Don't know about the legalities of it. But Off Grid is normally battery power based.
Panels to Inverter to ??? x 2v cells. then drawn through Inverter or regulator to household.
On Grid is panels to inverter. 240v direct to house.
You'd need to convert 240 inverter output to whatever battery's voltages are.
Or run 240 from grid input direct to a 240 power board in house?.
A lot would depend on your consumables in house.
12\24\\240v and what needs what power.
Could get pretty complex. If converting from existing mix of.
Pretty easy if setting up from new.
I have a deadmans sw in my main power line to house. B4 the powerbox.
and a socket to suit plug from my generator. (out of sight....)
When we have powerout. I just throw sw. plug in my genny. and run house from it.
Power co's boxes have an auto trip off to solar whenever supply to house is cut.
So I can't use that. Bummer.