Staring Directly into the Sun - Solar Collection Made More Efficient

A mirror alignment measurement device, invented by Rich Diver, a researcher at Sandia National Laboratories, may soon make one of the most popular solar collector systems—parabolic troughs— more affordable and energy efficient.

Diver’s new theoretical overlay photographic (TOP) technology is drawing interest from the solar industry due to its simplicity and effectiveness.

“TOP alignment could cure a significant problem with trough systems—inaccurate mirror alignment that prevents sunlight from precisely focusing on solar receivers,” Diver said. “Improperly aligned mirrors result in lost and wasted energy.”

Parabolic troughs use mirrored surfaces curved in a parabolic shape. The mirrors focus sunlight on a receiver tube running the length of the trough. Oil runs through the focal region where it is heated to high temperatures and then goes through a heat exchanger to generate steam. The steam is then used to run a conventional power plant.

Borrowing from variations on methods used to align mirrors in solar dish systems, Diver’s TOP alignment is an optical approach to rapidly and effectively evaluate the alignment of mirrors in parabolic trough power plants and prescribe corrective actions.

“This method could be used during trough power-plant construction to improve the performance of existing power plants or for routine maintenance,” Diver said.

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. The middle camera photographs the module’s center, where a boresight gauge is attached, which is used to vertically center, or “boresight,” the pole to the trough module.

With vector algebra and projection theory, it is possible to predict the theoretical projected image of the receiver for perfectly aligned mirrors. The calculated theoretical image of the receiver for perfectly aligned mirrors is overlaid on the photographs of the actual receiver image position in the mirrors. The images and the actual image are compared to show how the mirrors should be aligned. It then becomes a matter of adjusting the mirrors to the correct alignment.

“Once the mirrors are aligned … the mirrors are aligned for the life of the plant,” Diver said.

The next steps will be to test the system at Kramer Junction in Calfornia’s Mojave Desert and eventually license the technology to parabolic trough power-plant operators and/or trough project developers. EC


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