Abstract: System and method of operating the system. The system having a heat pump cycle, a turbine cycle, a medium storage cycle and a water storage cycle. By way of the heat pump cycle, heat of a working fluid can be transferred to a thermal medium (M) for storing thermal energy. By way of the turbine cycle, heat of the thermal medium (M) can be transferred to a working fluid (F). In so doing electric energy can be converted into thermal energy or transferred from thermal energy into electric energy by operating either the heat pump cycle or the turbine cycle. The thermal coupling between the water storage cycle and the heat pump cycle is provided by a water-to-fluid heat exchanger and the thermal coupling between the water storage cycle and the turbine cycle is provided by a fluid-to-water heat exchanger. The water storage cycle additionally contains an air-cooled water-cooling unit that can be operated independent from the water-to-fluid heat exchanger.