The planning and installation of an offshore platform requires precise knowledge of the subsoil, as large rocks discovered too late can delay planning and construction, thus rendering the whole project more expensive. Hence, construction preparation measures are always carried out before the construction of transformer platforms. Fraunhofer IWES employed the new method to check whether there are boulders in the subsurface of a wind farm area that had already been presurveyed for 50Hertz’s Ostwind 3 project. The seismic detection can be utilized to clarify whether it might be necessary to change the position of the transformer platform at an early stage to avoid damage during installation.

Data acquisition for boulder detection with the Manta Ray G1

With the aid of the patented Manta Ray G1, the IWES scientists can localize rocks and boulders at a depth of up to 100 m below the seafloor. The measuring system comprises a towed array equipped with seismic sensors (hydrophones) as well as positioning systems. During the survey of an area, the hydrophones pick up the reflected sound waves previously emitted by a signal source. This allows the subseafloor to be recorded step-by-step and mapped in three dimensions. Not only does the measuring system map the sediment layers, but its special design also enables the detection of boulders buried in the seafloor. This is possible thanks to the method of diffraction imaging, through which the acoustic energy diffracted by the boulders can be traced back to its point of origin. This method thus allows accurate localization of rocks within the mapped seafloor sediments.

Seismic measuring results reduce risks

“For us, precise knowledge of subsoil conditions is important for avoiding possible installation risks. It allows us to avoid construction delays and thus save costs. The technique has proved that it is effective and delivers the essential measurements that we need for precise planning,” said Dr. Henrich Quick, Head of Offshore Projects at 50Hertz.

Dr. Benedict Preu, Head of Department Subsurface Investigation at the Fraunhofer IWES, explained: “We employ our seismic measuring techniques to help 50Hertz to plan the platform as precisely as possible and minimize risks. We are continuously developing the technology further and know from our experience in preceding projects that the method works well and the data acquired are meaningful. This allows us to support the entire offshore industry in acquiring accurate knowledge of the subsoil and thus identify suitable solutions for all construction projects. In doing so, we are driving the expansion of the wind energy sector further.”

The detection on behalf of 50Hertz was performed within just one week aboard the survey vessel MV Situla. During this period, the vessel was mobilized, i.e., all the equipment and technology was made ready for use and tested, the measurements were performed, and the vessel was subsequently demobilized again.

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Contact person at the Fraunhofer Institute for Wind Energy Systems IWES
Project coordination, Dr. Benedict Preu, Head of Department Subsurface Investigation
Phone: +49 471 14290-189
E-mail: benedict.preu@iwes.fraunhofer.de

Contact partner at 50Hertz Volker Gustedt, Pressesprecher Kommunikation & Politik
Phone: +49 30 5150 2878
E-mail: Volker.Gustedt@50hertz.com

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About Fraunhofer IWES
Fraunhofer IWES secures investments in technological developments through validation, shortens innovation cycles, accelerates certification procedures, and increases planning accuracy by means of innovative measurement methods in the wind energy and hydrogen technology sectors. There are currently around 300 scientists and employees as well as more than 150 students employed at nine locations: Bochum, Bremen, Bremerhaven, Emden/Leer, Görlitz, Hamburg, Hannover, Leuna, and Oldenburg.
www.iwes.fraunhofer.de/en

About 50Hertz
50Hertz operates the electricity transmission system in the north and east of Germany, which it expands as needed for the energy transition. Our extra high voltage grid has an electrical circuit length of more than 10,000 kilometres, or the distance between Berlin and Rio de Janeiro. The 50Hertz control area covers Brandenburg, Mecklenburg-Western Pomerania, Saxony, Saxony-Anhalt, and Thuringia, as well as the city states of Berlin and Hamburg. Within these regions, 50Hertz and its around 1,400 employees ensure that 18 million people are supplied with electricity around the clock. 50Hertz is a forerunner in the field of secure integration of renewable energy. In our grid area, we want to integrate 100 percent renewable energies securely into the grid and system by 2032 - calculated over the year. The shareholders of 50Hertz are the Belgian holding Elia Group (80 percent), which is listed on the stock exchange, and the KfW bank group with 20 percent. As a European TSO, 50Hertz is a member of the European Network of Transmission System Operators for Electricity (ENTSO-E).
www.50hertz.com/en/