I turned them off before the recent inclement weather as advised by our local council.
I meant to do it last week, but I kept forgetting.
I turned the DC and the AC back on in the reverse of the order suggested for turning them off.
I watched the panels from across the road for a bit, to watch for anything obviously amiss. (I assume sparks, smoke and fire to be the obvious problems to watch for). We didn’t and up getting hit by the terrible weather event, so I wasn’t too worried.
The panels seemed to come up ok.
Nope, basically all solar inverters will switch off if the grid goes down. They need the 50hz signal to synchronise. Even with a battery, unless you buy the separate box, your battery will switch off without the grid.
There are hybrid inverters that support dark start (no grid) but yes, as you mentioned, they only do this when they have internally dropped the grid feed, to prevent such a back feed event.
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Yes, this is a requirement in order for the inverters to be certified and thus be sold. So unless someone imports something directly from China and it happens to be made very dodgy, the inverters will shut off when the mains input goes down.
There was even a bit of an issue with micro-inverters. The regulations in the EU said the inverter should physically disconnect, but a lot of micro-inverters used solid state switches to disconnect. IIRC the language was then changed to just specify it should disconnect and not how it should do that.