—An analysis of the operating conditions of a power transformer with the introduction of photovoltaic (PV) panels and Electric Vehicles (EV) in an eco-district is conducted. The study focuses on: (a) determining the optimal transformer sizing when there is neither PV nor EV; and (b) characterizing the overloading periods of the transformer induced by the penetration of PV sources and EVs in the district. We compare two EV integration strategies: they are either considered as unmanaged loads, or controlled by an Energy Management System (EMS) with Vehicle-to-Grid (V2G) capabilities. Transformer operating curves and rated power are deduced from technical standards supplied by Schneider Electric. The results show that EVs and PV introduction has a substantial impact on overloading periods. However, the latters are seriously mitigated both in terms of energy flows and peak power with the implementation of the EMS.