The energy modeling of an eco-district, composed of residential and commercial facilities, is proposed. First, an optimal strategy aiming at sizing the rated power of the substation transformer is introduced. Then, considering the introduction of photovoltaic (PV) panels and electric vehicles (EV) in the district, the new operating conditions of the transformer are detailed. In order to reduce (a) the peak power of the transformer and (b) the cumulative durations of the transformer overloading periods, an Energy Management System (EMS) is implemented. The latter uses the district EVs, which have Vehicle-to-grid (V2G) capabilities, as flexibility providing units. An economics layer is added in order to compute the electricity costs considering the French pricing. This approach is used to deduce the optimal contracted power with the local system operator. Results show a reduction of 70% in overloading durations, 71% in average overloading power, and 17% in electricity costs with the EMS. I. INTRODUCTION Urbanization, population growth and climate change put increasing pressure on electricity consumption and CO 2 emission reductions. These challenges have fostered the development of Renewable Energy Sources (RES) (such as photo-voltaic (PV) panels, wind turbines, etc.) in power systems. Their penetration rate has substantially increased during the last few years. In France, even though a slight decrease in growth rate was observed in 2013, the development of RES sources is expected to continue [1]. Similarly, plug-in Electric Vehicles (EV) appear as promising solutions to deal with the aforementioned issues. EV sales went up by 60% in Europe in 2014, and by around 20% in France for privately-owned EVs [2]. The expected trends in battery cost reduction and charging station deployment should strengthen the EV sales in the near future. However, the increasing penetration of these two new units brings up concerns regarding their impacts on the electrical