When you sustain entire grid, you don't need batteries. We didn't use to have batteries, yet we use electricity - yes, over grids - all the time. When we add t

When you sustain entire grid, you don't need batteries. We didn't use to have batteries, yet we use electricity - yes, over grids - all the time. When we add to always-on generators (fossil, hydro, nuclear) sometimes-on ones (solar and wind), we employ the fact that for large grids it doesn't happen that Sun is not shining everywhere at once and wind doesn't blow everywhere at once - at least this is a reasonable model, continent being at night notwithstanding. The bigger you have a grid - and you can get effects from relatively small ones - the less batteries you need.