Vanadium Redox Flow Batteries: Characteristics and Economic Value

Nowadays, the decarbonization of the global and national economies by shifting from using fossil energy sources to using renewable energy sources represents an upward trend. The greatest potential has wind and photovoltaic sources, which are characterized by intermittency and unpredictability due to the intermittent nature of wind speed and solar irradiance. Thus, the main challenge for the integration of variable renewable energy sources (VRESs) into existing power systems is the gap between the electricity load of final users and the electricity generation of VRES. The main solutions for this challenge include using the reserve generation capacity and/or the energy storage systems (ESSs). Energy storage can be realized at different levels of the power systems: the end-users, the power plants, or the electricity grid. In this paper, we present the feasibility evaluation of the different types of ESS (battery and fuel cells) for the smoothing of the peak generation curve of the power plants using VRESs and the economically optimal capacity of ESSs.

The battery energy storage system has become an indispensable part of the current electricity network due to the vast integration of renewable energy sources (RESs). This paper proposes an optimal charging method of a vanadium redox flow battery (VRB)-based energy storage system, which ensures the maximum harvesting of the free energy from RESs by maintaining safe operations of the battery. The VRB has a deep discharging capability, long cycle life, and high energy efficiency with no issues of cell-balancing, which make it suitable for large-scale energy storage systems. The proposed approach determines the appropriate charging current and the optimal electrolyte flow rate based on the available time-varying input power. Moreover, the charging current is bounded by the limiting current, which prevents the gassing side-reactions and protects the VRB from overcharging. The proposed optimal charging method is investigated by simulation studies using MATLAB/Simulink.

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.

Energy storage is a dominant factor. It can reduce power fluctuations, enhance system flexibility, and enable the storage and dispatch of electricity generated by variable renewable energy sources such as wind and solar. Different storage technologies are used with wind energy system or with hybrid wind systems and each one of them have its proper proprieties as lifetime, costs, density and efficiency. It can be electrical, chemical or electrochemical (Nickel-cadmium, Lead-acid, Sodium-sulfur, Lithium ion, Vanadium-Redox Flow batteries…). It can also be hydrogen storage and in this case different modes are used (compressed, liquefied, metal hydride, etc.). Thermal storage is generally used for wind energy management applications and its applications are around industrial cooling, building cooling and industrial heat storage. Mechanical storage (flywheel energy, pumped hydro energy, compressed air energy) is the most storage applied in wind energy conversion system for power quality and short duration.KeywordsWind PowerThermal Energy StorageVanadium Redox Flow BatteryFlow BatterieSuper CapacitorThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The operation of electric and heat grids alike is complicated due to the dynamic demand, with the increasing penetration of renewable energy sources adding to the problem. In order to improve the integration of variable renewable energy sources, the flexibility of the system needs to be improved. This paper proposed a novel characterization of the short-term energy flexibility, which was further utilized for the district heating capacity extension. The soft-linking of the models includes feedback, but the added computational complexity is kept at a minimum. Compared to the other literature in the field, due to the accurate characterization of the dynamics of the energy flexibility, flexibility is utilized much more frequently. The method was demonstrated for the case of the district heating of Zagreb. Results showed that both capital and operational savings can be achieved by adopting the proposed method. In the best performing scenario, which included the capacity extension planning, the savings of the district heating system were 5.4%. The extensive power exchange in the best performing scenario meant that the flexibility was used to help balancing the power grid as well.

This paper focuses on technology state of the art for the charge/discharge of electric energy storage supported by vanadium redox flow battery linked to the electric grid. Properties of vanadium, the main configuration and the reaction of charge/discharge of a vanadium redox flow battery are addressed. The vanadium redox flow battery has the highest cell voltage among the other redox flow battery, implying higher power and energy density which favours application at power plants. This electric energy storage is viewed as a promising contribution to be integrated in power system due to a reasonably bulky size and to successful applications currently allowing storage of energy at power plants or at electrical grids. For instances, allowing storage of energy as an economic improvement providing spin reserve to avoid penalty for imbalances between the energy delivered and energy contracted at closing of electricity market or as an economic improvement to diminish the cost of electricity usage of a consumer. The vanadium redox flow battery has the advantages of scalability customized to meet requirements for power and energy capacity and of excellent combination of energy efficiency, capital cost and life cycle costs compared with other technology.

Co-operation of electricity and natural gas systems including electric vehicles and variable renewable energy sources based on a continuous-time model approach

In developed countries like Austria the renewable energy potential might outpace the demand. This requires primary energy efficiency measures as well as an energy system design that enables the integration of variable renewable energy sources. Municipal energy systems, which supply customers with heat and electricity, will play an important role in this task. The cumulative exergy consumption methodology considers resource consumption from the raw material to the final product. It includes the exergetic expenses for imported energy as well as for building the energy infrastructure. In this paper, we determine the exergy optimal energy system design of an exemplary municipal energy system by using cumulative exergy consumption minimisation. The results of a case study show that well a linked electricity and heat system using heat pumps, combined heat power plants and battery and thermal storages is necessary. This enables an efficient supply and also provides the necessary flexibilities for integrating variable renewable energy sources.

The integration of renewable energy into electric power grid is of significant importance to meet the future energy demand. The urgent need to solve the global environmental concern, i.e. emission of CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , lead to the penetration of renewable energy sources into the electric grid. The development of power electronic devices, technologies and control schemes play a significant role in conversion and control of electric energy. Among available renewable energy sources, wind and solar are commonly used and the paper focuses on various power electronic configurations and topologies and their role in integration of renewable energy sources into the micro grid.

A comparative sustainability assessment of several grid energy storage technologies

The increasing integration of variable renewable energy sources (VRESs) into modern power systems presents significant challenges in ensuring operational flexibility, highlighting the need for robust methodologies to evaluate and ensure system reliability. The Insufficient Ramping Resource Expectation (IRRE) has emerged as a critical metric for quantifying the probability of ramping deficiencies in power systems. However, its traditional application, designed primarily for capacity-constrained systems, may not fully capture the operational dynamics of energy-constrained systems, such as those dominated by hydropower generation. This study analyzes the IRRE methodology and proposes enhancements to incorporate additional constraints, including seasonal and monthly hydrological variability and operational reserve requirements, to better reflect the flexibility limitations in energy-constrained systems. A case study of the Brazilian electricity system evaluates these modifications by comparing traditional and enhanced IRRE results across varying scenarios, including higher VRES penetration. Results reveal that, under stricter constraints, IRRE values increased by over 11 times for monthly hydrological limits in the Northeast subsystem, compared to the traditional IRRE. Additionally, combining these constraints with a 5% operational reserve requirement led to ramping deficits in up to 5% of the hours in a year for the same subsystem, highlighting the critical impact of operational constraints. Furthermore, scenarios with 30% and 100% VRES growth resulted in deficits increasing by 56 times and 418 occurrences, respectively, in certain subsystems. These findings demonstrate the enhanced IRRE’s effectiveness in evaluating flexibility challenges and its relevance for supporting planning and operational strategies in systems undergoing rapid renewable energy expansion.

Coordinated operation schedule of microgrids in consideration of penetration of variable renewable energy sources

Nowadays, the challenge of reducing air pollutants, which passes through increasingly stringent regulations on emissions, is also central in the maritime sector. A possible solution to overcome these limits could be the introduction of alternative propulsion systems to classic diesel engines. In the present work, the performance of a Hybrid Propulsion System (HPS) in marine, consisting of an internal combustion engine and a Vanadium Redox Flow Battery (VRFB) allowing an independent power and capacity sizing, was analyzed. Specifically, through a dynamic modeling, a daily work cycle has been simulated on the basis of a real load request. The possibility of implementing a hybrid system independent from a ground-based charging system was evaluated, in relation to the analyzed work cycle, by identifying the size of the battery (70 kW/ 5.8 kWh) and its minimum charging power (23 kW) necessary for the autonomous operation. Together with the results of the dynamic analysis, experimental results obtained on a real VRFB prototype of the innovative concept design implemented are provided.

Energy storage systems critically assist in the implementation of renewable energy sources. However, greenhouse gas emissions associated with the energy storage methods have received insufficient attention, especially for arid climate implementation. This paper considers three energy storage techniques that can be suitable for hot arid climates namely; compressed air energy storage, vanadium redox flow battery, and molten salt thermal storage and performs a comprehensive life cycle assessment analysis to comparatively evaluate the environmental impacts per kWh of energy. The results show that, when solar photovoltaic electricity is stored, the redox-flow battery has the highest global warming potential, corresponding to 0.121 kg CO2 eq./kWh, whereas the molten salt has the least with a value of 0.0306 kg CO2 eq./kWh. In contrast, the lowest ozone layer depletion is observed for the compressed air storage unit with a value of 7.24×10−13 kg R11 eq./kWh. In sensitivity analysis, it is found that using solar photovoltaic electricity for the considered energy storage methods rather than grid electricity critically reduces the associated environmental impacts, emphasizing the importance of implementing more renewables in the grid mix. The global warming potentials of compressed air and vanadium redox flow battery decrease by 0.599 and 0.420 kg CO2 eq,/kWh, respectively in case photovoltaic electricity is stored instead of grid electricity. It is also found that the production stage of the storage systems accounts for the highest share of carbon footprint.

This paper presents a control design methodology that addresses high penetration of variable generation or renewable energy sources and loads for networked AC /DC microgrid systems as an islanded subsystem or as part of larger electric power grid systems. High performance microgrid systems that contain large amounts of stochastic sources and loads is a major goal for the future of electric power systems. Alternatively, methods for controlling and analyzing AC/ DC microgrid systems will provide an understanding into the tradeoffs that can be made during the design phase. This method develops both a control design methodology and realizable hierarchical controllers that are based on the Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) methodology that regulates renewable energy sources, varying loads and identifies energy storage requirements for a networked AC/DC microgrid system. Both static and dynamic stability conditions are derived. A renewable energy scenario is considered for a networked three DC microgrids tied into an AC ringbus configuration. Numerical simulation results are presented.