Evaluating vehicle-to-grid as a participation-dependent system flexibility resource: evidence from charging profiles and policy scenarios

Vehicle-to-grid (V2G) is increasingly discussed as a system flexibility resource, yet its system-level relevance depends less on technological capability than on whether electric vehicles can effectively participate under real-world institutional, behavioral, and operational conditions. This study examines pathways for system-relevant V2G deployment in South Korea by integrating a participation-oriented policy framework with a quantitative assessment of observed EV charging behavior. Using hourly EV charging electricity sales data for 2021–2023, this study constructs seasonal charging profiles and percentile-based charging peaks, and develops charging demand scenarios for 2030 and 2050. V2G potential is evaluated through an effective participation rate capturing five interdependent dimensions—user enrollment, plug-in availability, technical readiness, energy-related constraints, and operational feasibility—that shape realizable flexibility. Results show that accelerating EV diffusion intensifies evening charging peaks, increasing demand for peak-oriented system flexibility. Under these conditions, the scale and relevance of V2G are far more sensitive to effective participation than to the size of the underlying technical resource pool. Even modest participation can yield policy-relevant, gigawatt-scale V2G potential in the long term, whereas insufficient participation renders V2G systemically marginal regardless of technological capability. By conceptualizing participation as a multiplicative and policy-sensitive determinant of system outcomes, this study clarifies why many technically feasible V2G options remain unrealized in practice. The proposed framework links policy design, user behavior, and system impacts, providing a transferable basis for designing phased policy interventions that enable V2G to evolve from pilot applications to a system-level flexibility resource.