What is a solar thermal collector?

TO THETalking about solar energy, we always think first of photovoltaic energy through which, and thanks to sunlight, we can generate electricity. But there is also another type of energy that is less known but no less important, which is solar thermal energy, thanks to which we can heat water.

A solar thermal collector or solar thermal collector or solar thermal panel, is a device that allows us to take advantage of solar thermal energy , that is, it serves to capture solar thermal energy through solar radiation and thus heat water. The hot water can be used both at home and at an industrial level, such as to heat the water in the swimming pool , bath or shower or as a heating system for water carried by pipes capable of heating the rooms they pass through.

Through the use of solar thermal collectors we can have hot water and heating in a clean and environmentally friendly way.

It should be noted that solar thermal energy can also be used to generate electricity. This is carried out in solar thermal power plants that heat water and generate steam capable of moving a turbine that is used to produce electrical energy. When harnessing solar energy to generate electricity for domestic use, a photovoltaic solar installation is always recommended .

Operation of a solar thermal collector

A solar thermal collector is made up of various elements:

• Covers or thermal plates. They are usually made of glass or special plastics. When the sun shines on them, they capture all the energy possible, minimizing losses due to convection.
• The air channel. It may or may not be empty and is responsible for separating the cover from the absorber. The thickness of this channel varies depending on the convective losses and the excessively high temperatures that can occur if it is too narrow.
• The absorber. As its name indicates, it is in charge of absorbing solar energy and transmitting it to the fluid in which that heat is stored. It is essential that it has a high absorption capacity and a reduced thermal emission, for which a mixture of various materials such as copper or aluminum is used, with titanium oxide treatments.
• The accumulator. Not all solar thermal installations have it, although it is a practical element. It is made up of a tank where hot water is stored, that is, the thermal energy collected, so that it can be used whenever it is needed, even in the hours when there is no sun.
• Ducts, circuits, insulating layers and other elements. Through the pipe system, the installation fluid and the insulating elements can be transported to avoid energy losses. The main and secondary circuits allow its proper operation.

Types of solar thermal collector

Regarding solar thermal collectors for domestic use, the three most common types are:

• Flat solar collectors: Composed of tempered glass and with a design designed to capture solar energy and transmit it through ducts to a heat-carrying fluid, which when heated will transport the energy where it is needed. They are one of the most demanded and effective, being indicated fundamentally for the production of hot water and also for heating swimming pools, low temperature heating and absorption cooling.
  There are two main classes of flat solar collectors: normal and selective.The former are not suitable for areas of low temperatures or with diffuse irradiation, while the selective ones are suitable for both situations since, as their name indicates, they offer a selective coating that makes it possible.
• Vacuum tube collectors: Composed of a set of solar tubes that keep a vacuum and inside which we find the heat-carrying fluid. Compared to flat solar collectors, they offer greater performance at high working temperatures. They are recommended for areas with very low insolation or for installations where it is necessary to work with high temperatures. They are also indicated for heating that needs a lot of solar input and absorption cooling, as well as in industrial processes.
• Polypropylene collectors: They do not have a glass cover and are made of plastic material. Its operation is very similar to that of flat solar collectors although they are cheaper. They are only used to heat the water in swimming pools that are uncovered due to their poor performance at medium and high working temperatures and in cold climates.

In addition to these types, solar thermal collectors are also classified according to the power of their accumulators:

• Low temperature accumulators. They provide heat less than 65 degrees. These are usually the ones used in the home.
• Medium temperature accumulators . They provide heat between 100 and 300 degrees. These are most used for industrial processes that require temperatures of over 100 degrees.
• High temperature accumulators. They provide heat greater than 500 degrees. They are the ones used to generate electrical energy by means of steam.