A computer-implemented method and related device are disclosed for determining a plurality of operating scenarios of an energy system. The method comprises obtaining a plurality of performance measures of the energy system as a function of time corresponding to a plurality of sets of values of input variables. The method comprises clustering the plurality of sets of values of the input variables and the performance measures associated therewith into groups and defining a descriptor for each of the groups. The method also comprises outputting the descriptors of the groups for use in an online prediction or offline estimation of the energy system.