Surely the PV output (± battery) does not have to join at the origin?

If the PV array shares a distribution circuit, does it need RCD protection at all?

Does it come down to the inverter having simple separation. Transformer-less inverters may be able to feed a DC fault current into the AC side (Reference COP) The DC element May blind the split board RCD and potential leave other circuits without RCD protection. 

Does it come down to the inverter having simple separation. Transformer-less inverters may be able to feed a DC fault current into the AC side (Reference COP) The DC element May blind the split board RCD and potential leave other circuits without RCD protection.