Don't have time for a proper response, just a short note:
Yep people are looking into that, but it ain't trivial. Apparently one needs a fairly specific slope for it to be econom at the moment (competitive with chemical batteries). If you look on YouTube for the (clickbaity, unfortunately) title "the truth about pumped storage" (iirc), you should find a video from some engineering channel where some of this is mentioned. Another keyword might be Ireland. There's gotta be more information-dense / less time-consuming sources than that video though, it's just the one I got this from. My point being, if it were this simple, yeah. Looks like we'll (recurring theme) need a bit of everything to get there on the timescale we're looking at to avoid worse issues.
Yep people are looking into that, but it ain't trivial. Apparently one needs a fairly specific slope for it to be econom at the moment (competitive with chemical batteries). If you look on YouTube for the (clickbaity, unfortunately) title "the truth about pumped storage" (iirc), you should find a video from some engineering channel where some of this is mentioned. Another keyword might be Ireland. There's gotta be more information-dense / less time-consuming sources than that video though, it's just the one I got this from. My point being, if it were this simple, yeah. Looks like we'll (recurring theme) need a bit of everything to get there on the timescale we're looking at to avoid worse issues.