Record-setting solar power

By Chris Burroughs

On a perfect New Mexico day Sandia and Stirling Energy Systems (SES) set a new solar-to-grid system conversion efficiency record by achieving a 31.25 percent net efficiency rate.

"This advances our dish engine systems well beyond the capacities of any other solar dish collectors," says Bruce Osborn, SES president and CEO, "and moves it one step closer to commercializing an affordable system."

An SES dish unit consists of 82 mirrors formed in a parabolic dish shape to focus the light to an intense beam. The solar dish generates electricity by focusing the sun's rays onto a receiver, which transmits the heat energy to a Stirling engine, which is a sealed system filled with hydrogen. As the gas heats and cools, its pressure rises and falls. The change in pressure drives the pistons inside the engine, producing mechanical power, which drives a generator and makes electricity.

Sandia provides technical and analytical support to SES in a relationship that dates back more than 10 years. Dishes at the six-dish Model Power Plant at Sandia’s Solar Thermal Test Facility produce up to 150 kilowatts (kW) of grid-ready electrical power each day.

The record-setting test ran for two and a half hours. During the testing phase, the system produced 26.75 kW net electrical power.

Lead Sandia project engineer Chuck Andraka says several technical advancements to the systems made jointly by SES and Sandia led to the record-breaking solar-to-grid conversion efficiency. SES owns the dishes and all the hardware.

Osborn says SES has signed power purchase agreements with two major Southern California utilities (Southern California Edison and San Diego Gas & Electric) for up to 1,750 mega-watts (MW) of power, two of the largest solar power contracts ever granted. Collectively, these contracts require up to 70,000 solar dish engine units.

"This exciting record shows that using these dishes will be a cost-effective and environmen-tally friendly way of producing power," Osborn says. "SES is actively engaged in the commer-cialization of a system called the 'SunCatcher.' The demonstrated high efficiency means more energy is generated for the given investment, lowering the cost of the energy delivered."