The Vanadium Redox Flow Battery
The Redox Flow Cell is an electrochemical storage system which allows energy to be stored in two solutions containing different redox couples. Unlike conventional batteries, the redox flow cell stores energy in the solutions so that the capacity of the system is determined by the size of the electrolyte tanks, while the system power is determined by the size of the cell stacks. The diagram below demonstrates such a scheme :
There are a number of other technical advantages that this technology holds over other storage solutions :
Energy is stored in tanks – separate from the cell stack
· The system's capacity can be readily increased simply by adding more solution.
· The cost per kWh decreases as the energy storage capacity increases.
· Land space can be saved by building underground electrolyte storage tanks.
· This system offers greater safety since there is less risk of instantaneously mixing the electrolytes and causing a sudden release of energy.
· There is the possibility of mechanical or "instant recharge" by replacing the electrolytes.
Vanadium solution is used in both half cells
· Cross-mixing of electrolytes across the membrane does not lead to the contamination of electrolytes.
· The solutions have an indefinite life so that replacement costs are low.
· Indefinite life of solution means that they can be continuously recycled so that there are no waste disposal problems - shelf life is theoretically unlimited.
· Vanadium redox couples are electrochemically reversible so that high energy efficiencies are possible.
· The system can be recharged at high rates at a fraction of the time needed for the lead-acid battery.
· Vanadium is readily available and relatively low cost, so manufacturing and capital costs are low.
The same solution is pumped through each cell in the stack which means that every cell is at the same state of charge.
· By monitoring electrolyte state-of-charge, the capacity of the battery can be easily measured and therefore the capacity of the whole system can be easily controlled.
· Trim cells can be used to adjust the voltage as required.
· The system does not require overcharging for cell equalization so the hydrogen explosion hazard is eliminated.