"Ironically, what originally motivated pumped storage installations was the inflexibility of nuclear power. Nuclear plants’ large steam turbines run best at full power. Pumped storage can defer surplus nuclear power generated overnight (when consumption is low) to help meet the next day’s demand peak."

https://spectrum.ieee.org/a-pumped-hydro-energystorage-renai...

Main challenge with pumped storage is its geographically limited, always a custom project, and large scale deployment.