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8
Hot Air as Fuel
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Anyone who lives in an attic apartment will tell you: Heat rises. But Australian entrepreneur Roger Davey has proposed using this simple fact of physics to create vast amounts of clean energy without burning any carbon fuels.

Davey's company, EnviroMission, wants to build a massive, 2,600-foot-tall (792.5-meter-tall) structure called a solar updraft tower in the Arizona desert [source: Almasy]. Instead of relying on solar panels to convert the sun's energy to electricity, the solar updraft tower would use a large, translucent sloping canopy, about as wide as a football field, to trap the sun's heat like a greenhouse. The hot air in the tent would reach a scorching 194 degrees Fahrenheit (90 degrees Celsius) and would flow into and up through the tower. As it rose, it would turn 32 turbines, spinning them fast enough to power generators and produce 200 megawatts of electricity per day, enough to provide power to 100,000 households [source: Almasy].

The concept has been demonstrated already on a smaller, experimental scale. In the early 1980s, a German construction company, Schlaich, Bergermann and Partner, built an iron tower capable of generating 50 kilowatts of energy on the Spanish plains, and operated it successfully seven years until its support cables broke during a storm. EnviroMission's improved $750 million design calls for the tower to be built from sturdier, more resilient steel and cement, which wouldn't need to depend on support cables, and company officials say it would last for 80 years, far longer than the average life of most conventional solar-generating facilities. According to EnviroMission, which already has worked a deal to resell its electricity to a southern California utility company, the small amount of carbon pollution created by the manufacture and shipment of the cement and other materials needed to build the tower would be offset after two-and-a-half years of power generation. A similar project also is being developed by a company in China [source: Almasy].

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