Good question, with a power failure you cannot get power to use from the panels, for that luxury you need battery back up and right now cost benefit wise, just not worth it, and tomorrow who knows what will pop up, like CSIRO have just announced super doper Led acid batteries, but, with any battery back up you need compatibility with your existing inverter, it can get complicated.
SAPN here in Adelaide announced cheap/subsidised Tesla batter back up and I have a sunny boy inverter so for a few thousand dollars I can get the bits and pieces to make it all work, unfortunately it's only for certain suburbs and certain streets in those suburbs, I drew the short straw and missed out. SAPN may also have withdrawn the offer by now, I'm content to wait to see what is around the corner.
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