Giant kites to tap power of the high wind

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.

The blades of modern commercial windmills sit around 80 metres from the ground, where the wind speed is almost five metres per second. At 800 metres, however, wind speed rises to seven metres per second, potentially generating considerably more energy.

It would be virtually impossible to build a standard turbine to take advantage of the wind at 800 metres, but kites could easily get to these heights. Furthermore, thanks to the high-speed jet stream, countries such as the UK, the Netherlands, Ireland and Denmark are particularly suited to flying kites.

'Pretty much anywhere in the UK you could run a kite plant economically, but you couldn't run a wind turbine economically,' said Allister Furey of the University of Sussex, who develops computer control mechanisms to maximise the power generated from kites.

A kite generates power by pulling on a string attached to generators on the ground. When it has reached its maximum height, it is reeled back down to repeat the process.

Using computer models, 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, which is comparable to coal power and less than half the cost of electricity from wind turbines.

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