Wind turbines convert wind energy into electrical power, but it takes a lot of material to build them. Freiburg researchers are developing tethered airplanes and kites that could serve as an alternative: They use less material and are even more efficient at harvesting wind energy than wind turbines. “Such kites are the same size as the wing tips of a fixed wind turbine,” explains Moritz Diehl, professor of systems theory, control engineering, and optimization.