Thermal efficiency is the proportion of available sunlight that is converted into heat and available to generate electricity in the power block. It is used to predict the performance of a given parabolic trough and compare competing technologies. NREL tests show the SkyTrough's thermal efficiency at 350 ˚C (662 ˚F) to be over 73%, meaning that nearly three quarters of the solar radiation striking the trough surface is converted into thermal energy.
NREL's results confirm that the SkyTrough® delivers performance comparable to or exceeding that of the previous, proven, utility-grade trough systems at a cost that is well below industry standards. "A lot of thoughtful engineering went into the SkyTrough® so we were confident our efficiency would be high, but NREL's confirmation really validates our technology. We couldn't be more pleased with NREL's assessment", said Randy Gee, SkyFuel's Chief Technology Officer.
NREL scientists combine the results of two tests to establish a collector's thermal efficiency. Performance of the optical elements of the SkyTrough was measured at the Optical Efficiency Test Loop in Golden, Colorado.
The test facility design allows study of the optical performance independent of the receiver's heat loss characteristics. Optical efficiency is a direct gauge of the design elements that set the SkyTrough® apart - mirror reflectance, parabolic accuracy, receiver alignment to the focal line of the trough, and the system's tracking precision. "The SkyTrough solar collector is a new, low-weight design that takes advantage of the patented reflector film jointly developed by SkyFuel and NREL," said Chuck Kutscher, Principal Engineer and Manager of NREL's Thermal Systems Group. "Helping industry achieve higher efficiencies and lower costs is central to the mission of our Concentrating Solar Power (CSP) research program."
In a separate test at NREL's Parabolic Trough Receiver Heat Loss Test Stand, scientists measured the heat loss from the SkyTrough's SCHOTT PTR80 receiver. This is crucial because, no matter how well the SkyTrough's optical elements perform, the overall ability of the system to deliver usable heat for power generation depends on how well the receiver retains the heat it collects. The new 8 cm diameter SCHOTT PTR80 performed well - on par with SCHOTT's 7 cm PTR70, the current industry standard for utility grade parabolic trough systems.
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