In this paper a hybrid microgrid system, composed of RES (Renewable Energy System) and CHP (Combined Heat and Power) systems together with a battery based storage system is presented. The microgrid is accompanied by a centralized energy management system (CEMS) in order to optimize the microgrid operation both in grid-connected and in stand-alone modes. In grid-connected mode the optimization of the economic exploitation of the microgrid is privileged by applying optimization techniques. In stand-alone mode, management functions are applied to improve the reliability of the facility by means of islanding operation capability. The optimizationanalysis has been carried out in simulation while the reliability improvement of the microgridoperation has been analyzed in simulation and proven experimentally.