Pioneering achievement on the high seas

This marks the beginning of a new era in wind energy

The first German wind farm, “alpha ventus”, has been built in 30 meters of water some 45 kilometers north of the island of Borkum. The 12 turbines of this wind farm, each with an output of 5 MW, will supply electricity for around 50,000 people. The intention is to install a total of up to 25,000 MW of power by 2020.

Foundation for transformer station

The foundation for the alpha ventus transformer station is made from four tubular steel piles, each approx. 40 meters long and weighing up to 110 tons. The combination of vibration and impact-driving enabled several conditions to be fulfilled.

After detaching the transport apparatus, the vibrator was mounted directly on the steel pile, thus holding and aligning it. Load distribution plates with two clamp grips are used to transfer the force of the vibrator to the pile. This dispenses with the need for an elaborate guiding frame and a tool to suspend the pile. That in turn saves space on the already very congested installation platform. A pile-mounted vibrator permits simple vertical installation and optimum driving time and is extremely cost-efficient.

Foundation for the wind turbines.

The amount of steel used in a wind turbine structure is about 1,000 tons, which is equivalent to the weight of 200 fully grown elephants or 22 railway carriages. The rotor catches the wind over an area roughly equal to one-and-a-half football pitches. When rotating at maximum speed, the tips of the rotor blades cut through the air at almost 320 kilometers per hour.

Obviously, anchoring these installations securely to the seabed is a major challenge. Once the transformer station had been constructed, six wind turbines were mounted on tripods – frameworks anchored to the seabed by means of steel piles. In this project three piles – each weighing approx. 130 to 160 tons – were driven into the seabed per tripod.

The dimensions are extraordinary: The hub of the wind turbines is 90 meters above sea level. Added to this are another 30 meters below the waterline. A complete system, including the rotor, reaches around 155 meters, almost as high as Cologne cathedral.