Kite surfing is more than just a hobby for some researchers at TU Berlin. The five-person Airborne Wind Energy Systems research group is pursuing the vision of using this option to breathe fresh wind into the sails of the energy revolution.
“This technology has the potential in the near future to provide millions of people with cost-effective, more or less non-location specific, climate-neutral electricity,” says Alexander von Breitenbach. “This would represent an evolutionary step in the history of wind power.” Von Breitenbach is a researcher in the Chair of Fluid Dynamics at TU Berlin (Faculty V – Mechanical Engineering and Transport Systems) led by Professor Oliver Paschereit.
Wind energy has been a permanent feature of the German energy mix since the 1990s. In 2018, wind energy provided approximately 20 percent of electricity generated in Germany. However, it is now reaching its limits. “The areas of Germany with the most wind are already fully utilized and there is a limit to how high you can build these gigantic wind turbine structures to fully utilize the strongest winds,” von Breitenbach adds. Airborne wind energy systems can help provide a solution. Three-blade wind turbines cover large areas of the European countryside, providing people with a clean alternative to fossil energy sources such as coal, gas or oil. The hubs of these structures are positioned at a height of 130 meters. The higher you go, the stronger and more constant the winds are, meaning that airborne wind energy systems located at between 300 and 700 meters can tap into a stronger, more constant, all-year-round wind source.
How does an airborne wind energy system work? The kite element spirals up in the wind, unwinding the holding rope and driving the generator in the ground station which in turn creates electricity. The kite element spirals ever higher, generating more and more electricity via the rope connection as it does so.
A further advantage of the system: Airborne wind energy systems can provide enormous savings in material and investment costs: Rotor blades weighing tons, solid towers and reinforced concrete foundations that absorb the aerodynamic forces generated on the rotor surface currently account for more than 50 percent of investment costs. These would become surplus to needs, as the ground station of an airborne wind energy system including generator need not be bigger than a car and has the added advantage of being mobile and thus not tied to a specific location. Airborne systems can achieve 75 percent of full capacity annually, compared with conventional wind plants which achieve only 35 percent. Re-using the foundations of off-shore wind plants for airborne systems rather than having to rebuild the towers every twenty years enables a further huge saving in terms of concrete and raw materials.
“Airborne wind energy systems, whether in the form of kites, zeppelins, or other forms of airship, are still very much in their infancy,” says Dr. Christian Nayeri, head of the Airborne Wind Energy Systems research group. “We are primarily concerned with creating the scientific foundations for this technology of the future.” This includes optimizing the aerodynamics of the system, plotting and calculating the best aerial routes, conducting computer simulations and experiments using models in TU Berlin's wind tunnels as well as under water in the University's 250-meter-long towing tank, one of the largest scientific towing tanks in Europe, and, above all, the design of the automated self-control of the airborne turbines, which have to regulate their heights or their alignment to the wind independently as there is no pilot on board. Industry is also taking a close interest, as the research group’s work actively contributes to the regenerative energy revolution of tomorrow.