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Solar panels can absorb sunlight and use it for energy, but can they absorb the heat that is generated from their use and use the heat for energy?

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Yes, there are indeed combined PV-T (photovoltaic-thermal) hybrid panels that turn some of the incident light into electricity, and have a circulating fluid and heat exchanger to put some of the heat into a heat store.

There's very little take-up of them, because they're just not economic in most circumstances.

The theory looks great: PV panels are more efficient when they're colder, so extracting the heat from them should give a double win - useful heat is harvested, and more electricity is generated.

In practice, it adds complexity. And PV is a mass consumer product as well as a mass utility-scale product - over a billion PV panels have been installed globally - so PV sees all the economies of scale and learning-by-doing, whereas PV-T remains an oddity and a niche.

In almost all circumstances, it's preferable just to install one or the other technology. In some circumstances, it might be appropriate to install both, but separately. There are some edge cases where space is very limited and it's appropriate to install both technologies - and those edge cases are the market for PV-T panels.

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  • $\begingroup$ At what temperatures and flow-return split do PV-T systems typically deliver hot water? Could be another limiting factor to use. $\endgroup$ – mart Apr 27 '17 at 10:51
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Both thermo-electric and photo-electric cells work on the same physical principles. A photon is absorbed by an electron in the outermost orbital which causes ionization and voltage potential. The photo-cell is tuned with with doping to semi-conductor substrate to specific wavelength photons for that of light in the visible or UV spectrum whereas thermo-electric cells would be tuned for absorbing photons in the infrared wavelengths.

For this type of hybrid system to work efficiently, there would have to be filters set up to not pass through photons that are not in the wavelengths of interest. Otherwise we would have photons that are not useful for the electric potential generation striking the cells and just heating them up.

You will often find filters on photo-cell arrays to increase their efficiency. Of course different materials and thus different filters will be required for the different wavelengths.

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  • $\begingroup$ As the other answer suggested; it's definitely possible to extract the heat mechanically through piped fluid. You wouldn't require a different panel or filter, just some system to extract the heat from the PV panel. It's just a very niche market with an added complexity system, so it's hard to get meaningful performance out of it. $\endgroup$ – JMac Apr 26 '17 at 17:23

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