3 ms·

Would there be unintended consequences of half the world’s roofs being black?

nostrademons 5y ago
Largely it cools the house, which is usually a desirable byproduct. Instead of solar energy being converted into thermal energy by the roof and then radiating into (and off of) the house, it's converted into electrical energy by the panels. We had a home energy audit guy come into our house and point an infrared camera at the roof, and you could very clearly see the outline of the panels as a detectable cool spot in the ceilings. Half of the world's roofs are probably already black or at least dark brown - asphalt shingles, slate, vinyl, many wood varieties.
- tamaharbor 5y ago
  So more heating energy will be required in the winter?
  - nostrademons 5y ago
    Yeah, but incident solar radiation is rarely a large component of the energy used to heat a home. If it were, we could just live in greenhouses and forget the whole fireplace vs. gas vs. oil vs. electric vs. heat pump debate. You get a much bigger boost to heating efficiency by having new windows installed or cleaning your ductwork than by keeping your roof sunny. Also, heat pumps can be up to 400% efficient, so the electrical energy that comes from a solar panel could actually turn a profit thermally if used to run a heat pump.
- WalterGR 5y ago
  > Largely it cools the house, which is usually a desirable byproduct. ... you could very clearly see the outline of the panels as a detectable cool spot in the ceilings. Based on my cursory googling, it seems that this is indeed the case, since the solar panels absorb the sun's energy, rather than the roof. I'm having a hard time finding reliable sources, but my sense is that those black solar panels may warm the surrounding environment. e.g. https://e360.yale.edu/features/urban-heat-can-white-roofs-help-cool-the-worlds-warming-cities https://e360.yale.edu/features/urban-heat-can-white-roofs-he... (2018) " Urban Heat: Can White Roofs Help Cool World’s Warming Cities? It has long been known that installing white roofs helps reduce heat buildup in cities. But new research indicates that making surfaces more light-reflecting can have a significant impact on lowering extreme temperatures – not just in cities, but in rural areas as well. " > Half of the world's roofs are probably already black or at least dark brown - asphalt shingles, slate, vinyl, many wood varieties. Fair point. So... Would there be unintended consequences of an increase in the world’s number of black roofs? ;)

Largely it cools the house, which is usually a desirable byproduct. Instead of solar energy being converted into thermal energy by the roof and then radiating into (and off of) the house, it's converted into electrical energy by the panels. We had a home energy audit guy come into our house and point an infrared camera at the roof, and you could very clearly see the outline of the panels as a detectable cool spot in the ceilings. Half of the world's roofs are probably already black or at least dark brown - asphalt shingles, slate, vinyl, many wood varieties.

tamaharbor 5y ago
So more heating energy will be required in the winter?
- nostrademons 5y ago
  Yeah, but incident solar radiation is rarely a large component of the energy used to heat a home. If it were, we could just live in greenhouses and forget the whole fireplace vs. gas vs. oil vs. electric vs. heat pump debate. You get a much bigger boost to heating efficiency by having new windows installed or cleaning your ductwork than by keeping your roof sunny. Also, heat pumps can be up to 400% efficient, so the electrical energy that comes from a solar panel could actually turn a profit thermally if used to run a heat pump.
WalterGR 5y ago
> Largely it cools the house, which is usually a desirable byproduct. ... you could very clearly see the outline of the panels as a detectable cool spot in the ceilings. Based on my cursory googling, it seems that this is indeed the case, since the solar panels absorb the sun's energy, rather than the roof. I'm having a hard time finding reliable sources, but my sense is that those black solar panels may warm the surrounding environment. e.g. https://e360.yale.edu/features/urban-heat-can-white-roofs-help-cool-the-worlds-warming-cities https://e360.yale.edu/features/urban-heat-can-white-roofs-he... (2018) " Urban Heat: Can White Roofs Help Cool World’s Warming Cities? It has long been known that installing white roofs helps reduce heat buildup in cities. But new research indicates that making surfaces more light-reflecting can have a significant impact on lowering extreme temperatures – not just in cities, but in rural areas as well. " > Half of the world's roofs are probably already black or at least dark brown - asphalt shingles, slate, vinyl, many wood varieties. Fair point. So... Would there be unintended consequences of an increase in the world’s number of black roofs? ;)