Yes, and they deliberately use high e glass to shed heat.
Well that was a mistake! roof heat
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McKravitts
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The topic brings up an interesting fact;
Albedo is the fraction of light that a surface reflects. If it is all reflected, the albedo is equal to 1. If 30% is reflected, the albedo is 0.3.
The earths average albedo is about .3.
The avearge albedo of solar panels is .23.
The average albedo of roofing material is .17.
Hence solar panels on an average roof help cool the planet, whereas ground mount solar panels add heat to the planet.
The average albedo of a white roof is about .7.
Replacing that with a .23 albedo is going to increase heat absorption
Albedo is the fraction of light that a surface reflects. If it is all reflected, the albedo is equal to 1. If 30% is reflected, the albedo is 0.3.
The earths average albedo is about .3.
The avearge albedo of solar panels is .23.
The average albedo of roofing material is .17.
Hence solar panels on an average roof help cool the planet, whereas ground mount solar panels add heat to the planet.
The average albedo of a white roof is about .7.
Replacing that with a .23 albedo is going to increase heat absorption
Bluedog225
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I’m going to paint my panels white. 
McKravitts
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Hydro Solar has panels that take the excessive heat and put it into your domestic hot water tank.
There is no grid to sell your excess hot water to.
Might be a great idea for a laundromat.
Hedges
I See Electromagnetic Fields!
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I'm thinking the white roof reflected visible and maybe IR [edit: UV] from sun.
The PV panels converted 80% of the sun to IR, which was emitted 50% up, 50% down.
The white roof absorbed the IR.
With steep ground-mount panels, I noticed how hot it was standing under them.
Anybody got a spectrophotometer handy?
The PV panels converted 80% of the sun to IR, which was emitted 50% up, 50% down.
The white roof absorbed the IR.
With steep ground-mount panels, I noticed how hot it was standing under them.
Anybody got a spectrophotometer handy?
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Just like renewable credits for PV SRCs there is a market for renewable credits for thermal heat generated, called TRCs.
Agreed large load of an apartment building or something to pre heat water before it the water heater, is best use.
Bluedog225
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This changes, my whole solar panels on my conex plan as well. Dang
zanydroid
Solar Wizard
What about insulating the roof enough so that the heat preferentially goes up instead of down?
Does the electricity generated * cooling COP exceed the worse albedo? Most likely, otherwise rooftop solar would never work for powering AC
Does the electricity generated * cooling COP exceed the worse albedo? Most likely, otherwise rooftop solar would never work for powering AC
zanydroid
Solar Wizard
Raises albedo, potentially.
It depends on the type of terrain the panels are put on. If it’s going over asphalt parking lot, it’s definitely a net win I think without bringing GHG displacement into the convo
Desert? Probably a net loss. But it also displaces GHG
Some will still go into the building but insulation reduces that by a lot. My shed is r13 insulated so the energy load is minimal.
By a lot.
I'm saying i don't think albedo cools or heats the planet. The energy coming from the sun, is the energy coming from the sun. If some gets reflected where does it go?
My understanding is that if using bi-facial they only work if the material behind is white.
Also 5 inches is not enough airflow.
You can probably easily correct this situation by creating a frame to lift the panels on one end
zanydroid
Solar Wizard
Albedo definitely cools or heats the planet. At least, that’s what I learned from playing SimEarth and watching geology videos. It can be a positive cooling feedback loop — ie if earth freezes solid with icecaps albedo is at like .9 and it has a hard time thawing out.
The reflected radiation goes into space, modulo the amount that is absorbed on the way out.
zanydroid
Solar Wizard
Right, so the folks on this thread thinking that these results say solar is a bad idea bc it heats your house need to reevaluate.
Yeah the difference between white roof vs solar panels is not enough to matter. In either case the shed requires ac lol
Bluedog225
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Solar on the roof doesn’t provide much shade cooling. Counterintuitive. Makes ground mount more appealing.
It depends on the color of the roof doesn't it?
This is an excellent cut because he tests a dark roof, a white roof and compares the shading from the panels vs non pv shading
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And if it is a metal roof. Metal roofs are far better at reflecting heat from sun then asphalt shingles.
That's only because of their color though. A dark metal roof is going to have about the same absorption as a dark shingle roof if the Solar Reflective Index (SRI) is the same, since emissivity is similar
ksmithaz1
Solar / EV Junkie
Stick with it. Don't confuse "shade" with temperature. Sunlight and UV tears up plastics on a car. Blocking sunlight is going to be a net win, with adequate ventilation vs direct sunlight.Dang.
I’ve had this multi year obsession with putting panels on my cabin for shade. So many hours of research into micro inverters and roof mounted string inverters. I was even contemplating putting dead panels up there just to get some cooling.
All to get the old Land Rover safari shaded roof thing going.
Gonna be hard to let the dream go.
Hedges
I See Electromagnetic Fields!
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Use spectrophotometer to obtain spectrum falling on roof directly from the sun.
Spectrum falling on roof from backside of a panel.
Spectrum reflected from roof in each case. (ideally a representative white roof ... Oh, you've got one! You're the OP!)
My theory is that the panel does wavelength conversion from visible & UV to IR, and white roof does a poorer job of reflecting that IR.
Spectrum plus intensity for each incident and reflected case should allow calculation of power, and would show if roof does absorb IR.
I played with such an instrument in the short UV range. Had trouble at first getting any signal from the deuterium lamp I was using until I removed the lens on the end of the plastic fiber optic cable. Although they denied it, I thought someone in the lab I borrowed it from must have cooked the lens with a laser. It was basically opaque, according to instrument readings.
Also measure air temperature below panels and over roof without panels as well. That won't say where the heat is coming from, but thermal transfer from hot air could be another theory.
I see shields blocking the gap of some panel installations. Could be for aesthetic reasons, could be to reduce tear-off force of wind. Certainly doesn't help the heat situation.
Exactly. If the panels were regular PV (not bifacial) I doubt there would have been as much heat going into the roof. Most bifacial panel installation instructions call for 1 meter of space between the panel and the reflective surface.
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