24" on center or 48"?

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CaptTurbo
CaptTurbo Solar Expert Posts: 66 ✭✭✭✭
in Solar Beginners Corner #1
I have some guys from the installation company here and I'm trying to decide whether I should have rail mounts every two feet or every four feet. They tell me that 48" apart is good for 120 mph winds. The worry I have is that this house has already been through Hurricane Charley which brought us 140-145 mph winds.

So I'd like to ask you all if 24" apart mounts would be a smart thing to do for a large solar system here in Ft. Myers, Florida? I realize that it would mean many more penetrations but I sure don't want my investment destroyed for not making it as strong as possible.

I would appreciate any insight and comments. Thanks.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #2
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    Re: 24" on center or 48"?

    What did the PE submit for the application?

    Unless your whole house is cat4 rated, little point trying to over engineer the railing, its only as strong as the weakest point, typically, that would be the trusses or truss to wall anchors. Not sure the panels themselves are rated over 120 either, so while the frames may stay, the glass and cells could just get sucked out in the uplift.

    My two cents is let the professionals do there job and stop worrying about then end of the earth situations. If you have those type winds, they will be full of debris, the panels won't have a chance.
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  • pbartko
    pbartko Solar Expert Posts: 37 ✭✭
    #3
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    Re: 24" on center or 48"?

    I don't know what rail system your installer is planning on using.

    But a a quick run of Unirac's design software shows that 4' spacing between feet would be acceptable for winds in the 140-150mph range using their Solar Mount frame.

    So it is entirely possible that your installer's design is suitable for your application in a hurricane prone region.

    Pete B
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  • CaptTurbo
    CaptTurbo Solar Expert Posts: 66 ✭✭✭✭
    #4
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    Re: 24" on center or 48"?
    pbartko wrote: »
    I don't know what rail system your installer is planning on using.

    But a a quick run of Unirac's design software shows that 4' spacing between feet would be acceptable for winds in the 140-150mph range using their Solar Mount frame.

    So it is entirely possible that your installer's design is suitable for your application in a hurricane prone region.

    Pete B

    I hope you are right about that. I have the heavier duty Unirack rail system. I am thinking about "meeting in the middle" by using double anchors on the ends and the middle but would enjoy more input.
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  • CaptTurbo
    CaptTurbo Solar Expert Posts: 66 ✭✭✭✭
    #5
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    Re: 24" on center or 48"?

    Guppy, as already stated, the home has been through a strong cat 4 and the new metal roof makes her stronger still. So, the worries are about the solar gear much more so then the house.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
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    Re: 24" on center or 48"?

    i also agree with solar guppy that even if you get the pvs to stay in place that the wind blown debris will certainly take them out. i believe there was a thread started by dapdan about mounting pvs for a hurricane. in most cases the weather will win with cat4 and cat5 hurricanes unless you can quickly take them down and store them in your cat4 proof house, which is not very likely you'll be doing that given time constraints and other pressing matters.
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  • russ
    russ Solar Expert Posts: 593 ✭✭
    #7
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    Re: 24" on center or 48"?

    With the addition of the panels on the roof with a space underneath you would be creating additional lift. Next cat 4 storm the roof will take more stress than last time.

    Or so it seems anyway - here we have no hurricanes, just earthquakes.
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  • CaptTurbo
    CaptTurbo Solar Expert Posts: 66 ✭✭✭✭
    #8
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    Re: 24" on center or 48"?

    What we decided to do was to double up the number of "L" feet on the ends and the middle of the array. I think it's a good way to beef things up without getting carried away.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #9
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    Re: 24" on center or 48"?

    Thats where the stresses are, on the edges according to the PE that approved my home brew mounting

    Glad to see things are progressing and that Solar Source is doing the install, post some pictures of the work!
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  • newenergy
    newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    #10
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    Re: 24" on center or 48"?

    The unirac installation manual has a lot of info on how to calculate the wind loads for the pullout of the points of attachement and the strength of the rail, but I'm pretty sure you'll find out that every 48" is more than sufficient and as others have said something else would fail first like the roof structure or the modules themselves.

    At prosolar's office they have a nice picture of an array that got hit by katrina and the roofing was all torn off except under the array and the array which was still there.
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  • CaptTurbo
    CaptTurbo Solar Expert Posts: 66 ✭✭✭✭
    #11
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    Re: 24" on center or 48"?

    Still no permit in hand but they decided to go with getting the structure stuff in place and will hold off on the electrical wiring.

    As far as the roof failing (or whatever), I sank all 5000+ 3" screws myself. The roof will stay put in winds up to and perhaps above 175 mph. It has already tested to 145 before I did this considerable upgrade.
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