Great point, How much battery capacity and energy the utility will require (big expense for project proponent they have to inevitably recover from ratepayers) for solar or wind farms is another Aspect that has to be studied
Batteries exist in a different economic regime than rate payers. Where the price per megawatt varies by 2X or more. Which makes it easier for batteries to make money be arbitrage. As in buy power at 10am for $40/MWH, sell it at 7pm the same day for $80/MWH.
So making $40/MWH * 100 MWH/day = $4000 per day * 365 day/yr = 1.4 million revenue per year. Not enough to pay back $100 million.
Like you said The economics of it keep improving though Imp