Confused- should this be off-grid or on-grid?

[pvdude]

A little confused about off-grid/on-grid.
I had the idea I was building an “off-grid” system, now not sure.
Reading the installation manual for my Schneider Electric Conext XW Pro 6848 Hybrid Inverter/Charger and attached Conext XW+ Mini Power Distribution Panel.

I did not know it had a built in battery charger that can use AC from the utility to charge the battery bank. There is a section that shows how do the wiring/bonding/grounding for this.
It is done differently than the “off-grid” instructions.

It would be great to have AC charging the battery bank, as there are times (hurricane season) that there will be no Sun for a few days as the storm approaches. If the utility can keep the battery bank charged until the storm takes down the grid, we would be ready to go w/ full batteries.

Is there any reason I should not connect the AC circuit in this, so as to charge the batteries?

 

[Hedges]

Utility grid connection would already have neutral and ground bonded together, probably at your main panel. Ground rod also provided.

Grid to keep batteries charged is a good thing.
One issue is voltage spikes and lightning strikes. Consider protection devices such as what Midnight sells, which have LED indicating "protected" and "Failed"

 

[pvdude]

Ok, thanks, I’ll connect it to the grid.
I have implemented as much of the Motorola R56 standards as I can afford here to deal with the lightning.
Where I am located gets the highest rate of strikes in North America.
I am a HAM, so protecting antennas and radio equipment is necessary.
Fire in the shack is “bad”, and that is where the solar gear is being installed too.

 

[Hedges]

Right in the heart of it!

Flying back from the East coast one time, pilot pointed out a light show off to the side. It lasted about 15 minutes - that's 150 miles worth.

You'll want MOV type devices on both utility and PV inputs. Midnight has those:

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

Maybe also a spark gap on utility. Lightning rods above PV array.

Some of my SMA inverters come with replaceable MOV. I expected them to be just above peak grid voltage, but I measured them around 800V.
I will buy lower voltage MOV one of these days and put on PV side.
I've added 200V protection on my utility side.

Testing Metal-Oxide Varistors (MOV)

Surge arrestors are used on AC and DC side of PV inverters for protection, to clamp high voltage transients. One inverter I have (actually several) are in the SMA family SUNNY BOY 5000-US / 6000-US / 7000-US / 8000-US. These come with a kit of MOV to protect the DC side: The MOVs are about...

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I originally installed Delta "Silicon Oxide Varistors" on both AC and DC side.
I've since decided they do not provide the protection I want - don't fire even at 5000Vrms.
Maybe for a much higher voltage hit they would fire, then clamp at voltages shown in spec.
Perhaps they would work as a spark gap. I don't have a way to test at this time.

Delta LA 602 Lightning Arrestor "Hey! Is this thing on??"

I've been using Delta Lightning Arrestors on my system since they were spec'd by Real Goods as part of the package I bought from them. I now have a surge capacitor on the AC input as well, which is supposed to slow rising edge of voltage so it doesn't get as high before the Silicon Oxide...

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