Interesting idea in The Economist:
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’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.
Mr Shepard, however, thinks he has a way out. Stabilising and directing a conventional helicopter requires that the pitch of the individual blades be adjusted with every rotation—up to a thousand times a minute. That puts massive stress on the turning mechanism and wears it out rapidly. On a four-rotor arrangement, you can achieve the same effect by changing the pitch of one or two whole rotors, rather than adjusting the pitch of individual blades. Mr Shepard reckons that this will make a big difference, and will increase the periods between maintenance enough to make the project viable.
See also:
- Canada’s Magenn Power, 1km floating turbines