Wind power

Wind power

Overview


Wind power is the conversion of wind energy
Wind energy
Wind energy is the kinetic energy of air in motion; see also wind power.Total wind energy flowing through an imaginary area A during the time t is:E = ½ m v2 = ½ v 2...

 into a useful form of energy, such as using wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...

s to make electricity, windmill
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...

s for mechanical power, windpump
Windpump
A windpump is a windmill used for pumping water, either as a source of fresh water from wells, or for draining low-lying areas of land. Once a common fixture on farms in semi-arid areas, windpumps are still used today where electric power is not available or too expensive.-History:Windmills were...

s for water pumping
Water pumping
The pumping of water is a basic and practical technique, far more practical than scooping it up with one's hands or lifting it in a hand-held bucket. This is true whether the water is drawn from a fresh source, moved to a needed location, purified, or used for irrigation, washing, or sewage...

 or drainage
Drainage
Drainage is the natural or artificial removal of surface and sub-surface water from an area. Many agricultural soils need drainage to improve production or to manage water supplies.-Early history:...

, or sail
Sail
A sail is any type of surface intended to move a vessel, vehicle or rotor by being placed in a wind—in essence a propulsion wing. Sails are used in sailing.-History of sails:...

s to propel ships.

The total amount of economically extractable power available from the wind is considerably more than present human power use from all sources. At the end of 2010, worldwide nameplate capacity
Nameplate capacity
Nameplate capacity, also known as the rated capacity, nominal capacity, installed capacity or maximum effect, refers to the intended technical full–load sustained output of a facility such as a power plant, a chemical plant, fuel plant, metal refinery, mine, and many others.For dispatchable power,...

 of wind-powered generators was 197 gigawatts (GW).
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Encyclopedia


Wind power is the conversion of wind energy
Wind energy
Wind energy is the kinetic energy of air in motion; see also wind power.Total wind energy flowing through an imaginary area A during the time t is:E = ½ m v2 = ½ v 2...

 into a useful form of energy, such as using wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...

s to make electricity, windmill
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...

s for mechanical power, windpump
Windpump
A windpump is a windmill used for pumping water, either as a source of fresh water from wells, or for draining low-lying areas of land. Once a common fixture on farms in semi-arid areas, windpumps are still used today where electric power is not available or too expensive.-History:Windmills were...

s for water pumping
Water pumping
The pumping of water is a basic and practical technique, far more practical than scooping it up with one's hands or lifting it in a hand-held bucket. This is true whether the water is drawn from a fresh source, moved to a needed location, purified, or used for irrigation, washing, or sewage...

 or drainage
Drainage
Drainage is the natural or artificial removal of surface and sub-surface water from an area. Many agricultural soils need drainage to improve production or to manage water supplies.-Early history:...

, or sail
Sail
A sail is any type of surface intended to move a vessel, vehicle or rotor by being placed in a wind—in essence a propulsion wing. Sails are used in sailing.-History of sails:...

s to propel ships.

The total amount of economically extractable power available from the wind is considerably more than present human power use from all sources. At the end of 2010, worldwide nameplate capacity
Nameplate capacity
Nameplate capacity, also known as the rated capacity, nominal capacity, installed capacity or maximum effect, refers to the intended technical full–load sustained output of a facility such as a power plant, a chemical plant, fuel plant, metal refinery, mine, and many others.For dispatchable power,...

 of wind-powered generators was 197 gigawatts (GW). Wind power now has the capacity to generate 430 TWh annually, which is about 2.5% of worldwide electricity usage. Over the past five years the average annual growth in new installations has been 27.6 percent. Wind power market penetration is expected to reach 3.35 percent by 2013 and 8 percent by 2018. Several countries have already achieved relatively high levels of wind power penetration, such as 21% of stationary electricity production in Denmark
Wind power in Denmark
Wind power provided 18.9% of electricity production and 24.1% of generation capacity in Denmark in 2008, Denmark was a pioneer in developing commercial wind power during the 1970s, and today almost half of the wind turbines around the world are produced by Danish manufacturers such as Vestas and...

, 18% in Portugal
Wind power in Portugal
In December 2010, there was 3,937 MW of wind power nameplate capacity installed in Portugal. The major wind turbine manufacturers in the Portuguese market are Enercon, Vestas and Gamesa...

, 16% in Spain
Wind power in Spain
Spain is the world's fourth biggest producer of wind power, after China, the United States and Germany, with an installed capacity of 19,959 megawatts at the end of 2010, a rise of 1,609 MW for the year...

, 14% in Ireland and 9% in Germany
Wind power in Germany
In 2010, the installed capacity of wind power in Germany was 27.2 GW. Wind power currently produces about seven percent of Germany’s total electrical power. More than 21,607 wind turbines are located in the German federal area and the country has plans to build more wind turbines...

 in 2010. As of 2011, 83 countries around the world are using wind power on a commercial basis.

A large wind farm
Wind farm
A wind farm is a group of wind turbines in the same location used to produce electric power. A large wind farm may consist of several hundred individual wind turbines, and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other...

 may consist of several hundred individual wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...

s which are connected to the electric power transmission
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...

 network. Offshore wind power can harness the better wind speeds that are available offshore compared to on land, so offshore wind power’s contribution in terms of electricity supplied is higher.
Small onshore wind facilities are used to provide electricity to isolated locations and utility companies increasingly buy back surplus electricity
Net metering
Net metering is an electricity policy for consumers who own renewable energy facilities or V2G electric vehicles. "Net", in this context, is used in the sense of meaning "what remains after deductions" — in this case, the deduction of any energy outflows from metered energy inflows...

 produced by small domestic wind turbines. Although a variable source of power, the intermittency of wind seldom creates problems when using wind power to supply up to 20% of total electricity demand, but as the proportion rises, increased costs, a need to use storage such as pumped-storage hydroelectricity
Pumped-storage hydroelectricity
Pumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps...

, upgrade the grid, or a lowered ability to supplant conventional production may occur. Power management techniques such as excess capacity, storage, dispatchable backing supply (usually natural gas), exporting and importing power to neighboring areas or reducing demand when wind production is low, can mitigate these problems.

Wind power, as an alternative to fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...

s, is plentiful, renewable
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

, widely distributed, clean, produces no greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...

 emissions during operation, and uses little land. In operation, the overall cost per unit of energy produced is similar to the cost for new coal and natural gas installations. The construction of wind farms is not universally welcomed,
but any effects on the environment from wind power are generally much less problematic than those of any other power source.

History




Humans have been using wind power for at least 5,500 years to propel sailboat
Sailboat
A sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in the size are not strictly defined and what constitutes a sailing ship, sailboat, or a...

s and sailing ship
Sailing ship
The term sailing ship is now used to refer to any large wind-powered vessel. In technical terms, a ship was a sailing vessel with a specific rig of at least three masts, square rigged on all of them, making the sailing adjective redundant. In popular usage "ship" became associated with all large...

s. Windmill
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...

s have been used for irrigation pumping and for milling grain since the 7th century AD in what is now Afghanistan
Afghanistan
Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...

, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 and Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...

.

In the US, the development of the "water-pumping windmill" was the major factor in allowing the farming and ranching of vast areas otherwise devoid of readily accessible water. Windpumps contributed to the expansion of rail transport systems throughout the world, by pumping water from water wells for the steam locomotive
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

s. The multi-bladed wind turbine atop a lattice tower made of wood or steel was, for many years, a fixture of the landscape throughout rural America. When fitted with generators and battery banks, small wind machines provided electricity to isolated farms.

In July 1887, a Scottish academic, Professor James Blyth
James Blyth (engineer)
Professor James Blyth MA, LLD, FRSE , was a Scottish electrical engineer and academic at Anderson's College, now the University of Strathclyde, in Glasgow...

, undertook wind power experiments that culminated in a UK patent in 1891. In the US, Charles F. Brush
Charles F. Brush
Charles Francis Brush was a U.S. inventor, entrepreneur and philanthropist.-Biography:Born in Euclid Township, Ohio, Brush was raised on a farm about 10 miles from downtown Cleveland...

 produced electricity using a wind powered machine, starting in the winter of 1887-1888, which powered his home and laboratory until about 1900. In the 1890s, the Danish scientist and inventor Poul la Cour
Poul la Cour
Poul la Cour was a Danish scientist, inventor and educationalist. Today la Cour is especially recognized for his early work on wind power, both experimental work on aerodynamics and practical implementation of wind power plants. He worked most of his life at Askov Folk High School where he...

 constructed wind turbines to generate electricity, which was then used to produce hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

. These were the first of what was to become the modern form of wind turbine.

Small wind turbines for lighting of isolated rural buildings were widespread in the first part of the 20th century. Larger units intended for connection to a distribution network were tried at several locations
including Balaklava
Balaklava
Balaklava is a former city on the Crimean peninsula and part of the city of Sevastopol which carries a special administrative status in Ukraine. It was a city in its own right until 1957 when it was formally incorporated into the municipal borders of Sevastopol by the Soviet government...

 USSR in 1931
and in a 1.25 megawatt (MW) experimental unit in Vermont
Smith-Putnam wind turbine
In 1941 the Smith-Putnam wind turbine, the world's first megawatt-size wind turbine, was connected to the local electrical distribution system on Grandpa's Knob in Castleton, Vermont, USA. It was designed by Palmer Cosslett Putnam and manufactured by the S. Morgan Smith Company...

 in 1941.

In the 1970s, U.S. industries teamed with NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 in a research program which created the NASA wind turbines
NASA wind turbines
Starting in 1975, NASA developed technologies and was the technical manager for the United States Department of Energy and the United States Department of Interior on a program to develop utility-scale wind turbines for the production of electric power, in response to the increase in oil prices.A...

, developing and testing many of the features of modern utility-scale turbines.

The modern wind power industry
Wind power industry
The wind power industry is involved with the design, manufacture, construction, and maintenance of wind turbines. The modern wind power industry began in 1979 with the serial production of wind turbines by Danish manufacturers...

 began in 1979 with the serial production of wind turbines by Danish manufacturers Kuriant, Vestas
Vestas
Vestas Wind Systems A/S is a Danish manufacturer, seller, installer, and servicer of wind turbines. It is the largest in the world, but due to very rapid growth of its competitors, its market share decreased from 28% in 2007 to 12.5% in 2009...

, Nordtank
NEG Micon
NEG Micon is a former Danish wind turbine manufacturer. It was formed in 1997 as a result of a merger between Nordtank Energy Group and Micon....

, and Bonus
Siemens
Siemens may refer toSiemens, a German family name carried by generations of telecommunications industrialists, including:* Werner von Siemens , inventor, founder of Siemens AG...

.
These early turbines were small by today's standards, with capacities of 20–30 kW each. Since then, they have increased greatly in size, with the Enercon E-126 capable of delivering up to 7 MW, while wind turbine production has expanded to many countries.

Today, wind generated energy is the fastest growing source of renewable energy . Wind power is expected to grow worldwide in the twenty-first century.

Wind energy



The Earth is unevenly heated by the sun, such that the poles receive less energy from the sun than the equator; along with this, dry land heats up (and cools down) more quickly than the seas do. The differential heating drives a global atmospheric convection system reaching from the Earth's surface to the stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...

 which acts as a virtual ceiling. Most of the energy stored in these wind movements can be found at high altitudes where continuous wind speeds of over 160 km/h (99.4 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat throughout the Earth's surface and the atmosphere.

The total amount of economically extractable power available from the wind is considerably more than present human power use from all sources. The most comprehensive study as of 2005 found the potential of wind power on land and near-shore to be 72 TW, equivalent to 54,000 MToE (million tons of oil equivalent) per year, or over five times the world's current energy use in all forms. The potential takes into account only locations with
mean annual wind speeds ≥ 6.9 m/s at 80 m. The study assumes six 1.5 megawatt, 77 m diameter turbines per square kilometer on roughly 13% of the total global land area (though that land would also be available for other compatible uses such as farming). The authors acknowledge that many practical barriers would need to be overcome to reach this theoretical capacity.

Others authors disagree with the bottom-up methodology and cites problems with such methods which can be "violating the first principle of energy conservation". The principle is that the amount of energy which can be extracted from wind power can actually exceed the power currently present in the lower atmosphere using such bottom-up analyses. (i.e. There is 100 TW of total power in the lower 200m of the entire atmosphere and somes studies go well over that limit. ) Their results show 1 TWe for the limit of wind power energy, which is much lower than previous estimates.

The practical limit to exploitation of wind power will be set by economic and environmental factors, since the resource available is far larger than any practical means to develop it.

Distribution of wind speed


The strength of wind varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there. To assess the frequency of wind speeds at a particular location, a probability distribution function is often fit to the observed data. Different locations will have different wind speed distributions. The Weibull model closely mirrors the actual distribution of hourly wind speeds at many locations. The Weibull factor is often close to 2 and therefore a Rayleigh distribution can be used as a less accurate, but simpler model.

Wind farms




A wind farm is a group of wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...

s in the same location used for production of electric power. A large wind farm may consist of several hundred individual wind turbines, and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other purposes. A wind farm may also be located offshore.

Many of the largest operational onshore wind farms are located in the US. As of November 2010, the Roscoe Wind Farm
Roscoe Wind Farm
The Roscoe Wind Farm in Roscoe, Texas, owned and operated by E.ON Climate & Renewables is the world's largest capacity wind farm with 627 wind turbines and a total installed capacity of 781.5 MW, which surpasses the nearby 735.5 MW Horse Hollow Wind Energy Center.Roscoe was constructed in four phases...

 is the largest onshore wind farm in the world at 781.5 MW, followed by the Horse Hollow Wind Energy Center
Horse Hollow Wind Energy Center
Horse Hollow Wind Energy Center is a large wind farm with 735.5 megawatt capacity. It consists of 291 GE 1.5 MW wind turbines and 130 Siemens 2.3 MW wind turbines spread over nearly 47,000 acres of land in Taylor and Nolan County, Texas....

 (735.5 MW). As of November 2010, the Thanet Wind Farm in the UK is the largest offshore wind farm in the world at 300 MW, followed by Horns Rev II (209 MW) in Denmark.

There are many large wind farms under construction and these include BARD Offshore 1
BARD Offshore 1
BARD Offshore 1 is a 400 megawatt North Sea offshore wind farm that is presently under construction and is expected to be fully operational by 2012. It will be an 80-turbine wind farm, located northwest of the isle Borkum, in Germany, in water which is deep.Laying of cables to connect the...

 (400 MW), Clyde Wind Farm
Clyde Wind Farm
The Clyde Wind Farm is a 548 megawatt wind farm under construction near Abington in South Lanarkshire, Scotland. When completed, it will be Europe's largest onshore wind farm...

 (548 MW), Greater Gabbard wind farm (500 MW), Lincs Wind Farm
Lincs Wind Farm
The Lincs Wind Farm is a wind farm currently under construction off Skegness on the east coast of England. Construction of the 270 megawatt project began in 2010 using 75 3.6 MW Siemens Wind Power‎ wind turbines. The project, due to be operational in 2012, will cost £725 million ...

 (270 MW), London Array
London Array
The London Array is an offshore wind farm under construction in the outer Thames Estuary in the United Kingdom. With 1,000 megawatt capacity, it is expected to become the world's largest offshore wind farm. The site is off the North Foreland on the Kent coast in the area of Long Sand and...

 (1000 MW), Lower Snake River Wind Project
Lower Snake River Wind Project
The Lower Snake River Wind Project is under construction in Washington’s Garfield and Columbia counties. The wind farm is being developed in phases with the first phase consisting of 149 Siemens wind turbines rated at 2.3 MW each for a maximum generating capacity of 343 MW...

 (343 MW), Macarthur Wind Farm
Macarthur Wind Farm
The Macarthur Wind Farm is a wind farm under construction in Victoria, Australia, being built by a joint venture formed by AGL Energy and Meridian Energy. The project is located in Macarthur, Victoria on a 5,500 ha site and it has been permitted to generate up to 420 MW. The wind farm will...

 (420 MW), Shepherds Flat Wind Farm
Shepherds Flat Wind Farm
The Shepherds Flat Wind Farm is an 845 megawatt wind farm under construction in Oregon, United States. The project is located in Eastern Oregon in both Morrow and Gilliam counties, near Arlington. Approved in 2008 by state regulators, groundbreaking came in 2009...

 (845 MW), Sheringham Shoal
Sheringham Shoal Offshore Wind Farm
Sheringham Shoal Offshore Wind Farm is an offshore wind farm under construction in the United Kingdom by Scira, owned by Statoil and Statkraft with 50% each. Scira has leased the area from The Crown Estate for 40 years. The first turbine was connected to the grid in August 2011. The nearest turbine...

 (317 MW), and the Walney Wind Farm
Walney Wind Farm
Walney Wind Farm is an offshore wind farm currently under construction 14km west of Walney Island off the coast of Cumbria, in the Irish Sea, England. It is being developed by Walney Offshore Windfarms Limited, a partnership between Dong Energy and Scottish and Southern Energy. The farm is...

 (367 MW).

Wind power usage



Worldwide there are now many thousands of wind turbines operating, with a total nameplate capacity
Nameplate capacity
Nameplate capacity, also known as the rated capacity, nominal capacity, installed capacity or maximum effect, refers to the intended technical full–load sustained output of a facility such as a power plant, a chemical plant, fuel plant, metal refinery, mine, and many others.For dispatchable power,...

 of 194,400 MW. World wind generation capacity more than quadrupled between 2000 and 2006, doubling about every three years. The United States pioneered wind farms and led the world in installed capacity in the 1980s and into the 1990s. In 1997 German installed capacity surpassed the U.S., a position it held until passed by the U.S. in 2008. China rapidly expanded its wind installations in the late 2000s and passed the U.S. in 2010 to become the world leader.

Europe accounted for 48% of the world total in 2009. In 2010, Spain became Europe's leading producer of wind energy, achieving 42,976 GWh. However, Germany holds the first place in Europe in terms of installed capacity, with a total of 27,215 MW at December 31, 2010. Wind power accounts for approximately 21% of electricity use in Denmark
Wind power in Denmark
Wind power provided 18.9% of electricity production and 24.1% of generation capacity in Denmark in 2008, Denmark was a pioneer in developing commercial wind power during the 1970s, and today almost half of the wind turbines around the world are produced by Danish manufacturers such as Vestas and...

, 18% in Portugal
Wind power in Portugal
In December 2010, there was 3,937 MW of wind power nameplate capacity installed in Portugal. The major wind turbine manufacturers in the Portuguese market are Enercon, Vestas and Gamesa...

, 16% in Spain
Wind power in Spain
Spain is the world's fourth biggest producer of wind power, after China, the United States and Germany, with an installed capacity of 19,959 megawatts at the end of 2010, a rise of 1,609 MW for the year...

, 14% in the Republic of Ireland, and 9% in Germany
Wind power in Germany
In 2010, the installed capacity of wind power in Germany was 27.2 GW. Wind power currently produces about seven percent of Germany’s total electrical power. More than 21,607 wind turbines are located in the German federal area and the country has plans to build more wind turbines...

.
Top 10 countries by nameplate windpower capacity (2010)
Country Windpower capacity (MW)
China 44,733
United States 40,180
Germany 27,215
Spain 20,676
India 13,066
Italy 5,797
France 5,660
United Kingdom 5,204
Canada 4,008
Denmark 3,734

Top 10 EU
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

 countries by windpower electricity production (December 2010)
Country Windpower electricity production (GWh)
Spain 42,976
Germany 35,500
United Kingdom 11,440
France 9,600
Portugal 8,852
Denmark 7,808
Netherlands 3,972
Sweden 3,500
Ireland 3,473
Greece 2,200
Austria 2,100

Growth trends


]

In 2010, more than half of all new wind power was added outside of the traditional markets in Europe and North America. This was largely from new construction in China, which accounted for nearly half the new wind installations (16.5 GW).

Global Wind Energy Council (GWEC) figures show that 2007 recorded an increase of installed capacity of 20 GW, taking the total installed wind energy capacity to 94 GW, up from 74 GW in 2006. Despite constraints facing supply chains for wind turbines, the annual market for wind continued to increase at an estimated rate of 37%, following 32% growth in 2006. In terms of economic value, the wind energy sector has become one of the important players in the energy markets, with the total value of new generating equipment installed in 2007 reaching €25 billion, or US$36 billion.

Although the wind power industry
Wind power industry
The wind power industry is involved with the design, manufacture, construction, and maintenance of wind turbines. The modern wind power industry began in 1979 with the serial production of wind turbines by Danish manufacturers...

 was affected by the global financial crisis in 2009 and 2010, a BTM Consult
BTM Consult
BTM Consult is an independent consultancy company specializing in services pertaining to renewable energy commercialization. The company was founded in 1986 and named after founder Birger T. Madsen. Staff at BTM Consult have been working with wind power utilization since 1979.In March 2010, BTM...

 five year forecast up to 2013 projects substantial growth. Over the past five years the average growth in new installations has been 27.6 percent each year. In the forecast to 2013 the expected average annual growth rate is 15.7 percent. More than 200 GW of new wind power capacity could come on line before the end of 2013. Wind power market penetration is expected to reach 3.35 percent by 2013 and 8 percent by 2018.

Offshore wind power


Offshore wind power refers to the construction of wind farms in bodies of water to generate electricity from wind. Better wind speeds are available offshore compared to on land, so offshore wind power’s contribution in terms of electricity supplied is higher.

Siemens
Siemens
Siemens may refer toSiemens, a German family name carried by generations of telecommunications industrialists, including:* Werner von Siemens , inventor, founder of Siemens AG...

 and Vestas
Vestas
Vestas Wind Systems A/S is a Danish manufacturer, seller, installer, and servicer of wind turbines. It is the largest in the world, but due to very rapid growth of its competitors, its market share decreased from 28% in 2007 to 12.5% in 2009...

 are the leading turbine suppliers for offshore wind power. DONG Energy
DONG Energy
-History:The Danish state company Dansk Naturgas A/S was founded in 1972 to manage resources in the Danish sector of the North Sea. After some years, the company was renamed to Dansk Olie og Naturgas A/S . At the beginning of 2000s, DONG started to extend itself into the electricity market by...

, Vattenfall
Vattenfall
Vattenfall is a Swedish power company. The name Vattenfall is Swedish for waterfall, and is an abbreviation of its original name, Royal Waterfall Board...

 and E.ON
E.ON
E.ON AG, marketed with an interpunct as E•ON, is the holding company of the world's largest investor-owned energy service provider based in Düsseldorf, Germany. The name comes from the Greek word aeon which means eternity....

 are the leading offshore operators. As of October 2010, 3.16 GW of offshore wind power capacity was operational, mainly in Northern Europe. According to BTM Consult
BTM Consult
BTM Consult is an independent consultancy company specializing in services pertaining to renewable energy commercialization. The company was founded in 1986 and named after founder Birger T. Madsen. Staff at BTM Consult have been working with wind power utilization since 1979.In March 2010, BTM...

, more than 16 GW of additional capacity will be installed before the end of 2014 and the UK and Germany will become the two leading markets. Offshore wind power capacity is expected to reach a total of 75 GW worldwide by 2020, with significant contributions from China and the US.

Electricity generation


In a wind farm
Wind farm
A wind farm is a group of wind turbines in the same location used to produce electric power. A large wind farm may consist of several hundred individual wind turbines, and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other...

, individual turbines are interconnected with a medium voltage (often 34.5 kV), power collection system and communications network. At a substation, this medium-voltage electric current is increased in voltage with a transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

 for connection to the high voltage electric power transmission
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...

 system.

The surplus power produced by domestic microgenerators can, in some jurisdictions, be fed into the network and sold to the utility company, producing a retail credit for the microgenerators' owners to offset their energy costs.

Grid management


Induction generator
Induction generator
An induction generator or asynchronous generator is a type of AC electrical generator that uses the principles of induction motors to produce power. Induction generators operate by mechanically turning their rotor in generator mode, giving negative slip...

s, often used for wind power, require reactive power for excitation
Excitation (magnetic)
An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred...

 so substations
Electrical substation
A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions...

 used in wind-power collection systems include substantial capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

 banks for power factor correction. Different types of wind turbine generators behave differently during transmission grid disturbances, so extensive modelling
Wind energy software
Specialized wind energy software applications aid in the development and operation of wind farms.- Program management :Programs involve equipment vendors and service providers that collaborate throughout the project. Documentation, lease management, asset tracking and warranty management are some...

 of the dynamic electromechanical characteristics of a new wind farm is required by transmission system operators to ensure predictable stable behaviour during system faults (see: Low voltage ride through
Low voltage ride through
In electricity supply and generation,low voltage ride through , or fault ride through , is what an electric device, especially wind generator, may be required to be capable of when the voltage in the grid is temporarily reduced due to a fault or load change in the grid. The voltage may be reduced...

). In particular, induction generators cannot support the system voltage during faults, unlike steam or hydro turbine-driven synchronous generators. Doubly fed machines generally have more desirable properties for grid interconnection. Transmission systems operators will supply a wind farm developer with a grid code to specify the requirements for interconnection to the transmission grid. This will include power factor
Power factor
The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load over the apparent power in the circuit, and is a dimensionless number between 0 and 1 . Real power is the capacity of the circuit for performing work in a particular time...

, constancy of frequency
Utility frequency
The utility frequency, line frequency or mains frequency is the frequency at which alternating current is transmitted from a power plant to the end-user. In most parts of the world this is 50 Hz, although in the Americas it is typically 60 Hz...

 and dynamic behavior of the wind farm turbines during a system fault.

Capacity factor


Since wind speed is not constant, a wind farm's annual energy production is never as much as the sum of the generator nameplate ratings multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor
Capacity factor
The net capacity factor or load factor of a power plant is the ratio of the actual output of a power plant over a period of time and its potential output if it had operated at full nameplate capacity the entire time...

. Typical capacity factors are 20–40%, with values at the upper end of the range in particularly favourable sites. For example, a 1 MW turbine with a capacity factor of 35% will not produce 8,760 MW·h in a year (1 × 24 × 365), but only 1 × 0.35 × 24 × 365 = 3,066 MW·h, averaging to 0.35 MW. Online data is available for some locations and the capacity factor can be calculated from the yearly output.

Unlike fueled generating plants, the capacity factor is affected by several parameters, including the variability of the wind at the site, but also the generator size- having a smaller generator would be cheaper and achieve higher capacity factor, but would make less electricity (and money) in high winds. Conversely a bigger generator would cost more and generate little extra power and, depending on the type, may stall out at low wind speed. Thus an optimum capacity factor can be used, which is usually around 20-35%.

In a 2008 study released by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, the capacity factor achieved by the wind turbine fleet is shown to be increasing as the technology improves. The capacity factor achieved by new wind turbines in 2004 and 2005 reached 36%.

Penetration


Wind energy "penetration" refers to the fraction of energy produced by wind compared with the total available generation capacity. There is no generally accepted "maximum" level of wind penetration. The limit for a particular grid will depend on the existing generating plants, pricing mechanisms, capacity for storage or demand management, and other factors. An interconnected electricity grid will already include reserve generating and transmission capacity to allow for equipment failures; this reserve capacity can also serve to regulate for the varying power generation by wind plants. Studies have indicated that 20% of the total electrical energy consumption may be incorporated with minimal difficulty. These studies have been for locations with geographically dispersed wind farms, some degree of dispatchable energy, or hydropower with storage capacity, demand management, and interconnection to a large grid area export of electricity when needed. Beyond this level, there are few technical limits, but the economic implications become more significant. Electrical utilities continue to study the effects of large (20% or more) scale penetration of wind generation on system stability and economics.

At present, a few grid systems have penetration of wind energy above 5%: Denmark (values over 19%), Spain and Portugal (values over 11%), Germany and the Republic of Ireland (values over 6%).
But even with a modest level of penetration, there can be times where wind power provides a substantial percentage of the power on a grid. For example, in the morning hours of 8 November 2009, wind energy produced covered more than half the electricity demand in Spain, setting a new record.

Variability and intermittency


Electricity generated from wind power can be highly variable at several different timescales: from hour to hour, daily, and seasonally. Annual variation also exists, but is not as significant. Related to variability is the short-term (hourly or daily) predictability of wind plant output. Like other electricity sources, wind energy must be "scheduled". Wind power forecasting methods are used, but predictability of wind plant output remains low for short-term operation.

Because instantaneous electrical generation and consumption must remain in balance to maintain grid stability, this variability can present substantial challenges to incorporating large amounts of wind power into a grid system. Intermittency and the non-dispatchable nature of wind energy production can raise costs for regulation, incremental operating reserve
Operating reserve
In electricity networks, the operating reserve is the generating capacity available to the system operator within a short interval of time to meet demand in case a generator goes down or there is another disruption to the supply...

, and (at high penetration levels) could require an increase in the already existing energy demand management
Energy demand management
Energy demand management, also known as demand side management , is the modification of consumer demand for energy through various methods such as financial incentives and education...

, load shedding, or storage solutions or system interconnection with HVDC
High-voltage direct current
A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses...

 cables. At low levels of wind penetration, fluctuations in load and allowance for failure of large generating units requires reserve capacity that can also regulate for variability of wind generation. Wind power can be replaced by other power stations during low wind periods. Transmission networks must already cope with outages of generation plant and daily changes in electrical demand. Systems with large wind capacity components may need more spinning reserve (plants operating at less than full load).

Pumped-storage hydroelectricity
Pumped-storage hydroelectricity
Pumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps...

 or other forms of grid energy storage
Grid energy storage
Grid energy storage refers to the methods used to store electricity on a large scale within an electrical power grid. Electrical energy is stored during times when production exceeds consumption and the stores are used at times when consumption exceeds production...

 can store energy developed by high-wind periods and release it when needed. Stored energy increases the economic value of wind energy since it can be shifted to displace higher cost generation during peak demand periods. The potential revenue from this arbitrage
Arbitrage
In economics and finance, arbitrage is the practice of taking advantage of a price difference between two or more markets: striking a combination of matching deals that capitalize upon the imbalance, the profit being the difference between the market prices...

 can offset the cost and losses of storage; the cost of storage may add 25% to the cost of any wind energy stored, but it is not envisaged that this would apply to a large proportion of wind energy generated. For example, in the UK, the 2 GW Dinorwig pumped storage plant evens out electrical demand peaks, and allows base-load suppliers to run their plant more efficiently. Although pumped storage power systems are only about 75% efficient, and have high installation costs, their low running costs and ability to reduce the required electrical base-load can save both fuel and total electrical generation costs.

In particular geographic regions, peak wind speeds may not coincide with peak demand for electrical power. In the US states of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 and Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

, for example, hot days in summer may have low wind speed and high electrical demand due to air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

. Some utilities subsidize the purchase of geothermal heat pumps by their customers, to reduce electricity demand during the summer months by making air conditioning up to 70% more efficient; widespread adoption of this technology would better match electricity demand to wind availability in areas with hot summers and low summer winds. Another option is to interconnect widely dispersed geographic areas with an HVDC "Super grid
Super grid
A super grid is a wide area transmission network that makes it possible to trade high volumes of electricity across great distances. It is sometimes also referred to as a "mega grid".-History:...

". In the US it is estimated that to upgrade the transmission system to take in planned or potential renewables would cost at least $60 billion.

In the UK, demand for electricity is higher in winter than in summer, and so are wind speeds. Solar power
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...

 tends to be complementary to wind. On daily to weekly timescales, high pressure area
High pressure area
A high-pressure area is a region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment. Winds within high-pressure areas flow outward due to the higher density air near their center and friction with land...

s tend to bring clear skies and low surface winds, whereas low pressure area
Low pressure area
A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...

s tend to be windier and cloudier. On seasonal timescales, solar energy typically peaks in summer, whereas in many areas wind energy is lower in summer and higher in winter. Thus the intermittencies of wind and solar power tend to cancel each other somewhat. The Institute for Solar Energy Supply Technology of the University of Kassel
University of Kassel
The University of Kassel, founded in 1970, is one of the newer universities in the state of Hesse. The university is in Kassel, and as of September 2010 has about 18,113 students...

 pilot-tested a combined power plant
Virtual power plant
A virtual power plant is a cluster of distributed generation installations which are collectively run by a central control entity....

 linking solar, wind, biogas
Biogas
Biogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen. Organic waste such as dead plant and animal material, animal dung, and kitchen waste can be converted into a gaseous fuel called biogas...

 and hydrostorage
Pumped-storage hydroelectricity
Pumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps...

 to provide load-following power around the clock, entirely from renewable sources.

A report on Denmark's wind power noted that their wind power network provided less than 1% of average demand 54 days during the year 2002. Wind power advocates argue that these periods of low wind can be dealt with by simply restarting existing power stations that have been held in readiness or interlinking with HVDC. Electrical grids with slow-responding thermal power plants and without ties to networks with hydroelectric generation may have to limit the use of wind power.

Conversely, on particularly windy days, even with penetration levels of 16%, wind power generation can surpass all other electricity sources in a country. In Spain, on November 8, 2009 wind power production reached the highest percentage of electricity production till then, with wind farms covering 53% of the total demand.

Three reports on the wind variability in the UK issued in 2009, generally agree that variability of wind needs to be taken into account, but it does not make the grid unmanageable; and the additional costs, which are modest, can be quantified. A 2006 International Energy Agency
International Energy Agency
The International Energy Agency is a Paris-based autonomous intergovernmental organization established in the framework of the Organisation for Economic Co-operation and Development in 1974 in the wake of the 1973 oil crisis...

 forum presented costs for managing intermittency as a function of wind-energy's share of total capacity for several countries, as shown:

Increase in system operation costs, Euros per MW·h, for 10% and 20% wind share

10% 20%
Germany 2.5 3.2
Denmark 0.4 0.8
Finland 0.3 1.5
Norway 0.1 0.3
Sweden 0.3 0.7

Capacity credit and fuel saving


Many commentators concentrate on whether or not wind has any "capacity credit" without defining what they mean by this and its relevance. Wind does have a capacity credit, using a widely accepted and meaningful definition, equal to about 20% of its rated output (but this figure varies depending on actual circumstances). This means that reserve capacity on a system equal in MW to 20% of added wind could be retired when such wind is added without affecting system security or robustness. But the precise value is irrelevant since the main value of wind (in the UK, worth 5 times the capacity credit value) is its fuel and CO2 savings.

According to a 2007 Stanford University study published in the Journal of Applied Meteorology and Climatology, interconnecting ten or more wind farms can allow an average of 33% of the total energy produced to be used as reliable, baseload electric power, as long as minimum criteria are met for wind speed and turbine height.

Cost trends




Wind power has low ongoing costs, but a moderate capital cost. The estimated average cost
Average cost
In economics, average cost or unit cost is equal to total cost divided by the number of goods produced . It is also equal to the sum of average variable costs plus average fixed costs...

 per unit incorporates the cost of construction of the turbine and transmission facilities, borrowed funds, return to investors (including cost of risk), estimated annual production, and other components, averaged over the projected useful life of the equipment, which may be in excess of twenty years. Energy cost estimates are highly dependent on these assumptions so published cost figures can differ substantially. A 2011 report from the American Wind Energy Association stated, "Wind's costs have dropped over the past two years, in the range of 5 to 6 cents per kilowatt-hour recently.... about 2 cents cheaper than coal-fired electricity, and more projects were financed through debt arrangements than tax equity structures last year.... winning more mainstream acceptance from Wall Street's banks.... Equipment makers can also deliver products in the same year that they are ordered instead of waiting up to three years as was the case in previous cycles.... 5,600 MW of new installed capacity is under construction in the United States, more than double the number at this point in 2010. Thirty-five percent of all new power generation built in the United States since 2005 has come from wind, more than new gas and coal plants combined, as power providers are increasingly enticed to wind as a convenient hedge against unpredictable commodity price moves."

A British Wind Energy Association report gives an average generation cost of onshore wind power of around 3.2 pence (between US 5 and 6 cents) per kW·h (2005). Cost per unit of energy produced was estimated in 2006 to be comparable to the cost of new generating capacity in the US for coal and natural gas: wind cost was estimated at $55.80 per MW·h, coal at $53.10/MW·h and natural gas at $52.50. Similar comparative results with natural gas were obtained in a governmental study in the UK in 2011. Other sources in various studies have estimated wind to be more expensive than other sources. A 2009 study on wind power in Spain by Gabriel Calzada Alvarez Universidad Rey Juan Carlos concluded that each installed MW of wind power led to the loss of 4.27 jobs, by raising energy costs and driving away electricity-intensive businesses. The U.S. Department of Energy found the study to be seriously flawed, and the conclusion unsupported. The presence of wind energy, even when subsidised, can reduce costs for consumers (€5 billion/yr in Germany) by reducing the marginal price by minimising the use of expensive 'peaker plants'.

The marginal cost
Marginal cost
In economics and finance, marginal cost is the change in total cost that arises when the quantity produced changes by one unit. That is, it is the cost of producing one more unit of a good...

 of wind energy once a plant is constructed is usually less than 1 cent per kW·h. In 2004, wind energy cost a fifth of what it did in the 1980s, and some expected that downward trend to continue as larger multi-megawatt turbines
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...

 were mass-produced. However, capital costs have increased. For example, in the United States, installed cost increased in 2009 to $2,120 per kilowatt of nameplate capacity, compared with $1,950 in 2008, a 9% increase. Not as many facilities can produce large modern turbines and their towers and foundations, so constraints develop in the supply of turbines resulting in higher costs.

Incentives


Wind energy in many jurisdictions receives financial or other support to encourage its development. Wind energy benefits from subsidies
Subsidy
A subsidy is an assistance paid to a business or economic sector. Most subsidies are made by the government to producers or distributors in an industry to prevent the decline of that industry or an increase in the prices of its products or simply to encourage it to hire more labor A subsidy (also...

 in many jurisdictions, either to increase its attractiveness, or to compensate for subsidies received by other forms of production which have significant negative externalities.

In the US, wind power receives a tax credit for each kW·h produced; at 1.9 cents per kW·h in 2006, the credit has a yearly inflationary adjustment. Another tax benefit is accelerated depreciation
Accelerated depreciation
Accelerated depreciation refers to any one of several methods by which a company, for 'financial accounting' or tax purposes, depreciates a fixed asset in such a way that the amount of depreciation taken each year is higher during the earlier years of an asset’s life...

. Many American states also provide incentives, such as exemption from property tax, mandated purchases, and additional markets for "green credits". Countries such as Canada
Wind Power Production Incentive
The Wind Power Production Incentive, or WPPI, was a program of the Canadian Government that promoted the generation of electricity from wind power in Canada to reduce the amount of greenhouse gas that would otherwise enter the atmosphere from burning fossil fuels...

 and Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 also provide incentives for wind turbine construction, such as tax credits or minimum purchase prices for wind generation, with assured grid access (sometimes referred to as feed-in tariff
Feed-in Tariff
A feed-in tariff is a policy mechanism designed to accelerate investment in renewable energy technologies. It achieves this by offering long-term contracts to renewable energy producers, typically based on the cost of generation of each technology...

s). These feed-in tariffs are typically set well above average electricity prices. The Energy Improvement and Extension Act of 2008 contains extensions of credits for wind, including microturbines.

Secondary market forces also provide incentives for businesses to use wind-generated power, even if there is a premium price for the electricity. For example, socially responsible manufacturers
Corporate social responsibility
Corporate social responsibility is a form of corporate self-regulation integrated into a business model...

 pay utility companies a premium that goes to subsidize and build new wind power infrastructure. Companies use wind-generated power, and in return they can claim that they are undertaking strong "green" efforts. In the US the organization Green-e monitors business compliance with these renewable energy credits.

Full costs and lobbying


A House of Lords
House of Lords
The House of Lords is the upper house of the Parliament of the United Kingdom. Like the House of Commons, it meets in the Palace of Westminster....

 Select Committee report (2008) on renewable energy in the UK reported a "concern over the prospective role of wind generated and other intermittent sources of electricity in the UK, in the absence of a break-through in electricity storage technology or the integration of the UK grid with that of continental Europe".

Commenting on the EU's 2020 renewable energy target
Energy policy of the European Union
Although the European Union has legislated in the area of energy policy for many years, and evolved out of the European Coal and Steel Community, the concept of introducing a mandatory and comprehensive European energy policy was only approved at the meeting of the European Council on 27 October...

, Helm is critical of how the costs of wind power are cited by lobbyists. Helm also says that wind's problem of intermittent supply will probably lead to another dash-for-gas
Dash for Gas
The Dash for Gas was the significant shift by the newly privatized electric companies in the United Kingdom towards generation of electricity using natural gas during the 1990s....

 or dash-for-coal in Europe, possibly with a negative impact on energy security
Energy security
Energy security is a term for an association between national security and the availability of natural resources for energy consumption. Access to cheap energy has become essential to the functioning of modern economies. However, the uneven distribution of energy supplies among countries has led...

.

In the US, the wind power industry has recently increased its lobbying efforts considerably, spending about $5 million in 2009 after years of relative obscurity in Washington. By comparison, the US nuclear industry alone spent over $650 million on its lobbying efforts during a single ten year period ending in 2008.

Environmental effects




Compared to the environmental impact of traditional energy sources, the environmental impact of wind power is relatively minor. Wind power consumes no fuel, and emits no air pollution
Air pollution
Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....

, unlike fossil fuel power sources. The energy consumed to manufacture and transport the materials used to build a wind power plant is equal to the new energy produced by the plant within a few months. While a wind farm may cover a large area of land, many land uses such as agriculture are compatible, with only small areas of turbine foundations and infrastructure made unavailable for use.

There are reports of bird and bat mortality at wind turbines as there are around other artificial structures. The scale of the ecological impact may or may not be significant, depending on specific circumstances. Prevention and mitigation of wildlife fatalities, and protection of peat bogs, affect the siting and operation of wind turbines.

A study on wind farm noise reported that people are annoyed by sound from wind turbines at far less sound levels than they are by noises from railroads, aircraft, or road traffic. The study found the percentage of respondents who found noise levels highly annoying rose quickly as sound levels increased above about 37dbA
Sound pressure
Sound pressure or acoustic pressure is the local pressure deviation from the ambient atmospheric pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water...

 (about the level of a conversation).

Small-scale wind power




Small-scale wind power is the name given to wind generation systems with the capacity to produce up to 50 kW of electrical power. Isolated communities, that may otherwise rely on diesel
Diesel generator
A diesel generator is the combination of a diesel engine with an electrical generator to generate electrical energy....

 generators may use wind turbines to displace diesel fuel consumption. Individuals may purchase these systems to reduce or eliminate their dependence on grid electricity for economic or other reasons, or to reduce their carbon footprint
Carbon footprint
A carbon footprint has historically been defined as "the total set of greenhouse gas emissions caused by an organization, event, product or person.". However, calculating a carbon footprint which conforms to this definition is often impracticable due to the large amount of data required, which is...

. Wind turbines have been used for household electricity generation in conjunction with battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

 storage over many decades in remote areas.

Grid-connected wind turbines may use grid energy storage
Grid energy storage
Grid energy storage refers to the methods used to store electricity on a large scale within an electrical power grid. Electrical energy is stored during times when production exceeds consumption and the stores are used at times when consumption exceeds production...

, displacing purchased energy with local production when available. Off-grid system users can either adapt to intermittent power or use batteries, photovoltaic or diesel systems to supplement the wind turbine. Equipment such as parking meters or wireless Internet gateways may be powered by a wind turbine that charges a small battery, replacing the need for a connection to the power grid.

In locations near or around a group of high-rise buildings, wind shear generates areas of intense turbulence, especially at street-level. The risks associated with mechanical or catastrophic failure have thus plagued urban wind development in densely populated areas, rendering the costs of insuring urban wind systems prohibitive.
Moreover, quantifying the amount of wind in urban areas has been difficult, as little is known about the actual wind resources of towns and cities.

A new Carbon Trust study into the potential of small-scale wind energy has found that small wind turbines could provide up to 1.5 terawatt hours (TW·h) per year of electricity (0.4% of total UK electricity consumption), saving 0.6 million tonnes of carbon dioxide (Mt CO2) emission savings. This is based on the assumption that 10% of households would install turbines at costs competitive with grid electricity, around 12 pence (US 19 cents) a kW·h.

Distributed generation
Distributed generation
Distributed generation, also called on-site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity from many small energy sources....

 from renewable resource
Renewable resource
A renewable resource is a natural resource with the ability of being replaced through biological or other natural processes and replenished with the passage of time...

s is increasing as a consequence of the increased awareness of climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

. The electronic interfaces required to connect renewable generation units with the utility
Utility
In economics, utility is a measure of customer satisfaction, referring to the total satisfaction received by a consumer from consuming a good or service....

 system can include additional functions, such as the active filtering to enhance the power quality.

Research and development


Despite growing worldwide demand for wind energy, present wind technology is not optimized and there are still significant challenges. Most of the research has occurred in industry, and is not always easily shared. According to a research agenda from from a coalition of researchers from universities, industry, and government, supported by the Atkinson Center for a Sustainable Future
Atkinson Center for a Sustainable Future
The David R. Atkinson Center for a Sustainable Future is a research organization created in Fall 2007 at Cornell University. ACSF advances multidisciplinary research in Energy, the Environment and Economic Development, and cultivates collaborations within and beyond Cornell.- History :ACSF,...

, wind energy research requires a drastic transformation. According to the report:
The gains that we are seeking require new innovations in fluid dynamics, control, materials, manufacturing, structures, and electric power distribution, as well of new ways of engaging the public in appreciating and accepting this technology, the associated transmission infrastructure and its effects on reducing climate change. Design and analysis tools need to be developed. Common computer codes need to be shared and refined in an open collegial way that cannot occur in industry. Researchers need to disseminate, debate, and share results openly, accelerating innovation in the subject.

See also

  • Airborne wind turbine
    Airborne wind turbine
    An airborne wind turbine is a design concept for a wind turbine that is supported in the air without a tower. Airborne wind turbines may operate in low or high altitudes; they are part of a wider class of airborne wind energy systems addressed by high-altitude wind power...

  • Controlled aerodynamic instability phenomena
    Controlled Aerodynamic Instability Phenomena
    The term controlled aerodynamic instability phenomena was first used by Cristiano Augusto Trein in the Nineteenth KKCNN Symposium on Civil Engineering held in Kyoto – Japan in 2006...

  • Floating wind turbine
    Floating wind turbine
    A floating wind turbine is an offshore wind turbine mounted on a floating structure that allows the turbine to generate electricity in water depths where bottom-mounted towers are not feasible...

  • High altitude wind power
    High altitude wind power
    High-altitude wind power has been imagined as a source of useful energy since 1833 with John Etzler's vision of capturing the power of winds high in the sky by use of tether and cable technology...

  • List of countries by electricity production from renewable sources
  • Lists of offshore wind farms by country
  • Lists of wind farms by country
  • List of wind turbine manufacturers
  • Sustainable energy
    Sustainable energy
    Sustainable energy is the provision of energy that meets the needs of the present without compromising the ability of future generations to meet their needs. Sustainable energy sources include all renewable energy sources, such as hydroelectricity, solar energy, wind energy, wave power, geothermal...

  • Vertical axis wind turbine
    Vertical axis wind turbine
    Vertical-axis wind turbines are a type of wind turbine where the main rotor shaft is set vertically and the main components are located at the base of the turbine...

  • Wind profiler
    Wind profiler
    A wind profiler is a type of weather observing equipment that uses radar or sound waves to detect the wind speed and direction at various elevations above the ground. Readings are made at each kilometer above sea level, up to the extent of the troposphere...

  • Wind rights
    Wind rights
    Wind rights are rights relating to windmills, wind turbines and wind power. Historically in the Low Countries wind rights were manorial rights and obligations relating to the operation and profitability of windmills...

  • Wind-diesel hybrid power system
  • Wind power in the United States
    Wind power in the United States
    As of the third quarter of 2011, the cumulative installed capacity of wind power in the United States was 43,461 megawatts , making it second in the world, behind China. In 2010 wind power accounted for 2.3% of the electricity generated in the United States...


External links