YET BETTER SOLAR FARMS

Sandia invention to make parabolic trough solar collector systems more energy efficient; Simple design of new technology excites solar industry
Chris Burroughs, May 15, 2007 (Sandia National Laboratories via EurekAlert)
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WHO
Rich Diver, researcher, Sandia National Laboratories

WHAT
Theoretical Overlay Photographic (TOP) technology: a device to measure mirror alignment and make it possible for reflecting surfaces to capture the maximum possible solar light for conversion to electrical energy

WHEN
The technology has been 20 years in development. Shakedown testing was done in March and October 2006. The next stage of testing will be later this year. The technology is not presently available.

WHERE
The largest parabolic trough facilities in the world are near Barstow, Calif., in the Mojave Desert. One is near Kramer Junction. Nevada and Arizona have plants in the works.

WHY
- By maximizing the light reflected from collecting mirrors to photovoltaic surfaces, parabolic trough solar systems become more efficient, increasing the return on investment in both energy and money.
- A parabolic trough is a curved mirrored surface focusing sunlight on a tube with oil in it. When the oil is heated, it runs a generator that produces steam which runs a conventional power plant, generating electricity.

- The large parabolic trough facilities studied: 9 plants, 354 megawatts at peak output (14 to 80 megawatts each). Example: A 30 megawat plant w/10,000 modules, each module=20 mirrors. Therefore, inaccurate mirror alignment=significant loss of light, heat & energy.
- Basics: A pole w/5 cameras; 4 cameras take digital photographic images of 4 rows of mirrors in a parabolic module. The middle camera photographs the a boresight guage at the center, centering the pole. Vector algebra and projection theory predict perfect alignment. Actual images are compared to perfect alignment and the mirrors are realigned. For commercial sized operation, the apparatus can be moved on a trailer pulled by a van to take images for future evaluations and alignments.

QUOTES
- Diver: "TOP alignment could cure a significant problem with trough systems -- inaccurate mirror alignment that prevents sunlight from precisely focusing on solar receivers…Improperly aligned mirrors result in lost and wasted energy."
Working with Diver on the project is Tim Moss, who serves as project manager and primary software and hardware developer.
- Diver: "This method could be used during trough power-plant construction to improve the performance of existing power plants or for routine maintenance…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."
- Diver: "This whole process is very simple…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."