A wind turbine is a rotating machine which converts the kinetic energy of wind into mechanical energy. It uses the effect of lift on an aerofoil blade to cause the blades to rotate, driving a generator via a gearbox to generate electricity.
Wind turbines come in sizes ranging from a few kilowatts (micro wind) to multiples of megawatts. Most wind turbines tend to be horizontal axis machines with the blades pointed into the prevailing wind direction. However, there are also a number of vertical axis machines, where the blade mechanism is vertical. These machines have the advantage of not needing to be pointed into the wind to be effective, and are therefore suited to sites with variable wind direction. However, they tend to be more expensive and have generally lower outputs then horizontal axis machines.
The decision as to whether or not to install a wind turbine depends on a number of factors, but the main one is a good wind resource, with minimal turbulence. Wind conditions for any area of the U.K. mainland can be found at the BWEA web site which has the U.K. wind speed database. This allows mean wind speed data based on grid references or postcodes to be displayed for any location in the U.K., and provides a good starting point for analysis.
Wind turbine location is also an important factor, as it is important to minimize the effects of turbulence and wind shear; turbines operate best with laminar air flow. This is usually achieved by mounting on a mast, as elevation of the blades reduces turbulence and wind shear effects which are more pronounced closer to ground level.
A recent feasibility study carried out by Square 1 indicated that for a 250kW wind turbine located at a site in Cleveland with a mean wind speed of 6.5m/s up to 550MWh of electricity a year could be produced, providing cost savings of approximately £60,000 and 300 tonnes CO2 per year, based on an electricity price of 7.3p/kWh and including Renewable Obligation Certificate income. For an estimated installed cost of £350,000, this gives a simple payback of under 6 years.