Tuesday, October 11, 2005

Solar Chimneys and Tornado Power

Mongabay.com, Unplugged Living and we-make-money-not-art have all pointed to an interesting (odd?) power experiment: generating electricity by creating "artificial whirlwinds that can be controlled." According to the original source, an article in The Economist, Canadian engineer Louis Michaud's concept
...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.

This vortex would be produced inside a large cylindrical wall, 200 metres in diameter and 100 metres tall. Warm air at ground level enters via tangential inlets around the base of the wall. Steam is also injected to get the vortex started. Once established, the heat content of the air at ground level is enough to keep the vortex going. As the air rises, it expands and cools, and water vapour condenses, releasing even more heat. This is, in fact, what powers a hurricane, which can be thought of as a heat engine that takes in warm, humid air at its base, releases cold, watery air at the top of the troposphere, about 12 kilometres up, and liberates a vast amount of energy in the process. (Just as water requires heat to make it boil, it releases heat as it condenses back into a liquid.)
Mongabay's post has more information on solar chimneys, a concept WorldChanging has also covered in some detail. Perhaps I'm showing my ignorance of engineering, but this seems like the closest thing to a genuine perpetual motion machine I've ever seen. I'm not clear on the amount of energy that has to be fed back into the machine to run it vs. excess energy that can be fed to the grid, though.

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