Overcoming the performance limitations of hybrid redox flow batteries with modular operation

To help solve the energy trilemma, energy storage technologies must demonstrate low cost and high efficiency to avoid inflating the cost of renewable power. Hybrid redox-flow batteries are a promising multi-hour storage technology, as they use low cost chemicals in an easily recyclable format. However, they suffer from low efficiency at low power output, and require periodic maintenance downtime to remove metal from the anode. Here, we show that a modular system can overcome these challenges with appropriate control. A novel optimisation model for modular operation with periodic maintenance is parametrised from a commercial zinc-bromine hybrid RFB. Independent module control was predicted to improve operational efficiency, with six modules achieving 73 % compared to the peak efficiency of 80 %. A non-obvious schedule for maintenance was determined algebraically, where energy is transferred from a module due maintenance to one that is fresh. It is found that staggering the strip cycles across several days and performing them when PV and load are roughly in balance in the morning is the optimal timing. The findings are significant as they show that maintenance does not preclude hybrid RFB from firm power provision, and that high efficiency is possible during operation through modular control.