Panels photovoltaic solar energy

Installation of thermal solar energy

Solar power plant
Thermoelectric

Hybrid Solar Panel

Hybrid Solar Panel

A hybrid solar panel (more correctly defined as a PVT collector, an acronym P hoto V oltaic and T hermal) is a device that allows the conversion of the energy radiated by the sun partly into electrical energy and partly into thermal energy through the combination of the effect of a photovoltaic module and a thermal solar panel (photovoltaic cogeneration).

Therefore, a hybrid solar panel is composed 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 hybrid solar panel or PVT

From the origin of the photovoltaic conversion, it has been observed that the conversion rate 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. As this conversion rate is of the order of 15-20% (for the common crystalline silicon cells), it turns out that the residual 80-85% is converted into heat energy or sensible heat (ie, the cell is heated) and this significantly reduces the performance of the photovoltaic panel.

By way of 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 falls to 14% at about 70 ° C .

A solution to this problem has been identified in the possibility of cooling the cells using a thermodynamic heat transfer fluid that eliminates 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 overall energy performance (ie, considering heat recovered and electricity produced as a useful effect) normally exceeds 40%, and can reach 50-60% under favorable conditions.

Structure of a PVT hybrid solar collector

A PVT hybrid solar collector is an association of a photovoltaic collector and a heat exchanger. The photovoltaic collector is almost always of the glazed type, to reduce heat loss.

Let's analyze different types of solar collectors.

Solar collectors with frontal air chamber

The solar collectors with frontal air chamber exploit the greenhouse effect. They are used almost exclusively for the exchange of heat with air.

Solar Collectors without a tube

Solar collectors without a tube are the most common collector.

In this type of collectors the exchange of thermal energy takes place in the back of the photovoltaic collector; it is a mandatory structure in the case of liquid cooling, since the exchanger would mask the photovoltaic cells. In any case, it has the advantage of a subsequent location of the supply and fluid extraction pipes, which would otherwise pose shading problems.

Liquid Solar Collectors

Compared with a normal photovoltaic panel, in a liquid collector there is the addition of a heat exchanger and its isolation. This exchanger can be of various forms; in the most frequent cases, it consists of adherent copper pipes, with several technologies, to the backing sheet or, more effectively, it consists of an aluminum roll exchanger that allows a better heat transmission. The heat exchange with the liquid collector is very effective to cool the photovoltaic cells, increasing their performance.

Collectors concentration dollars

By abandoning the use of silicon cells and the introduction of thin-film technology, it is possible to design a hybrid panel that looks at the use of solar concentration. An interesting application sees the presence of a concentrator (CPC English Parabolic Concentrator Concentrate) in whose focus a tube is placed on the lateral surface of which sits a film of thin-film solar cells (for example, CIS or CIGS).

This configuration makes it possible to achieve higher yields of photovoltaic cells (due to the concentration), but at the same time a more efficient heat removal (since the whole cell is in contact with the heat transfer fluid).

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Last review: August 29, 2018

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