The Economist is struck by how jet-stream winds are stronger and blow more consistently than ground-level winds, and can carry up to a hundred times more energy. This provides an incentive for to inventing a whole new technology for harvesting wind: electricity generators that fly.
Sky WindPower of San Diego, led by Dave Shepard,proposes a 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 as the surface of a kite does, 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 thinks he has a way to reduce rotor balance wear and tear.. 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,putting massive stress on the turning mechanism and wears it out rapidly. With 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
In Canada a company called Magenn Power has developed a proposal for a wind generator filled with helium. It turns around a horizontal axis, rather like a water mill, and could fly at an altitude of up to 1km.
Wubbo Ockels of the Delft University of Technology's idea is to launch a kite (without rotor blades) from a ground station, turning a generator as it rises to an altitude of several hundred metres. When it reaches its maximum altitude the kite alters its shape to catch less wind, and can thus be reeled back in using much less energy than it produced when it was being paid out. An arrangement of two or more of these kites could act together to produce a steady supply of power.
While one kite was being released, some of the electricity produced would be used to reel another kite back in, and vice versa. This system has the advantage that it requires only simple parts—generators, kites and cables—and should therefore be much cheaper to build than a conventional wind turbine. To test the idea Dr Ockels's team is building a 100-kilowatt prototype. He hopes to start testing a full-scale device, which would generate 10 megawatts, within five years.