The present paper deals with the topic of the planning of distribution networks, equipped with Dispersed Generation (DG), and so active grids. Different issues related of this topic are widely present in the scientific literature of the last years, due to the big spread of renewable energy sources (RES), typically in small generation power plants connected to the Medium Voltage (MV) and Low Voltage (LV) systems. The research team, authoring this paper, has been involved in a National Project, named SINERGREEN (Smart INtelligent EneRgy GREEN) dealing with the topic of the smart grids and energy efficiency. In the framework of the project, the researchers have developed a simulation tool, dedicated to the electrical grids, able to calculate some energy performance indicators, that can be used for evaluating operation of the network and so for addressing the decisions of a Distribution System Operator (DSO) in terms of planning and development of its grids for a better integration of RES power plants in DG. In the present paper the tool is presented, the main Indicators are reported and the results of the application of the methodology implemented to a case study are reported. © 2016 AEIT.