Flow batteries have become a popular choice in the development of large-scale energy storage systems due to their helpful features. They offer very long cycle life, low-cost options for applications that depend on high energy to power ratios, as well as high energy efficiencies. They are useful for electric power customers which include industries and office buildings that are in need of backup power with the help of auxiliary gas tank for generator and increased capacities, using generator auxiliary fuel tanks.  

While solid-state batteries are known to store energy in solid electrode material like metal, flow batteries operate differently. They store energy in electrolyte liquids. Most flow batteries operate by using two electrolyte liquids – a negatively charged cathode and a positively charged anode. Each of these electrolyte liquids are separated into two tanks by an ion-exchange membrane which results in an electrical potential without degradation. If they are not separated, there will be a shortage and replacement will be necessary. When not in use, the chemical energy contained in the electrolyte is released in the reverse reaction causing electrical energy to be transferred from the electrodes. When activated there’s a pump in the circulation of the electrolytes within the storage tanks. 

One major differentiating factor of flow batteries is the separation of the power and energy components and the ability to scale independently. Its capacity is as a result of the quantity of electrolyte and the concentration of the active ions. On the other hand, its power is as a result of the combined effort of electrodes within the cell. Though they can be assembled to meet voltage requirements, the electrolyte tanks are kept external to the system and diesel light tower.

Increasing the capacity of flow batteries to store extra power basically involves employing bigger tanks of electrolytes. One popular electrolyte component is vanadium due to its endless cycles of metal charges and discharges. Studies reveal that China is building the world’s largest vanadium flow battery which is expected to be activated in 2020. The battery will store 800 megawatt-hours of energy, capable of powering several homes and industries. Research experts have predicted a positive ride in the market as vanadium cells and zinc-bromide flow battery types could grow to about $1 billion yearly. 

TYPES OF FLOW BATTERIES

Zinc-Bromide 

A modern variety of the flow battery is the zinc-bromine battery. This battery functions as a result of the reaction between two readily available components, zinc and bromine. It is composed of a zinc negative electrode and a bromine positive electrode with a separating microporous body. Two separate reservoirs are placed containing an aqueous solution of zinc bromide. The compartment containing the bromine is not able to mix up with the aqueous solution of zinc bromide. The next cycle will start as soon as the zinc-bromine battery is totally discharged leaving all the formed metallic zinc on the negative electrode to dissolve into the electrolyte.

The dissolved zinc bromide salt leaves the electrolyte aqueous. As the charge is initiated, zinc is plated from the electrolyte solution onto the surface of the negative electrode within the cell stacks. The storage medium for the produced bromine is the base of the positive electrolyte in the form of a chemically complex organic reaction. Some of its main features include deep discharges, high energy density and negligible self-discharge.

Polysulphide bromide battery

This battery type uses two salt solution electrolytes- sodium bromide and sodium polysulphide.  Being a regenerative fuel cell technology, the battery is able to store energy through the means of a reversible reaction between these salt solutions. The two electrolytes are contained within a cell with a polymer membrane preventing contact. The membrane only allows the passage of positive sodium ions thus generating voltage throughout the system. Unlike the vanadium redox battery (VRB), the roundtrip efficiency is lower and all the energy density is 20-30n l. When in a state of rest with charged electrolytes the system is responsive under a short interval. Its power capacity and lifecycle  extends to over 15 years 

 Vanadium redox battery

The vanadium redox battery stores energy with the use of vanadium redox couples in the negative and positive half cells. A less concentrated sulphuric acid solution is used to store these redox couples contained in two electrolyte tanks. As a charge-discharge cycle takes place, hydrogen ions are released between the two tanks with the support of a hydrogen-ion permeable polymer membrane. This type of flow battery has some advantages such as high efficiency, a long-running period that surpasses 10,000 cycles and deep discharges. 

The buying costs vary and are proportional to the capacity with low levels when concerning bigger systems. Vanadium redox batteries are useful in a wide range of energy storage applications for large industries and electricity utilities. Further features include improves power capacity, increased security of supply and connection with other renewable energy sources, uninterrupted supply of power. Due to the low energy density of vanadium redox battery, the majority of development work is centred on fixed applications. 

CONCLUSION

While there is a large and growing market opportunity, the adoption of flow batteries is limited due to many technical and economic barriers. As there is an increased decentralised approach for power generation with the advent of renewable energy sources there will be a need to increase load factors in order to meet up to peak demand and also stop the intermittency of sources that do not have potential to be available. These high-demand applications will need storage for energy with fast charge-discharge and increased megawatt range. 

Some additional innovations can be made to the energy density. Electrodes with improved catalytic properties, porous nature and three-dimensional have the potential to increase power output for a particular electrode. The main goals are to reduce the costs of electrode and membrane materials at the cell level and provide the required control systems for using power management and aluminium fabrication. An improvement in the engineering design will also have a significant impact on performance.