• Can be charged and discharged over 12,000 times without degradation
• Extremely low self discharge
• Sized up to tens of megawatt hours
• Designed for unattended operation with very low maintenance
• Can be easily upgraded with more capacity
• Applications include:
• load leveling
• utility ancillary services
• electrical power arbitrage
• renewable energy capacity support (wind and solar power).
  

The Vanadium Redox Battery Energy Storage System (VRB-ESS) is an electrical energy storage system based on the patented vanadium-based redox regenerative fuel cell that 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 the 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, tens of thousands of times throughout the life cycle.

The principle of the VRB is shown in more detail in Figure 1 – it consists of two electrolyte tanks, each containing active vanadium electrolyte charged to opposite states. These energy-bearing liquids are circulated in the cell stack by pumps. The stack consists of many cells connected in series, each of which contains two half-cells that are separated by a membrane. The electrochemical reactions in the half-cells take place on inert carbon felt polymer composite electrodes from which current may be used to charge or discharge the battery.

The VRB employs vanadium ions in both half-cell electrolytes. Therefore, cross-contamination of ions through the membrane separator has no detrimental influence 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.