Minimum EVCS Aggregation Requirements for Reliable Customer Baseline Load in Electricity Markets

The electrification of the transportation sector, driven by decarbonization policies, can significantly impact power demand patterns. Strategically integrated electric vehicles (EVs) can serve as flexible grid resources by enabling load shifting, voltage regulation, and frequency stabilization. In particular, to evaluate their potential participation in the wholesale electricity market, it is essential to assess whether aggregated electric vehicle charging stations (EVCSs) meet the eligibility and reliability criteria required for existing demand response (DR) programs. This study analyzes the reliability of aggregated EVCSs based on their aggregation level using an average-based Customer Baseline Load (CBL) method, performance metrics such as RRMSE and RMAE, and a two-stage random sampling approach. The analysis utilizes load data from 873 EVCSs located in Jeju, Korea, as of 2023. The results show that as the level of aggregation increases, both RRMSE and RMAE decrease, significantly reducing CBL estimation errors. Furthermore, it was confirmed that aggregating EVCSs beyond 10 MW of capacity or 500kWh of average hourly load achieves reliability levels comparable to those of traditional DR resources. These findings provide a practical foundation for the integration of EV-based loads into wholesale market participation and grid control strategies, while contributing to the development of CBL methods and evaluation metrics for small-scale resources.