Method for operating a power plant

A method for operating a power plant having a gas turbine, a heat recovery steam generator connected downstream of the gas turbine, a steam turbine connected to the heat recovery steam generator, an auxiliary heat source and a control system, the method comprising:

• controlling, via the control system, the power plant such that the heat recovery steam generator receives an input of heat from the gas turbine;
• determining, by the control system, the gas turbine is operating at its maximum capacity or at an upper end of its control range and the power plant is operating at less than a target value for a power plant capacity;
• in response to determining the gas turbine is operating at its maximum capacity or at the upper end of its control range and the power plant is operating at less than the target value for the power plant capacity, determining, by the control system, a target pressure value immediately upstream of the steam turbine, in order to achieve a predefined power plant capacity,
• wherein the target pressure value is derived from a primary pressure for the steam turbine and a steam turbine capacity for the steam turbine;
• wherein the target pressure value is a target value for the auxiliary heat source;
• wherein the auxiliary heat source is a heat store arranged outside the heat recovery steam generator;
• and
• based upon the target pressure value, controlling the heat store arranged outside the heat recovery steam generator to release heat into the heat recovery steam generator to achieve the predefined power plant capacity.