Studies have evaluated the economic feasibility of 100% renewable power systems using the optimization approach, but the mechanisms determining the results remain poorly understood. Based on a simple but essential model, this study found that the bottleneck formed by the largest mismatch between demand and power generation profiles determines the optimal capacities of generation and storage and their trade-off relationship. Applying microeconomic theory, particularly the duality of quantity and value, this study comprehensively quantified the relationships among the factor cost of technologies, their optimal capacities, and total system cost. Using actual profile data for multiple years/regions in Japan, this study demonstrated that hybrid systems comprising cost-competitive multiple renewable energy sources and different types of storage are critical for the economic feasibility of any profile.