This is the power flow at home incuding my two Tesla PowerWall 2's.
I want to double both my solar and battery installation. It will be cheaper and easier to double the batteries, since they are smaller and we have room for them already, and probably easier to purchase (especially if we wait a few years, but I think now would be easy too), however it wouldn't cover all our needs to just double batteries for winter. Doubling the solar will be more difficult. During summer, we serve nearly all our needs even with the existing batteries on many days, but doubling solar is necessary for winter.
Flow to four device groups are graphed: