14 October 2009

Breakthough in Flow Batteries?

So there's been a little Google explosion on the subject of flow batteries recently, with a German group claiming a breakthrough. From the press release,
Until now, however, redox flow batteries have had the disadvantage of storing significantly less energy than lithium-ion batteries. The vehicles would only be able to cover about a quarter of the normal distance – around 25 kilometers – which means the driver would have to recharge the batteries four times as often. “We can now increase the mileage four or fivefold, to approximately that of lithium-ion batteries,” Noack enthuses.
Mmm... vague, yes? As anyone who has been following the alternative energy scene for any length of time knows, the bigger the claim and the fewer facts behind it, the more likely it is to be BS. As always, it pays to be skeptical rather than credulous.

If you aren't familiar with the technology of flow batteries, I suggest you buck up to Wikipedia and take a read. The strong point of flow batteries has always been that the power and energy storage characteristics are decoupled: the power is a function of the size of exchange membrane, while the energy storage is determined by the volume of the storage tanks. In this fashion, they are a lot like fuel cells except that they are reversible. However, the energy density (as a function of weight or volume) has never been terribly impressive, lying around that of lead acid batteries.

The engineer who is quoted in the story, Noack, appears to be involved with the design of the exchange membrane and I can't see the mechanical bits resulting in a 4 - 5 fold improvement in energy density. I found a paper he wrote here comparing the various known chemistries applied to a new membrane stack design. There must have been some new chemistry developed, either that or there's smoke and no fire here. The article does mention collaboration with the University of Applied Sciences, Ostphalia [sic], but I can't find anything pertinent on the university's web site.

The previous king of the various redox flow battery chemistries is the Vanadium redox battery. It can, in general, obtain a 75 % round-trip efficiency which is fairly decent, being roughly in-between Li-ion batteries and Nickel-metal hydride batteries. The Achilles heel has always been the chicken and egg problem of the cost of Vanadium. Vanadium is not a particularly rare element, but it isn't mined in large quantities due to lack of demand and hence it is quite expensive. A single utility scale redox battery would consume a significant portion of the world's annual Vanadium production. Thus the conundrum, if no one can afford to buy a Vanadium redox battery, you'll never generate enough demand for Vanadium to open up new mines and drive the price down. The best hope, I always thought, was for one of the Vanadium-contaminated oil deposits of the world to be developed and glut the world Vanadium market.

As far as I know the intellectual property behind the Vanadium redox battery was held by VRB Power Systems but they went bankrupt earlier this year. They seem to have been acquired by a Chinese firm, Prudent Energy. It's probably worthwhile that the dollar numbers for Vanadium redox batteries didn't work out, even way back in 2005 when I last looked at it.

4 comments:

Vanadium said...

Then you are in luck, in fact the whole world is in luck. A huge low-cost vanadium deposit was discovered recently in Madagascar by www.uraniumstar.com It is sediment-hosted so much much cheaper to extract than all others (which are volcanic intrusives). So that solves one issue. the other issue you brought up is the patent... well read this article in the National Post (bit.ly/1Gkvyh)and you'll learn that VRB's patent expired and now the world should brace itself for a vanadium battery revolution that will allow solar/wind/tidal power to become the main sources to national power grids.

Follow my vanadium tweets @VandiumJoe if you want to learn more about the exciting future of vanadium.

MMOSHARK said...
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Cyril R said...

I've heard that a big part of today's vanadium production is from petroleum refining (vanadium is after all quite corrosive at elevated temperatures). If the peak oil people are correct this could lead to a production issue (unlikely an ultimate reserves issue since vanadium as you mention isn't that rare).

What other metals could potentially be used for flow batteries?

There's also vanadium-borium fuel cell type battery being developed:

http://www.greencarcongress.com/2008/07/researchers-d-2.html

Effective and efficient regeneration would make that system very useful for a lot of applictions.

Steve said...

Come on, the German researchers are protecting their technology and won't give you the details so that someone can copy their idea. Makes complete sense to me. :)