Comment by DanielHB

Grid-storage batteries are not only viable today it is also very attractive cost-wise, but not for the reason you might think. They are not meant to be "dumping place" for excess green energy (although they can be used for that), but rather to reduce the need of peak power plants.

Power generation usually has "baseload" powerplants (always on) and "peak" powerplants (can spin up when there is high demand). Peak powerplants are much more costly per unit of energy generated and burn a lot more fuel. Grid storage systems can make sense even in 100% fossil fuel grids.

There is one big exception, if you have a lot of hydro power then grid storage is not as effective because hydro can work as a peaker plant by letting more water go through the turbines. But it depends on the hydro power plant and grid characteristics, even in some cases where there is a lot of hydro it might still make sense

https://en.wikipedia.org/wiki/Peaking_power_plant

frequency regulation is something that grid storage batteries really excel at and can be very expensive to achieve with conventional power plants:

https://en.wikipedia.org/wiki/Ancillary_services_(electric_p...

The tradeoff of course is the high initial capital investment to get the grid storage plants built