Flying wind farms

If it ever seems windy where you live, be thankful you do not live 10km up in the air. At that height, the jet-stream winds blow stronger and more constantly than ground level winds, carrying up to a hundred times more energy.

So, just as oil companies are drilling deeper and in more remote locations in search of new reserves, pioneer wind-power engineers are looking higher in the sky for new sources of energy. Conventional turbines will not take them there—the highest to date is just over 200 metres tall. So they are trying to invent a whole new technology for harvesting wind: electricity generators that fly.
One of the most ambitious ideas has been developed by Sky WindPower, a company based in San Diego and led by Dave Shepard. Mr Shepard began his career cracking Japanese military codes during the Second World War, then developed machines for reading written text. His work led to the squared-off numbers still seen on bank cards today.

Mr Shepard’s flying generator looks like a cross between a kite and a helicopter. It has four rotors at the points of an H-shaped frame that is tethered to the ground by a long cable. The rotors act like the surface of a kite, providing the lift needed to keep the platform in the air. As they do so, they also turn dynamos that generate electricity. This power is transmitted to the ground through aluminium cables. Should there be a lull in the wind, the dynamos can be used in reverse as electric motors, to keep the generator airborne.

Mr Shepard estimates these rigs could produce power for as little as two cents a kilowatt hour. That is cheaper than the three to five cents conventional energy generation costs. It is an attractive idea, but a flying generator is difficult thing to build—and there is a limit to how helpful existing helicopter technology will be. Aircraft require maintenance after a few days of operation, if not sooner. To operate cost-effectively, wind turbines will need to keep turning for many months without upkeep.

The Economist