Energy futureWorld solar-to-grid conversation efficiency record set
Sandia, SES achieve solar-to-grid conversion efficiency rate of 31.25 percent; increasing conversion rate, coupled with the rising price of oil and worries about the environment, make solar power more attractive
On a clear day in New Mexico you can see forever. On a recent winter day, with the sky almost 10 percent brighter than usual, Sandia National Laboratories and Phoenix, Arizona-based Stirling Energy Systems (SES) set a new solar-to-grid system conversion efficiency record by achieving a 31.25 percent net efficiency rate. The old 1984 record of 29.4 percent was toppled on 31 January on SES’s “Serial #3” solar dish Stirling system at Sandia’s National Solar Thermal Test Facility. The conversion efficiency is calculated by measuring the net energy delivered to the grid and dividing it by the solar energy hitting the dish mirrors. Auxiliary loads, such as water pumps, computers and tracking motors, are accounted for in the net power measurement.
Serial #3 was erected in May 2005 as part of a prototype six-dish model power plant at the Solar Thermal Test Facility that produces up to 150 kilowatts (kW) of grid-ready electrical power during the day. Each dish unit consists of 82 mirrors formed in a 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. The engine 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 in turn drives a generator and makes electricity. The advancements to the solar dish-engine system that helped Sandia and SES beat the energy conversion record were a new, more effective radiator that also costs less to build and a new high-efficiency generator.
All the enhancements led to a better system, but one aspect made it happen on a beautiful New Mexico winter day — the weather. The temperature, which hovered around freezing, allowed the cold portion of the engine to operate at about 23 degrees C, and the brightness means more energy was produced while most parasitic loads and losses are constant. The test ran for two and a half hours, and a 60-minute running average was used to evaluate the power and efficiency data, in order to eliminate transient effects. During the testing phase, the system produced 26.75 kW net electrical power.
SES was formed in 1996 to develop and commercialize advanced solar technology. The company maintains its corporate headquarters in Phoenix, Ariz, project and technical development offices in Tustin, Calif, and engineering and test site operations at Sandia National Laboratories in Albuquerque.
