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.
As solar collectors, those with flat plates, those with vacuum tubes and absorber collectors without protection or isolation are known. 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 metal 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 by ultrasonic welded tubes.
The solar collectors are composed of the following elements:
- Cover: It's transparent, it can 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 occur if it is too narrow.
- Absorbing plate: The absorbing plate is the element that absorbs solar energy and transmits it to the liquid that circulates in the pipes. The main characteristic of the plate is that it must have a great 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.
- Tubes or conduits: The tubes are touching (sometimes welded) the absorber 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.
Flat plate solar collectors
The core of the system is a vertical gate of metal tubes, to simplify, which conduct the cold water in parallel, connected down by a horizontal tube to the cold water intake and above by another similar to the return.
The grill is fitted in a cover, like the one described above, usually with double glass on top and insulation on the back.
In some models, the vertical tubes are welded to a metal plate to take advantage of the insolation between the tube and the tube.
"All glass" vacuum tube solar collectors
In this system the metal tubes of the previous system are replaced by glass tubes, encapsulated, one by one, in another glass tube between which the vacuum is made as insulation. The great advantages of these types of collectors are their high performance and that, in case one of the tubes is damaged, it is not necessary to change the entire panel with a new one, but only the affected tube must be changed. On the contrary, as a disadvantage we have that, in relation to flat plates, these are more expensive.
Vacuum 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 made of 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 outer part is in contact with liquid transporter, which being colder than the vapor of the tube captures the heat and causes the steam 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.
Last review: May 31, 2018Back