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Saved By the Sun

New Ways to Catch Rays

With evidence mounting that the global warming trend is accelerating, finding solutions to our dependence on fossil fuels for our growing energy needs is becoming increasingly urgent. A significant part of the solution may well lie in solar energy. Today, a host of scientists and entrepreneurs are busy developing new means of harnessing the abundant, renewable, and entirely free energy of the sun. In this slide show, take a look at six of the hottest new solar technologies.—Evan Schwartz


Thermal trough
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Thermal trough
This is the world's largest solar power plant, situated on a stretch of land larger than New York's Central Park. Out in the Mojave Desert, three hours from Los Angeles, rows of trough-shaped mirrors collect and concentrate the sun's heat and ultraviolet radiation to cook tubes of synthetic oil up to 750°F. The hot oil is piped to a generating station to flash-boil water, making steam that drives a traditional power turbine. Built in the mid-1980s, the Kramer Junction plant has been reliably providing about 350 megawatts of peak power to the L.A. grid, enough to power more than 150,000 homes.



Thermal trough
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Thermal trough (continued)
A second major "thermal trough" plant of this kind, called Nevada Solar One, is expected to open in spring 2007 just outside Las Vegas, Nevada. Improved technology will provide 64 megawatts of power to the grid, enough for 32,000 homes.



Mirrored dish
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Mirrored dish
Resembling large satellite dishes, these giant mirrored dishes collect solar radiation and use it to generate electricity in a novel way. Each dish bears its own Stirling engine, which works by using heat to expand a hot gas that drives pistons to produce electricity. Developed by Stirling Energy Systems, early versions are in use at Sandia National Laboratories in New Mexico.



Mirrored dish
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Mirrored dish (continued)
Two large California utilities have signed contracts to buy 800 to 1,750 megawatts of electricity from 32,000 to 70,000 of these Stirling dishes, to be located in southern California deserts (see artist's rendering at right). Construction is slated to begin in late 2008.



Thin film
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Thin film
The solar films seen on the roof of this home aren't as efficient as silicon panels in converting sunlight into electricity. But the materials, which are made by United Solar Ovonic, are so flexible that they can be made into aesthetically pleasing shingles.



Thin film
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Thin film (continued)
Flexible thin-film modules form the solar roof of New York's Stillwell Avenue subway station. It's one of the world's largest thin-film, building-integrated installations. Sixty thousand square feet of panels generate 210 kilowatts of power, enough to meet two-thirds of the station's energy requirements.



Triple-junction cell
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Highly concentrated sunlight
This is one of three High Concentration Photovoltaic arrays operating at Nevada's Clark Power Station. These giant panels, produced by Amonix Corp., use optical lenses to concentrate an intense amount of sunlight onto solar cells. Since each lens channels "250 suns" worth of light to each square in the panel, the same amount of electricity can be produced using a fraction of the silicon material typically required. Each array generates 25 kilowatts of electricity, enough to power about a dozen homes.

Solar paint
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Solar paint
Imagine generating electricity via the paint on your house or business. Nano-solar paint, now under development, works just like a silicon solar panel but at a fraction of the cost. At its heart is a dark, sunlight-absorbing paint coated onto the surface of aluminized mylar, which conducts electricity. A protective clear layer of indium tin oxide that covers the paint also conducts electricity. When sunlight strikes the paint, electrons are knocked loose, reaching wires that channel electricity to the home.



Sun-grown biofuel
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Sun-grown biofuel
This is a bioreactor that recycles carbon dioxide emissions from a traditional power plant. The apparatus traps the carbon within ordinary algae cells, which multiply through natural photosynthesis. This prototype bioreactor, created by GreenFuel Technologies Corp., was originally tested on the rooftop of a power plant at MIT. More recently, a larger version was installed at the Redhawk natural gas power plant in Arlington, Arizona.



Sun-grown biofuel
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Sun-grown biofuel (continued)
After the algae cultures trap the carbon, most of the water is removed, and the green sludge is put in large tubes and shipped to a conventional biodiesel processing plant, where liquid biogas is produced for diesel cars and trucks.



Interactives

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Evan Schwartz is a writer and producer for "Saved By the Sun" and the author of Juice: The Creative Fuel That Drives World-Class Inventors (Harvard Business School Press, 2004).

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