As the share of variable energy resources (VERs), increases in power systems, their role and impact on system are expanding. The current method for evaluating the effective capacity of VERs is based on the exceedance level approach. This paper examines whether the existing method is appropriate for high-penetration systems. This paper analyzed the contribution of VERs to system reliability and compared with the existing method. The analysis revealed different criteria were deemed necessary for determining peak contributions for each resource. Additionally, methods to mitigate the variability of peak contributions caused by changes in VER utilization patterns were explored. Based on the scenario analysis results, criteria for determining the peak contributions of VERs were proposed, and the changes in effective capacity resulting from the applying the proposed method were further analyzed.