Plug-in electric vehicles (PEVs) are expected to balance the fluctuation of renewable energy sources (RES). To investigate the contribution of PEVs, understanding the availability of mobile battery storage and the residual load fluctuation is crucial. This seminar introduces a method for characterizing fluctuating renewable generation and compares different parameters for California and Germany. Based on this method of describing renewable fluctuation and residual load, the balancing potential of grid-connected vehicles is analyzed for a 2030 scenario using the agent-based simulation model PowerACE. The analysis reveals that integrating fluctuating RES is possible with less effort in California because of a higher correlation between RES generation and the load curve here. In addition, RES capacity factors are higher for California and therefore the ratio of installed capacity to peak load is lower. Germany, on the other hand, faces extreme residual load changes between periods with and without RES supply. In both power system scenarios, grid-connected vehicles could play an important role in reducing residual load fluctuation if smart charging is used. Uncontrolled charging or static time-of-use tariffs do not significantly improve the grid integration of RES.