What is a wind turbine and how does it work?

A wind energy system transforms the kinetic energy of the wind into mechanical or electrical energy that can be harnessed for practical use. Mechanical energy is most commonly used for pumping water in rural or remote locations. Wind electric turbines generate electricity for homes and businesses and for sale to utilities.

There are two basic designs of wind electric turbines: vertical-axis, or "egg-beater" style, and horizontal-axis machines. Horizontal-axis wind turbines are most common, comprising more than 95% of the "utility-scale" (100 kilowatts (kW) capacity and larger) turbine market.

Turbine subsystems include:
  • a rotor, or blades, which convert the wind's energy into rotational shaft energy;
  • a nacelle containing a drive train, usually including a gearbox* and a generator;
  • a tower, to support the rotor and drive train; and
  • electronic equipment such as controls, electrical cables, ground support equipment, and interconnection equipment.

*Some turbines operate without a gearbox.

Wind turbines vary in size. This chart depicts a variety of turbine sizes and the amount of electricity they are each capable of generating (the turbine's capacity, or power rating)

How big is a wind turbine?

The average size of onshore turbines being manufactured today is around 2.5-3 MW, with blades of about 50 metres length. It can power more than 1,500 average EU households.

An average offshore wind turbine of 3.6 MW can power more than 3,312 average EU households.

  • In 1985, wind turbines were under 1 MW with rotor diameters of around 15 metres. In 2012, the average size is 2.5 MW with rotor diameters of 100 metres.

7.5 MW turbines are the largest today with blades about 60 metres long – over half the length of a rotor diameter of over 120 metres – longer thanĀ  a football field. 15 MW turbines are planned and 20 MW turbines are considered to be theoretically possible.

What is a wind turbine?

A wind turbine is a machine that transforms the kinetic energy of the wind into mechanical or electrical energy. Wind turbines consist of a foundation, a tower, a nacelle and a rotor. The foundation prevents the turbine from falling over. The tower holds up the rotor and a nacelle (or box).

The nacelle contains large primary components such as the main axle, gearbox, generator, transformer and control system. The rotor is made of the blades and the hub, which holds them in position as they turn. Most commercial wind turbines have three rotor blades. The length of the blades can be more than 60 metres.

What is a wind turbine made of?

The towers are mostly tubular and made of steel or concrete, generally painted light grey. The blades are made of fibreglass, reinforced polyester or wood-epoxy. They are light grey because it is inconspicuous under most lighting conditions. The finish is matt, to reduce reflected light.

How is a wind farm designed?

There are many factors at play when designing a wind farm. Ideally, the area should be as wide and open as possible in the prevailing wind direction, with few obstacles. Its visual influence needs to be considered – few, larger turbines are usually better than many smaller ones.

The turbines need to be easily accessible for maintenance and repair work when needed. Noise levels can be calculated so the farm is compatible with the levels of sound stipulated in national legislation. The turbine supplier defines the minimum turbine spacing, taking into account the effect one turbine can have on others nearby – the 'wake effect'.

Then, the right type of turbine must be chosen. This depends on the wind conditions and landscape features of the location, local/national rules such as on turbine height, noise levels and nature conservation, the risk of extreme events such as earthquakes, how easy it is to transport the turbines to the site and the local availability of cranes.

How long does it take to build a wind farm?

Construction time is usually very short – a 10 MW wind farm can easily be built in two months. A larger 50 MW wind farm can be built in six months.

What are the costs of building a wind farm?

Costs vary but the biggest cost is the turbine itself. This is a capital cost that has to be paid up front and typically accounts for 75% of the total.

Once the turbine is up and running there are no fuel and carbon costs, only operation and maintenance costs (O&M), which are minimal compared to e.g. a gas power plant where O&M is 40-70% of total costs, and the rest of the cost is fuel.

How efficient are wind turbines?

Wind turbines start operating at wind speeds of 4 to 5 metres per second and reach maximum power output at around 15 metres/second. At very high wind speeds, that is gale force winds of 25 metres/second, wind turbines shut down. A modern wind turbine produces electricity 70-85% of the time, but it generates different outputs depending on the wind speed.

Over the course of a year, it will typically generate about 24% of the theoretical maximum output (41% offshore). This is known as its capacity factor. The capacity factor of conventional power stations is on average 50%-80%. Because of stoppages for maintenance or breakdowns, no power plant generates power for 100% of the time.

Why do some of the turbines in a wind farm sometimes stand still?

Turbines sometimes have to be stopped for maintenance, for repairing components or if there is a failure that needs to be checked. Another reason can be too little or too much wind: if the wind is too strong, the turbine needs to be shut down because it could be damaged.

How long does a wind turbine work for?

Wind turbines can carry on generating electricity for 20-25 years. Over their lifetime they will be running continuously for as much as 120,000 hours. This compares with the design lifetime of a car engine, which is 4,000 to 6,000 hours.

What are a turbine’s lifetime emissions?

Wind turbines produce no greenhouse gas emissions during their operation. It takes a turbine just three to six months to produce the amount of energy that goes into its manufacture, installation, operation, maintenance and decommissioning after its 20-25 year lifetime. During its lifetime a wind turbine delivers up to 80 times more energy than is used in its production, maintenance and scrapping. Wind energy has the lowest ‘lifecycle emissions’ of all energy production technologies.

What other environmental benefits does wind power bring?

Wind energy emits no toxic substances such as mercury and air pollutants like smog-creating nitrogen oxides, acid rain-forming sulphur dioxide and particulate deposits. These pollutants can trigger cancer, heart disease, asthma and other respiratory diseases, can acidify terrestrial and aquatic ecosystems, and corrode buildings.

Wind energy creates no waste or water pollution. Unlike fossil fuel and nuclear power plants, wind technology uses very little water to produce electricity. Given the fact that water scarcity is pressing and will be exacerbated by climate change and population growth, wind energy is key to preserving water resources.

How much of our daily CO2 emissions can wind avoid?

Each year we release millions of tonnes of carbon dioxide by burning fossil fuels (oil, coal and gas) contributing to climate change.

Wind energy produces no greenhouse gas emissions during its operation. A turbine will produce up to 80 times more energy than is used to build, install, operate, maintain and decommission it.

EWEA estimates that wind energy avoided the emission of 140 million tonnes of CO2 in 2011 in the EU, equivalent to taking 33% of cars in the EU – 71 million vehicles – off the road. This avoided CO2 costs of around €1.4 billion. In 2020 wind energy will avoid 342 million tonnes of CO2, equivalent to taking 80% of the EU’s car fleet off the road and avoiding CO2 costs of around € 8.5 bn.

In 2030 wind energy is projected to avoid 646 million tonnes of CO2, equivalent to taking 152% of the EU’s car fleet off the road and avoiding CO2 costs of around € 26 bn.