Technological advances and cost reductions combined with the need for greater environmental sustainability have led to an enormous increase in installed photovoltaic (PV) capacity in recent years. This deployment involves not only photovoltaic panels but also wind turbines, storage systems, electric vehicles (EVs), and numerous other resources, which together are referred to as Distributed Energy Resources (DER). The increase in these Renewable Energy Sources (RES) encompasses several issues related mainly to their extreme variability and limited predictability, which involve the grid itself. The historical top-down approach of the electricity grid is contrasted with new models for the future in which the owners of RES assume central importance; they no longer behave as mere consumers under the grid control, but on the contrary, act as active prosumers in a decentralized framework.