Painting panels black

erik.calco said:

The

Aluminum thermal conductivity ~230 W/mK, Copper ~330/mK, glass 1 W/mK. No, glass does not have a decent thermal conductivity, unless the word decent is redefined

Click to expand...

On that chart I linked, the thermal conductivity of air is 0.0262. Glass is 1.05. That sounds decent to me. ;p It is obviously not on par with metals. Metals aren't decent. They are spectacularly conductive.

Click to expand...

& compared to vacuum, glass is infinitely more conductive!

Here is a way to cool panels but not financialy viable.

Air is considered as a (very) good thermal insulator (almost all the insulation products are based on the principle of trapping air between fibers), glass is an insulator but bordeline conductor, metals are bad to pretty good conductors, but diamond and graphene are extremly good conductors (silver and copper are ridiculous in comparison).

@MBR The best are panels with PV on front and waterblocks on the back, you have both electricity and hot water plus the added efficiency of cooler panels of course. But they are expensive...

Heat transfer between two mediums is proportional to the temperature difference between those mediums; heat-sinking a 50℃ panel in 50℃ ambient temperature will not cool the panel down. You could quadruple the heatsink surface area, paint them in Black 2.0 (of any thickness), add 5kW of fans or travel down the road at 100mph, they still will not be cooled. Even shouting at them has mixed results

Covering them in peltier-effect cells might work if the efficiency gained through cooling generated more energy than the peltier-effect cell required.

tictag said:

Heat transfer between two mediums is proportional to the temperature difference between those mediums; heat-sinking a 50℃ panel in 50℃ ambient temperature will not cool the panel down. You could quadruple the heatsink surface area, paint them in Black 2.0 (of any thickness), add 5kW of fans or travel down the road at 100mph, they still will not be cooled. Even shouting at them has mixed results

Click to expand...

Only conductive heat transfer is proportional to the deltaT between the two bodies. Radiative heat transfer is proportional to the differences in the 4th power of temperature of the two bodies.
The best way to cool solar panels mounted on RV rooftops is attach a coil of thin-walled copper tubing to the back of the panel and circulate water - essentially a hybrid PV-thermal panel that gives you electrical power & warm water.

fat_old_sun said:

The best way to cool solar panels mounted on RV rooftops is attach a coil of thin-walled copper tubing to the back of the panel and circulate water

Click to expand...

But using the same principle, you would still have to somehow extract the heat from the water-filled copper tubing; copper tubing at 50℃ is not going to cool a panel at 50℃. Latent heat cooling (i.e. evaporation), OK, Venturi effect (i.e. compressor), OK, thermoelectric effect (i.e. Peltier etc), OK, but circulating a similar temperature fluid is not going to cool anything. Or I may well be missing something fundamental here (quite possible!).

tictag said:

But using the same principle, you would still have to somehow extract the heat from the water-filled copper tubing; copper tubing at 50℃ is not going to cool a panel at 50℃. Latent heat cooling (i.e. evaporation), OK, Venturi effect (i.e. compressor), OK, thermoelectric effect (i.e. Peltier etc), OK, but circulating a similar temperature fluid is not going to cool anything. Or I may well be missing something fundamental here (quite possible!).

Click to expand...

The water is not circulated. Instead the water is used for showering, preheating water for coffee, cooking, etc. Heating water takes a lot of energy. Using the wasted heated of a panel makes a lot of sense in an RV, esp. when boondocking.

fat_old_sun said:

The water is not circulated. Instead the water is used for showering, preheating water for coffee, cooking, etc. Heating water takes a lot of energy. Using the wasted heated of a panel makes a lot of sense in an RV, esp. when boondocking.

Click to expand...

I think what tictag is implying is that if you shower with 37ºC (~100ºF), the water is curently at that temperature. So you won't be able to cool the panels that much.
What I've been thinking for a while, have you seen those pool solar heaters done with the black flexible pipes? I would burrow those "collectors" 1 meter below ground to act as radiators instead. Then you can water cool your panels.

About the link posted by MBR, wouldn't that produce steam that would lower the PV performance?
I think the best way to watercool panels would be to attach giant waterblocks on the back of the panels and try to keep the water as cold as possible

Long and wandering thread that hasn't had a post in over a year . . . I shall revive it

Hybrid panels offering PV and water cooling have been around for quite a while. I ran across these a few years back and wanted to use them, but they fell into the category of solar hot water (which requires special safety valves to prevent boiling) at which point I needed to get a plumber and permits which cost more than just heating the water with a heat pump. Using it to heat a pool means that the water temperature stays around 28 to 30C and if you use it for hot water, then you run the panels up to 50C. The maximum water temperature is 70C.




The cooling on the back was essentially corflute with manifolds glued on each end with the inlet and outlet tubes. Easy construction. Corflute is typically made from polyethylene which is your standard black water pipe. Polyethylene is very difficult to glue, so not sure if they used a different material or some special glue. Nice tidy design, though.