The Element That Could Change the World

Making green energy work may depend on three unlikely heroes: an Australian engineer, a battery, and the

element vanadium.

by Bob Johnstone

Published online September 29, 2008

Schematic depicts the inner workings of a vanadium battery, now in use in a Utah plant, that can supply 250

kilowatts for eight hours.

VRB Power Systems

February 27, 2008, was a bad day for renewable energy. A cold front moved through West Texas, and the winds

died in the evening just as electricity demand was peaking. Generation from wind power in the region rapidly

plummeted from 1.7 gigawatts to only 300 megawatts (1 megawatt is enough to power about 250 average-size

houses). The sudden loss of electricity supply forced grid operators to cut power to some offices and factories

for several hours to prevent statewide blackouts.

By the next day everything was back to normal, but the Texas event highlights a huge, rarely discussed

challenge to the adoption of wind and solar power on a large scale. Unlike fossil fuel plants, wind turbines and

photovoltaic cells cannot be switched on and off at will: The wind blows when it blows and the sun shines when

it shines, regardless of demand. Even though Texas relies on wind for just over 3 percent of its electricity, that

is enough to inject uncertainty into the state’s power supplies. The problem is sure to grow more acute as states

and utilities press for the expanded use of zero-carbon energy. Wind is the fastest-growing power source in the

United States, solar is small but also building rapidly, and California is gearing up to source 20 percent of its

power from renewables by 2017.

Experts reckon that when wind power provides a significant portion of the electricity supply (with ―significant‖

defined as about 10 percent of grid capacity), some form of energy storage will be essential to keeping the grid

stable. ―Without storage, renewables will find it hard to make it big,‖ says Imre Gyuk, manager of energy

systems research at the U.S. Department of Energy.

Fortunately, there is a promising solution on the horizon: an obscure piece of technology known as the

vanadium redox flow battery. This unusual battery was invented more than 20 years ago by Maria Skyllas-

Kazacos, a tenacious professor of electrochemistry at the University of New South Wales in Sydney, Australia.

The vanadium battery has a marvelous advantage over lithium-ion and most other types of batteries. It can

absorb and release huge amounts of electricity at the drop of a hat and do so over and over, making it ideal for

smoothing out the flow from wind turbines and solar cells.

Skyllas-Kazacos’s invention, in short, could be the thing that saves renewable energy’s bacon.

To the engineers who maintain the electrical grid, one of the greatest virtues of a power supply is predictability,

and that is exactly why renewable energy gives them the willies. Nuclear- and fossil fuel–powered plants

produce electricity that is, in industry speak, ―dispatchable‖; that means it can be controlled from second to

second to keep the grid balanced, so the amount of energy being put into the wires exactly matches demand. If

the grid goes out of balance, power surges can damage transmission lines and equipment. Generators are

therefore designed to protect themselves by going off-line if the grid becomes unstable. Sometimes this can

amplify a small fluctuation into a cascading disaster, which is what happened in the northeastern United States

and eastern Canada in August 2003, plunging 50 million people into a blackout. Unless the reliability of

renewable energy sources can be improved, as these sources contribute more and more electricity to the grid,

engineers will have an increasingly difficult time keeping the system balanced. This raises the specter of more

blackouts, which nobody would tolerate. ―We want to make renewables truly dispatchable so we can deliver

given amounts of electricity at a given time,‖ Gyuk says.

The way to make renewables more reliable is to store the excess electricity generated during times of plenty

(when there are high winds, for instance, or strong sun) and release it later to match the actual demand. Utilities

have been using various storage techniques for decades. Hydroelectric plants, for instance, often draw on

reservoirs to generate additional electricity at peak times, and then pump some of the water back uphill in off-

peak periods. Compressed air is another, less common form of large-scale energy storage. It can be pumped into

underground cavities and tapped later. These technologies have been suggested as ways of storing renewable

energy, but both approaches rely on unusual geographical conditions.

―For most of us right now, the real key to effective storage is batteries,‖ says Jim Kelly, senior vice president of

transmission and distribution at Southern California Edison. Specifically, what is needed is a battery that can

store enough energy to pull an entire power station through a rough patch, can be charged and discharged over

and over, and can release large amounts of electricity at a moment’s notice. Several promising battery

technologies are already in early-stage commercialization, but the vanadium battery may have the edge in terms

of scalability and economy.

We need a rechargeable battery that can store enough energy to pull a power station through a rough patch And

release Electricity at a moment’s notice.

Like the battery in your cell phone or car, vanadium batteries are rechargeable, but chemically and structurally

they go their own way. A vanadium battery consists of three main components: a stack where the electricity is

generated and two tanks that hold liquid electrolytes. An electrolyte is any substance containing atoms or

molecules that have positive or negative electrical charges. These charged atoms or molecules are known as

ions, and the amount of charge on an ion is known as its oxidation state. In a battery, electrolytes are used as an

energy storage medium. When two electrolytes, each containing ions with different oxidation states, are allowed

to exchange charges, the result is an electric current. The technical term for this kind of charge exchange is a

redox reaction, which is why the vanadium battery is formally known as the vanadium redox battery.

A traditional battery, such as the familiar AA dry cell, holds electrolytes in its own sealed container. But the

vanadium battery is a flow system—that is, liquid electrolytes are pumped from external tanks into the stack,

where the electricity-generating redox reaction takes place. Want to store more power? Use bigger tanks. The

bigger the tanks, the more energy-rich electrolytes they can store. The downside is that flow batteries tend to be

big. It takes a flow battery the size of a refrigerator, incorporating a 160-gallon tank of electrolytes, to store

20,000 *watt-hours of electricity, enough to power a full-size HDTV for about three days. This is because the

energy density in the liquid electrolytes is relatively low compared with that of the chemicals in lithium-ion

batteries. (Energy density is a measure of the amount of energy that can be extracted from a given volume or

mass of a battery.) For this reason, flow batteries are unlikely to be found in mobile applications, like laptops or

electric cars. In those cases the battery of choice remains lithium-ion, which has an energy density five times

that of vanadium.

For large-scale energy storage, the rules are very different. Typical rechargeable batteries are unsuitable because

it is difficult to get a lot of energy out of them quickly; when the grid is on the verge of crashing, you want an

energy infusion now. Ordinary rechargeables also wear out easily. A typical laptop battery will die after a few

hundred charge-discharge cycles. In contrast, flow batteries can be charged and discharged many thousands of

times.

A vanadium battery generates electricity in a stack,

where electrolytes with different

oxidation states (indicated by the numbers)

are allowed to react via a central membrane,

so that V(+5) becomes V(+4)

and V(+2) becomes V(+3). Bigger tanks

allow more electricity to be stored.

VRB Power Systems

The vanadium battery’s indefatigable nature echoes that of its creator, Skyllas-Kazacos, a single-minded

researcher whose no-nonsense manner is frequently punctuated by an unexpected easy laugh. Her path to the

vanadium battery began quite by accident in 1978 at Bell Laboratories in Murray Hill, New Jersey, where she

was a member of the technical staff. She had applied to work on solar energy. At the time, Bell Labs was

developing liquid-junction photovoltaics (a type of solar cell that employs liquid electrolytes), which seemed

like a nice fit for her electrochemical training. But the director of the lab’s battery section picked up her job

application first and liked what he saw. Much to her surprise, when Skyllas-Kazacos arrived she was assigned

to do research on batteries, which she had never worked on before.

Her serendipitous experience in batteries was put to good use five years later after her return to Sydney, where

she had grown up after immigrating with her family from Greece in 1954. She took a position at the University

of New South Wales. A colleague there asked her to co-supervise a student who wanted to investigate ways of

storing solar energy. The project sounded interesting, so she agreed.

Skyllas-Kazacos started her research by building on the foundational work on flow batteries done by NASA in

the mid-1970s. The space agency’s scientists recognized that flow batteries could store solar power on a

spacecraft, but they gave up on them after hitting a snag known as cross-contamination. When two liquid

electrolytes made of different substances are separated by a membrane, sooner or later the membrane is

permeated and the two substances mix, rendering the battery useless. The early NASA flow batteries, which

used iron and chromium, quickly ran down as a result.

―We thought the way to solve this problem was to find an element that could be used on both sides,‖ Skyllas-

Kazacos says. Technically, cross-contamination would still occur, but with essentially the same substance doing

double duty, the problem would be moot. The key was to pick an element that could exist in a variety of

electrical, or oxidation, states.

Skyllas-Kazacos chose vanadium, a soft, bright white, relatively abundant metal named for Vanadis, the

Scandinavian goddess of beauty and youth. Vanadium has four oxidation states, known as V(+2), V(+3), V(+4),

and V(+5); in each state the element carries a different amount of electric charge. Often oxidation states are

hard to tell apart, but in this case nature was kind: V(+2) is purple, V(+3) green, V(+4) blue, and V(+5) yellow.

Simply having different oxidation states is not enough to make an element work for a liquid battery. The

element has to be soluble, too. NASA had considered and rejected vanadium because the technical literature

insisted that the solubility—and hence energy density—of the useful V(+5) form of the element was extremely

low. Skyllas-Kazacos recognized, however, that just because something appears in print does not necessarily

mean it is true. Previous studies had started by leaving a compound of vanadium, vanadium pentoxide, to

dissolve in solution. This was a very slow process that could take days, and it never produced more than a tiny

amount of V(+5) in solution. Skyllas-Kazacos approached the problem from a less direct route. ―I started off

with a highly soluble form, V(+4), then oxidized it up to produce a supersaturated solution of V(+5). I found

that I could get much higher concentrations. From then on it became clear that the battery would actually work.‖

In 1986 came a major milestone: Her university filed for a patent on the Skyllas-Kazacos vanadium battery. But

proving the concept turned out to be the easy part. ―We thought we would take the device to a certain level, and

then some industry group would come and take it off our hands,‖ Skyllas-Kazacos says with her laugh. ―What

we didn’t realize was that the task was enormous. We had to develop the membranes, the conducting plastic for

the electrodes, the structures, the materials, the designs, the control systems—everything!‖ In 1987 Agnew

Clough, an Australian vanadium mining company, took out a license on the technology. But nothing came of

the deal.

The vanadium battery finally got its first chance to shine in 1991, when Kashima-Kita Electric Power, a

Mitsubishi subsidiary located north of Tokyo, took out a new license on the technology. Kashima-Kita powers

its generators with Venezuelan pitch, a fuel rich in vanadium. Skyllas-Kazacos’s battery was a perfect fit. Here

was a technology that allowed the company to recycle the vanadium from its soot and flatten out fluctuations in

demand for its electricity at the same time. The world’s first large-scale vanadium battery went into operation in

1995, able to deliver 200 kilowatts for four hours—enough to power about 100 homes. It was a success, but

Kashima-Kita sold the license and didn’t build another.

The buyer, Sumitomo Electric Industries, a giant Osaka-based company, had been working on NASA-style

iron-chromium flow batteries since the early 1980s. Things looked up for Skyllas-Kazacos’s invention when

Sumitomo switched to vanadium and licensed the technology in 1997. Three years later Sumitomo began

selling vanadium batteries, including a 1.5-megawatt model that provides backup power to a Japanese liquid

crystal display factory. By maintaining power during blackouts and thus preventing production losses, the

battery reportedly paid for itself in six months.

Sumitomo sold a 1.5-megawatt battery that provides backup to a liquid crystal display factory by maintaining

power in blackouts and preventing production losses, it paid for itself in six months.

Sumitomo has since demonstrated vanadium technology in at least 15 other implementations, including a 170-

kilowatt battery at a wind farm in Hokkaido. All are located in Japan, their development subsidized by the

government. Sumitomo doesn’t sell outside Japan, possibly due to the battery’s high manufacturing cost.

One company is now taking up the vanadium banner worldwide: VRB Power Systems, a Vancouver, British

Columbia, start-up that bought most of the early intellectual property rights to the technology. The company is

targeting the market for hybrid systems used to power remote, off-grid telecom applications. ―In places like

Africa, cell phone towers are typically powered by little putt-putt diesel engines that run 24/7,‖ VRB CEO Tim

Hennessy says. By adding a vanadium battery to the system, one can run the diesel generator while charging the

battery, turn the diesel off, run the battery, then repeat the cycle nonstop. ―The beauty of the battery is that you

can cycle it as many times as you like,‖ Hennessy says. ―The electrolyte doesn’t wear out.‖

VRB has installed 5-kilowatt batteries at two sites in Kenya. Hennessy claims that these can produce ―at least a

50 percent reduction in the burning of diesel fuel, plus the diesels will need less maintenance and last much

longer. It promises to make a huge difference to our customers’ operating expenses.‖ The firm’s other recent

sales include a 20-kilowatt system, worth $300,000, that will deliver nine hours of backup power for an

undisclosed major telecom company in Sacramento, California. These customers are learning firsthand what

Skyllas-Kazacos learned two decades ago. The vanadium battery really works.