What is wind energy?
Wind energy is the kinetic energy of the wind, which a wind turbine converts into rotation and then, through a generator, usually into electricity. Traditional windmills used wind power directly to grind, saw or pump water. Modern turbines supply the grid or a building.
How it works
- The wind turns the blades. Modern turbines use aerofoil blades that generate lift, like an aircraft wing.
- The rotor drives a generator, directly or through a gearbox.
- The nacelle turns automatically into the wind, and the turbine is shut down in storms.
Two rules of physics
- Wind speed matters most: the power in the wind rises with the cube of wind speed. Twice the wind speed means, in theory, eight times the power. A slightly windier site or a taller mast makes a big difference.
- Never all of it: a wind turbine can in theory extract at most about 59 per cent of the energy in the wind (the Betz limit). In practice efficiency is lower.
Wind energy at home
Large turbines stand in wind farms on land and at sea. Small turbines are sold to homeowners, but with important caveats:
- Little, turbulent wind in built-up areas: between houses and trees the wind is weaker and more turbulent. A roof-mounted turbine in a residential area is therefore rarely cost-effective; solar panels usually yield more per pound or euro invested.
- Open site needed: a small turbine only stands a chance on an open, exposed site, such as a farmyard in open country, with a mast well clear of obstacles.
- Permission: most turbines need planning permission or must meet strict permitted-development conditions. Check with your local authority first.
- Noise and shadow flicker: consider the neighbours. Even small turbines produce noise and vibration, especially on roofs.
- Structure: a turbine on a roof puts fluctuating loads and vibration into the roof structure. Always have it checked by a structural engineer.
Related terms
- Venturi wind turbine
- Windmill
- Heat pump
- Cogeneration
- Building permit
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