A quarterly research and development magazine
An approach to aligning the parabolic mirrors of solar trough-type power plants is drawing interest from the solar power industry because of its simplicity, affordability, and energy efficiency.
The new alignment system, called theoretical overlay photographic (TOP) alignment, uses a pole outfitted with precisely placed cameras to evaluate the existing alignment of parabolic mirrors and prescribe adjustments.
“TOP alignment could cure a significant problem with trough systems — inaccurate mirror alignment that prevents sunlight from precisely focusing on solar receivers,” says Sandia researcher Rich Diver. “Improperly aligned mirrors result in lost and wasted energy.”
The curved mirrors of parabolic troughs direct sunlight onto a receiver tube running the length of the trough along the parabolic focal line. Oil flowing through the tube is heated by the focused sunlight to high temperatures and routed through a heat exchanger to generate steam. The steam runs a conventional power turbine to generate electricity.
Previous methods for aligning mirrors in parabolic modules have been cumbersome. Diver, working with Tim Moss, came up with TOP alignment using a 20-year-old parabolic mirror system located at the National Solar Thermal Test Facility at Sandia in Albuquerque.
Four of the five cameras on a TOP fixture take digital images of the four rows of mirrors on the parabolic module. The fifth camera photographs the module‘s center, where a boresight gauge is attached to vertically center the pole to the trough module.
Computer algorithms calculate the best possible mirror alignment. The calculated image is overlaid onto the photographs showing the actual mirror alignment. The mirrors can then be adjusted to match the ideal alignment.
The method could be used during troughplant construction, to improve the performance of existing power plants, or for routine maintenance, Diver says.
“This whole process is very simple,” Diver says. “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.”
Technical contact: Rich Diver,
(505) 844-0195, rbdiver@sandia.gov
Media contact: Chris Burroughs,
(505) 844-0948, coburro@sandia.gov