The invention relates to a method for charging and discharging a storage medium (for example, H2O), which according to the invention can be exchanged between a cooler reservoir (12w) and a warmer reservoir (12h) via a heat exchanger (35). Thus, thermal energy can be absorbed or output by means of the heat exchanger. The thermal energy can come from a wind turbine (11), for example. In a charging process, a working fluid such as CO2 is compressed by means of a compressor (22) and is decompressed after passing through the heat exchanger (35). In order to convert the stored thermal energy back into electrical energy if necessary, propane, for example, is heated by means of the heat exchanger (35) and decompressed by means of a turbine (25) as a working gas. The advantage of this arrangement is that water, which is an environmentally friendly liquid, can be used as the storage medium. The water can be stored in large amounts, whereby large heat capacities can be realized. The working fluids mentioned enable operation in a comparatively narrow process window for the water, e.g., 40°C in the cooler reservoir (12w) and 97°C in the warmer reservoir (12h).
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