Modern electrical industry is facing a paradigm shift in the production, delivery and in the end use of electricity. The introduction and integration of decentralized energy resources has a positive impact on emerging systems such as micro grids and smart grids. At the same time, they significantly change the demand role toward a real and active force of competitive energy markets. This paper shows the integration possibilities of decentralized energy resources (which includes distributed generation, disperse generation, energy storage, and demand resources) with current centralized electricity systems. We conclude that the technical and economical evaluation of centralized energy resources is applicable to decentralized energy resources, and the integration of both resources enable the diversification of the energy offer and ensures electric supply at short, medium and long terms.