The vanadium redox battery is a type of rechargeable flow battery that employs
vanadium ions in different oxidation states to store chemical potential
energy. The vanadium redox battery exploits the ability of vanadium to
exist in solution in four different oxidation states, and uses this property
to make a battery that has just one electroactive element instead of two.
For several reasons, including their relatively bulky size, most vanadium
batteries are currently used for Grid energy storage, such as being attached
to power plants or electrical grids. Building on earlier research on flow
batteries, the possibility of creating a vanadium battery was explored variously
by Pissoort, NASA researchers, and Pellegri and Spaziante. The first
successful demonstration of the all-vanadium redox flow battery
employing vanadium in a solution of sulfuric acid in each half was by Maria
Skyllas-Kazacos and co-workers at the University of New South Wales in the
1980s. Their design used sulfuric acid electrolytes, and was patented by the
University of New South Wales in Australia in 1986.
Organizations involved in funding and developing vanadium redox batteries
include UniEnergy Technologies and Ashlawn Energy in the United States,
Renewable Energy Dynamics Technology in Ireland, Gildemeister AG in Germany,
Cellennium in Thailand, Rongke Power and Prudent Energy in China, Sumitomo in
Japan and H2, Inc. in South Korea. The main advantages of the vanadium
redox battery are that it can offer almost unlimited capacity simply by
using larger storage tanks, it can be left completely discharged for long
periods with no ill effects, it can be recharged simply by replacing the
electrolyte if no power source is available to charge it, and if the
electrolytes are accidentally mixed the battery suffers no permanent damage. The
main disadvantages with vanadium redox technology are a relatively poor
energy-to-volume ratio, although recent research at the Pacific Northwest
National Laboratory has doubled energy density, and the system complexity in
comparison with standard storage batteries.
Operation A vanadium redox battery consists of an
assembly of power cells in which the two electrolytes are separated by a proton
exchange membrane. Both electrolytes are vanadium based, the electrolyte in the
positive half-cells contains VO2+ and VO2+ ions, the electrolyte in the
negative half-cells, V3+ and V2+ ions. The electrolytes may be prepared by any
of several processes, including electrolytically dissolving vanadium
pentoxide in sulfuric acid. The solution remains strongly acidic in use.
In vanadium flow batteries, both half-cells are additionally connected to
storage tanks and pumps so that very large volumes of the electrolytes can be
circulated through the cell. This circulation of liquid electrolytes is
somewhat cumbersome and does restrict the use of vanadium flow batteries in
mobile applications, effectively confining them to large fixed
installations. When the vanadium battery is charged,
the VO2+ ions in the positive half-cell are converted to VO2+ ions when
electrons are removed from the positive terminal of the battery. Similarly in
the negative half-cell, electrons are introduced converting the V3+ ions into
V2+. During discharge this process is reversed and results in a typical
open-circuit voltage of 1.41 V at 25 °C. Other useful properties of vanadium flow
batteries are their very fast response to changing loads and their extremely
large overload capacities. Studies by the University of New South Wales have
shown that they can achieve a response time of under half a millisecond for a
100 % load change, and allowed overloads of as much as 400 % for 10 seconds. The
response time is mostly limited by the electrical equipment. Sulfuric
acid-based vanadium batteries only work between about 10 to 40 °C. Below that
temperature range, the ion-infused sulfuric acid crystallizes. Round trip
efficiency in practical applications is around 65–75 %.
= Proposed improvements= Second generation vanadium redox
batteries may approximately double the energy density and increase the
temperature range in which the battery can operate.
Despite the traditional pumping requirements, one company has focused on
electric vehicle applications, using rapid replacement of electrolyte to
refuel the battery. Energy density
Current production vanadium redox batteries achieve an energy density of
about 25 Wh/kg of electrolyte. More recent research at UNSW indicates that
the use of precipitation inhibitors can increase the density to about 35 Wh/kg,
with even higher densities made possible by controlling the electrolyte
temperature. This energy density is quite low as compared to other
rechargeable battery types; and lithium ion, 80–200 Wh/kg).
Researchers at the Fraunhofer Institute for Chemical Technology claim to have
built a prototype for an improved cell stating "We can now increase the mileage
four or fivefold, to approximately that of lithium-ion batteries,". This same
article makes a very optimistic claim that vanadium flow batteries can be
recharged at a gas station by simply filling the vehicle tanks with fresh
electrolytes. Applications
The extremely large capacities possible from vanadium redox batteries make them
well suited to use in large power storage applications such as helping to
average out the production of highly variable generation sources such as wind
or solar power, helping generators cope with large surges in demand or leveling
out supply/demand at a transmission constrained region.
The limited self-discharge characteristics of vanadium redox
batteries make them useful in applications where the batteries must be
stored for long periods of time with little maintenance while maintaining a
ready state. This has led to their adoption in some military electronics,
such as the sensor components of the GATOR mine system.
Their extremely rapid response times also make them superbly well suited to
UPS type applications, where they can be used to replace lead–acid batteries and
even diesel generators. Also the fast response time makes them well-suited for
frequency regulation. Economically neither the UPS or frequency regulation
applications of the battery are currently sustainable alone, but rather
the battery is able to layer these applications with other uses to
capitalize on various sources of revenue. Also, these capabilities make
Vanadium redox batteries an effective "all-in-one" solution for microgrids
that depend on reliable operations, frequency regulation and have a need for
load shifting. = Installations=
There are several notable currently installed vanadium batteries:
A 1.5 MW UPS system in a semiconductor fabrication plant in Japan.
A 600 kW, six hour system, installed by Prudent Energy in Oxnard, California,
USA. A 275 kW output balancer in use on a
wind power project in the Tomari Wind Hills of Hokkaido.
A 200 kW, 800 kW·h output leveler in use at the Huxley Hill Wind Farm on King
Island, Tasmania. A 250 kW, 2 MW·h load leveler in use at
Castle Valley, Utah. Two 5-kW units installed in St.
Petersburg, Florida, under the auspices of USF's Power Center for Utility
Explorations. A 100 kWh unit supplied with 18 kW
stacks manufactured by Cellstrom has been installed in Vierakker as part of
an integrated energy concept called 'FotonenBoer'/'PhotonFarmer'
A 400 kW, 500 kWh output balancer in use on a solar power project in the
Bilacenge Village in Sumba Island, Indonesia.
A 50 kW, 100 kWh peak shaving for manufacturing facility in Gongju, South
Korea. A 5 kW, 60 kWh unit integrated with
photovoltaic generation at University of Évora, Portugal.
A 100 kW, 1.26 MWh installation is planned for the island of Gigha,
Scotland. A 5 MW, 10 MWH system at the Woniushi
wind power farm was connected to the Liaoning Power Grid, China, on 23 May
2013 [1]. 1 MW, 5 MWh installed by Sumitomo
Electric Industries in Yokohama 100 kW, 600 kWh unit, installed by
Prudent Energy & ABB in Kolarovo, Slovakia.
See also Polysulfide bromide battery
Battery Flow battery
Lead–acid battery Electrochemical cell
Fuel cell Energy storage
References Additional references
Presentation paper from the IEEE summer 2001 conference
UNSW Site on Vanadium batteries Report by World Energy
World Map Of Global Vanadium Deposits Vanadium geology is fairly unique
compared to a base metals ore body. External links
VRB at UNSW VRB at everything2
The Need for Vanadium Redox Energy Storage in Wind Turbine Generators Net
electricity generation from all forms of renewable energies in America increased
by over 15% between 2005 and 2009.