Keeping top performance of vanadium redox flow battery at minimal costs


Vanadium flow batteries (VFBs) are a type of rechargeable battery that uses vanadium ions in two electrolyte solutions separated by a membrane to store energy. They are a type of redox flow battery, which means that the energy is stored and released by means of chemical reactions that occur between the vanadium ions contained in the electrolyte solutions. VFBs consist of two electrolyte tanks, one containing a positive electrolyte solution and the other containing a negative electrolyte solution. The two electrolytes flow in the cell electrodes that are separated by a membrane, which allows the anions or cations to move between the two solutions but prevents electron and vanadium ions crossing and the two electrolytes mixing. A potential difference established between the two electrolytes. When the battery is charged, the vanadium ions are oxidized in the positive electrolyte solution, and reduced in the negative electrolyte solution. When the battery is discharged, the reverse reaction occurs, with the vanadium ions being reduced in the positive electrolyte solution and oxidized in the negative electrolyte solution. This creates an ionic current between the two electrolytes in the membrane, which closes in an external circuit as electron current, to absorb electric power from a source or to release it to an electrical load. One of the advantages of VFBs is that they can be scaled up to store and release large amounts of energy. This is because the amount of energy that can be stored in vanadium flow batteries is determined by the size of the electrolyte in the tanks, rather than the size of the electrodes. Large vanadium flow batteries can be used for applications such as grid-scale energy storage, where large amounts of energy need to be stored and discharged over long periods of time. Another advantage of VFBs is that they have a long cycle life, with the ability to be charged and discharged tens of thousands of times without significant degradation in performance. Consequently, they are well-suited for applications where the battery is used frequently, such as in renewable energy systems.

However, vanadium flow batteries also have some disadvantages. One of these is that they have a relatively low energy density compared to other battery technologies, meaning that they require a larger physical footprint to store the same amount of energy. Additionally, VFBs are currently more expensive than other battery technologies in terms of stored energy [$/kWh] unless they are sized for long discharge durations (above 4-6 hours), although this cost is expected to decrease as the technology improves and becomes more widely adopted. However, they present a lower cost of managed energy {$/kWh/cycles]. The economic viability of VFBs has been analyzed in several studies, considering different assumptions. Another challenge characterizing the applicability of VFBs is their ability to undergo electrolyte oxidation from atmospheric hydrogen and/or oxygen evolution due to operations at extreme states of charge. This results in electrolyte imbalance which degrades the battery capacity and cycle life. In these cases, electrochemical rebalancing is needed though it cannot be achieved using simple mixing operations.

On this account, PhD candidate Nicola Poli, Dr. Andrea Trovò, Dr. Peter Fischer, Dr. Jens Noack, led by Professor Massimo Guarnieri from the University of Padua presented a sizing analysis of the electrochemical rebalancing process for VFBs. Specifically, they adopted an electrochemical method based on an electrolysis reactor consisting of stacks of several cells. The economic feasibility of this method was also assessed using a techno-economic model considering the major parameters affecting the reactor and process performance as well as investment and operating expenditure analysis. Their work is currently published in the peer-reviewed Journal of Energy Storage.

The investment and operative expenditures analysis showed that relatively frequent rebalancing operations are economically feasible. Performing a rebalancing process once a year proved suitable only with a slow regeneration process, lasting 5 – 10 h, and the power required by the process exceeded that of the VFB system. As regards the investment and operation expenditure, the results revealed that minimum total costs were achieved at a current density consistent with the sporadic use of stacks. A 70% cost reduction could be achieved by running a 10-hour process every three months instead of once a year. In order to successfully reduce further the operational costs, it is important to carry out the rebalancing procedure without missing the remunerative VFB commercial service.

In summary, Professor Massimo Guarnieri and colleagues reported a new ad-hoc balancing method for the electrochemical rebalancing of VFBs and an analysis of its operation from economic and technical perspectives. The power rating was defined in terms of rebalancing key parameters, including electrolyte imbalance rate, VFB energy rating, periodicity, active area, cell number, and rebalancing duration. With proper optimization, this electrochemical rebalancing could remarkably reduce the overall investment and operational cost more than chemical rebalancing processes. In a statement to Advances in Engineering, the lead and corresponding author, Professor Massimo Guarnieri stated that the findings would promote the use of VFBs for energy storage in different applications. Indeed, VFBs are a promising technology for large-scale long-duration energy storage applications, and ongoing research and development is likely to make them even more competitive in the future.

About the author

Nicola Poli has been a PhD candidate in electrical engineering at the University of Padua since 01.10.2020. He graduated in chemical engineering in Padua in 2019. He carried out a master’s thesis, lasting six months, on the regeneration of vanadium flow batteries at the Fraunhofer-Institut für Chemische Technologie (Pfinztal, Germany). He then worked, for seven months, at the Electrochemical Energy Storage and Conversion Laboratory (EESCoLab) of the University of Padua, as a research fellow before starting the PhD. He authored seven papers indexed by Scopus. The topic of his research is related to the energy storage sector, in particular vanadium flow batteries. His studies are focused on the regeneration of the electrolyte, the evaluation of the life cycle of such batteries, the optimization of their performance and the stack design. He is a co-founder of an Italian Start-up which works on energy storage technologies.

About the author

Andrea Trovò received the M.Sc. degree in Mechanical Engineering with honors from the University of Padua (UNIPD) in 2015. The same year, he started working in the research group “Fuel Cell laboratory” of the Department of Industrial Engineering (DII) of UNIPD. In 2016 enrolled in the PhD Course in Electric Energy Engineering at UNIPD and in this position he worked at developing technology for vanadium flow batteries. He became Doctor of Philosophy in 2020. After graduation he continued research focusing on experimental and numerical study of the electric and hydraulic features of redox flow batteries, and was involved in the installation, commissioning and start-up of an industrial-scale Vanadium Redox Flow Battery (VRFB) test facility. He received the National Scientific Qualification (ASN) as associate professor in Electrical Engineering in 2022. In June 2022, he became an assistant professor at the University of Padua. Andrea Trovò participate to the research activities of the Electrochemical Energy Storage and Conversion Laboratory (EESCoLab) of the DII from its institution. He is co-author of 23 scientific publications indexed in Scopus and three book chapters. His Scopus H-index is 14. He delivered oral presentations at several international conferences (Electrimacs, IESES, ICIT, ECS, ISE, IFBF etc.) three of which were awarded as best-presentation. He is lecturer of course “Energy Storage Engineering” for the master degree in Electric Energy Engineering at UNIPD. He tutored and co-tutored more than twenty B.Sc. and M.Sc. theses in electrical and chemical engineering. He is the inventor of three patents on Vanadium Redox Flow Battery (VRFB) technology.

About the author

Mr. Fischer gained his PhD in Physical Chemistry at Heinrich-Heine-University Düsseldorf. Since 2005 he works with energy converters like fuel cells and flow batteries. Before he worked on flow batteries, he developed analytical instruments for PEM-fuel cells, e.g. locally resolved micro- Raman probes for the detection of gases in PEM – fuel cells in collaboration with German Aerospace Center (DLR) Stuttgart and Center of fuel cell research (ZBT) in Duisburg. Since 2011 he is the group leader of the Redox Flow Battery Group at the Applied Electrochemistry Department at Fraunhofer Institute for Chemical Technology (ICT). In his position, he was responsible for the light-house project RedoxWind. In this project a large-scale vanadium redox flow battery has been installed on the ground of Fraunhofer ICT. He is also active in several EU projects, e.g. he has led the EU-funded Marie Skłodowska-Curie ETN-Doctoral Network FlowCamp on next generation flow battery technology as well as the FLORES network, a network of 15 EU projects devoted to flow battery research. His research interests are vanadium as well as bromine chemistry as well as stack technology.

About the author

Jens Noack studied chemical engineering and environmental technology at the Dresden University of Applied Sciences and earned his doctorate at the Karlsruhe Institute of Technology. Since 2007, he has been working at the Fraunhofer Institute for Chemical Technology in the Applied Electrochemistry department, where he mainly works as a project manager, scientist and engineer on the development of redox flow batteries as storage for renewable energy sources. Since 2020, he has been an Adjunct Associate Professor at the University of New South Wales in Sydney/Australia and Deputy Director of the “German-Australian Alliance for Electrochemical Technologies for Storage of Renewable Energy” CENELEST in Sydney. Jens Noack is the author of more than 100 publications, co-editor of a three-volume standard work on redox flow batteries, and a member of the Electrochemical Society (ECS) and the International Society of Electrochemistry (ISE). He is also a member of numerous national and international standardisation committees on stationary energy storage, batteries, redox flow batteries and fuel cells, and is chairman of the German standardisation group on redox flow batteries.

About the author

Massimo Guarnieri is full professor of Electrical Engineering at the Department of Industrial Engineering, University of Padua. He received a Master degree in Electrical Engineering with honors in Padua in 1979, a Master in Business Administration at CUOA (I) in 1986 and a PhD in Electrical Sciences in Rome in 1987.

He sat on the Chair of the Mater Program in Electrical Engineering, the Chair of the Teaching Board of the Department of Industrial Engineering, coordinating ten degree programs, and was a member of the Scientific Council at the University of Padua. He taught at the Italian National School for Doctorates in Electrical in Engineering “F. Gasparini”.

For twenty years he contributed research programs on Nuclear Fusion at the RFX Consortium, on the RFX Experiment, working and leading the Magnetic Group, that was in charge of designing, auding the construction and commissioning the Magnetic System of the RFX. Within these duties he developed original computational methods for studying the large inductor systems (up to 8 m in diameter, 50 kA, 200 kV). He developed analyses on numerical multi-physic modeling and automatic optimization of complex electromagnetic devices, for which he founded the Computational Electrical Engineering Laboratory at the University of Padua.

From twenty-three years he is involved in research on electrochemical energy storage, including fuel cells, electrolyzers, Li-ion batteries and flow batteries, both with numerical modeling and experimental methods, for which he founded the Electrochemical Energy Storage and Conversion Laboratory of the University of Padua, at the University of Padua.

He led several projects funded by the Italian Mistry of University and Research, the Italian Ministry of the Environment, the University of Padua, and several Public and Private Companies.

He set collaborations with University of Tennessee in Knoxville (USA), Tokyo University of Agriculture and Technology (J), Vanderbilt University of Nashville (USA), Fraunhofer-Institute for Chemical Technologies (Germany), Skoltech University of Moscow (Russia), Chalmers University of Technology (Sweden).

He represents the University of Padua in the Energy Storage Joint Program of EERA the European Energy Research Alliance. Batteries Europe Project, providing roadmap to the European Commission, he sits in the Executive Board of Flow Batteries Europe and chairs its Technological Committee.

He authored over 310 papers (IRIS), 165 indexed by Scopus. He wrote 33 books (with later editions). He registered seven patents. He is listed in the World’s Top 2% Scientists Ranking of the Stanford University (yearly and career).


Poli, N., Trovò, A., Fischer, P., Noack, J., & Guarnieri, M. (2023). Electrochemical rebalancing process for vanadium flow batteries: Sizing and Economic Assessment. Journal of Energy Storage, 58, 106404.

Go To Journal of Energy Storage

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