This 200 B.C. invention, earlier known as wind mill as it was used primarily to grind grains and in addition cut lumbers and pump water for irrigation, has seen continuous improvement in design and efficiency. These were essentially vertical axis windmills having long vertical drive shafts with rectangular shaped blades.
It became known as wind power generators, once it was started to be used for converting mechanical energy created by the rotation of the blades into rotating a turbine to generate electricity. These generators are generally of two types.
Horizontal axis wind power generators have a rotor component. It is a three blade component that converts wind energy into rotational mechanical energy. The generator component electronically controlled electric generators with a gearbox component for converting incoming rotational energy to high speed turbine rotation most suited for electricity generation. The structural part comprises of a tower and rotor mechanism. Wind power generators may also be used in conjunction with a vertical solar updraft tower to obtain solar heated wind energy. Some such assemblage has a visitor's deck too.
Vertical axis wind power generators have a vertical arrangement of main rotor shaft. This has an advantage of not requiring turbine to be pointed into the wind for more efficiency. This becomes advantageous in locations where there is highly variable wind direction. The generator and the gear box are placed near the ground requiring no need of support from the tower. This facilitates easy maintenance. However, some design may generate unwanted pulsating torque. These are often installed on ground or on roof top. The wind energy at such places is usually low. There may also be turbulence in the air flow which can create vibration and noise. This results in the faster wearing of bearings. Higher mounting such as building tops gives higher wind energy and less turbulence.
Some more versions of wind power generators are also in use. Eggbeater turbine wind power generators have higher efficiency but are unreliable due to large torque ripples and cyclic stress on the tower. They generally require some kind of external power source since the starting torque is not sufficient to speed up the blades. The torque ripple is reduced by using three or more blades giving higher solidity i.e. higher ratio of blade area to rotor area. The self starting cycloturbine a subtype of Eggbeater uses straight blades in place of curved ones having variable pitch to minimize torque vibration. This gives high starting torque and is more efficient.
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