Sounds like you've got a much higher essential demand than what I figured on - desalinization?
Sorry for the delayed reply but I was re-running the numbers :)
When I was doing the calcs originally, I was really only interested in staving off power outages like we had with Sandy, which was about two weeks worth... not being completely off-grid. So focusing on hurricane season as a baseline, a 7kW system with 6kWh of storage would provide essentially unlimited off-grid capability from April through December *if* I managed my power consumption to essentials with just a little bit of creature comfort.
The winter months, however, result in a deep, DEEP deficit. I'd need 10kW of PV with 80 kWh of storage to be completely off-grid based on PVWatts data (with no power management). Of course, that's still relying only on Solar, and being completely off-grid was never the intention.
I don't pertain my own home is a good proxy for a regional or national grid, though ;)