wind pm turbine
Mostly only big wind generators use gearboxes.
Why?.. The gearbox is used to control and maintain a constant and most efficient speed that will be transfer to the generator. At the same time protecting the generator from an overload.
Others reasons why smaller wind generators do not use gearboxes are money (that will increase the price of the wind generator), weight penalties, loosing some of the power made from the wind, and because not much power is made anyway, that will make the small wind generator less efficient.
Even though the big wind generators will loose some of the power as well, the difference is less noticeable because of the size.
Well hope that helps a little to make sense of the use of a gearbox.
JR