Battery Selection
Selection of an appropriate storage plays a crucial role in the project. Cost of storage system, technical and physical characteristics are important factors to consider for this process. We adopted a structured process of researching suitable technologies, compiling and comparing them based on a weighted selection criteria before finally making our selection based on the outcomes of our process.
Selection Criteria
The energy density of a battery refers to the amount of energy that can be stored in the battery per unit volume or unit mass. In other words, it is a measure of how much energy the battery can store relative to its size or weight.
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Refers to the efficiency of the battery when it is either charging or discharging. It is the ratio of the amount of energy that can be retrieved during the discharge process to the amount of energy that is put into the battery during the charging process. It is usually expressed as a percentage.
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The response time
of a battery refers to the time it takes for the battery to start delivering power
in response to a demand
for power. In other words,
it is the time it takes for the battery to ramp up its power output from a low level
to a higher level in response to a change in demand.
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A measure of the efficiency of the entire charging and discharging cycle of the battery. It takes into account the energy losses that occur during both the charging and discharging processes. In other words, it is the ratio of the energy output of the battery during discharge to the energy input required to recharge the battery.
Energy Density
Charge/Discharge Efficiency
Response Time
Round Trip Efficiency
Flow Batteries
Chemical species in the electrolytes undergo redox reactions during charging and discharging.
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Multiple electrochemical cells arranged in a stack. Each cell contains an electrode on each side,
one for oxidation and one
for reduction, where the redox reactions occur.​
Electrical energy from
an external source is used to drive the redox reactions
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Flow batteries offer excellent scalability. The energy storage capacity can be easily increased by adjusting the size of the electrolyte tanks, allowing customization for various applications.
Principle
Cell Stack
Charging and Discharging
Scalability
Vanadium Redox Flow Batteries
Based on our comparative analysis, the team decided to move ahead
with the Vanadium Redox Flow Batteries (VRFB)
Principle
VRFB utilizes vanadium ions in different oxidation states (V2+ and V3+ for the negative side, V4+ and V5+ for the positive side) as the electroactive species in the electrolytes
Separated Electrolyte Tanks
Separate electrolyte tanks for each half-cell. typically vanadium sulphate solutions dissolved in sulfuric acid, exchanging ions through a proton exchange membrane
Large Storage Capacity
High energy storage capacity due to the large volume of electrolytes in the tanks. Capacity can be adjusted by adjusting the electrolyte volume thus offering flexibility
Deep Discharge and Long Cycle Life
Can be discharged to a low state of charge frequently without affecting their cycle life.
VRFBs also offer a long cycle life, typically several thousand cycles, with minimal capacity degradation.
High Efficiency
High round-trip efficiency, due to the low voltage loss during energy conversion and the ability to operate at near-constant cell voltage
Enhanced Safety
Relatively safe due to the use of non-flammable and non-explosive aqueous electrolytes. Separation of the electrolytes and the absence of volatile or hazardous components contribute to their inherent safety characteristics.
References
[1] Leung, P., Ponce de León, C., Low, C. T. J., & Shah, A. A. (2013). An Overview of Redox Flow Battery Technology. Renewable and Sustainable Energy Reviews
[2] Li, L., Zeng, Y., & Li, X. (2016). Recent Progress of Vanadium Redox Flow Battery: A Review. Journal of Energy Chemistry
[3] Skyllas-Kazacos, M., Chakrabarti, M. H., Hajimolana, S. A., Mjalli, F. S., & Saleem, M. (2011). Progress in Vanadium Redox Flow Batteries. Advances in Energy Research
[4] Zhao, Y., An, L., & Zeng, Y. (2013). Vanadium Redox Flow Battery for Energy Storage: Prospects and Challenges. Journal of Applied Electrochemistry