Research on vehicle-to-grid flexibility potential to the grid in China based on the coupled transportation-power model

With the increasing penetration of intermittent renewable energies, power systems face growing demand for flexibility resources. The rapid expansion of electric vehicles (EVs) provides a large pool of distributed flexibility capacities. However, their flexibility potential for the power grid, interactions with storage and transmission, and performance under different policy constraints remain insufficiently quantified. This study develops a coupled transportation-power system modeling framework to assess system flexibility potential of EVs. The impacts of uncontrolled charging (UC), smart charging (V1G), vehicle-to-grid (V2G), and sensitivity scenarios on system operation are analyzed based on the data from 31 Chinese provinces. The modeling results show that V2G reduces national load variance by 48.02% and intraday peak-valley differences by 51.46%. Importantly, this study identifies a temporal reorientation of system value, whereby V2G increasingly contributes to seasonal system balancing. Under high renewable penetration, summer discharge remains negligible, while winter discharge accounts for 49.22% of the annual total to compensate for the misalignment between renewable output and demand. At the provincial level, V2G value is driven by resource-load alignment rather than fleet scale. Guangdong has the largest EV fleet but contributes little discharge. V2G also changes infrastructure needs, reducing national new transmission capacity from 416.32 GW under UC to 362.33 GW under V2G, while selected renewable electricity transmission corridors remain important. It further changes the operating rhythm of conventional storage, indicating that EV flexibility interacts with conventional storage rather than simply replacing it. These findings suggest that future V2G planning should be region-specific and coordinated with storage deployment, transmission expansion, and compensation mechanisms for seasonal availability.