Redox Flow Battery Energy Storage Research Articles

Design of A Two-Stage Control Strategy of Vanadium Redox Flow Battery Energy Storage Systems for Grid Application

The low energy conversion efficiency of the vanadium redox flow battery (VRB) system poses a challenge to its practical applications in grid systems. The low efficiency is mainly due to the considerable overpotentials and parasitic losses in the VRB cells when supplying highly dynamic charging and discharging power for grid regulation. Apart from material and structural advancements, improvements in operating strategies are equally essential for achieving the expected high-performance VRB system, although an optimized solution has not been fully exploited in the existing studies. In this paper, a two-stage control strategy is thus developed based on a proposed and experimental validated multi-physics multi-time-scale electro-thermo-hydraulic VRB model. Specifically, in the first stage, the optimal flow rate of the VRB is obtained based on online optimization to reduce parasitic loss and enhance instantaneous system efficiency, and the result serves as the set point of a feedback flow rate controller. In the second stage, dual time scales are specifically considered. And the current and flow rate controllers are designed to meet the highly varying power demands for grid-connected applications. The effectiveness of the proposed control strategy is verified under a scenario to smooth wind power generation. Comparative studies show that compared to the prevailing approaches, higher efficiency can be achieved in tracking the theoretical optimal power profiles for online battery control.

Solar PV driven hybrid gravity power module—Vanadium redox flow battery energy storage for an energy efficient multi‐storied building

This article presents an innovative perspective of using a gravity energy storage system namely gravity power module (GPM) around a multi-storied building. Two number of GPMs have been vertically fixed around the walls of a multi-storied building and have not been placed underground following the traditional way. The grid-connected proposed hybrid system consisting of solar PV, GPMs and vanadium redox flow battery is focused to supply the maximum possible amount of an essential load of a high-riser, through renewable energy. All of the storage systems are charged through solar PV. Whereas, the grid is used, to procure energy for the unmet load demand and sell the excess renewable energy. Results simulated for each month following seasonal load variation show that net energy supplied by the hybrid system is 99% of the full load demand of essential equipment of the building for the month of February and 90% to 91% for the month of January, November and December. During all the months, the supply of gravity energy storage is restricted to supply within the 18th to 24th hour to reduce the peak demand of the grid. The gravity energy storage is also considered as the primary storage system during those intervals. The yearly average of energy supply from the renewable resource in the proposed system toward the building load is found to be 47.77%. While considering the renewable energy sale toward the grid along the load supply of the building the yearly average of renewable energy penetration becomes 48.89%.

Optimal allocation of vanadium redox flow battery energy storage systems in active distribution networks considering multiple operation strategies

Optimal allocation of vanadium redox flow battery energy storage systems in active distribution networks considering multiple operation strategies

Study on operating conditions of household vanadium redox flow battery energy storage system

A 10 kW household vanadium redox flow battery energy storage system (VRFB-ESS), including the stack, power conversion system (PCS), electrolyte storage tank, pipeline system, control system, etc., was built to study the operation conditions. The VRFB-ESS has been run at different current density. And the system performance was further studied, including system charge & discharge energy, stack polarization voltage, the energy consumption of each unit etc. The experimental results showed that when running at 74 A (current density 150 mA·cm−2), the energy storage system can charge 24.9 kWh and discharge 15.2 kWh, with a system efficiency of 61.0%. While the system energy consumption accounts for 39%, of which 6.03% is consumed by the pump, 10.99% by the PCS, 16.26% by the internal resistance of the stack, 4.66% by the pipeline, and 1.06% by the control system. stack has good stability, and the temperature of the system only rises 1.6 ℃. The experiment provides effective data support for the subsequent improvement of system performance.

Study on energy loss of 35 kW all vanadium redox flow battery energy storage system under closed-loop flow strategy

A large all vanadium redox flow battery energy storage system with rated power of 35 kW is built. The flow rate of the system is adjusted by changing the frequency of the AC pump, the energy efficiency, resistance, capacity loss and energy loss of the stack and under each flow rate is analyzed. The energy efficiency of the system is calculated by combining with the pump loss. The results show that with the increase of flow rate, the energy efficiency of the stack is improved and the stack resistance is reduced, but pump loss increases greatly. At 180 mA•cm−2 current density and 110 L/min flow rate, the energy efficiency of the stack reached 77.10% and the system reached 69.49%. In the battery system, the loss of resistance energy accounted for 80.27% of the total energy consumption, and the pipeline and transfer energy loss accounted for 18.73%. Therefore, reducing the energy consumption of the pump and reducing the energy loss of the resistance in the system are very important for improving the energy efficiency of the all vanadium redox flow battery energy storage system.

Research on All-Vanadium Redox Flow Battery Energy Storage Device Based on Energy-Saving and Environmentally-Friendly New Energy Power Station Interface Technology

In the context of energy conservation and environmental protection, new wind energy power generation has obvious random, intermittent, uncontrollable and anti-peak-shaving characteristics. The large-scale grid connection of wind power has brought grid peaking and stable and safe operation the huge pressure has caused more serious wind curtailment and power rationing, which has seriously affected the effective use of wind resources and economic benefits. Under the dispatch of the energy management system, the all-vanadium redox flow battery energy storage power station smooths the output power of wind power generation, and cooperates with the wind farm power forecast system to improve the wind farm tracking planned power generation capacity and improve the grid-connected power quality of the wind farm. Based on this, the thesis studied the external operating characteristics of the all-vanadium flow battery (VFB) energy storage system, and carried out the modeling and simulation of the energy storage system (ESS) based on the electrochemical properties of the VFB. Systematically analyse the actual operating data of the energy storage system and evaluate the impact of its overload operation on dispatch control, and fit key parameters such as state of charge (SOC), electromotive force and equivalent resistance, and obtain functional relationships.

Optimal configuration of the energy storage system in ADN considering energy storage operation strategy and dynamic characteristic

To meet the needs of energy storage system configuration with distributed power supply and its operation in the active distribution network (ADN), establish the dynamics of the all-vanadium redox flow battery energy storage system (BESS). On this basis, an energy storage operation of ADN strategy is proposed to stabilise the power fluctuation of the system. The energy storage configuration model with optimising objectives such as the fixed cost, operating cost, direct economic benefit and environmental benefit of the BESS in the life cycle of the energy is constructed, and the energy storage installation capacity, power and installation position are used as decision variables, which are solved by the dynamic programming algorithm. On the basis of case 33 and case 69 node examples and typical daily load and distributed generations output curve, the simulation analysis is carried out to obtain the optimal configuration result. At the same time, the system tie-line power and the dynamic characteristics of the energy storage system before and after the installation of the energy storage device are obtained. The simulation results show the validity of the model.

(Invited) 100MW Class Vanadium Flow Battery Project Plan in China

With the rapid development of modern society and industries, the resource depletion and environmental problems caused by the large amount of energy consumption are imminent.Although new energy is a solution to power shortage, the discontinuity and instability causes serious energy waste. Large-scale energy storage technology has received remarkable achievements in solve energy waste problems, which has attracted the attention of various countries. Vanadium redox flow battery is considered as an ideal large-scale energy storage technology because of its long cycle life, fast reaction, high conversion efficiency and reliable safety. This paper takes China, one of the major new energy markets, as an example. It introduces the plan of China on large-scale 100MW-class vanadium redox flow battery energy storage projects in the coming future, and specifies on Zaoyang 3MW/12WMh energy storage project, which is the pioneer project of 100MW-class energy storage project in Wuhan, Hubei Province, China..

An Enhanced Equivalent Circuit Model of Vanadium Redox Flow Battery Energy Storage Systems Considering Thermal Effects

Thermal issue is one of the major concerns for safe, reliable, and efficient operation of the vanadium redox flow battery (VRB) energy storage systems. During the design of the operational strategy for a grid-connected VRB system, a suitable mathematical model is needed to predict the dynamic behaviors under various operating conditions. However, conventional VRB models usually neglect the impact of temperature variations on system performance. This work develops an enhanced VRB model with the consideration of the coupling effects between the electrochemical and the thermal behaviors. The proposed model consists of two equivalent circuits. First, the electrochemical behaviors of the VRB are modeled by a second-order RC network taking account of the effects of concentration variation of the vanadium ions and the electrochemical activation. Second, a third-order Cauer network is used to model the heat transfer process in the VRB system, and the dynamic thermal behaviors of stacks, pipes and heat exchangers are characterized. Well-designed experiments and particle swarm optimization algorithm are use to identify the parametric values of the developed model. The proposed modeling method was validated experimentally using a 5kW/3kWh VRB platform, and the results show that the model is capable of accurately predicting the VRB performance under variable temperature conditions. The developed coupled electro-thermal model is then used for simulating and analyzing the performance of a VRB system operated in conjunction with a wind power plant under real-world conditions.

High electro-catalytic graphite felt/MnO2 composite electrodes for vanadium redox flow batteries

A mild and simple synthesis process for large-scale vanadium redox flow batteries (VRFBs) energy storage systems is desirable. A graphite felt/MnO2 (GF-MNO) composite electrode with excellent electrocatalytic activity towards VO2+/VO2+ redox couples in a VRFB was synthesized by a one-step hydrothermal process. The resulting GF-MNO electrodes possess improved electrochemical kinetic reversibility of the vanadium redox reactions compared to pristine GF electrodes, and the corresponding energy efficiency and discharge capacity at 150 mA cm − 2 are increased by 12.5% and 40%, respectively. The discharge capacity is maintained at 4.8 A h L − 1 at the ultrahigh current density of 250 mA cm − 2. Above all, 80% of the energy efficiency of the GF-MNO composite electrodes is retained after 120 charge-discharge cycles at 150 mA cm − 2. Furthermore, these electrodes demonstrated that more evenly distributed catalytic active sites were obtained from the MnO2 particles under acidic conditions. The proposed synthetic route is facile, and the raw materials are low cost and environmentally friendly. Therefore, these novel GF-MNO electrodes hold great promise in large-scale vanadium redox flow battery energy storage systems.

Voltammetric and Impedance Investigation of Vanadium Oxidation States in Sulfuric Acid

Redox flow battery is a system in which energy is derived from electrochemical reaction of a pair of solutions, of which one is reduced and the other is oxidized during discharge; the opposite process then takes place during charging. One such system is based on solutions of vanadium in several states dissolved and supported by SO4 2-anion in sulfuric acid. In principle, the starting material for both the positive and negative electrode electrolyte is identical, therefore, mixing of the two solutions through leakage or accident will lead to discharge, but not to chemical degradation of the stock material. Therefore, vanadium redox flow cells enjoy lot of attention in the energy storage industry. Our aim was to carry out more fundamental studies of the redox processes on graphite electrodes in solutions of vanadium salts. The experimental setup was using a rotated disk electrode and voltammetric, and impedance measurements were performed. Data obtained from impedance measurements enjoy lot of attention in electrochemical studies, because they provide wealth of information relevant to static, as well as dynamic, parameters of the system. The nature of proper impedance data collection (and successful interpretation) requires that the data be collected while the system under observation is stable, at equilibrium, although the equilibrium can be static, as well as dynamic. With this requirement in mind, and also due to some complexity, most impedance analyzers (or their software) will not perform other task while impedance data are taken. However, with fast instrumentation, slow change in bias polarization, deemed sufficiently benign to operate at a (pseudo)equilibrium of the system, should allow impedance data collection as a function of the bias potential. We present here data taken with Solartron ModuLab setup, which we programmed to perform extremely slow potential scans, and to collect simultaneously impedance data. A control study was performed on potassium hexacyanoferrate (II)in potassium nitrate solution; a classical redox couple. The electro-chemical experiment performed was cyclic voltammetry on a rotated disk electrode and voltammetry of vanadium(IV) in sulfuric acid. This is a system relevant to the redox flow battery energy storage system. A rather slow voltammetric scan (1 mV/s), coupled with rapid data collection using the multi-sine impedance function, was successfully used to collect impedance data without distortion caused by the changing voltage bias during the voltammetric scan. While the instrument facilitates collection of the data series as described, it does not have a built in data processing that would allow sequential evaluation of all the impedance data series collected. We have developed such an evaluation routine and we are presenting, for the first time, detailed impedance data results running in parallel with the data for voltammetric measurements. Impedance evaluation usually relies on fitting the data to a suitable equivalent circuit. Attached file is an example shoving variation of one model resistor in the circuit in response to the applied potential. Figure 1

The Control Strategy of VRB-ESS for Wind Power

【Aiming at the application of Vanadium Redox-Flow Battery Energy Storage System (VRBESS) on wind power, this paper studied on the control strategy of BESS under the different time scale. Firstly, the paper introduced the operation mode of BESS under different working condition and the judgment principle for operation mode switch, which based on the comprehensive characteristics of wind power prediction, SOC of BESS and control objective of wind power-BESS. According to the technical requirements, the control strategy of BESS was presented, namely smooth control based on ultra-short-term wind power prediction. The smooth control works on smooth the rapid fluctuation of power output from wind farm with time scale 0-15min, it is very helpful to improve the power quality of wind power and reduce the influence from wind power on the frequency regulation capability of power system. Lastly, by means of simulation, the control strategy was applied to a study wind farm to verify the effectiveness.】

05/01567 Possible use of vanadium redox-flow batteries for energy storage in small grids and stand-alone photovoltaic systems

05/01567 Possible use of vanadium redox-flow batteries for energy storage in small grids and stand-alone photovoltaic systems

Possible use of vanadium redox-flow batteries for energy storage in small grids and stand-alone photovoltaic systems

The all-vanadium redox-flow battery is a promising candidate for load leveling and seasonal energy storage in small grids and stand-alone photovoltaic systems. The reversible cell voltage of 1.3 to 1.4 V in the charged state allows the use of inexpensive active and structural materials. In this work, studies on the performance of inexpensive active materials for use in vanadium redox-flow batteries are reported. Additionally, a cost analysis for a load leveling and a seasonal energy storage system is given based on a flow battery technology well established in Zn-flow batteries.