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Sandia pushes limits of solar technology

Can a heat engine invented in 1816 make solar dishes a viable electricity source for utilities Photo: Sandia and Stirling's solar setup

A Sandia National Laboratories project in New Mexico will test whether a farm of solar dishes can compete with conventional fuels for electricity generation.

The initiative calls for the installation of six dishes by the end of the year, which should create enough electricity to power 150 kilowatts of grid-ready electricity--enough to supply 40 homes. Stirling Energy Systems will supply the dishes and test the efficacy of the network of dishes with Sandia researchers.

The dishes, which have 82 individual mirrors in them, can automatically move to capture the most sun during the course of the day and then shut down at sunset. The system, which can be monitored via the Internet, requires minimal maintenance, according to Stirling Energy.

The installation will create the world's largest array of solar dishes that use the so-called Stirling system, according to Chuck Andraka, the Sandia project leader.

The invention of the heat-driven Stirling engine dates to 1816, but its use until now has been limited to specialized applications. The Stirling system in the Sandia project converts heat from the sun to power a motor, which generates electricity.

The Stirling engine had a brief moment of notoriety three years ago in the hoopla that preceded the unveiling of the Segway scooter. When the rumored device was still known as Ginger and details were few, some clues suggested--erroneously, as it turned out--that the device might be Stirling-powered.

Sandia's solar dishes direct the sun's rays onto a receiver that transfers the heat to an engine filled with hydrogen. As the hydrogen is heated and then cools, the pressure on the engine changes. That changing pressure drives the pistons, which in turn power an electrical generator.

Stirling Energy researchers believe that large formations of these dishes are viable--and pollution-free--energy sources for utility companies in the southwest, where there is a lot of sun, or potentially remote areas, such as the Navajo reservation.

Hypothetically, a solar-dish farm covering 11 square miles could produce as much electricity per year as the Hoover Dam, said Bob Liden, Stirling Energy's executive vice president and general manager.

The Stirling system dishes are more efficient than commonly used photovoltaic solar cells at converting the sun's heat to electricity, Liden said. The net solar-to-electricity conversion is 30 percent, which is substantially higher than what photovoltaic cells are capable of.

"Ultimately SES envisions 20,000 systems to be placed in one or more solar-dish farms and providing electricity to southwest utility companies," said Andraka, in a statement.

Liden said these prototype systems cost about $150,000. Once built in production, the cost could go down to $50,000 per unit, which would be competitive with some commonly used fuels.

According to the Department of Energy, about 70 percent of electricity in the United States is created by fossil fuels--coal, natural gas and petroleum. Nuclear power represents about 17.5 percent of electricity generation, and hydroelectric power is 6.7 percent. Other sources, including solar power, are about 2.7 percent.