This is one of the most confusing topics in Irish solar, because installers give different answers. Some fit changeover or isolation switches for "island mode" (running part of the house off solar and battery during a grid outage), while others say it isn't permitted. Installers read the wiring rules differently, so a homeowner can't easily tell who's right.
The core safety principle behind the cautious view is real: any backup/island setup must be wired so it can't backfeed the grid and endanger linesmen, and a firefighter pulling the mains at the meter box should be able to assume the house is dead. Done improperly — without correct earthing/bonding and isolation — it's genuinely dangerous and non-compliant. Done properly, with the right equipment, backup power during an outage is achievable, but it needs the right equipment: a properly wired changeover switch for a few circuits, or an automatic backup unit for the whole house, never a simple socket on the inverter.
Before paying for it, weigh whether you actually need it. For most homes, grid outages are rare and short, so the extra cost is hard to justify. A manual changeover switch for a few circuits usually costs a few hundred euro (the quote check allows €500 for one); an automatic whole-house backup unit costs a good deal more. It makes more sense if you genuinely can't be without power — for example medical equipment, or a rural property where a well pump and water treatment mean no electricity equals no running water. If you do want it, get an installer who'll do it compliantly and can explain exactly how the isolation and earthing work, and be wary of both a flat "it can't be done" and a quick fix such as a socket wired to the inverter. The answer is in between.