We refer to high-temperaturesolar thermal energy to those solar systems that use solar collectors that work at temperatures above 500 Celsius degrees. In this type of installations, once the solar radiation has been transformed into heat energy, the next objective is to transform this heat into electrical energy.
There are different technologies to take advantage of high-temperature solar thermal energy. However, all solutions are based on the same principles:
- First, concentrate the solar radiation at a point
- Raise the temperature of a fluid to increase, in this way, its internal energy. In this way, energy can be transported.
- To generate steam to be able to drive, thanks to its thermodynamic properties, the steam turbines and convert the energy into mechanical energy.
- Operate the electric generators thanks to the kinetic energy provided by the steam turbine.
The technologies used in high temperature thermal solar energy are:
- The parabolic trough sensors.
- The tower centrals.
- The parabolic discs.
- The Fresnel linear receivers.
Parabolic Trough Solar Collectors
The parabolic trough collectors concentrate the solar radiation through parabolic mirrors in an absorbent pipe that passes through the axis of the parabola. In the interior of this absorbent pipe, a fluid that can reach temperatures of up to 450ºC is heated.
Depending on the solar application and the temperature at which you want to reach, one type of fluid or another is used. For a maximum temperature of 200 Celsius degrees, demineralized water or Ethylene Glycol can be used as working fluids and for higher temperatures up to 450 Celsius degrees, synthetic oils are used.
To obtain an optimal energy performance, this type of concentration sensor must change its position adapting to the position of the Sun by turning around the axis parallel to its focal line to take advantage of direct Sun radiation.
Solar Tower Power Stations
This solar thermal system is based on the concentration of solar radiation towards a point in a tower. It is also known as central receiver systems.
The tower systems are formed by a field of heliostats (mobile mirrors on 2 axes). The heliostats capture and concentrate the solar radiation on a receiver, installed on the top of a central tower.
The operation of this type of renewable energy plant is simple, the central solar receiver generates steam at high temperature. The generated steam is subsequently used to move a steam turbine. Thanks to the steam turbine, mechanical work is obtained in the form of kinetic energy (an axis in rotation) that, thanks to an electrical generator, will be converted into electrical energy.
Parabolic discs are systems that concentrate solar energy at a point where the solar receiver is located and a Stirling motor or a microturbine that is coupled to an alternator.
The fluid located in the receiver is heated to temperatures of more than 750 ° C thereby 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 contribution can be made by concentrated solar energy. An alternator coupled to the Stirling engine takes advantage of the movement 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 the tower or the parabolic mirrors.
Linear Fresnel Receivers
The Fresnel linear reflectors is a system of concentration of solar radiation 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.