Solar collectors are the elements that capture solar radiation and convert it into thermal energy, into heat. It is a type of solar panel designed for use in solar thermal installations. It is also known as a solar collector.
Solar collectors are those with flat plates, evacuated tubes and absorber collectors without protection or isolation. The flat (or flat plate) collection systems with glass cover are the common ones in the production of sanitary hot water. The glass lets the rays of the Sun pass, they heat up metallic tubes that transmit heat to the liquid inside. The tubes are dark in color, as dark surfaces heat up more.
They consist of a closed aluminum shell resistant to marine environments, an eloxat aluminum frame, a silicone-free perimeter gasket, thermal insulation that respects the rock wool environment, high transparency solar glass cover, and finally ultrasonic welded tubes.
Components of a solar collector
The solar collectors are composed of the following elements:
- Cover: The cover of a solar collector is transparent, it may be present or not. It is usually made of glass, although plastic is also used, since it is less expensive and manageable, but it must be a special plastic. Its function is to minimize the losses by convection and radiation and therefore it must have a solar transmittance as high as possible. The presence of the cover improves the thermodynamic performance of the solar panel.
- Air channel: It is a space (empty or not) that separates the cover of the absorbent plate. Its thickness will be calculated taking into account the purpose of balancing the losses by convection and the high temperatures that can be produced if it is too narrow.
- 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 a high solar absorption and a reduced thermal emission. As common materials do not meet this requirement, combined materials are used to obtain the best absorption / emission ratio.
- Pipes or ducts: The tubes are touching (sometimes welded) the absorbing plate so that the exchange of energy is as large as possible. For the tubes circulates the liquid that will heat up and go to the accumulation tank.
- Insulating layer: The purpose of the insulating layer is to cover the system to avoid and minimize losses. Why the insulation is the best possible, the insulating material should have a low thermal conductivity to reduce the thermodynamic transfer of heat to the outside.
- Accumulator: the accumulator is an ocional element, sometimes it is an integral part of the solar panel and, in these cases, it is often immediately visible above or in the immediate vicinity. Very often the accumulator is not part of the solar panel but of the thermal system.
Types of solar collectors
The solar thermal collectors can be divided into some types of construction:
- Flat solar thermal collectors
- unglazed or uncovered
- Evacuated solar thermal collectors
- Heat pipe
- Solar thermal panels with integrated tank.
- Concentrated thermosolar panels.
Of these types of solar panel we highlight the following:
Flat plate solar collectors
The soul of a flat plate solar collector is a vertical gate of metal tubes, to simplify, which conduct the cold water in parallel, connected down a horizontal tube to the cold water intake and above by another similar to the return.
The grill is fitted in a cover, as described above, usually with double glass on top and insulation on the back.
In some models of flat plate solar collectors, the vertical tubes are welded to a metal plate to take advantage of the insolation between the tube and the tube.
Evacuated tube solar collectors "all glass"
In a solar collector of evacuated tubes, the metal tubes of the previous system are replaced by glass tubes. The glass tubes are encapsulated, one by one, in another glass tube between which the vacuum is made as insulation.
The great advantages of evacuated tube solar collectors are their high performance. On the other hand, in case one of the tubes is damaged, it is not necessary to change the entire panel with a new one, but only change the affected tube. On the contrary, as a drawback we have that, in relation to flat plate solar collectors, these are more expensive.
Evacuated tube solar collectors with "heat pipes" by phase change
This system takes advantage of the change of phase from vapor to liquid inside each tube, to deliver energy to a second transport liquid circuit.
The elements are closed tubes, usually copper, which contain the liquid that, when heated by the sun, boils and becomes steam that rises to the top where there is a wider head (condensation zone), which in the The exterior is in contact with liquid transporter, which, being colder than the vapor of the tube, captures the heat and causes the vapor to condense and fall in the lower part of the tube to restart the cycle.
The liquid of the tube can be water that, having reduced the pressure by doing a partial vacuum, will have a low boiling point to work even with the insolation of the infrared rays in case of cloud.
The heat pipe can be wrapped with a jacket made of special materials to minimize losses due to irradiation.
The heat pipe is closed inside another glass tube between which the vacuum is made to isolate. Resistant glass tubes are often used to reduce damage in the event of small hailstorms.
Use of solar collectors
In the case of collectors for domestic hot water and heating, the tank stores the domestic water that comes into contact with the fluid by means of 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 it can be used to supplement the heating of the rooms' floor (10% integration). Solar thermal panels are capable of supplying hot water in good quantities, but can not completely replace the usual methods of heating due to the inconstancy 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 water vapor into electrical energy. This type of system is called solar thermodynamics and requires large spaces for the installation of solar panels and a constant presence of sunlight. Examples of these plants have been installed in the deserts.
Last review: April 25, 2019Back