On Deck. Stirling prototype for concentrating solar collector is at Sandia National Laboratory.

A proposed concentrating solar facility in California’s Mojave Desert could generate more electricity than all U.S. photovoltaic projects combined, if built. The 500-MW project, which is still subject to Public Utilities Commission approval, would be the world’s largest solar power facility.

Stirling Energy Systems Inc., Phoenix, and Southern California Edison Corp., Rosemead, Calif., recently announced a 20-year purchase-development agreement to build a solar generating station on 4,500 acres, 70 miles northeast of Los Angeles. Project costs have not been disclosed. It would use 20,000, 37-ft-dia parabolic dishes, each generating 25 kW, with an option to add 34,000 dishes for 350 MW more.

Stirling would finance, build, own, operate and maintain the plant, selling 100% of its electricity to SCE at an undisclosed fixed price. The U.S. Dept. of Energy announced its support for 1,000 MW worth of concentrating solar power projects throughout the Southwest earlier this year.

The system generates electricity with an engine using the Stirling cycle, a process that heats a sealed-in gas from an external source. Stirling’s concentrating solar dish harnesses heat from the sun with 82 mirrors, magnifying sunlight to 1,350°F and reflecting it toward a series of hydrogen-filled tubes that expand when heated. Cycling back and forth from cold to hot, the expanding gas drives a four-piston Stirling electric engine that generates up to 25 kW.

"Although concentrating solar dish technology has demonstrated high efficiencies, the issues have been with the reliability, operation and maintenance of the Stirling engines," says Terry Peterson, a solar consultant with the Electrical Power Research Institute, Palo Alto, Calif. "There is no performance data for anything this large to date."

"We've gone through two DOE contracts on dish engine critical components, and our efforts were characterized as one of the most successful solar projects ever," counters Bruce Osborn, Stirling’s CEO. "Maybe [EPRI] was thinking of other external combustion engines."

A six-dish, 150-kW Stirling prototype is operating at Sandia National Laboratory, Albuquerque. Stirling plans to have a 1-MW test facility operating by 2007 and the 500-MW plant by late 2011, says Osborn. A contractor and engineer have not been named.

(Photo courtesy of Randy J. Montoya/Sandia National Laboratories)