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

BilljustBill · September 2020

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.

mike95490 · September 2020

I think in any case, the panel frames have to be grounded. The - or+ cables may not have a grounding requirement.

BB. · September 2020

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.

-Bill

BilljustBill · February 2021

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. · February 2021

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.

-Bill

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

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