Working principle of a horizontal axis wind turbine.

In a wind power plant, the kinetic energy of the flowing air mass is transformed into mechanical energy of the blades of the rotor. A gearbox is used in a connection between a low speed rotor and the generator. The generator transforms mechanical energy into electrical energy. New types of horizontal axis turbines use a multipolar generator that is connected directly to the rotor of the turbine instead of using a gearbox.

The main part of the turbine consists of rotor blades. These need to meet stringent criteria with regards to the strength of wind and centrifugal forces they have to withstand. The right profile and angle of attack of the rotor blades is the most important prerequisite if maximum efficiency is to be reached. The minimum wind speed the turbines need to work is between 3 and 4 m/s (6—8 knots). Optimal power output is reached at 15 m/s (30 knots) while at speeds over 25 m/s (50 knots), the turbines are stopped to prevent damage.