Turbina eólica

Machine which converts wind energy into mechanical and electric energy

Este artículo trata sobre generadores eléctricos eólicos. Para la maquinaria de energía eólica utilizado para grano molido o el agua de la bomba, ver molino de viento y Windpump .

Parque eólico Thorntonbank , que utiliza turbinas de 5 MW REpower 5M en el Mar del Norte frente a las costas de Bélgica .

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v t mi

Una turbina de viento es un dispositivo que convierte el viento energía cinética en energía eléctrica .

Los aerogeneradores se fabrican en una amplia gama de tamaños, con ejes horizontales o verticales. Se estima que cientos de miles de grandes turbinas , en instalaciones conocidas como parques eólicos , ahora generan más de 650 gigavatios de energía, con 60 GW agregados cada año. ^[1] Son una fuente cada vez más importante de energía renovable intermitente y se utilizan en muchos países para reducir los costos de energía y reducir la dependencia de los combustibles fósiles . Un estudio afirmó que, a partir de 2009 ^[update], la energía eólica tenía las "emisiones relativas más bajas de gases de efecto invernadero, las menores demandas de consumo de agua y ... los impactos sociales más favorables" en comparación con la energía fotovoltaica, hidroeléctrica, geotérmica, carbón y gas.^[2]

Las turbinas eólicas más pequeñas se utilizan para aplicaciones como la carga de baterías para energía auxiliar para barcos o caravanas , y para alimentar señales de advertencia de tráfico. Las turbinas más grandes pueden contribuir a un suministro de energía doméstico mientras venden la energía no utilizada al proveedor de servicios públicos a través de la red eléctrica .

Historia

Artículo principal: Historia de la energía eólica

La turbina eólica generadora de electricidad de James Blyth , fotografiada en 1891

Turbinas eólicas Nashtifan en Sistan , Irán.

La rueda de viento de Hero of Alexandria (10 d. C. - 70 d. C.) marca uno de los primeros casos registrados de energía eólica en la historia. ^{[3] [4]} Sin embargo, las primeras plantas de energía eólica prácticas conocidas se construyeron en Sistan , una provincia oriental de Persia (ahora Irán), a partir del siglo VII. Estos " Panemone " eran molinos de viento de eje vertical, que tenían ejes de transmisión verticales largos con palas rectangulares. ^[5] Hechos de seis a doce velas cubiertas con esteras de caña o material de tela, estos molinos de viento se usaban para moler granos o extraer agua, y se usaban en las industrias de molienda y caña de azúcar. ^[6]

La energía eólica apareció por primera vez en Europa durante la Edad Media . Los primeros registros históricos de su uso en Inglaterra datan de los siglos XI o XII, hay informes de cruzados alemanes que llevaron sus habilidades de fabricación de molinos de viento a Siria alrededor de 1190. ^[7] En el siglo XIV, los molinos de viento holandeses se usaban para drenar áreas del delta del Rin . Las turbinas eólicas avanzadas fueron descritas por el inventor croata Fausto Veranzio . En su libro Machinae Novae (1595) describió aerogeneradores de eje vertical con palas curvas o en forma de V.

La primera turbina eólica generadora de electricidad fue una máquina de carga de baterías instalada en julio de 1887 por el académico escocés James Blyth para iluminar su casa de vacaciones en Marykirk , Escocia. ^[8] Algunos meses más tarde, el inventor estadounidense Charles F. Brush pudo construir la primera turbina eólica operada automáticamente después de consultar a los profesores y colegas de la Universidad local Jacob S. Gibbs y Brinsley Coleberd y obtener con éxito los planos revisados ​​por pares para la producción de electricidad en Cleveland. Ohio . ^[8] Aunque la turbina de Blyth se consideró antieconómica en el Reino Unido, ^[8]La generación de electricidad mediante turbinas eólicas resultó más rentable en países con poblaciones muy dispersas. ^[7]

La primera turbina eólica operada automáticamente, construida en Cleveland en 1887 por Charles F. Brush. Tenía 60 pies (18 m) de altura, pesaba 4 toneladas (3,6 toneladas métricas) y funcionaba con un generador de 12 kW . ^[9]

En Dinamarca en 1900, había alrededor de 2500 molinos de viento para cargas mecánicas, como bombas y molinos, que producían una potencia máxima combinada estimada de unos 30 MW . Las máquinas más grandes estaban en torres de 24 metros (79 pies) con rotores de cuatro palas de 23 metros (75 pies) de diámetro. En 1908, había 72 generadores eléctricos impulsados ​​por viento operando en los Estados Unidos de 5 kW a 25 kW. Alrededor de la época de la Primera Guerra Mundial, los fabricantes de molinos de viento estadounidenses producían 100.000 molinos de viento agrícolas cada año, principalmente para bombear agua. ^[10]

En la década de 1930, los generadores eólicos para electricidad eran comunes en las granjas, principalmente en los Estados Unidos, donde aún no se habían instalado sistemas de distribución. En este período, el acero de alta resistencia era barato y los generadores se colocaban encima de torres de celosía de acero abiertas prefabricadas.

Un precursor de los modernos generadores eólicos de eje horizontal estuvo en servicio en Yalta , URSS en 1931. Este era un generador de 100 kW en una torre de 30 metros (98 pies), conectado al sistema de distribución local de 6,3 kV. Se informó que tenía un factor de capacidad anual del 32 por ciento, no muy diferente de las máquinas eólicas actuales. ^{[11] [12]}

En el otoño de 1941, la primera turbina eólica de clase megavatio se sincronizó con una red de servicios públicos en Vermont . La turbina eólica Smith-Putnam funcionó solo durante 1.100 horas antes de sufrir una falla crítica. La unidad no fue reparada debido a la escasez de materiales durante la guerra.

La primera turbina eólica conectada a la red de servicios públicos que funcionó en el Reino Unido fue construida por John Brown & Company en 1951 en las Islas Orkney . ^{[8] [13]}

A pesar de estos diversos desarrollos, los desarrollos en los sistemas de combustibles fósiles eliminaron casi por completo cualquier sistema de turbinas eólicas más grande que el tamaño supermicro. Sin embargo, a principios de la década de 1970, las protestas antinucleares en Dinamarca impulsaron a los mecánicos artesanales a desarrollar microturbinas de 22 kW . La organización de los propietarios en asociaciones y cooperativas llevó al cabildeo del gobierno y las empresas de servicios públicos y proporcionó incentivos para turbinas más grandes a lo largo de la década de 1980 y posteriores. Activistas locales en Alemania, fabricantes nacientes de turbinas en España y grandes inversores en los Estados Unidos a principios de la década de 1990 presionaron luego por políticas que estimularan la industria en esos países.

Se ha argumentado que la expansión del uso de la energía eólica conducirá a una mayor competencia geopolítica sobre los materiales críticos para las turbinas eólicas, como los elementos de tierras raras neodimio, praseodimio y disprosio. Pero esta perspectiva ha sido criticada por no reconocer que la mayoría de las turbinas eólicas no utilizan imanes permanentes y por subestimar el poder de los incentivos económicos para expandir la producción de estos minerales. ^[14]

Recursos

Artículo principal: energía eólica

La densidad de energía eólica (WPD) es una medida cuantitativa de la energía eólica disponible en cualquier ubicación. Es la potencia anual media disponible por metro cuadrado de área barrida de una turbina y se calcula para diferentes alturas sobre el suelo. El cálculo de la densidad de la energía eólica incluye el efecto de la velocidad del viento y la densidad del aire. ^[15]

Las turbinas eólicas se clasifican según la velocidad del viento para la que están diseñadas, desde la clase I hasta la clase III, siendo A a C la intensidad de la turbulencia del viento. ^[dieciséis]

Clase	Velocidad media del viento (m / s)	Turbulencia
I A	10	dieciséis%
IB	10	14%
IC	10	12%
IIA	8.5	dieciséis%
IIB	8.5	14%
IIC	8.5	12%
IIIA	7.5	dieciséis%
IIIB	7.5	14%
IIIC	7.5	12%

Eficiencia

La conservación de la masa requiere que la cantidad de aire que entra y sale de una turbina sea igual. En consecuencia, la ley de Betz da la máxima extracción alcanzable de energía eólica por una turbina eólica como 16/27 (59,3%) de la velocidad a la que la energía cinética del aire llega a la turbina. ^[17]

La salida de potencia teórica máxima de una máquina eólica es, por tanto, 16/27 veces la velocidad a la que la energía cinética del aire llega al área efectiva del disco de la máquina. Si el área efectiva del disco es A y la velocidad del viento v, la salida de potencia teórica máxima P es:

${\displaystyle P={\frac {16}{27}}{\frac {1}{2}}\rho v^{3}A={\frac {8}{27}}\rho v^{3}A}$,

donde ρ es la densidad del aire .

La eficiencia viento-rotor (incluida la fricción y el arrastre de las palas del rotor ) se encuentran entre los factores que afectan el precio final de la energía eólica. ^[18] Otras ineficiencias, como las pérdidas de la caja de cambios , las pérdidas del generador y del convertidor, reducen la potencia entregada por una turbina eólica. Para proteger los componentes del desgaste indebido, la potencia extraída se mantiene constante por encima de la velocidad de funcionamiento nominal a medida que la potencia teórica aumenta en el cubo de la velocidad del viento, lo que reduce aún más la eficiencia teórica. En 2001, las turbinas comerciales conectadas a los servicios públicos entregaron entre el 75% y el 80% del límite Betz de potencia extraíble del viento, a la velocidad nominal de funcionamiento. ^{[19] [20] [ necesita actualización]}

La eficiencia puede disminuir ligeramente con el tiempo, una de las principales razones es el polvo y los cadáveres de insectos en las palas, lo que altera el perfil aerodinámico y esencialmente reduce la relación de sustentación y arrastre del perfil aerodinámico . El análisis de 3128 turbinas eólicas de más de 10 años en Dinamarca mostró que la mitad de las turbinas no tuvo disminución, mientras que la otra mitad experimentó una disminución de la producción del 1,2% anual. ^[21]

En general, las condiciones meteorológicas más estables y constantes (sobre todo la velocidad del viento) dan como resultado un promedio de un 15% más de eficiencia que la de un aerogenerador en condiciones climáticas inestables, lo que permite un aumento de hasta un 7% en la velocidad del viento en condiciones estables. Esto se debe a una estela de recuperación más rápida y un mayor arrastre de flujo que se produce en condiciones de mayor estabilidad atmosférica. Sin embargo, se ha descubierto que las estelas de las turbinas eólicas se recuperan más rápidamente en condiciones atmosféricas inestables que en un entorno estable. ^[22]

Se ha descubierto que diferentes materiales tienen efectos variables sobre la eficiencia de las turbinas eólicas. En un experimento de la Universidad de Ege, se construyeron tres turbinas eólicas (cada una con tres palas con un diámetro de un metro) con palas hechas de diferentes materiales: vidrio y vidrio / epoxi de carbono, vidrio / carbono y vidrio / poliéster. Cuando se probaron, los resultados mostraron que los materiales con masas totales más altas tenían un mayor momento de fricción y, por lo tanto, un coeficiente de potencia más bajo. ^[23]

Tipos

Los tres tipos principales: VAWT Savonius , HAWT con torre; VAWT Darrieus como aparecen en funcionamiento

Las turbinas eólicas pueden girar sobre un eje horizontal o vertical, siendo el primero más antiguo y más común. ^[24] También pueden incluir cuchillas o no tener cuchillas. ^[25] Los diseños verticales producen menos energía y son menos comunes. ^[26]

Eje horizontal

Los componentes de una turbina eólica de eje horizontal (caja de cambios, eje del rotor y conjunto de freno) se elevan a su posición

Un convoy de palas de turbina pasando por Edenfield , Inglaterra

Turbinas eólicas offshore de eje horizontal (HAWT) en el parque eólico Scroby Sands, Inglaterra

Turbinas de viento de eje horizontal en tierra en Zhangjiakou , Hebei , China

Las grandes turbinas eólicas de eje horizontal de tres palas (HAWT) con las palas a barlovento de la torre producen la abrumadora mayoría de la energía eólica en el mundo actual. Estas turbinas tienen el eje del rotor principal y el generador eléctrico en la parte superior de una torre, y deben apuntar hacia el viento. Las turbinas pequeñas son apuntadas por una simple veleta , mientras que las turbinas grandes generalmente usan un sensor de viento junto con un sistema de guiñada. La mayoría tiene una caja de cambios, que convierte la rotación lenta de las palas en una rotación más rápida que es más adecuada para impulsar un generador eléctrico. ^[27]Algunas turbinas utilizan un tipo diferente de generador adecuado para una entrada de velocidad de rotación más lenta. Estos no necesitan una caja de cambios y se denominan transmisión directa, lo que significa que acoplan el rotor directamente al generador sin caja de cambios en el medio. Si bien los generadores de accionamiento directo de imanes permanentes pueden ser más costosos debido a los materiales de tierras raras requeridos, estas turbinas sin engranajes a veces se prefieren a los generadores de caja de engranajes porque "eliminan el incrementador de velocidad de engranajes, que es susceptible a una carga de par de fatiga acumulada significativa, confiabilidad relacionada problemas y costos de mantenimiento ". ^[28] También existe el mecanismo de accionamiento pseudo directo, que tiene algunas ventajas sobre el mecanismo de accionamiento directo de imán permanente. ^{[29] [30]}

Se está configurando el rotor de una turbina eólica sin engranajes . Esta turbina en particular fue prefabricada en Alemania, antes de ser enviada a los EE. UU. Para su ensamblaje.

La mayoría de las turbinas de eje horizontal tienen sus rotores a barlovento de la torre de soporte. Se han construido máquinas de sotavento, porque no necesitan un mecanismo adicional para mantenerlas alineadas con el viento. En vientos fuertes, también se puede permitir que las palas se doblen, lo que reduce su área de barrido y, por lo tanto, su resistencia al viento. A pesar de estas ventajas, se prefieren los diseños a barlovento, porque el cambio en la carga del viento cuando cada pala pasa por detrás de la torre de soporte puede dañar la turbina.

Las turbinas que se utilizan en los parques eólicos para la producción comercial de energía eléctrica suelen ser de tres palas. Estos tienen una ondulación de par baja , lo que contribuye a una buena fiabilidad. Las palas suelen ser de color blanco para la visibilidad diurna de los aviones y tienen una longitud de 20 a 80 metros (66 a 262 pies). El tamaño y la altura de las turbinas aumentan año tras año. Las turbinas eólicas marinas se construyen hoy en día hasta 8 MW y tienen una longitud de pala de hasta 80 metros (260 pies). Se están preparando diseños con 10 a 12 MW. ^[31] Las turbinas habituales de varios megavatios tienen torres de acero tubular con una altura de 70  ma 120  my en los extremos hasta 160  m.

Eje vertical

Una turbina de eje vertical tipo Twisted Savonius.

Las turbinas eólicas de eje vertical (o VAWT) tienen el eje del rotor principal dispuesto verticalmente. Una ventaja de esta disposición es que la turbina no necesita apuntar hacia el viento para ser efectiva, lo cual es una ventaja en un sitio donde la dirección del viento es muy variable. También es una ventaja cuando la turbina está integrada en un edificio porque es intrínsecamente menos orientable. Además, el generador y la caja de cambios se pueden colocar cerca del suelo, utilizando un accionamiento directo desde el conjunto del rotor a la caja de cambios en el suelo, mejorando la accesibilidad para el mantenimiento. Sin embargo, estos diseños producen mucha menos energía promediada a lo largo del tiempo, lo cual es un gran inconveniente. ^{[26] [32]}

Los diseños de turbinas verticales tienen una eficiencia mucho menor que los diseños horizontales estándar. ^[33] Las desventajas clave incluyen la velocidad de rotación relativamente baja con el consecuente par más alto y, por lo tanto, un mayor costo del tren de transmisión, el coeficiente de potencia inherentemente más bajo , la rotación de 360 ​​grados del perfil aerodinámico dentro del flujo del viento durante cada ciclo y, por lo tanto, el carga altamente dinámica en la pala, el par pulsante generado por algunos diseños de rotor en el tren de transmisión y la dificultad de modelar el flujo del viento con precisión y, por lo tanto, los desafíos de analizar y diseñar el rotor antes de fabricar un prototipo. ^[34]

Cuando se monta una turbina en un tejado, el edificio generalmente redirige el viento sobre el tejado y esto puede duplicar la velocidad del viento en la turbina. Si la altura de una torre de turbina montada en la azotea es aproximadamente el 50% de la altura del edificio, está cerca del óptimo para la máxima energía eólica y la mínima turbulencia eólica. Si bien las velocidades del viento dentro del entorno construido son generalmente mucho más bajas que en los sitios rurales expuestos, ^{[35] [36] el} ruido puede ser una preocupación y una estructura existente puede no resistir adecuadamente el estrés adicional.

Los subtipos del diseño del eje vertical incluyen:

Aerogenerador Darrieus

Las turbinas "batidoras de huevos", o turbinas Darrieus, recibieron su nombre del inventor francés Georges Darrieus. ^[37] Tienen buena eficiencia, pero producen una gran ondulación de par y tensión cíclica en la torre, lo que contribuye a una baja fiabilidad. Por lo general, también requieren alguna fuente de alimentación externa o un rotor Savonius adicional para comenzar a girar, porque el par de arranque es muy bajo. La ondulación del par se reduce mediante el uso de tres o más palas, lo que da como resultado una mayor solidez del rotor. La solidez se mide por el área de la pala dividida por el área del rotor. Las turbinas más nuevas del tipo Darrieus no están sostenidas por cables de sujeción, sino que tienen una superestructura externa conectada al cojinete superior. ^[38]

Giromill

Un subtipo de turbina Darrieus con palas rectas, en oposición a curvas. La variedad de cicloturbina tiene un paso variable para reducir la pulsación del par y es de arranque automático. ^[39] Las ventajas del paso variable son: alto par de arranque; una curva de par ancha y relativamente plana; un coeficiente de rendimiento más alto ; operación más eficiente en vientos turbulentos; y una relación de velocidad de la hoja más baja que reduce las tensiones de flexión de la hoja. Se pueden utilizar hojas rectas, en V o curvas. ^[40]

Aerogenerador Savonius

Estos son dispositivos de tipo arrastre con dos (o más) palas que se utilizan en anemómetros, ventilaciones Flettner (que se ven comúnmente en techos de autobuses y furgonetas) y en algunas turbinas de energía de baja eficiencia y alta confiabilidad. Siempre se inician automáticamente si hay al menos tres cucharadas.

Twisted Savonius es un savonius modificado, con palas helicoidales largas para proporcionar un par suave. Esto se usa a menudo como una turbina eólica en la azotea e incluso se ha adaptado para barcos . ^[41]

Paralelo

La turbina paralela es similar al ventilador de flujo cruzado o al ventilador centrífugo. Utiliza el efecto suelo . Las turbinas de eje vertical de este tipo se han probado durante muchos años: una unidad que produce 10 kW fue construida por el pionero eólico israelí Bruce Brill en la década de 1980. ^{[42] [ fuente no confiable? ]}

Tipos no convencionales

Artículo principal: aerogeneradores no convencionales

Aerogenerador contrarrotante

Aerogenerador de eje vertical costa afuera

Aerogenerador de poste ligero

Diseño y construcción

Main article: Wind turbine design

Components of a horizontal-axis wind turbine

Inside view of a wind turbine tower, showing the tendon cables

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 electrical generator,^[43][44] the control electronics, and most likely a gearbox (e.g., planetary gear box),^[45] adjustable-speed drive, or continuously variable transmission^[46] 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.^[47]

Nacelle of a wind turbine

A 1.5 (MW) wind turbine of a type frequently seen in the United States has a tower 80 meters (260 ft) high. The rotor assembly (blades and hub) weighs 22,000 kilograms (48,000 lb). The nacelle, which contains the generator, weighs 52,000 kilograms (115,000 lb). The concrete base for the tower is constructed using 26,000 kilograms (58,000 lb) reinforcing steel and contains 190 cubic meters (250 cu yd) of concrete. The base is 15 meters (50 ft) in diameter and 2.4 meters (8 ft) thick near the center.^[48]

Turbine monitoring and diagnostics

See also: Wind turbine prognostics

Due to data transmission problems, structural health monitoring 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 and stereophotogrammetry 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.^[49] Three dimensional point tracking has also been used to measure rotating dynamics of wind turbines.^[50]

Recent developments in technology

Wind turbine rotor blades are being made longer to increase efficiency. This requires them to be stiff, strong, light and resistant to fatigue.^[51] Materials with these properties are composites such as polyester and epoxy, while glass fiber and carbon fiber have been used for the reinforcing.^[52] Construction may use manual layup or injection molding.

New designs

Development in size and power of wind turbines, 1990-2016

Companies seek ways to draw greater efficiency from their designs. A predominant way has been to increase blade length and thus rotor diameter. Retrofitting existing turbines with larger blades reduces the work and risks of redesigning the system. The current longest blade is 107 m,^[53] producing 13 MW. Longer blades need to be stiffer to avoid deflection, which requires materials with higher stiffness-to-weight ratio. Because the blades need to function over a 100 million load cycles over a period of 20–25 years, the fatigue of the blade materials is also critical.

Blade materials

Materials commonly used in wind turbine blades are described below.

Glass and carbon fibers

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.^[54]

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 which experiences high tensile loading.^[52] A 100-m glass fiber blade could weigh up to 50 metric tons, while using carbon fiber in the spar saves 20% to 30% weight, about 15 metric tons.^[55] However, because carbon fiber is ten times more expensive, glass fiber is still dominant.

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 8 m 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 ^[56]

Nano-engineered polymers and composites

Additions of small amount (0.5 weight %) of nanoreinforcement (carbon nanotubes or nanoclay) in the polymer matrix of composites, fiber sizing or interlaminar 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

As of 2019^[update], a wind turbine may cost around $1 million per megawatt.^[57]

For the wind turbine blades, while the material cost is much higher for hybrid glass/carbon fiber blades than all-glass fiber blades, labor costs can be lower. Using carbon fiber allows simpler designs that use less raw material. The chief manufacturing process in blade fabrication is the layering of plies. Thinner blades allow reducing the number of layers and so the labor, and in some cases, equate to the cost of labor for glass fiber blades.^[58]

Non-blade materials

Wind turbine parts other than the rotor blades (including the rotor hub, gearbox, frame, and tower) are largely made of steel. Smaller turbines (as well as megawatt-scale Enercon turbines) have begun using aluminum alloys for these components to make turbines lighter and more efficient. This trend may grow if fatigue and strength properties can be improved. Pre-stressed concrete has been increasingly used for the material of the tower, but still requires much reinforcing steel to meet the strength requirement of the turbine. Additionally, step-up gearboxes are being increasingly replaced with variable speed generators, which requires magnetic materials.^[51] In particular, this would require an greater supply of the rare earth metal neodymium.

Modern turbines use a couple of tons of copper for generators, cables and such.^[59] As of 2018^[update], global production of wind turbines use 450,000 tonnes of copper per year.^[60]

Material supply

Nordex wind turbine manufacturing plant in Jonesboro, Arkansas, United States

A 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 current material consumption and stock 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, currently the EU has 3% of world supply of fluorspar and it requires 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 diodes (LEDs), photo voltaics (PVs) and liquid crystal displays (LCDs), their demand is expected to grow.^[61]

A 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 metal use would not increase much compared to available supply, however rare 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.^[62]

Permanent magnets for wind turbine generators contain rare metals such as neodymium (Nd), praseodymium (Pr), Terbium (Tb) and dysprosium (Dy). Systems that use magnetic direct drive turbines require greater amounts of rare 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 1200 tons. These values are a quarter to half of current production. However, these estimates are very uncertain because technologies are developing rapidly.^[63]

Reliance on rare earth minerals 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.^[64] However, in recent years other producers have increased production and China has increased export quotas, leading to a higher supply and lower cost, and a greater viability of large scale use of variable-speed generators.^[65]

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.^[66]

Wind turbines on public display

Main article: Wind turbines on public display

The Nordex N50 wind turbine and visitor centre of Lamma Winds in Hong Kong, China

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.^[67] 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.

Small wind turbines

Main article: Small wind turbine

A small Quietrevolution QR5 Gorlov type vertical axis wind turbine in Bristol, England. Measuring 3 m in diameter and 5 m high, it has a nameplate rating of 6.5 kW to the grid.

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. Hybrid solar and wind powered units are increasingly being used for traffic signage, particularly in rural locations, as they avoid the need to lay long cables from the nearest mains connection point.^[68] 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.^[69] 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, and 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 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^[70] conducted by Charles Meneveau of Johns Hopkins University^[71] and Johan Meyers of Leuven University in Belgium, based on computer simulations^[72] that take into account the detailed interactions among wind turbines (wakes) as well as with the entire turbulent atmospheric boundary layer.

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 neighbouring turbines to move in the same direction as they approach one another.^[73]

Operability

Maintenance

Wind turbines need regular maintenance to stay reliable and available. In the best case turbines are available to generate energy 98% of the time.^[74][75] Ice accretion on turbine blades has also 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.^[76] De-icing is mainly performed by internal heating, or in some cases by helicopter spraying clean warm water on the blades,^[77]

Modern turbines usually have a small onboard crane for hoisting maintenance tools and minor components. However, large, heavy components like generator, gearbox, 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.^[78]

Repowering

Main article: 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

Older turbines were in some early cases not required to be removed when reaching the end of their life. Some still stand, waiting to be recycled or repowered.^[79][80]

A demolition industry develops to recycle offshore turbines at a cost of DKK 2–4 million per (MW), to be guaranteed by the owner.^[81]

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 a thermosetting matrix and glass fibers or a combination of glass and carbon fibers. Thermosetting matrix cannot be remolded to form new composites. So the options are either to send the blade to landfill, to reuse the blade and the composite material elements found in the blade, or to transform the composite material into a new source of material. In Germany, wind turbine blades are commercially recycled as part of an alternative fuel mix for a cement factory. In the USA the town of Casper, Wyoming has buried 1,000 non-recyclable blades in its landfill site, earning $675,000 for the town. It pointed out that wind farm waste is less toxic than other garbage. Wind turbine blades represent a “vanishingly small fraction” of overall waste in the US, according to the American Wind Energy Association.^[82]

In the United Kingdom, a project will trial cutting blades into strips for use as rebar in concrete, with the aim of reducing emissions in the construction of High Speed 2.^[83]

Comparison with fossil-fuel turbines

Advantages

Wind turbines produce electricity at between two and six cents per kilowatt hour, which is one of the lowest-priced renewable energy sources.^[84][85] 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, because wind is a freely available natural resource, most of which is untapped.^[84] The main cost of small wind turbines is the purchase and installation process, which averages between $48,000 and $65,000 per installation. The energy harvested from the turbine will offset the installation cost, as well as provide virtually free energy for years.^[86]

Wind turbines provide a clean energy source, use little water,^[2] emitting no greenhouse gases and no waste products. Over 1,500 tons of carbon dioxide per year can be eliminated by using a one-megawatt turbine instead of one megawatt of energy from a fossil fuel.^[87]

Disadvantages

Wind turbines can be very large, reaching over 140 m (460 ft) tall and with blades 55 m (180 ft) long,^[88] and people have often complained about their visual impact.

Environmental impact of wind power includes effect on wildlife, but can be mitigated if proper monitoring and mitigation strategies are implemented.^[89] Thousands of birds, including rare species, have been killed by the blades of wind turbines,^[90] though wind turbines contribute relatively insignificantly to anthropogenic avian mortality. Wind farms and nuclear power stations are responsible for between 0.3 and 0.4 bird deaths per gigawatt-hour (GWh) of electricity while fossil fueled power stations are responsible for about 5.2 fatalities per GWh. In 2009, for every bird killed by a wind turbine in the US, nearly 500,000 were killed by cats and another 500,000 by buildings.^[91] In comparison, conventional coal fired generators contribute significantly more to bird mortality, by incineration when caught in updrafts of smoke stacks and by poisoning with emissions byproducts (including particulates and heavy metals downwind of flue gases). Further, marine life is affected by water intakes of steam turbine cooling towers (heat exchangers) for nuclear and fossil fuel generators, by coal dust deposits in marine ecosystems (e.g. damaging Australia's Great Barrier Reef) and by water acidification from combustion monoxides.

Energy harnessed by wind turbines is intermittent, 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 ridges or bluffs to maximize the access of wind they have, but this also limits the locations where they can be placed.^[84] In this way, wind energy is not a particularly reliable source of energy. However, it can form part of the energy mix, which also includes power from other sources. Notably, the relative available output from wind and solar sources is often inversely proportional (balancing)^{[citation needed]}. Technology is also being developed to store excess energy, which can then make up for any deficits in supplies.

Records

This section needs to be updated. Please update this article to reflect recent events or newly available information. (December 2018)

Fuhrländer Wind Turbine Laasow, in Brandenburg, Germany, among the world's tallest wind turbines

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

See also List of most powerful wind turbines

Most powerful, tallest, largest and with highest 24-hour production

GE Wind Energy's Haliade-X is the most powerful wind turbine in the world, at 12MW. It also is the tallest, with a hub height of 150 m and a tip height of 260m. It also has the largest rotor of 220 m and largest swept area at 38000 m^2[92] It also holds the record for the highest production in 24 hours, at 312 MWh.^[93]

Largest capacity conventional (non-direct) drive

The Vestas V164 has a rated capacity of 8 MW,^[94] later upgraded to 9.5 MW.^[95][96] The wind turbine has an overall height of 220 m (722 ft), a diameter of 164 m (538 ft), is for offshore use, and is the world's largest-capacity wind turbine since its introduction in 2014. Conventional drive trains consist of a main gearbox and a medium-speed PM generator. Prototype installed in 2014 at the National Test Center Denmark nearby Østerild. Series production began end of 2015.

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.^[97] It has a nameplate capacity of 3.8 MW.^[98]

Largest 1-bladed turbine

The largest single-bladed wind turbine design to be put into complete operation is the MBB Messerschmitt Monopteros M50, with a total power output of no less than 640 kW at full capacity. As far as the number of units is concerned, only three ever have been installed at an actual wind park, of which all went to the Jade Wind Park.^[99]

Largest 2-bladed turbine

The biggest 2-bladed turbine is built by Mingyang Wind Power in 2013. It is a SCD6.5MW offshore downwind turbine, designed by aerodyn Energiesysteme GmbH.^{[100][101][102]}

Highest tower

Fuhrländer installed a 2.5 MW turbine on a 160m lattice tower in 2003 (see Fuhrländer Wind Turbine Laasow and Nowy Tomyśl Wind Turbines).

Most rotors

Lagerwey has build Four-in-One, a multi rotor wind turbine with one tower and four rotors near Maasvlakte.^{[citation needed]} In April 2016, Vestas installed a 900 kW four rotor test wind turbine at Risø, made from 4 recycled 225 kW V29 turbines.^{[103][104][105]}

Most productive

Four turbines at Rønland Offshore Wind Farm in Denmark share the record for the most productive wind turbines, with each having generated 63.2 GWh by June 2010.^[106]

Highest-situated

Since 2013 the world's highest-situated wind turbine was made and installed by WindAid and is located at the base of the Pastoruri Glacier in Peru at 4,877 meters (16,001 ft) above sea level.^[107] The site uses the WindAid 2.5 kW wind generator to supply power to a small rural community of micro entrepreneurs who cater to the tourists who come to the Pastoruri glacier.^[108]

Largest floating wind turbine

The world's largest floating wind turbine is any of the five 6 MW turbines in the 30 MW Hywind Scotland offshore wind farm.^[109]

See also

• Airborne wind turbine
• Compact wind acceleration turbine
• Éolienne Bollée
• Floating wind turbine
• IEC 61400
• Renewable energy
• Tidal stream generator
• Unconventional wind turbines
• Wind lens
• Windbelt
• Windpump

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Further reading

• Tony Burton, David Sharpe, Nick Jenkins, Ervin Bossanyi: Wind Energy Handbook, John Wiley & Sons, 2nd edition (2011), ISBN 978-0-470-69975-1
• Darrell, Dodge, Early History Through 1875 Archived 2 December 2010 at the Wayback Machine, TeloNet Web Development, Copyright 1996–2001
• Ersen Erdem, Wind Turbine Industrial Applications
• Robert Gasch, Jochen Twele (ed.), Wind power plants. Fundamentals, design, construction and operation, Springer 2012 ISBN 978-3-642-22937-4.
• Erich Hau, Wind turbines: fundamentals, technologies, application, economics Springer, 2013 ISBN 978-3-642-27150-2 (preview on Google Books)
• Siegfried Heier, Grid integration of wind energy conversion systems John Wiley & Sons, 3rd edition (2014), ISBN 978-1-119-96294-6
• Peter Jamieson, Innovation in Wind Turbine Design. Wiley & Sons 2011, ISBN 978-0-470-69981-2
• J. F. Manwell, J. G. McGowan, A. L. Roberts, Wind Energy Explained: Theory, Design and Application, John Wiley & Sons, 2nd edition (2012), ISBN 978-0-47001-500-1
• David Spera (ed,) Wind Turbine Technology: Fundamental Concepts in Wind Turbine Engineering, Second Edition (2009), ASME Press, ISBN 9780791802601
• Alois Schaffarczyk (ed.), Understanding wind power technology, John Wiley & Sons, (2014), ISBN 978-1-118-64751-6
• Hermann-Josef Wagner, Jyotirmay Mathur, Introduction to wind energy systems. Basics, technology and operation. Springer (2013), ISBN 978-3-642-32975-3
• GA Mansoori, N Enayati, LB Agyarko (2016), Energy: Sources, Utilization, Legislation, Sustainability, Illinois as Model State

External links

Wikimedia Commons has media related to Wind turbine.

• Harvesting the Wind (45 lectures about wind turbines by professor Magdi Ragheb
• DIY wind turbine at home Complete video and image Guide by Newphysicist
• Guided tour on wind energy
• Wind Energy Technology World Wind Energy Association
• Wind turbine simulation, National Geographic
• Airborne Wind Industry Association international
• Top 21 Biggest Wind Turbines in the World
• The Tethys database seeks to gather, organize and make available information on potential environmental effects of offshore wind energy development