Tuesday, August 11, 2009

Solar Grid

Solar Thermal Power May Make Sun-Powered Grid a Reality

It's solar's new dawn. For five decades solar technologies have delivered more promises than power. Now, new Breakthrough Award–winning innovations are exiting the lab and plugging into the grid—turning sunlight into serious energy.
Published in the November 2008 issue.

Solar Stirling Engine: Each Stirling Energy SunCatcher dish can produce 60,000 kilowatt-hours of electricity a year—enough to power a dozen U.S. homes. (Photograph by Jamey Stillings)

Planted in the New Mexico desert near Albuquerque, the six solar dish engines of the Solar Thermal Test Facility at Sandia National Laboratories look a bit like giant, highly reflective satellite dishes. Each one is a mosaic of 82 mirrors that fit together to form a 38-ft-wide parabola. The mirrors’ precise curvature focuses light onto a 7-in. area. At its most intense spot, the heat is equivalent to a blistering 13,000 suns, producing a flux 13 times greater than the space shuttle experiences during re-entry. “That’ll melt almost anything known to man,” says Sandia engineer Chuck Andraka. “It’s incredibly hot.”

The heat is used to run a Stirling engine, an elegant 192-year-old technology that creates mechanical energy from an external heat source, as opposed to the internal fuel combustion that powers most auto­mobile engines. Hydrogen gas in a Stirling engine’s four 95 cc cylinders expands and contracts as it is heated and cooled, driving pistons to turn a small electric generator. The configuration of the dish and engine represent the fruit of more than a decade of steady improvements, developed in collaboration with Arizona-based Stirling Energy Systems.

On a crisp morning this past January, Andraka and his colleagues fired up Dish No. 3. The temperature was around freezing, and the sky was 8 percent brighter than average—the contrast between the cold air and the hot sun helps the engine run more efficiently. When power began to flow from the 25-kilowatt system, it did so with the highest conversion efficiency ever recorded in a commercial solar device: 31.25 percent of the energy shining onto the giant dish flowed into the grid.

To Bruce Osborn, president and CEO of Stirling Energy, this merely confirmed something that he already knew: to read more click here


BBC World Service | Home