Statistical Characterization of Battery Energy Storage Systems in Mixed and Stacked Service Electrical Grid Operations

Battery energy storage system (BESS) is a key enabler of the modern renewable- and inverter-heavy electric grid. It facilitates integration of variable power generation such as wind and solar, and can provide a host of ancillary grid services and help defer infrastructure upgrades. Longevity and safety of BESS, however, remain unclear when subjected to such duties diverse in timescale, power, and state-of-charge (SOC). Much of the existing deployment of BESS provide a single grid service such as frequency regulation or load shifting. Further, the contemporary operating envelope of the BESS is deliberately conservative. In the work reported here, we extract essential characteristics of existing field operation and systematically develop methods to estimate the effect of extended range of services on BESS performance and safety. This extended range includes a multitude of ancillary services dispatched simultaneously (stacked duty) and sequentially (mixed duty) using wider envelope of timescale, power, and state-of-charge of BESS. The designed laboratory experiments can be used to construct regression models of BESS performance and safety, and to calibrate parameters of physics-inspired electrochemical representations such as the extended SPMeT model presented in a companion paper [1].