Handbook of Energy Storage for Transmission or ... - W2agz.com

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pumps turned off. This mode eliminates pumping losses and self discharge during
downtime. When the battery is called into service, a minute or two would be required to
start the pumps and transport electrolyte to the stacks.
Environmental impact
The VRB stacks, plumbing, and tanks, are primarily composed of recyclable plastic
materials, and the electrolyte can be refurbished and reused. There are no toxic
chemicals that must be disposed of at the end of life, such as found in other
electrochemical storage technologies. For this reason, the VRB is promoted as a “green”
storage technology.
The only chemical in the VRB system is the vanadium electrolyte, ionic vanadium in
sulfuric acid at approximately the same concentration found in flooded lead-acid
batteries. Its handling and safety requirements are the same as sulfuric acid. The
electrolyte is internally contained within industrial-grade HDPE tanks and pressure-rated
PVC pipe and fittings. The VRB is placed within a spill containment area compliant with
local regulations.
As with all storage technologies, every charge/discharge cycle results in some loss of
energy due to system inefficiencies. For typical grid-connected applications, this means
that from a global perspective, there may be increased air emissions associated with the
generation of this lost energy. Of course, for renewable energy applications, there are no
air emissions considerations, and in some applications, the VRB serves to increase the
utilization of renewable sources.
DC Electrical Characteristics
In most VRB systems, the DC bus is connected to the cell stack terminals. The DC
voltage is determined by the cell count, and is typically 100 V or more. When power
requirements exceed the current ratings of a single stack, multiple stacks are connected in
parallel. However, other configurations are possible. Stacks can be placed in series to
boost DC voltage, but this requires separate electrolyte hydraulic plumbing and storage to
minimize ion flow losses (“shunt currents”) that increase with voltage. Cellenium is
developing an unconventional power conversion technology in which individual cells are
tapped and switched, providing near-sinusoidal outputs with incremental voltage steps
equal to the cell voltage.
Vanadium Redox Battery 12