It took only a few windy autumn weeks to erect the six REpower wind turbines, each with a rated output of 5 megawatts (MW) and a height of 155 meters from sea level to the tip of the turbine blade. "Despite the partly adverse weather conditions of the last few weeks, this turbine construction project went quickly and smoothly – due to the experience that we gained from similar wind turbine construction projects, such as the Thornton Bank offshore wind farm," emphasizes Norbert Giese, Director of Offshore Projects at REpower Systems AG.
Unlike the construction of the Belgian offshore wind farm Thornton Bank, REpower worked with a larger transport jack-up barge this time so that one complete turbine – made up of rotor star, nacelle, and two tower components – could be shipped to the location at a time. Moreover, the wind, wave, and tide time windows were much better exploited thanks to an improved installation device. "Due to the outstanding cooperation between all the people involved in the project, we were able to erect one turbine in almost a day," explains Giese. And he continues: "Under favorable conditions, we are confident that the first REpower turbines of this offshore wind farm will be supplying power to the grid before the end of this year."
In the meantime, REpower has successfully built 23 REpower 5M wind turbines, 14 of those are located in the open sea at water depths of up to 45 meters. Such successful projects are enabling the company to further expand its position as a market leader in the multi-megawatt offshore turbine sector for turbines far from shore and in deep water. Each of the six turbines constructed at alpha ventus is slated to supply the electricity grid with around 18 million kilowatt hours (kWh) of wind power per year. All in all, this wind farm will be able to supply about 50,000 homes with wind energy electricity annually.
The Alpha Ventus wind farm in shallow water 45 kilometres from the island of Borkum is invisible from land because the tips of the rotors, 155 metres above the water, are almost below the horizon. The project chief said the last of the 12 had been erected and would be generating electricity within a few weeks.
Alpha Ventus is officially a pilot site costing 250 million euros (370 million dollars). It took seven months to build and was financed by a consortium of the EWE, E.ON and Vattenfall electricity companies. Its annual output is to meet the needs of 50,000 homes. Project chief Wilfried Hube said the project was a lot more difficult than those that already exist in other nations and was testing two different makes of German wind turbine on two different sorts of seabed foundation.
"Basically you could say we have built two different wind farms," said Hube. One set of six has been operating since August and has already produced 13 million kilowatt-hours of electricity. In September, the German government approved zoning regulations that allow turbines to be sited at places in Germany’s exclusive economic zone, outside the 12-mile territorial limit.
The Federal Agency for Marine Transport and Hydrography BSH has already approved permits for 25 wind farms, 22 of them in the North Sea. The plans lagged for more than a decade because of engineers’ fears the turbines would break down in such a stormy place. Piles of stone and rubble had to be dumped into water 30 metres deep to form heavy foundations so that the towers do not tip over in hurricane-force winds.