question

@esusa

Yes it will work.

We have ESS installed with alot of grid blackouts (so off grid in that part). There were a few issues with generator use (which do have work arounds) since you don't ever want it to feedback to the generator.

You do have the option of the PV inverter assistant, which i have also used, it is designed for offgrid application specifically. It will switch off the pv invterter when grid/generator connects. And frequency shifts the inverter during normal use.

Very cool you can actually see the frequency shift in the vrm tab and on the GX in real time. The other side effect is if your led lighting does not have enough smoothing capacitors (so cheaper bulbs) they will flicker at certain frequency inputs.

Charging battery from AC pv makes the inverter run hot, so it is less efficient than DC mppt charging for that use. Make sure you have both types in your set up.

Yes frequency shift works ok in an off grid setup, the only issue I had with my off grid setup is you can get voltage spikes to your batteries here and there when you either have very large loads turning on and off or the sun suddenly appears very quickly from behind clouds and the battery is getting close to full, it's because there is a slight delay for the frequency shift to happen.
If I was to do my setup again I personally wouldn't use an AC inverter with an off grid setup again, when I get time I will remove the Fronius and replace with MPPT's, as said above the MPPT's are more efficient and I get a much smoother charge from the one MPPT I currently have.
There is also the Fronius flicker which is a pain, it's better now than it was but there are still times it happens, just not as bad.