Solar Thermal energy: How does it work
In contrary to photovoltaics, solar thermal power plants indirectly generate power from sun light. The conversion of solar irradiation into thermal energy follows the principle of Absorption. It can be performed by solar collectors, which directly absorb the sun irradiation.
Large thermal solar power plants work with concentrators following the principle of reflection. The concentrators bundle the sun beams to increase the intensity of the incident light on the absorber. Thus the temperature in the heat carrier is increased.
Thermal solar power plants use different methods for power generation, three of them work with focusing mirrors.
Parabolic trough focus the sun beams on an absorber tube filled with a fluid. The fluid is transported to a heat engine, where the heat is converted to electricity, which boosts as gas a turbine.
Parabolic solar dish
A parabolic dish system uses large, reflective, parabolic dishes. It focuses all the sunlight that strikes the dish up onto a single point above the dish, where a receiver captures the heat and transforms it into a useful form. Typically the dish is coupled with a Stirling engine, but also sometimes a steam engine is used. Parabolic solar dish systems are known to have the highest efficiency of all solar technologies.
Power towers or heliostat power plants
Power towers capture and focus the sun's thermal energy with thousands of tracking mirrors (called heliostats). A tower is placed in the center of the heliostat field. The heliostats focus concentrated sunlight on a central absorber, which is on top of the tower. Within the absorber the concentrated sunlight heats up to over 538 °C. The steam drives a standard turbine to generate electricity