Concentrating Solar Power

Concentrating Solar Power's (CSP) relatively low cost and ability to deliver power during periods of peak demand—when and where we need it—means it can be a major contributor to the nation's future needs for distributed sources of energy. Large-scale concentrating solar power technologies include parabolic troughs and power towers.

A photo of rows of parabolic troughs. Photo credit: Warren Gretz. An illustration of a parabolic trough is positioned slightly over the photo. The illustration shows the U-shaped curvature of a parabolic trough's reflector with a receiver positioned in the middle.

There are more than 350 megawatts of parabolic trough systems connected to the electricity grid in southern California. Photo credit: Warren Gretz.

Parabolic troughs have a proven track record as a technology that can function effectively for large-scale power needs. They currently provide the least expensive way to produce solar electricity. Parabolic-trough systems concentrate the sun's energy through long rectangular, curved (U-shaped) reflectors. The reflectors are tilted toward the sun, focusing the sun's energy on a pipe that runs down the center (focal point) of the trough. The sun's energy heats oil flowing through the pipe, and the hot oil then is used to boil water in a conventional steam generator to produce electricity.

Power towers have also shown their efficiency in demonstration projects and one is in commercial operation in Spain, but they are not yet in use commercially in the United States. A power tower system uses a large field of reflectors to concentrate the sun's energy onto the top of a tower, where it heats a receiver filled with a heat-exchange fluid, such as oil. The heated fluid is then used to generate electricity in a conventional steam generator. Systems using molten salt as the heat-exchange fluid retain heat very efficiently, enabling them to produce electricity up to three hours after the sun has set.

Where It's Available

Concentrating solar power technologies function most efficiently in the southwestern United States, which receives the greatest amount of solar energy.

This map shows the solar resource for concentrating solar power systems.

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