Even more important, if you're on batteries as opposed to grid-tied, your battery costs can go down significantly. Since the worst days of the year tend to be w

Even more important, if you're on batteries as opposed to grid-tied, your battery costs can go down significantly. Since the worst days of the year tend to be winter and overcast, if you can install enough capacity to still generate a significant fraction of your needs on those days (eg at 10% of summer peak) the size of the required batteries can be much smaller. It doesn't work so well in the north east, but if weather is only bad for a few days, you might need much less backup or generator power. Batteries and generator power tends to be much less than adding excess solar.