When it comes toconcentrated solar energywe refer to the typical technology of athermodynamic solar systemalso known assolar thermoelectric power plantorconcentrated solar power plant.
Thermodynamic solar systems are divided into four types: with linear parabolic collectors, with linear collectors with Fresnel reflectors, with solar energy tower and with circular parabolic reflectors. Regardless of the type of thermodynamic solar system, the differences with other plants for the exploitation of solar energy reside in one more step for the generation of electricity.
Difference between solar thermal and solar thermodynamic
L'solar powerto concentrationowes its name to the phase ofcapture of incident solar energyalready present in common solar thermal systems, unlike the classic solar thermal system, with the concentration solar proper a cycle is addedthermodynamicfor the transformation of the heat collected by means of a steam turbine plus alternator.
Difference between concentrated solar and photovoltaic solar
L'concentrated solar energyuses solar radiation as its primary source but in this case it is not converted directly into electricity as is the case withphotovoltaic, rather it is accumulated in the form ofheatby means of techniques ofsolar concentration, only in the second step, the accumulated heat is converted into electricity.
An example of a system that exploits theconcentrated solar energyit is the solar tower in Spain where the energy accumulated in the form of heat heats a liquid that generates steam, the steam then drives an electricity generator.
Concentrated solar energy
As stated, there are severalthermodynamic solar systems which differ in the type of heliostat (mirrors or reflectors) or the type of receiver. Let's see in detail:
- Thermodynamic solar system with linear parabolic collectors
In this type of installation, the parabolic mirrors rotate on a single axis and reflect the sunlight on a receiver tube placed in the fire (the point where all the sun's rays are concentrated).
A heat carrier flow flows in the receiver tube which stores and transports the heat transmitted by the mirrors. The fluid transports solar energy to a heat exchanger in order to produce steam.
The thermal energy reached the heat exchanger leads to the production of steam. The steam is used to drive one or more turbines in cascade, connected in turn to an alternator (the turbine + alternator complex is called "turbo-alternator") which leads to the production of electricity.
Note # 1
To optimize the production of electricity from the sun, the heat transfer fluid, in moments of energy peak, can also transport solar energy (always in the form of heat) to a storage tank and then use it in the evening.
Note # 2
Thethermodynamic solar power plantsthey employ different types of heat transfer fluid. Initially, diathermic oil was used while today the so-called salt mixtures are more widespreadmolten salts. Diathermic oil has the disadvantage of dissociating at temperatures above 400 ° C. In thermodynamic solar power plants that use diathermic oil, the operating limit temperature is 400 ° C while for thermodynamic solar power plants that use molten salts the limit temperature exceeds 550 ° C. With the use of molten salt mixtures it is also possible to improve the heat storage capacity of the system, extending its productivity even up to many hours without exposure to the sun.
- Thermodynamic solar system with linear Fresnel reflector mirrors
Fresnel reflectors consist of several narrow and parallel strips of plane mirrors suitably inclined to concentrate the solar radiation on the receiving tubes. The receiver tubes are placed on top and run parallel to the rows of flat mirrors.
This approach allows for a greater reflective surface for the same area occupied. In addition, the flat mirrors are cheaper than the parabolic linear mirrors seen in the previous implant type. Otherwise, the heat transfer fluid behaves in the same way and may differ as described inNote # 2.
- Solar energy tower thermodynamic system
These are the most exemplary structures!
Here, the reflecting mirror system is independent and concentrates the solar energy on a receiver fixed on the top of theSolar tower which is placed at the center of the system. The solar tower concentrates the rays collected by all the heliostats (reflective mirrors that track the sun by constantly projecting light radiation on the tower's receiver).
In this case, thethermodynamic power plantit is saidcentral tower systemorsolar power plant tower. In Europe the most exemplary examples are in Spain, we are talking about the Solar Tower of Seville PS10 and PS20. In the receiver at the top of the tower flows the heat transfer fluid which transfers the heat to a steam generator, which feeds a turbo-alternator. With this system it is possible to reach concentration factors, and therefore temperatures, higher than with linear parabolic collectors.
- Thermodynamic solar system with circular parabolic reflector
A point-like central focus is developed that "concentrates" all the solar radiation. The solar tracking is operated through movements on two axes.
If you liked this article and are interested in the topic, you may also like to read our other article: Solar Thermodynamic: how it works