Coupled thermal-electrical lumped parameter modeling of high-temperature sodium-sulfur battery

Solar power plants and wind turbine generators, harvesting renewable energy sources, have become important participants in power networks and microgrids. Due to their stochastic availability, energy storage has become an inevitable factor in electricity system optimization. Among others, high-temperature sodium‑sulfur batteries offer a proper solution for installed battery energy storage systems, resulting from their advantageous technical and economic aspects. The technology provides a long life expectancy since no side reactions occur during operation due to the molten state of the electrodes without phase transition. However, to keep the sodium and sulfur in liquid phase, the required operational temperature range of the cells is 300–350 °C. Consequently, an advanced battery management system and careful thermal design are crucial, and the thermal aspects of the battery should be properly considered during energy storage system optimization. However, computational demand is an important factor in system-level simulations, analyzing long operational periods. Therefore, this paper presents a coupled thermal-electrical lumped parameter model, representing a reasonable compromise between model accuracy and run time. Calculated cell temperature is validated with experimental data from the literature. The average deviation between the reference data and the results is 6 °C. The thermal balance of the module is investigated and improved capture of the cooldown process is highlighted. Charging and discharging processes are comprehensively analyzed and potentially dangerous operation modes are identified. • Thermal-electric model with low computational demand for NaS battery is presented. • Battery thermal balance is analyzed and critical operation modes are identified. • Model results are compared to experimental data. • The presented model is suitable for further system-level analyses.