Providing RCD protection for any power source that is connected in parallel with the grid is not something that should be undertaken lightly.
An RCD which would disconnect the supply from an inverter, generator, transformer, whatever would not necessarily disconnect the grid.
One of the reasons I was querying where the RCD is sited and what it is protecting is because if it is in the wrong place, the part of the installation fed from the grid would still be live and in fault condition.
The Sunny Boy has an in built RCD, so any fault anywhere in the installation should cause it to trip.
However the installation will still be live because it is connected to the grid.
If we were to place another RCD just after where the inverter is connected to the grid, any fault down stream would cause that RCD to trip.
That would just leave the cable from the inverter to where it connects to the grid and the DNO supply cables still live.
If were to place the RCD just before where the inverter cable is connected to the grid, on the grid side any fault in the installation would cause the RCD to trip and also the in build RCD in the inverter.
The only live cables would be the DNO supply cables.
Clear labelling informing users about the two supplies and correct safe isolation procedures are obviously very necessary.
I would consider very carefully the manufacturer’s instructions regarding RCD protection.
This is a German manufacturer and what has been translated might not actually be what they mean.
It may be that they are referring to standard requirements for RCD protection such as socket-outlets, circuits of locations containing baths or showers and for cables concealed in walls.