Vanadium flow batteries at variable flow rates

The growing demand for renewable energy has increased the need to develop large-scale energy storage systems that can be deployed remotely in decentralised and deregulated networks. Vanadium flow batteries employ all-vanadium electrolytes that are stored in external tanks feeding stack cells through dedicated pumps. These batteries can possess near limitless capacity, which makes them instrumental both in grid-connected applications and in remote areas. A laboratory-scale single cell vanadium redox flow battery (VRFB) was constructed with an active area of 64 cm2. The electrolyte was produced by dissolving vanadium pentoxide in sulphuric acid. The battery was tested to assess its performance; it achieved a coulombic efficiency of 97%, a voltage efficiency of 74.5% and an energy efficiency of 72.3%. The battery was used to study the effect of electrolyte flow rate on the overall performance. The results indicated that an increased flow rate increased the capacity. The tests revealed that there is a compromise between the increase in capacity and the overall efficiency that could be achieved by tuning the flow rate. The results suggested that operating the battery at a variable flow rate yields high capacity at a higher energy efficiency.