panel mounting and point load

topper
topper Solar Expert Posts: 113 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
I am still in the pen and paper phase of my project.
I had 2 different installers come by. I need your 2 cents.
I am in the snow zone south Saskatchewan. Rafters are 2x4 truss rated for 50 lb/ft2 snow load.
Both systems sit on 3 inch unirack mounts with flashings.

One configuration uses 32 suntech panels on unirack sunframe at 4ft OC. This gives me a point load of 718 lbs. Seems rather excessive to me.
Estimated cost 5500.00.
The second proposal from the same installer is the same only @ 2ft centers. Point load of 359 lbs.
Est cost 7700.00
The second installer's configuration uses 36 panels on unirack solarmount at 2 ft centers. Point load is 266 lbs. Somewhat more reasonable to me.
Est cost 6700.00

Now engineering is telling me that all proposals are acceptable.
Given all of your knowledge and experience, I would really like your 2 cents. Dollars come second to safety and integrity of our home.

If any of you have worked with the "sunframe" or "Solarmount" , I would like your opinions.
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Comments

  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #2
    Re: panel mounting and point load

    Hi topper,

    Have you gone to the UniRac site, and used the calculator yourself?
    This link may work:
    http://www.unirac.com/?q=residential/residential-products/solar-mount-residential

    On this page, thre is a button in the upper third of the page "Configure Your Project"
    It allows you to what-if some scenarios, and output Engineering data, if desired.

    I do not know exactly what you mean by "2X4 Trusses". I am not in the snow belt, and used Uni SolarMount for a recent project, but this was on an over-designed 2X12 16" OC raftered roof. Given your snows, hope that your roof has a good slope to it.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • topper
    topper Solar Expert Posts: 113 ✭✭
    #3
    Re: panel mounting and point load

    Just punched in the designs and looks like the installers numbers are from unirack's website.
    Rafters are 2x4 truss style @24" on center. 4/12 pitch=18.4*
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  • SessionMan
    SessionMan Registered Users Posts: 8 ✭✭
    #4
    Re: panel mounting and point load

    Topper, see my post regarding snow loads. If you post your snow loads I can give you what the reduced load would be.
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