In addition to the comments above about solar/wind inconsistency, it is also a lot cheaper to run baseload power plants constantly rather than to ramp peaker pl

In addition to the comments above about solar/wind inconsistency, it is also a lot cheaper to run baseload power plants constantly rather than to ramp peaker plants up and down. So, if they can store the baseload power and then tap it later the total cost of electricity will come down. Plus, storage makes it easier to level the grid to make output match demand.