ALBUQUERQUE, N.M. —On a perfect New Mexico winter day — with the sky almost 10 percent brighter than usual — Sandia National Laboratories and 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 Jan. 31 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.
“Gaining two whole points of conversion efficiency in this type of system is phenomenal,” says Bruce Osborn, SES president and CEO. “This is a significant advancement that takes our dish engine systems well beyond the capacities of any other solar dish collectors and one step closer to commercializing an affordable system.”
Phenomenal? If it took them 24 years to gain 2% of efficiency and it is still more expensive than coal electric or nuclear (and that's probably the case) then I'm not so excited.
Improved optics helped to achieve this record.
Andraka says the first and probably most important advancement was improved optics. The Stirling dishes are made with a low iron glass with a silver backing that make them highly reflective —focusing as much as 94 percent of the incident sunlight to the engine package, where prior efforts reflected about 91 percent. The mirror facets, patented by Sandia and Paneltec Corp. of Lafayette, Colo., are highly accurate and have minimal imperfections in shape.
Note, however, that they also benefited from a cold day. This suggests that in sustained operation the real efficiency would be lower.
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.
Still, they've moved the state of the art closer to commercial feasibility. But will nanomaterial photovoltaics blow right past stirling engines for lower cost solar power? Or can the solar concentrator approach fall substantially in cost too?
|Share |||Randall Parker, 2008 February 13 09:36 PM Energy Solar|