Alpha Ventus Offshore Wind Farm

Alpha Ventus project - Borkum, Germany

Challenge

The Alpha Ventus project was the first offshore wind farm, which was constructed in the German Bight - 45 kilometres from the coast of Borkum in a very hostile environment with water depths  of approximately 30 m. On top of that, Alpha Ventus was the first project in the offshore wind industry where jacket foundations were pre – piled.

Secondly the turbines needed to be installed on the jacket foundations. The turbines, being 5 MW Repower turbines, were the largest and heaviest turbines on the market.

Our solution

 
For the installation of the piles, GeoSea provided the jack-up platform Buzzard, equipped with a heavy lift crane and assisting tug boat. Firstly, a centre frame was positioned on the seabed. Secondly a guiding frame was positioned next to the centre frame with a connection between the two steel structures. The piles were then lifted and placed inside the guiding frame and hammered in the ground. Once the first pile had been driven into the seabed, the guiding frame had to be repositioned along the second side of the centre frame and the second pile could then be hammered. 4 piles were installed this way per foundation, with 6 foundations in total.
The turbines, each consisting out of 2 tower sections, 1 nacelle and 1 assembled rotor, were transported from the harbour to the offshore site by GeoSea’s jack-up platform Buzzard. The Buzzard could load all components for one wind turbine at once, which saved costs and time compared to an installation jack-upplatform sailing between harbour and site for each turbine. Once arrived on site the Buzzard positioned itself next to the installation jack-up platform Goliath. The Goliath – equipped with a Liebherr LR 1800 crane – lifted the turbine components directly from the Buzzard onto the jacket foundation for erection and commissioning of the turbines.
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