Seasonal Challenges for a Zero-Carbon Grid in California

Today resource adequacy is most often maintained by installing natural gas plants to meet the peak load. In California, the current risk of inadequate electricity supply is highest around sunset in late summer. In a zero-carbon grid, resource adequacy will increasingly require adequate stored energy throughout the entire year. Here we seek to develop an intuition about the times of the year when resource adequacy may be most challenged for a solar-dominant system. We use a simplified approach and show that the month of the biggest challenge occurs in winter and can shift by more than two months depending on the amount of solar and storage that are built.