 5.4 cents per kilowatt-hour (kWh), and the median unsubsidized LCOE for offshore wind is 8.6 cents per kWh.
In comparison, the analysis finds that the lowest-cost conventional source, Gas Combined Cycle, has a cost range of 4.4 to 7.3 cents per kwh.
In 2021, the United States Energy Information Administration estimated that the unsubsidized, levelized cost of new onshore wind energy entering service in 2023 will be 3 cents per kwh.
The report also cautioned that levelized costs can be misleading. While levelized cost reflects the cost of building and operating a power plant, it does not recognize the relative value of energy from dispatchable sources such as gas turbine compared to non-dispatchable sources such as wind farms. The report also calculates levelized avoided cost of energy (LACE), which can be used to better reflect the economic value of an energy source.
Subsidies such as the investment tax credit and production tax credit further reduce the current cost of wind energy. These subsidies are scheduled to decline and expire in the coming years.
In 2015, Utah State University published a Koch-funded study stating that the cost of wind energy is higher than most cost estimates calculate. 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.
Renewable portfolio standards require renewable energy to exist (most of them intermittent such as wind and solar), but at the expense of utilities and consumers. Subsidizing this with production tax credits makes wind power cheaper for utilities and consumers, but at the expense of taxpayers.
National trends.
Production.
As of 2020, the United States has over 122 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 (see image on the right). 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 for
10,459 GW of onshore wind power. The capacity could generate 37 petawatt-hours (PW·h) 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 became the first state in the nation to generate 50% of its electricity from wind power in 2020, as predicted in 2015.
The five states with the most wind capacity installed at the end of 2020 were:
The top five states according to percentage of generation by wind in 2020 were:
Texas.
In 2016 Texas surpassed the 20,000 MW mark by adding over 1800 MW of generating capacity. In 2011, Texas had become the first state to surpass the 10,000 MW mark.
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.
On completion in 2016, the Los Vientos Wind Farm became Texas's most powerful wind farm with a total installed capacity of 912 MW. It is spread out over two counties in South Texas. It is followed by the Roscoe Wind Farm with 627 wind turbines and a total installed capacity of 781.5 MW which is located about 200 miles (320 km) west of Fort Worth in an area that spans parts of four Texas counties. The Horse Hollow Wind Energy Center is third with 735.5 MW.
Iowa.
More than 57 percent of the electric power generated in Iowa now comes from wind power as of February 2021. Iowa had over 10,950 megawatts (MW) of generation capacity at the end of 2020, with over 1,500 megawatts planned to come online in the near future. Electrical energy generated in Iowa by wind in 2020 amounted to over 34 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 (377 feet) 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 (east of San Francisco); Tehachapi Pass Wind Farm (south east of Bakersfield), and San Gorgonio Pass Wind Farm (near Palm Springs, east of Los Angeles). The giant new Alta Wind Energy Center, is also located within the Tehachapi Pass region.
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 (DOE) 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 (MOU) 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 (NREL) 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 (230 feet). 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 (NWTC). First Wind (formerly called UPC Wind Partners, LLC) 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 (PTC) of $15 per MW·h (in 1995 dollars) 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 (the latest year for which statistics are available), accounting for 37% ($5.936 billion) 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 (PTC), 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 (TW·h) 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 smaller $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 and was completed in December 2016 to become the first offshore wind farm in the United States.
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. In September 2020, New Jersey officials halted the Ørsted Ocean Wind Project citing concerns about misrepresented economic benefits of offshore wind, including construction of monopoles, utilization of women- and minority-owned businesses, union labor, possible negative effects on the fishing industry.
Coastal Virginia Offshore Wind (CVOW) is an offshore wind energy pilot project located about 27 miles (43 km) off the coast of Virginia Beach, Virginia. The two-turbine, 12-MW pilot project, constructed in 2020, is the second utility scale offshore wind farm operating in the United States. Dominion Energy and Ørsted US Offshore Wind collaborated on the project.
Wind energy meteorology.
Winds in the Central Plains region of the U.S. are variable on both short (minutes) and long (days) 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.
All offshore wind development requires either federal or state approval and a lease since offshore land is government property. Offshore wind regulation authority has shifted through several federal agencies since the early 2000s. Prior to 2005, offshore wind turbine and farm permits were under the jurisdiction of the US Army Corps of Engineers. In 2005, with the passing of the Energy Policy Act, the Minerals Management Service within the Department of the Interior had authority over wind turbine development on federal waters, like the Outer Continental Shelf, and was responsible for evaluating economic value, potential environmental impacts, and coordinating with federal and state agencies when approving wind power permits. Finally, in 2010, the Minerals Management Service was divided into three agencies, of which the Bureau of Ocean Energy Management is responsible for leasing, permitting, monitoring, and regulating offshore wind energy.
The harassment of any marine mammal species in U.S. waters is a violation of the Marine Mammal Protection Act of 1972 (50 CFR 18).
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.


Adani Power

Adani Power Limited is the power business subsidiary of Indian conglomerate Adani Group with head office at Ahmedabad, Gujarat. It is a private thermal power producer, with capacity of 12,450 MW.
It also operates a mega solar plant of 40 MW at Naliya, Bitta, Kutch, Gujarat. It is India's company that synchronises the supercritical technology.
Adani Godda Power is implementing a 1,600 MW plant at Jharkhand. The company has signed long term power purchase agreements of about 9,153 MW with government of Gujarat, Maharashtra, Haryana, Rajasthan, Karnataka, and Punjab.
History.
Adani Power was started as a power trading company in 1996.
Key people.
Gautam Adani is the chairman of the company. He completed his schooling from Sheth Chimanlal Nagindas Vidyalaya in Ahmedabad. He enrolled in a college but dropped out to work as a diamond sorter at Mahindra Bros in Mumbai. After a couple of years, Adani established his own diamond brokerage unit. In 1988, he established Adani Exports Limited, now known as Adani Enterprises Limited – the holding company of the Adani Group. He is the chairman and founder of the Adani Group.
Future projects.
As of January 2011, the company has 16,500 MW under implementation and planning stage. Included are a 3,300 MW coal-based TPP at Bhadreswar in Gujarat; a 2,640 MW TPP at Dahej, Gujarat; a 1,320 MW TPP at Chhindwara in Madhya Pradesh; a 2,500 MW TPP at Anugul, Orissa; a 2,000 MW TPP at Sambalpur, Orissa; and a 2,000 MW gas-based power project at Mundra, Gujarat. The company is bidding for a 1,000 MW lignite coal-based power plant in Kosovo.
In November 2017, Adani Power (Jharkhand) signed a long-term pact with Bangladesh Power Development Board to supply electricity from its upcoming 1,600 MW plant at Godda in Jharkhand.
As of 2019, the Adani Group is in talks with the Rural electrification Corporation (REC Limited) and Power Finance Corporation (PFC) to set up a 1600 MW Godda Power Project in Jharkhand at a cost of approximately Rs 14,000 crores.
Awards/Recognition.
The company has won many awards and recognition. In 2017, it was named the Most Innovative Young Power Professional by IPPAI (Independent Power Producers Association of India) at the 18th Regulators & Policymakers Retreat. In 2017, CSR Works International with support of British Chamber of Commerce and High Commission of Canada, recognised thefirm for best sustainability reporting in Asia, in Singapore. In 2018, it received the Recognition for Best Environment Management practices by Srishti Publications.


Top cap

In vacuum tube technology, a top cap is a terminal at the top of the tube envelope that connects one of the electrodes, the other electrodes being connected via the tube socket.
Top caps have most commonly been used for:
A few amplifier tubes used two top caps, symmetrically placed, one for anode and the other for grid.
In audio amplifier tube application, the top cap was originally used for the grid connection, and a serviceman could apply a moist finger to the terminal to confirm that the stage and subsequent circuits were working by listening for the hum this produced in the loudspeaker. This practice led to some nasty accidents when anode top caps were first introduced to amplifier stages (they had been used on rectifiers for some time).


Old Dominion Power


Audion

The Audion was an electronic detecting or amplifying vacuum tube invented by American electrical engineer Lee de Forest in 1906. It was the first triode, consisting of an evacuated glass tube containing three electrodes: a heated filament, a grid, and a plate. It is important in the history of technology because it was the first widely used electronic device which could amplify; a small electrical signal applied to the grid could control a larger current flowing from the filament to plate.
The original triode Audion had more residual gas in the tube than later versions and vacuum tubes; the extra residual gas limited the dynamic range and gave the Audion non-linear characteristics and erratic performance. Originally developed as a radio receiver detector by adding a grid electrode to the Fleming valve, it found little use until its amplifying ability was recognized around 1912 by several researchers, who used it to build the first amplifying radio receivers and electronic oscillators. The many practical applications for amplification motivated its rapid development, and the original Audion was superseded within a few years by improved versions with higher vacuum.
History.
It had been known since the middle of the 19th century that gas flames were electrically conductive, and early wireless experimenters had noticed that this conductivity was affected by the presence of radio waves. De Forest found that gas in a partial vacuum heated by a conventional lamp filament behaved much the same way, and that if a wire were wrapped around the glass housing, the device could serve as a detector of radio signals. In his original design, a small metal plate was sealed into the lamp housing, and this was connected to the positive terminal of a 22–volt battery via a pair of headphones, the negative terminal being connected to one side of the lamp filament. When wireless signals were applied to the wire wrapped around the outside of the glass, they caused disturbances in the current which produced sounds in the headphones.
This was a significant development as existing commercial wireless systems were heavily protected by patents; a new type of detector would allow De Forest to market his own system. He eventually discovered that connecting the antenna circuit to a third electrode placed directly in the current path greatly improved the sensitivity; in his earliest versions, this was simply a piece of wire bent into the shape of a grid-iron (hence "grid").
The Audion provided power gain; with other detectors, all of the power to operate the headphones had to come from the antenna circuit itself. Consequently, weak transmitters could be heard at greater distances.
Patents and disputes.
De Forest and everybody else at the time greatly underestimated the potential of his original device, imagining it to be limited to mostly military applications. It is significant that he apparently never saw its potential as a telephone repeater amplifier, even though crude electromechanical "note magnifiers" had been the bane of the telephone industry for at least two decades. (Ironically, in the years of patent disputes leading up to World War I, it was only this "loophole" that allowed vacuum triodes to be manufactured at all since none of De Forest's patents specifically mentioned this application).
De Forest was granted a patent for his early two-electrode version of the Audion on November 13, 1906 (), and the "triode" (three-electrode) version was patented in 1908 (). De Forest continued to claim that he developed the Audion independently from John Ambrose Fleming's earlier research on the thermionic valve (for which Fleming received Great Britain patent 24850 and the American Fleming valve patent ), and De Forest became embroiled in many radio-related patent disputes. De Forest was famous for saying that he "didn't know why it worked, it just did".
He always referred to the vacuum triodes developed by other researchers as "Oscillaudions", although there is no evidence that he had any significant input to their development. It is true that after the invention of the true vacuum triode in 1913 (see below), De Forest continued to manufacture various types of radio transmitting and receiving apparatus, (examples of which are illustrated on this page). However, although he routinely described these devices as using "Audions", they actually used high-vacuum triodes, using circuitry very similar to that developed by other experimenters.
In 1914, Columbia University student Edwin Howard Armstrong worked with professor John Harold Morecroft to document the electrical principles of the Audion. Armstrong published his explanation of the Audion in "Electrical World" in December 1914, complete with circuit diagrams and oscilloscope graphs. In March and April 1915, Armstrong spoke to the Institute of Radio Engineers in New York and Boston, respectively, presenting his paper "Some Recent Developments in the Audion Receiver", which was published in September. A combination of the two papers was reprinted in other journals such as the "Annals of the New York Academy of Sciences". When Armstrong and De Forest later faced each other in a dispute over the regeneration patent, Armstrong was able to demonstrate conclusively that De Forest still had no idea how it worked.
The problem was that (possibly to distance his invention from the Fleming valve) De Forest's original patents specified that low-pressure gas inside the Audion was essential to its operation (Audion being a contraction of "Audio-Ion"), and in fact early Audions had severe reliability problems due to this gas being adsorbed by the metal electrodes. The Audions sometimes worked extremely well; at other times they would barely work at all.
As well as De Forest himself, numerous researchers had tried to find ways to improve the reliability of the device by stabilizing the partial vacuum. Much of the research that led to the development of true vacuum tubes was carried out by Irving Langmuir in the General Electric (GE) research laboratories.
Kenotron and Pliotron.
Langmuir had long suspected that certain assumed limitations on the performance of various low-pressure and vacuum electrical devices, might not be fundamental physical limitations at all, but simply due to contamination and impurities in the manufacturing process.
His first success was in demonstrating that, contrary to what Edison and others had long asserted, incandescent lamps could function more efficiently and with longer life if the glass envelope was filled with low-pressure inert gas rather than a complete vacuum. However, this only worked if the gas used was meticulously 'scrubbed" of all traces of oxygen and water vapor.
He then applied the same approach to producing a rectifier for the newly developed "Coolidge" X-ray tubes. Again contrary to what had been widely believed to be possible, by virtue of meticulous cleanliness and attention to detail, he was able to produce versions of the Fleming Diode that could rectify hundreds of thousands of volts. His rectifiers were called "Kenotrons" from the Greek "keno" (empty, contains nothing, as in a vacuum) and "tron" (device, instrument).
He then turned his attention to the Audion tube, again suspecting that its notoriously unpredictable behaviour might be tamed with more care in the manufacturing process.
However he took a somewhat unorthodox approach. Instead of trying to stabilize the partial vacuum, he wondered if it was possible to make the Audion function with the total vacuum of a Kenotron, since that was somewhat easier to stabilize.
He soon realized that his "vacuum" Audion had markedly different characteristics from the De Forest version, and was really a quite different device, capable of linear amplification and at much higher frequencies. To distinguish his device from the Audion he named it the "Pliotron", from the Greek "plio" (more or extra, in this sense meaning gain, more signal coming out than went in).
Essentially, he referred to all his vacuum tube designs as Kenotrons, the Pliotron basically being a specialized type of Kenotron. However, because Pliotron and Kenotron were registered trademarks, technical writers tended to use the more generic term "vacuum tube". By the mid-1920s, the term "Kenotron" had come to exclusively refer to vacuum tube rectifiers, while the term "Pliotron" had fallen into disuse. Ironically, in popular usage, the sound-alike brands "Radiotron" and "Ken-Rad" outlasted the original names.
Applications and use.
De Forest continued to manufacture and supply Audions to the US Navy up until the early 1920s, for maintenance of existing equipment, but elsewhere they were regarded as well and truly obsolete by then. It was the vacuum triode that made practical radio broadcasts a reality.
Prior to the introduction of the Audion, radio receivers had used a variety of detectors including coherers, barretters, and crystal detectors. The most popular crystal detector consisted of a small piece of galena crystal probed by a fine wire commonly referred to as a "cat's-whisker detector". They were very unreliable, requiring frequent adjustment of the cat's whisker and offered no amplification. Such systems usually required the user to listen to the signal through headphones, sometimes at very low volume, as the only energy available to operate the headphones was that picked up by the antenna. For long distance communication huge antennas were normally required, and enormous amounts of electrical power had to be fed into the transmitter.
The Audion was a considerable improvement on this, but the original devices could not provide any subsequent amplification to what was produced in the signal detection process. The later vacuum triodes allowed the signal to be amplified to any desired level, typically by feeding the amplified output of one triode into the grid of the next, eventually providing more than enough power to drive a full-sized speaker. Apart from this, they were able to amplify the incoming radio signals prior to the detection process, making it work much more efficiently.
Vacuum tubes could also be used to make superior radio transmitters. The combination of much more efficient transmitters and much more sensitive receivers revolutionized radio communication during World War I.
By the late 1920s such "tube radios" began to become a fixture of most Western world households, and remained so until long after the introduction of transistor radios in the mid-1950s.
In modern electronics, the vacuum tube has been largely superseded by solid state devices such as the transistor, invented in 1947 and implemented in integrated circuits in 1959, although vacuum tubes remain to this day in such applications as high-powered transmitters, guitar amplifiers and some high fidelity audio equipment.


Geothermal energy in the United States

Geothermal energy in the United States was first used for electric power production in 1960. The Geysers in Sonoma and Lake counties, California was developed into what is now the largest geothermal steam electrical plant in the world, at 1,517 megawatts. Other geothermal steam fields are known in the western United States and Alaska. Geothermally generated electric power can be dispatchable to follow the demands of changing loads. Environmental impact of this energy source includes hydrogen sulfide emissions, corrosive or saline chemicals discharged in waste water, possible seismic effects from water injection into rock formations, waste heat and noise.
History.
According to archaeological evidence, geothermal resources have been in use on the current territory of the United States for more than 10,000 years. The Paleo-Indians first used geothermal hot springs for warmth, cleansing, and minerals.
The first commercial geothermal power plant producing power to the U.S. utility grid opened at The Geysers in California in September 1960, producing eleven megawatts of net power. The Geysers system continues to operate successfully today, and the complex has grown into the largest geothermal development in the world, with an output of 750 MW.
The largest dry steam field in the world is the Geysers, north of San Francisco. It was here that Pacific Gas and Electric began operation of the first successful geothermal electric power plant in the United States in 1960. The original turbine lasted for more than 30 years and produced 11 MW net power. The Geysers has 1517 megawatt (MW) of active installed capacity with an average capacity factor of 63%. Calpine Corporation owns 15 of the 18 active plants in the Geysers and is currently the United States' largest producer of geothermal energy. Two other plants are owned jointly by the Northern California Power Agency and the City of Santa Clara's municipal Electric Utility (now called Silicon Valley Power). The remaining Bottle Rock Power Plant owned by the US Renewables Group has only recently been reopened. A nineteenth plant is now under development by Ram Power, formerly Western Geopower. Since the activities of one geothermal plant affects those nearby, the consolidation plant ownership at The Geysers has been beneficial because the plants operate cooperatively instead of in their own short-term interest. The Geysers is now recharged by injecting treated sewage effluent from the City of Santa Rosa and the Lake County sewage treatment plant. This sewage effluent used to be dumped into rivers and streams and is now piped to the geothermal field where it replenishes the steam produced for power generation.
Another major geothermal area is located in south central California, on the southeast side of the Salton Sea, near the cities of Niland and Calipatria, California. In 2001, there were 15 geothermal plants producing electricity in the area. CalEnergy owns about half of them and the rest are owned by various companies. Combined the plants have a capacity of about 570 MW. Hudson Ranch I geothermal plant, a 50 MW plant opened in May 2012, the first in the area in 20 years. A second similar plant is to open in 2013.
The Basin and Range geologic province in Nevada, southeastern Oregon, southwestern Idaho, Arizona and western Utah is now an area of rapid geothermal development. Several small power plants were built during the late 1980s during times of high power prices. Rising energy costs have spurred new development. The capacity of all 19 currently active geothermal power plants in Nevada is more than 486 MW. The largest plant is the McGinnis Hills facility operated by Ormat with a capacity of 96MW. Other geothermal plants in Nevada are at Steamboat Springs, Brady/Desert Peak, Dixie Valley, Soda Lake, Stillwater and Beowawe.
Production.
With 3,676 MW of installed geothermal capacity as of 2019, the United States remains the world leader with about 25% of the online capacity total. The future outlook for expanded production from conventional and enhanced geothermal systems is positive as new technologies promise increased growth in locations previously not considered.
By state.
Installed geothermal capacity in megawatts (MW) by state as of February 2012:
Research and development.
As of August 2008, 103 new projects are under way in 13 U.S. states. When developed, these projects could potentially supply up to 3,979 MW of power, meeting the needs of about 4 million homes. At this rate of development, geothermal production in the United States could exceed 15,000 MW by 2025.
The most significant catalyst behind new industry activity is the Energy Policy Act of 2005. This Act made new geothermal plants eligible for the full federal production tax credit, previously available only to wind power projects and certain kinds of biomass. It also authorized and directed increased funding for research by the Department of Energy, and enabled the Bureau of Land Management to address its backlog of geothermal leases and permits.
In April 2008, exploratory drilling began at Newberry Volcano in Oregon.
In 2009, investment bank Credit Suisse calculated that geothermal power costs 3.6 cents per kilowatt-hour, versus 5.5 cents per kilowatt-hour for coal, if geothermal receives loans with lower rates than offered by the market."
A report released in late May 2019 by the Department of Energy suggests that U.S. geothermal power capacity could increase by more than twenty-six times by 2050, reaching a total installed capacity of 60 GW, thanks to accelerated technological development and adoption. (Also see figure on the left.) The report also demonstrates the benefits of geothermal power for residential and industrial heating. Energy Secretary Rick Perry announced his Department had provided funding for a $140-million research facility at the University of Utah on man-made geothermal energy.
Reliability.
Unlike some other renewable power sources such as wind and solar, geothermal energy is dispatchable, meaning that it is both available whenever needed, and can quickly adjust output to match demand. According to the US Energy Information Administration (EIA), of all types of new electrical generation plants, geothermal generators have the highest capacity factor, a measure of how much power a facility actually generates as a percent of its maximum capacity. The EIA rates new geothermal plants as having a 92% capacity factor, comparable to those of nuclear (90%), and higher than gas (87%), or coal (85%), and much higher than those of intermittent sources such as onshore wind (34%) or solar photovoltaic (25%). While the carrier medium for geothermal electricity (water) must be properly managed, the source of geothermal energy, the Earth's heat, will be available, for most intents and purposes, indefinitely.
In 2008 the USDOE funded research in Enhanced Geothermal Systems (EGS) to learn more about the fracture systems in geothermal reservoirs and better predict the results of reservoir stimulation. The DOE Geothermal Technologies Program (part of the American Recovery and Reinvestment Act of 2009) provided funding to establish the National Geothermal Data System (NGDS). Through the NGDS, many older paper archives and drill logs that are stored at state geological surveys are now being digitized and made available for free to the public.
Environmental effects.
The underground hot water and steam used to generate geothermal power may contain chemicals that could pollute the air and water if released at the surface.
Hydrogen sulfide, which is toxic in high concentrations, is sometimes found in geothermal systems. Newer methods of generating geothermal power separate the hot steam collected underground from the steam used to power turbines, and substantially reduce the risk of releasing air-polluting contaminants.
The water mixed with the steam contains dissolved salts that can damage pipes and harm aquatic ecosystems. Some subsurface water associated with geothermal sources contain high concentrations of toxic elements such as boron, lead, and arsenic.
Injection of water in enhanced geothermal systems may cause induced seismicity. Earthquakes at the Geysers geothermal field in California, the largest being Richter magnitude 4.6, have been linked to injected water.
"Possible effects include scenery spoliation, drying out of hot springs, soil erosion, noise pollution, and chemical pollution of the atmosphere and of surface- and groundwaters."
Due to volcanic activities the Puna Geothermal Venture had to be closed and was affected by lava flows later.


Centrifugal compressor

Centrifugal compressors, sometimes called radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.
They achieve a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller. This kinetic energy is then converted to an increase in potential energy/static pressure by slowing the flow through a diffuser. The pressure rise in the impeller is in most cases almost equal to the rise in the diffuser.
Theory of operation.
In the case where flow passes through a straight pipe to enter a centrifugal compressor the flow is axial, uniform and has no vorticity, ie swirling motion. As the flow passes through the centrifugal impeller, the impeller forces the flow to spin faster as it gets further from the rotational axis. According to a form of Euler's fluid dynamics equation, known as the "pump and turbine equation", the energy input to the fluid is proportional to the flow's local spinning velocity multiplied by the local impeller tangential velocity.
In many cases, the flow leaving the centrifugal impeller is travelling near the speed of sound. It then flows through a stationary compressor causing it to decelerate. The stationary compressor is ducting with increasing flow-area where energy transformation takes place. If the flow has to be turned in a rearward direction to enter the next part of the machine, eg another impeller or a combustor, flow losses can be reduced by directing the flow with stationary turning vanes or individual turning pipes (pipe diffusers). As described in Bernoulli's principle, the reduction in velocity causes the pressure to rise.
Historical contributions, the pioneers.
Over the past 100 years, applied scientists including Stodola (1903, 1927–1945), Pfleiderer (1952), Hawthorne (1964), Shepard (1956), Lakshminarayana (1996), and Japikse (many texts including citations), have educated young engineers in the fundamentals of turbomachinery. These understandings apply to all dynamic, continuous-flow, axisymmetric pumps, fans, blowers, and compressors in axial, mixed-flow and radial/centrifugal configurations.
This relationship is the reason advances in turbines and axial compressors often find their way into other turbomachinery including centrifugal compressors. Figures 1.1 and 1.2 illustrate the domain of turbomachinery with labels showing centrifugal compressors. Improvements in centrifugal compressors have not been achieved through large discoveries. Rather, improvements have been achieved through understanding and applying incremental pieces of knowledge discovered by many individuals.
Figure 1.1 represents the aero-thermo domain of turbomachinery. The horizontal axis represents the energy equation derivable from The first law of thermodynamics. The vertical axis, which can be characterized by Mach Number, represents the range of fluid compressibility (or elasticity). The Z-axis, which can be characterized by Reynolds number, represents the range of fluid viscosities (or stickiness). Mathematicians and physicists who established the foundations of this aero-thermo domain include: Isaac Newton, Daniel Bernoulli, Leonhard Euler, Claude-Louis Navier, George Stokes, Ernst Mach, Nikolay Yegorovich Zhukovsky, Martin Kutta, Ludwig Prandtl, Theodore von Kármán, Paul Richard Heinrich Blasius, and Henri Coandă.
Figure 1.2 represents the physical or mechanical domain of turbomachinery. Again, the horizontal axis represents the energy equation with turbines generating power to the left and compressors absorbing power to the right. Within the physical domain the vertical axis differentiates between high speeds and low speeds depending upon the turbomachinery application. The Z-axis differentiates between axial-flow geometry and radial-flow geometry within the physical domain of turbomachinery. It is implied that mixed-flow turbomachinery lie between axial and radial. Key contributors of technical achievements that pushed the practical application of turbomachinery forward include: Denis Papin, Kernelien Le Demour, Daniel Gabriel Fahrenheit, John Smeaton, Dr. A. C. E. Rateau, John Barber, Alexander Sablukov, Sir Charles Algernon Parsons, Ægidius Elling, Sanford Alexander Moss, Willis Carrier, Adolf Busemann, Hermann Schlichting, Frank Whittle and Hans von Ohain.
Turbomachinery similarities.
Centrifugal compressors are similar in many ways to other turbomachinery and are compared and contrasted as follows:
Similarities to axial compressor.
Centrifugal compressors are similar to axial compressors in that they are rotating airfoil-based compressors. Both are shown in the adjacent photograph of an engine with 5 stages of axial compressor and one stage of centrifugal compressor. The first part of the centrifugal impeller looks very similar to an axial compressor. This first part of the centrifugal impeller is also termed an "inducer". Centrifugal compressors differ from axials as they use a significant change in radius from inlet to exit of the impeller to produce a much greater pressure rise in a single stage (eg 8 in the Pratt & Whitney Canada PW200 series of helicopter engines) than does an axial stage. The 1940s-era German Heinkel HeS 011 experimental engine was the first aviation turbojet to have a compressor stage with radial flow-turning part-way between none for an axial and 90 degrees for a centrifugal. It is known as a mixed/diagonal-flow compressor. A diagonal stage is used in the Pratt & Whitney Canada PW600 series of small turbo fan.
Centrifugal fan.
Centrifugal compressors are also similar to centrifugal fans of the style shown in neighboring figure as they both increase the flows energy through increasing radius. In contrast to centrifugal fans, compressors operate at higher speeds to generate greater pressure rises. In many cases the engineering methods used to design a centrifugal fan are the same as those to design a centrifugal compressor, so they can look very similar.
This relationship is less true in comparison to the squirrel-cage fan shown in the accompanying figure.
For purposes of generalization and definition, it can be said that centrifugal compressors often have density increases greater than 5 percent. Also, they often experience relative fluid velocities above Mach number 0.3 when the working fluid is air or nitrogen. In contrast, fans or blowers are often considered to have density increases of less than five percent and peak relative fluid velocities below Mach 0.3.
Centrifugal pump.
Centrifugal compressors are also similar to centrifugal pumps of the style shown in the adjacent figures. The key difference between such compressors and pumps is that the compressor working fluid is a gas (compressible) and the pump working fluid is liquid (incompressible). Again, the engineering methods used to design a centrifugal pump are the same as those to design a centrifugal compressor. Yet, there is one important difference: the need to deal with cavitation in pumps.
Radial turbine.
Centrifugal compressors also look very similar to their turbomachinery counterpart the radial turbine as shown in the figure. While a compressor transfers energy into a flow to raise its pressure, a turbine operates in reverse, by extracting energy from a flow, thus reducing its pressure. In other words, power is input to compressors and output from turbines.
Turbomachinery using centrifugal compressors.
A partial list of turbomachinery that may use one or more centrifugal compressors within the machine are listed here.
Components of a simple centrifugal compressor.
A simple centrifugal compressor has four components: inlet, impeller/rotor, diffuser, and collector. Figure 3.1 shows each of the components of the flow path, with the flow (working gas) entering the centrifugal impeller axially from right to left. As a result of the impeller rotating clockwise when looking downstream into the compressor, the flow will pass through the volute's discharge cone moving away from the figure's viewer.
Inlet.
The inlet to a centrifugal compressor is typically a simple pipe. It may include features such as a valve, stationary vanes/airfoils (used to help swirl the flow) and both pressure and temperature instrumentation. All of these additional devices have important uses in the control of the centrifugal compressor.
Centrifugal impeller.
The key component that makes a compressor centrifugal is the centrifugal impeller, Figure 0.1, which contains a rotating set of vanes (or blades) that gradually raises the energy of the working gas. This is identical to an axial compressor with the exception that the gases can reach higher velocities and energy levels through the impeller's increasing radius. In many modern high-efficiency centrifugal compressors the gas exiting the impeller is traveling near the speed of sound.
Impellers are designed in many configurations including "open" (visible blades), "covered or shrouded", "with splitters" (every other inducer removed) and "w/o splitters" (all full blades). Both Figures 0.1 and 3.1 show open impellers with splitters. Most modern high efficiency impellers use "backsweep" in the blade shape.
Euler's pump and turbine equation", plays an important role in understanding impeller performance.
Diffuser.
The next key component to the simple centrifugal compressor is the diffuser. Downstream of the impeller in the flow path, it is the diffuser's responsibility to convert the kinetic energy (high velocity) of the gas into pressure by gradually slowing (diffusing) the gas velocity. Diffusers can be vaneless, vaned or an alternating combination. High efficiency vaned diffusers are also designed over a wide range of solidities from less than 1 to over 4. Hybrid versions of vaned diffusers include: wedge, channel, and pipe diffusers. Some turbochargers have no diffuser.
Bernoulli's fluid dynamic principle plays an important role in understanding diffuser performance.
Collector.
The collector of a centrifugal compressor can take many shapes and forms. When the diffuser discharges into a large empty chamber, the collector may be termed a "Plenum". When the diffuser discharges into a device that looks somewhat like a snail shell, bull's horn or a French horn, the collector is likely to be termed a "volute" or "scroll". As the name implies, a collector’s purpose is to gather the flow from the diffuser discharge annulus and deliver this flow to a downstream pipe. Either the collector or the pipe may also contain valves and instrumentation to control the compressor.
Applications.
Below, is a partial list of centrifugal compressor applications each with a brief description of some of the general characteristics possessed by those compressors. To start this list two of the most well-known centrifugal compressor applications are listed; gas turbines and turbochargers.
Performance.
While illustrating a gas turbine's Brayton cycle, Figure 5.1 includes example plots of pressure-specific volume and temperature-entropy. These types of plots are fundamental to understanding centrifugal compressor performance at one operating point. The two plots show that the pressure rises between the compressor inlet (station 1) and compressor exit (station 2). At the same time the specific volume decreases while the density increases. The temperature-entropy plot shows that the temperature increases with increasing entropy (loss). Assuming dry air, and the ideal gas equation of state and an isentropic process, there is enough information to define the pressure ratio and efficiency for this one point. The compressor map is required to understand the compressor performance over its complete operating range.
Figure 5.2, a centrifugal compressor performance map (either test or estimated), shows flow, pressure ratio for each of 4 speed-lines (total of 23 data points). Also included are constant efficiency contours. Centrifugal compressor performance presented in this form provides enough information to match the hardware represented by the map to a simple set of end-user requirements.
Compared to estimating performance which is very cost effective (thus useful in design), testing, while costly, is still the most precise method. Further, testing centrifugal compressor performance is very complex. Professional societies such as ASME (i.e. PTC–10, Fluid Meters Handbook, PTC-19.x), ASHRAE (ASHRAE Handbook) and API (ANSI/API 617-2002, 672-2007) have established standards for detailed experimental methods and analysis of test results. Despite this complexity, a few basic concepts in performance can be presented by examining an example test performance map.
Performance maps.
Pressure ratio and flow are the main parameters needed to match the Figure 5.2 performance map to a simple compressor application. In this case, it can be assumed that the inlet temperature is sea-level standard. This assumption is not acceptable in practice as inlet temperature variations cause significant variations in compressor performance. Figure 5.2 shows:
As is standard practice, Figure 5.2 has a horizontal axis labelled with a flow parameter. While flow measurements use a variety of units, all fit one of 2 categories:
Mass flow per unit time.
Mass flow units, such as kg/s, are the easiest to use in practice as there is little room for confusion. Questions remaining would involve inlet or outlet (which might involve leakage from the compressor or moisture condensation). For atmospheric air, the mass flow may be wet or dry (including or excluding humidity). Often, the mass flow specification will be presented on an equivalent Mach number basis, formula_1. It is standard in these cases that the equivalent temperature, equivalent pressure and gas is specified explicitly or implied at a standard condition.
Volume flow per unit time.
In contrast, all volume flow specifications require the additional specification of density. Bernoulli's fluid dynamic principal is of great value in understanding this problem. Confusion arises through either inaccuracies or misuse of pressure, temperature and gas constants.
Also as is standard practice, Figure 5.2 has a vertical axis labelled with a pressure parameter. There is a variety of pressure measurement units. They all fit one of two categories:
The pressure rise may alternatively be specified as a ratio which has no units:
Other features common to performance maps are:
Constant speed lines.
The two most common methods for producing a map for a centrifugal compressor are at constant shaft speed or with a constant throttle setting. If the speed is held constant, test points are taken along a constant speed line by changing throttle positions. In contrast, if a throttle valve is held constant, test points are established by changing speed and repeated with different throttle positions (common gas turbine practice). The map shown in Figure 5.2 illustrate the most common method; lines of constant speed. In this case we see data points connected via straight lines at speeds of 50%, 71%, 87%, and 100% RPM. The first three speed lines have 6 points each while the highest speed line has five.
Constant efficiency islands.
The next feature to be discussed is the oval shaped curves representing islands of constant efficiency. In this figure we see 11 contours ranging from 56% efficiency (decimal 0.56) to 76% efficiency (decimal 0.76). General standard practice is to interpret these efficiencies as isentropic rather than polytropic. The inclusion of efficiency islands effectively generates a 3-dimensional topology to this 2-dimensional map. With inlet density specified, it provides a further ability to calculate aerodynamic power. Lines of constant power could just as easily be substituted.
Design or guarantee point(s).
Regarding gas turbine operation and performance, there may be a series of guaranteed points established for the gas turbine’s centrifugal compressor. These requirements are of secondary importance to the overall gas turbine performance as a whole. For this reason it is only necessary to summarize that in the ideal case, the lowest specific fuel consumption would occur when the centrifugal compressors peak efficiency curve coincides with the gas turbine's required operation line.
In contrast to gas turbines, most other applications (including industrial) need to meet a less stringent set of performance requirements. Historically, centrifugal compressors applied to industrial applications were needed to achieve performance at a specific flow and pressure. Modern industrial compressors are often needed to achieve specific performance goals across a range of flows and pressures; thus taking a significant step toward the sophistication seen in gas turbine applications.
If the compressor represented by Figure 5.2 is used in a simple application, any point (pressure and flow) within the 76% efficiency would provide very acceptable performance. An "End User" would be very happy with the performance requirements of 2.0 pressure ratio at 0.21 kg/s.
Surge.
Surge - is a flow phenomenon at low mass flow rate operation for which the impeller cannot add enough energy to overcome the system resistance or backpressure. At low mass flow rate operation, the pressure ratio over the impeller is high. The high back pressure, downstream of the impeller, pushes flow back over the tips of the rotor blades towards the impeller eye (inlet). This rapid flow reversal (i.e., surge) exhibits a strong rotational component, which affects the flow angles at the leading edge of the blades. The deterioration of the flow angles causes the impeller to be inefficient and less flow is delivered downstream. (Therefore, surge is sometimes referred to as axi-symmetric stall.) Thereby, the plenum downstream of the impeller is emptied and the (back) pressure drops. As a result, less flow reverses over the rotor tips and the impeller gains becomes again efficient. This cyclic events cause large vibrations, increase temperature and change rapidly the axial thrust. These occurrences can damage the rotor seals, rotor bearings, the compressor driver and cycle operation. Most turbomachines are designed to easily withstand occasional surging. However, if the machine is forced to surge repeatedly for a long period of time, or if it is poorly designed, repeated surges can result in a catastrophic failure. Of particular interest, is that while turbomachines may be very durable, the cycles/processes that they are used within can be far less robust.
Surge line.
The surge-line shown in Figure 5.2 is the curve that passes through the lowest flow points of each of the four speed lines. As a test map, these points would be the lowest flow points possible to record a stable reading within the test facility/rig. In many industrial applications it may be necessary to increase the stall line due to the system backpressure. For example, at 100% RPM stalling flow might increase from approximately 0.170 kg/s to 0.215 kg/s because of the positive slope of the pressure ratio curve.
As stated earlier, the reason for this is that the high-speed line in Figure 5.2 exhibits a stalling characteristic or positive slope within that range of flows. When placed in a different system those lower flows might not be achievable because of interaction with that system. System resistance or adverse pressure is proven mathematically to be the critical contributor to compressor surge.
Maximum flow line versus choke.
Choke occurs under one of 2 conditions. Typically for high speed equipment, as flow increases the velocity of the flow can approach sonic speed somewhere within the compressor stage. This location may occur at the impeller inlet "throat" or at the vaned diffuser inlet "throat". In contrast, for lower speed equipment, as flows increase, losses increase such that the pressure ratio eventually drops to 1:1. In this case, the occurrence of choke is unlikely.
The speed lines of gas turbine centrifugal compressors typically exhibit choke. This is a situation where the pressure ratio of a speed line drops rapidly (vertically) with little or no change in flow. In most cases the reason for this is that close to Mach 1 velocities have been reached somewhere within the impeller and/or diffuser generating a rapid increase in losses. Higher pressure ratio turbocharger centrifugal compressors exhibit this same phenomenon. Real choke phenomena is a function of compressibility as measured by the local Mach number within an area restriction within the centrifugal pressure stage.
The maximum flow line, shown in Figure 5.2, is the curve that passes through the highest flow points of each speed line. Upon inspection it may be noticed that each of these points has been taken near 56% efficiency. Selecting a low efficiency (<60%) is the most common practice used to terminate compressor performance maps at high flows. Another factor that is used to establish the maximum flow line is a pressure ratio near or equal to 1. The 50% speed line may be considered an example of this.
The shape of Figure 5.2's speed lines provides a good example of why it is inappropriate to use the term choke in association with a maximum flow of all centrifugal compressor speed lines. In summary; most industrial and commercial centrifugal compressors are selected or designed to operate at or near their highest efficiencies and to avoid operation at low efficiencies. For this reason there is seldom a reason to illustrate centrifugal compressor performance below 60% efficiency.
Many industrial and commercial multistage compressor performance maps exhibits this same vertical characteristic for a different reason related to what is known as stage stacking.
Dimensional analysis.
To weigh the advantages between centrifugal compressors it is important to compare 8 parameters classic to turbomachinery. Specifically, pressure rise (p), flow (Q), angular speed (N), power (P), density (ρ), diameter (D), viscosity (μ) and elasticity (e). This creates a practical problem when trying to experimentally determine the effect of any one parameter. This is because it is nearly impossible to change one of these parameters independently.
The method of procedure known as the Buckingham π theorem can help solve this problem by generating 5 dimensionless forms of these parameters. These Pi parameters provide the foundation for "similitude" and the "affinity-laws" in turbomachinery. They provide for the creation of additional relationships (being dimensionless) found valuable in the characterization of performance.
For the example below Head will be substituted for pressure and sonic velocity will be substituted for elasticity.
Buckingham Π theorem.
The three independent dimensions used in this procedure for turbomachinery are:
According to the theorem each of the eight main parameters are equated to its independent dimensions as follows:
Classic turbomachinery similitude.
Completing the task of following the formal procedure results in generating this classic set of five dimensionless parameters for turbomachinery. Full similitude is achieved when each of the 5 Pi-parameters are equivalent. This of course would mean the two turbomachines being compared are geometrically similar and running at the same operating point.
Turbomachinery analysts gain tremendous insight into performance by comparisons of these 5 parameters with efficiencies and loss coefficients which are also dimensionless. In general application, the flow coefficient and head coefficient are considered of primary importance. Generally, for centrifugal compressors, the velocity coefficient is of secondary importance while the Reynolds coefficient is of tertiary importance. In contrast, as expected for pumps, the Reynolds number becomes of secondary importance and the velocity coefficient almost irrelevant. It may be found interesting that the speed coefficient may be chosen to define the y-axis of Figure 1.1, while at the same time the Reynolds coefficient may be chosen to define the z-axis.
Other dimensionless combinations.
Demonstrated in the table below is another value of dimensional analysis. Any number of new dimensionless parameters can be calculated through exponents and multiplication. For example, a variation of the first parameter shown below is popularly used in aircraft engine system analysis. The third parameter is a simplified dimensional variation of the first and second. This third definition is applicable with strict limitations. The fourth parameter, specific speed, is very well known and useful in that it removes diameter. The fifth parameter, specific diameter, is a less often discussed dimensionless parameter found useful by Balje.
It may be found interesting that the specific speed coefficient may be used in place of speed to define the y-axis of Figure 1.2, while at the same time, the specific diameter coefficient may be in place of diameter to define the z-axis.
Affinity laws.
The following "affinity laws" are derived from the five Π-parameters shown above. They provide a simple basis for scaling turbomachinery from one application to the next.
Aero-thermodynamic fundamentals.
The following equations outline a fully three-dimensional mathematical problem that is very difficult to solve even with simplifying assumptions. Until recently, limitations in computational power, forced these equations to be simplified to an Inviscid two-dimensional problem with pseudo losses. Before the advent of computers, these equations were almost always simplified to a one-dimensional problem.
Solving this one-dimensional problem is still valuable today and is often termed "mean-line analysis". Even with all of this simplification it still requires large textbooks to outline and large computer programs to solve practically.
Conservation of mass.
Also termed "continuity", this fundamental equation written in general form is as follows:
Conservation of momentum.
Also termed the "Navier–Stokes equations", this fundamental is derivable from Newton's second law when applied to fluid motion. Written in compressible form for a Newtonian fluid, this equation may be written as follows:
Conservation of energy.
The first law of thermodynamics is the statement of the conservation of energy. Under specific conditions, the operation of a Centrifugal compressor is considered a reversible process. For a reversible process, the total amount of heat added to a system can be expressed as formula_7 where formula_4 is temperature and formula_9 is entropy. Therefore, for a reversible process:
Since U, S and V are thermodynamic functions of state, the above relation holds also for non-reversible changes. The above equation is known as the fundamental thermodynamic relation.
Equation of state.
The classical ideal gas law may be written:
The ideal gas law may also be expressed as follows
where formula_13 is the density, formula_14 is the adiabatic index (ratio of specific heats), formula_15 is the internal energy per unit mass (the "specific internal energy"), formula_16 is the specific heat at constant volume, and formula_17 is the specific heat at constant pressure.
With regard to the equation of state, it is important to remember that while air and nitrogen properties (near standard atmospheric conditions) are easily and accurately estimated by this simple relationship, there are many centrifugal compressor applications where the ideal relationship is inadequate. For example, centrifugal compressors used for large air conditioning systems (water chillers) use a refrigerant as a working gas that cannot be modeled as an ideal gas. Another example are centrifugal compressors design and built for the petroleum industry. Most of the hydrocarbon gases such as methane and ethylene are best modeled as a real gas equation of state rather than ideal gases. The Wikipedia entry for equations of state is very thorough.
Structural mechanics, manufacture and design compromise.
Ideally, centrifugal compressor impellers have thin air-foil blades that are strong, each mounted on a light rotor. This material would be easy to machine or cast and inexpensive. Additionally, it would generate no operating noise, and have a long life while operating in any environment.
From the very start of the aero-thermodynamic design process, the aerodynamic considerations and optimizations [29,30] are critical to have a successful design. during the design, the centrifugal impeller's material and manufacturing method must be accounted for within the design, whether it be plastic for a vacuum cleaner blower, aluminum alloy for a turbocharger, steel alloy for an air compressor or titanium alloy for a gas turbine. It is a combination of the centrifugal compressor impeller shape, its operating environment, its material and its manufacturing method that determines the impeller's structural integrity.


RPSG Group

The RP-Sanjiv Goenka Group, commonly known as RPSG Group, is an Indian industrial and services conglomerate headquartered in Kolkata, West Bengal. It was founded by Sanjiv Goenka, the younger son of Rama Prasad Goenka, on 13 July 2011.
With a US$6 billion asset base and US$4 billion revenue, the Group's businesses include power and energy, carbon black manufacturing, retail, IT-enabled services, FMCG, media and entertainment, infrastructure and education.
History and Acquisitions.
Rama Prasad Goenka established RPG Enterprises in 1979 with Phillips Carbon Black, Asian Cables, Agarpara Jute and Murphy India as the constituents.
In 1981, the group acquired CEAT Tyres India. KEC International was acquired in 1982.In 1986, it acquired the music company Gramophone Company of India Ltd, now known as Saregama. Harrisons Malayalam, the tea and rubber plantations was acquired in 1988. In the following year, Calcutta Electric Supply Corporation (CESC Limited), Raychem Technologies, and Spencer's were acquired.
In 1993, Noida Power Company Limited (NPCL) was formed as a JV between the group and Greater Noida Industrial Development Authority, to distribute power in the Greater Noida region.In 2009, the Group entered into media with the launch of Open Magazine, a weekly current affairs and features magazine.
In 2010, the Group's businesses were divided between Rama Prasad Goenka's sons, Harsh Goenka and Sanjiv Goenka. RP-Sanjiv Goenka Group was founded on 13th July 2011, with Sanjiv Goenka as its Chairman.


RETMA tube designation

The Radio Electronics Television Manufacturers' Association was formed in 1953, as a result of mergers with other trade standards organisations, such as the RMA. It was principally responsible for the standardised nomenclature for American vacuum tubes - however the standard itself had already been in use for a long time before 1953; for example, the 6L6 was introduced in July 1936.
American-made tubes bear a RETMA designation to allow for easy cross-referencing. The RETMA tube designation does not incorporate the purpose of each tube in the designation. The Anglo-European Mullard–Philips tube designation does include tube use information in the designation.


Solar flower tower

AORA's Solar Flower Tower is a hybrid power generator that utilizes solar and alternative fuels, including diesel fuel, natural gas, liquefied natural gas, biogas, and other biofuels, to provide a constant green power source targeted for community-sized production. A module, dubbed the Solar Flower Tower because it looks like a golden yellow tulip, creates about 100 kW of electricity. The basis of the design is to use solar heated compressed air to spin a micro turbine. What makes the micro turbine unique is the efficiency of smaller power blocks, which allows small-scale construction, meaning simpler operation and less land needed.
AORA.
Formerly known as EDIG Solar, AORA is an Israeli based company that develops solar-hybrid power generators. The EDIG group of companies has contracted engineering project with organizations such as Ministry of Defense (Israel), El Al Israel Airlines, and the National Health Service Provider. EDIG presently has a relationship with the Weizmann Institute of Science, providing engineering services. It was at the Weizmann Institute of Science where the solar thermal technology was developed. After the technology was licensed to EDIG, continued advancement was developed until they decided to turned their new solar division into a sub-company, EDIG Solar, now known as AROA.
How the tower works.
In half an acre of land (about 40% of a football field), a solar tower module is surrounded by thirty heliostats reflecting the sun ray into a special solar receiver inside the module. The receiver heats the turbine's compressed air to about 1,000°C, and the heated air is sent into the turbine's expander to create electricity.


GivePower

GivePower is a 501(c)(3) non-profit organization that develops clean water and energy systems in communities across the world. GivePower has installed 2,650 solar power installations in villages across 17 different countries and in underdeveloped areas of the United States.
History.
GivePower was co-founded in 2013 in California by Hayes Barnard and Lyndon Rive as the non-profit branch of SolarCity, which was created in 2006 by Elon Musk. After SolarCity merged with Tesla in 2016, GivePower was spun off into an independent organization just before the merger was completed. The president of GivePower is Hayes Barnard.
In 2014, the organization’s first focus was to provide one school with solar-powered lighting for every megawatt of solar system installed by SolarCity that year.
Projects.
In 2016, GivePower began developing solar powered desalination technology that could be exported to developing regions. The desalination systems are contained within 20-foot shipping containers and can desalinate up to 75,000 gallons of seawater and/or brackish water into potable water per day.
In 2018, GivePower installed its first desalination plant in Kiunga, Kenya, which is also solar powered. The project cost $500,000 and took one month to construct. As of 2019, the Kiunga plant could produce enough drinking water for up to 50,000 people per day and requires minimal maintenance.
As of 2018, GivePower had installed 2650 solar power installations in villages through seventeen different countries for institutions like primary schools and medical clinics. They have also developed solar installations in underdeveloped areas of the United States, including the Standing Rock Indian Reservation. Once installations are completed, GivePower transfers the maintenance and running of them to local communities.
In 2019, GivePower built a 300 kilowatt solar farm on the Standing Rock Indian Reservation which became the largest solar installation in North Dakota. The project was a partnership between Empowered by Light and GivePower, and the total cost was $470,000. The maintenance of the solar farm also created jobs for the Sioux Nation Tribe.