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Energy production in flight

Bye-bye windmills? Engineers at the University of Freiburg are researching airborne wind turbines

Anyone who has ever flown a kite during a strong windstorm is familiar with the kind of power tugging at the kite’s line. Relying on stunt kites, Moritz Diehl, professor for systems control and optimization laboratory at the Department of Microsystems Engineering at the University of Freiburg is working with the strength of high-altitude wind that is constantly blowing at 300 to 500 meters.  

A major advantage over existing wind turbines lies in the material savings because producing energy from wind using stunt kites does not require enormous wind turbines, but rather delicate kites or aircraft, which siphon off the wind energy on a rope high in the air. “With our kites, we reduce a windmill to a single wingtip,” explains Moritz Diehl. The typical concrete towers and rotor blades are thus rendered obsolete. Even when it’s suddenly still on the ground and the windmills are standing still, the wind is almost always blowing at higher altitudes. A kite should be able to produce twice as much energy in the future as a traditional windmill.

Energy product operates through the rope attached to the kite and to a winch, the power generator, located on the ground. Relying on the wind’s energy, the rope is pulled up and down like a yo-yo. In order to harvest the utmost energy, the stunt kites have to move in certain trajectories, at best in the form of an eight. In order to achieve this, the Freiburg researchers require control technology because otherwise the stunt kites would collide.

“We are working on improving take-off and landing because both of these processes are particularly critical and costly,” Diehl says. Similar to a chain carousel, the aircraft should become airborne with a rotation take-off. A device rotates the aircraft first in a circle, then the rope lengthens and the aircraft rises into a power-generating position. It should also reach the ground in the same way.

 In addition to a lot of programming work, everything is tested on a prototype in a hangar on the campus of the Faculty of Engineering in Freiburg. High-altitude wind research is still in its infancy, but Diehl has come a good deal closer to achieving it.