[compumike]

It can be dangerous to backfeed (which is why you're supposed to have an interlock for a generator inlet, ensuring utility power is disconnected). But:

1. These grid tie inverters are designed and tested to shut off completely if there's no grid power. (This is a big design tradeoff: it means they don't provide any power during a grid power outage, even if it's very sunny out.)

2. Even if I had a beefy generator that was unsafely backfeeding my house while the utility power was still connected, the generator would be trying to power not just my house, but all my neighbors too! And the circuit breaker and/or inverter on the generator would likely trip and shut down almost instantly.

There's still a possible risk from #2, especially if the downed wire being repaired is relatively local (i.e. your house only).

But I think #1 and #2 mitigate this risk very well.

[fhdkweig]

On point 1, you can pay extra to get an inverter that does "islanding mode". During an external outage the inverter stops sending power out of the house but keeps supplying power inside the house. Whole-house backup batteries such as the Tesla Powerwall (and competitors) also have this capability.

Anyone who is looking for a generator to power their house during a regional outage should look into other types of generation that will do islanding mode.