> and with batteries you end up fully self sufficient when the grid goes down.

My understanding is that the majority of installs are not capable (allowed?) to run when the grid is down. I do know that at the very least you'd need a transfer switch to ensure you're not backfeeding the grid when it's not expecting it, like with a generator.

Now that I think about it, I wonder if a generator could provide the reference signal for the inverters to synchronize against. You'd still be burning fuel at whatever the generator's idle consumption is, but that'll be less than actually using it for power.