This is one of the most confusing topics among Irish solar owners, because installers give flatly contradictory answers — some fit changeover/isolation switches for "island mode" (running the house off solar and battery during a grid outage), while others insist it isn't permitted, and a few go as far as calling anyone who fits them a cowboy. The honest situation is that there's a lot of genuine confusion and conflicting interpretation of the regulations among installers themselves, so a consumer 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 typically needs a specific (and often pricey) backup unit rather than 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 (often several hundred euro) is hard to justify. 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 "it's illegal, full stop" and "sure I'll just stick a socket on the inverter" — the truth is in between.