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Linear Concentrator System Basics for Concentrating Solar Power

August 20, 2013 - 4:45pm

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Photo of numerous parallel rows of parabolic trough collectors tracking the sun. Cooling towers and other generator equipment are in the midst of the troughs, and two water tanks are in the background.
The Solar Electric Generating Station IV power plant in
California consists of many parallel rows of parabolic
trough collectors that track the sun. The cooling towers
can be seen with the water plume rising into the air,
and white water tanks are in the background.
Credit: Sandia National Laboratory / PIX 14955

Linear concentrating solar power (CSP) collectors capture the sun's energy with large mirrors that reflect and focus the sunlight onto a linear receiver tube. The receiver contains a fluid that is heated by the sunlight and then used to create superheated steam that spins a turbine that drives a generator to produce electricity. Alternatively, steam can be generated directly in the solar field, which eliminates the need for costly heat exchangers.

Linear concentrating collector fields consist of a large number of collectors in parallel rows that are typically aligned in a north-south orientation to maximize annual and summer energy collection. With a single-axis sun-tracking system, this configuration enables the mirrors to track the sun from east to west during the day, which ensures that the sun reflects continuously onto the receiver tubes.

Parabolic Trough Systems

The most common CSP system in the United States is a linear concentrator that uses parabolic trough collectors. In such a system, the receiver tube is positioned along the focal line of each parabola-shaped reflector. The tube is fixed to the mirror structure, and the heated fluid—either a heat-transfer fluid or water/steam—flows through and out of the field of solar mirrors to where it is used to create steam (or, in the case of a water/steam receiver, it is sent directly to the turbine).

The largest individual trough systems generate 80 megawatts of electricity. However, individual systems being developed will generate 250 megawatts. In addition, individual systems can be co-located in power parks. Their capacity would be constrained only by the transmission capacity of nearby power lines and the availability of contiguous land.

Illustration of a linear concentrator power plant using parabolic trough collectors. Sunlight is shown reflecting off the parabolic troughs and onto the receivers positioned along the focal line of each trough. The hot heat-transfer fluid exiting the receivers flows to a turbine, generating electricity that is fed into the power grid. The cool heat-transfer fluid exiting the turbine flows into a steam condenser to be further cooled and sent back into the solar field. Thermal storage tanks are shown between the turbine and the steam condenser.
A linear concentrator power plant using parabolic trough collectors.

Trough designs may incorporate thermal storage. In these systems, the collector field is oversized to heat a storage system during the day that can be used in the evening or during cloudy weather to generate additional steam to produce electricity. Parabolic trough plants can also be designed as hybrids, meaning that they use fossil fuel to supplement the solar output during periods of low solar radiation. In such a design, a natural gas-fired heater or gas-steam boiler/reheater is used. In the future, troughs may be integrated with existing or new combined-cycle natural-gas- and coal-fired plants.

Linear Fresnel Reflector Systems

Illustration of a linear concentrator power plant using linear Fresnel collectors. Sunlight is shown reflecting off the mirrors on the ground and onto receivers located above the mirrors. The hot heat-transfer fluid exiting the receivers flows to a turbine, generating electricity that is fed into the power grid. The cool heat-transfer fluid exiting the turbine flows into a steam condenser to be further cooled and sent back into the solar field.
A linear Fresnel reflector power plant.

A second linear concentrator technology is the linear Fresnel reflector system. Flat or slightly curved mirrors mounted on trackers on the ground are configured to reflect sunlight onto a receiver tube fixed in space above the mirrors. A small parabolic mirror is sometimes added atop the receiver to further focus the sunlight.

More Information

For more information about linear concentrator power plant technologies, visit the National Renewable Energy Laboratory's TroughNet website or the EERE Solar Energy Technologies Office's Linear Concentrators Research and Development page.

To learn about other types of concentrating solar power systems, see:

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