The components of a solar thermal power plant are:
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Solar collectors
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Primary and secondary circuits.
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Heat exchanger
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Storage tank and pumps
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Pipelines
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Main control panel.
The objective of a solar thermal energy installation is to take advantage of solar energy to generate heat. The solar panels of these installations capture the heat from the solar radiation. The different ways of taking advantage of this heat allow us to use this type of renewable energy in multiple applications.
Solar thermal energy is a solar energy system whose objective is to take advantage of the Sun to obtain heat. Solar thermal power plants use this energy system to produce electricity concentreting the sun energy. However, in this article we focus mainly on domestic installations for the production of domestic hot water and heating.
Solar collector
The solar collector is a type of solar panel designed to take advantage of solar thermal energy. These elements capture solar radiation and convert it into thermal energy, into heat.
They are often covered by glass. The glass that covers the collector not only protects the installation but also conserves heat. The glass presence produces a greenhouse effect that improves the performance of the collector.
Solar collectors are made up of the following elements:
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Cover: It is transparent, it may or may not be present. Usually, it is made of glass, although plastic is also used, since it is less expensive and manageable. Nevertheless, it must be a special plastic. Its function is to minimize convection and radiation losses and therefore it must have as high a solar transmittance as possible.
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Air channel: It is a space (empty or not) that separates the cover from the absorbent plate. Its thickness will be calculated taking into account in order to balance the losses due to convection and the high temperatures that can occur if it is too narrow.
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Absorbent plate: The absorbent plate is the element that absorbs solar energy and transmits it to the liquid that circulates through the pipes. The main characteristic of the plate is that it must have high solar absorption and low thermal emission.
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Pipes or ducts: The pipes are touching (sometimes welded) the absorbent plate so that the energy exchange is as great as possible. Through the tubes circulates the heat transfer fluid that will be heated and will go to the storage tank.
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Insulating layer: The purpose of the insulating layer is to cover the system to avoid and minimize losses. Because the insulation is the best possible, the insulating material should have low thermal conductivity.
What are the types of solar collectors?
The three main types of solar collectors are:
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Flat plate solar thermal collectors.
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Thermal solar collectors with vacuum tubes.
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Parabolic trough solar thermal collectors.
In flat-plate solar collectors, the soul of the system is a vertical fence of metal tubes, to simplify, that conducts cold water in parallel.
In solar thermal collectors of vacuum tubes, the metal tubes of the preceding system are replaced by glass tubes, encapsulated, one by one, in another glass tube between which the vacuum is made as insulation.
Parabolic solar thermal collectors have a parabolic shape to concentrate the sun radiation received on a surface at a point through which the thermal fluid passes.
Parabolic trough systems are generally used to generate steam and with the steam to power turbines with which to obtain electricity. It is a way of obtaining electrical energy through solar energy without using photovoltaic panels.
Primary circuit
The primary circuit of a solar thermal energy installation is a closed circuit, it transports the heat from the collector to the accumulator (system that stores heat). The heated liquid (water or a mixture of substances that can transport heat) carries the heat to the accumulator. Once cooled, it returns to the collector to reheat, and so on.
Molten salt is used as a heat transfer fluid and thermal energy storage in solar power plants.
Heat exchanger
The heat exchanger heats the drinking water through the heat captured from solar heating systems. It is located in the primary circuit, at its end. It is shaped like a serpentine, since this way, it is possible to increase the contact surface and therefore, the efficiency.
The water entering the tank, as long as it is colder than the coil, will heat up. This water, heated in sunny hours, will be available for later consumption.
Storage tank
The storage tank is a tank where the heated water useful for consumption accumulates. It has an inlet for cold water and an outlet for hot. The cold enters below the accumulator where it meets the exchanger, as it heats it moves upwards, which is where the hot water will come out for consumption.
Internally it has a system to avoid the corrosive effect of hot water stored on the materials. On the outside, it has a layer of insulating material that prevents heat loss and is covered by a material that protects the insulation from possible humidity and blows.
Secondary circuit
The secondary or consumption circuit, (open circuit), enters cold supply water and at the other end the heated water is consumed (shower, sink, ...). The cold water goes through the accumulator first, where it heats the hot water until it reaches a certain temperature. Outdoor hot water pipes must be covered by insulation.
Hydraulic bombs
Hydraulic pumps, in case the installation is forced circulation, are of the recirculation type (there are usually two per circuit). A pump works one half of the day, and the couple, half the remaining time.
Nothing to do with the hydraulic pumps used in a hybrid solar and hydropower system.
Pipelines
The pipes of the installation are covered with a thermal insulator to minimize thermodynamic loss with the environment.
Control Panel
There is also the main control panel in the solar thermal installation, where the temperatures are displayed at all times (a thermal regulator) so that the operation of the system can be controlled at any time. The clocks in charge of the exchange of bombs also appear.
