A wind turbine is a rotating machine that converts the kinetic energy in wind into mechanical energy. The kinetic energy of an object is the extra Energy which it possesses due to its motion Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) In Physics, mechanical energy describes the Potential energy and Kinetic energy present in the components of a mechanical system. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill. A windmill is a machine that is powered by the energy of the wind If the mechanical energy is then converted to electricity, the machine is called a wind generator, wind turbine, wind power unit (WPU) or wind energy converter (WEC). Electric power is defined as the rate at which Electrical energy is transferred by an Electric circuit.
This article discusses electric power generation machinery. Windmill discusses machines used for grain-grinding, water pumping, etc. A windmill is a machine that is powered by the energy of the wind The article on wind power describes turbine placement, economics, public concerns, and controversy. Wind Power is the conversion of wind energy into a useful form such as electricity using Wind turbines At the end of 2007 worldwide capacity of wind-powered generators was The wind energy section of that article describes the distribution of wind energy over time, and how that affects wind-turbine design. Wind Power is the conversion of wind energy into a useful form such as electricity using Wind turbines At the end of 2007 worldwide capacity of wind-powered generators was See environmental concerns with electricity generation for discussion of environmental problems with wind-energy production. Modern technology uses large amounts of electrical power This is normally generated at Power plants which convert some other kind of energy into electrical power
Wind machines were used for grinding grain in Persia as early as 200 B. This article is about the history of Wind power. Early history Sailboats and Sailing ships have been using wind power for at least The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. Castleton is a New England town located in Rutland County, Vermont, United States. C. . This type of machine was introduced into the Roman Empire by 250 A. The Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial D. By the 14th century Dutch windmills were in use to drain areas of the Rhine River delta. A windmill is a machine that is powered by the energy of the wind The Rhine (Rhein Rijn Rhin Reno Rain Rhenus is one of the longest and most important Rivers in Europe at 1320 kilometres (820 mi with an average discharge In Denmark by 1900 there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW. The Kingdom of Denmark ( ˈd̥ænmɑɡ̊ (archaic ˈd̥anmɑːɡ̊ commonly known as Denmark, is a country in the Scandinavian region of northern Europe The first windmill for electricity production was built in Cleveland, Ohio by Charles F Brush in 1888, and in 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. Cleveland is a City in the US state of Ohio and the County seat of Cuyahoga County, the most populous county in the state The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, most for water-pumping.  By the 1930s windmills for electricity were common on farms, mostly in the United States where distribution systems had not yet been installed. In this period, high-tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers.
A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. Yalta (Ялта Yalta is a city in Crimea, southern Ukraine, on the north coast of the Black Sea. The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991 This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6. 3 kV distribution system. It was reported to have an annual capacity factor of 32 per cent, not much different from current wind machines. The net capacity factor of a Power plant is the ratio of the actual output of a power plant over a period of time and its output if it had operated at full nameplate capacity
The very first electricity generating windmill operated in the UK was a battery charging machine installed in 1887 by James Blyth in Scotland. The first utility grid-connected wind turbine operated in the UK was built by the John Brown Company in 1954 in the Orkney Islands. It had an 18 metre diameter, three-bladed rotor and a rated output of 100 kW.
The amount of power transferred to a wind turbine is directly proportional to the density of the air, the area swept out by the rotor, and the cube of the wind speed. Wind turbines are designed to exploit the wind energy that exists at a location In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for
The usable power P available in the wind is given by:
where P = power in watts, α = an efficiency factor determined by the design of the turbine, ρ = mass density of air in kilograms per cubic meter, r = radius of the wind turbine in meters, and v = velocity of the air in meters per second. 
As the wind turbine extracts energy from the air flow, the air is slowed down, which causes it to spread out. Albert Betz, a German physicist, determined in 1919 (see Betz' law) that a wind turbine can extract at most 59% of the energy that would otherwise flow through the turbine's cross section, that is α can never be higher than 0. Albert Betz ( 25 December 1885 - 16 April 1968) was a German Physicist and a pioneer of Wind turbine technology Please see discussion accessed from the above tab for issues related to proof 59 in the above equation. The Betz limit applies regardless of the design of the turbine.
This equation shows the effects of the mass rate of flow of air traveling through the turbine, and the energy of each unit mass of air flow due to its velocity. As an example, on a cool 15 °C (59 °F) day at sea level, air density is 1. 225 kilograms per cubic metre. An 8 m/s (28. 8 km/h or 18 mi/h) breeze blowing through a 100 meter diameter rotor would move almost 77,000 kilograms of air per second through the swept area. The total power of the example breeze through a 100 meter diameter rotor would be about 2. 5 megawatts. Betz' law states that no more than 1. 5 megawatts could be extracted.
Wind turbines can be separated into two types based by the axis in which the turbine rotates. Turbines that rotate around a horizontal axis are more common. Vertical-axis turbines are less frequently used.
Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. ROTOR was a huge and elaborate air defence Radar system built by the British Government in the early 1950s to counter possible attack by Soviet Bombers In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. A weather vane, also called a wind vane, is a movable device attached to an elevated object such as a roof for showing the direction of the wind A servomechanism, or servo is an automatic device which uses error-sensing Feedback to correct the performance of a mechanism Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive a generator.
Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. In Fluid dynamics, turbulence or turbulent flow is a fluid regime characterized by chaotic Stochastic property changes Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted up a small amount.
Downwind machines have been built, despite the problem of turbulence, because they don't need an additional mechanism for keeping them in line with the wind, and because in high winds, the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Since turbulence leads to fatigue failures, and reliability is so important, most HAWTs are upwind machines.
There are several types of HAWT:
The Eclipse windmill factory was set up around 1866 in Beloit. Wisconsin and soon became a huge success building mills for farm water pumping and railroad tank filling. Other firms like Star, Dempster, and Aeromotor also entered the market. Hundreds of thousands of these mills were produced before rural electrification and small numbers continue to be made.  They typically had many blades, operated at tip speed ratios (defined below) not better than one, and had good starting torque. Some had small direct-current generators used to charge storage batteries, to provide a few lights, or to operate a radio receiver. The American rural electrification connected many farms to centrally-generated power and replaced individual windmills as a primary source of farm power by the 1950s. The Rural Electrification Administration ( REA) was an agency of the United States federal government created on May 11, 1935 through They were also produced in other countries like South Africa and Australia (where an American design was copied in 1876). Such devices are still used in locations where it is too costly to bring in commercial power.
In Schiedam, the Netherlands, a traditional style windmill (the Noletmolen) was built in 2005 to generate electricity. Schiedam is a city and municipality in the province of South Holland in the Netherlands and is part of the Rotterdam The Netherlands ( Dutch:, ˈnedərlɑnt is the European part of the Kingdom of the Netherlands, which consists of the Netherlands the Netherlands  The mill is one of the tallest Tower mills in the world, being some 42. Heckington Windmill 01JPG|thumb|right|180px| Heckington Windmill ]]Schiedam molen De Noord 5 metres (139 ft) tall.
Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. This type is produced by Danish and other manufacturers. These have high tip speeds of up to six times the wind speed, high efficiency, and low torque ripple which contributes to good reliability. The blades are usually colored light gray to blend in with the clouds and range in length from 20 to 40 metres (65 to 130 ft) or more. The tubular steel towers range from about 200 to 300 feet (60 to 90 metres) high. The blades rotate at 10-22 revolutions per minute.  A gear box is commonly used to step up the speed of the generator, though there are also designs that use direct drive of an annular generator. Some models operate at constant speed, but more energy can be collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system. All turbines are equipped with high wind shut down features to avoid over speed damage.
Cyclic stresses fatigue the blade, axle and bearing material failures were a major cause of turbine failure for many years. Cyclic stress in engineering refers is an internal distribution of forces (a stress that changes over time in a repetitive fashion An axle is a central shaft for a rotating Wheel or Gear. In some cases the axle may be fixed in position with a bearing or Bushing A bearing is a device to permit constrained relative motion between two parts typically rotation or linear movement Because wind velocity often increases at higher altitudes, the backward force and torque on a horizontal-axis wind turbine (HAWT) blade peaks as it turns through the highest point in its circle. The tower hinders the airflow at the lowest point in the circle, which produces a local dip in force and torque. These effects produce a cyclic twist on the main bearings of a HAWT. The combined twist is worst in machines with an even number of blades, where one is straight up when another is straight down. To improve reliability, teetering hubs have been used which allow the main shaft to rock through a few degrees, so that the main bearings do not have to resist the torque peaks.
When the turbine turns to face the wind, the rotating blades act like a gyroscope. A gyroscope is a device for measuring or maintaining orientation, based on the principles of Angular momentum. As it pivots, gyroscopic precession tries to twist the turbine into a forward or backward somersault. Precession refers to a change in the direction of the axis of a rotating object For each blade on a wind generator's turbine, precessive force is at a minimum when the blade is horizontal and at a maximum when the blade is vertical. This cyclic twisting can quickly fatigue and crack the blade roots, hub and axle of the turbines.
Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically. Vertical-axis wind turbines (VAWT are a type of Wind turbine where the main rotor shaft runs vertically Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable. VAWTs can utilize winds from varying directions.
With a vertical axis, the generator and gearbox can be placed near the ground, so the tower doesn't need to support it, and it is more accessible for maintenance. Drawbacks are that some designs produce pulsating torque. Drag may be created when the blade rotates into the wind.
It is difficult to mount vertical-axis turbines on towers, meaning they are often installed nearer to the base on which they rest, such as the ground or a building rooftop. The wind speed is generally slower at a lower altitude, so less wind energy is available for a given size turbine. Air flow near the ground and other objects can create turbulent flow, which can introduce issues of vibration, including noise and bearing wear which may increase the maintenance or shorten the service life. However, when a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this often doubles the wind speed at the turbine. If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence.
Wind turbines can also be classified by the location in which they are to be used. Lake Erie (ˈɪəriː is the fourth largest Lake (by surface area of the five Great Lakes, and the tenth largest globally Lackawanna is a City in Erie County, New York, US, located just south of the city of Buffalo in the western part of New York Wind Power is the conversion of wind energy into a useful form such as electricity using Wind turbines At the end of 2007 worldwide capacity of wind-powered generators was Onshore, offshore, or even aerial wind turbines have unique design characteristics, which are explained in more detail in the section on turbine design and construction.
Wind turbines are designed to exploit the wind energy that exists at a location. Wind turbines are designed to exploit the wind energy that exists at a location Aerodynamic modeling is used to determine the optimum tower height, control systems, number of blades, and blade shape.
Virtually all modern wind turbines convert wind energy to electricity for energy distribution. The turbine can be divided into three components. The rotor component, which is approximately 20% of the wind turbine cost, includes the blades for converting wind energy to low speed rotational energy. The generator component, which is approximately 34% of the wind turbine cost, includes the electrical generator, the control electronics, and most likely a gearbox component for converting the low speed incoming rotation to high speed rotation suitable for generating electricity. In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic The structural support component, which is approximately 15% of the wind turbine cost, includes the tower and rotor pointing mechanism. 
Utility-scale wind turbine generators have minimum temperature operating limits which apply in areas that experience temperatures less than –20 °C. Wind turbines must be protected from ice accumulation, which can make anemometer readings inaccurate and which can cause high structure loads and damage. An anemometer is a device for measuring wind speed and is one instrument used in a Weather station. Some turbine manufacturers offer low-temperature packages at a few percent extra cost, which include internal heaters, different lubricants, and different alloys for structural elements. If the low-temperature interval is combined with a low-wind condition, the wind turbine will require an external supply of power, equivalent to a few percent of its rated power, for internal heating. For example, the St. Leon, Manitoba project has a total rating of 99 MW and is estimated to need up to 3 MW (around 3% of capacity) of station service power a few days a year for temperatures down to –30 °C. St Leon is a community in Manitoba, Canada. It is located to the southwest of Winnipeg, near the American border Manitoba (English ˌmænɨˈtoʊbə French /manitoba/ is a province of Canada, spanning 647797 square kilometres (250116  sq mi of North America This factor affects the economics of wind turbine operation in cold climates.
One E-66 wind turbine at Windpark Holtriem, Germany carries an observation deck, open for visitors to see. Constructed in 1998 Windpark Holtriem is one of the largest European Windfarms comprising thirty-three Enercon E-66 Wind turbines Holtriem is a low lying Another turbine of the same type, with an observation deck, is located in Swaffham, England. Swaffham is a Market town and Civil parish in the English County of Norfolk. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland
A series of lighter-than-air wind turbines are in development in Canada by Magenn Power. They deliver power to the ground by a tether system. 
Wind turbines may also be used in conjunction with a large vertical solar updraft tower to extract the energy due to air heated by the Sun. The solar updraft tower is a proposed type of renewable-energy Power plant.
Small wind turbines may be as small as a fifty watt generator for boat or caravan use. Small units often have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind. Direct current ( DC) is the unidirectional flow of Electric charge. Larger, more costly turbines generally have geared power trains, alternating current output, flaps and are actively pointed into the wind. Direct drive generators and aeroelastic blades for large wind turbines are being researched.
A small wind turbine can be installed on a roof. Installation issues then include the strength of the roof, vibration, and the turbulence caused by the roof ledge. A small-scale, rooftop wind turbine is said to be able to generate power from 10% to up to 25% of the electricity requirements of a regular house. 
Small scale turbines for residential-scale use are available that are approximately 7 feet (2 m) to 25 feet (8 m) in diameter and produce electricity at a rate of 900 watts to 10,000 watts at their tested wind speed. Some units are designed to be very lightweight, e. g. 16 kilograms (35 lb), allowing rapid response to wind gusts typical of urban settings and easy mounting much like a television antenna. It is claimed that they are inaudible even a few feet under the turbine.  Dynamic braking regulates the speed by dumping excess energy, so that the turbine continues to produce electricity even in high winds. Dynamic braking is the use of the electric Traction motors of a Railroad vehicle as generators when slowing the vehicle The dynamic braking resistor may be installed inside the building to provide heat (during high winds when more heat is lost by the building, while more heat is also produced by the braking resistor). The location makes low voltage (around 12 volt) distribution practical.
In the United States, residential wind turbines with outputs of 2-10 kW, typically cost between $12,000 and $55,000 installed ($6 per watt), although there are incentives and rebates available in 19 states that can reduce the purchase price for homeowners by up to 50 percent, to ($3 per watt). The United States of America —commonly referred to as the  The US manufacturer "Southwest Windpower," estimates a turbine to pay for itself in energy savings in 5 to 10 years. 
The American Wind Energy Association has released several studies on the small wind turbine market in the U. The American Wind Energy Association (AWEA which formed in 1974 is the national trade association of the U S. and abroad, showing that the U. S. continues to dominate the Small Wind industry.  According to another organization, the World Wind Energy Association, it is difficult to assess the total number or capacity of small-scaled wind turbines, but in China alone, there are roughly 300,000 small-scale wind turbines generating electricity. 
The dominant models on the market, especially in the United States, are horizontal-axis wind turbines (HAWT). A wind turbine is a rotating machine which converts the Kinetic energy in Wind into Mechanical energy.
There have been a number of recent developments of mini-turbines which could be adapted to home use, including:
Some hobbyists have built wind turbines from kits, sourced components, or from scratch. A hobby is a spare-time Recreational pursuit Etymology A Hobby horse is a wooden or Wickerwork toy made to be Do it yourself or DIY-wind turbine construction has been made popular by magazines such as OtherPower and Home Power, websites as Instructables, and by TV-series as Jericho and The Time Machine. Instructables is a website specializing in user-created and uploaded Do-it-yourself projects which other users can comment on and rate for quality Jericho is an American Serial drama The Time Machine is a 2002 Science fiction film adapted from the 1895 novel of the same name by H DIY-made wind turbines are usually smaller (rooftop) turbines of ~ 1kW or less.  These small wind turbines are usually tilt-up or fixed/guyed towers. Tilt up or tilt-slab is a type of Building, and a Construction technique using Concrete.  However, larger (freestanding) and more powerful windtubines are sometimes built as well. The latter can generate power of up to 10 kW.  In addition, people are also showing interest in DIY-construction of wind turbines with special designs as the Savonius, Panemone, wind turbine to boost power generation. Savonius wind turbines are a type of vertical-axis Wind turbine ( VAWT) used for converting the power of the Wind into Torque on a rotating  When compared to similar sized commercial wind turbines, these DIY turbines tend to be cheaper.  Through the internet, the community is now able to obtain plans to construct DIY-wind turbines.  and there is a growing trend toward building them for domestic requirements. The DIY-wind turbines are now being used both in developed countries and in developing countries, to help power residences and small businesses. Developing countries are countries that haven't reached Western-style standards of democratic government free market economy industrialization social programs and human rights guaranties At present, organizations as Practical Action have designed DIY wind turbines that can be easily built by communities in developing nations and are supplying concrete documents on how to do so. Practical Action is a development charity registered in the United Kingdom which works directly in four regions of the developing world – Latin America  To assist people in the developing countries, and hobbyists alike, several projects have been open-sourced (e. Open design is the application of Open source methods to the creation of physical products machines and systems g. the Jua Kali wind turbine, Hugh Piggot's wind turbine, ForceField Wind Turbine, etc. ). 
The world's largest turbines are manufactured by the Northern German companies Enercon and REpower. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Enercon GmbH, based in Aurich, Northern Germany, is the third-largest Wind turbine manufacturer in the world and the Market leader REpower is a German Wind turbine company founded in 2001 Its product range comprises several types of turbines with rated outputs of between 1 The Enercon E-126 delivers up to 6 MW, has an overall height of 198 m (650 ft) and a diameter of 126 meters (413 ft). The Repower 5M delivers up to 5 MW, has an overall height of 183 m (600 ft) and has a diameter of 126 m (413 ft).
The turbine closest to the North Pole is a Nordex N-80 in Havoygelvan near Hammerfest, Norway. The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is subject to the caveats explained below defined as the point in the northern is a city and municipality in the county of Finnmark, Norway. Norway ( Norwegian: Norge ( Bokmål) or Noreg ( Nynorsk) officially the Kingdom of Norway, is a Constitutional The ones closest to the South Pole are two Enarcan E-30 in Antarctica, used to power the Australian Research Division's Mawson Station. The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the southernmost point on the surface of the Earth. Mawson Station is a permanent base in Antarctica managed by the Australian Antarctic Division (AAD 
Matilda, was a wind turbine located on Gotland, Sweden. is a county, province and municipality of Sweden and the largest Island in the Baltic Sea. "Sverige" redirects here For other uses see Sweden (disambiguation and Sverige (disambiguation. It produced a total of 61,4 GWh in the 15 years it was active. That is more renewable energy than any other single power plant has ever produced. It was demolished on June 6th, 2008.
Researcher and pediatrician Nina Pierpont has allegedly discovered an illness she calls 'wind turbine syndrome,' which may be affecting those living near wind turbines. These residents report symptoms such as: sleep problems, headaches, exhaustion, irritability, and dizziness, possibly due to the constant sound. Several researchers suggest that any loud wind turbines be installed a mile or more away from residential areas. Audiologist Kenneth Smith, a fellow with the American Academy of Audiology, says low-frequency sounds can cause health disorders, but he cautions that much more study needs to be done on wind turbines before drawing conclusions. "The wind industry says the evidence so far is only anecdotal. "
It seems possible that such symptoms may be the result merely of noise levels that are too high rather than anything specifically related to wind turbines. There are other allegations about illness caused by infrasound from wind turbines but this does not appear to have any scientific basis and again seems more likely to be related to the noise level. However, wind turbines do have an incessant and continuous modulation of sound (often called "swish") which may make the sound more unacceptable than other sounds.
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