Assessing the Design and Operation of Redox Flow Batteries through Levelized Cost Analysis

Energy storage is expected to play an important role in enabling deep decarbonization of the electric sector by addressing the intermittencies of renewable power generation1. The redox flow battery (RFB) is a potential energy storage solution whose unique decoupling of energy and power make it increasingly competitive, on a capital cost basis, at longer discharge durations2. While the capital cost benefits to RFBs are well-described in the literature3, there are additional economic benefits associated with operation and maintenance of open systems (e.g., tune-ups, sparing strategies)4 as compared to closed systems like lithium-ion batteries. For example, crossover, undesirable species transport through the semi-permeable membrane that separates the positive and negative electrolytes, leads to comparatively rapid capacity fade in RFBs5 but can be remediated via electrolyte rebalancing, replacement, or other servicing, all of which can be performed without sacrificing or altering the reactor components. The costs necessary to maintain battery performance over time impact its economic viability, but are not captured in the conventional capital cost estimations6. This motivates the development of techno-economic models that consider the variable operating principles of different battery formats and chemistries. In this presentation, we describe a simple levelized cost of storage (LCOS) model for RFBs that captures long-term performance changes and maintenance costs by including capacity fade and recovery7. We use this model to assess the impact of different design and operational decisions on RFB cost. Specifically, we contemplate different chemistries (symmetric vs. asymmetric, finite lifetime vs. infinite lifetime), operating strategies (e.g., rebalancing schedule), performance improvements (e.g., reducing fade rates), design decisions (e.g., battery sizing), and investment approaches (e.g., electrolyte leasing). We find that there are tradeoffs in capital and operating expenses, and in many cases upfront investments pay off in long-term savings. We anticipate this analysis will provide new insights into the cost-drivers for RFBs and motivate further research efforts in the evaluation and development of new chemistries, component materials, and reactor configurations. Acknowledgements We gratefully acknowledge funding from the MIT Energy Initiative. References Intergovernmental Panel on Climate Change. Global Warming of 1.5 C. https://www.ipcc.ch/sr15/ (2018). Darling, R. M., Gallagher, K. G., Kowalski, J. A., Seungbum, H. & Brushett, F. R. Pathways to low-cost electrochemical energy storage: a comparison of aqueous and nonaqueous flow batteries. Energy Environ. Sci. 7, 3459–3477 (2014). Viswanathan, V. et al. Cost and performance model for redox flow batteries. J. Power Sources 247, 1040–1051 (2014). Yuan, X.-Z. et al. A review of all-vanadium redox flow battery durability: Degradation mechanisms and mitigation strategies. Int. J. Energy Res. 1–40 (2019) doi:10.1002/er.4607. Prifti, H., Parasuraman, A., Winardi, S., Lim, T. M. & Skyllas-Kazacos, M. Membranes for redox flow battery applications. Membranes vol. 2 275–306 (2012). US Department of Energy. Grid Energy Storage. https://www.energy.gov/sites/prod/files/2014/09/f18/Grid Energy Storage December 2013.pdf (2013). Rodby, K. E. et al. Assessing the levelized cost of vanadium redox flow batteries with capacity fade and rebalancing. J. Power Sources 460, 227958 (2020).