Domestic PEI and islanding mode PFC

Hybrid inverters having DC PV inputs, DC battery inputs, and a limited output to feed "emergency" loads in islanding mode appear to be getting very commonly available. I am receiving enquiries from my domestic customers, but am struggling with a seeming lack of significant info. 

Pulling up data sheets for numerous hybrid inverter models, I can't find any data for any of them relating to inverter PFC during "islanding mode" when the emergency loads are supplied directly, during network power failures, or presumably during planned periods. 

Reference 826.1.2.1. "Overload and short circuit currents shall be determined at every point..." And  I am getting no response from manufacturers I have emailed in this regard. 

I appreciate the PEFC might well be related to the local earth rod (assuming a situation of an otherwise connected external TN earth failure), and the short circuit PFC might be related to the chosen battery internal impedance characteristic in some way..

The inverter data sheets typically state only the power output capability/current (steady and peak values) for the emergency/backup load supply. How is one supposed to take these to and plan appropriate protection? The lack of info seems to be quiet universal with these devices.