<P> Typical modern wind turbines have diameters of 40 to 90 metres (130 to 300 ft) and are rated between 500 kW and 2 MW . As of 2017 the most powerful turbine, the Vestas V - 164, is rated at 9.5 MW and has a rotor diameter of 164m . </P> <P> Increasingly large wind turbines are being designed, manufacturere have not yet come close to the maimum size . The largest turbines are or will be as big as skyscrapers . </P> <P> The nacelle is housing the gearbox and generator connecting the tower and rotor . Sensors detect the wind speed and direction, and motors turn the nacelle into the wind to maximize output . </P> <P> In conventional wind turbines, the blades spin a shaft that is connected through a gearbox to the generator . The gearbox converts the turning speed of the blades 15 to 20 rotations per minute for a large, one - megawatt turbine into the faster 1,800 revolutions per minute that the generator needs to generate electricity . Analysts from GlobalData estimate that gearbox market grows from $3.2 bn in 2006 to $6.9 bn in 2011, and to $8.1 bn by 2020 . Market leaders were Winergy in 2011 . The use of magnetic gearboxes has also been explored as a way of reducing wind turbine maintenance costs . </P>

Horizontal axis windmills enable all of the blades to capture the wind energy simultaneously