Vanadium - the key to the VRB-ESS.

• "The Element That Could Change the World"

    Discover Website, from the October 2008 issue, published online September 29, 2008

  • "Making green energy work may depend on three unlikely heroes: an Australian engineer, a battery, and the element vanadium." 

  • Extensive discussion on the history, technology and application of the vanadium redox flow battery.

• "The increase in oxidation state of an atom through a chemical reaction is known as an oxidation; a decrease in oxidation state is known as a reduction. Such reactions involve the formal transfer of electrons, a net gain in electrons being a reduction and a net loss of electrons being an oxidation."  Wikipedia...

   

• "The chemistry of vanadium is noteworthy for the accessibility of four adjacent oxidation states. The common oxidation states of vanadium are +2 (lilac), +3 (green), +4 (blue) and +5 (yellow)." Wikipedia...

The Vanadium Redox Battery converts chemical energy into electrical energy. Energy is stored chemically in different ionic forms of vanadium in a dilute sulfuric acid electrolyte. The electrolyte is pumped from separate plastic storage tanks into flow cells across a proton exchange membrane (PEM) where one form of electrolyte is electrochemically oxidized and the other is electrochemically reduced. This creates a current that is collected by electrodes and made available to an external circuit. The reaction is reversible allowing the battery to be charged, discharged and recharged.

The principle of the VRB is shown in more detail above - it consists of two electrolyte tanks, containing active vanadium species in different oxidation states (positive: V(IV)/V(V) redox couple, negative: V(II)/(III) redox couple). These energy-bearing liquids are circulated through the cell stack by pumps. The stack consists of many cells, each of which contains two half-cells that are separated by a membrane. In the half-cells the electrochemical reactions take place on inert carbon felt polymer composite electrodes from which current may be used to charge or discharge the battery.

The VRB-ESS employs vanadium ions in both half-cell electrolytes. Therefore, cross-contamination of ions through the membrane separator has no permanent effect on the battery capacity, as is the case in redox flow batteries employing different metal species in the positive and negative half-cells. The vanadium half-cell solutions can even be remixed bringing the system back to its original state.

The VRB-ESS is a device that is capable of storing energy in multi megawatt ranges and for durations of hours or days - from any available input source such as the Grid, Renewable Resources or local generator. The stored energy can then be provided back into the Grid or supplied to a load as required and directed. It is uniquely capable of being charged as quickly as it was discharged and is able to respond to all forms of power quality variations so it can be operated in an Uninterruptible Power Supply (UPS) mode as well. For loads which require reactive energy, the VRB-ESS is fully rated to provide VARS at nameplate on a continuous basis either when charging or discharging.

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