[Gav]

There is a reason that solar systems switch off during a power outage.
Electrical transformers will work stepping down voltage but if you liven the secondary side such as what Ash may or may not be suggesting in the above post they will produce HV on the primary side (read it will fry the linesman working on the system).
Hard wired Generator back up systems have a changeover switch that isolates the incoming supply when they are put on line, if you must do something like what has been suggested ISOLATE THE INCOMING POWER SUPPLY AT THE MAIN SWITCH.

Or move somewhere that has a decent supply grid.