Our solar panels are fitted with a Solis inverter, our Solax Triple 5.8kWh battery is fitted with an AC Solax inverter , in the vent of a power failure our system shuts down completely. I was originally told the system would still power the house, unfortunately I know fitted that is extra.
You would need a changeover/transfer switch.
As with any island system the regs surrounding it to offer not only you protection but, also offer protection on the grid side. A TT (earth rod) earthing system would be the minumum required ensuring disconnection from the suppliers earthing system when in island mode whils’t still affording you protection in the event of a fault on the backu power side. More complex earthing arrangements affording a lower sustainable zs can be connected in parallel with the suppliers earth. That said your existing earthing method may already be based on a TT system.