ALBUQUERQUE, New Mexico, USA, June 6, 2007.
A U.S. national laboratory has invented a design that will increase the efficiency of parabolic trough solar collector systems.
Rich Diver, a researcher at Sandia National Laboratories, designed a mirror alignment measurement device that will make parabolic troughs more affordable. His theoretical overlay photographic (TOP) technology addresses the inability of parabolic trough systems to provide accurate mirror alignment and, as a result, prevents maximum efficiency.
Borrowing from variations on methods used to align mirrors in solar dish systems, Diver designed the TOP alignment, an optical approach to rapidly and effectively evaluate the alignment of mirrors in parabolic trough power plants and prescribe corrective actions. Parabolic troughs use mirrored surfaces curved in a parabolic shape which focus sunlight on a receiver tube running the length of the trough.
“TOP alignment could cure a significant problem with trough systems; inaccurate mirror alignment that prevents sunlight from precisely focusing on solar receivers,” explains Diver. “Improperly aligned mirrors result in lost and wasted energy.”
The world's largest parabolic trough facilities are located in the Mojave Desert and consist of nine plants generating 354 MW of solar power at peak output. The plants range in size from 14 to 80 MW, and the 30 MW plants each have 10,000 modules with each module comprising 20 mirrors. A 64 MW trough plant will go online soon to supply electricity to Las Vegas (Nevada) and a 1 MW plant is operating in Arizona.
“This method could be used during trough power-plant construction to improve the performance of existing power plants or for routine maintenance,” says Diver. “It should be an ideal mirror alignment technique because it is simple to set up, requires a minimum of sophisticated hardware, and does not require removal of the receiver.”
The TOP approach consists of a pole with five cameras positioned along it. Four of the cameras take digital photographic images of the four rows of mirrors on the parabolic module, and the middle camera photographs the module's centre where an attached boresight gauge is used to vertically centre the pole to the trough module.
Vector algebra and projection theory are used to predict the theoretical projected image of the receiver for perfectly aligned mirrors. The calculated theoretical image of the receiver is overlaid on photographs of the actual receiver image position in the mirrors, and those images and the actual image are compared to show how the mirrors should be aligned.
“This whole process is very simple,” Diver adds. “Once the mirrors are aligned, the energy savings start. It's like picking money off the ground and the mirrors are aligned for the life of the plant.”
The TOP technique was developed using a 20-year-old parabolic module located at the Sandia National Solar Thermal Test Facility in Albuquerque. Researchers tested the technique at a trough plant near Tucson, last year and the next step is to test more systems later this year and then license the technology to parabolic trough power plant operators or trough project developers.
“It should be an ideal mirror alignment technique because it is simple to set up, requires a minimum of sophisticated hardware, and does not require removal of the receiver,” adds Diver.
Sandia is a multi-program laboratory operated by Sandia, a Lockheed Martin company, for the U.S. Department of Energy's National Nuclear Security Administration.