A method for operating a power plant, the method comprising providing a power target setpoint to a power plant controller, dependent on said power target setpoint, determining a setpoint of at least one first power plant operation parameter, operating the power plant at a set power output (P GT, P ST) and with said at least one first operation parameter adjusted to the setpoint of said operation parameter, applying a measurement to determine an actual value of at least one second operation parameter, applying a theoretical power plant model to determine an expected value of said at least one second operation parameter, comparing the expected value of said at least one second operation parameter and said measured value of the at least one second operation parameter, applying a calibration loop for the theoretical power plant model, said calibration loop comprising: applying a comparison step to determine a deviation between the expected value of the at least one second operation parameter and the measured value of the at least one second operation parameter, modifying the theoretical power plant model, re-calculating the expected value of the at least one second operation parameter, repeating the calibration loop until a best match between the expected value of the at least one second operation parameter and the measured value of the at least one second operation parameter is achieved, thus obtaining a calibrated power plant model (501, 502) after terminating the calibration loop. the method being characterized by further comprising applying the calibrated power plant model (501, 502) to forecast the at least one second operation parameter for a multitude of values of the at least one first operation parameter and at least for the set power output (PGT, PST), predicting a response of a power plant operating parameter on a variation of the at least one first operation parameter in applying the calibrated power plant model (501, 502), adapting the setpoint of the at least one first operation parameter in order to adjust the power plant operating parameter to match with a power plant operator operation target, and operating the power plant at the set power output (P GT, P ST) with the at least one first operation parameter adapted to the adapted setpoint of the at least one first operation parameter; wherein the power plant operating parameter is selected from the group comprising: operation cost per power output; environmental impact; power plant reliability; power plant power reserve; power plant frequency response capability. applying a comparison step to determine a deviation between the expected value of the at least one second operation parameter and the measured value of the at least one second operation parameter, modifying the theoretical power plant model, re-calculating the expected value of the at least one second operation parameter, repeating the calibration loop until a best match between the expected value of the at least one second operation parameter and the measured value of the at least one second operation parameter is achieved, thus obtaining a calibrated power plant model (501, 502) after terminating the calibration loop. the method being characterized by further comprising applying the calibrated power plant model (501, 502) to forecast the at least one second operation parameter for a multitude of values of the at least one first operation parameter and at least for the set power output (PGT, PST), predicting a response of a power plant operating parameter on a variation of the at least one first operation parameter in applying the calibrated power plant model (501, 502), adapting the setpoint of the at least one first operation parameter in order to adjust the power plant operating parameter to match with a power plant operator operation target, and operating the power plant at the set power output (P GT, P ST) with the at least one first operation parameter adapted to the adapted setpoint of the at least one first operation parameter; wherein the power plant operating parameter is selected from the group comprising: operation cost per power output; environmental impact; power plant reliability; power plant power reserve; power plant frequency response capability. operation cost per power output; environmental impact; power plant reliability; power plant power reserve; power plant frequency response capability.