Modern wind turbines are an evolution of traditional windmills. A collection of wind turbines in one location is referred to as a wind farm.
There are four key parts to a modern wind turbine:
- the blade assembly
- the nacelle
- the tower
- the foundations
Most wind turbines have three or two blades, which rotate around a central hub on a horizontal axis. The turning blades drive a generator housed in the nacelle at the top of a steel tower. Some wind turbines have blades which rotate on a vertical axis.
Blades are made from a variety of materials, such as fibreglass, carbon fibre, or wood laminates. A turbine with long blades can capture more of the energy in the wind and therefore generate more electricity than a turbine with shorter blades.
The nacelle is the large housing at the top of the tower which contains the generator and other important components such as the gearbox and control equipment. An anemometer and a wind vane, which respectively measure wind speed and direction, sit on top of the nacelle.
Towers are usually tubular steel, although some turbines have lattice towers (more like an electricity transmission pylon). Steel towers are usually painted a light colour, with a non-reflective paint, to help them blend into the background.
The tower sits in a steel reinforced concrete foundation – the dimensions of which depend on the size of the turbine. The foundation is a substantial structure as it is designed to ensure that the turbine can withstand very strong winds, however it is always below ground level and not visible once construction is complete.
How does a wind turbine create electricity?
Wind turbines generate electricity by using the natural power in the wind. A wind turbine’s blades are like an aeroplane wing: as the air flows past the blade it causes lift, which creates a turning force.
When the wind changes direction, motors turn the nacelle, and the blade assembly along with it, around to face into the wind (this movement is called yaw). The blades also ‘pitch’ or angle to ensure that the optimum amount of power is extracted from the wind.
The rotating blades turn a shaft inside the nacelle, which goes into the gearbox. The gearbox increases that rotation speed for the generator, which uses magnetic fields to convert the rotational energy into electrical energy. Some turbines use direct drive technology, which connects the rotating hub directly to the generator.
The electricity from the generator goes via cables to a transformer housed either inside or outside of the base of the tower. The transformer converts the electricity to the right voltage for the grid or local network, which transmits the electricity into homes and businesses.
Most wind turbines operate automatically or by remote control and do not require staff to be on site all the time. Periodic checks are carried out by visiting technicians but a computer continuously monitors power output and the performance of each turbine component and this information is usually relayed through to a central office location. If it detects any problems it sends an alarm to alert the operator that some maintenance is required and it may automatically shut the turbine down until the problem is fixed.
Improvements in technology
From the outside, wind turbines look much the same as they did 10 years ago, if a bit larger. But like other forms of technology such as cellphones and computers, wind turbine technology has improved rapidly in recent years especially in the area of power control electronics.
Modern turbines can provide “ancillary services” such as reactive power and frequency keeping services. These functions help to stabilise the grid or local network a wind farm is connected into.
Technological improvements have also substantially reduced the cost of wind energy. At a given site, a single modern wind turbine annually produces roughly 180 times more electricity per year and at less than half the cost per kilowatt-hour (or "unit" of electricity) than its equivalent of 20 years ago.