This can be dangerous for utility company workers.
When a line needs to be repaired, the technician takes steps to ensure the line isn’t carrying current from known sources. A panel plugged in by a civilian via a home outlet is not known. The technician can be killed by the unexpected current.
The panels are designed to not provide current if no current is detected on the mains. Otherwise you would also have a live plug at the end of the panel. Killing your own customers is typically not a good business strategy, so quite a lot of safety has been focused on ensuring this isn't a problem.
Not just designed not to provide current, in general they simply can't. They follow the phase from the mains (the sine curve of voltage and current), without the mains there isn't a phase to follow and they simply can't output anything
This was a contributing factor in the Spain blackout, because even large-scale solar and wind plants were using the same type of simple inverters
Not really, the full report refuted this. Issue in Spain was much more nuanced. Mostly related to lax voltage controls and outdated and slow control mechanisms at the grid, high voltage net.
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.
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.
FUD. Every inverter currently on the market immediately drops the connection if the grid isn't present, there is absolutely no way this could happen with these puny inverters.
When a line needs to be repaired, the technician takes steps to ensure the line isn’t carrying current from known sources. A panel plugged in by a civilian via a home outlet is not known. The technician can be killed by the unexpected current.