In an expansion system (11) of the heat transfer medium circuit (1) of a solar thermal power plant, comprising a plurality of expansion tanks (12a, 12b, 12c) and/or flooding tanks which are arranged in the heat transfer medium circuit (1), a solution is to be created which enables a technically simplified and constructionally less costly compensating or expansion system to be created. This is achieved by the expansion system (11) comprising a plurality of expansion tanks (12a, 12b, 12c) which are arranged at basically the same height level and are in fluid-conducting communication.