Wind turbines produce electricity by harnessing the power of moving air.

The turbine's blades turn faster as wind speeds pick up.

The movement of the blades then turns a shaft, which passes the mechanical energy created by the wind to a generator which transforms the energy into electricity.

This process produces no carbon dioxide, although the manufacture of the turbines does release some C02.

But, on the down side, energy is only produced when the wind blows; the British Wind Energy Association (BWEA) estimates that most turbines will be active 70-85% of the time.

The UK has some of Europe's windiest weather, providing it with many good sites for turbines.

The wind is strongest at high altitudes, away from buildings and natural barriers, like trees.

But the rise of turbines across the UK's countryside has not been without controversy. Some see them as an unwelcome eyesore and an attempt to industrialise rural areas.

Building wind farms offshore would seem to solve some of these problems. In addition offshore wind farms benefit from faster wind speeds, due to the lack of obstacles on surface of the water.

There is also more available space to site larger turbines at sea, which can increase efficiency, although construction costs at sea are higher and turbine maintenance can be made more difficult due to the corrosive effect of saltwater.

By 2007, approximately 1.65% of the UK's electricity supply was derived from wind turbines, according to the BWEA. This compares with 10% in Germany.

Putting a price on the electricity produced from wind turbines is complex. In 2007 Centrica estimated that electricity from offshore wind farms costs over 10p per kilowatt hour to produce, compared to natural gas at around 4p per kilowatt hour.

The BWEA put the figure for onshore wind turbines at 3-4p per unit.

Wind power is likely to become more competitive in the future, if oil and gas prices remain high and through improvements in technology.