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: 9,298 ✭✭✭✭✭
    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 ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • BB.BB. Super Moderators, Administrators Posts: 31,783 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
  • BilljustBillBilljustBill Solar Expert Posts: 219 ✭✭✭
    Bill, it's been a long while since you were so kind to respond to my question.  The company, based in Dallas, did little to complete the contracted work.  After 3 months, a 4 way phone conference, 3 attempts at getting clear and accurate layout plans for my home's project, and a deposit of $6,500, yet, all I was getting was data sheets for the future install that were so full of "mistakes", I tried twice to end the contract.  The final straw came when I received "The Final Version" of their use of the "Helioscope" software where one inverter's specs were use at the top of the data sheet, but in totally different font, a the name of a totally different inverter was listed as if "pasted in".  The vice president said someone else in the company did the Helioscope sheets and it was all a mistake....  If "Helioscope" saw how they used their software, they would turnover in their grave....   While I should gladly give the company name,  in this case, the old saying, "The more you stir it, the more it stinks.", prevents me. 

    I wrote the newly installed company president, but never received any contact.  When I told the company's "Vice President" I would be turning this over to the large and well known credit card company to dispute the payment, and their 25% cancellation fee toward a $20,000 total install price and to law enforcement in Dallas County and in my county.  Due to repeatedly sent substandard data to be provided for a new meter account, the local electric company's solar supervisor couldn't even use the solar company's data because only a salesman had ever physically been on the property,  I "Mutually Agreed"  total refund was in order.  They made me wait an additional "15 Business Days" which is really another 3 WEEKS to credit the credit card company for the entire amount.  In doing that, I had fears that they were in a cash flow problem, or they were delaying the refund on purpose.  In either case, a company like this is not one I would ever trust, but the full refund came through.

    A wasted three months and I still have no solar panel generation project started, but many thanks to you Bill for your time and help on this forum.
  • BB.BB. Super Moderators, Administrators Posts: 31,783 admin
    You are very welcome Bill. And sorry to hear about the trials you have had to go through for a "simple" Grid Tied system.

    I think at one point you asked them about a hybrid GT/Off Grid system--And they punted that over to engineering... From what little I have seen, the GT systems are "cookie cutter designs" and if you want a Hybrid system--Probably most of the GT Solar companies will fail to deliver a well planned/documented system that will meet your needs for years to come.

    Your posts about the issues/questions you have had with/about your installer are helpful too... We all are learning here.

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