EnergyPLAN soft-link to GENeric OPTimizer. With this code optimality theory with the generic optimization program (GenOpt) is used in an innovative method of soft-linking of EnergyPLAN. This soft-link enables simulation-based optimization, guided with the chosen optimization algorithm, rather than manual adjustments of the decision vectors. In order to obtain EnergyPLAN simulations within the optimization loop of GenOpt, the decision vectors should be chosen and explained in GenOpt for scenarios created in EnergyPLAN. The result of the optimization loop is an optimal national energy master plan (as a case study, energy policy in Serbia was taken), followed with sensitivity analysis of the exogenous assumptions and with focus on the contribution of the smart electricity grid to the achievement of EU2030 goals. This general method could be further improved and used worldwide in the optimal planning of sustainable national energy systems.