The blades began turning at Germany's first offshore wind farm, 45 kilometres off the coast in the North Sea, with 12 turbines producing energy for 50,000 households.

The turbines, each 150 metres high, produce 12 megawatts of power and the total cost of the project was €250 million, the consortium of energy companies that built the farm said.

The wind farm was designed as a "test ground" to examine the environmental damage on local species from such turbines, which are embedded 30 metres below the surface.

Germany aims to achieve a capacity of 25,000 megawatts in offshore wind energy by 2030, said Environment Minister Norbert Roettgen, formally opening the park.

The project, named Alpha Ventus, was financed by Germany's number-one energy provider EON, Vattenfall Europe, a subsidiary of the Swedish energy giant, and EWE.