The invention is concerned with a device for adapting a wind wheel to an electric power generator in such a way that the wind wheel will always be operated with a maximum performance coefficient, that another source of energy, e.g. a prime mover, can supply the power deficit if the wind power is not sufficient, and that the generator at the output of the facility is kept mains-synchronous of constant speed and constant voltage. According to the invention, the shaft power of the wind power engine is transmitted to a first generator driving an electromotor. The motor is coupled to a second generator feeding into a consumer grid. By means of an anemometer the excitation output of the motor is controled in such manner that the speed of the generator is practically constant-provided a sufficient supply of wind is available. On the shaft of the output generator a prinse mover, e.g. a Diesel engine, is mounted being controllable for contant speed by means of a controll device in such a way that the prime mover takes over the missing amount of power if the wind supply falls short of the power taken off at the generator output.