This paper investigates the potential of storing photovoltaic (PV) electricity in electric vehicle (EV) batteries and reinjecting the stored electricity into the grid (V2G) during high electricity demand periods. We developed a geographical methodology to quantify the mobility and EV charging needs across Europe. Scenarios of charging behaviour are then used to distribute the charging needs among locations corresponding to residential areas, workplaces, or points of interest (e.g., shops, restaurants, etc.). Resulting load curves and maps of the charging demand, with a resolution of one hectare, are then compared to a potential PV production obtained from typical meteorological data of irradiance, solar panel performance, and building coverage. This comparison is conducted hourly over one year, monitoring the evolution of the daily storage capacity of the EV fleet. Case studies were conducted on three cities in Switzerland: Sion, Neuchâtel, and Zürich. Three scenarios are used to compare home charging behaviour, balanced home and work charging behaviour, and charging at points of interest. Results highlight the impact of charging behaviour on the flexibility potential, with higher potential when charging at work and point of interest is privileged. The methodology is implemented in the online platform citiwatts [1].