Underwater pumped storage power plant for temporary reversible storage of electrical energy from other power plants, such as wind power stations and/or photovoltaic systems, comprising: an accumulator system with a modular design, having at least two pressure vessels that can be filled with water and that constitute a common accumulator volume, a water outlet to allow water to flow out of the accumulator system directly into the surrounding ocean against the hydrostatic water pressure corresponding to the water depth, a pump located at the water outlet to pump water out of the accumulator system into the surrounding ocean, wherein the pump converts electrical energy into the potential energy corresponding to the displaced water column when pumping the water out against the hydrostatic water pressure of the surrounding ocean, a water inlet to allow water to flow into the accumulator system directly from the surrounding ocean with the hydrostatic water pressure corresponding to the water depth, a common generator located at the water inlet, wherein the common generator converts the potential energy of the previously displaced water column back into electrical energy when the water flows in with the hydrostatic water pressure corresponding to the water depth, a base body for accommodating the pressure vessels, the pump and the generator, electric lines to transport the electrical energy from the ocean surface to the underwater pumped storage power plant and back, wherein the pressure vessels are pressure resistant such that they can be pumped empty by means of the pump and be resistant to deformation from the hydrostatic water pressure at the ocean floor, wherein the pressure vessels are connected to one another by a sump, the sump constituting the lowest or at least one of the lowest points of the accumulator system, wherein the water outlet is located at the sump, and wherein the pressure vessels and/or the base body are designed such, that in an emptied state are lighter than water and thus can float on the ocean surface so that these components can be brought to the installation site while floating and can be sunk at the installation site. an accumulator system with a modular design, having at least two pressure vessels that can be filled with water and that constitute a common accumulator volume, a water outlet to allow water to flow out of the accumulator system directly into the surrounding ocean against the hydrostatic water pressure corresponding to the water depth, a pump located at the water outlet to pump water out of the accumulator system into the surrounding ocean, wherein the pump converts electrical energy into the potential energy corresponding to the displaced water column when pumping the water out against the hydrostatic water pressure of the surrounding ocean, a water inlet to allow water to flow into the accumulator system directly from the surrounding ocean with the hydrostatic water pressure corresponding to the water depth, a common generator located at the water inlet, wherein the common generator converts the potential energy of the previously displaced water column back into electrical energy when the water flows in with the hydrostatic water pressure corresponding to the water depth, a base body for accommodating the pressure vessels, the pump and the generator, electric lines to transport the electrical energy from the ocean surface to the underwater pumped storage power plant and back, wherein the pressure vessels are pressure resistant such that they can be pumped empty by means of the pump and be resistant to deformation from the hydrostatic water pressure at the ocean floor, wherein the pressure vessels are connected to one another by a sump, the sump constituting the lowest or at least one of the lowest points of the accumulator system, wherein the water outlet is located at the sump, and wherein the pressure vessels and/or the base body are designed such, that in an emptied state are lighter than water and thus can float on the ocean surface so that these components can be brought to the installation site while floating and can be sunk at the installation site.