Boosting solar energy plants efficiency

Researchers at Sandia National Laboratories have invented a new way to make solar collector systems more energy efficient. The theoretical overlay photographic (TOP) technology developed at Sandia uses mirrors to focus radiation from the sun as a source of heat for power generation. In fact, they've created a mirror alignment measurement device for parabolic troughs which is drawing interest from the solar industry because it is affordable and because we need to find solutions for global warming. This device has already been successfully tested at a solar plant near Tucson, Arizona.

Researchers at Sandia National Laboratories have invented a new way to make solar collector systems more energy efficient. The theoretical overlay photographic (TOP) technology developed at Sandia uses mirrors to focus radiation from the sun as a source of heat for power generation. In fact, they've created a mirror alignment measurement device for parabolic troughs which is drawing interest from the solar industry because it is affordable and because we need to find solutions for global warming. This device has already been successfully tested at a solar plant near Tucson, Arizona. And it should soon be tested in commercial solar plants in California.

Calibrating solar dish collectors at Sandia

On the picture above, you can see Sandia researcher Rich Diver setting up a device he has developed to calibrate parabolic trough-type solar dish collectors to maximize the amount of sunlight they capture. As he says, "TOP alignment could cure a significant problem with trough systems -- inaccurate mirror alignment that prevents sunlight from precisely focusing on solar receivers. (Credit for photo: Randy Montoya, Sandia) Here is a link to a larger version of this photo.

Now, here are some details about current parabolic trough facilities.

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.

The world's largest parabolic trough facilities, located in the Mojave Desert near Barstow, Calif., consist of nine plants producing 354 megawatts of power at peak output. The plants range in size from 14 to 80 MW. The 30 MW plants near Kramer Junction, for example, each have about 10,000 modules with each module comprising 20 mirrors. A 64 MW trough plant, which will supply power to Las Vegas, Nev., is expected to go on line soon. A 1 MW plant also exists in Arizona.

And here are some details about the TOP technology developed at Sandia.

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.

Vector algebra and projection theory are then used 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.

Even if it's not mentioned in the Sandia news release, this research work has been published by the Journal of Solar Energy Engineering under the name "Practical Field Alignment of Parabolic Trough Solar Concentrators" (Volume 129, Issue 2, Pages 153-159, May 2007). Here is a link to the abstract.

And for even more information, you should read two Sandia presentations given to National Renewable Energy Laboratory (NREL) members, "Practical Field Alignment of Parabolic Trough Concentrators" (Golden, Colorado, November 10, 2005, PDF format, 22 pages), and "Current Status of TOP Alignment" (Denver, Colorado, March 8-9, 2007, PDF format, 17 pages).

I'll leave the last words of this post to Rich 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." He added that the process was 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."

Sources: Sandia National Laboratories news release, via EurekAlert!, May 15, 2007; and various websites

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