Since the Paris Agreement adopted in 2015, global societies are increasingly aware of the needs to limit global warming to 1.5 C and reach global carbon neutrality by 2050. However, current commitments of global societies are not sufficient, party owing to the lack of cost-effective decarbonization measures. The SolarEV City concept is proposed for cost-effective urban decarbonization combining rooftop PV with EV through bi-directional charging in a city scale. In this study, we conducted techno-economic analyses to test the concept in Paris and Ile-de-France. PV+EV systems are found to add value to rooftop PV systems raising selfconsumption and self-sufficiency, when the roof coverage by PV is reached to 50-60% for Paris and 20-30% for Ile-de-France, allowing to bypass expensive stand-alone battery storage. The system allows CO2 emissions reduction through accelerated development of EV.