Pumped Hydro like Bath County Pumped Storage Station does exist but do not seem to buy cheap renewable when the price is low and resell it when it is high, but rather operate as a balancer for PJM Interconnection which get almost all its power from fossil fuels.

So do you have a link for a profitable battery that buys energy from renewables when there is an overproduction from renewable sources and then later sold when the prices has risen? That would be a solar / wind and storage combination. Using energy from fossil fuels to pump water is just not the same, even if doing so creates a profit for the company.

Every time I have read about a new storage facility they usually start with first describing capacity, then go on to say that this can enable a future use with renewables, but that right now it operate to balance the grid of existing (mostly fossil fuel based) power plants. I would very much like to be proven wrong and that there exist a viable commercial operation where we can see X amount of green energy produced by wind and solar going into the storage, and X (minus a conversion cost) of that energy going out, with one table showing how much the green energy costed when going in and an other table showing how much they got in profit when it went out.