Solar PV inverter/system which can operate in island mode during loss of network power.

This is a thoeretical queston about building integrated solar PV operating with a battery in a black out. 


I am doing a university project and have to design a renewable back up power supply for a real scenario.


The breif states the building already had a battery for back up but can only provide critical loads for 24 hours. A certain installed capacity of solar PV could increase this to a minimun 48 hours in winter. 
However I understand that typically grid tied inverters will shut sown in black start scenario. 
Is there a solution that will allow the solar system to opperate in island mode which aviods dc-dc coupled solar and battery? (The battery unit is a black box with AC  input)

Barnaby, I can see no logical reason why a solar PV inverter should not work with the emergency battery inverter. As long as one inverter is locked to the grid frequency, call it the clock inverter, then all other inverters could be locked to the clock inverter, on loss of gridAs the battery backup will have an inverter already locked to the grid mains frequency then the PV inverters could lock to the battery inverter frequency.I believe the reason for PV inverters to lock out on loss of grid, is because the buildings incoming supply does not normally disconnect from the rest of the supply grid, so the inverter would try to supply the grid. In the case of emergency UPS supplies the incoming power supply is disconnected from the inverter on grid loss and the inverter only supplies its own designated loads free from the dead grid. A PV inverter working on the emergency load side of the UPS should think it is still connected to the grid frequency.Hope this helps