Mathematic Modeling and Performance Analysis of Vanadium Redox Flow Battery

The Redox Flow Battery (RFB) systems are unique chemically, mechanically, and electrically compared to other kinds of batteries. Among RFBs, the Vanadium Redox Flow Batteries (VRFBs) are the most commercialized type. VRFBs are a suitable option for large-scale energy storage with exceptional advantages like the decoupled power and energy design (scalability), long life-time, safe battery chemistry (non-toxic, and non-flammable), etc. The power and energy designs in VRFBs are decoupled, known as the scalability benefit of the VRFBs. This implies more output energy from the battery is possible only by adding more electrolytes to the reservoir tanks.There are only a few research studies in the literature about the optimized operation of the Vanadium redox flow batteries. Most of these papers are not applicable to develop in real practice. The introduced optimized operation algorithms of VRFBs in this lecture can help the participants learn how to improve the performance of the battery and operate the battery more efficiently. Different objective functions are considered in this lecture to be optimized, e.g. minimizing the time duration of battery charging (for fast charging), energy loss, voltage loss, and capacity loss of the battery. The participants can find the results of this useful in optimized operation and implementation of the VRFBs.High charging current density results in faster charging and reduces the capacity fading in Vanadium Redox Flow Batteries (VRFB). On the other hand, it leads to the reduced energy efficiency of the battery. Also, the lower electrolyte flow rate in VRFBs results in less energy consumption by the pumps leading to the higher energy efficiency of the VRFBs. However, higher flow rates have the benefit of reducing voltage loss of VRFBs. To address these trade-offs, closed-loop charge control and flow management in VRFBs are necessary. In this lecture, a multi-objective optimization is proposed in first section to optimize the charging duration and flow management of the VRFB simultaneously during its charging. An innovative method is proposed for modeling pump consumption based on affinity laws for centrifugal pumps, which leads to new electrolyte flow management. Further, three case studies are defined in charging mode on a nine-cell VRFB unit laboratory prototype to validate the proposed optimization's performance, involving the duration of charging, flow management, and energy efficiency of the VRFB. The method is compared with previously published research studies on the optimal operation of VRFBs, which shows the uniqueness and consistency of the proposed optimization method for simultaneous controlling VRFB's charging duration and flow management.Capacity fade in Vanadium Redox Flow Batteries (VRFB) relies on the loss of electrolyte volume in each of charge and discharge cycles. The loss of volume in each cycle, also known as the bulk electrolyte osmosis, is due to Vanadium ions' diffusion from the membrane. The lower electrolyte flow rate in VRFB can reduce capacity fade as the electrolyte's velocity across the membrane decreases. However, the lower electrolyte flow increases the battery’s voltage loss. A new electrolyte flow management is introduced in second section of the lecture to address this trade-off, which considers the decrease of both capacity fade and voltage loss in VRFBs simultaneously. The proposed multi-objective flow management shows a significant reduction of both capacity and voltage losses in VRFBs.Moreover, typically complex electrochemical models and equations are needed to model capacity fade in VRFBs, which are not straightforward to model. The capacity fade modeling can lead to the estimation of available capacity and the battery’s State of Health (SoH). Therefore, a new mathematical model is proposed for the VRFB’s available capacity based on the electrochemical-based capacity fade model results. The model further is developed to estimate the State of Charge (SoC) and the SoH of VRFBs per cycle of charge and discharge.

Insights into energy efficiency for vanadium redox flow battery (VRFB) using the artificial intelligence technique

The transition to renewable energy systems is critically dependent on the development and optimization of large-scale energy storage technologies, among which Vanadium Redox Flow Batteries (VRFBs) stand out for their scalability, flexibility, and long cycle life. However, the operational efficiency and lifespan of VRFBs are significantly undermined by shunt currents—unwanted internal currents that bypass the electrochemical reaction zones, leading to energy losses and accelerated degradation. Previous studies have predominantly employed lumped electrical circuit models to investigate these currents, a method that, while providing initial insights, substantially oversimplifies the complex interplay of ionic and electronic transport mechanisms within the VRFB electrolytes.This study proposes a novel multiphysics modeling framework that eschews the simplifications of previous models in favor of a detailed representation that captures the coupled dynamics of ionic conduction, electronic conduction, and fluid flow within the VRFB. By integrating the Navier-Stokes equations for fluid dynamics with the Nernst-Planck equation for ionic transport, and the Poisson equation for electric fields, this model aims to provide a holistic view of the factors contributing to shunt currents. This approach not only facilitates a deeper understanding of the underlying physical phenomena but also opens new avenues for identifying effective mitigation strategies.The superiority of this multiphysics approach lies in its ability to accurately simulate the complex interdependencies within the VRFB system, which are overlooked by simpler models. This enables the identification of specific structural and operational factors that contribute to shunt currents, facilitating the development of targeted optimization strategies. Through the application of this advanced modeling framework, the research can precisely quantify the impact of various physical parameters, such as membrane permeability, electrode porosity, and flow channel design, on the magnitude and distribution of shunt currents, guiding the engineering of VRFB components for minimal energy loss and enhanced efficiency.Moreover, the multiphysics model paves the way for innovative optimization techniques, such as the strategic placement of barriers or the adjustment of flow patterns, to disrupt or redirect shunt pathways effectively. These strategies, informed by a deep understanding of the underlying physics, promise to significantly improve VRFB performance, offering a path to more reliable, durable, and efficient energy storage systems.The implications of this research extend beyond academic interest, offering practical insights for the design and operation of more efficient and sustainable VRFBs. As the demand for reliable large-scale energy storage solutions grows in the context of global renewable energy integration, the findings of this study promise to contribute significantly to the advancement of VRFB technology, aligning with the broader goals of energy sustainability and environmental stewardship. References Tang, J. McCann, J. Bao, M. Skyllas-Kazacos, Investigation of the effect of shunt current on battery efficiency and stack temperature in vanadium redox flow battery, J. Power Sources, 242, (2013) 349 - 356, doi: 10.1016/j.jpowsour.2013.05.079.Viswanathan, A. Crawford, D. Stephenson, S. Kim, W. Wang, B. Li, G. Coffey, E. Thomsen, G. Graff, P. Balducci, M. Kintner-Meyer, V. Sprenkle, Cost and performance model for redox flow batteries, J. Power Sources, 247, (2014) 1040 – 1051. doi: 10.1016/j.jpowsour.2012.12.023Skyllas-Kazacos, J. McCann, Y. Li, J. Bao, A. Tang, The Mechanism and Modelling of Shunt Current in the Vanadium Redox Flow Battery, ChemistrySelect, 1(10), (2016) 2249–2256. doi: 10.1002/slct.201600432. Moro, A. Trovò, S. Bortolin, D. Del Col, M. Guarnieri, An alternative low-loss stack architecture for vanadium redox flow battery: comparative assessment, J. Power Sources, 340, (2017) 229-241.doi:10.1016/j.jpowsour.2016.11.042.Trovò, G. Marini, A. Sutto, P. Alotto, M. Giomo, F. Moro, M. Guarnieri, Standby thermal model of a vanadium redox flow battery stack with crossover and shunt-current effects, Appl Energy, 240, (2019) 893-906. doi: 10.1016/j.apenergy.2019.02.067. Trovò, F. Picano, M. Guarnieri, Comparison of energy losses in a 9 kW vanadium redox flow battery, J. Power Sources, 440, (2019) 227144. doi: 10.1016/j.jpowsour.2019.227144. Figure 1

Vanadium redox flow batteries (VRFBs) are an attractive technology for a variety of energy storage applications.1,2 The catholyte and the anolyte in these batteries are circulated through the electrodes from reservoirs. The active species in the catholyte are VO2+ and VO2 + (i.e. VIV and VV) while the active species in the anolyte are V3+ and V2+. VRFBs have a major advantage over other flow batteries in that cross-contamination due to transport through the separating membrane is effectively eliminated.3 Monitoring of the state of charge (SoC) is important for any battery system. Additionally, in VRFBs, transfer of vanadium ions across the membrane4 and side reactions such as hydrogen formation5 at the negative electrode can result in SoC becoming unbalanced (e.g. more VV on the positive side than VII on the negative). Therefore independent monitoring of SoC of both electrolytes is important for effective operation of VRFB technology.Both overall SoC of a VRFB and individual SoCs of the positive and negative sides (determined by the VIII/VII and VIV/VV ratios in the respective electrolytes) may be monitored in a number of ways using electrodes. However, these methods have drawbacks.6 Spectroscopic monitoring of SoC is independent of electrochemistry and offers the possibility of performing in-situ analysis. VII, VIII, VIV, and VV aqueous species have strong absorbance spectra in the visible region.6- 12 If the absorbance is a linear combination of that of the constituents UV-visible spectroscopy is a straightforward method of measuring the concentration and ratio of mixtures: e.g. for VIII-VII mixtures or very dilute VIV-VV mixtures.6-12 At higher concentrations, the absorbance of VIV-VV mixtures is a highly non-linear function of the mole fraction of VIV. For VIV-VV mixtures, this non-linearity has been shown to be due to the formation of a complex between the VIV and VV species. 6-8 Tang et al. 10 and Liu et al. 11 addressed the problem of non-linearity by developing an empirical method of estimating SoC. However, the non-linearity can be quantitatively explained6-8 allowing precise methods12 of optical monitoring of SoC in VRFBs. Factors, such as the concentration of sulphate and vanadium, can significantly affect this non-linearity.6,8 In this presentation, we present a detailed study of these factors in relation to spectroscopic SoC measurement. Acknowledgements The authors acknowledge funding from Enterprise Ireland through Commercialisation Fund CF/2013/3303. The material in this research is partly based upon works supported by Science Foundation Ireland through the Charles Parson Initiative (CPI). References H. Bindner, C. Ekman, O. Gehrke and F. Isleifsson, in Characterization of Vanadium Flow Battery, Risø Report (2011)M.J. Watt-Smith, P. Ridley, R.G.A. Wills, A.A. Shah and F.C. Walsh, J. Chem. Technol. Biotechnol. 88, 126 (2013)M. Rychcik and M. Skyllas-Kazacos, J. Power Sources 22, 59 (1988)J. Xi, Z. Wu, X. Qiu and L. Chen, J. Power Sources 166, 531 (2007)A.H. Whiteheadand M. Harrer, J. Power Sources 230, 271 (2013)D.N. Buckley, X. Gao, R.P. Lynch, N. Quill, and M.J. Leahy, J. Electrochem. Soc. 161 (4), A524 (2014)X. Gao, R.P. Lynch, M. Leahy and D. N. Buckley, ECS Transactions 45 (26), 25 (2013)P. Blanc, C. Madic and J.P. Launay, Inorg. Chem. 21, 2923 (1982)M. Skyllas-Kazacos and M. Kazacos, J. Power Sources 196, 8822 (2011)Z. Tang, D.S. Aaron, A.B. Papandrew and T.A. Zawodzinski, Jr., ECS Trans. 41 (23), 1 (2012)L. Liu, J. Xi, Z. Wu, W. Zhang, H. Zhou, W. Li and X. Qiu, J. Appl. Electrochem. 42(12), 1025 (2012)D.N. Buckley, X. Gao, R.P. Lynch, M.J. Leahy, A. Bourkeand G. Flynn, European Patent EP 13195315 (Application Date: 2 December 2013)

The worldwide effort to decarbonize the electricity grid has made battery energy storage system (BESS) an essential technology. A promising technology for long duration storage on the grid is Vanadium Redox Flow Batteries (VRFBs), which can support the grid by regulating peak load, reducing intermittency of large-scale renewables, and as emergency power supply. There are two primary methods of integrating a BESS to the grid. Frist, the BESS is directly connected to the DC-link of a DC-AC converter that interfaces with the grid. Second, the BESS is connected to a DC-DC converter that in turn interfaces with the DC-link of a DC-AC converter. These converters all have a characteristic ripple voltage and current during operation. The magnitude and frequency of the ripples depend on topology and switching frequency of a converter, controller design and protocol, type of connection to the grid, voltage magnitude and load characteristics. Currently, studies on the impact of ripples have been limited to Lithium-ion and Lead-Acid batteries. The impact of ripple current and voltage has not been studied in VRFBs. In a VRFB, potential impact includes excessive gassing of hydrogen and carbon corrosion of the bipolar plate and porous electrode and cell heating. To better integrate and operate VRFBs to the electricity grid, the impact of ripples needs to be studied in detail.Using a novel experimental platform, where both magnitude and frequency of ripples will be incorporated, we will emulate the performance of different power electronic converter configurations. It will comprise standard 5cm2 VRFB cells with a carbon felt electrode and Nafion ion exchange membrane. The various converter ripples in an electricity grid setting will be emulated by superimposing the signals from a potentiostat (constant current) and a high frequency transformer (modulated ripples), which will be connected to the cathode of the cells.The experimental testbed will be used to cycle the VRFB cells at various states of charge with ripples that emulate the performance of power electronic converters during grid operations and disturbances. Varied parameters will include ripple amplitude, ripple frequency, electrolyte flow rate, applied current density and state of charge. Measurement data from monitoring voltage of each electrode, cell voltage and current, gas generation, electrolyte crossover and electrolyte loss will be analyzed to determine the impact of ripples on VRFB cells. Finally, the cells will be monitored for signs of gas generation and postmortem signs of carbon corrosion.Our analysis will determine the impact of various ripple magnitude and frequencies on VRFBs in a simulated grid integration environment. This work will facilitate the development of design standards for power electronic converters that are intended for battery applications, while also informing future efforts to optimize VRFB cell and stack performance.

The electrode is a key component to optimize in the vanadium redox flow battery (VRFB) to achieve high battery performance and market competitiveness. Generally, carbon based materials are the most prevalent type of electrode utilized in commercial and experimental VRFBs.1 Fibrous carbon materials and their derivatives are widely used as electrodes in VRFB system because they are porous to allow electrolyte penetration, resistant to the electrolyte chemical environment and relatively low-cost. Recently, significant performance improvement of VRFB has been achieved by utilization of carbon paper materials with enhanced surface properties.2 Mass transport is a major factor in the efficiency loss in VRFB, particularly at low states of charge. Ohmic, activation and mass transport overpotential losses cause efficiency loss in an electrochemical system.3The electrode loss is mainly comprised of activation and mass transport losses, while the ohmic loss is mainly due to separator resistance. The activation overpotential is caused by limited reaction rate of redox couple and limited surface area. The mass transport overpotential is caused by reaction active species depletion due to insufficient active species supply on electrode surface. Because of the slow motion of cation in solution, it is critical to understand the relationship between the electrode properties and mass transport in electrode. Future material development and system optimization can benefit from this work. The properties of the carbon electrode can have a strong influence on the active species mass transport inside the cell. In Figure 1, the IR corrected polarization curves of positive and negative redox reactions on SGL 10AA and X-2 in VRFB are shown at varying electrolyte flow rates. The electrode materials were housed in a 5 cm2 battery hardware (Fuel Cell Technologies Inc.) with serpentine flow field. The electrolyte was composed of 1.7 M vanadium ions with 5 M total sulfate/bisulfate. The state of charge was maintained at 55% during the entire polarization curve measurement. In both reactions, the polarization curves show a typical mass transport limiting current density (iMT ) at high overpotential. In both reactions, higher iMT on 10AA indicates the better mass transport towards the surface of 10AA in the experimental scenario. X-2 is advantageous in reaction kinetics, since the activation overpotential is always lower on X-2 than 10AA in both reactions. However, the current density on 10AA generally surpasses that of X-2 at elevated overpotential. This trend should be attributed to better mass transport property of 10AA, though the detailed mechanism is not clear yet. We will present a thorough study of the mass transport properties of carbon paper electrode in VRFB cell. A systematic study of the physical properties and their influence on the convective and diffusive transport of redox active species within the electrode will be discussed. The transport study will be correlated to electrochemical test to develop a protocol to evaluate the mass transport properties’ influence on battery’s performance. This work is supported by Dr. Imre Gyuk, Office of Electricity Delivery and Energy Reliability, US Department of Energy. Reference: 1. M. H. Chakrabarti, N. P. Brandon, S. A. Hajimolana, F. Tariq, V. Yufit, M. A. Hashim, M. A. Hussain, C. T. J. Low, and P. V. Aravind, J. Power Sources, 253, 150–166 (2014) 2. A. M. Pezeshki, J. T. Clement, G. M. Veith, T. A. Zawodzinski, and M. M. Mench, J. Power Sources, 294, 333–338 (2015) 3. D. S. Aaron, Z. Tang, A. B. Papandrew, and T. A. Zawodzinski, J. Appl. Electrochem., 41, 1175–1182 (2011). Figure 1. IR corrected discharging polarization curves of negative and positive redox couple on SGL 10AA and X-2 in 5 cm2 FCT flow battery cell of varying flow rates with 1.7 M V2/3+/5 M bisulfate/sulfate electrolyte at 55% SoC. Figure 1

The vanadium redox flow battery (VRB) system involves complex multi-physical and multi-timescale interactions, where the electrolyte flow rate plays a pivotal role in both static and dynamic performance. Traditionally, fixed flow rates have been employed for operational convenience. However, in today’s highly dynamic energy market environment, adjusting flow rates based on operating conditions can provide significant advantages for improving VRB energy conversion efficiency and cost-effectiveness. Unfortunately, incorporating the electrolyte flow rate into conventional multi-physical models is overly complex for VRB management and control systems, as real-time operations demand low-computational and low-complexity models for onboard functionalities. This paper introduces a novel data-driven approach that integrates flow rates into VRB modeling, enhancing data processing capabilities and prediction accuracy of VRB behaviors. The proposed model adopts a gated recurrent unit (GRU) neural network as its fundamental framework, exhibiting exceptional proficiency in capturing VRB’s nonlinear voltage segments. The GRU network structure is carefully designed to optimize the predictive ability of the model, with flow rate considered as a crucial input parameter to account for its influence on VRB behavior. Model refinement involves analyzing well-designed simulation results obtained during VRB operations under various flow rates. Laboratory experiments were also designed and conducted, covering different conditions of currents and flow rates to validate the proposed data-driven modeling method. Comparative analyses were performed against several state-of-the-art algorithms, including equivalent circuit models and other data-driven models, demonstrating the superiority of the proposed GRU-based VRB model considering flow rates. Thanks to the GRU’s outstanding capability in processing time series data, the proposed model delivers impressively accurate terminal voltage predictions with a low error margin of no more than 0.023 V (1.3%) under wide operating ranges. These results indicate the efficacy and robustness of the proposed approach, highlighting the novelty and significance of accounting for flow rates in accurate VRB modeling for management and control system design.

Sensorless parameter estimation of vanadium redox flow batteries in charging mode considering capacity fading

Vanadium Redox Battery (VRB) has the advantages of large capacity, long life, safety and environmentally friendly. This paper proposes a double closed-loop charge-discharge control strategy of VRB based on cerebellar model arithmetic computer (CMAC) to ensure safe charge-discharge and shorten the charge-discharge time. The proposed control strategy consists of two main control loops: an outer voltage loop and an inner current loop. The outer control loop is designed as a voltage loop with CMAC controller which uses kernel voltage for feedback, and the inner current loop adopts PI regulator with amplitude limiting. In this paper, we first build a mathematical model of VRB of 5 kW/30kW· h. Then, the proposed control strategy and conventional PID control strategy are respectively applied to VRB model and comparisons are made. Results show that under the proposed control strategy, charging time of VRB shortened by 3.03%, discharging time of VRB shortened by 9.37% compared with conventional PID control strategy, and the terminal voltage can be guaranteed in a safe range, thus realizing fast and safe charge-discharge of VRB.

Numerical investigation on the dispersion effect in vanadium redox flow battery

Energy demand is increasing due to the world’s growing population and rising quality of life, accompanied by increasing CO2 emissions. A shift towards renewable energy sources like solar and wind is needed to sustainably meet our growing energy requirements. However, the intermittent nature of renewable resources creates the need for energy storage technologies, which would store excess energy and then supply this stored energy when it is needed. Pumped hydroelectric is the most used electrical energy storage method, but is limited to specific geographical regions, leading to a push towards development of redox flow batteries (RFBs). Despite the unique ability of RFBs to decouple energy and power density while having high current densities, their commercial viability is limited by high costs. In particular, All Vanadium Redox Flow Batteries (VRFBs, i.e., (VO2+/VO2 +//V2+/V3+)) have received much interest due to the use of the common element vanadium that removes the issue of cross-contamination, leading to higher Coulombic efficiencies. The sluggish kinetics of V2+/V3+ redox couple on the negative electrode (Reaction 1), however, is found to limit VRFBs efficiency.1 Thus, improving V2+/V3+ kinetics can lead to higher current densities, reducing the overall cost of energy storage. Studies indicate the V2+/V3+ reaction is an inner sphere electron transfer based on differences in activity on certain surfaces,2 but there is a lack of the mechanistic understanding needed to further improve rates. V2+→ V3+ + e‾ (Reaction 1) Eº = −0.255 V vs SHE Traditionally, VRFBs use porous graphite felts with sulfuric acid (H2SO4) as an electrolyte, often without accurate area estimates needed for obtaining normalized current densities. Recent studies have shown increased stability of V ions and higher energy capacities for mixed H2SO4 and HCl electrolytes,3 but the effect of electrolyte on kinetics is also not well understood. Here, we study the V2+/V3+ reaction kinetics on a controlled electrode surface in H2SO4 and HCl, and show that the kinetics increase with State of Charge (SoC) and in the presence of Cl-, where Cl- also changes the V3+ coordination shell as detected by UV-Vis. We use a polished glassy carbon disk as the reaction surface, with high conductivity and controlled electrochemical surface area as compared to graphite felts. We find the V2+/V3+ reaction rates are independent of the total vanadium ion concentration, but instead depend on SoC. SoC was estimated by deconvoluting the individual V2+ and V3+ concentrations from UV-Vis. Exchange current densities for oxidation (iO,oxidation ) decrease with decreasing SoC, whereas Tafel slopes for oxidation (boxidation ) remain constant with SoC. Rate measurements at varied temperature (23.3 – 40.0 °C) were conducted to evaluate effective activation energies (Ea ) for the V2+/V3+ reaction at different SoC by two independent measurements, a) iO,oxidation and b) Charge Transfer Resistance (Rct ). The two independent methods for determining Ea matched closely, and show that Ea increases with decreasing SoC (Figure 1). This dependence of Ea on SoC along with high magnitudes (42 – 44 kJ mol-1 for 50% SoC, as compared to ∼13 kJ mol-1 for the outer sphere ferri-ferrocyanide redox couple4) confirms V2+/V3+ is an inner sphere reaction. This variation of iO,oxidation and Ea with SoC is indicative of a mechanism involving an adsorbed V intermediate affecting reaction kinetics. We measure higher iO,oxidation in HCl compared to H2SO4, which we hypothesize is due to a change in the coordination shell of the reacting specie, leading to formation of a different transition state with lower Ea . V2+ and V3+ ions in pure water typically exist as [V(H2O)6]2+ and [V(H2O)6]3+ (Oh symmetry) respectively with six labile water molecules constituting their first coordination sphere.5 We use UV-Vis to determine the structure of the coordination shell with anions present, by a shift in peak locations (based on ligand field strength) and absolute absorbance (depicting changes in molecular symmetry). The V2+ UV-Vis spectra remained unchanged in H2SO4, HCl, and mixed acid electrolytes of varied concentrations, indicating [V(H2O)6]2+ was the dominant species, with no anions in the first coordination sphere. However, the UV-Vis spectra of V3+ had a shift in peak locations with reduced absolute absorbance in HCl relative to H2SO4, indicating formation of a different V3+ complex, which we hypothesize is related to the change in redox kinetics.

A study of the effects of electrolyte flow inside the tanks on electrical performance of an industrial-size Vanadium Redox Flow Battery (VRFB) is presented. The concentration of electrolytes feeding the stacks of VRFBs is crucial in determining the device voltage and overall power performance. Usually, the assumption of perfect mixing in the tanks is assumed, but the hydraulic behavior of large VRFB can deviate significantly from this assumption depending on the electrolyte flow rate, stochiometric factor and geometry of the tanks. In this study, the State of Charge (SoC) measurements have been analyzed, starting from the signal produced by an Open Circuit Voltage (OCV) cell. An experimental campaign has been conducted during charge/discharge roundtrip cycles at different current levels and constant stoichiometric factor. Building on the delay in the voltage response of the battery, a fluid-dynamic model was developed to study how the hydraulic behavior of electrolytes inside tanks influences the electrolyte concentration and, consequently, the SoC of the electrolyte that feeds the stack and the electrical time response of the battery. The model indicated that a stratification of charged electrolyte is responsible for this delay resulting in an initial voltage plateau. A different hydraulic behavior was found in each tank and in each charge/discharge phase. These results highlight the tank role in the industrial-scale VRFB performance. References Sanchez-Diez, E. Ventosa, M. Guarnieri, A. Trovò, C. Flox, R. Marcilla, F. Soavi, P. Mazur, E. Aranzabe, R. Ferret, “Redox flow batteries: status and perspective towards sustainable stationary energy storage”, J. Power Sources, 481, (2021) 228804.Kurilovich, A. Trovò, M. Pugach, K. J. Stevenson, M. Guarnieri. Prospect of Modeling Industrial Scale Flow Batteries – from Experimental Data to Accurate Overpotential Identification, Renew. Sust. Energ. Rev. 167, (2022) 112559.Trovò, V. Di Noto, J. E. Mengou, C. Gambaro, M. Guarnieri. Fast Response of kW-Class Vanadium Redox Flow Batteries, IEEE Trans. Sustain. Energy 12, (2021) 2413–2422.Trovò, M. Rugna, N. Poli, M. Guarnieri. Prospects for industrial vanadium flow batteries, Ceram. Int., 49 (14), (2023) 24487-24498.Maggiolo, A. Trovò, M. Guarnieri, “Reactant Flow in Flow Batteries”, in L. Cabeza (ed.), Encyclopedia of Energy Storage, vol. 4, pp. 231-242. Oxford: Elsevier. March 2022.A. Prieto-Díaz, S. E. Ibáñez, M. Vera. Fluid dynamics of mixing in the tanks of small vanadium redox flow batteries: Insights from order-of-magnitude estimates and transient two-dimensional simulations, Int. J. Heat Mass Transf. 216, (2023) 124567.Trovò, N. Poli, M. Guarnieri. New strategies for the evaluation of Vanadium Flow Batteries: testing prototypes, Cur. Opin. Chem. Eng. 37, (2022) 100853. Figure 1

Background: Remote mining operations in Western Australia are faced with the challenge of transitioning to renewable energy solutions to achieve net-zero carbon emissions by 2050. A promising strategy for these off-grid sites is to integrate wind and solar energy with battery storage systems, reducing their reliance on fossil fuel-based energy sources like natural gas turbines. Objectives: This study investigates the feasibility of using two types of battery energy storage system – Lithium-Ion (Li-ion) and Vanadium Flow Batteries (VFB) – in off-grid Western Australian mine sites to achieve the net-zero emissions reduction target. Li-ion batteries possess the advantages of higher energy density, higher efficiency and widespread commercial availability whilst VFBs offer scalability, long cycle life and inherent safety features. Methods: A microgrid model was developed using HOMER (Hybrid Optimization of Multiple Energy Resources) Pro version 3.17.1. Key economic parameters – including the capital, operations and maintenance costs of wind turbines, photovoltaic panels, natural gas turbines, converters and batteries – were integrated into the model. Results: For each storage configuration, the simulation results which yielded the lowest discounted cash flows relative to a configuration in which only natural gas turbines were used to meet 100% of the projected load may be seen in Figure 1. The 4-hr Li-ion batteries (80% DOD) had the lowest initial capital costs for both the 0% and 10% capacity shortage simulations of all cases which met the minimum renewable fraction criteria. This was because of the higher round trip efficiency of the Li-ion batteries when compared to VFBs and the high DOD when compared to the 60% DOD Li-ion simulations. These factors resulted in fewer MWh of 4-hr Li-ion packs being needed to meet the projected load. However, the 80% DOD also resulted in the Li-ion batteries needing to be replaced more frequently than the 60% DOD Li-ion batteries, as shown by the sudden drops in the Total Discounted Cash Flow plot. By the end of the 20-year simulation period, the configurations supported by 10-hour duration VFBs yielded the highest cash flow increase due to their longer lifespan.Figure 1. Cumulative cash flow over a 20-year period for a Western Australian mine site microgrid implementing Li-ion batteries and VFBs.All storage options dramatically reduced the levelised cost of energy (LCOE) when compared to the ‘No Storage’ configurations, as shown in Table 1. This was due to a greater amount of solar and wind power generation being required when no storage was present, as shown in the Total Power Capacity results in Figure 1. These results also revealed that when storage was present, the simulations which produced the lowest net present cost had no wind power generation. This was due to a significant overlap in the periods of peak wind and solar generation in the region and the relatively low projected cost of solar generation. The results also showed that allowing a capacity shortage of 10% dramatically reduced the LCOE and cumulative costs associated with each storage type; however, further analysis is needed to assess the impact of shutting down the mine site during these shortage periods.Table 1. Levelized cost of energy associated with each storage configuration over the twenty-year simulation period. System Levelized Cost of Energy (AUD/kWh) 0% Capacity Shortage 10% Capacity Shortage Natural Gas Turbines Only (0% Renewable Fraction) 0.095 0.089 Solar + Natural Gas Turbines + Wind + No Storage (50% Renewable Fraction) 0.180 0.143 Solar + Natural Gas Turbines + 4-hr Li-Ion Packs (60% DOD) (50% Renewable Fraction) 0.124 0.112 Solar + Natural Gas Turbines + 4-hr Li-Ion Packs (80% DOD) (50% Renewable Fraction) 0.119 0.109 Solar + Natural Gas Turbines + 4-hr VFB Packs (80% DOD) (50% Renewable Fraction) 0.108 0.101 Solar + Natural Gas Turbines + 10-hr VFB Packs (80% DOD) (50% Renewable Fraction) 0.109 0.099 Figure 1

Practical and commercial issues in the design and manufacture of vanadium flow batteries

Photoangulator