Pumped hydro mostly just needs a hill. But building the dikes might cost more than building liquid CO2 tankage, for a given storage capacity. It will all come

Pumped hydro mostly just needs a hill. But building the dikes might cost more than building liquid CO2 tankage, for a given storage capacity. It will all come down to what is cheapest, overall. That will take time to learn. If opex is cheap, a more expensive will remain equally useful as a method that turns out, eventually, to be cheaper to build.