Synergy and Competition between Long and Short Duration Storage in Renewable Power Grids

Long duration storage (LDS) resources are increasingly important to address the seasonal intermittency of variable renewable generation in decarbonized systems. An energy system optimization model is used to simulate a net-zero carbon 2045 California grid, with attention to LDS and short duration storage (SDS). The Energy Usage metric is created to characterize the diverse operation profiles and roles of LDS and SDS and quantify the value of these storage resources in the system overall. Through this metric, four distinct operating regimes are defined: 1) Synergistic LDS and SDS, 2) Dominant LDS, 3) Underutilized LDS, and 4) Underutilized LDS and SDS. Each of these regimes captures a unique set of operating patterns, where the application of storage ranges from peaker power source to flexible clean baseload. The regimes are also useful assessments of the system costs based on the storage resources alone: the cheapest systems all exhibit synergistic storage or dominant LDS. Moreover, the Energy Usage metric highlights that LDS is only competitive with SDS when it is cheap and equally efficient. In addition, introducing more reliable generation sources such as carbon capture and storage or wind power often reduces the efficient utilization of LDS and in some cases fully displaces LDS from the least-cost system. Finally, we also perform an analysis on the comparative system-level advantages of efficient LDS versus LDS with low power costs. Improvements in efficiency can still be useful when they incur higher costs, although the merits of this trade-off depend substantially on the specific technoeconomic parameters of the storage resource. By shedding light on how SDS and LDS are valued and actually operated in decarbonized systems at an hourly, weekly, and seasonal resolution and contextualizing these results to a systemic level, this study informs future policymaking and research and development in the nascent area of long duration storage.