Scientists from Delft University of Technology in the Netherlands harnessed energy from the wind by flying a 10-sq metre kite tethered to a generator, producing 10 kilowatts of power.
An Italian company, Kitegen, has come up with a theoretical design for a system that could generate a gigawatt, as much power as a standard coal-fired power station. Its idea involves flying 12 sets of lines with four 500-sq metre kites on each. Kitegen has been covered several times by this site.
Researchers have plans to test a 50kW version of their invention, called Laddermill, eventually building up to a proposed version with multiple kites that they claim could generate 100 megawatts, enough for 100,000 homes.
Furey has worked out that flying kites in a figure of eight pattern means the air flowing over them travels even faster than the ambient wind speed. When a kite needs to be reeled in, it is angled so that it falls out of the sky like a glider, without the need for much power. Ockels's system uses these flying patterns to maximise the power the kites can generate. He is also looking at extending his basic prototype to use multiple kites that yo-yo: when one goes up, another goes down. Ockels estimates that kites could generate power at less than 4p per kilowatt-hour.
Google.org, the philanthropic arm of the Californian web-search company, invested $10m (about £5m) last year in a US kite company called Makani Power Inc.
The aim of both teams is to tap into high-altitude wind, which is an energy source that is more abundant and reliable than the ground-level wind on which normal turbines depend.
Ken Caldeira, a climate scientist at Stanford University's Carnegie Institution, has estimated that the total energy contained in wind is 100 times the amount needed by everyone on the planet. But most of this energy is at high altitude.