Offshore wind turbines Low-noise foundations are designed to protect harbor porpoises

Offshore wind turbines Low-noise foundations are designed to protect harbor porpoises

Offshore wind turbines Low-noise foundations are designed to protect harbor porpoises

In the North Sea, new foundations for wind turbines are to be tested in commercial operation, which can do without piling work and major noise pollution for the sensitive harbor porpoises. The Canadian energy company Northland Power, which is building the “Deutsche Bucht” wind farm with 31 turbines 95 kilometers northwest of Borkum far out on the open sea, will build two additional wind turbines on so-called suction bucket foundations. A corresponding approval from the Federal Maritime and Hydrographic Agency (BSH) has been in place since May, said Northland Power.

The two “buckets” in the wind farm are 61 meter high steel structures with a weight of 1100 tons. At their lower end they form an open cylinder with an outside diameter of 19 meters. The cylinder is placed on the seabed and the water is pumped out. Due to the negative pressure and its own weight, the bucket foundation digs up to 18 meters deep into the sea floor. This is followed by an intermediate piece and the wind turbine, in this case a Vestas model with an output of 8.4 megawatts. The work is planned for the 2nd quarter of 2019.

So far, the most common technique has been to anchor a heavy support pillar in the sea to support the wind turbine. The steel girder is driven into the seabed with a hydraulic hammer. A ramming impact creates a noise of more than 180 decibels, significantly more than a jet jet taking off. The impact can still be felt several kilometers away underwater. The sensitive porpoises in particular, which, like bats, use an acoustic image of their environment for orientation, can be seriously damaged, but so can seals, fish and inhabitants of the seabed.

Almost 1200 wind turbines were built in this way in the German North Sea alone, and twice as many will follow. Strict limit values ​​and various measures – for example bubble curtains, i.e. hoses that produce veils from air bubbles around the source of the noise in the water – are intended to keep the noise level as low as possible. But in addition to the construction noise, there is noise from the ship’s engines, the laying of cables on the seabed and the sonar of the ships. “The marine mammals can hardly find quiet areas to feed and reproduce,” says Kim Cornelius Detloff, marine protection expert at the environmental organization Nabu.

The vacuum bucket attempt met with applause from nature conservationists, but they also expressed criticism: “The problem is the long planning times of several years, during which the foundations are already being tilled,” says Detloff. That is why only 2 bonus wind turbines in the “Deutsche Bucht” wind farm will be built with the new technology beyond the actual permit, while the remaining 31 turbines will be built with conventional technology.

Vattenfall already has a smaller wind farm under construction off Scotland, which will be built entirely with suction buckets. Ørsted used this technology in 20 of 56 foundations in the “Borkum Riffgrund 2” wind farm. Both need three legs for the foundation. For the first time in the world, only one pillar is used in the “Deutsche Bucht” wind farm (mono buckets). This not only reduces the impact on the environment, but also costs. “The findings from this pilot project could enable Northland to build faster and more cost-effectively under certain site conditions,” says CEO John Brace.

The future of offshore wind energy could be wind farms that no longer stand on the sea floor, but on floating platforms. They are held in place with anchors weighing several tons. The technology has been tried and tested in oil and gas production, but stronger forces act on wind turbines. After all, five larger floating wind turbines are already in operation at Statoil’s “Hywind” wind farm off Scotland. The advantage: Wind farms could no longer be built in water depths of up to 60 meters, but far beyond. This would make huge expanses of sea possible locations for wind power plants.