I know of some pumped hydro sites that have been given up due to opex, with no clear change of mind due to changing circumstances in the decarbonisation age yet

I know of some pumped hydro sites that have been given up due to opex, with no clear change of mind due to changing circumstances in the decarbonisation age yet in sight. What they do have in common, I think, is low head. There's just a lot of water to carry traces of sediment into the mechanism, and so much reservoir ground to keep from leaking for a given amount of capacity. But you don't arrive at isobaric storage looking at mineshaft pumped hydro wondering if it could be improved upon. You start looking at constant volume (A-)CAES, either in high pressure tanks at/near the surface or in salt caverns, and go from there, what of we did not have to deal with a very wide range of operation pressure.