A solar thermal collector is a component of a solar thermal installation responsible for capturing solar radiation and transforming it into thermal energy. This type of solar panel is also called thermal solar panel.
There are many types of solar thermal energy installations, depending on the purpose for which they are designed. Some common uses of solar collectors are:
Pool water heating.
Domestic hot water (DHW)
Electricity production in large solar thermal power plants.
What Are the Different Types of Solar Collectors?
There are many solar thermal collector types. The solar collector used will depend on the use that is going to be given to it. The classification of solar thermal collectors in the solar energy market is the following:
1. Flat Plate Collectors
Flat solar collectors capture the solar radiation received on a surface to heat a fluid. The greenhouse effect is often used to reduce heat loss.
The core of this type of flat plate solar collector is a set of vertically oriented metal tubes that conduct cold water in parallel. These pipes are connected at the bottom by a horizontal pipe to the cold water intake and another similar pipe to the outlet at the top.
The tubes are encased by a cover at the top, which is usually double glass, and at the bottom by an insulating material.
This type of solar collectors are used in low-temperature installations (below 80 degrees Celsius), such as for heating swimming pools.
2. Evacuated Tube Collectors
An evacuated tube solar collector is similar to a flat plate solar collector, but glass tubes replace the metal tubes. These glass tubes are encapsulated, one by one, in another glass tube between which a vacuum is made for insulation.
This type of thermal solar panel has a higher performance, but its cost is higher.
3. Concentrating Collectors
This type of collector captures the radiation received on a relatively large surface and concentrates it using flat mirrors or parabolic troughs on a smaller surface.
The objective of focus collectors is to concentrate the solar energy received on a surface at one point to obtain high temperatures. This technique is used in high and very high-temperature solar installations.
Usually, this type of solar collector is used to generate the very high-pressure water vapor and electricity as in a conventional thermal power plant.
Components of a Flat Plate Solar Collector
Standard solar collectors are made up of the following elements:
The cover: The cover of a solar collector is transparent. It may or may not be present. It is usually made of glass, although plastic is also used. Its function is to minimize heat losses by convection and thermal radiation.
Air channel: It is a space that can be empty that separates the cover from the absorbent plate. Its thickness is calculated by considering the purpose of balancing convection losses and the high temperatures that can occur if it is too narrow.
Absorbent plate: it 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.
Tubes or ducts: these elements touch (sometimes welded) the absorber plate so that the energy exchange is as large as possible. The liquid circulating throw the pipes that will be heated and go to the accumulation tank.
Insulating layer: The purpose of the insulating layer is to cover the system to avoid and minimize losses.
Accumulator: The accumulator is an optional element. Sometimes it is an integral part of the solar panel, and, in these cases, it is often visible immediately above or in the immediate vicinity.
Use of Solar Collectors
Solar collectors mainly supply hot water for DHW and heating or generate electricity.
In the case of collectors for domestic hot water and heating, the Solar storage tanks the domestic water that contacts the fluid using a coil. The coil allows the fluid to transfer the stored heat energy to the water without contaminating the water.
This water can be used as hot water in homes (80% integration) or to complement the floor heating of the rooms (10% integration). Thermal solar collectors can supply hot water in abundance but cannot completely replace the usual heating methods due to the lack of solar energy.
Solar collectors intended for electricity generation require that the heat exchanger be heated until it is boiling. Once the liquid has completed the thermodynamic phase change and has passed into the gas phase, it is sent to a thermoelectric turbine that will convert the movement of steam into electrical energy.
This type of system is called solar thermodynamics and requires large spaces for installing solar panels and a constant presence of the sun. Examples of these plants have been installed in the deserts.