Bidirectional V2G enhances wind and solar integration in China's 2030 sector coupled energy system

Integrating high shares of variable renewable energy in China is increasingly constrained by system flexibility. System-level evidence on how electric vehicle charging paradigms reshape these integration limits remains limited. This paper utilizes an hourly, sector-coupled framework to evaluate diverse 2030 wind-solar portfolios. The study identifies a structural asymmetry: wind power is easier to integrate, whereas solar power faces sharper curtailment due to midday concentration. Comparing three charging paradigms, results indicate that dump charging provides negligible benefits and reinforces evening ramps. Smart charging reduces curtailment by shifting 180 to 240 GWh of charging demand toward midday peaks. Bidirectional charging and discharging delivers the highest system value. This technology combines midday absorption with 100 to 180 GWh of evening discharge capacity. It reduces annual CO2 emissions to below 5.4 Gt and fuel consumption to under 25 PWh. These outcomes correspond to reductions of nearly 50% and 15% to 22% relative to the baseline, respectively. These findings show that bidirectional electric-vehicle flexibility can raise the technical ceiling of wind and solar integration and highlight the need to align transport electrification with flexibility-oriented market incentives in China's high-renewable transition.