Modeling of zinc energy storage system for integration with renewable energy

Utility scale energy storage devices have been considered for integration with renewable energy systems to improve their sustainability and dispatch. In this paper, we analyze and model an advanced zinc energy storage device (ZESS), for grid level applications. This energy storage system has high energy and power density, high efficiency and long life. A series of tests have been conducted on the ZESS in order to develop an electrical model that describes its behavior. The modeling is based on the observation that, at constant temperature, both the open circuit voltage of the ZESS and its internal resistance are exclusive functions of its state of charge (SOC). Since the value of the SOC is crucial to the developed model, and due to the inexistence of charge sensors, Kalman filtering is used to estimate the SOC of the ZESS at any operating point. The model and the SOC estimator are necessary blocks to use when integrating the ZESS with some renewable energy system so that the controller can decide whether the ZESS should store/release energy from/to the system.