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I'm wondering whether installing solar panels on a sloped home rooftop would have a net positive or negative effect on the heat radiating into a home from sunlight on the roof.

Panels are generally black, so presumably they have a very low albedo - lower than the shingles beneath - and heat up more than the roof would without the panels. But they also convert some of the solar radiation directly to electricity, so that subtracts from the heat produced. They're also set off a few inches from the rooftop, so there should generally be airflow between the panel and shingles, and with a sloped rooftop, convection should bring in cooler air.

Assume that it's summer, so the primary electrical load is for cooling (A/C) and any radiative heating from the roof to the house is undesirable.

Under what range of assumptions would the net heat flow to the house be greater than it would be without the panels installed?

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  • $\begingroup$ At least one layer is black, but is there a high-albedo layer beneath that that would keep the unused energy from going all the way through to the roof, as it were? Also, solar panels are shiny, which might offset their blackness to some extent. $\endgroup$ – MissMonicaE Oct 14 '16 at 13:12
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I think the radiant heating of the roof from the warm panels would be much less than the direct solar heating without them. This could be calculated. But usually with a sloped roof you have a ventilated attic space with insulation on the bottom (on top of the ceilings of the rooms below). Even if you have no attic space, with instead a sloped ceiling on the underside of the rafters, there should be insulation between the rafters. If you are well insulated, heat from the roof should not be a big issue. If you don't have insulation, installing it might be a better investment than solar panels.

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