Standby thermal management system for a kW-class vanadium redox flow battery

Standby is a condition that may occur several times and for long periods in the operation of a redox flow battery for energy storage services in electrical grids (from a national grid down to smart grids, microgrids, …), so that the efficient operation of these batteries calls for specific standby management procedures, capable of minimizing losses while avoiding solutes precipitation. This paper describes the characteristics of a standby thermal management system capable of performing these tasks with high efficiency. Its design resorts to an experimental and numerical investigation that made use of a cell-resolved dynamic thermal model, determining the stack voltage, self-discharge and temperature evolutions. Two different standby modes were analyzed: one with no electrolyte flow (named “swamped standby mode”) and the other with a small electrolyte cooling flow rate (named “streamed standby mode”). In addition, the critical conditions which may lead to V(V) precipitation were identified based on published experimental data. As regards the swamped standby mode, an advanced strategy consisting of smart intermittent washings was designed and tested on a kW-scale vanadium redox flow battery system, showing a dramatic reduction of self-discharge losses compared to a conventional fixed periodic washing. As regards the streamed standby mode, the optimal value of the cooling electrolyte flow rate that minimizes self-discharge was identified. With respect to the swamped one, the streamed standby mode ensures the battery readiness to provide fast power service in safe conditions. To the best of the authors’ knowledge, this is the first work in which such thermal management strategy during standby, supported by experimental validation on a kW-class vanadium redox flow battery, is presented.