A power plant which collects and concentrates sunlight for harvesting Solar energy required for heating up a fluid to a high temperature in order to generate electricity is called solar thermal power plant. Heats are transferred from fluid to water and creates extremely-heated steam. Turbines in the power plant can be rotated by utilizing this steam. A generator is used in order to convert this mechanical energy into electricity. In conventional electricity generation system, combustion of fossil fuels are required which causes environmental pollution. But, in solar thermal power plant, only heated steam produced from solar energy is used to generate electricity. In this type of power plant, solar collectors are used to concentrate the sun's rays on one point for getting required high temperatures. In order to collect solar radiation and store it, two types of systems are used. They are: passive systems and active systems. Solar thermal power plants are considered active systems. These plants are designed in such a system that it can operate by using only solar energy.

Although there are various types of solar thermal power plants, all of them work on same principle wherein mirrors are utilized in order to reflect and concentrate sunlight on a point. Solar energy is collected and converted to heat energy at this particular point. It produces extremely heated steam which helps to rotate turbines and run the generator in order to generate electricity.

 

Parabolic Troughs

Parabolic Troughs are also familiar as line focus collectors. They consist a long, parabolic shaped reflector that concentrates incident sunlight on a pipe that runs down the trough. A single-axis solar tracking system can be used in collectors in order to get maximum solar energy incident on the mirrors.  When the trough focuses sun at highest times its normal intensity, then the receiver pipe in the center can reach highest temperatures. These troughs are lined up in rows on a solar field. When it is run through the pipes in the parabolic trough, a heat transfer fluid is heated. This fluid then returns to heat ex-changers at a central location where the heat is transferred to water, generating high-pressure extremely heated steam. This steam helps to rotate turbines to run generators and generate electricity. After then, the heat transfer fluid is cooled and return back through the solar field.

 

Parabolic Dishes

In this types of dishes, motors are used to track the sun. These are large parabolic dishes. In this case,  highest possible amount of incoming solar radiation are received in order to concentrate at the focal point of the dish. These dishes are comparatively better than parabolic troughs in terms of concentrating sunlight. They can concentrate maximum sunlight and the fluid flows through them can achieve highest temperatures. In order to covert heat to mechanical energy, a Stirling engine is used in this system. It is done by compressing working fluid when cold and letting the heated fluid to flow outward in a piston or move through a turbine. After then, this mechanical energy is converted to electricity by the generator.

 

Solar Towers

These are large towers which perform as a central receiver for solar energy. These solar towers are located at the center of a large array of mirrors. They concentrate sunlight on a particular point in the tower. The heat exchange fluid is warmed in a heat ex-changer which is mounted in the tower. In this particular point, the heat can be extremely concentrated than incident sunlight. Steam is produced by the extremely hot fluid which assists to rotate turbines and run generator in order to generate electricity.