I believe APS now offers UPS that will start up off the internal battery without being connected to the wall outlet (or grid). That might get the inverter started. The Outback inverter that I used in a mobile application would take the shore power input and charged the batteries with whatever current was left over from driving the connected load.
How about utilizing a transfer switch in a different way?
Connect the output of the grid tie inverter to the LOAD terminals.
Connect the Grid terminals to the grid.
Connect the house loads to the Generator terminals.
When the grid is present, the GTI feeds into the grid. When the grid goes away, manually transfer the GTI to power up house loads. The transfer switch only has to be sized to match the inverter output or the house loads whichever is larger.
There has to be a second contactor or transfer switch to isolate the powered up house loads from the grid.
Or just use a large central battery bank to feed a bunch of local battery less UPS's and let each UPS take care of its local load. The UPS's do not have to synched to each other. Use a central charge controller to keep the batteries in shape.
