Solar cooker pots -- Does their color matter?

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8 replies · 2K views
entityfree
theory 'a' is we can cook all of our vegan food and heat our water with sunlight. what kind of difference would it make if i got a red painted pot? can you compare that to one painted black? and maybe also to a metallic one. please share some equations.
 

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yes, directly, probably using a fresnel lens or parabolic mirror or foil, to heat a metal pot with some kind of paint or enamel(?). if you like how quickly and to what temperature does a red painted metal sheet, black painted metal sheet, other color metal sheet, and non-painted metal sheet, and metals of different colors, reach when exposed to bright sunlight with no clouds? under cloudy conditions? and why? (say in, 5, 10, 25, 60, and 120 minutes?) (but i also want to use it on gas or electric if i need at the moment). we think that black absorbs all radiation? doesn't a red colored object absorb red radiation before it emits it though, thereby heating up? what color does the sun emit? how important is visible light in solar cookers anyway? what about infrared? i was able to get water to boil with the lens in losangeles so i know it can work! and foil type cookers can heat very well too.
 
CWatters said:
Is this pot going to be heated by putting it out in the sun? Or is it electrically heated using solar PV?
Doing it via PV is not a very efficient use of the available capture area. If you are trying to be green about this then you would need to consider the environmental impact of producing the PV array in the first place, compared with manufacturing a low quality aluminium reflector. There's a lot of thermal energy to be had from IR wavelengths in sunlight which PV cells actually find more of an embarrassment as their efficiency goes down with increasing temperature. On a sunny day with the sun high in the sky you can get a long way to the ball park figure of 1kW per sq metre and the focusser doesn't need to produce a particularly sharp image of the sun if you are trying to heat up a largish cooking pot.
Talking about efficiency, the bits of the pot that aren't receiving the focused beam should be insulated and even shiny to reduce heat loss to the surroundings.
 
CWatters said:
If it's direct then you want the side facing the reflector or lens to be black. All other surfaces not collecting sunlight should be polished to reduce losses.
I would say that some serious insulation (lagging) should be added to all surfaces that are not actually receiving the focussed sunlight (white or silver surface would also help). A big pot with less than 1kW of energy arriving will take some time to warm up and you must reduce heat losses as much as possible. Fibreglass lagging is pretty heat resistant.
Tracking the Sun in the sky can be worth while over a long period.