A power plant having a steam circuit which can be supplied, in the region of a heat recovery steam generator, with thermal energy for producing steam, the steam circuit has, in the region of the heat recovery steam generator, a high pressure part, a medium pressure part and a low pressure part. In addition, a heat reservoir which has a phase change material and which is not situated in the region of the heat recovery steam generator is included, wherein, in order to supply the heat reservoir with thermally processed water, a supply line which leads out from the high pressure part or the medium pressure part is included and a discharge line which leads into the medium pressure part, the low pressure part or a steam turbine is included for discharging thermally processed water from the heat reservoir.