Cameron Bracken , Nathalie Voisin, Youngjun Son, Sha Feng, Osten Anderson, Xiaodong Chen, Li He, Konstantinos Oikonomou

Variable renewable energy (VRE) droughts are periods of low renewable electricity production due to natural variability in the weather and climate. These compound renewable energy droughts occur when two or more (typically wind and solar) generation sources are in low availability conditions at the same time. Compound wind and solar droughts are most commonly studied at the hourly and daily timescale due to the short-term nature of energy markets and battery storage capacity. However the seasonal time scale allows for the examination of broader climate and hydrologic patterns that influence a broader renewable energy portfolio and inform the needs for long-duration energy storage. In this study, we use a newly developed dataset of coincident renewable generation to characterize seasonal compound VRE droughts which include wind, solar and hydropower at grid-relevant spatial scales across the contiguous United States. Along with the frequency, duration, magnitude, and spatial scale, we specifically examine these climate patterns with a composite climate analysis. Results for the historical period (1982-2019) indicate that seasonal compound VRE droughts can last up to 5 months and occur most frequently in the Fall. While not an established ``climate stress'' to consider in reliability studies yet, we demonstrate the impact of seasonal energy droughts on a resource adequacy study over the Western US interconnection using a nodal bulk power grid model. We further discuss how seasonal compound VREs can inform the sizing of long-duration energy storage and market incentives to manage short-term extreme events like heat waves and cold snaps while considering seasonal conditions.