Wind turbine

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

A wind turbine is a device that converts the kinetic energy of wind into electrical energy. As of 2024, hundreds of thousands of large turbines, in installations known as wind farms, were generating over 1,136 gigawatts of power, with 117 GW added each year. Wind turbines are an increasingly important source of intermittent renewable energy. They are used in many countries to lower energy costs and reduce reliance on fossil fuels. One study claimed that, as of 2009, wind had the "lowest relative greenhouse gas emissions, the least water consumption demands and the most favorable social impacts" compared to photovoltaic, hydro, geothermal, coal and gas energy sources.

Wind turbines come in a wide range of sizes, with either horizontal or vertical axes, though horizontal is the most common. Commercial horizontal-axis turbines usually have three blades, placed upwind of their towers. Vertical-axis turbines can be built in many designs, including the "eggbeater" Darrieus, the giromill with straight blades, the Savonius with scoops suitable for rooftops and ships, airborne types with wings tethered to the ground, floating types mounted on a floating platform, and various unconventional types such as those with counter-rotating blades.

Blades are most commonly made of glass fiber composites, but carbon fiber, which is stiffer, stronger, and less dense, is also used. Smaller wind turbines are used for tasks such as battery charging and for remote devices like traffic warning signs. Larger turbines can help supply power to a home while selling unused power back to the utility supplier through the electrical grid.

Wind turbines produce some of the cheapest renewable energy and are clean, emitting no greenhouse gases. They have a significant environmental impact, such as on wildlife, but this can be reduced. The power produced changes with the wind, not with demand, so it is an unreliable source of energy unless energy storage is available.

Main article: History of wind power

History

The windwheel of Hero of Alexandria (10–70 CE) is one of the first recorded uses of wind to power a machine. The first known practical wind power plants were built from the 7th century in Sistan, an eastern province of Persia (now Iran). These panemone windmills had long vertical drive shafts and rectangular blades made of six to twelve sails covered in reed matting or cloth. They were used to grind grain, draw up water, and in the gristmilling and sugarcane industries. Wind power later appeared in Europe during the Middle Ages. German crusaders are reported to have taken windmill-making skills to Syria around 1190, and Croatian inventor Fausto Veranzio described vertical-axis windmills in his book Machinae Novae (1595).

The first electricity-generating wind turbine was installed by Josef Friedländer at the Vienna International Electrical Exhibition in 1883. It drove a dynamo and was supplied by a company in Batavia, Illinois. Its electricity was stored in batteries that powered tools and lamps. In July 1887, Scottish academic James Blyth used a wind-powered battery-charging machine to light his holiday home in Marykirk, Scotland. Some months later, American inventor Charles F. Brush built the first automatically operated wind turbine. By 1908, 72 wind-driven electric generators were operating in the United States, and in Denmark about 2500 windpumps and windmills were in use by 1900. Use of wind turbines in rural areas declined in the 1930s as the distribution system extended to those areas. The first megawatt-class wind turbine, the Smith–Putnam wind turbine in Vermont, was connected to a power grid in 1941, but it ran for only about five years before a blade broke off. Later, anti-nuclear protests in Denmark in the early 1970s encouraged people to build small turbines, and interest in wind power grew in the following decades. Some people have argued that wider use of wind power could lead to competition over rare earth elements such as neodymium, praseodymium, and dysprosium, though others have dismissed this view because most wind turbines do not use permanent magnets.

Wind power density

Main article: Wind power

Wind power density (WPD) is a way to measure how much wind energy is available at a place. It is the average power available for each area a turbine sweeps, and it is worked out for different heights above the ground. The calculation takes into account wind speed and air density.

Wind turbines are grouped into classes by the wind speed they are designed for, from class I to class III. The letters A to C refer to how bumpy or uneven the wind is.

Efficiency

A wind turbine can only capture part of the energy in the wind. The conservation of mass and the conservation of energy mean that some energy always leaves in the moving air. Betz's law gives the most a turbine can capture as 16⁄27, or 59.3%, of the energy that reaches it. Real turbines capture less because of losses in the rotor blades, the gearbox, the generator, and the converter. These losses affect the price of wind power. The turbine's output also stays steady above its rated speed to protect its parts, because theoretical power increases as the cube of wind speed. In 2001, commercial turbines connected to the power grid delivered 75% to 80% of the Betz limit at rated operating speed. Efficiency is also affected by the air density and by friction on the blades.

Efficiency can drop a little over time, mainly because dust and insect remains build up on the blades and change their shape. This lowers the lift to drag ratio of the airfoil. A study of 3128 Danish turbines older than 10 years found that half had no drop, while the other half lost 1.2% of production per year. Steady, constant weather, especially wind speed, gives about 15% more efficiency than unstable weather. The blade material also matters, since heavier materials such as epoxy blades create more friction. The location matters too: winds are stronger near the shore and on mountain ridges, and a windbreak can increase wind speed near a turbine.

Types

Wind turbines can turn around a horizontal axis or a vertical axis. The horizontal kind is older and more common. Large horizontal turbines usually have three blades and sit at the top of a tower, where they must face the wind. They often have a rotor shaft and an electrical generator at the top, and small ones are pointed by a simple wind vane. Turbines used in wind farms to make electricity usually have three blades, which are often painted white so aircraft can see them in the daytime.

Vertical-axis wind turbines have a main shaft that stands upright. They do not need to be pointed into the wind, which helps where the wind often changes direction. However, these designs produce much less energy over time. Some types, such as the Darrieus wind turbine, were named after Georges Jean Marie Darrieus, who patented a design in the 1920s. Other designs include the Savonius turbine, which uses scoops and is sometimes used on rooftops. Airborne wind turbines use wings or a small aircraft tied to the ground to reach faster winds. A floating wind turbine is an offshore turbine held up by a floating platform, which lets it be placed in deeper water and further from land.

Main article: Unconventional wind turbines

Design and construction

See also: Wind turbine prognostics

Most wind turbines have three main parts. The rotor, which is about 20% of the cost, has blades that turn wind energy into slow spinning motion. The generator, which is about 34% of the cost, makes the electricity. It includes the electrical generator and a gearbox (such as a planetary gear box), an adjustable-speed drive, or a continuously variable transmission that speeds up the slow rotation so electricity can be made. The surrounding structure, which is about 15% of the cost, includes the tower and the rotor yaw mechanism.

A 1.5 MW wind turbine of a type often seen in the United States has a tower 80 meters (260 ft) high. Its rotor, made of blades and a hub, is about 80 meters (260 ft) across. The nacelle, which holds the generator, is 15.24 meters (50.0 ft) long and weighs around 300 tons. Because of data transmission problems, structural health monitoring of wind turbines is usually done with several accelerometers and strain gages attached to the nacelle to watch the gearbox and equipment. Digital image correlation and stereophotogrammetry are used to measure how wind turbine blades move, which helps find defects.

Technology

Wind turbine blades must be stiff, strong, durable, light, and able to resist fatigue. Composites such as polyester and epoxy are used, with glass fiber or carbon fiber for reinforcement. Generally, longer blades make turbines more efficient. Turbines have an average lifespan of 30 years, while blades and gearboxes usually last up to 25 years.

The capital cost of a wind turbine was about $2,324 per kilowatt in 2010. By 2024, this had fallen to $1,041 per kilowatt of nameplate capacity. Modern turbines use about two tons of copper for wiring, generators, transformers, and grounding systems. Some parts also rely on rare earth minerals, so their supply and price can change.

Blade materials

Glass and carbon fibers

Material supply

Wind turbines on public display

Some places have used the eye-catching nature of wind turbines by putting them on public display. Some have visitor centers around their bases, and others have viewing areas farther away. These turbines usually have the common design with three blades. They generate power for electrical grids, but they also show new technology, help a public image, and teach people.

The Bahrain World Trade Center has wind turbines displayed prominently for the public. It is the first skyscraper to build wind turbines into its design.

Small wind turbines

Main article: Small wind turbine

Small wind turbines can power homes, telecom towers, offshore platforms, rural schools and clinics, and remote monitoring equipment, especially where there is no electric grid or where the grid is unreliable. The smallest ones can be as small as a fifty-watt generator for use on a caravan or boat. Hybrid units that use both solar and wind power are increasingly used for traffic signs, particularly in rural areas, because they avoid the need to lay long cables from the nearest power connection. The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) defines small wind turbines as those up to 100 kilowatts. Small units often produce direct current electricity and use a vane to point into the wind.

Wind turbine spacing

On most horizontal wind turbine farms, turbines are often spaced about 6 to 10 times the width of their rotor (the part with the spinning blades). For large wind farms, spacing about 15 rotor widths apart should be more economical, based on typical costs for wind turbines and land. Researchers Charles Meneveau of Johns Hopkins University and Johan Meyers of Leuven University in Belgium reached this conclusion using computer simulations. These simulations looked at how the wind moves around and between turbines, as well as through the whole turbulent layer of air near the ground.

Research by John Dabiri of Caltech suggests that vertical wind turbines can be placed much closer together. This works if the turbines spin in an alternating pattern, so that the blades of neighbouring turbines move in the same direction as they pass each other.

Operability

Wind turbines need regular maintenance to stay reliable and available. In the best case, turbines can make energy 98% of the time. Ice on the blades greatly lowers how well a turbine works. This is a common problem in cold places where in-cloud icing and freezing rain happen. Deicing is mainly done by heating inside the turbine. In some cases, helicopters or drones spray clean warm water on the blades. Most modern turbines have a small crane inside for lifting tools and small parts. Big, heavy parts like generators, gearboxes, and blades are rarely replaced, and they need a heavy lift external crane. If the access road is difficult, a containerized crane can be lifted up by the internal crane to handle heavier lifting.

Main article: Repowering

Installing new wind turbines can be controversial. One option is repowering, where old turbines are replaced with bigger, more powerful ones, sometimes in smaller numbers. Some turbines that are no longer used are recycled or repowered. About 85% of turbine materials can be easily reused or recycled, but the blades are harder to process because they are made of a composite material. The blades are made of fiberglass with carbon fibers in epoxy resin, which cannot be remolded into new composites. According to the wind-industry trade association, American Wind Energy Association, wind turbine blades make up only a small part of overall waste in the US. Several companies and researchers are working on ways to reuse or recycle blades. Vestas has developed technology that can separate the fibers from the resin. In Germany, blades are recycled as part of a fuel mix for a cement factory. In the United Kingdom, a project will test cutting blades into strips for use as reinforcing bars in concrete, to help reduce emissions in building High Speed 2. In 2026, Chinese manufacturer Ming Yang developed the first fully recyclable wind turbine, which uses pultruded carbon fiber panels instead of fiberglass.

Comparison with other power sources

Wind turbines are one of the lowest-cost sources of renewable energy, along with solar panels. As the technology improved, prices went down too. For small wind turbines, the main cost is buying and installing them, which averages between $48,000 and $65,000 per installation. Usually, the energy they collect is worth more than the cost of the turbines. Wind turbines are also a clean energy source. They use little water and give off no greenhouse gases or waste products while running. Using a one-megawatt turbine instead of one megawatt of energy from a fossil fuel can eliminate over 1,400 tonnes (1,500 short tons) of carbon dioxide per year.

Environmental impact of wind power includes effects on wildlife, but these can be reduced when good strategies are used. Thousands of birds, including rare species, have been killed by turbine blades, though wind turbines cause relatively few bird deaths compared with other human causes. Wind farms and nuclear power plants are responsible for between 0.3 and 0.4 bird deaths per gigawatt-hour of electricity, while fossil fuel power stations are responsible for about 5.2. Wind energy is also not a "dispatchable" source, meaning it depends on whether the wind is blowing, not on when electricity is needed. Turbines can be placed on ridges or bluffs to catch more wind, but this limits where they can go. Wind can still be part of the energy mix alongside other sources, and technology is being developed to store extra energy for when supplies fall short. Turbines are also noisy, so in the UK they are not allowed within 500m of homes for turbines up to 100kW, or within 1,000m for larger ones. Turbines have blinking lights to warn aircraft, but nearby residents, especially in rural areas, have complained that these lights are a bother and a form of light pollution. One approach turns the lights on only when radar detects aircraft within certain height and distance limits.

Records

See also: List of most powerful wind turbines

Wind turbines with special constructive features

The following wind turbines have special constructive features, but use turbines that can be bought commercially.