Talk:Photovoltaic array

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[edit] Properties of Solar Panels: A question.

––Do Solar panels, by absorbing light energy and converting it to electrical energy reduce ambient temperature? Or do they, in the process of attempting to absorb more energy end up giving off more heat energy throughout the day.

My question stems from a notion a friend had that a large array of solar panels in use over flat roofed houses in desert nations would not only serve as a electrical power source but would reduce the need for air conditioning or other temperature controls or just outright reduce ambient temperature. I mean, aren't efficient arrays starting to absorb about 30% of light energy? Thechosenone021 01:26, 20 July 2006 (UTC)

Interesting question. I'm no expert, but here's one thought: it must also depend upon what use the generated electricity is put to. If it is used locally to drive any kind of appliances (including fridges!), then almost all of it will finally be converted into local heat (out of light energy). But if it were run into (efficient) batteries, or run by wires off to some other location, there may be some local cooling. But don't forget that they convert light into electricity, not heat - although that light energy would otherwise be absorbed by something else and heat it too. It's still counter-intuitive because, having been around solar panels, I know how hot they get in direct sunlight too! --Nigelj 17:45, 20 July 2006 (UTC)

Right, I was aware that that might be the case given that the panels are usually a dark color to absorb more light energy that would usually be reflected so they heat up. Of course that reflected light would go somewhere else eventually. I guess any study would need to be large enough to account for all that. Thanks though, I hope maybe someone has seen some sort of study on this topic? Thechosenone021 01:28, 21 July 2006 (UTC)

Actually, heat is bad for them, and it lowers their efficiency. Many have a metal backing, so that they radiate away that heat. In fact, you might do well to solder a solar hot water collector to their bottom, to cool them off. linas 21:36, 22 July 2006 (UTC)

A researcher at BP Solar (British Petroleum) gave me these figures:

Of every 100W of light falling on a typical module, 50W reflected, 17W converted to electricity, 33W absorbed as heat. This was a while ago and I doubt if they are any more than a rough indication, but it is clear that a) there can be a heat build-up and b) this reduces the efficiency of the PV conversion. There are various ways to use the heat in a building. I believe there are some modules that incorporate solar water heating panels as Linas said, but DIY enthusiasts should think twice before putting water in close proximity to DC electricity. Another way is to draw the heat into the building as part of the mechanical or passive ventilation system, and then it can be dumped to a thermal store of some kind, e.g. it can be turned into hot water with an air-to-water heat pump. There are some references around for some of these solutions. Itsmejudith 21:42, 28 July 2006 (UTC)

Right, but the original question is pertaining to Solar Panels effect on ambient temp. If a tree's photosynthetic process reduces temperature in the shaded areas, couldn't a photo array have a similar effect? Thechosenone021 17:34, 29 July 2006 (UTC)

Ah, but trees are famous for transpiration and also deep roots. Sucking up cool underground water and causing all that evaporation (latent heat) is bound to have a cooling effect. Unlike a hot, dry, black silicon panel in the direct sun. I just dunno. --Nigelj 20:53, 29 July 2006 (UTC)