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Comment by LeanderK | Hacker News Reader

> They remain costly, though, with a capital cost of around US $800 per kilowatt-hour, more than twice that of lithium-ion batteries.

I was surprised by this! Since this is not commercialised on a broad scale, I would have thought that the cost is nowhere near competitive. Twice seems very close. How close are we to introducing flow-batteries at a competitive price?

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> Liu estimates that the tubular design should cut the cost of flow-battery power modules by roughly half. Plus, all the components in the cell are off the shelf, and scaling up the reactor cell design should be easy, since it is based on a commonly used design in the chemical industry.

So if this research pans out it sounds like very close. This isn’t a new concept and it’s mature so the probability of continuing savings is less than traditional battery technologies (eg there’s new kinds of batteries coming out that are cheaper and more energy dense than lithium ion). However, at grid scale this may have additional advantages beyond pure cost that make it attractive still.

I can't imagine this is more mature then lithium ion batteries, or traditional batteries in general. They are everywhere in my apartment but afaik flow batteries are not used yet.

I agree, especially on the industrial design and manufacturing side. The concept has exited for ages, and I love decoupling power and energy density for all kinds of reasons (though I'm sure standard batteries are just tuned perfectly enough in large facilities that it's no big difference).

But the big cost reductions don't happen because an idea is mature, they occur because they're being produced at large enough scale that lots of people have spent time and energy on all of the thousand tiny things that individually reduce the cost. The stuff in this article is borderline just industrial design and they're talking a 3x change in footprint?

There has to be lots of other low hanging fruit... we're still improving lithium battery electrodes and each improvement really does improve them. The same will be true for flow batteries if they ever get made at enough scale.

Agreed. Lithium itself is 7x the low price it was 5 years ago. https://www.dailymetalprice.com/metalpricecharts.php?c=li&u=...

Emphasis on "more than". Lithium-ion batteries have been below $200 per kilowatt-hour for quite some time.

Basically the statement is lying through omission.

I find that number dubious, since the per-kWh cost of flow batteries should be low: just make the tanks larger.

It sounds like the energy capacity and power output can be scaled independently of one another. But as this article is meant for a wide audience, I think they simplified the discussion by making some assumptions about the desired power output per kWh stored.

Not unreasonable. The details are always in the research paper after all.

Your max power output probably doesn't go up ny "just making the tank larger"?

kWh does not measure max power, it measures capacity. A kWh is a constant factor multiple of Joules. I’d think you could absolutely make the capacity larger (ie store more energy) by just making the tanks larger. The flow rate is the thing that seems to determine the power output.

Yes, but I wasn't talking about capacity. I was talking about max output power.

Increasing the size of the tanks to increase the energy storage capacity, without increasing output power would be... useless.

Extreme example: a huge expensive 100 MWh battery that you can only draw a max power of 100 W from = useless.

I think it's actually closer to 4x as much. You can get about 4KWhs of LiPoFE4 for about $800. At least you could 2-3 years ago.

I recently got 7.4kWh at $160/kWh grade B cells for what it’s worth. Surely there are better deals out there, especially for used cells.

Even 4x as much is still way closer than what I've thought. This is not commercialised on a mass scale yet, but batteries are and have been for ages. Billions and billions of dollars got invested into cheaper, better and faster. Even 4x just seems right around the corner if you consider just how much work went into making batteries cheaper.

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