Why do you need to be connected to the grid .1% of the time? A 12kW solar roof system with two Powerwalls costs less than $75k, with costs continuing to trend

Why do you need to be connected to the grid .1% of the time? A 12kW solar roof system with two Powerwalls costs less than $75k, with costs continuing to trend downwards, and large government subsidies on top of that. Amortized over 20 years it's reasonable, and much safer for fire prone areas. You can have a backup generator as well if you want to be totally confident.