Efficiency Of Vanadium Redox Flow Battery Research Articles

The study of energy filtering management process for microgrid based on the dynamic response model of vanadium redox flow battery

For the efficient application of vanadium redox flow battery (VRB) in microgrid containing the clean renewable energy and advanced coal-fired power system such as the supercritical carbon dioxide (S-CO2) Brayton cycle power plant, a feasible energy filtering optimization process is proposed in this paper. A coupled dynamic response model of VRB and an optimized load distribution algorithm are covered in the process. First, the Ustack-Ibattery-SOC curves are fitted based on the coupled calculation model of VRB. The equivalent resistance of the simplified equivalent circuit model is further calculated. The dynamic response model is refined for the fast calculation of real-time efficiencies. Second, a basic operation scheme and an optimized operation scheme based on the moving average filtering method are selected as the load distribution algorithms. An energy filtering optimization management process that includes a configuration optimization design part and a load distribution part is further constructed. Finally, a case application is carried out to verify the feasibility of the proposed energy management process. The relevant results are presented as follows. First, the combination of the experimental data and the fitted curves can be used to calculate the equivalent resistance of the dynamic response model. The maximum Ustack of 86.14 V is obtained at the SOC of 0.99 and Ibattery of 10A when charging. Second, when applying the optimized operation scheme, the time average efficiency of VRB is operating at an efficient level of 82.75%. The change frequency of load command for each equipment and its dynamic response characteristic can be well matched. Finally, compared to the case where the basic operation scheme is selected in the experimental system, the time average efficiency of VRB is increased from 69.50% to 82.13%., the time average efficiency of S-CO2 power plant is increased from 39.79% to 40.02%. The application of energy filtering optimization management process for the actual microgrid is feasible. The study can provide the operation scheme and case application for VRB energy storage system in the actual microgrid.

The configuration optimized design method based on real-time efficiency for the application of vanadium redox flow battery in microgrid

To realize the efficient, economical and stable operation of vanadium redox flow battery (VRB) in a microgrid containing a high proportion of renewable energy, a coupling calculation model is constructed and a configuration optimized design method is proposed in this paper. First, the coupling calculation model involving the fluid mechanics model and electrochemistry model is established to obtain the real-time efficiency of VRB. Second, an economic model of VRB is constructed considering the investment costs, operation costs, economic benefits and renewable energy utilization. Finally, a configuration optimized design method based on typical load and real-time efficiency is further proposed to cope with practical application scenarios. Two different objectives, including the lowest average daily cost and the lowest renewable energy curtailment, are selected in the method. The results are presented as follows. First, the energy efficiency of the battery is increased from 76.90% to 80.45% with the increase of electrolyte flow rate. With the optimal selection of porous electrode porosity, the merit energy efficiency and system efficiency are presented. Better VRB performance can be obtained at the electrolyte flow rate of 120 ml/min and the porous electrode porosity of 0.93. Second, the novel proposed configuration design method can be implied to improve the renewable energy consumption capacity while ensuring system economics. Finally, with the lowest average daily cost as the objective, the optimal configuration of VRB is 891 kW and 7344 kWh, respectively, while the time average efficiency is 79.26%. The total amounts of renewable energy curtailment in one day decreases from 12,380 kWh to 6,281 kWh. At the same time, the power supply quality is significantly improved after accessing various distributed energy sources to the microgrid.

Antimony-decorated graphite felt electrode of vanadium redox flow battery in mixed-acid electrolyte: Promoting electrocatalytic and gas-evolution inhibitory properties

• The shift of electrode gas-evolution potential by antimony. • Utilizing the electrocatalytic properties of antimony in stabilizing the electrode. • Improving vanadium redox flow battery efficiency by facilitating redox reactions. Facilitation of redox reactions and inhibition of gas evolution in the graphite felt electrode of vanadium redox flow battery (VRFB) is investigated by adding antimony ions to the electrolyte. The electrolyte is used as a mixture of sulfuric acid and hydrochloric acid to stabilize the vanadium ion. Antimony has quasi-reversible reactions prior to the electrochemical reactions of vanadium ion pairs. In general, as shown by the results of scanning electron microscopy, metallic antimony is decorated on the surface of graphite felt during charge–discharge cycles. The results of full-window cyclic voltammetry indicate an increase in the cyclic stability of samples containing antimony, especially at a concentration of 7.5 mM. This is due to the electrocatalytic properties of antimony and the facilitation of vanadium electrochemical reactions. Ease of reactions is also closely related to the improvement of vanadium ion diffusion coefficients in samples containing antimony. The reduction peak of V 3+ to V 2+ in the bare sample practically disappears after a few cycles, which is due to the superiority of hydrogen gas evolution. Linear sweep voltammograms confirm the effectiveness of antimony in shifting the potential position of hydrogen and oxygen evolution. Wettability and contact angle tests show more water adsorption by antimony-decorated graphite felts compared to the bare one which has a direct effect on improving the performance of the electrodes. Although antimony is added to anolyte in VRFB and has the most beneficial effect on the negative electrode, antimony cross-contamination does not have a bad effect on positive electrode performance and even it also stabilizes the reduction–oxidation currents ratio on positive electrode based on cyclic voltammetry results. In general, the presence of antimony increases all three types of coulombic, voltage, and energy efficiency in VRFB.

Synchrotron X-Ray radiography of vanadium redox flow batteries – Time and spatial resolved electrolyte flow in porous carbon electrodes

A porous carbon electrode fully saturated with electrolyte is one crucial aspect of vanadium redox flow battery efficiency. It determines the electrochemically active surface area, provides more active sites for the reaction during operation, and prevents local degradation due to inhomogeneities in electrolyte distribution. We investigate the electrolyte invasion and distribution at open-circuit potential in heat-treated carbon felt electrodes at varying compression ratios and flow field configurations, using synchrotron X-ray radiography. The quantitative analysis yields time-resolved saturation values of the injection and resolves local changes in saturation to detect areas of lower electrolyte accessibility. Compression ratios of 50% and above lead to a high electrode utilization with more than 97% saturation over the felt thickness. In contrast, carbon felts at 25% and 17% compression only reach 49% and 15% saturation near the flow fields. However, increasing the flow velocity after the injection causes the boundary area next to the flow field to fill even at low compressions. This area is especially critical for the electrode utilization since it is invaded after the bulk. Depending on the compression level, it does not reach full saturation.

Numerical investigation on the dispersion effect in vanadium redox flow battery

• An reactive transport model considering dispersion effect for VRFBs is reported. • The related parameters effected by dispersion are determined accurately. • The model is employed to analyze the performance characteristics of VRFBs. The vanadium redox flow battery (VRFB) is a promising energy-storage technology for the power supply from intermittent renewable energy sources. An understanding of the characteristics of coupled mass transport and electrochemical reactions in a VRFB is of great importance for increasing the storage capacity and improving the efficiency. However, the dispersion effect in the porous electrode of VRFBs has been ignored in existing modelings. This paper reports on an reactive transport model considering dispersion effect for VRFBs, and the model is developed based on a comprehensive description of mass, charge, and momentum transport and conservation in porous electrodes and combined with a kinetic model for electrochemical reactions. In particular, considering the influences of dispersion on the reactive transport behaviors, the effective diffusivities of ions and the local mass transfer coefficient are accurately determined by experiments wherein the dispersion effect included. A good agreement is demonstrated between the simulated cell performance and experimental data over the full range of the state of charge (SOC). Compared with the results resolved from using the effective diffusivity as Bruggemann correction, the cell voltages have little discrepancies while the distributions of vanadium ions concentrations and local current density show obvious differences. The model is then employed to analyze the performance characteristics of VRFBs and to investigate the effects of various operating conditions and structural parameters on the cell performance and system efficiency. The numerical results allow us to identify the key areas of potential improvements to the storage capacity and efficiency of VRFBs.

Enhancing the vanadium redox flow battery efficiency by adjusting the electrode configuration

The vanadium redox flow battery (VRFB) is being investigated as one of the promising candidates for large-scale energy storage systems. In the present work, the role of electrode shape on a single VRFB cell performance has been studied through a 3D numerical model. The model accounts for the coupling between electrochemistry and fluid mechanic physics. Seven cases of electrode configurations at the same volume size (10 cm3) have been simulated to investigate the overall battery performance. Results from the simulation show that the configuration (case 7) has the best battery efficiency, while the worse one is (case 4) under the same operating conditions, e.g., 71.72% and 63.82%, respectively. Also, the ratio of output to input power for (case 7) is 0.72, while 0.63 for (case 4). In addition, there is an optimal flow rate for each case to get maximum battery efficiency, which means a balance between electrochemical reactions and pumping losses is required. Overall, adopting a thicker electrode (cases 2, 3 and 4) results in lower battery performance due to the poor voltage responses. One feature of the introduced model is its capability to predict the performance of most flow batteries cell configurations.

Carbon sheet-decorated graphite felt electrode with high catalytic activity for vanadium redox flow batteries

A carbon sheet-decorated graphite felt electrode was synthesized by in situ polymerization and subsequent high-temperature calcination under an inert atmosphere. The resultant material brings an improved wettability, numerous defect sites, and abundant O, N and P elements as additional catalytic sites to elevate the reaction kinetics and efficiency of vanadium redox flow batteries (VRFBs). The unique CS modifier enriches electrolyte diffusion pathways, which even show a unique capillary flow. The GF@CS displays a high catalytic activity towards the VO2+/VO2+, V3+/VO2+ and V2+/V3+ oxidation-reduction couples and a reduced cathodic and anodic peak potential difference of 355 mV (vs. 564 mV for GF). The improvement to the electrode results in a GF@CS-based battery presenting an increased capacity of 20.8 Ah L−1 compared to 13.0 Ah L−1 of the GF-based battery and an increase in power density from 225 mA cm−2 to 300 mA cm−2. Furthermore, the battery exhibited a 74.79% energy efficiency (EE) at 150 mA cm−2, with no attenuation even at 300 cycles. GF@CS greatly elevates the reaction kinetics and efficiency of VRFBs.

Application of flexible integrated microsensor to internal real-time measurement of vanadium redox flow battery

The temperature distribution and vanadium flow rate distribution in the vanadium redox flow battery are the key to its performance. The reaction process in the vanadium redox flow battery is very complex, in the course of power generation, the uniformity and expendability of vanadium liquid distribution will result in nonuniform temperature distribution. Local high temperature will accelerate the ions through the membrane material, the vanadium electrolyte concentration decreases obviously, so that the overall generating efficiency of vanadium redox flow battery is influenced. On the other hand, under the limitation of low flow rate, the waste heat generated by vanadium redox flow battery is unlikely to be carried away by the flow field, so that the internal temperature of vanadium redox flow battery rises. On the contrary, in the condition of high flow rate, the waste heat in the vanadium redox flow battery dissipates rapidly, the temperature is low, the vanadium redox flow battery efficiency is increased slightly, proving that the flow control is also important to the vanadium redox flow battery performance. However, the authentic information inside the vanadium redox flow battery cannot be obtained accurately and instantly by outside, theory and simulation at the present stage. Therefore, according to the requirement for technical application of internal real-time microscopic diagnosis to vanadium redox flow battery, this study proposes using micro-electro-mechanical systems technology to develop a flexible integrated (temperature and flow) microsensor embedded in the vanadium redox flow battery for real-time measurement. The advantages of this technology include: (1) compactness; (2) flexible measurement position and accurate embedding and (3) accurate measurement, high sensitivity and quick response.

Optimal Sizing of Vanadium Redox Flow Battery Systems for Residential Applications Based on Battery Electrochemical Characteristics

The penetration of solar photovoltaic (PV) systems in residential areas contributes to the generation and usage of renewable energy. Despite its advantages, the PV system also creates problems caused by the intermittency of renewable energy. As suggested by researchers, such problems deteriorate the applicability of the PV system and have to be resolved by employing a battery energy storage system (BESS). With concern for the high investment cost, the choice of a cost-effective BESS with proper sizing is necessary. To this end, this paper proposes the employment of a vanadium redox flow battery (VRB), which possesses a long cycle life and high energy efficiency, for residential users with PV systems. It further proposes methods of computing the capital and maintenance cost of VRB systems and evaluating battery efficiency based on VRB electrochemical characteristics. Furthermore, by considering the cost and efficiency of VRB, the prevalent time-of-use electricity price, the solar feed-in tariff, the solar power profile and the user load pattern, an optimal sizing algorithm for VRB systems is proposed. Simulation studies are carried out to show the effectiveness of the proposed methods.

Optimal operating strategy and revenue estimates for the arbitrage of a vanadium redox flow battery considering dynamic efficiencies and capacity loss

Vanadium redox flow batteries (VRBs) are a promising solution to facilitate the expansion of intermittent renewables. The efficiency of VRBs is dynamically dependent on the instantaneous operating states, including the output power level and state of charge (SOC). In addition, VRB capacity fades over long-term cycling and thus might limit the market revenue. Modelling these two factors would assist deciding better operating strategy, enhance and more precisely evaluate the economics of VRBs. This study establishes an operation optimisation model that integrates the characteristics of the dynamic efficiency performance and the capacity loss of VRBs. First, the dynamic efficiency functions of the operating states are transformed into VRB power functions using a fitting technique to be compatible with the operation optimisation model and reduce the computational complexity. The VRB power functions are then embedded into the operation optimisation model, which decides the optimal charge-discharge schedule of VRBs to maximise the revenue. The capacity loss model is also implemented to estimate the revenue decrease caused by capacity loss, which could help decide the preventive measures and capacity restoration from an economic perspective. The validity of the proposed model is demonstrated by case study results based on the market prices of ERCOT in 2014.

Study of Transient Behavior of Vanadium Redox Flow Battery at Varying Flow Rates and States of Charge

The Vanadium Redox Flow Battery (VRB) is one promising candidate for grid type storage because of its long life time, modularity, active thermal management, and good cycle life. There are various parameters that affect the performance of VRB for example: temperature, flow rate, state of charge etc. Flow rate is an important parameter, since the electrolyte flow rate influences the reaction rate of the vanadium ions. It is also important because it has a substantial influence on the system efficiencies.Ma et al. [1] investigated the effect of flow rate on the system capacity and the efficiency. Fetlawai [2] investigated the effect of flow rate on the charge-discharge characteristics and on the gas evolution. It was established that flow rate is one of the important parameters which should be controlled to obtain high efficiency of VRB. The effect of the flow rate on the transient behavior of the battery has not got much attention which motivated this study.We will present experimental results on the transient behavior of a VRB at various flow rates up to ca. 1 L/min. The battery was at 80% state of charge during experiment. It was observed that flow rate has a strong effect on the transient behavior of the battery (a typical examples is shown in Fig. 1). The load of the battery was varied in a regime typical for applications of VRBs. The results showed clear trends of the transient behaviour of the battery with changes of flow rate. The implications of these findings for the development of control systems in grid energy storage system design with VRBs will be discussed.[1] X. Ma, H. Zhang, C. Sun, Y. Zou, and T. Zhang, “An optimal strategy of electrolyte flow rate for vanadium redox flow battery,” J. Power Sources, vol. 203, pp. 153–158, Apr. 2012.[2] H. A.-Z. A.-Y. Al-Fetlawi, “Modelling and simulation of all-vanadium redox flow batteries.” 14-Apr-2011.[3]J. Chahwan, C. Abbey, and G. Joos, “VRB Modelling for the Study of Output Terminal Voltages, Internal Losses and Performance,” 2007 IEEE Canada Electr. Power Conf., pp. 387–392, Oct. 2007.

Development of nitrogen-doped carbons using the hydrothermal method as electrode materials for vanadium redox flow batteries

Nitrogen-doped carbons are suggested as electrochemically active materials for V(IV)/V(V) redox couples for a vanadium redox flow battery (VRB). These materials were synthesized using a hydrothermal reaction of aqueous glucose solution in the presence of ethylenediamine as a nitrogen source. The physical and electrochemical properties of the nitrogen-doped carbons are characterized by cyclic voltammetry, high-resolution transmission electron microscopy and X-ray photoelectron spectrometry. These results reveal that the hydrothermal method is an effective way to synthesize high-content nitrogen-doped carbons. Nitrogen doping significantly improves catalytic activity and reversibility. Therefore, use of nitrogen-doped carbon is expected to increase the energy storage efficiency of VRBs.

Synthesis and characteristics of aminated vinylbenzyl chloride-co-styrene-co-hydroxyethyl acrylate anion-exchange membrane for redox flow battery applications

We have synthesized a VBC-co-St-co-HEA copolymer using 4-vinylbenzyl chloride (VBC), styrene (St), and 2-hydroxyethyl acrylate (HEA) in order to manufacture anion-exchange membranes for all vanadium flow battery. Through the quaternarization and crosslinkage of vinylbenzyl chloride-co-styrene-co-hydroxyethyl (VSH) copolymer, anion-exchange membranes of the aminated VBC-co-St-co-HEA (AVSH) were manufactured. In order to find out the variation of the degree of crosslinking according to the amount of adipic acid as a crosslinking agent and to confirm the structure of the VSH and the AVSH copolymer, Fourier transform infrared (FT-IR) analysis was conducted, and also Differential scanning calorimetry (DSC) analysis was conducted in order to find out their thermal properties. The water uptake, anion-exchange capacity, electric resistance, and ionic conductivity of the AVSH anion-exchange membrane and the efficiency of an all vanadium redox-flow battery containing such an AVSH anion-exchange membrane were measured. The maximum water uptake, maximum anion-exchange capacity, the electric resistance, swelling and ionic conductivity of the AVSH anion-exchange membrane were 40.2%, 1.18meq/g, 1.9Ωcm2, 7.36% and 0.00351S/cm, respectively. All vanadium redox-flow battery efficiency was measured and charge–discharge, voltage, energy efficiency were 95.2%, 74.9%, 75.3% and 89.6%, respectively.

Vanadium Redox Flow Battery Efficiency and Durability Studies of Sulfonated Diels Alder Poly(Phenylene)s

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Vanadium redox flow battery efficiency and durability studies of sulfonated Diels Alder poly(phenylene)s

Sulfonated Diels Alder poly(phenylene) (SDAPP) was examined for vanadium redox flow battery (VRFB) use. The ion exchange capacity (IEC) was varied from 1.4, 1.6 and 2.0meq/g in order to tune the proton conductivity and vanadium permeability. Coulombic efficiencies between 92 to 99% were observed, depending on IEC (lower IEC, higher coulombic efficiencies). In all cases the SDAPP displayed comparable energy efficiencies (88–90%) to Nafion 117 (88%) at 50mA/cm2. Membrane durability also was dependent on IEC; SDAPP with the highest IEC lasted slightly over 50cycles while SDAPP with the lowest IEC lasted over 400cycles and testing was discontinued only due to time constraints. Durability screening tests were initialed with SDAPP, by soaking films in a 0.1MV5+ and 5.0M total SO4−2 solution. The rate of degradation was also proportional with IEC; the 2meq/g sample dissolved within 376h, the 1.6meq/g sample dissolved after 860h, while the 1.4meq/g sample broke apart after 1527h.

Energy Efficiency of Vanadium Redox-Flow Battery: Dependence on Concentration and Charge Density

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