Journal of Energy Storage xxx (xxxx) xxx Please cite this article as: Ravendra Gundlapalli, Sreenivas Jayanti, Journal of Energy Storage, https://doi.org/10.1016/j.est.2020.102078 2352-152X/© 2020 Elsevier Ltd. All rights reserved. Case studies of operational failures of vanadium redox fow battery stacks, diagnoses and remedial actions Ravendra Gundlapalli, Sreenivas Jayanti * Department of Chemical Engineering & DST-Solar Energy Harnessing Centre, IIT Madras, Chennai-600036, India A R T I C L E INFO Keywords: Redox fow batteries Battery stacks Operational failures Membrane puncture Electrolyte crossover Diagnosis ABSTRACT Vanadium redox fow batteries show enormous scope in large-scale storage and load balancing of energy from intermittent renewable energy sources. Although a number of studies have been published in the last two de- cades on various aspects of these fow batteries, very few have reported on practical aspects such as design considerations, guidelines and operational failures. Adequate attention to engineering aspects, failure detection and diagnosis are essential for smooth operation of the fow batteries. This paper discusses a few case studies of operational failures during the design and development of kilowatt-scale fow batteries together with their di- agnoses and remedial actions. Specifcally, failures in the membrane, tubing network and state of electrode have been discussed and suitable recommendations and guidelines are given to avoid these. In each case, rectifcation of the malfunction was confrmed through results obtained using electrochemical testing protocols established in previous studies. Based on these experiences, good practice guidelines have been recommended for proper fabrication, assembly and characterization of stacks. 1. Introduction Increasing penetration of renewable energy sources such as wind and solar energy into the energy mix of major economies of the world ne- cessitates large-scale energy storage to cope with the intermittency and natural fuctuations in these energy sources. Although the Li-ion batte- ries have seen tremendous growth in the battery electric vehicle tech- nology, their inherent issues like capacity fade, safety and requirement of speciality materials for volume expansion may restrict application in large-scale and long-duration storage [1–3]. On the other hand, fow batteries, due to their long cycle life, absence of fre hazard and ease of scalability to very large capacities, show great promise in accommoda- ting the dynamic output of large solar and wind farms. Of the various types of fow batteries, the all-liquid vanadium redox fow battery (VRFB) has received most attention from researchers and energy pro- moters for medium and large-scale energy storage due to its mitigated cross-over problem by using same metal ion in both the positive and negative electrolytes [4–6]. Numerous studies have been reported on the improvement of performance of VRFBs through material treatments [7, 8], design of fow felds [9–18] and operational strategies [19–22]. Some studies have been reported on design considerations, guidelines and safety issues in the assembly and operation of stack. These are briefy reviewed here. For application in grid-scale storage, cell size should be as large as possible and the cell should be operated at lowest possible fow rate in order to maintain good system level energy effciency [23]. Over- charging the cell beyond certain limits may release hydrogen and oxy- gen gases which may lead to corrosion of current collector [24]. General failures in the operation of VRFB may arise primarily from poor cell design and malfunction of the balance of plant [25]. Therefore, design, fabrication and operation of large-scale fow battery stacks need special attention towards mechanical arrangements, piping network and diag- nosis of failures in addition to the electrochemical operational strategies [14]. Stalnaker and Lieberman [26] recommended that the stack must be compressed to a uniform compression level across the active area by ensuring the same torque in the tie rods. Whitehead et al. [27] pre- scribed prior checks for the pinholes in membrane which would allow electrolyte mixing and cause failure in performance. Although a pin hole in membrane can cause internal shorting, relatively small amount of active species between the electrodes compared to that stored in external reservoirs and high heat capacity of aqueous electrolyte would release limited energy while shorting. Schreiber et al. [28] investigated self-discharge of VRFB and found that it is proportional to the electrolyte volume in the cells. Gandomi et al. [29] reviewed several diagnostics * Corresponding author. E-mail address: sjayanti@iitm.ac.in (S. Jayanti). Contents lists available at ScienceDirect Journal of Energy Storage journal homepage: www.elsevier.com/locate/est https://doi.org/10.1016/j.est.2020.102078 Received 24 August 2020; Received in revised form 14 October 2020; Accepted 3 November 2020