Panel roof mount/rack

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Arkansasoffgrid
Arkansasoffgrid Solar Expert Posts: 117 ✭✭
in Solar Beginners Corner #1
Completed the installation of my unistrut roof mounted rack this weekend. Noticed after installation that the unit strut is not perfectly flat, it has a minor arch in it, probably due to roof not being perfectly flat. Question is will the solar panels be okay to bolt down to this, or will I need to shim each one so it's perfectly flat? As in is there any flex to the panel frames or are they completely rigid? Panels laying horizontal are 64 1/2 inches wide 38.75 inches tall with unistrut running vertical 16 inches from either end.
8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Panel roof mount/rack

    How minor is the arch? A washer thickness? Or something that's going to put stress on the panel frames?
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #3
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    Re: Panel roof mount/rack

    Panels will flex a bit. Not to worry about not being perfectly flat. Do worry about violating the panel warranty though. Read the fine print in the installation instructions and the warranty. Don't modify the panels at all. No drilled holes, no paint, don't change the connectors, and they generally have to be supported in the right places. 16" in from the end may be too much.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #4
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    Re: Panel roof mount/rack

    If done correctly, little of the "arch" should translate to the panels. The panels are only mounted in 4 points, and would only be a problem if you "twist" the panels when mounting them.

    You may have to shim the rails (not the panels?) if the panels will not set "flat" on the mounts (more than minor pressure to make them flat).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Arkansasoffgrid
    Arkansasoffgrid Solar Expert Posts: 117 ✭✭
    #5
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    Re: Panel roof mount/rack

    The "package" I bought has 50' mc4 cables, is there a problem with using that full cable length to locate the combiner box in the solar room with the charger/batt/inverter/service panel?
    8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: Panel roof mount/rack
    Arkansasoffgrid wrote: »
    The "package" I bought has 50' mc4 cables, is there a problem with using that full cable length to locate the combiner box in the solar room with the charger/batt/inverter/service panel?

    Usually you locate the combiner where the panels come together. That way you use less wire (albeit larger gauge) from the combiner to the charge controller.

    The alternative is a 'home run' from each panel string to the combiner, and that can add up to a lot of wire. (Note that this can also be a lot of 'antenna' for stray voltage, i.e. lightning.)

    Otherwise the only issue with long wire runs is whether or not the wire size is large enough to handle the maximum current @ Voltage and keep V-drop to a minimum.
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  • Arkansasoffgrid
    Arkansasoffgrid Solar Expert Posts: 117 ✭✭
    #7
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    Re: Panel roof mount/rack

    Let me make sure I'm understanding this, it's better to locate the combiner box on the roof and just coil up the excess from the 50' mc4 cables and purchase 20' of heavy gauge wire to go from combiner box to charge controller. Because my rookie thought process was that the 50' mc4 cables are sufficient to allow the combiner box to be located indoors with only about 3 foot distance to cc.
    8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: Panel roof mount/rack
    Arkansasoffgrid wrote: »
    Let me make sure I'm understanding this, it's better to locate the combiner box on the roof and just coil up the excess from the 50' mc4 cables and purchase 20' of heavy gauge wire to go from combiner box to charge controller. Because my rookie thought process was that the 50' mc4 cables are sufficient to allow the combiner box to be located indoors with only about 3 foot distance to cc.

    Where are these 50' cables coming from and going to? From each panel string to the combiner? It's a bit odd to use that much wire there regardless of box location.
    Normally you keep all wiring as short as possible. Minimal lengths from panels to combiner box, and minimal lengths of larger wire from combiner to charge controller.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #9
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    Re: Panel roof mount/rack

    But yes, the warranty paperwork says to not cut/shorten the panel cables. So, panels cables just get tied up (and out of the way of small chewing/nesting animals).

    You can put the combiner next to the panels or next to the charge controller. The cost of copper is similar (4 small gauge runs, or 1 pair of 4x thicker--about 6 AWG heavier--Cables--Same amount of copper in either case).

    I would put the combiner box under some protection against direct rain and sun if possible (heat and water are always bad for electrical stuff).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #10
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    Re: Panel roof mount/rack
    Arkansasoffgrid wrote: »
    Let me make sure I'm understanding this, it's better to locate the combiner box on the roof and just coil up the excess from the 50' mc4 cables and purchase 20' of heavy gauge wire to go from combiner box to charge controller. Because my rookie thought process was that the 50' mc4 cables are sufficient to allow the combiner box to be located indoors with only about 3 foot distance to cc.

    It is common to run the PV-to-Combiner cables in conduit. Trying to pull cables with attached MC connectors through conduit can be difficult, and requires larger conduit. So, in order to avoid cutting the MC connectors off of the PVs (and voiding the PV Warranty, usually), one does buy MC extender cables, which are often ordered about double the required run-length. These are cut in "two" -- allowing correct gender MCs for the PVs and a free end with no MC, allowing an easy pull through conduit to the Combiner, wherever it needs to be.

    The less exposure of the PV cabling to the elements and pesky animals, etc, the fewer problems that might arise ... in general.

    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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