wind turbine: Definition from Answers.com

Background

A wind turbine is a machine that converts the wind's kinetic energy into rotary mechanical energy, which is then used to do work. In more advanced models, the rotational energy is converted into electricity, the most versatile form of energy, by using a generator.

For thousands of years people have used windmills to pump water or grind grain. Even into the twentieth century tall, slender, multi-vaned wind turbines made entirely of metal were used in American homes and ranches to pump water into the house's plumbing system or into the cattle's watering trough. After World War I, work was begun to develop wind turbines that could produce electricity. Marcellus Jacobs invented a prototype in 1927 that could provide power for a radio and a few lamps but little else. When demand for electricity increased later, Jacobs's small, inadequate wind turbines fell out of use.

The first large-scale wind turbine built in the United States was conceived by Palmer Cosslett Putnam in 1934; he completed it in 1941. The machine was huge. The tower was 36.6 yards (33.5 meters) high, and its two stainless steel blades had diameters of 58 yards (53 meters). Putnam's wind turbine could produce 1,250 kilowatts of electricity, or enough to meet the needs of a small town. It was, however, abandoned in 1945 because of mechanical failure.

With the 1970s oil embargo, the United States began once more to consider the feasibility of producing cheap electricity from wind turbines. In 1975 the prototype Mod-O was in operation. This was a 100 kilowatt turbine with two 21-yard (19-meter) blades. More prototypes followed (Mod-OA, Mod-1, Mod-2, etc.), each larger and more powerful than the one before. Currently, the United States Department of Energy is aiming to go beyond 3,200 kilowatts per machine.

Many different models of wind turbines exist, the most striking being the vertical-axis Darrieus, which is shaped like an egg beater. The model most supported by commercial manufacturers, however, is a horizontal-axis turbine, with a capacity of around 100 kilowatts and three blades not more than 33 yards (30 meters) in length. Wind turbines with three blades spin more smoothly and are easier to balance than those with two blades. Also, while larger wind turbines produce more energy, the smaller models are less likely to undergo major mechanical failure, and thus are more economical to maintain.

Wind farms have sprung up all over the United States, most notably in California. Wind farms are huge arrays of wind turbines set in areas of favorable wind production. The great number of interconnected wind turbines is necessary in order to produce enough electricity to meet the needs of a sizable population. Currently, 17,000 wind turbines on wind farms owned by several wind energy companies produce 3.7 billion kilowatt-hours of electricity annually, enough to meet the energy needs of 500,000 homes.

Raw Materials

A wind turbine consists of three basic parts: the tower, the nacelle, and the rotor blades. The tower is either a steel lattice tower similar to electrical towers or a steel tubular tower with an inside ladder to the nacelle. Most towers do not have guys, which are cables used for support, and most are made of steel that has been coated with a zinc alloy for protection, though some are painted instead. The tower of a typical American-made turbine is approximately 80 feet tall and weighs about 19,000 pounds.

The nacelle is a strong, hollow shell that contains the inner workings of the wind turbine. Usually made of fiberglass, the nacelle contains the main drive shaft and the gearbox. It also contains the blade pitch control, a hydraulic system that controls the angle of the blades, and the yaw drive, which controls the position of the turbine relative to the wind. The generator and electronic controls are standard equipment whose main components are steel and copper. A typical nacelle for a current turbine weighs approximately 22,000 pounds.

The most diverse use of materials and the most experimentation with new materials occur with the blades. Although the most dominant material used for the blades in commercial wind turbines is fiberglass with a hollow core, other materials in use include lightweight woods and aluminum. Wooden blades are solid, but most blades consist of a skin surrounding a core that is either hollow or filled with a lightweight substance such as plastic foam or honeycomb, or balsa wood. A typical fiberglass blade is about 15 meters in length and weighs approximately 2,500 pounds.

Wind turbines also include a utility box, which converts the wind energy into electricity and which is located at the base of the tower. Various cables connect the utility box to the nacelle, while others connect the whole turbine to nearby turbines and to a transformer.

The Manufacturing
Process

Before consideration can be given to the construction of individual wind turbines, manufacturers must determine a proper area for the siting of wind farms. Winds must be consistent, and their speed must be regularly over 15.5 miles per hour (25 kilometers per hour). If the winds are stronger during certain seasons, it is preferred that they be greatest during periods of maximum electricity use. In California's Altamont Pass, for instance, site of the world's largest wind farm, wind speed peaks in the summer when demand is high. In some areas of New England where wind farms are being considered, winds are strongest in the winter, when the need for heating increases the consumption of electrical power. Wind farms work best in open areas of slightly rolling land surrounded by mountains. These areas are preferred because the wind turbines can be placed on ridges and remain unobstructed by trees and buildings, and the mountains concentrate the air flow, creating a natural wind tunnel of stronger, faster winds. Wind farms must also be placed near utility lines to facilitate the transfer of the electricity to the local power plant.

Preparing the site

Wherever a wind farm is to be built, the roads are cut to make way for transporting parts. At each wind turbine location, the land is graded and the pad area is leveled. A concrete foundation is then laid into the ground, followed by the installation of the underground cables. These cables connect the wind turbines to each other in series, and also connect all of them to the remote control center, where the wind farm is monitored and the electricity is sent to the power company.

Erecting the tower

Although the tower's steel parts are manufactured off site in a factory, they are usually assembled on site. The parts are bolted together before erection, and the tower is kept horizontal until placement. A crane lifts the tower into position, all bolts are tightened, and stability is tested upon completion.

Nacelle

The fiberglass nacelle, like the tower, is manufactured off site in a factory. Unlike the tower, however, it is also put together in the factory. Its inner workings—main drive shaft, gearbox, and blade pitch and yaw controls—are assembled and then mounted onto a base frame. The nacelle is then bolted around the equipment. At the site, the nacelle is lifted onto the completed tower and bolted into place.

Rotary blades

Aluminum blades are created by bolting sheets of aluminum together, while wooden blades are carved to form an aerodynamic propeller similar in cross-section to an airplane wing.
By far the greatest number of blades, however, are formed from fiberglass. The manufacture of fiberglass is a painstaking operation. First, a mold that is in two halves like a clam shell, yet shaped like a blade, is prepared. Next, a fiberglass-resin composite mixture is applied to the inner surfaces of the mold, which is then closed. The fiberglass mixture must then dry for several hours; while it does, an air-filled bladder within the mold helps the blade keep its shape. After the fiberglass is dry, the mold is then opened and the bladder is removed. Final preparation of the blade involves cleaning, sanding, sealing the two halves, and painting.
The blades are usually bolted onto the nacelle after it has been placed onto the tower. Because assembly is easier to accomplish on the ground, occasionally a three-pronged blade has two blades bolted onto the nacelle before it is lifted, and the third blade is bolted on after the nacelle is in place.

Installation of control systems

The utility box for each wind turbine and the electrical communication system for the wind farm is installed simultaneously with the placement of the nacelle and blades. Cables run from the nacelle to the utility box and from the utility box to the remote control center.

Quality Control

Unlike most manufacturing processes, production of wind turbines involves very little concern with quality control. Because mass production of wind turbines is fairly new, no standards have been set. Efforts are now being made in this area on the part of both the government and manufacturers.

While wind turbines on duty are counted on to work 90 percent of the time, many structural flaws are still encountered, particularly with the blades. Cracks sometimes appear soon after manufacture. Mechanical failure because of alignment and assembly errors is common. Electrical sensors frequently fail because of power surges. Non-hydraulic brakes tend to be reliable, but hydraulic braking systems often cause problems. Plans are being developed to use existing technology to solve these difficulties.

Wind turbines do have regular maintenance schedules in order to minimize failure. Every three months they undergo inspection, and every six months a major maintenance checkup is scheduled. This usually involves lubricating the moving parts and checking the oil level in the gearbox. It is also possible for a worker to test the electrical system on site and note any problems with the generator or hookups.

Environmental Benefits
and Drawbacks

A wind turbine that produces electricity from inexhaustible winds creates no pollution. By comparison, coal, oil, and natural gas produce one to two pounds of carbon dioxide (an emission that contributes to the greenhouse effect and global warming) per kilowatt-hour produced. When wind energy is used for electrical needs, dependence on fossil fuels for this purpose is reduced. The current annual production of electricity by wind turbines (3.7 billion kilowatt-hours) is equivalent to four million barrels of oil or one million tons of coal.

Wind turbines are not completely free of environmental drawbacks. Many people consider them to be unaesthetic, especially when huge wind farms are built near pristine wilderness areas. Bird kills have been documented, and the whirring blades do produce quite a bit of noise. Efforts to reduce these effects include selecting sites that do not coincide with wilderness areas or bird migration routes and researching ways to reduce noise.

The Future

The future can only get better for wind turbines. The potential for wind energy is largely untapped. The United States Department of Energy estimates that ten times the amount of electricity currently being produced can be achieved by 1995. By 2005, seventy times current production is possible. If this is accomplished, wind turbines would account for 10 percent of the United States' electricity production.

Research is now being done to increase the knowledge of wind resources. This involves the testing of more and more areas for the possibility of placing wind farms where the wind is reliable and strong. Plans are in effect to increase the life span of the machine from five years to 20 to 30 years, improve the efficiency of the blades, provide better controls, develop drive trains that last longer, and allow for better surge protection and grounding. The United States Department of Energy has recently set up a schedule to implement the latest research in order to build wind turbines with a higher efficiency rating than is now possible. (The efficiency of an ideal wind turbine is 59.3 percent. That is, 59.3 percent of the wind's energy can be captured. Turbines in actual use are about 30 percent efficient.) The United States Department of Energy has also contracted with three corporations to research ways to reduce mechanical failure. This project began in the spring of 1992 and will extend to the end of the century.

Wind turbines will become more prevalent in upcoming years. The largest manufacturer of wind turbines in the world, U.S. Windpower, plans to expand from 420 megawatt capacity (4,200 machines) to 800 megawatts (8,000 machines) by 1995. They plan to have 2,000 megawatts (20,000 machines) by the year 2000. Other wind turbine manufacturers also plan to increase the numbers produced. International committees composed of several industrialized nations have formed to discuss the potential of wind turbines. Efforts are also being made to provide developing countries with small wind turbines similar to those Marcellus Jacobs built in the 1920s. Denmark, which already produces 70 percent to 80 percent of Europe's wind power, is developing plans to expand manufacture of wind turbines. The turn of the century should see wind turbines that are properly placed, efficient, durable, and numerous.

Where To Learn More

Books

Assessment of Research Needs for Wind Turbine Rotor Materials Technology. National Academy Press, 1991.

Eggleston, David M. Wind Turbine Engineering Design. Van Nostrand Reinhold, 1987.

Hunt, Daniel V. Windpower: A Handbook on Wind Energy Conversion Systems. Van Nostrand Reinhold, 1981.

Kovarik, Tom, Charles Pupher, and John Hurst. Wind Energy. Domus Books, 1979.

Park, Jack. The Wind Power Book. Cheshire Books, 1981.

Putnam, Palmer Cosslett. Power from the Wind. Van Nostrand Company, 1948.

Periodicals

Frank, Deborah. "Blowing in the Wind," Popular Mechanics, August, 1991, pp. 40-43+.

Mohs, Mayo. "Blowin' in the Wind," Discover. June, 1986, pp. 68-74.

Moretti, Peter M. and Louis V. Divone. "Modern Windmills," Scientific American. June, 1986, pp. 110-118.

Price, Marshall. "Basement-Built Wind Generator," Mother Earth News. July-August, 1986, p. 103.

Stefanides, E. J. "Hydraulic Yaw Control Upgrades Wind Turbine," Design News. March 3, 1986, p. 240.

Vogel, Shawna. "Wind Power," Discover. May, 1989, pp. 46-49.

[Article by: Rose Secrest]

This article is about wind-powered electrical generators. For wind-powered machinery used to grind grain or pump water, see windmill.

Offshore wind farm using 5MW turbines REpower 5M in the North Sea off Belgium

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 pumping water, the device is called a windmill or wind pump. Developed for over a millennium, today's wind turbines are manufactured in a range of vertical and horizontal axis types. The smallest turbines are used for applications such as battery charging or auxiliary power on sailing boats; while large grid-connected arrays of turbines are becoming an increasingly large source of commercial electric power.

Contents

1 History
2 Resources
3 Types
- 3.1 Horizontal axis
- 3.2 Vertical axis design
  - 3.2.1 Subtypes
4 Turbine design and construction
5 Unconventional wind turbines
6 Small wind turbines
7 Wind turbine spacing
8 Accidents
9 Records
10 See also
11 References
12 Further reading
13 External links

History

Main article: History of wind power

James Blyth's electricity generating wind turbine photographed in 1891

Windmills were used in Persia (present-day Iran) as early as 200 B.C.^[1] The windwheel of Heron of Alexandria marks one of the first known instances of wind powering a machine in history.^[2]^[3] However, the first known practical windmills were built in Sistan, a region between Afghanistan and Iran, from the 7th century. These "Panemone" were vertical axle windmills, which had long vertical driveshafts with rectangular blades.^[4] Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, and were used in the gristmilling and sugarcane industries.^[5]

Windmills first appeared in Europe during the middle ages. The first historical records of their use in England date to the 11th or 12th centuries and there are reports of German crusaders taking their windmill-making skills to Syria around 1190.^[6] By the 14th century, Dutch windmills were in use to drain areas of the Rhine delta.

The first electricity generating wind turbine, was a battery charging machine installed in July 1887 by Scottish academic James Blyth to light his holiday home in Marykirk, Scotland.^[7] Some months later American inventor Charles F Brush built the first automatically operated wind turbine for electricity production in Cleveland, Ohio.^[7] Although Blyth's turbine was considered uneconomical in the United Kingdom^[7] electricity generation by wind turbines was more cost effective in countries with widely scattered populations.^[6]

The first automatically operated wind turbine, built in Cleveland in 1887 by Charles F. Brush. It was 60 feet (18 m) tall, weighed 4 tons (3.6 metric tonnes) and powered a 12kW generator.^[8]

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 largest machines were on 24-metre (79 ft) towers with four-bladed 23-metre (75 ft) diameter rotors. By 1908 there were 72 wind-driven electric generators operating in the US from 5 kW to 25 kW. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, mostly for water-pumping.^[9] By the 1930s, wind generators 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 the generators were placed atop prefabricated open steel lattice towers.

A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931. This was a 100 kW generator on a 30-metre (98 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.^[10] In the fall of 1941, the first megawatt-class wind turbine was synchronized to a utility grid in Vermont. The Smith-Putnam wind turbine only ran for 1,100 hours before suffering a critical failure. The unit was not repaired because of shortage of materials during the war.

The first utility grid-connected wind turbine to operate in the UK was built by John Brown & Company in 1951 in the Orkney Islands.^[7]^[11]

Resources

Main article: Wind power

A quantitative measure of the wind energy available at any location is called the Wind Power Density (WPD) It is a calculation of the mean annual power available per square meter of swept area of a turbine, and is tabulated for different heights above ground. Calculation of wind power density includes the effect of wind velocity and air density. Color-coded maps are prepared for a particular area described, for example, as "Mean Annual Power Density at 50 Meters." In the United States, the results of the above calculation are included in an index developed by the US National Renewable Energy Lab and referred to as "NREL CLASS". The larger the WPD calculation, the higher it is rated by class. Classes range from Class 1 (200 watts per square meter or less at 50 meters altitude) to Class 7 (800 to 2000 watts per square meter). Commercial wind farms generally are sited in Class 3 or higher areas, although isolated points in an otherwise Class 1 area may be practical to exploit.^[12]

Types

The three primary types:VAWT Savonius, HAWT towered; VAWT Darrieus as they appear in operation.

Wind turbines can rotate about either a horizontal or a vertical axis, the former being both older and more common.^[13]

Horizontal axis

Components of a horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position

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. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.^[14]

Since a tower produces turbulence behind it, the turbine is usually positioned upwind of its supporting tower. 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 forward into the wind a small amount.

Downwind machines have been built, despite the problem of turbulence (mast wake), 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 cyclical (that is repetitive) turbulence may lead to fatigue failures, most HAWTs are of upwind design.

eleven 7.5 MW E126 Estinnes Windfarm, Belgium, July 2010, one month before completion, with unique two-part blades

Modern wind turbines

Turbine blade convoy passing through Edenfield, UK

Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. These have high tip speeds of over 320 km/h (200 mph), high efficiency, and low torque ripple, which contribute 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 (66 to 130 ft) or more. The tubular steel towers range from 60 to 90 metres (200 to 300 ft) tall. The blades rotate at 10 to 22 revolutions per minute. At 22 rotations per minute the tip speed exceeds 90 metres per second (300 ft/s).^[15]^[16] A gear box is commonly used for stepping up the speed of the generator, although designs may also 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 protective features to avoid damage at high wind speeds, by feathering the blades into the wind which ceases their rotation, supplemented by brakes.

Vertical axis design

Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged 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, for example when integrated into buildings. The key disadvantages include the low rotational speed with the consequential higher torque and hence higher cost of the drive train, the inherently lower power coefficient, the 360 degree rotation of the aerofoil within the wind flow during each cycle and hence the highly dynamic loading on the blade, the pulsating torque generated by some rotor designs on the drive train, and the difficulty of modelling the wind flow accurately and hence the challenges of analysing and designing the rotor prior to fabricating a prototype.^[17]

With a vertical axis, the generator and gearbox can be placed near the ground, using a direct drive from the rotor assembly to the ground-based gearbox, hence improving accessibility for maintenance.

When a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double 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. It should be borne in mind that wind speeds within the built environment are generally much lower than at exposed rural sites.^[18]

Another type of vertical axis is the Parallel turbine similar to the crossflow fan or centrifugal fan it uses the Ground effect. Vertical axis turbines of this type have been tried for many years^[19] The Magenn WindKite blimp uses this configuration as well, chosen because of the ease of running.^[20]

Subtypes

Darrieus wind turbine of 30 m in the Magdalen Islands

Darrieus wind turbine: "Eggbeater" turbines, or Darrieus turbines, were named after the French inventor, Georges Darrieus.^[21] They have good efficiency, but produce large torque ripple and cyclical stress on the tower, which contributes to poor reliability. They also generally require some external power source, or an additional Savonius rotor to start turning, because the starting torque is very low. The torque ripple is reduced by using three or more blades which results in greater solidity of the rotor. Solidity is measured by blade area divided by the rotor area. Newer Darrieus type turbines are not held up by guy-wires but have an external superstructure connected to the top bearing.^[22]

Giromill: A subtype of Darrieus turbine with straight, as opposed to curved, blades. The cycloturbine variety has variable pitch to reduce the torque pulsation and is self-starting.^[23] The advantages of variable pitch are: high starting torque; a wide, relatively flat torque curve; a lower blade speed ratio; a higher coefficient of performance; more efficient operation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V, or curved blades may be used.^[24]

Twisted Savonius

Savonius wind turbine: These are drag-type devices with two (or more) scoops that are used in anemometers, Flettner vents (commonly seen on bus and van roofs), and in some high-reliability low-efficiency power turbines. They are always self-starting if there are at least three scoops.

Twisted Savonius: Twisted Savonius is a modified savonius, with long helical scoops to give a smooth torque, this is mostly used as roof windturbine or on some boats (like the Hornblower Hybrid).

Turbine design and construction

Components of a horizontal-axis wind turbine

Size comparison of a five year old child in a wind turbine rotor hub without blades (Enercon E-70).

Main article: Wind turbine design

Wind turbines are designed to exploit the wind energy that exists at a location. Aerodynamic modelling is used to determine the optimum tower height, control systems, number of blades and blade shape.

Wind turbines convert wind energy to electricity for distribution. Conventional horizontal axis turbines 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 (e.g. planetary gearbox,^[25] adjustable-speed drive ^[26] or continuously variable transmission^[27]) component for converting the low speed incoming rotation to high speed rotation suitable for generating electricity.
The structural support component, which is approximately 15% of the wind turbine cost, includes the tower and rotor yaw mechanism.^[28]

A 1.5 MW wind turbine of a type frequently seen in the United States has a tower 80 meters high. The rotor assembly (blades and hub) weighs 48,000 pounds (22,000 kg). The nacelle, which contains the generator component, weighs 115,000 pounds (52,000 kg). The concrete base for the tower is constructed using 58,000 pounds (26,000 kg) of reinforcing steel and contains 250 cubic yards (190 cubic meters) of concrete. The base is 50 feet (15 m) in diameter and 8 feet (2.4 m) thick near the center.^[29]

Unconventional wind turbines

Main article: Unconventional wind turbines

One E-66 wind turbine at Windpark Holtriem, Germany, carries an observation deck, open for visitors. Another turbine of the same type, with an observation deck, is located in Swaffham, England. Airborne wind turbines have been investigated many times but have yet to produce significant energy. Conceptually, 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.

Wind turbines which utilise the Magnus effect have been developed.[2]

The Ram air turbine is a specialist form of small turbine that is fitted to some aircraft. When deployed, the RAT is spun by the airstream going past the aircraft and can provide power for the most essential systems if there is a loss of all on–board electrical power.

Small wind turbines

A small wind turbine being used in Australia

Main article: Small wind turbine

Small wind turbines may be used for a variety of applications including on- or off-grid residences, telecom towers, offshore platforms, rural schools and clinics, remote monitoring and other purposes that require energy where there is no electric grid, or where the grid is unstable. Small wind turbines may be as small as a fifty-watt generator for boat or caravan use. The US Department of Energy's National Renewable Energy Laboratory (NREL) defines small wind turbines as those smaller than or equal to 100 kilowatts.^[30] Small units often have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind.

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.

Wind turbine spacing

On most horizontal windturbine farms, a spacing of about 6-10 times the rotor diameter is often upheld. However, for large wind farms distances of about 15 rotor diameters should be more economically optimal, taking into account typical wind turbine and land costs. This conclusion has been reached by research^[31] conducted by Charles Meneveau of the Johns Hopkins University^[32] and Johan Meyers of Leuven University in Belgium, based on computer simulations^[33] that take into account the detailed interactions among wind turbines (wakes) as well as with the entire turbulent atmospheric boundary layer. Moreover, recent research by John Dabiri of Caltech suggests that vertical wind turbines may be placed much more closely together so long as an alternating pattern of rotation is created allowing blades of neighboring turbines to move in the same direction as they approach one another.^[34]

Accidents

Several cases occurred where the housings of wind turbines caught fire. As housings are normally out of the range of standard fire extinguishing equipment, it is nearly impossible to extinguish such fires on older turbine units which lack fire suppression systems. In several cases one or more blades were damaged or torn away.^[35] In 2010 70 mph (110 km/h; 61 kn) storm winds damaged some blades, prompting blade removal and inspection of all 25 wind turbines in Campo Indian Reservation in the US State of California.^[36] Several wind turbines also collapsed.

Severe wind turbine accidents have had relatively low impacts on the communities where the accidents occurred. In comparison, nuclear accident sites such as the Chernobyl and Fukushima disasters have created emergency evacuation zones the size of Switzerland which will remain in place for many decades, if not centuries.

Place	Date	Type	Nacelle height	Rotor dia.	Year built	Reason	Ref.	Other info
Ellenstedt, Germany	October 19, 2002						[3]
Schneebergerhof, Germany	December 20, 2003	Vestas V80		80 m			[4]
Wasco, Oregon, USA	August 26, 2007						[5]	1 worker killed, 1 injured
Stobart Mill, UK	December 30, 2007	Vestas			1982		[6]
Hornslet, Denmark	February 22, 2008	Nordtank NKT 600-180	44.5 m	43 m	1996	Brake failure	[7]	Collapse was filmed [8]
Searsburg, Vermont, USA	October 16, 2008	Zond Z-P40-FS			1997	Rotor blade collided with tower during strong wind and destroyed it	[9]
Altona, New York, USA	March 6, 2009						[10]
Fenner, New York, USA	December 27, 2009						[11]
Kirtorf, Germany	June 19, 2011	DeWind D-6	68.5 m	62 m	2001		[12]
Ayrshire, Scotland	December 8, 2011						[13]

Records

Enercon E-126, highest rated capacity

Fuhrländer Wind Turbine Laasow, world's tallest

Éole, the largest vertical axis wind turbine, in Cap-Chat, Quebec

Highest-situated wind turbine, at the Veladero mine in San Juan Province, Argentina

Rønland, most productive turbines, in Denmark

Largest capacity: The Enercon E-126 has a rated capacity of 7.58 MW,^[37] has an overall height of 198 m (650 ft), a diameter of 126 m (413 ft), and is the world's largest-capacity wind turbine since its introduction in 2007.^[38] At least five companies are working on the development of a 10MW turbine:

American Superconductor^[39]
Wind Power Ltd are developing a 10 MW VAWT, the Aerogenerator X^[40]
Sway AS announced the proposed development of a prototype 10 MW wind turbine with a height of 162.5 m (533 ft) and a rotor diameter of 145 m (475 ft).^[40]^[41]^[42]
Astralux Ltd are developing vertical axis magneto levitated 10 MW turbine with 230 m height and 260 m rotor diameter^[43]^[44]
Clipper Windpower were developing the Britannia 10 MW HAWT, but terminated the project due to financial challenges.^[39]^[40]^[41]^[45]

Largest swept area: The turbine with the largest swept area is a prototype installed by Gamesa at Jaulín, Zaragoza, Spain in 2009. The G10X – 4.5 MW has a rotor diameter of 128m.

^[46]

Tallest: The tallest wind turbine is Fuhrländer Wind Turbine Laasow. Its axis is 160 meters above ground and its rotor tips can reach a height of 205 meters. It is the only wind turbine in the world taller than 200 meters.^[47]
Largest vertical-axis: Le Nordais wind farm in Cap-Chat, Quebec has a vertical axis wind turbine (VAWT) named Éole, which is the world's largest at 110 m.^[48] It has a nameplate capacity of 3.8MW.^[49]
Most southerly: The turbines currently operating closest to the South Pole are three Enercon E-33 in Antarctica, powering New Zealand's Scott Base and the United States' McMurdo Station since December 2009^[50]^[51] although a modified HR3 turbine from Northern Power Systems operated at the Amundsen-Scott South Pole Station in 1997 and 1998.^[52] In March 2010 CITEDEF designed, built and installed a wind turbine in Argentine Marambio Base.^[53]
Most productive: Four turbines at Rønland wind farm in Denmark share the record for the most productive wind turbines, with each having generated 63.2 GWh by June 2010^[54]
Highest-situated: The world's highest-situated wind turbine is made by DeWind installed by the Seawind Group and located in the Andes, Argentina around 4,100 metres (13,500 ft) above sea level. The site uses a type D8.2 - 2000 kW / 50 Hz turbine. This turbine has a new drive train concept with a special torque converter (WinDrive) made by Voith and a synchronous generator. The WKA was put into operation in December 2007 and has supplied the Veladero mine of Barrick Gold with electricity since then.^[55]
Largest floating wind turbine: The world's largest—and also the first operational deep-water large-capacity—floating wind turbine is the 2.3 MW Hywind currently operating 10 kilometres (6.2 mi) offshore in 220-meter-deep water, southwest of Karmøy, Norway. The turbine began operating in September 2009 and utilizes a Siemens 2.3 MW turbine^[56]^[57]

References

^ "Part 1 — Early History Through 1875". http://www.telosnet.com/wind/early.html. Retrieved 2008-07-31.
^ A.G. Drachmann, "Heron's Windmill", Centaurus, 7 (1961), pp. 145–151
^ Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp. 1–30 (10f.)
^ Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology: An illustrated history, p. 54. Cambridge University Press. ISBN 0-521-42239-6.
^ Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69. (cf. Donald Routledge Hill, Mechanical Engineering)
^ ^a ^b Morthorst, Poul Erik; Redlinger, Robert Y.; Andersen, Per (2002). Wind energy in the 21st century: economics, policy, technology and the changing electricity industry. Houndmills, Basingstoke, Hampshire: Palgrave/UNEP. ISBN 0-333-79248-3.
^ ^a ^b ^c ^d "James Blyth". Oxford Dictionary of National Biography. Oxford University Press. http://www.oxforddnb.com/public/dnb/100957.html. Retrieved 2009-10-09.
^ A Wind Energy Pioneer: Charles F. Brush. Danish Wind Industry Association. http://www.windpower.org/en/pictures/brush.htm. Retrieved 2008-12-28.
^ Quirky old-style contraptions make water from wind on the mesas of West Texas
^ Alan Wyatt: Electric Power: Challenges and Choices. Book Press Ltd., Toronto 1986, ISBN 0-920650-00-7
^ Anon. "Costa Head Experimental Wind Turbine". Orkney Sustainable Energy Website. Orkney Sustainable Energy Ltd. http://www.orkneywind.co.uk/costa.html. Retrieved 19 December 2010.
^ http://www.nrel.gov/gis/wind.html Dynamic Maps, GIS Data and Tools
^ "Wind Energy Basics". American Wind Energy Association. http://www.awea.org/faq/wwt_basics.html. Retrieved 2009-09-24. ^{[dead link]}
^ http://www.windpower.org/en/tour/wtrb/comp/index.htm Wind turbine components retrieved November 8, 2008
^ <</en/15mw/specs.htm 1.5 MW Wind Turbine Technical Specifications
^ Size specifications of common industrial wind turbines
^ About the wind flow modeling uncertainty at the AWS Open-Wind website
^ About urban vs. rural wind speeds with actual readings. See also Urban wind turbines tech analysis
^ A large unit producing up to 10 kW was built by Israeli wind pioneer Bruce Brill in 1980s. See his patent. (The device is mentioned in Dr. Moshe Dan Hirsch's 1990 report, which decided the Israeli energy department investments and support in the next 20 years)
^ a blog with several images of different horizontal parallel turbine concepts
^ http://www.symscape.com/blog/vertical_axis_wind_turbine
^ Exploit Nature-Renewable Energy Technologies by Gurmit Singh‏, Aditya Books, pp 378
^ http://www.awea.org/faq/vawt.html
^ About blade stress and bending at the Springer Publishing website
^ Hansen Industrial Transmissions W4
^ Adjustable speed drive used on wind turbines
^ Continuously variable transmission for wind turbines
^ "Wind Turbine Design Cost and Scaling Model," Technical Report NREL/TP-500-40566, December, 2006, page 35,36. http://www.nrel.gov/docs/fy07osti/40566.pdf
^ [1]
^ http://www.nrel.gov/wind/smallwind/
^ J. Meyers and C. Meneveau, "Optimal turbine spacing in fully developed wind farm boundary layers" (2011), Wind Energy DOI: 10.1002/we.469
^ Optimal spacing for wind turbines
^ M. Calaf, C. Meneveau and J. Meyers, "Large Eddy Simulation study of fully developed wind-turbine array boundary layers" (2010), Phys. Fluids 22, 015110
^ Dabiri, J. Potential order-of-magnitude enhancement of wind farm power density via counter-rotating vertical-axis wind turbine arrays (2011), J. Renewable Sustainable Energy 3, 043104
^ www.windbyte.co.uk
^ www.signonsandiego.com
^ http://www.enercon.de/p/downloads/EN_Produktuebersicht_0710.pdf
^ "New Record: World's Largest Wind Turbine (7+ Megawatts) — MetaEfficient Reviews". MetaEfficient.com. 2008-02-03. http://www.metaefficient.com/news/new-record-worlds-largest-wind-turbine-7-megawatts.html. Retrieved 2010-04-17.
^ ^a ^b "Wind Turbines go Super-Sized". Energy Efficiency & Technology. 2009-09-01. http://eetweb.com/wind/wind-turbines-go-supersized-20091001/. Retrieved 2010-07-26.
^ ^a ^b ^c Vidal, John (2010-07-26). "Engineers race to design world's biggest offshore wind turbines". The Guardian. http://www.guardian.co.uk/environment/2010/jul/26/offshore-turbine-britain. Retrieved 2010-07-26.
^ ^a ^b "Offshore wind turbines may be 10 MW giants: Veritas". Reuters. 2010-03-29. http://www.reuters.com/article/idUSTRE62S2ZP20100329. Retrieved 2010-07-26.
^ http://www.google.com/hostednews/afp/article/ALeqM5j-BZEK4lR-_hxsz2hQ-92_c0oSHQ Retrieved 2010-02-13
^ "10MW Wind Turbine Quadruples Power". Property Magazine. 2011-05-18. http://pptymag.com/10mw-wind-turbine-quadruples-power/4730/. Retrieved 2011-06-28.
^ "10 MW Vertical Axis Wind Turbine". Astralux Website. 2011-06-28. http://newwindturbine.com/wind-turbines/10-mw-wind-turbine/. Retrieved 2011-06-28.
^ http://www.nawindpower.com/e107_plugins/content/content.php?content.8467
^ "Gamesa Presents G10X-4.5 MW Wind Turbine Prototype". http://www.renewable-energy-sources.com/2009/06/29/gamesa-presents-g10x-4-5-mw-wind-turbine-prototype/. Retrieved 2010-07-26.
^ "FL 2500 Noch mehr Wirtschaftlichkeit" (in German). Fuhrlaender AG. http://fuhrlaender.de/produkte/index_de.php?produkt_gesucht=1&produkt_name=FL+2500. Retrieved 2009-11-05.
^ "Visits > Big wind turbine". http://www.eolecapchat.com/e_1b-grande.html. Retrieved 2010-04-17.
^ "Wind Energy Power Plants in Canada - other provinces". 2010-06-05. http://www.industcards.com/wind-canada.htm. Retrieved 2010-08-24.
^ Antarctica New Zealand
^ New Zealand Wind Energy Association
^ Bill Spindler, The first Pole wind turbine.
^ GENERADOR DE ENERGÍA EÓLICA EN LA ANTÁRTIDA
^ "Surpassing Matilda: record-breaking Danish wind turbines". http://www.energynumbers.info/surpassing-matilda-record-breaking-danish-wind-turbines. Retrieved 2010-07-26.
^ http://www.voithturbo.com/vt_en_pua_windrive_project-report_2008.htm
^ Patel, Prachi (2009-06-22). "Floating Wind Turbines to Be Tested". IEEE Spectrum. http://www.spectrum.ieee.org/green-tech/wind/floating-wind-turbines-to-be-tested. Retrieved 2011-03-07. "will test how the 2.3-megawatt turbine holds up in 220-meter-deep water."
^ Madslien, Jorn (8 September 2009). "Floating challenge for offshore wind turbine". BBC News (BBC). http://news.bbc.co.uk/2/hi/8235456.stm?ls. Retrieved 2011-03-07. "world's first full-scale floating wind turbine"

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