A wind turbine is a device that

converts Conversion or convert may refer to: Arts, entertainment, and media * ''The Convert'', a 2023 film produced by Jump Film & Television and Brouhaha Entertainment * "Conversion" (''Doctor Who'' audio), an episode of the audio drama ''Cyberman'' * ...

the

kinetic energy In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion. In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

into

electrical energy Electrical energy is the energy transferred as electric charges move between points with different electric potential, that is, as they move across a voltage, potential difference. As electric potential is lost or gained, work is done changing the ...

. , hundreds of thousands of large turbines, in installations known as

wind farm A wind farm, also called a wind park or wind power plant, is a group of wind turbines in the same location used to produce electricity. Wind farms vary in size from a small number of turbines to several hundred wind turbines covering an exten ...

s, were generating over 650

gigawatt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named in honor ...

s of power, with 60 GW added each year. Wind turbines are an increasingly important source of intermittent

renewable energy Renewable energy (also called green energy) is energy made from renewable resource, renewable natural resources that are replenished on a human lifetime, human timescale. The most widely used renewable energy types are solar energy, wind pow ...

, and are used in many countries to lower energy costs and reduce reliance on

fossil fuel A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geolog ...

s. One study claimed that, wind had the "lowest relative greenhouse gas emissions, the least water consumption demands and the most favorable social impacts" compared to

photovoltaic Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially ...

hydro Hydro (from ) may refer to: Energy technologies * Water-derived power or energy: ** Hydropower, derived from water ** Hydroelectricity, in electrical form * "Hydro", AC mains electricity in parts of Canada * Micro hydro, a type of hydroelect ...

, geothermal,

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

and

gas Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...

energy sources. Smaller wind turbines are used for applications such as

battery charging A battery charger, recharger, or simply charger, is a device that energy storage, stores energy in an electric battery by running electric current, current through it. The charging protocol—how much voltage and current, for how long and what ...

and remote devices such as traffic warning signs. Larger turbines can contribute to a domestic power supply while selling unused power back to the utility supplier via the

electrical grid An electrical grid (or electricity network) is an interconnected network for electricity delivery from producers to consumers. Electrical grids consist of power stations, electrical substations to step voltage up or down, electric power tran ...

. Wind

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced can be used for generating electrical ...

s are manufactured in a wide range of sizes, with either horizontal or vertical axes, though horizontal is most common.

History

The windwheel of

Hero of Alexandria Hero of Alexandria (; , , also known as Heron of Alexandria ; probably 1st or 2nd century AD) was a Greek mathematician and engineer who was active in Alexandria in Egypt during the Roman era. He has been described as the greatest experimental ...

(10–70 CE) marks one of the first recorded instances of wind powering a machine. However, the first known practical wind power plants were built in

Sistan Sistān (), also known as Sakastān (, , current name: Zabol) and Sijistan (), is a historical region in south-eastern Iran and extending across the borders of present-day south-western Afghanistan, and south-western Pakistan. Mostly correspond ...

, an Eastern province of

Persia Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

(now Iran), from the 7th century. These " Panemone" were vertical axle windmills, which had long vertical

drive shaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power (physics), power, torque, and rotation, usually ...

s with rectangular blades. 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

gristmill A gristmill (also: grist mill, corn mill, flour mill, feed mill or feedmill) grinds cereal grain into flour and Wheat middlings, middlings. The term can refer to either the grinding mechanism or the building that holds it. Grist is grain that h ...

ing and sugarcane industries. Wind power first appeared in Europe during the

Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of global history. It began with the fall of the Western Roman Empire and ...

. The first historical records of their use in England date to the 11th and 12th centuries; there are reports of German

crusaders The Crusades were a series of religious wars initiated, supported, and at times directed by the Papacy during the Middle Ages. The most prominent of these were the campaigns to the Holy Land aimed at reclaiming Jerusalem and its surrounding ...

taking their windmill-making skills to Syria around 1190. By the 14th century, Dutch windmills were in use to drain areas of the

Rhine The Rhine ( ) is one of the List of rivers of Europe, major rivers in Europe. The river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps. It forms part of the Swiss-Liechtenstein border, then part of the Austria–Swit ...

delta. Advanced wind turbines were described by Croatian inventor

Fausto Veranzio Fausto Veranzio (; ; Hungarian language, Hungarian and Latin regional pronunciation, Vernacular Latin: ''Verancsics Faustus'';Andrew L. SimonMade in Hungary: Hungarian contributions to universal culture/ref>vertical axis wind turbines with curved or V-shaped blades. Friedlander Wind Turbine 1883

The first electricity-generating wind turbine was installed by the

Austria Austria, formally the Republic of Austria, is a landlocked country in Central Europe, lying in the Eastern Alps. It is a federation of nine Federal states of Austria, states, of which the capital Vienna is the List of largest cities in Aust ...

n Josef Friedländer at the Vienna International Electrical Exhibition in 1883. It was a Halladay windmill for driving a

dynamo "Dynamo Electric Machine" (end view, partly section, ) A dynamo is an electrical generator that creates direct current using a commutator. Dynamos employed electromagnets for self-starting by using residual magnetic field left in the iron cores ...

. Friedländer's diameter Halladay "wind motor" was supplied by U.S. Wind Engine & Pump Co. of Batavia,

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

. The windmill drove a dynamo at ground level that fed electricity into a series of batteries. The batteries powered various electrical tools and lamps, as well as a threshing machine. Friedländer's windmill and its accessories were prominently installed at the north entrance to the main exhibition hall ("

Rotunde The Rotunde () in Vienna's Leopoldstadt district was a building erected for the 1873 Vienna World's Fair (). The building was a partially covered circular wrought iron construction, tall, with a diameter of . While the Rotunda stood, its dome w ...

") in the Vienna Prater. In July 1887, Scottish academic James Blyth installed a battery-charging machine to light his holiday home in

Marykirk Marykirk () is a village in the Kincardine and Mearns area of Aberdeenshire Aberdeenshire (; ) is one of the 32 Subdivisions of Scotland#council areas of Scotland, council areas of Scotland. It takes its name from the Shires of Scotland, ...

, Scotland. Some months later, American inventor Charles F. Brush was able to build the first automatically operated wind turbine after consulting local University professors and his colleagues Jacob S. Gibbs and Brinsley Coleberd and successfully getting the blueprints peer-reviewed for electricity production. Although Blyth's turbine was considered uneconomical in the United Kingdom, electricity generation by wind turbines was more cost effective in countries with widely scattered populations. Wind turbine 1888 Charles Brush

Denmark Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...

by 1900, there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30

megawatts The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named in honor o ...

(MW). The largest machines were on towers with four-bladed diameter rotors. By 1908, there were 72 wind-driven electric generators operating in the United States from 5

kilowatts The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named in honor of ...

(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. By the 1930s, use of wind turbines in rural areas was declining as the distribution system extended to those areas. A forerunner of modern horizontal-axis wind generators was in service at

Yalta Yalta (: ) is a resort town, resort city on the south coast of the Crimean Peninsula surrounded by the Black Sea. It serves as the administrative center of Yalta Municipality, one of the regions within Crimea. Yalta, along with the rest of Crime ...

, USSR, in 1931. This was a 100 kW generator on a tower, connected to the local 6.3 kV distribution system. It was reported to have an annual

capacity factor The net capacity factor is the unitless ratio of actual electrical energy output over a given period of time to the theoretical maximum electrical energy output over that period. The theoretical maximum energy output of a given installation is def ...

of 32 percent, not much different from current wind machines. In the autumn of 1941, the first megawatt-class wind turbine was synchronized to a utility grid in

Vermont Vermont () is a U.S. state, state in the New England region of the Northeastern United States. It borders Massachusetts to the south, New Hampshire to the east, New York (state), New York to the west, and the Provinces and territories of Ca ...

. The Smith–Putnam wind turbine only ran for about five years before one of the blades snapped off. The unit was not repaired, because of a shortage of materials during the war. The first utility grid-connected wind turbine to operate in the UK was built by

John Brown & Company John Brown and Company of Clydebank was a Scottish Naval architecture, marine engineering and shipbuilding firm. It built many notable and world-famous ships including , , , , , and ''Queen Elizabeth 2 (ship), Queen Elizabeth 2''. At its heig ...

in 1951 in the

Orkney Islands Orkney (), also known as the Orkney Islands, is an archipelago off the north coast of mainland Scotland. The plural name the Orkneys is also sometimes used, but locals now consider it outdated. Part of the Northern Isles along with Shetland ...

. In the early 1970s, however, anti-nuclear protests in Denmark spurred artisan mechanics to develop microturbines of 22 kW despite declines in the industry. Organizing owners into associations and co-operatives led to the lobbying of the government and utilities and provided incentives for larger turbines throughout the 1980s and later. Local activists in Germany, nascent turbine manufacturers in Spain, and large investors in the United States in the early 1990s then lobbied for policies that stimulated the industry in those countries. It has been argued that expanding the use of wind power will lead to increasing geopolitical competition over critical materials for wind turbines, such as

rare earth elements The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set of ...

neodymium Neodymium is a chemical element; it has Symbol (chemistry), symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth element, rare-earth metals. It is a hard (physics), hard, sli ...

praseodymium Praseodymium is a chemical element; it has symbol Pr and atomic number 59. It is the third member of the lanthanide series and is considered one of the rare-earth metals. It is a soft, silvery, malleable and ductile metal, valued for its magnetic ...

, and

dysprosium Dysprosium is a chemical element; it has symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, it ...

. However, this perspective has been critically dismissed for failing to relay how most wind turbines do not use permanent magnets and for underestimating the power of economic incentives for the expanded production of these minerals.

Wind power density

Wind Power Density (WPD) is a quantitative measure of wind energy available at any location. It is the mean annual power available per square meter of swept area of a turbine, and is calculated for different heights above ground. Calculation of wind power density includes the effect of wind velocity and air density. Wind turbines are classified by the wind speed they are designed for, from class I to class III, with A to C referring to the turbulence intensity of the wind.

Efficiency

Conservation of mass In physics and chemistry, the law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter the mass of the system must remain constant over time. The law implies that mass can neith ...

requires that the mass of air entering and exiting a turbine must be equal. Likewise, the

conservation of energy The law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be Conservation law, ''conserved'' over time. In the case of a Closed system#In thermodynamics, closed system, the principle s ...

requires the energy given to the turbine from incoming wind to be equal to that of the combination of the energy in the outgoing wind and the energy converted to electrical energy. Since outgoing wind will still possess some kinetic energy, there must be a maximum proportion of the input energy that is available to be converted to electrical energy. Accordingly,

Betz's law In aerodynamics, Betz's law indicates the maximum Power (physics), power that can be extracted from the wind, independent of the design of a wind turbine in open flow. It was published in 1919 by the German physicist Albert Betz.Betz, A. (1966) ' ...

gives the maximal achievable extraction of wind power by a wind turbine, known as Betz's coefficient, as (59.3%) of the rate at which the kinetic energy of the air arrives at the turbine. The maximum theoretical power output of a wind machine is thus times the rate at which kinetic energy of the air arrives at the effective disk area of the machine. If the effective area of the disk is A, and the wind velocity v, the maximum theoretical power output P is: :

P=\frac\frac\rho v^3 A = \frac\rho v^3 A

, where ''ρ'' is the

air density The density of air or atmospheric density, denoted '' ρ'', is the mass per unit volume of Earth's atmosphere at a given point and time. Air density, like air pressure, decreases with increasing altitude. It also changes with variations in atmosph ...

. Wind-to-rotor efficiency (including rotor blade

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...

and drag) are among the factors affecting the final

price A price is the (usually not negative) quantity of payment or compensation expected, required, or given by one party to another in return for goods or services. In some situations, especially when the product is a service rather than a ph ...

of wind power. Further inefficiencies, such as

gearbox A transmission (also called a gearbox) is a mechanical device invented by Louis Renault (who founded Renault) which uses a gear set—two or more gears working together—to change the speed, direction of rotation, or torque multiplication/r ...

, generator, and converter losses, reduce the power delivered by a wind turbine. To protect components from undue wear, extracted power is held constant above the rated operating speed as theoretical power increases as the cube of wind speed, further reducing theoretical efficiency. In 2001, commercial utility-connected turbines delivered 75% to 80% of the Betz limit of power extractable from the wind, at rated operating speed. Efficiency can decrease slightly over time, one of the main reasons being dust and insect carcasses on the blades, which alter the aerodynamic profile and essentially reduce the lift to drag ratio of the

airfoil An airfoil (American English) or aerofoil (British English) is a streamlined body that is capable of generating significantly more Lift (force), lift than Drag (physics), drag. Wings, sails and propeller blades are examples of airfoils. Foil (fl ...

. Analysis of 3128 wind turbines older than 10 years in Denmark showed that half of the turbines had no decrease, while the other half saw a production decrease of 1.2% per year. In general, more stable and constant weather conditions (most notably wind speed) result in an average of 15% greater efficiency than that of a wind turbine in unstable weather conditions, thus allowing up to a 7% increase in wind speed under stable conditions. This is due to a faster recovery wake and greater flow entrainment that occur in conditions of higher atmospheric stability. However, wind turbine wakes have been found to recover faster under unstable atmospheric conditions as opposed to a stable environment. Different materials have varying effects on the efficiency of wind turbines. In an Ege University experiment, three wind turbines, each with three blades with a diameter of one meter, were constructed with blades made of different materials: A glass and glass/carbon

epoxy Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy Resin, resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide fun ...

, glass/carbon, and glass/polyester. When tested, the results showed that the materials with higher overall masses had a greater friction moment and thus a lower power coefficient. The air velocity is the major contributor to the turbine efficiency. This is the reason for the importance of choosing the right location. The wind velocity will be high near the shore because of the temperature difference between the land and the ocean. Another option is to place turbines on mountain ridges. The higher the wind turbine will be, the higher the wind velocity on average. A

windbreak A windbreak (shelterbelt) is a planting usually made up of one or more rows of trees or shrubs planted in such a manner as to provide shelter from the wind and to protect soil from erosion. They are commonly planted in hedgerows around the ed ...

can also increase the wind velocity near the turbine.

Types

Wind turbines can rotate about either a horizontal or a vertical axis, the former being both older and more common. They can also include blades or be bladeless. Household-size vertical designs produce less power and are less common.

Horizontal axis

Large three-bladed horizontal-axis wind turbines (HAWT) with the blades upwind of the tower (blades facing the incoming wind) produce the overwhelming majority of wind power in the world today. These turbines have the main

rotor ROTOR was an elaborate air defence radar system built by the British Government in the early 1950s to counter possible attack by Soviet bombers. To get it operational as quickly as possible, it was initially made up primarily of WWII-era syst ...

shaft and

electrical generator In electricity generation, a generator, also called an ''electric generator'', ''electrical generator'', and ''electromagnetic generator'' is an electromechanical device that converts mechanical energy to electrical energy for use in an extern ...

at the top of a tower and must be pointed into the wind. Small turbines are pointed by a simple

wind vane A wind vane, weather vane, or weathercock is an list of weather instruments, instrument used for showing the wind direction, direction of the wind. It is typically used as an architectural ornament to the highest point of a building. The word ' ...

, while large turbines generally use a wind sensor coupled with a yaw system. 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. Some turbines use a different type of generator suited to slower rotational speed input. These do not need a gearbox and are called direct-drive, meaning they couple the rotor directly to the generator with no gearbox in between. While

permanent magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, c ...

direct-drive generators can be more costly due to the rare earth materials required, these gearless turbines are sometimes preferred over gearbox generators because they "eliminate the gear-speed increaser, which is susceptible to significant accumulated fatigue torque loading, related reliability issues, and maintenance costs". There is also the pseudo direct drive mechanism, which has some advantages over the permanent magnet direct drive mechanism. Most horizontal axis turbines have their rotors upwind of the supporting tower. Downwind machines have been built, because they don't need an additional mechanism for keeping them in line with the wind. In high winds, downwind blades can also be designed to bend more than upwind ones, which reduces their swept area and thus their wind resistance, mitigating risk during gales. Despite these advantages, upwind designs are preferred, because the pulsing change in loading from the wind as each blade passes behind the supporting tower can cause damage to the turbine. Turbines used in

s for commercial production of electric power are usually three-bladed. These have low

torque ripple Torque ripple is an effect seen in many electric motor designs, referring to a periodic increase or decrease in output torque as the motor shaft rotates. It is measured as the difference in maximum and minimum torque over one complete revolution, ge ...

, which contributes to good reliability. The blades are usually colored white for daytime visibility by aircraft and range in length from . The size and height of turbines increase year by year. Offshore wind turbines are built up to 8 MW today and have a blade length up to . Designs with 10 to 12 MW were in preparation in 2018, and a "15 MW+" prototype with three blades was planned to be constructed as of 2022. The average hub height of horizontal axis wind turbines is 90 meters.

Vertical axis

Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically. One advantage of this arrangement is that the turbine does not need to be pointed into the wind to be effective, which is an advantage on a site where the wind direction is highly variable. It is also an advantage when the turbine is integrated into a building because it is inherently less steerable. Also, the generator and gearbox can be placed near the ground, using a direct drive from the rotor assembly to the ground-based gearbox, improving accessibility for maintenance. However, these designs produce much less energy averaged over time, which is a major drawback. Vertical turbine designs have much lower efficiency than standard horizontal designs. The key disadvantages include the relatively low rotational speed with the consequential higher

torque In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...

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. 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 a rooftop mounted turbine tower is approximately 50% of the building height it is near the optimum for maximum wind energy and minimum wind turbulence. While wind speeds within the built environment are generally much lower than at exposed rural sites, noise may be a concern and an existing structure may not adequately resist the additional stress. Subtypes of the vertical axis design include:

Darrieus wind turbine

"Eggbeater" turbines, or Darrieus turbines, were named after the French inventor, Georges Darrieus. They have good efficiency, but produce large

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 the blade area divided by the rotor area.

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. The advantages of variable pitch are high starting torque; a wide, relatively flat torque curve; a higher

coefficient of performance The coefficient of performance or COP (sometimes CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work (energy) required. Higher COPs equate to higher efficiency, lower energy ( ...

; 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.

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 is a modified savonius, with long helical scoops to provide smooth torque. This is often used as a rooftop wind turbine and has even been adapted for ships.

Airborne wind turbine

Airborne wind turbines consist of wings or a small aircraft tethered to the ground. They are useful for reaching faster winds above which traditional turbines can operate. There are prototypes in operation in east Africa.

Floating wind turbine

These are offshore wind turbines that are supported by a floating platform. By having them float, they are able to be installed in deeper water allowing more of them. This also allows them to be further out of sight from land and therefore less public concern about the visual appeal.

Unconventional types

Design and construction

Wind turbine design is a careful balance of cost, energy output, and fatigue life.

Components

Wind turbines convert wind energy to electrical energy for distribution. Conventional horizontal axis turbines can be divided into three components: * The rotor, which is approximately 20% of the wind turbine cost, includes the blades for converting wind energy to low-speed rotational energy. * The generator, which is approximately 34% of the wind turbine cost, includes the

, the control electronics, and most likely a

(e.g., planetary gear box),

adjustable-speed drive A motor drive is a physical system that includes a motor. An adjustable speed motor drive is a system that includes a motor that has multiple operating speeds. A variable speed motor drive is a system that includes a motor that is continuously v ...

, or

continuously variable transmission A continuously variable transmission (CVT) is an automated Transmission (mechanical device), transmission that can change through a continuous range of gear ratios, typically resulting in better fuel economy in gasoline applications. This contr ...

component for converting the low-speed incoming rotation to high-speed rotation suitable for generating electricity. * The surrounding structure, which is approximately 15% of the wind turbine cost, includes the tower and rotor yaw mechanism. A 1.5 ( MW) wind turbine of a type frequently seen in the United States has a tower high. The rotor assembly (blades and hub) measures about in diameter. The

nacelle A nacelle ( ) is a streamlined container for aircraft parts such as Aircraft engine, engines, fuel or equipment. When attached entirely outside the airframe, it is sometimes called a pod, in which case it is attached with a Hardpoint#Pylon, pylo ...

, which contains the generator, is and weighs around 300 tons.

Turbine monitoring and diagnostics

Due to data transmission problems,

structural health monitoring Structural health monitoring (SHM) involves the observation and analysis of a system over time using periodically sampled response measurements to monitor changes to the material and geometric properties of engineering structures such as bridges ...

of wind turbines is usually performed using several accelerometers and strain gages attached to the nacelle to monitor the gearbox and equipment. Currently,

digital image correlation Digital image correlation and tracking is an optical method that employs tracking and image registration techniques for accurate 2D and 3D measurements of changes in 2D images or 3D volumes. This method is often used to measure full-field displac ...

and

stereophotogrammetry Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant ima ...

are used to measure dynamics of wind turbine blades. These methods usually measure displacement and strain to identify location of defects. Dynamic characteristics of non-rotating wind turbines have been measured using digital image correlation and photogrammetry. Three dimensional point tracking has also been used to measure rotating dynamics of wind turbines.

Technology

Generally, efficiency increases along with turbine blade lengths. The blades must be stiff, strong, durable, light and resistant to fatigue. Materials with these properties include composites such as polyester and epoxy, while glass fiber and carbon fiber have been used for the reinforcing. Construction may involve manual layup or injection molding. Retrofitting existing turbines with larger blades reduces the task and risks of redesign. As of 2021, the longest blade was , producing 15 MW. Blades usually last around 20 years, the typical lifespan of a wind turbine.

Blade materials

Materials commonly used in wind turbine blades are described below.

Glass and carbon fibers

Turbine Blade Convoy Passing through Edenfield

The stiffness of composites is determined by the stiffness of fibers and their volume content. Typically, E-glass fibers are used as main reinforcement in the composites. Typically, the glass/epoxy composites for wind turbine blades contain up to 75% glass by weight. This increases the stiffness, tensile and compression strength. A promising composite material is glass fiber with modified compositions like S-glass, R-glass etc. Other glass fibers developed by Owens Corning are ECRGLAS, Advantex and WindStrand. Carbon fiber has more tensile strength, higher stiffness and lower density than glass fiber. An ideal candidate for these properties is the spar cap, a structural element of a blade that experiences high tensile loading. A glass fiber blade could weigh up to , while using carbon fiber in the spar saves 20% to 30% weight, about .

Hybrid reinforcements

Instead of making wind turbine blade reinforcements from pure glass or pure carbon, hybrid designs trade weight for cost. For example, for an blade, a full replacement by carbon fiber would save 80% of weight but increase costs by 150%, while a 30% replacement would save 50% of weight and increase costs by 90%. Hybrid reinforcement materials include E-glass/carbon, E-glass/aramid. The current longest blade by LM Wind Power is made of carbon/glass hybrid composites. More research is needed about the optimal composition of materials.

Nano-engineered polymers and composites

Additions of small amount (0.5 weight %) of nanoreinforcement (

carbon nanotubes A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized: * ''Single-walled carbon nanotubes'' (''SWC ...

or nanoclay) in the polymer matrix of composites, fiber sizing or inter-laminar layers can improve fatigue resistance, shear or compressive strength, and fracture toughness of the composites by 30% to 80%. Research has also shown that incorporating small amounts of carbon nanotubes (CNT) can increase the lifetime up to 1500%.

Costs

, the

capital cost {{no footnotes, date=December 2016 Capital costs are fixed, one-time expenses incurred on the purchase of land, buildings, construction, and equipment used in the production of goods or in the rendering of services. In other words, it is the total ...

of a wind turbine was around $1 million per megawatt of

nameplate capacity Nameplate capacity, also known as the rated capacity, nominal capacity, installed capacity, maximum effect or gross capacity, Modern turbines use a couple of tons of copper for generators and cables and such. , global production of wind turbines use of copper per year.

Material supply

A 2015 study of the material consumption trends and requirements for wind energy in Europe found that bigger turbines have a higher consumption of precious metals but lower material input per kW generated. The material consumption and stock at that time was compared to input materials for various onshore system sizes. In all EU countries, the estimates for 2020 doubled the values consumed in 2009. These countries would need to expand their resources to meet the estimated demand for 2020. For example, the EU had 3% of world supply of

fluorspar Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs scal ...

, and it would require 14% by 2020. Globally, the main exporting countries are South Africa, Mexico, and China. This is similar with other critical and valuable materials required for energy systems such as magnesium, silver and indium. The levels of recycling of these materials are very low, and focusing on that could alleviate supply. Because most of these valuable materials are also used in other emerging technologies, like

light emitting diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

s (LEDs), photo voltaics (PVs) and

liquid crystal display A liquid-crystal display (LCD) is a flat-panel display or other Electro-optic modulator, electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers to display information. Liq ...

s (LCDs), their demand is expected to grow. A 2011 study by the United States Geological Survey estimated resources required to fulfill the US commitment to supplying 20% of its electricity from wind power by 2030. It did not consider requirements for small turbines or offshore turbines because those were not common in 2008 when the study was done. Common materials such as cast iron, steel and concrete would increase by 2%–3% compared to 2008. Between 110,000 and 115,000 metric tons of fiber glass would be required per year, a 14% increase. Rare-earth metal use would not increase much compared to available supply, however rare-earth metals that are also used for other technologies such as batteries which are increasing its global demand need to be taken into account. Land required would be 50,000 square kilometers onshore and 11,000 offshore. This would not be a problem in the US due to its vast area and because the same land can be used for farming. A greater challenge would be the variability and transmission to areas of high demand. Permanent magnets for wind turbine generators contain rare-earth metals such as

(Nd),

(Pr),

terbium Terbium is a chemical element; it has Symbol (chemistry), symbol Tb and atomic number 65. It is a silvery-white, rare earth element, rare earth metal that is malleable and ductile. The ninth member of the lanthanide series, terbium is a fairly ele ...

(Tb), and

(Dy). Systems that use magnetic direct drive turbines require greater amounts of rare-earth metals. Therefore, an increase in wind turbine manufacture would increase the demand for these resources. By 2035, the demand for Nd is estimated to increase by 4,000 to 18,000 tons and for Dy by 200 to 1,200 tons. These values are a quarter to half of current production. However, these estimates are very uncertain because technologies are developing rapidly. Reliance on

rare earth mineral A rare-earth mineral contains one or more rare-earth elements as major metal constituents. Rare-earth minerals are usually found in association with alkaline to peralkaline igneous magmas in pegmatites or with carbonatite intrusives. Perovs ...

s for components has risked expense and price volatility as China has been main producer of rare earth minerals (96% in 2009) and was reducing its export quotas. However, in recent years, other producers have increased production and China has increased export quotas, leading to higher supply, lower cost, and greater viability of large-scale use of variable-speed generators. Glass fiber is the most common material for reinforcement. Its demand has grown due to growth in construction, transportation and wind turbines. Its global market might reach US$17.4 billion by 2024, compared to US$8.5 billion in 2014. In 2014, Asia Pacific produced more than 45% of the market; now China is the largest producer. The industry receives subsidies from the Chinese government allowing it to export cheaper to the US and Europe. However, price wars have led to anti-dumping measures such as tariffs on Chinese glass fiber.

Wind turbines on public display

A few localities have exploited the attention-getting nature of wind turbines by placing them on public display, either with visitor centers around their bases, or with viewing areas farther away. The wind turbines are generally of conventional horizontal-axis, three-bladed design and generate power to feed electrical grids, but they also serve the unconventional roles of technology demonstration, public relations, and education. The Bahrain World Trade Center is an example of wind turbines displayed prominently for the public. It is the first skyscraper to integrate wind turbines into its design

Small wind turbines

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 Caravan or caravans may refer to: Transport and travel *Campervan, a type of vehicle also known as a motor caravan *Caravan (travellers), a group of travellers journeying together **Caravanserai, a place where a caravan could stop *Caravan (trail ...

use. Hybrid solar- and wind-powered units are increasingly being used for traffic signage, particularly in rural locations, since they avoid the need to lay long cables from the nearest mains connection point. The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) defines small wind turbines as those smaller than or equal to 100 kilowatts. Small units often have direct-drive generators,

direct current Direct current (DC) is one-directional electric current, flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor (material), conductor such as a wire, but can also flow throug ...

output, aeroelastic blades, and lifetime bearings and use a vane to point into the wind.

Wind turbine spacing

On most horizontal wind turbine 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 economical, taking into account typical wind turbine and land costs. This conclusion has been reached by research conducted by Charles Meneveau of Johns Hopkins University and Johan Meyers of Leuven University in Belgium, based on computer simulations that take into account the detailed interactions among wind turbines (wakes) as well as with the entire turbulent atmospheric boundary layer. 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 neighbouring turbines to move in the same direction as they approach one another.

Operability

Maintenance

Wind turbines need regular

maintenance The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure and supporting utilities in industrial, business, and residential installa ...

to stay

reliable Reliability, reliable, or unreliable may refer to: Science, technology, and mathematics Computing * Data reliability (disambiguation), a property of some disk arrays in computer storage * Reliability (computer networking), a category used to des ...

and available. In the best case turbines are available to generate energy 98% of the time. Ice accretion on turbine blades has been found to greatly reduce the efficiency of wind turbines, which is a common challenge in cold climates where in-cloud icing and freezing rain events occur.

Deicing De-icing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only de-ice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or pr ...

is mainly performed by internal heating or in some cases, by helicopters spraying clean warm water on the blades. Modern turbines usually have a small onboard crane for hoisting maintenance tools and minor components. However, large, heavy components like generators, gearboxes, blades, and so on are rarely replaced, and a heavy lift external crane is needed in those cases. If the turbine has a difficult access road, a containerized crane can be lifted up by the internal crane to provide heavier lifting.

Repowering

Installation of new wind turbines can be controversial. An alternative is repowering, where existing wind turbines are replaced with bigger, more powerful ones, sometimes in smaller numbers while keeping or increasing capacity.

Demolition and recycling

Some wind turbines which are out of use are

recycled Recycling is the process of converting waste materials into new materials and objects. This concept often includes the recovery of energy from waste materials. The recyclability of a material depends on its ability to reacquire the propert ...

or repowered. 85% of turbine materials are easily reused or recycled, but the blades, made of a composite material, are more difficult to process. Interest in recycling blades varies in different markets and depends on the waste legislation and local economics. A challenge in recycling blades is related to the composite material, which is made of

fiberglass Fiberglass (American English) or fibreglass (English in the Commonwealth of Nations, Commonwealth English) is a common type of fibre-reinforced plastic, fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened i ...

with carbon fibers in epoxy resin, which cannot be remolded to form new composites. Wind farm waste is less toxic than other garbage. Wind turbine blades represent only a fraction of overall waste in the US, according to the wind-industry

trade association A trade association, also known as an industry trade group, business association, sector association or industry body, is an organization founded and funded by businesses that operate in a specific Industry (economics), industry. Through collabor ...

American Wind Energy Association The American Wind Energy Association (AWEA) was a Washington, D.C.–based national trade association formed in 1974, representing wind power project developers, equipment suppliers, service providers, parts manufacturers, utilities, researchers ...

. Several utilities, startup companies, and researchers are developing methods for reusing or recycling blades. Manufacturer

Vestas Vestas Wind Systems A/S is a Danish manufacturer, seller, installer, and servicer of wind turbines that was founded in 1945. The company operates manufacturing plants in Denmark, Germany, the Netherlands, Taiwan, India, Italy, Romania, the Un ...

has developed technology that can separate the fibers from the resin, allowing for reuse. In Germany, wind turbine blades are commercially recycled as part of an alternative fuel mix for a cement factory. In the United Kingdom, a project will trial cutting blades into strips for use as rebar in

concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...

, with the aim of reducing emissions in the construction of

High Speed 2 High Speed 2 (HS2) is a high-speed railway which has been under construction in England since 2019. The line's planned route is between Handsacre – in southern Staffordshire – and London, with a Spur line, branch to Birmingham. HS2 is to ...

. Used wind turbine blades have been recycled by incorporating them as part of the support structures within pedestrian bridges in Poland and Ireland.

Comparison with other power sources

Advantages

Wind turbines is one of the lowest-cost sources of renewable energy along with

solar panel A solar panel is a device that converts sunlight into electricity by using photovoltaic (PV) cells. PV cells are made of materials that produce excited electrons when exposed to light. These electrons flow through a circuit and produce direct ...

s. As technology needed for wind turbines continued to improve, the prices decreased as well. In addition, there is currently no competitive market for wind energy (though there may be in the future), because wind is a freely available natural resource, most of which is untapped. The main cost of small wind turbines is the purchase and installation process, which averages between $48,000 and $65,000 per installation. Usually, the total amount of energy harvested amounts to more than the cost of the turbines. Wind turbines provide a clean energy source, use little water, emitting no greenhouse gases and no waste products during operation. Over of carbon dioxide per year can be eliminated by using a one-megawatt turbine instead of one megawatt of energy from a fossil fuel.

Disadvantages

Wind turbines can be very large, reaching over tall with blades long, and people have often complained about their visual impact.

Environmental impact of wind power The environmental impact of electricity generation from wind power is minor when compared to that of Fossil fuel power station, fossil fuel power. Wind turbines have some of the lowest global warming potential per unit of electricity generated ...

includes effect on wildlife, but can be mitigated if proper strategies are implemented. Thousands of birds, including rare species, have been killed by the blades of wind turbines, though wind turbines contribute relatively insignificantly to anthropogenic avian mortality (birds killed by humans). Wind farms and

nuclear power plant A nuclear power plant (NPP), also known as a nuclear power station (NPS), nuclear generating station (NGS) or atomic power station (APS) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power st ...

s are responsible for between 0.3 and 0.4 bird deaths per gigawatt-hour (GWh) of electricity while

fossil fuel power station A fossil fuel power station is a thermal power station that burns fossil fuel, such as coal, oil, or natural gas, to produce electricity. Fossil fuel power stations have machines that convert the heat energy of combustion into mechanical ene ...

s are responsible for about 5.2 fatalities per GWh. In comparison, conventional coal-fired generators contribute significantly more to bird mortality. A study on recorded bird populations in the United States from 2000 to 2020 found the presence of wind turbines had no significant effect on bird population numbers. Energy harnessed by wind turbines is variable, and is not a "dispatchable" source of power; its availability is based on whether the wind is blowing, not whether electricity is needed. Turbines can be placed on

ridge A ridge is a long, narrow, elevated geomorphologic landform, structural feature, or a combination of both separated from the surrounding terrain by steep sides. The sides of a ridge slope away from a narrow top, the crest or ridgecrest, wi ...

s or bluffs to maximize the access of wind they have, but this also limits the locations where they can be placed. In this way, wind energy is not a particularly reliable source of energy. However, it can form part of the

energy mix The energy mix is a group of different primary energy, primary energy sources from which secondary energy for direct use - such as electricity - is produced. Energy mix refers to all direct uses of energy, such as transportation and housing, and ...

, which also includes power from other sources. Technology is also being developed to store excess energy, which can then make up for any deficits in supplies. Wind turbines have blinking lights that warn aircraft, to avoid collisions. Residents living near windfarms, especially those in rural areas, have complained that the blinking lights are a bothersome form of

light pollution Light pollution is the presence of any unwanted, inappropriate, or excessive artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting sources, during the ...

. A light mitigation approach involves Aircraft Detection Lighting Systems (ADLSs) by which the lights are turned on, only when the ADLS's

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

detects aircraft within thresholds of altitude and distance.

Records

''See also List of most powerful wind turbines''

References

External links

Global Wind Energy Council

World's Largest Wind Turbine

Harvesting the Wind (45 lectures about wind turbines by professor Magdi Ragheb
{{Authority control Aerodynamics Bright green environmentalism Electric power Electrical generators Electromechanical engineering Energy conversion Wind farms