Wind energy

Wind energy capacity must be increased by at least 9 gigawatts a year between now and 2030 in order to produce enough CO₂-free electricity for Germany. To achieve these targets, increasing the size and capacity of offshore wind energy plants will be vital − as will optimizing plant operations and reducing downtime. Wind energy is based on highly ad­vanced plant technology, which is also the result of a plethora of innovative research projects. In the last five years, the Fraun­hofer Institute for Wind Energy Systems IWES alone worked on 500 research proj­ects, covering everything from planning processes, development, construction and operation to machine monitoring, repair processes, service life and the removal and reuse of all components.

But it will take even more research to exploit the full potential of offshore tech­nologies. After all, the conditions that these gigantic plants must work in are extreme − salt water, hurricanes with 12 force winds, and waves that tower at 15 meters. And there are other challenges too. Because laying foundations at sea is such an ex­pensive business, the plants are built at the largest scale possible. The largest biggest prototype to date has a rotor di­ameter of 222 meters and a maximum capacity of 14 megawatts. Before construc­tion, the plants and their components must be tested extensively and under realistic conditions. Fraunhofer IWES has built the necessary testing infrastructure and is assisting the industry sector in testing the latest prototypes and continuously ad­vancing development of their validation methods.

But extreme storms are not the only challenge for high-tech offshore plants – major risks for the construction of these enormous facilities lurk at the bottom of the sea as well. Objects like boulders on the sea floor are a particularly serious risk, as the foundation structures could hit them during installation. If this results in such severe damage to the structures that they have to be removed and replaced, this could cause direct costs of up to 15 million euros – with additional secondary costs in the multidigit million range. However, that risk can now be significantly reduced thanks to a measurement process devel­oped by Fraunhofer IWES and the Uni­versity of Bremen. “We generate acoustic signals from an electrical or pneumatic source and transmit them to the ground. If there’s an object there, it will reflect the sound – and we can measure that,” says Dr. Benedict Preu, Head of the Sub-surface Investigations department at Fraunhofer IWES. Word of this innovative approach got around quickly in the world of wind farm operators. “We already have requests for up to 120 million euros for the next few years, coming from all over the world – far more than we can manage,” relates Dr. Preu. Licensing agreements are now being put in place to help meet the deluge of requests. The impact of the technology has even spread to the insurance business. Insurance providers take the Fraunhofer IWES investigation technique into ac­count when calculating premiums.

The IWES also aims to develop the technique further, so that it can detect cables laid in the ground – like the high-voltage cables for transporting pow­er from the wind farms to land. According to government requirements, the position and depth of these cables must be checked once a year, to ensure they do not present any risks to fishing or sharply increase the temperature of the sea floor. However, when using conventional procedures, these checks entail turning off the power cables for up to two weeks. As a single high-volt­age cable often carries power from up to ten wind farms, this quickly racks up some serious costs. “With our technology, for the first time, it’s possible to exhaustively survey the position and depth of the cables, even during active operation,” says Dr. Preu.