Flow Battery, Flow!

Brent Cullimore

The field of positive psychology is devoted to making so-called “normal people” happier. A key observation is that people tend to be happiest when they are in a state called Flow. (As much as I would like to live the State of Flow, Colorado comes close!)

In this state of relaxed concentration, people are performing an activity (knitting, fly fishing, solving crossword puzzles etc.) to which they can devote themselves exclusively ... at least for a little while, and which they do well.

So is a flow battery a happy battery because it is doing just one thing, and doing it well?

Or was I just experiencing flow while building math models of flow batteries? After all, just adding the word “flow” to anything gets my attention, living as I do on the Wet Side of Mechanical Engineering Boulevard.

So why should a battery flow? Other than the American Declaration of Independence asserting that pursuing happiness is everyone’s unalienable right, of course.

Perhaps the biggest advantage of a flow battery is that there is no design constraint between the maximum rate of energy that you can put in or take out of one, and the amount of energy that you can store inside. You can design a flow battery that accepts a mere 1MW charge or discharge rate, yet holds 5GWh of energy. Or you can design one that can charge at an astounding 5GW rate but which only holds 1MJ of energy. Why you do either of those extremes is beyond me, but the point is: you could.

If that isn’t impressive, then please learn to be disturbed when some press release says “a 50 MW battery” but doesn’t say how big it is. Or if it says “a 50 MWh battery” but doesn’t say how fast you can discharge it. C’mon people, we’re engineers. We have full right to get upset when a journalist can’t tell amps from amp-hours!

Do a search on “flow battery” maybe sprinkling in keywords like vanadium (VRFB) or iron-chromium (ICFB) or zinc-bromine (ZNBR). You’ll be amazed at what is already available and has been life-tested for decades, and what is being developed for the next generation. You might start with a little overview, such as this:

As I have mentioned in a prior blog, we need grid-scale batteries, and most technologies struggle to reach that scale and yet stay cost-effective.

There is an incredible amount of research and investment happening in the energy storage world, and flow batteries are but one recipient. A majority of the attention (and R&D money) is still flowing into dry cells, especially that stalwart: the lithium-ion battery. The press is full of stories of advances in that technology.

In fact, it is darn hard to wax effusive about flow batteries in the same week that Tesla and Panasonic showcase their Nevada-based lithium-ion battery Gigafactory.

That’s OK, CRTech software can model lithium-ion batteries too, at least in regard to thermal management and investigations of runaway. In fact, here’s a model derived from a Panasonic battery that happens to be a lot like the ones that Tesla uses:

Modeling a dry cell may not bring the same joy, but if I were a betting man (meaning: "if I were not an engineer") I would bet on some variation of a lithium-ion battery winning the Charge Wars, especially for vehicles.

Still, I’d hedge with a side bet on flow batteries, since it really is too soon to tell which one will win the race for utility-scale batteries. Both types have already been deployed for that application. I personally think that extra research money should flow toward flow batteries for grid-scale electrical energy storage because of scalability, longevity, and safety. Yes, you read that right: I’m OK betting someone else’s money on flow batteries!

May you find happiness in whatever you enjoy and excel. And may both you and your batteries flow.