An autopilot system could help energy-harvesting kites generate power from high-altitude winds.
With the average wind speed at altitudes beyond 1,000m above sea level reaching more than 300km/h, researchers have realised that putting wind energy generators high in the air would unlock enormous potential.
However, proven mechanisms to control such high-flying wind turbines are as yet non-existent.
Researchers at the Swiss Institute of Technology in Lausanne (EPFL) have now introduced a device that could make kite generators more controllable and thus more feasible.
"The trajectory of such kites must be adjusted continuously and accurately, otherwise it quickly crashes against the ground,” said Sean Costello, PhD student at the Automatic Control Laboratory at the EPFL, who designed the system.
“This type of energy-producing device requires continuous monitoring. Obviously, it is impossible for a human to control it round the clock. This is why we studied the development of an autopilot system."
The kite’s sail, acting as a wind turbine blade, resists the wind creating mechanical tension in its restraining cable. This tension, causing the cable to twist, flex and unwind, can drive an electricity generator that could be either located on board the kite or on the ground.
"The stronger the cable tension is, the higher the energy production capacity,” Costello said. “The autopilot that we have developed is able to find, in any given situation, the most efficient way to control the wind so that it moves as quickly as possible and generates a maximum tension in the cable. In general, the kite’s trajectory will have the shape of the number eight. Since some flight paths turn out more successful than others, the autopilot will determine which one is best in each situation."
To increase the system’s efficiency, Costello had to analyse wind patterns and measure how the changing wind affects a sensor-equipped test kite. Using special software, he evaluated the kite’s movements and the tension of the restricting cable to identify the most effective models.
With average wind speeds at ground level reaching only 40km/h, more than seven times less than at altitudes above 1,000m, high-altitude kites could theoretically yield more energy than off-shore or on-shore wind turbines.
How does it work? Watch a video below: