His idea works on a similar principle to a solar chimney, which consists of a tall, hollow cylinder surrounded by a large greenhouse. The sun heats the air in the greenhouse, and the hot air rises. But its only escape route is via the chimney. A turbine at the base of the chimney generates electricity as the air rushes by. A small solar chimney was operated successfully in Spain in the 1980s, and EnviroMission, an Australian firm, is planning to build a 1,000-metre-high example in New South Wales. But the efficiency of such a system is proportional to the height of the chimney, notes Mr Michaud, which is limited by practical considerations. His scheme replaces the chimney with a tornado-like vortex of spinning air, which could extend several kilometres into the atmosphere.
Tornado
