A hybrid solar panel (more correctly defined as a PVT collector, an acronym P hoto V oltaic and T hermal) is an apparatus that allows the conversion of energy radiated by the sun in part into electrical energy and in part into thermal energy by combining of the effect of a photovoltaic module and a thermal solar panel (photovoltaic cogeneration).
Therefore, a hybrid solar panel is made up of a photovoltaic collector to which a heat exchanger is associated, capable of heating a fluid thanks to the part of the solar radiation not converted into electrical energy.
Origin of the hybrid solar panel or PVT
Since the origin of the photovoltaic conversion, it has been observed that the rate of conversion of solar radiation into electrical energy depends on the temperature of the solar photovoltaic cell that performs the conversion.
The performance of the solar panel decreases with the increase in the temperature of the photovoltaic cell. Since this conversion rate is of the order of 15-20% (for common crystalline silicon cells), it turns out that the residual 80-85% is converted into heat energy or sensible heat (i.e. the cell heats up) and this Significantly reduces the performance of the photovoltaic panel.
As an example, for polycrystalline cells with a typical yield decay rate of the order of 0.39% / ° C (relative), a yield of 17% at 25 ° C drops to 14% at approximately 70 ° C.
A solution to this problem has been identified in the possibility of cooling the cells using a thermodynamicheat transfer fluid that removes the heat produced. A secondary and important effect is related to the exploitation of this heat to satisfy a thermal user, similar to a thermal solar panel.
The general energy efficiency (that is, considering the heat recovered and the electricity produced as a useful effect) normally exceeds 40%, and can reach 50-60% under favorable conditions.
Structure of a PVT hybrid solar collector
Let's analyze different types of solar collectors.
Solar collectors with front air chamber
Tubeless Solar Collectors
Tubeless solar collectors are the most common collector.
In this type of collectors, the exchange of thermal energy is carried out at the rear of the photovoltaic collector; it is a mandatory structure in the case of liquid cooling, since the exchanger would mask the photovoltaic cells. In either case, it has the advantage of rear placement of the fluid supply and draw pipes, which would otherwise pose shading problems.
Liquid solar collectors
Compared to a normal photovoltaic panel, in a liquid collector there is the addition of a heat exchanger and its insulation. This exchanger can be of various shapes; in the most frequent cases, it consists of adherent copper tubes, with various technologies, to the backing sheet or, more effectively, it consists of an aluminum roll exchanger that allows better heat transmission. Heat exchange with the liquid collector is very effective in cooling photovoltaic cells, increasing their performance.
Dollars collectors concentration
By abandoning the use of silicon cells and introducing thin film technology, it is possible to design a hybrid panel that sees the use of solar concentration. An interesting application sees the presence of a concentrator (CPC English Parabolic Concentrator Compound) in whose focus a tube is placed on whose side surface a film of thin film solar cells (eg CIS or CIGS) is sitting.
This configuration makes it possible to achieve higher yields of photovoltaic cells (due to concentration), but at the same time more efficient heat removal (since the entire cell is in contact with the heat transfer fluid).