I’m going to preface this by saying, all I know is that know about the subject was one physics class in college… The teacher mentioned Hydro Pump Storage that pumps water into a reservoir when there is an excess of energy generation then releases it through turbines when there is a surge is energy needs on the grid. Wouldn’t this idea work in a very similar way? If so it would seem feasible as about 15% of the UKs STOR requirements are met in this way.
Yeh, again I’m not sure how efficient using water is but my instinct says it will be a lot better than any mechanical system as they are generally very inefficient!