Words: Birgit Niesing
The wind is always more constant at sea than on land – and much stronger. That’s why the wind energy industry is increasingly looking to offshore facilities. The first German wind farm in the North Sea – the ‘alpha ventus’ test and demonstration site – went online just a few months ago. Researchers are monitoring its progress.
45 kilometers north of Borkum, the climate is harsh. The wind speed averages 36 kilometers an hour (force five), the waves are several meters high, and the air is salty and damp. The area is now home to the first German offshore wind park, dubbed alpha ventus, which was completed a few months ago.
Erecting offshore wind farms in the North Sea off the German coast presents planners, constructors and operators with enormous challenges, for not far from the coastline lies the protected Wadden Sea National Park, a UNESCO World Heritage Site. The farms cannot be built close inshore; instead, they have to be sited out to sea beyond the Friesian Islands, which stretch from Sylt to Borkum. This gives rise to certain disadvantages. Firstly, the generating turbines have to be built in water that is 20 to 40 meters deep – a technically ground-breaking accomplishment. Secondly, anchoring them to the sea bed and connecting them to the power grid on the mainland is a time-consuming, laborious and expensive process.
The alpha ventus offshore wind park has to withstand extreme conditions. Its twelve wind turbines were erected in water around 30 meters deep and are connected to the mainland by a 60-kilometer long undersea cable. A joint pilot project involving EWE, E.ON Climate & Renewables and Vattenfall, the park is a pioneering technological and logistical achievement. The dozen wind turbines that make up the test field are all of the 5 megawatt class: six are of the Areva Multibrid M5000 type, while the remaining six are of the REpower 5M type. The turbines are constructed on two different kinds of steel foundation. While the Areva Multibrid systems stand on tripods, so-called jacket foundations (comprised of a steel tube support structure and special cast transition pieces) were chosen for the REpower systems.