Kilometer-High Solar Tower

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A new energy concept called a solar tower could generate enough electricity for 200,000 homes. Looking like a giant smokestack, it would release no noxious fumes — just sun-heated air. Demonstrated more than 20 years ago, the basic design calls for solar collectors to warm the air near Earth’s surface and then channel it up the tall central tower. Turbines placed at the bottom make electricity from the updraft.

"It’s a combination chimney, windmill, greenhouse," said Kim Forté of EnviroMission Limited in South Melbourne, Australia. EnviroMission has designed a kilometer-high solar tower (0.62 miles) and is now looking at possible sites in the southwestern United States. (livescience.com)