A method of controlling a thermal power plant for electricity generation, said power plant comprising at least one heat source to supply thermal energy to a working fluid circulation circuit. The circuit comprises a high pressure turbine mechanically connected to an electricity generator, a high pressure regulating valve controlling the steam supply to said high pressure turbine from a high pressure superheater associated with a high pressure storage tank. The fluid supply to said high pressure storage tank from a high pressure steam generator is controlled by a high pressure supply valve, and, in response to a need for additional electrical power, the opening of the high pressure regulating valve is increased the opening of the high pressure supply valve is reduced.