Using 7.5kw of panels on a metal roof with this inverter

The project will have 24 panels, 315w Warree mono.  They will be mounted on a metal R-panel roof. 
The inverter is an: SMA SB7.0-1SP-US-41, a transformerless design.

Is this a good match? 
How do the panels have to be mounted to be ungrounded as required?

Thank you for your help.



  • mike95490mike95490 Solar Expert Posts: 8,961 ✭✭✭✭✭
    I think in any case, the panel frames have to be grounded.   The - or+  cables may not have a grounding requirement.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
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  • BB.BB. Super Moderators, Administrators Posts: 30,939 admin
    As Mike says (and as I understand)...
    The "ungrounded part" is referencing the + and - power cables from the array... You just wire up in series/parallel (as required) and run the wires directly to the GT inverter's input.

    The panel frames and racking need to be grounded as normal (following code with something like a continuous run of 6 AWG cable from each frame, and ground the mounting frame work (per code, per installation manual for panels and frame). Down (typically) to a ground rod at the base of the frame/outside of wall (if roof mounted)--The ground rod beneath the array is usually a very good idea for lightning prone areas (you don't want to bring lightning into your home/home grounding system). Otherwise ground to your your home ground rod/cold water pipe (if you have two or more ground rods, run ground to nearest ground rod, and tie each "remote" ground rod with 6 AWG back to the main home ground rod/cold water pipe connection--This is to provide a safety ground for AC utility power, and your DC solar panel power--If shorts to ground ever occur).

    Surge suppressors can be a big help for Lightning prone areas too (see GT inverter manual for their recommendations/requirements).

    A "metal" siding building--The metal siding is not allowed (or a very good) as a safety ground (very thin, lightning and shorts to power sources can easily blow holes in the "tin". And metal siding to siding connections are not "electrical" electrical connections.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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