Domestic Battery Storage

Charge of the battery brigade

Stephen Luntz ABC Environment 26 Mar 2012

A Redflow battery sits outside a house in Newcastle. Credit: Ausgrid

ON A QUIET CUL-DE-SAC in Elermore Vale, Newcastle, where the lawns are clipped and houses humble, Paul Jeffkins surveys a fridge-sized object installed outside his house. But it's no beer fridge. Instead of stubbies, it stores electric charge, grabbing electricity during off-peak times to release when demand is high. The unit is one of 40 installed in houses in this suburb of Newcastle, as part of a trial by electricity infrastructure corporation Ausgrid. Most of the power currently being stored comes from coal fired power stations, but the success of these batteries may also prove important to initiating a future powered by sun and wind.

The new arrivals colonising this deliberately ordinary street are zinc-bromine flow batteries. Each can store 10 kilowatt-hours of electricity, around what a basic 1.5kW set of solar panels generates on a sunny day. Two tanks hold a solution of zinc and bromine that can be pumped past a stack of plastic electrodes. When the battery is charged, zinc is deposited from the solution and coated onto the negative electrode; while at the positive electrode bromine is produced for storage within a tank. Zinc and bromide ions reform during discharging.
Ausgrid hopes the household-sized batteries will reduce the need for them to build new power stations. Gas plants currently sit idle for much of the day in order to be brought online for brief spurts at maximum demand, making peak power enormously expensive, a cost that is worn by consumers. If everyone had a battery, there would not be the same need to fire up a power station at peak demand.
Moreover, while there is much talk of "the grid", as though there were only one, Ausgrid's energy efficiency expert Paul Myors says there are actually many subgrids, with some getting close to requiring upgrading in order to handle peak demand. "In the commercial heart of a major city demand peaks during business hours, but in the suburbs it's when people get home on a hot day and start their air conditioners".
Unfortunately this occurs well past peak production for rooftop solar. A better integrated grid could feed power from panels installed across homes to commercial centres during the day. However, not only does this require expensive infrastructure upgrades, larger substations and more powerlines can spark local opposition.
Batteries sitting under the eves of houses are much less likely to attract complaints than increased transmission infrastructure, let alone a suburban gas fired power station.
It is a matter of weeks since Ausgrid began installing the batteries, far too early for results. Jeffkins says he has had no problems with noise or other interference, making the $150 payment he received a good deal for the minor loss of space. He's also untroubled by the possibility of electrolyte leakage that has hampered installation of large battery systems in the past.
The batteries currently charge and discharge to and from the grid, but in the second year of the trial they will charge while the demand is low, and enable Jeffkins to cut his consumption during the top tariff. In combination with his pre-existing 3kW solar panels, Jeffkins foresees substantial savings to his electricity bills, as long as Ausgrid allows him to keep the battery. "If there is some way I can buy it at the end of the trial I'll be interested," he remarks.

Salts and batteries

Alessandro Volta, after whom voltage is named, produced his first crude battery in 1800, and the more efficient Daniell cell preceded widespread electrification by many decades. However, the batteries in your car, laptop or flashlight are expensive ways to store household-sized quantities of power. Moreover, these well developed technologies may have little promise of significant further improvement. Fortunately, however, other technologies are emerging to fill the gap.
Not all of these are batteries in the traditional sense. Solar thermal power plants now run well into the night, powered by molten salts that can store heat to drive turbines. Solid blocks of graphite, run through with heat exchangers, have been proposed for Cloncurry and King Island. Other proposals include compressed air and splitting water to produce hydrogen. Hydroelectric power plants and flywheels represent more traditional forms of mass storage that some inventors hope to give a new lease of life.
In many cases these forms of storage are less expensive than batteries, but are often unsuited to dispersed application - Ausgrid might have had considerably more difficulty persuading Jeffkins and his neighbours to participate if they'd been asked to store high temperature molten salts on their front verandah.
Bruce Ebzery of Redflow, the supplier of the zinc-bromine flow batteries for Elermore Vale, believes his technology holds great promise. "The difference between all types of flow batteries and existing forms, such as lead-acid or nickel-hydride, is that in flow batteries the parts that make the reaction work don't get involved in the reaction so they don't degrade," he says. "In theory you can charge and discharge the battery forever with no loss of performance." Ebzery acknowledges the theory does not always work out, but flow batteries are still capable of far more cycles, at far higher efficiency, than the lead-acid batteries popular in off-grid systems.
Ezbery says there is no theoretical reason for them to be more expensive either. "Zinc and bromine are both common materials that you can buy easily, not rare earths. All the other components are plastics - really just advanced shopping bags," he jokes. Nevertheless, the Redflows installed in Elermore Vale are still impractically expensive for widespread use, costing around $15,000. Asked why, Ebzery invites people to "come and look at our factory in Brisbane. We're making them by hand."
Flow batteries require two electrolytes, rather than the one used in conventional batteries and this greater complexity has hampered commercialisation, but if demand can reach levels suitable for mass production, Redflow hopes to reduce prices by two-thirds. Meanwhile what many consider the brightest prospect amongst flow batteries has been largely neglected in Australia, despite being invented here.
Dr Maria Skyllas-Kazacos came up with the idea of using a little-known metal called vanadium as the basis of flow batteries in the 1980s. Vanadium's advantage is that it has enough 'oxidative states' that both sides of the battery use vanadium as the electrolyte. Therefore the challenge of ensuring the two electrolytes never mix loses its urgency. Skyllas-Kazacos says vanadium batteries also avoid the drawback of zinc-bromine competitors, "Which can form needles that penetrate membranes and cause short circuits. It's very difficult to lay down a uniform zinc layer." On the downside, current vanadium batteries are much heavier for the same energy storage than those Ausgrid is installing.
Although it has been a slow haul from Skyllas-Kazacos' pioneering work at the University of New South Wales, vanadium redox flow batteries are now taking off worldwide. Mass production is starting, a 1.5MW system has been installed at a semi-conductor factory in Japan and China sees vanadium batteries as a big part of its energy future.
The company that was commercialising the technology in Australia, Pinnacle VRB, however, decided to devote itself to coal seam gas instead, leaving the batteries without a local champion. Worse still, when the large prototype installed to store wind-generated energy on King Island ran into trouble there was no local vanadium developer around to fix it.
Rights to the technology have now been returned to UNSW, who are negotiating with companies for local developers. Meanwhile Skyllas-Kazacos is working on what she calls second generation vanadium batteries. These take bromine's solubility, and incorporate it with her work on vanadium. "Instead of a zinc-bromide solution you have vanadium-bromide. Vanadium ions are formed and everything stays in solution, rather than plating metals over and over again, which is hard," she says.
While there are still technical problems to solve, the highly soluble vanadium-bromide electrolytes offer the possibility of batteries that store plenty of energy for a given weight, release this energy quickly when required, are highly reliable and capable of charging and discharging thousands of times with little loss of performance.
One day these batteries may store the power generated by wind and solar for use when the wind isn't blowing and the sun is not shining. Or they may simply take the edge of peak demand. Either way, all players in the energy industry have much to gain by charging down the battery path.

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