Device and methods associated with underwater pumped-hydro energy storage are disclosed. An underwater pumped-hydro energy storage device includes a submersible tank that includes an inlet and an outlet. A pump is disposed at the outlet of the submersible tank to evacuate water from the submersible tank in a surrounding body of water. A valve is disposed at the inlet of the at least one submersible tank to control a flow of the water into the submersible tank from the surrounding body of water. Moreover, a turbine power unit is to generate output electrical power from the flow water into the submersible tank.