During the construction phase of alpha ventus, the world's only three manufacturers of offshore wind turbines in the 5 MW class were REpower, AREVA Wind and the Bard Group. All three companies are based in Germany and manufacture their turbines there. For alpha ventus, six turbines from Repower (5M) and six turbines from AREVA Wind (M5000) were chosen.
Both machines were specially developed for offshore operation. Important components were doubled in order to minimize downtime, special ventilation systems were added in the nacelle and in the tower to prevent the infiltration of aggressive saline air and modern technology which allows the machines to be controlled from land were installed.
REpower's 5M turbines stand on a steel tower. From the rotor's hub to the water surface, the total height is 92 metres. With a length of 61.5 metres, the rotor blades each cover an area of 12,496 square metres. The entire rotor weighs 120 tons and the nacelle weighs 280 tons. Under optimal conditions, the wind turbine can produce a nominal output of up to five megawatts. The interior of the turbine resembles its counterparts on land. The slow rotations of the rotors are passed on to the transmission through a drive train, then translated into higher rotation speeds and passed on to a generator. The generator converts the mechanical energy of the rotor into electrical energy.
Foto: German Offshore Wind Energy Foundation, REpower, Detlef Gehring, 2009
The M5000 is a little smaller and more compact than the M5 but just as powerful. These turbines also stand on steel towers and have a hub height of 90 metres and a nominal capacity of 5 MW. The three 58-metre blades cover an area of 10,568 square metres. The nacelle weighs only 349 tons, including the rotor blades and the rotor hub. The system is therefore a real lightweight, because the drive train was dispensed with and a very compact transmission was developed and used.
Foto: German Offshore Wind Energy Foundation, AREVA Wind, 2009