Mapping the power performance of a state-of-the-art vanadium flow batteries system

This paper presents a comprehensive performance mapping carried out on a 10 kW/27 kW h industrial-scale vanadium flow battery upgraded test facility (IS-VFB-U). The system was instrumented to measure all electrical and thermo-hydraulic variables, in different charge states and load levels (1–10 kW). An extensive series of tests were carried out to quantify the losses at system level and the corresponding efficiency during charging and discharging, as well as to identify power operating limits, leading to the development of a multidimensional performance map. To ensure repeatability, a dedicated testing protocol was developed aimed at addressing typical operational issues of industrial VFB systems, such as electrolyte stratification and thermal drift due to shunt currents. Experiments were carried out under two flow regimes, i.e. constant flow factor and constant flow rate. Repeatability tests, performed over 10-day intervals, demonstrated high consistency (coefficient of variation 3 % for pumping power and ≈ 2 % for the net power provided to the electrolytes), validating the robustness of the system and protocol. Stack efficiencies during charge reached up to 95 % at high S o C and intermediate load levels in both regimes. The resulting efficiency maps, presented as functions of S o C and battery load, constitute unique experimental datasets for industrial VFBs and offer a solid foundation for model-based optimization and operational scheduling strategies.