Frame color and panel temperature

landyacht.318
landyacht.318 Solar Expert Posts: 82 ✭✭✭✭
in General Solar Power Topics #1
I painted the frame of my Kyocera 130 panel white, to match the roof of my campervan and to make it stealthier.

Today, out of curiosity, at 1:30, I put my IR thermometer right in the middle of the panel pressed up to the glass. 106.5 degrees. The panel right next to the frame was over 10 degrees cooler. The white Frame temperature was 77 degrees. The white fiberglass roof right next to the panel was 75 degrees. It was about 71 degrees ambient temp outside.

Now, I have touched a piece of aluminum angle left out in the sun before and it was extremely hot.

Since my panel was hottest in the middle of the panel, and coolest by the frame, it seems as if the white frame is dissipating some heat. I would think an unpainted frame would not be as cool, or might even be hotter than the black panel.

How much, if any effect would you surmise this white frame has on panel efficiency and output?
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Comments

  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #2
    Re: Frame color and panel temperature

    I don't know about Kyocera, but on the brands I use, it voids the warranty to paint the module frames.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Frame color and panel temperature

    the white framing is not dissipating heat, but is reflecting heat away so it does not absorb it as readily as other surfaces. to a small degree the frame does act like a heat sink for the pv and the edge will be slightly cooler, but black is a better radiator of heat. trouble is it is also the best absorber of heat too so the sun's energy will get absorbed and not allow the edge dissipation.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #4
    Re: Frame color and panel temperature

    Now if you could paint the underside of the frame "flat black" to radiate heat away, and leave the upper side shiny to reflect as much of the sun as possible - - - -
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  • david3
    david3 Solar Expert Posts: 37 ✭
    #5
    Re: Frame color and panel temperature

    Sort of related to this; if you were to mount the panels on a metal roof, would it be better for the solar panels if the roof was white, or some other color? Or would it matter at all?
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #6
    Re: Frame color and panel temperature
    waynefromnscanada wrote: »
    Now if you could paint the underside of the frame "flat black" to radiate heat away, and leave the upper side shiny to reflect as much of the sun as possible - - - -

    Don't think it works that way - once the heat is 'in' the material what ever color it is painted makes no difference in re-radiation of the heat away from the object.

    Having a cool roof is beneficial - be it due to color or materials.

    Russ
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #7
    Re: Frame color and panel temperature
    russ wrote: »
    Don't think it works that way - once the heat is 'in' the material what ever color it is painted makes no difference in re-radiation of the heat away from the object.
    Russ
    Some time when you have a hot frying pan with a clean, shiny metal bottom, and a very dark to black inside (non-stick) coating, hold it up near your face. With the bright shiny side next to your face, you'll feel very little heat being radiated to your face. Now flip the pan over so the black side is next to your face and be prepared to be amazed. This is a well known mechanism for heat transfer.
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #8
    Re: Frame color and panel temperature

    Not at all the same thing - the two pans have to be made of a different material or have a different thickness for that to happen.

    A material re-radiates the heat to the atmosphere with white, silver or black paint just the same.

    That can be changed if there is a reflective or insulating coating coating on the surface.

    A color can change the ability or capacity of a material to accept radiant energy - yes but re-radiate - no.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Frame color and panel temperature

    This conversation is missing certain key factors. Namely that colour only has an effect with visible light spectrum, which heat (infrared) is not a part of. Black absorbs more of the visible spectrum than white. Once absorbed into the material, atrophy causes the energy to slow from visible spectrum to infrared heat. The illusion that black radiates more is caused by the fact it absorbs more energy (from the visible) in the first place, and thus has more energy to radiate. Indeed it can cause the material to become energy saturated, forcing release. That is the same thing you see when you heat a piece of metal until it glows: the material has taken on all the energy it can and now has to radiate off excess because there's simply no room for it. The black radiation is on a smaller scale than that of course.

    I hope that's clear. It probably isn't. :blush:
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: Frame color and panel temperature

    From another thread:
    BB. wrote: »
    Niel is correct... Generally what radiates heat well also absorbs heat well.

    I remember years ago that NASA spent a bunch of time and money trying to find the right "paint" that would reflect heat from the sun well and radiate heat to space well... If I recall correctly, the best material was not much better than any of the other options.

    In the case of solar panels, I am not sure that it would make any difference at all... You have a slight insulation effect (paint is not a good conductor of heat, plus the back of the panels are plastic--also not a good heat conductor). And, you may end up with warranty problems--paints have solvents and additives which could attack the membrane materials on the back of the panels.

    If you want to keep your panels cool--ensure there is at least 5-6 inches of airspace behind/under the panels and a way for air to circulate.

    Ah--found one NASA report from 1983 (PDF file)... Has a whole bunch of information about colors/materials and their absorption and emission of heat. Hmm, looking at the results--I would probably be more tempted to paint the back of the panels white than black... Very similar emission results, and much less absorption with white.

    But of so much variability (materials, coating thicknesses, the way it is applied, mounting differences, etc.)--You would really have to do A/B testing of your specific panels and coatings.

    Don't think it is worth doing it...

    A white roof under "Bi-Facial" solar panels (which can absorb light from back of panel) would tend to collect a bit more power--but I would not re-roof for it. It would probably not be worth the roofing costs to do it (and the issues with your spouse and an ugly roof color).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #11
    Re: Frame color and panel temperature
    russ wrote: »
    Not at all the same thing - the two pans have to be made of a different material or have a different thickness for that to happen.
    .
    Not two different pans, ONE pan, shiny aluminum, or SS on the bottom side and dark coating (non stick for instance) on the other, top side.
    Actually take a couple of minutes and try it, you'll be amazed, as was I.
    The shiny side will radiate very little heat to your face, the dark side will radiate lots. I've done it, felt it. There's a huge difference.
    Been there, done it and I'll say no more on the subject.
    Peace be with you.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Frame color and panel temperature

    Wayne's experiment is correct. However, I feel his explanation for it isn't. So this is my take, for what little it's worth:

    First of all, for practical purposes an unheated frying pan has no heat to radiate: it is at room temperature. Without a difference in energy levels there is no exchange.

    Second, the shiny underside of the pan is flat. The black cooking surface is somewhat concave - like a parabolic reflector (although imperfectly so). So what you are actually detecting is not heat radiating from the black surface as opposed to not radiating from the shiny surface, but rather your body heat being reflected by the concave shape as opposed to the flat shape. Try this same experiment with both a wrought iron pan (black both sides) and a stainless steel one (shiny both sides) and see if you don't get the same result (although the non-stick coating may also play a role in the amount of reflection).

    If someone wanted to really test the colour vs. radiant idea, you would need two equal size and shape pieces of metal. One painted white, the other black - with the same type and thickness of paint. These would need to be heated a controlled amount, as by passing a fixed current through them. Placed in a completely dark room, so that no visible light energy is added to the possible outcome. Then measure the heat radiating off each piece with an infrared thermometer.

    The physics I earned tells me the result will be the same for each piece. But I learned that stuff long, long ago when dinosaurs ruled the Earth. I may have forgotten, gotten confused, or they may have changed the laws of physics since then. They do stuff like that just to mess with our minds. That's why mine is so messed up. :p
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #13
    Re: Frame color and panel temperature

    See my above link: -found one NASA report from 1983 (PDF file)

    Polished aluminum is a very poor emitter of heat... Almost any coating has 10-40x better emissivity.

    In general, Wayne should be correct in his explanation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
    Re: Frame color and panel temperature
    russ wrote: »
    Not at all the same thing - the two pans have to be made of a different material or have a different thickness for that to happen.

    A material re-radiates the heat to the atmosphere with white, silver or black paint just the same.

    That can be changed if there is a reflective or insulating coating coating on the surface.

    A color can change the ability or capacity of a material to accept radiant energy - yes but re-radiate - no.


    those 2 statements are 100% false as the darker the color with black being the darkest these absorb AND radiate best over the lighter or shiny colors.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
    Re: Frame color and panel temperature

    I think, my friends, you are misinterpreting the NASA data. As it clearly shows some coatings of the same colour having different emissivity and some coatings of different colour having the same emissivity. It is not the colour per se, but the coating that makes the difference. It is likely that black coatings in general have a denser composition and would therefor transfer heat better, whereas light-coloured coatings would have a less dense formula (especially aluminium) which would act with greater insulative characteristics. Note the repeated references to the need for careful control of the thickness of the coating.

    For those who want a less technically involved explanation, there is the Wikipedia entry http://en.wikipedia.org/wiki/Thermal_radiation:

    Lighter colors and also whites and metallic substances absorb less illuminating light, and thus heat up less; but otherwise color makes small difference as regards heat transfer between an object at everyday temperatures and its surroundings, since the dominant emitted wavelengths are nowhere near the visible spectrum, but rather in the far infrared. Emissivities at those wavelengths have little to do with visual emissivities (visible colors); in the far infrared, most objects have high emissivities.

    And this bit explains the shiny metal phenomenon:

    The main exception to this is shiny metal surfaces, which have low emissivities both in the visible wavelengths and in the far infrared. Such surfaces can be used to reduce heat transfer in both directions; an example of this is the multi-layer insulation used to insulate spacecraft.

    Perhaps physicists are still discussing this.

    One thing is for certain: in practical terms painting the frames of your panels any colour will have little effect on getting the heat generated within the panels to conduct through the glass (lousy heat conductor) and radiate to the atmosphere.
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #16
    Re: Frame color and panel temperature

    Thanks Coot - I agree with you 100%.

    In everyday items (light weight panel supports) there would be no difference. If you get into exotic stuff anything can happen - and NASA is case of the exotic - it is a requirement of their task of doing what hasn't been done before.

    Something that may confuse people is the emissivity of a material and use of IR temperature measuring devices. There are probably more poor measurements taken by IR guns than any other method. Unless in the hands of someone who knows the topic well they are useless. You can get whatever temperature you want with minor adjustments in emissivity though.
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  • landyacht.318
    landyacht.318 Solar Expert Posts: 82 ✭✭✭✭
    #17
    Re: Frame color and panel temperature

    Thanks for the responses. My router took a dump so I have not been online since I asked the original question.

    When I was researching Radiators, and specifically about painting aluminum radiators to inhibit corrosion, I learned about emissivity, and that black will radiate more heat than white, or even unpainted, as long as the paint was not too thick.
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #18
    Re: Frame color and panel temperature
    landyacht.318 wrote: »
    Thanks for the responses. My router took a dump so I have not been online since I asked the original question.

    When I was researching Radiators, and specifically about painting aluminum radiators to inhibit corrosion, I learned about emissivity, and that black will radiate more heat than white, or even unpainted, as long as the paint was not too thick.

    Pardon? Any reference to that as I believe it is not correct.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #19
    Re: Frame color and panel temperature
    russ wrote: »
    Pardon? Any reference to that as I believe it is not correct.

    sorry, but she is correct.

    i was taught it in college physics for one, but you can read it here too.
    http://answers.yahoo.com/question/index?qid=20080829235318AAcU0tI
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  • landyacht.318
    landyacht.318 Solar Expert Posts: 82 ✭✭✭✭
    #20
    Re: Frame color and panel temperature

    Thanks for the back up neil, but :"she"?

    Last time I looked down, I had external plumbing, haha
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #21
    Re: Frame color and panel temperature

    Sorry but wrong - no one should have learned this in any class as it is bad science - last time I will bother to make the point.

    I consider Yahoo answers the same as you tube or the wiki - they must be taken with a grain of salt as too much information is not accurate.

    The characteristic of the material determines how much heat it hold and radiates away from it.

    A coating may act as an insulator to reduce the radiation away from the body.

    Exotic materials and coverings such as at NASA are a different world at times.

    Take two identical pieces of steel plate - paint one white and one black with the same type of paint and they will radiate heat away from the body at the same rate.

    Absorbing radiation is a different thing totally - different mechanism.

    Now take everyone's favorite - the IR temperature measuring device to verify the temperatures and one can get some more strange and meaningless numbers.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #22
    Re: Frame color and panel temperature
    landyacht.318 wrote: »
    Thanks for the back up neil, but :"she"?

    Last time I looked down, I had external plumbing, haha

    oops, sorry as i was thinking of somebody else.:blush:
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