Wind Power – it’s all about trying to extract energy from Free Air.

Wind turbines try to catch the kinetic energy in the moving cylinder of air that is sliced by the turbine blade. Because air is so light, and wind has a generally low speed (compared to a jet engine thrust, say) there is a limited amount of energy to be collected.

And turbines can only catch a limited amount of this energy – to collect it all would require the turbine to catch all of that air and bring it to a dead stop. Naturally this never occurs and wind leaves the turbine will significant speed and energy. For an ideal turbine in an ideal wind speed the power co-efficient may only be in the 30-40% range.

Conversion of the energy collected by the blade to electrical energy is achieved in an electric generator, where more energy is lost. The generator is designed for the optimal blade speed. If the wind blows harder than expected, the excess energy cannot be caught by the generator and electricity generation levels out, until at about 25 m/s wind speed, the turbine cuts out to prevent damage in high winds. A standard power factor is about 35%.

Unfortunately generators are designed to run at high speed but turbines turn at low speeds. Therefore they need huge gearboxes which develop massive forces for which no effective lubricant is available. At high winds, gearboxes may overheat and catch fire.

For specific information of these and many other factors affecting the efficiency and costs of wind power see this document: http://carbon-sense.com/wp-content/uploads/2011/02/wind-power-hayden.pdf [PDF, 2 MB]