Metal reactions ?

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Arkansasoffgrid
Arkansasoffgrid Solar Expert Posts: 117 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
Wondering what if any preventive measures need to be taken, installing aluminum framed panels onto a galvanised frame? In portrait layout, so it's only touching in 4 spots.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
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    Re: Metal reactions ?
    Arkansasoffgrid wrote: »
    Wondering what if any preventive measures need to be taken, installing aluminum framed panels onto a galvanized frame? In portrait layout, so it's only touching in 4 spots.
    There definitely are such measures, and indeed the two metals should not be in direct contact anywhere if long term reliability is desired.
    Where the two metals are to be bolted together, use stainless steel bolts, nuts and washers, AND make sure there is a SS washer separating/between the two metals.
    In other areas where the two metals may be pressed together, insert UV stabilized plastic barriers between the two metals to prevent metal to metal contact.
    Good luck.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
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    Re: Metal reactions ?

    From here:

    http://www.engineersedge.com/galvanic_capatability.htm
    For harsh environments, such as outdoors, high humidity, and salt environments fall into this category. Typically there should be not more than 0.15 V difference in the "Anodic Index". For example; gold silver would have a difference of 0.15V being acceptable.
    For normal environments, such as storage in warehouses or non-temperature and humidity controlled environments. Typically there should not be more than 0.25 V difference in the "Anodic Index".
    For controlled environments, such that are temperature and humidity controlled, 0.50 V can be tolerated. Caution should be maintained when deciding for this application as humidity and temperature do vary from regions

    http://www.nstcenter.biz/writeup.aspx?title=Marine+Cathodic+Protection&page=NavyCommunityAppExtShipCathodicProtection.html

    Attachment not found.

    Solar panel frames are probably low alloy 6000 series aluminum. The problem is that aluminum has a wide range of electrical potential--At one end, it is very close to zinc (galvanizing). On the other end, it is far enough that you would have concerns with corrosion in weather.

    I could not quickly find the value for 6061 aluminum (guess)--So you should consider using a weather proof insulator between the racking and the panel frame.

    Assuming you don't install the array near the ocean--Corrosion concerns are probably less. Painting the mount with corrosion resistant paint would probably help?

    How is that for an answer/non-answer? Hopefully, somebody with experience of installing various arrays can help.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #4
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    Re: Metal reactions ?

    As the other folks have wrote, the key here is you want something besides the solar panel frame to be subject to corrosion, be easily replaceable, and strong. Not usually an issue but I have seen it happen. The hot dipped galvanize process is not always precise.
    Arkansasoffgrid wrote: »
    Wondering what if any preventive measures need to be taken, installing aluminum framed panels onto a galvanised frame? In portrait layout, so it's only touching in 4 spots.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    #5
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    Re: Metal reactions ?

    I have 10 panels bolted to galvanized unistrut. I ordered some HDPE sheet from McMaster Carr and cut some "washers" which are actually rectangular with a slot the width of the bolts. I used SS hardware and after the panels are installed with the bolts loose, I slide a washer on and snug it up. It was quick and worked well. Of course I am well way from the coast and am in low corrosion atmosphere. I also have an older array that has no isolation except for the original coating on the panel frames, they have been up for 10 plus years with no corrosion.

    In a coastal environment I used to see galvanic effects in a matter of months.
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #6
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    Re: Metal reactions ?

    Evidently waterproof coatings also help (in addition to stainless bolts and plastic washers/separators). Perhaps LPS Procyon (which I've had very good experience with in other applications).

    Or some type of design where the dissimilar metal joint is protected from the rain (under the panel?). Doesn't sound very practical.

    I am available for custom hardware/firmware development

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