Realistically you could get that number 6x smaller, because people could voluntarily cut their usage from 30kwh to 15 when the power is out, and 1.5 days of pow

Realistically you could get that number 6x smaller, because people could voluntarily cut their usage from 30kwh to 15 when the power is out, and 1.5 days of power is probably overkill when 12 hours would get you through 99% of power out scenarios in America. On top of that, when the grid is functioning normally, you could use the batteries to get cheaper electric rates with time of use pricing.