emerge as the industry standard: the three-bladed, horizontal axis, upwind machine. A modern wind turbine comprises a tubular tower of
rolled steel. Atop the tower is a nacelle that contains the generator and usually a gearbox that receives the relatively slow rotor shaft rotation and increases it for efficient generator operation. Note that direct drive options are becoming available. The rotor itself is commonly three-bladed with each blade having pitch control to maximize power harvesting at a particular wind speed. The rotor and nacelle assembly rotate on the top of the tower and are actively steered to face into the wind.
Over time, research and development has refined and improved these machines. In 1926, Albert Betz showed that an ideal turbine rotor can extract a maximum of 59% (16/27) of the power in wind.1 Modern rotor designs are approaching this Betz Limit with extraction
efficiencies in excess of 50%.