Sodium nickel chloride battery steady-state regime model for stationary electrical energy storage

The purpose of this paper is presenting a reliable modelling of sodium-chloride battery in order to have a powerful tool which is able to foresee the steady state battery behaviour in both discharge and charge operations. The proposed modelling approach allows representing both constant current operations and variable charge/discharge current ones. The model can be classified as an experimental one because it is based on a wide set of measures. All the main modelling steps are described and a comparison between the model results and real battery measures, with the same conditions, is presented. The very good agreement between measures and model confirms the robustness of the approach for steady state applications. The model was tested for fast transient operations also, by alternatively opening and closing the battery circuit during discharge/charge operations. In these conditions, the model is not able to perfectly follow the actual voltage behaviour, even if the battery voltage error is small. Therefore, the limit of this model is that it cannot represent the actual transient behaviour of the battery voltage. The paper proposes to adopt a set of standard battery measures from which it is possible to infer a simple but very precise modelling structure, in order to represent the steady state behaviour of NaNiCl2 batteries.