High-temperaturesolar thermal energy is the technique to generate electrical energy through solar radiation. The production of electrical energy is carried out in solar thermal power plants that use solar collectors to concentrate solar radiation at one point.
Using this concentration technique, temperatures above 500 degrees Celsius are achieved, which are used to produce steam. From here on, a solar thermal power plant works in the same way as a conventional thermal power plant:
Drive a steam turbine to obtain mechanical energy.
Drive an alternator to obtain electrical energy.
The difference between a solar thermal plant and a conventional thermal plant is that the solar thermal plant uses solar energy to generate steam, while the conventional plant uses fossil energy.
This type of energy is considered a clean, renewable energy source.
The technologies used in this type of facility are:
1. Parabolic Trough Solar Collectors
The parabolic trough collectors concentrate solar radiation through parabolic-shaped mirrors in an absorbing pipe that passes through the axis of the parabola. Inside this absorbent pipe a fluid is heated that can reach temperatures of up to 450ºC.
Depending on the solar application and the temperature to be reached, one type of fluid or another is used. For a maximum temperature of 200 degrees Celsius, demineralized water or Ethylene Glycol can be used as working fluids and for temperatures higher than 450 degrees Celsius, synthetic oils are used.
To obtain optimal energy efficiency, this type of concentration sensor must gradually modify its position, adapting to the position of the Sun by turning around the axis parallel to its focal line to take advantage of direct radiation from the Sun.
2. Solar Tower Plants
This solar thermal energy system is based on the concentration of solar radiation towards a point on a tower. It is also known as central receiver systems.
Tower systems are made up of a field of heliostats (2-axis mobile mirrors). Heliostats capture and concentrate solar radiation on a receiver, installed on top of a central tower.
The operation of this type of renewable power plant is simple, the central solar receiver generates steam at high temperature. The generated steam is later used to drive a steam turbine. Thanks to the steam turbine, mechanical work is obtained in the form of kinetic energy (a rotating shaft) that, thanks to an electrical generator, is going to be converted into electrical energy.
3. Parabolic Discs
Parabolic disks are systems that concentrate solar energy at a point where the solar receiver is located and a Stirling engine or a microturbine that is coupled to an alternator.
The fluid located in the receiver is heated to temperatures of more than 750 degrees Celsius, thus obtaining a certain heat energy. The thermal energy obtained is used by the Stirling engine or the microturbine to produce electricity.
A Stirling engine is an external combustion engine, which means that the energy supply can be made through concentrated solar energy. An alternator coupled to the Stirling engine takes advantage of the motion generated by the engine to produce electrical energy. The electricity generated by this renewable resource can be connected to the electricity grid for sale or in most cases it can be used for direct consumption.
This technology is still in experimentation and is still less profitable than that of tower or parabolic mirrors.
4. Linear Fresnel Receivers
Linear Fresnel reflectors are a solar radiation concentration system similar to parabolic trough mirrors. In this case, these linear solar collectors carry normal flat mirrors and simulate the curvature of parabolic trough mirrors (more expensive) by varying the angle of each row with a single tracking axis.
The main advantage of the Fresnel linear receiver system is its simple installation and its low cost, although the energy efficiency is lower than the Parabolic Cylinder Collector (CCP) technology.