Solar Thermal Electric
(Concentrating Solar) Technologies

While most solar technologies are used in small-scale applications, solar thermal technologies can also be used on a much larger scale. These technologies are similar in concept to solar heating technologies, using sunlight to generate heat. They differ in that they create enough heat to power a generator which is then used to produce electricity.

To generate this intense heat, solar thermal technologies employ arrays of reflective mirrors to concentrate sunlight onto a central receiver. The resulting heat is used to produce steam for a steam engine, or is fed directly to a heat engine. These engines then generate electricity which can be distributed through the electricity grid.

These systems are powerful, but require a large amount of space for their reflectors and depend on direct sunlight for their reflective components to function. Although there are opportunities to combine the concentration aspect of this technology for small-scale applications throughout the country, it is primarily used in the Southwest where land and direct sunlight are abundant. After the construction of several large facilities in the late 1980s and early 1990s, little new has been built because it remains considerably more expensive to generate electricity with solar thermal systems than with conventional power plants.

There are four main types of solar thermal electric systems.

Parabolic Trough Collectors

These collectors combine a curved mirror, shaped like a parabola to maximize the amount of sunlight collected, with an absorber tube embedded along the center of the mirror. The absorber tube is filled with oil or another fluid that can easily be heated. When sunlight hits these collectors, the mirrors focus it on the tube, heating the fluid inside. This hot fluid is then used to boil water and produce steam in a connected device and the steam is transferred to a generator that can produce electricity. A large array of connected parabolic trough collectors is needed to provide enough power for a generator.

Dish/Engine Systems

These systems use an array of mirrors, arranged in the shape of a dish, to concentrate sunlight onto a receiver placed at the focal point of the dish. The heat produced by these systems is transferred to a heat engine which converts the heat into mechanical energy. This energy then drives a generator to produce electricity.

Power Towers

Power tower systems use a circular array of mirrors that track the sunlight and concentrate it on a receiver, placed at the top of a central tower at the focal point of the array. In much the same way as parabolic trough collectors, heat produced by the receiver is used to create steam which then powers a generator.

Hybrid Systems

Hybrid systems combine power towers with natural gas generators, creating a system that can continuously generate electricity, even when the sun isn't shining. This technology is still in development and experimental systems have been connected to several utilities in the Southwest.

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