You can have a battery backup, they just don't want that connected to the grid.

Correct. You have to connect any in-home generator or in-home backup battery / inverter arrangment through a breaker arrangement that uses a physical interlock that prevents BOTH the commercial incoming AC feed and the generator source from being connected to the house wiring at the same time. The interlock sits between the commercial breaker and the breaker added for the in-home source so that the commercial breaker must be off before the interlock allows the in-home source breaker to be turned on, and vice versa.

An automatic switch can also be used so you don't have to throw the breakers manually so heat stays on, etc. if you are away from home but that gear costs around $600 versus $60-120 for a manual switch configuration. It also cannot guarantee zero outage time because it still has to turn one OFF before turning the other on. An auto-switch typically implements delay logic so it doesn't rapidly bounce back and forth if a storm is causing multiple interruptions. Once it swings to in-home, it may stay on that mode for 5-10 minutes, even if commercial power comes back in seconds.


WTH