Photovoltaic thermal hybrid solar collector

[5] PVT collectors generate solar heat and electricity basically free of direct CO2 emissions and are therefore regarded[by whom?]

In 2015, the provision of heating for use in buildings, industrial purposes and other applications accounted for around 52% (205 EJ) of the total energy consumed.

While 72% of the heat was provided by the direct combustion of fossil fuels, only 7% was from modern renewables such as solar thermal, biofuel or geothermal energy.

[8] The electricity demand in buildings and industry is expected to grow further due to ongoing electrification and sector coupling.

Photovoltaic cells typically reach an electrical efficiency between 15% and 20%, while the largest share of the solar spectrum (65% - 70%) is converted into heat, increasing the temperature of PV modules.

[3][12] The design and type of PVT collectors always implies a certain adaption to operating temperatures, applications, and giving priority to either heat or electricity generation.

In a standard fluid-based system, a working fluid, typically water, glycol or mineral oil circulates in the heat exchanger behind the PV cells.

Some versions of the PVT air collector can be operated in a way to cool the PV panels to generate more electricity and assist with reducing thermal effects on lifetime performance degradation.

PVT air collector configurations range from a basic enclosed shallow metal box with an intake and exhaust up to optimized heat transfer surfaces that achieve uniform panel heat transfer across a wide range of process and ambient conditions.

Despite their name, the solar cells are generally attached to the back side of a front glass and thus covered by it, but without an air gap.

While most PVT collectors are prefabricated units, some products are offered as heat exchangers to be retrofitted to off-the-shelf PV modules.

In both cases, a good and longtime durable thermal contact with a high heat transfer coefficient between the PV cells and the fluid is essential.

The insulating characteristics of the front cover increase the thermal efficiency and allow for higher operating temperatures.

However, there are also stationery PVT collector types that use nonimaging reflectors, such as the Compound Parabolic Concentrator (CPC), and do not have to track the Sun.

Under ideal conditions, about 75% of the Sun's power directly incident upon such systems can be gathered as electricity and heat at temperatures up to 160 °C.

[17][18] A limitation of high-concentrator (i.e. HCPV and HCPVT) systems is that they maintain their long-term advantages over conventional c-Si/mc-Si collectors only in regions that remain consistently free of atmospheric aerosol contaminants (e.g. light clouds, smog, etc.).

Power production is rapidly degraded because 1) radiation is reflected and scattered outside of the small (often less than 1–2 °) acceptance angle of the collection optics, and 2) absorption of specific components of the solar spectrum causes one or more series junctions within the multi-junction cells to under-perform.

The short-term impacts of such power generation irregularities can be reduced to some degree with inclusion of electrical and thermal storage in the system.

Depending on the type of heat transfer fluid, PVT collector technologies are suited for several applications:[20] PVT technologies can bring a valuable contribution to the world's energy mix and can be considered as an option for applications delivering renewable electricity, heat or cold.