The largest parabolic troughs in the concentrating solar power (CSP) game were recently installed as a 275 kilowatt demonstration system at the Sunray Energy facility in Daggett, California. The LAT 73 reflective troughs have a 7.3 meter aperture and were developed through a partnership between Gossamer Space Frames and 3M. The new technologies could help increase interest in CSP trough systems, which have suffered as prices for photovoltaics have dropped.
The technology also helps reduce the costs of CSP systems by more than 25 percent by using lightweight materials and the more efficient troughs. “Two things drive the energy cost for CSP systems—performance and capital cost,” said Dr. Dan Chen, business manager of 3M’s Renewable Energy Division. “Higher optical accuracy drives higher performance. Less components drive lower capital cost.”
Rather than rely on glass for the reflective troughs, they use 3M’s Solar Mirror Film 1100. The film, mounted on aluminum sheets. The sheets offer 94.5 percent reflectivity. “For the aperture (size) of panels that we are manufacturing, our optical accuracy is two to three times better,” Chen said. In fact, the National Renewable Energy Laboratory (NREL) has measured an optical accuracy of more than 99 percent for the CSP systems.
The sheets and film are also 50 percent lighter than glass. The lighter weight of the panels allowed Gossamer to use less materials in designing the structure to support the CSP troughs, hence reducing the cost of materials for the system.
The facility where the CSP systems were installed is owned and operated by Cogentrix Energy. It is the longest operating CSP facility in the U.S., according to 3M. Cogentrix sells the power produced by the system to Southern California Edison. The new system has been operating since October 2011, but a ribbon-cutting ceremony was held last week to celebrate it’s launch.
Already the companies are working on another such system. “The second LAT 73 project is on the same scale as the Daggett site,” Chen said. However, he did not elaborate further. The second project is in the southern U.S. and is slated for commissioning in June 2012.