black back sheet solar panels

mahendra
mahendra Solar Expert Posts: 188 ✭✭✭
in Solar Product Reviews & Opinions #1
hi there,i understand the black frame solar panels are for aesthetic purposes but whats the deal with black back sheet?Whats the purpose for that?thanks
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: black back sheet solar panels

    Two reasons I can think of...

    Pigments can reduce the effect of UV and sunlight degradation on the plastics and adhesives. Different pigments may have different costs and different effects on the plastic itself (processing, life, costs, quality, yield) (i.e., titanium dioxide (white) vs carbon black).

    Another issue may be that many times, black radiates heat better than white/light colors... But I am not sure it would make a big enough difference on a solar panel. Having a "flat surface" will radiate heat better than a glossy surface, etc...

    In the end, it just may be "price" of material... Whichever is cheaper/more available is what they get.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #3
    Re: black back sheet solar panels

    If the back sheet is white. you see it from the front as little white lines around all the cells. It looks terrible. For a PV array to look "nice" to those high-end discerning, asthetic minded customers, the panels need to be as close to ALL black as possible. One large field of black with nothing to distract the eye! Where I live, its a freaking local building department requirement to use black panels. They could care less about a good efficient installation - just has to look good!
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
    Re: black back sheet solar panels
    mahendra wrote: »
    hi there,i understand the black frame solar panels are for aesthetic purposes

    Its more than aesthetic, at least to some of the solar installers around here. According to several of them, ice & snow melt off quicker on black framed panels.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: black back sheet solar panels

    as to the better radiator of heat, the back may be better being black with the base color still being white to reflect the heat from being absorbed on the face of the pv. i'm ultimately not too sure what effect painting the backside of a pv would have or with what paints as paint chemistry may or may not degrade the pv. it would be interesting to pose the question of say spray painting the backside of the pv black to the manufacturers for their opinion if it would be a detriment and most importantly if it would void any warranties.
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #6
    Re: black back sheet solar panels

    White backing is better than black.
    Black attracts heat, so its a no brainier that there will be some voltage drop.
    I've also been told the black backing affects amperage as irradiant UV light that typically would reflect from the white backing can reflect back off the glass allowing the surface area to be more efficient, for solar cells to absorb irradiant UV.

    I would only recommend black backing for snow conditions.
    1.) snow works as a concentrator reflecting light, it intensifies UV light and allows light to reflect and bounce, increasing the amount of energy per metered sq. Amperage is higher in early mornign to later evenings, and because the colder ambient condition, and altitude, voltage will rise higher than STC because its a PTC condition that exceeds STC condition. Ever get sun burned on a cold 40 degree day while snowboarding or skiing, and still use sunblock?
    2.) Black backing is meant to help for conditions under 25* C, so it stabilizes voltage to be more inline with STC conditions by raising the panel temprature, when the ambient temperature is lower, that way fuses aren't consistently and redundantly blowing.

    Reminds me of a 3 megawatt project in colorado for a company I worked for. The engineers used white backing panels, derated the system accordingly to PTC. Failed at the fact that the installation used white panel backing for the system. After fuses had blown a few times the company I worked for substituted for the black panel backing. Fuses no longer blew out. bLack is better for below 25*C conditions, nothing more, nothing less to sum it up.

    If People are buying black backing panels other than for those reasons then they are just a bunch of goal zero yuppies talking about how cool it looks as there panels produce 50% less power when compared to the white backing panels.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #7
    Re: black back sheet solar panels

    While black, compared to white, unquestionably gets HOT when hit with sunlight, if the panels are properly positioned, the sun will be impinging the FRONT of the panel, not the back, thus the black back would be radiating heat, not "attracting" heat.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: black back sheet solar panels

    solarpowered,
    yes, i agree there are some superficial people out there being very meticulous. now i'm not saying you are wrong, but black isn't just good at absorbing heat as it is also a good radiator of heat. when there is a black surface that is hotter than the surrounding air it will radiate better than a lighter or white surface will and unless the sun hits the underside of the pv, it will not be absorbing any of the solar radiation. my possible take on this might be that the white reflective portion that may still be visible between some sections of the face of the pv on some possible makes may help to keep the pv ever so slightly cooler by reflection while the underside will radiate the heat away from the pv that it has absorbed.

    only discrepancy is that you say the white backed pvs put out more current than the black by trial. anybody else do this kind of comparison or ask the pv manufacturers?

    ah, i see wayne posted under me while i was typing and we seem to concur.
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #9
    Re: black back sheet solar panels

    Black works more like a heat exchanger. Radiators which radiate heat are heat exchangers. I concur it radiates heat, in order to radiate heat there is a point of thermal capacity which means once it hits the point past neutral from collecting or absorbing UV light the process then works to expell radiating heat. It exchanges or then transfers UV radiation as a concentration and uses it for heat. Anything black typically can exceed ambient temperatures by 15*~30*F depending on the angle of the sun.

    If some one on these forums has a black " 30watt Goal Zero Panel" or similar 30watt panel, run a 4 part test perfect due south angle of azimuth panel once at 9:30, again at 11:30, 1:30,3:30.
    I have a UPG solar 20 watt white backing panel that will outperform in volts and amps at the same times of this test. Just give the day and we can make it a show down, accept instead of guns we have panels!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: black back sheet solar panels

    Perhaps the ones to ask would be the companies making the black-backed panels. Surely they would have some explanation for their choice, and data from independent testing to back up any claims of improved performance.

    But don't bet on it. ;)
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #11
    Re: black back sheet solar panels
    Cariboocoot wrote: »
    Perhaps the ones to ask would be the companies making the black-backed panels. Surely they would have some explanation for their choice, and data from independent testing to back up any claims of improved performance.

    But don't bet on it. ;)

    A lot of these companies that do use black backing use it based off of NASA's technology as a claim that it improves performance.
    So there is partial truth to that. However the full truth is that panels that are in operation in outer space are operating in a condition -300F. Panels in space operate under a completely different PTC. Here on earth dealing with atmospheric and ambient conditions the most efficient solar cell that produces 20% conversion efficiency under atmospheric conditions, if used in outer space then becomes 90% conversion efficient. Black backing is used by NASA to use radiation to take frost bite off the panels so that they can operate. Exchanging radiation for heat in below freezing conditions.
    Other than that in an atmospheric environment black panel backing works to control PTC conditions in below 25*C conditions, to maintain a condition based of testing in a lab at 25*C.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #12
    Re: black back sheet solar panels

    "and ambient conditions the most efficient solar cell that produces 20% conversion efficiency under atmospheric conditions, if used in outer space then becomes 90% conversion efficient."

    i'm going to call you on this statement and ask that you show proof of that claim. it is imo the same pv conversion efficiency excepting that there is more solar radiation now hitting the pv from the vacuum of space due to no atmospheric filtering. there is no improvement in efficiency, but rather an increase in the solar radiation impinging upon the pv.
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #13
    Re: black back sheet solar panels
    niel wrote: »
    "and ambient conditions the most efficient solar cell that produces 20% conversion efficiency under atmospheric conditions, if used in outer space then becomes 90% conversion efficient."

    i'm going to call you on this statement and ask that you show proof of that claim. it is imo the same pv conversion efficiency excepting that there is more solar radiation now hitting the pv from the vacuum of space due to no atmospheric filtering. there is no improvement in efficiency, but rather an increase in the solar radiation impinging upon the pv.

    Well would you rather NASA divulge their STC condition for space @ -300F which would be -184.44C? It's all classified, and most of what is spoken is hypothetical. I don't have proof, I have hear say from engineers that claim there is no other way around it.
    Most of the manufacturing Technics that companies that schott solar, sun power provide are no different than what NASA was producing 20 year ago.
    Its been proven that just adjusting temperature less than the condition of consumer rated STC improves efficiency, does it not? Voltage increases as temperature falls below 25C, in space its colder so solar cells don't degrade, solar radiation UV is intensified increasing amperage.
    Ozone layer along with a plethora environmental conditions humidity, dew point, etc create a filter that prevents a solar PV cell from reaching any type of "peak" conversion. It's about ouput power density.
    The most we will probably ever see in our life time with improvement to PV glass, or implementing refridgerant systems to get the panels colder than STC would probably not exceed 30% conversion.

    QUOTED from Earthlinked:
    Typically PV modules convert only up to 15% of the solar energy they receive into
    power. The remaining 85% usually dissipates in the form of heat. The PV module
    thus “produces” much more heat than power, yet this heat is otherwise wasted.
    Adding EarthLinked PV Heat Recovery to a PV system design changes that by
    enabling the collection and productive use of that energy. The recovered heat can
    be used or stored for later use
    Major efforts and millions of dollars are expended annually to improve PV module
    efficiency by just a few percent. The described method can bring an average
    improvement in PV system output of 12-15%. That equates to a 15%± drop in
    the cost of PV energy (currently a reduction of about 6 cents/kWh); or
    alternatively, a 15%± increase in the power produced per square foot of roof
    space and for sale to the grid.

    So according to Earth Linked "heat and the "heat" that PV creates is not only from an environmental issue which part of the cause for most of the diminishing returns in conversion efficiency. Stick a panel in below 0 freezing conditions and see what type of out put it will produce.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
    Re: black back sheet solar panels

    sorry as you still haven't shown proof of your 90% statement because it's false. even though space is cold the pv still heats up tremendously when exposed to the sun. so now you will hide behind it's classified. no it sounds more like you're doing a bs dance.

    i have to ask why you dropped that link as those methods to improve the efficiency of the pv shown will not put it to 90% and even if it did the extra power expended to operate pumps or compressors by far degrade any gains you made at the pv. i am going to delete that link to the pdf as i don't agree with its content and the place has no addresses or contact for verification of its validity as a legit place of business. do not drop any more links to that business.
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #15
    Re: black back sheet solar panels

    Hey Niel, how do 10 panels with concentrators produce 18Kwh at the begining of its life span?
    http://www.boeing.com/boeing/defense-space/space/bss/factsheets/702/xmsatradio/xmradio.page
    Galiume/Arsenide Mono Crystalline. Yes Niel I know Boeing cells have been apart of NASA developement for the past 20 years now. Nothing new.
    The patented process for galiume/Arsenide is no different than what most of the panel companies are doing.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Re: black back sheet solar panels

    :confused: Putting black vinyl on the back of a PV is the same as making a Gallium/Arsenide one?

    How did this thread go from "why black backs" to "secrets NASA won't divulge"?

    That was a rhetorical question, by the way. Take it as a hint.
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #17
    Re: black back sheet solar panels
    Cariboocoot wrote: »
    :confused: Putting black vinyl on the back of a PV is the same as making a Gallium/Arsenide one?

    How did this thread go from "why black backs" to "secrets NASA won't divulge"?

    That was a rhetorical question, by the way. Take it as a hint.

    Agreed way off topic. Moving forward.
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