How CSP Works: Tower, Trough, Fresnel or Dish

Shouhang, one of the two main research-backed CSP developers in China, has made this descriptive video showing the details of how Tower CSP works:

All concentrating solar power (CSP) technologies use a mirror configuration to concentrate the sun’s light energy onto a receiver and convert it into heat. The heat can then be used to create steam to either drive a turbine to produce electrical power or it can be used directly by heavy industries as heat instead of fossil fuels.

Thermal energy storage

Thermal energy storage. is integral to CSP because it enables this heat-based form of solar to generate electricity at night and during cloudy periods. Thermal storage makes concentrating solar power the flexible and dispatchable form of solar energy. Liquids molten salts store the heat in currently commercial projects but new materials are being investigated. These includes gases like air, liquid metals and solids like ceramics. Materials that can attain higher temperatures have resulting efficiency gains leading to lower costs. High temperature solar heat can also replace fossil fuel heat use by industry.

See How CSP’s thermal energy storage works.

Basic summary of the four CSP technologies:

There are four types of CSP technologies: The earliest in use was trough, and the predominant technology now is tower. This is because tower CSP can attain higher temperatures, resulting in greater efficiency.

Tower Systems:

Power tower or central receiver systems utilize sun-tracking mirrors called heliostats to focus sunlight onto a receiver at the top of a tower. A heat transfer fluid heated in the receiver up to around 600ºC is used to generate steam, which, in turn, is used in a conventional turbine-generator to produce electricity. The National Renewable Energy Laboratory (NREL) maintains the global Tower deployment database.

Parabolic Trough Systems:

In a parabolic trough CSP system, the sun’s energy is concentrated by parabolically curved, trough-shaped reflectors onto a receiver pipe – the heat absorber tube – running along about a meter above the curved surface of the mirrors. The temperature of the heat transfer fluid flowing through the pipe, usually thermal oil, is increased from 293ºC to 393ºC, and the heat energy is then used in the thermal power block to generate electricity in a conventional steam generator.

A trough solar collector field comprises multiple parabolic trough-shaped mirrors in parallel rows aligned to enable these single-axis trough-shaped mirrors to track the sun from east to west during the day to ensure that the sun is continuously focused on the receiver pipes. Trough deployment database.

Linear Fresnel Systems:

Similar to the long arrays of a parabolic trough CSP system, a Linear concentrating collector field consists of a large number of collectors in parallel rows. These are typically aligned in a north-south orientation to maximize annual and summer energy collection. The mirrors are laid flat on the ground and reflect the sunlight to the pipe above. Like trough and tower, Fresnel can also incorporate storage in a power block, or generate steam for direct use. Fresnel deployment database.

Parabolic Dish Systems:

A Parabolic dish system consists of a parabolic-shaped point focus concentrator in the form of a dish that reflects solar radiation onto a receiver mounted at the focal point. These concentrators are mounted on a structure with a two-axis tracking system to follow the sun. The collected heat is typically utilized directly by a heat engine mounted on the receiver moving with the dish structure. Dish can attain extremely high temperatures, and holds promise for use in solar reactors for making solar fuels which require very high temperatures. Stirling and Brayton cycle engines are currently favored for power conversion, although dish has been seldom deployed commercially for power generation. Dish deployment database.

For information on all the applications of CSP and CST, read these publications from DLR, one of the world’s major concentrated solar research organizations: