Flow Cell Energy Storage: A Hybrid Storage Technology

The Energy Blog reported a while back on a new energy storage technology, Vanadium redox flow batteries. Flow batteries are called that because the electrolytes flow through the cells, giving up electrons to an external circuit. The redox reaction is reversible, so the cells can be charged or discharged. The significant fact about flow batteries is the potential to scale to very large storage sizes into the megawatt and multi-megawatt ranges. This is the type of storage capacity utilities have been looking for.

Performance

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The VRB has an availability of greater than 98%. Designed for unattended operation with very low maintenance costs.
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No degradation from repeated deep charges and discharges. The system can be discharged and charged greater than 13,000 times (20% to 80% SOC) without deterioration in system efficiencies.
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System round-trip efficiencies between 70% - 78%.
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The VRB-ESS has a charge/discharge window of 1:1 - allowing off-peak charging for on-peak dispatch - a fraction of the time required by other battery systems and ideal for wind generation applications.
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Cross mixing of electrolytes does not lead to contamination of electrolytes
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indefinite life of electrolyte (no disposal or contamination issues).
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Once charged, the electrolyte remains fully charged with low self-discharge.

Flow batteries are not generators, like regular fuel cells. Most fuel cells use up their fuel sources in an irreversible reaction. Flow batteries do not use up their electrolytes. The electrolytes are fully reusable, with recharging. And flow cells are not like regular batteries, since you recharge them by replacing the electrolyte. They are a new, hybrid form of chemical battery/fuel cell.

The best use for these cells will probably be as load levelers for utilities, and as backup power for large industrial facilities.

Here are more links:

Sandia
Wiki
ME
Geo