Today we are going to tell you which are the main elements of flat plate solar collectors, which are the majority of low-temperature solar panels on the market.
This type of solar panels is mainly used to heat water for sanitary use (DHW). However, even being the simplest equipment, to make a good choice it is essential to know the characteristics of the elements that make it up.
This information is useful to be able to evaluate the quality of the collectors and choose the most suitable one based on the weather conditions to which it will be subjected; the purpose of the installation; and the budget available.
The 4 elements of solar panels that we must look at are the transparent cover, the collector plate, the insulator, and the casing.
It is responsible for producing the greenhouse effect, reducing losses due to convection, and ensuring the water and airtightness of the collector in conjunction with the casing and the gaskets.
The greenhouse effect achieved by the cover consists in that the radiation that has passed through the cover and reaches the collector plate, a part is reflected towards the transparent cover with a wavelength for which it is opaque, with which it is possible to retain radiation inside. This effect defines the characteristics of the roof:
- The high transmission coefficient of solar panels radiation in the band from 0.3 to 3 mm, which must be conserved over the years.
- Low transmission coefficient for long waves, greater than 3m.
- Low coefficient of thermal conductivity, which hinders the passage of heat from the interior surface to the exterior, thus minimizing losses.
Its mission is to absorb solar panels’ radiation in the most efficient way possible and transform it into usable thermal energy by transferring it to the heat transfer fluid.
The face of the collector plate that is exposed to the sun must be protected from the sun’s rays by means of:
- Black or dark paint that absorbs solar panels radiation. It has the disadvantage of having an emission coefficient substantially equal to that of absorption, so it is not recommended for high temperatures.
- Selective surfaces. It has a high solar panels radiation absorption coefficient and a low emission coefficient. There are no simple materials that have this property, so it is achieved through layering or special surface treatments.
The collector plate is protected on the back and on the side by means of insulation to prevent thermal losses to the outside.
The characteristics of these insulators must be:
- Resist high temperatures without deteriorating, which is often achieved by placing a reflective layer between the plate and the insulation, which prevents the insulation from directly receiving radiation.
- Give off few vapors when decomposed by heat and in case they do not adhere to the cover.
- Not degrade by aging or another phenomenon at the usual working temperature.
- Withstand the humidity that can be produced inside the panels without losing its qualities.
The most used materials are fiberglass, rigid polyurethane foam, and expanded polystyrene. Whichever material is chosen, it must have a coefficient of expansion compatible with that of the other components of the solar panel.
It is in charge of protecting and supporting the elements that make up the solar collector, in addition to serving as a link with the building through the supports.
You must meet the following requirements:
- Rigidity and structural resistance to ensure stability. It is of utmost importance as it must withstand the pressure of the wind.
- Strength of the fixing elements: mechanical for the forces to be transmitted; and chemistry to withstand corrosion.
- Resistance to the elements, the corrosive effects of the atmosphere, and chemical instability due to inclement weather.
- Ventilation inside the collector to avoid condensation of the water inside the collector.
So far, the 4 elements that make up flat low-temperature solar panels. And you know, “For the cold and for the heat, renewable is the best.”