POWER December 2012 - 8

Vanadium Flow Battery
Juices Onion Plant
An emerging flow battery technology got
a major boost earlier this year when Gills
Onions, one of the largest fresh-cut onion
processing plants in the world-began operating
a 3.6-MWh vanadium redox battery
(VRB) energy storage system (ESS). The 14acre
processing facility in Oxnard, Calif.,
was already converting 100% of its daily
onion waste-up to 300,000 pounds-
into a combination of renewable energy
and cattle feed using an advanced energy
recovery system (AERS) that extracts juice
from onion peels and treats it in a highrate
anaerobic reactor to produce biogas
that powers two 300-kW fuel cells. But
Gills Onions thought it necessary to add
energy storage to its AERS to improve the
efficiency of the system and further reduce
electric costs, citing their main motivation
as wanting to shift electricity generation
from off-peak to on-peak periods while
warding off pricey demand spikes.
Encouraged by state cash rebates for
certain types of energy storage, Gills Onions
says it opted for the VRB-ESS that
consists of three 200-kW modules with
enough electrolyte to provide six hours
of storage capacity (Figure 1). Not only
can the VRB change from fully charging
to fully discharging in seconds so that the
full 600 kW are available 24 hours a day,
Gills Onions says the system also can pulse
an additional 50%-to 750 kW-for 10
minutes each hour, providing additional
capacity for motor starts or other spikes.
The project was built and is owned
and operated by Prudent Energy Corp.
subsidiary Prudent Energy Services. The
Bethesda, Md.-based company gets an
undisclosed share of the energy savings
resulting from the project in return, calculated
as avoided charges, costs, and
fees that would otherwise be paid by
Gills to the local utility.
As Prudent Energy describes it, the VRBESS
consists of cell stacks, allowing modular
systems to be assembled in large parallel
and series configurations-with no special
site requirements other than a substantial
footprint. The cell stacks themselves are
10-kW sealed devices that consist of many
cells, each of which contains two half-cells
separated by a membrane. Electrochemical
reactions occur in the half cells on inert
carbon felt electrodes, creating a current
used to charge or discharge the battery.
" When charged electrolyte fluids [from sep8
arate
storage tanks] pass through the cell
stack, different ionic forms of vanadium react,
resulting in a balancing electron flow
into an external DC circuit-thus completing
an electrochemical path for discharge, "
the company says. " Forcing current into
the stack from an external source recharges
electrolyte in the stack, with fluids then
pumped back into the reservoirs. " This
" re-dox " process is reversible, allowing the
battery to be charged and discharged repeatedly,
the company explains.
In its most basic sense, the system
stores energy chemically in different forms
of a single element-vanadium, which the
company has dubbed a " miracle metal " -
in a proprietary electrolytic mixture. The
mineral's marvels lie in its unique attributes,
particularly as a chemical catalyst
for electrolytes, the company says. " It is
a transition metal, which means it has the
typical properties of metals, but in addition,
high melting and boiling points, and
high density, " it explains. And, as Prudent
Energy highlights: " Vanadium forms stable,
concentrated electrolytic solutions in
four neighboring oxidations states. "
A selling point extolled by Gills Onions
is the life of the system. The technology
reportedly can produce more than 10,000
full-depth charge/discharge cycles with
no degradation in performance. Meanwhile,
the electrolyte never degrades and
can be fully recycled.
VFB solutions have long been recognized
for their edge over lithium-ion battery
storage, primarily because VFBs have
a practical advantage with their storage
duration limit of 10 hours-compared to a
1- to 2-hour range for lithium-ion storage
systems (though lithium-ion wins in terms
of round-trip efficiency).
Prudent's energy storage system isn't
unique. Several companies-including
U.S.-based Ashlawn Energy, Austria-based
Cellstrom GmbH, and Thailand-based Cellenium-have
entered the fray, competing for
global VFB market share. VFBs are already
being used in the European Union, China,
Japan, South Korea, and Australia-though
most are in the 100-kWh range. Billed as
the largest of its kind, the 3.6-MWh Gills
Onions installation compares only with another
Prudent Energy project completed in
March 2011 involving a 1-MWh VFB at the
China Electric Power Research Institute in
Zhangbei, Hebei Province.
Meanwhile, industry analysts foresee
tremendous growth of VFBs in the short
www.powermag.com
1. Storing onion juice. One of the
world's largest vanadium flow battery energy
storage systems began operation earlier this
year at Gills Onions, an Oxnard, Calif., freshcut
onions processing plant. The tennis court-
sized system consists of cell stack modules
that are connected in parallel configurations. It
stores electricity during lower-cost nighttime
hours and allows the Gills facility to rely on the
flow battery to generate 600 kW for as long as
six hours during higher-cost peak hours. Courtesy:
Gills Onions
term. A March 2012 study by Lux Research
predicts that VFBs could capture about
17% of the energy grid storage market
by 2017-assuming that developers can
reach a target of $750/kWh for a fully
installed system by then. The most significant
factor that could determine the
technology's success is availability and
pricing of vanadium, which is already seeing
heightened demand for its traditional
use: strengthening steel.
" Vanadium is not scarce, " says Prudent
Energy, claiming that it not only can be
mined naturally as an ore but can also be
recovered as a by-product of steel manufacturing,
coal-fired power generation,
and oil shale production. But analysts predict
a supply shortage, driven by increasing
consumption by China, which produces
40% of the world's vanadium supply (otherwise
dominated by Russia and South Africa),
as a result of a new rule that only
vanadium-containing reinforced steel bars
can be used for infrastructure and other
construction projects. Increased demand
for the mineral pegged to its use in flow
batteries will strain global supplies.
Compounding pricing concerns is the
quirk that, unlike many commodities, vanadium
does not trade on the open market;
deals are negotiated privately and
tend to surge when steel demand is high
and plunge during economic downturns.
This price volatility is a major deterrent
for battery producers, which require large
amounts of high-purity (greater than
98.4%) vanadium, analysts point out.
POWER | December 2012
http://www.powermag.com
POWER December 2012

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