While concentrated solar energy systems generate electrical energy, they also provide electricity generation from solar energy at night by storing solar energy.
Concentrating Solar Power (CSP) technologies, using mirrors, reflect sunlight spread over a wide area, collect it in a small area and convert it into heat (thermal energy). This thermal energy is also used to generate electricity.
Concentrated solar energy systems are used in projects for general use. The dense liquid in the receiver, where the mirrors in the CSP fields focus the sun rays and reaching high temperatures by heating, evaporate the water and use it to rotate a turbine with steam power or to run a motor connected to a generator. The resulting product is electricity. The mirrors are equipped with a moving system that allows them to follow the sun during the day. Smaller CSP systems, capable of generating 3 to 25 kilowatts of power, can be installed where energy is needed and directly utilized. The thermal energy collected in the CSP facility can be stored and used to generate electricity day or night when needed.
Different CSP systems have been developed according to the methods of concentrating solar energy.
Parabolic Trough Reflectors
They are systems using parabolic (trough-shaped) reflectors. The sunlight is collected by the receiver, a tube that runs in the direction of the focal point of the trough and is a fluid circulation tube. The reflector tracks the sun throughout the day with its tracking mechanisms. Parabolic trough systems are the most advanced among CSP technologies.
Compact Linear Fresnel Reflectors
In this system, which is structurally similar to groove reflector systems, sunlight is reflected to a pair of liquid circulating tubes using a large number of thin and long mirrors. This system is less costly because flat mirrors are cheaper than parabolic mirrors, and more daylight can be collected by placing more reflectors in an area of the same size than the parabolic trough system. Compact linear fresnel reflectors are mostly used in large capacity and advanced power plants.
Bowl Reflectors (Stirling Engine System) In The System
consisting of a large number of small flat mirrors placed in a bowl-shaped single parabolic reflector or parabolic bowl shape, the reflectors have a receiver containing liquid at the focal point, similar to other systems. The reflector follows the sun in two axes. Unlike other systems, it is used for energy generation in the stirling engine instead of producing heated liquid steam. This system provides the highest efficiency in the conversion of solar energy to electrical energy among other CSP technologies.
It consists of a central receiver on top of a tower and a number of flat reflectors (heliostats) that reflect the sun’s rays to this receiver. Computer controlled reflectors follow the sun in two axes. In this system, it is possible to reach much higher temperatures than others; this means more energy. It is used to generate electricity through the heated liquid steam. Although energy towers are less developed than the parabolic trough system, they offer a higher efficiency and better capacity in energy storage.
PV me CSP me?
Compared to photovoltaic (PhotoVoltaic – PV) systems, which convert solar rays into direct electrical energy, PV systems can be installed with very small scales and can cover both the residential and power plant sector, while CSP systems can be applied effectively only in projects larger than 20MW. While CSP needs direct sunlight, PV systems can generate electricity even with radiation from the sun. Therefore, the installation area of CSP is more limited than PV.
PV systems are technologically simpler and much more economical systems in small scales. The biggest advantage of CSP is that it can store heat and, when necessary, it can be converted into electrical energy quickly. CSP systems are preferred systems especially in power plant projects as they can provide energy when needed during peak times and day and night without difference.