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The suction bucket before immersion in the Tragstrukturen test centre in Hanover

© Fraunhofer IWES

The conventional method for laying the foundations of offshore wind energy systems consists of driving between one and four pylons into the seabed. This requires a heavy-duty, technical device that is noisy and this disturbs marine life.

Scientists at the Fraunhofer Institute IWES have now completed tests on an alternative technology which doesn’t have any of these disadvantages. The suction buckets are steel cylinders that are closed at the top whose shape resembles that of an upturned bucket. Pumps on the inside of the cylinder create a vacuum which ‘sucks’ the cylinder into the ground (suction). If the wind turbine has to be dismantled, the suction bucket can be completely removed.

After a six-month period, the project was successfully concluded at the end of February. Attention focused more particularly on measuring the impact of the push and pull effects prevalent in the sea on the suction budgets installed in the seabed. The seabed conditions and forces existing in the North Sea could be perfectly simulated at the Tragstrukturen test centre at Leibniz University in Hanover: a ten-metre deep pit with 1,250 m³ of sand and four wells for supplying water were needed. Artificially generated push and pull on the immersed suction bucket simulated the effect of the waves. The test centre in Hanover was built between June 2011 and May 2016 with funding amounting to EUR 12 million from the Federal Ministry for Economic Affairs and Energy (BMWi).

The tests performed demonstrated above all the advantages of this low-noise technology: in the space of just one hour, the steel cylinder sucked itself into the test ground.