The idea of reaching higher above ground for stronger, more consistent winds – using either taller turbines or some kind of tethering system – isn’t new, but a German company and researchers at the Fraunhofer Institute are pursuing a vision that falls somewhere in that vast terrain between crazy and inspired.
They’re using kites, but instead of doing so to hoist a turbine aloft, as we’ve seen, they’re using the kites – like the ones used in kitesurfing – to pull vehicles on rails around a circuit. The kinetic energy of the moving vehicles is then converted by generator to electricity.
“The energy yield of a kite far exceeds that of a wind turbine, whose rotor tips turn at a maximum height of 200 meters. Doubling the wind speed results in eight times the energy,” Joachim Montnacher, of Fraunhofer’s Institute for Manufacturing Engineering and Automation IPA in Stuttgart, said in a statement. “Depending on wind conditions, eight kites with a combined surface area of up to 300 square meters can equate to 20 conventional 1-megawatt wind turbines.”
As wacky as the idea sounds, the company NTS and the researchers from the IPA are dead serious here, inspired not only by the possibility of accessing those higher elevation winds – twice as likely to blow at 5 meters per second at 500 meters vs. at 100 meters – but also by doing so at low cost.
“It costs considerably less to build a system that, among other things, does not require towers each weighing hundreds of tons,” Fraunhofer said.
So the company and the institute are pushing ahead, with NTS charged with designing the kites and building the high-altitude wind farm, and the IPA working on the control and measuring technology. Franhoufer explained the importance of the control unit:
One of the jobs of the control unit is to transmit the measuring signals to the cable control and kite regulation mechanisms. A horizontal and vertical angle sensor located in each cable line and a force sensor within the cable distributor guarantee precise control of the kite’s movements as it follows either a figure-of-eight or sine-wave flight path up above. These flight maneuvers generate a high pulling power of up to 10 kilonewtons (kN) – meaning that a 20-square-meter kite has the capacity to pull one ton. Each vehicle is pulled by a different flight system.
Fraunhofer said that the researchers and NTS used remote control to test a kite along a 400-meter straight track, but the plan is to go to the automated system on a loop track.
“According to our simulations, we could use an NTS track running a total of 24 kites to generate 120 gigawatt hours a year (GWh/year). To put this into perspective, a 2-megawatt wind turbine produces around 4 GWh/year. So an NTS system could replace 30 2-megawatt turbines and supply power to around 30,000 homes,” said Guido Lütsch, managing director of NTS GmbH.