a steam power plant is suggested having , parallel to the preheater passage , a heat reservoir which is loaded with preheated condensate in weak - load times . this preheated condensate is taken from the heat reservoir for generating peak - load and inserted downstream of the preheater passage into the condensate line resp . the feed water container . thus it is possible to quickly control the power generation of the power plant in a wide range without significantly having to change the heating output of the boiler of the steam generator . a steam power plant equipped according to the invention can thus be operated with bigger load modifications and also provide more control energy .