Could high-flying drones power your home one day?
A growing number of companies believe using kites and drones is a viable way to harness the stronger and more consistent high-altitude winds. Could this tech release wind power's full potential, or will it always remain a niche solution?
Wind power generated five times more electricity in 2018 than in 2008, according to recent figures from the US Energy Information Administration. Yet it still only accounts for about 4% of the world's electricity.
Critics point to the fact that the wind doesn't always blow making this form of renewable energy unreliable. But winds at higher altitudes - above 500m - blow stronger and more consistently. An influential 2012 study from California's Lawrence Livermore National Laboratory found that high-altitude winds alone could provide 100 times the global energy need.
"Wind turbines have been getting bigger and bigger in a bid to access winds at high altitude," says Udo Zillmann of trade association Airborne Wind Europe. "But that means huge, expensive towers." So hi-tech drones and kites are now becoming accepted, lower-cost supplements, he argues.
"Airborne wind energy is a minimalistic version of a turbine, incorporating only the necessary elements: a blade and a tether measuring a few centimetres in diameter," he explains. "These systems require between 1% and 10% of the materials used to construct a turbine and can also be grounded if required, for example to ease the passage of migrating birds."
Makani, part of Google's parent company Alphabet, is one of the companies working in the high-altitude wind space. Its huge prototype kite is tethered to the ground and guided in loops by flight computers that use GPS and other sensors. As the kite completes its loops, rotors on the 26m (85ft) wing spin in the wind, powering generators to produce electricity down the tether to the grid.