A Worldchanging post rounds up three different airborne power-generation systems — a flying windmill, a windmill-equipped zeppelin, and a kite-based windmill.
According to their figures, one flying windmill rated at 240kW with rotor diameters of 35 feet could generate power for less than two cents per kilowatt hour–that would make them the cheapest power source in the world. For greater power needs, several units would be operated in the same location–Sky Windpower says that an installation "rated at 2.81 megawatts flying at a typical U.S. site with an eighty percent capacity factor projects a life cycle cost per kilowatt hour at 1.4 cents." And they would have far better uptime than most windmills–since the jetstream never quits, they should operate at peak capacity 70-90% of the time. Output would also be less dependent on location than it is on the ground, simply because terrain doesn't matter much when you're at 35,000ft; however, since the jetstream and other "geostrophic" winds don't blow much at latitudes near the equator, it would be useful primarily for middle- and higher-latitudes.
