An apparatus for storage of potential energy using water from a deep body of water is described. The apparatus comprises one module including a cylinder, a piston slidably connected to the cylinder, a column for storing the water from the deep body of water received through an inlet being in communication with the cylinder/piston, and a connecting tube which mutually connects the cylinder and the column. The apparatus further comprises driving means for reciprocally displacing the piston in relation to the cylinder, wherein the driving means is a crankshaft drivingly connected to the piston and at least one flywheel mounted to the crankshaft for counteracting the pressure as result of the water stored in the column.