Windfarms offshore Germany
NGI has participated in the development of offshore windfarms at Alpha Ventus at Borkum, northwest of Germany. This is Germany's first offshore windfarm
Foto: OWEC Tower
Six test structures were installed during the spring 2009 and additional six structures were installed by NorWind as EPCI contractor in June-August 2009.
The latter installations are based on OWEC Tower's jacket structure concept. The concept was most likely chosen because this type of foundation for an offshore wind mill was used for the first time two years ago for two test mills at the Beatrice field offshore Scotland, installed in about 50 m water.
NGI also contributed to the Beatrice field. One year ago these two test structures were the only ones in this water depth. As such, the concept had already proven feasible. The steel structures are supported by four driven piles. For different reasons the piles were installed prior to the jacket structures. Thereby the six jackets could be made identical.
The jackets are floated on a barge, lifted off and the platform legs are placed directly on to the pile tops. This installation requires that the pile heads after driving are positioned within narrow tolerances.
NGI was responsible for the design and driving analyses of the piles for OWEC Tower and NorWind. NorWind was responsible for the pile installation and NGI conducted the last part of the pile driving with specially developed measuring equipment. The inclination and positions of the piles were measured by NGI just after the pile driving.
Observed driving resistance was in close agreement with the predictions, and NGIs system for measurement of the position of the piles worked perfectly. The platform legs and pile heads matched perfectly and the jackets were installed in a vertical position, as specified.
The world's largest crane vessel "Thialf" was used for the lifting operation. Alpha Ventus represents the first time such jackets with preinstalled piles are used in full scale.
Read more on the projects webpages.