Utility scale parabolic trough solar concentrators harness the sun’s energy to make steam for electricity generation. The more efficiently that a trough can harness the sun’s energy and convert it to steam, the more electricity it will be able to make.

SkyFuel, a solar thermal power technology and service provider that was founded in 2007, today announced the results of thermal efficiency testing on its SkyTrough. DOE scientists at the National Renewable Energy Lab (NREL) performed the tests.

SkyTrough is the first utility-scale solar concentrator to employ ReflecTech Mirror Film, which was developed collaboratively by SkyFuel and NREL, instead of glass mirrors. For more on this technology, see “Should CSP Mirrors Be Glass or Metal?”

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 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 unique to the SkyTrough’s 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.”

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 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, according to the company.