Wind Turbines
Wind turbines are essentially aerofoils linked to a generator/turbine which produces electricity when sufficient wind is present to power the turbine. The power generated can be used immediately, stored in batteries or sold into the grid.
For “mid range” turbines power outputs may be around 50 to 300kW. A 100kW turbine, in a perfect situation, will for every hour the turbine turns, generate 100kW i.e 100kWh. However, variable wind speed clearly means this is not the case in practice. Because wind power is proportional to the cube of wind speed, small changes in wind speed have a significant effect on power output. In the UK those sites which have reasonable wind speeds are more likely to generate 30kWh on average from a 100kW turbine (annual output approx 230MWh).
Wind turbines produce power over a wide range of wind speeds. They cut in at between 3 and 4 m/s, reach their rated output at about 11 – 13 m/s and are regulated to produce their maximum output through to 25 m/s, when they typically shut down to protect the drive train, gearbox and structure from potential damage. This maximum speed is equal to 55 mph, which is above gale force 9, defined as when tree branches break
Large windfarms have been beset by perceived problems such as negative landscape effects, noise, devaluation of properties etc. which have caused local residents to object – often vociferously. There is of course a substantial difference between a single or small number of turbines at lower heights than some of the very large wind farm sites.
For more information download the Commercial Wind or Domestic Wind FACT sheets