Is the large box-shaped enclousure located on top of the tower. It houses the hub (attached to the blades), a gearbox and generator.
This is made of steel and is set in a concrete foundation block below ground level.
What are wind turbines made of?
The towers are mostly tubular and made of steel, generally painted light grey. The blades are made of glass-fibre reinforced polyester or a material known as wood-epoxy. They are light grey, as this colour is least conspicuous under most lighting conditions. The finish is matt, to reduce reflected light.
How big are they?
When do wind turbines work?
Wind turbines start operating at wind speeds of four to five metres per second (around 10 miles per hour) and reach maximum power output at around 15 metres per second (around 33 miles per hour). At very high wind speeds (gale force winds: 25 metres per second, or over 50 miles per hour) wind turbines shut down.
Generating electricity from the wind
Turbine blades: For the turbine blades to rotate, the face of the turbine must point into the wind. Because each blade of the wind turbine is angled in a special way - like an aeroplane's wing - a force known as a 'lift' is generated on one side, and the blades start to spin round. A sensor above the nacelle constantly monitors the wind direction and speed to make sure the turbine keeps pointing into the face of the wind.
Gearbox: To generate electricity, the shaft in the generator needs to turn very fast; well over 1,000 revolutions per minute. But this is too fast for the huge blades of a wind turbine. So a gearbox is used, enabling the shaft going into the front of the gearbox to rotate at low speed, with the shaft coming out of the back able to turn many times faster.
Anemometer: An 'anemometer' calculates how fast the wind is going, so that the turbine can brake if it's turning too fast. There are two braking systems on the turbine: one is on the blade tips, and the other is a disc brake connected to the high-speed shaft within the nacelle.
Nacelle: When the wind direction alters, the nacelle is rotated by hydraulic motors so that the rotor blades face into the wind to maximise the energy captured.
Cable to substation: The electrical energy is transmitted along cables to a substation. Here it's converted to a high voltage, before being delivered to homes and businesses.
Electricity generator: The shaft coming out of the gearbox is connected to a generator. This uses an electromagnetic field to convert the mechanical energy into electrical energy. The generator produces power at 690v, which is transformed to a higher voltage usually 20kV or above.
How fast do the blades turn?
The blades rotate at 50-100 revolutions per minute at constant speed. An increasing number of machines, however, operate at variable speed.
How much of the time do wind turbines produce electricity?
A modern wind turbine produces electricity 70% to 85% of the time, but it generates different outputs dependent on wind speed. So over the course of a year, it will generate about 30% of the theoretical maximum output. This is known as its load factor. The load factor of conventional power stations is about 50%.