Hacker News Reader

Comment by Workaccount2 | Hacker News Reader

I cannot see how this is useful outside of being a fun student learning program.

From the data it appears a battery with 1L of electrolyte provides about 18Wh of energy. Mind you this is at ~1.2V, which isn't especially useful without a boost converter. With a boost converter though you would need a low internal impedance from the battery, which I highly doubt is any good with a paper membrane (from what I understand it already isn't great for flow batteries).

Meanwhile a pair of 18650 lithium ion batteries can be had for $5 and can provide 24Wh at a very usable 7V with no power conditioning or a range of voltages with more than enough ability to source current. And it is a fraction the size, weight, and complexity.

I don't mean to tear apart the project, perhaps there is a key detail I am missing, but I just don't see what this is trying to do outside being a learning experience for students.

View on HN

Typically if you want to DIY something you first start with the smallest prototype possible and work your way up from there.

This demo cell isn't super interesting on its own but to validate the chemistry it's super helpful. Once you got that done you'd then work on a stack of cells, say 10 or 20 or 40 to get up to normal system voltages.

Once you have that working it's just a matter of making the tank as big as you want for your storage. Provided the initial chemistry is reasonable you could probably use a pair of IBC totes and really go somewhere.

Yeah! The thing about flow batteries is that if we manage to find good chemistries, they have the potential to be very cheap energy storage compared to ordinary batteries. High energy, low power, low cost.

Ie the small electrodes cost something but the big bag of fluid might be cheap.

Say, vitamin- like substances consisting of extremely common elements like hydrogen, oxygen, nitrogen, carbon etc could be used to store energy in a flow battery. Even with quite low performance, they could be very cheap compared to things like cobalt, nickel, manganese or lithium.

Or what about quinones? And sodium, sulphur, sodium are cheap too. There are a lot of very cheap chemistries that could be explored!

Bingo, this is exactly the plan. Of course there are non-trivial engineering challenges when scaling up, but that's the rough idea.

You are missing that this is just some salts dissolved in water, while the 18650 is a highly complex device.

How much does it cost to store 10m^3 of water? And hos much does it cost to store the same energy in 18650 batteries?

Also, the internal resistance depends entirely on how many cells you have. But a practical battery wouldn't use paper.

>Also, the internal resistance depends entirely on how many cells you have.

Right, from the one study I can find, commercial flow batteries have about 10-20x the internal resistance of a lithium ion battery, so the match the power and energy capabilities of a single li-ion cell you would need a liter of electrolyte and about 30 (!) cells (3 for voltage x 10 for power).

And that is for a commercial quality flow battery. And lithium ion batteries are wholesale in the $2 a piece range.

I'm not trying to say flow batteries are stupid or dumb, but their use cases are going to be very limited without some huge breakthroughs that will probably dramatically increase the complexity too.

Their use cases would become extremely relevant to people trying to rebuild society from scratch, I'd imagine. This device is so simple you could probably build one in the woods with nothing but a basic survival kit given a year or two alone.

So that's something. Learning how to build one from scratch seems worthwhile, much like learning to build a radio from scratch

Unless you're flying a drone, you don't need to match the power and energy capabilities of lithium ion.

On top of that, you don't have to match the internal resistance to match power. If you have plenty of material to absorb the heat, then you can tolerate more percentage points of loss.

In particular, while lithium ion batteries can be built to sacrifice discharge rate for a bit of extra capacity, something like a 3C discharge rate is easy enough to reach. And if your use case is powering a building for several hours, you might only need a .2C discharge rate. That would mean lithium ion as a technology is 15x overqualified, and a flow battery that gives you 10x less power would still be overqualified.

I see what you are saying, in reality the right energy storage is very application dependent. The crux of my argument is that I cannot think of many applications where a commercial grade flow battery is the best choice, much less a single application where a DIY flow battery is the best choice.

My main point is that while it definitely has to compete on price, it doesn't have to compete on price while also making you buy ten times as many cells.

Many elements of being the "best choice" are thresholds. Excess performance doesn't make it better. Price is extremely important, but power density is not so important for most use cases. So if it's even slightly cheaper, expect to see a lot of it.

> application where a DIY flow battery is the best choice

Christmas present for a battery enthusiast? :D

>The crux of my argument is that I cannot think of many applications where a commercial grade flow battery is the best choice

I think the argument against that is that we've spent tens of thousands of person-hours a millions of dollars more researching, developing, improving, and refining lithium-ion batteries than we have flow-batteries, and the purpose of the project in OP is to make it easier to tinker with flow-batteries.

Think of how much better lithium-ion batteries have gotten since we first started using them. We went from "You simply cannot achieve the energy density to propel (tethered) cars without fossil fuels" to "Oh wait we have electric cars now." in like a decade, and in the decade since them, lithium ion batteries have improved in every metric by at least an order of magnitude. We simply don't know how good flow-batteries can get, because we haven't tried, and it's silly to say "why bother trying, they're not very good right now" when we've just seen how much of a difference it makes to invest into this sort of technology.

A flow battery isn't going to burst into extremely high temperature flames in a self-sustaining not easily extinguishable fire that also spews toxic fumes in mass quantities.

I'll take a basement (or garage) with a flow battery over lithium ion ANY day of the week if I want battery backup for my house.

You would not use a laptop-style lithium battery for battery backup for your home. You would use LFP. It does not have the burst-into-flame problem you are thinking of.

At some point I expect we will look back at the era when we used really flammable electrolytes and laugh about how wild that was. I bet we are not that far from it being just a memory.

PowerWalls use NMC cells. And the majority of "diy powerwall" builds are reclaimed 18650 cells.

There's been a rumor for a while that Powerwall 3 is LFP, but I don't think anyone has actual confirmation on that.

I've seen occasional 18650 builds for DIY powerwalls but the vast majority are using prismatic LFP cells. Way easier to wire up, cheaper (unless you have a secret source for surplus 18650s), and minimal fire risk.

> I'm not trying to say flow batteries are stupid or dumb, but their use cases are going to be very limited without some huge breakthroughs that will probably dramatically increase the complexity too.

The largest use case is going to be grid scale storage, and for that one a bunch of dumb tanks and a bank of cells are far easier to handle and less risky than a bunch of li-ion cells that can go into runaway for whatever reason.

The thing is that there are like 50 other options for energy storage, it's not just lithium-ion that flow batteries have to out compete. Everything from electrolyzed hydrogen, to hot sand, to air pressure tanks, to sodium-ion and zinc air and LiFePo batteries.

Flow batteries are cool because the storage element is extremely easy to scale. But its not even that great because you also need to scale the amount of cells dramatically to make it useful outside of edge cases. At which point it probably makes more sense to just use another storage mechanism.

1 liter of electrolyte is nothing for a flow battery, the smallest scale they become a serious competitor is ~10m3 (10,000L) tanks which are ~(7 foot X 7 foot X 7 foot).

Start taking GWh of storage and lithium ion technology gets really expensive and has a lot of associated risks. Flow batteries on the other hand don’t need to worry about a single cell failure resulting in a fire which then spreads.

The amount of electrolyte doesn't scale the available power though, only the available energy.

Energy storage is the problem that needs a solution, e.g., storage from summer to winter.

Annual and long-tail storage are both problems that need solving, and fuel cells do look like a possible solution. But it's not clear at all what the winner will be for those applications.

Even hydrogen is competitive here. IMO, more competitive than that battery chemistry on the article.

Fuel cells are a possible solution (especially if one can build a dual mode electrolyzer/fuel cell), but combined cycle power plants burning hydrogen would also work, if only at very large scale (but then economical hydrogen storage likely requires large scale).

Seasonal energy storage is the last thing that needs to be addressed in the storage hierarchy. There are very high-value targets starting on very low time frames.

Seasonal energy storage is the last thing, but that also means it's the last caveat, as far as I can tell. If we figure out seasonal energy storage, that's it. Solar just wins. There's no further need for fossil fuels. We're done.

I guess there's still aircraft.

That just means you get to scale it independently.

While they both need to scale the amount of DC<>AC inverters based on peak power demand. If you want to discharge over 16 hours you’re using 2% of lithium ion’s peak power output and need a huge mess of wiring to move power from each internal cell to that inverter + complex battery packs with individual electronics cooling etc.

Flow batteries on the other hand can use a single pump (+ redundancy) and fat pipe to supply a huge array of ion-exchange membranes which then sit next to the inverters.

As someone completely ignorant in the field, my impression is that the point of this is to create something that relative amateurs (or research professionals on a budget) can use to tinker with various chemistries to achieve those huge breakthroughs (that we keep seeing in every other kind of battery, because it turns out batteries have a lot of room for breakthroughs).

Not a battery expert, but this seems the right ballpark for useful batteries.

Back of envelope stuff:

1liter for 18Wh.

1k liter 18KWh (this is an average hot tub).

10k litre for 180Kwh. This is a ~$1000 farming tank.

~100KWh lithium batteries are around the $20-30k. (Used Tesla pack for reference)

Quick google shows flow electrolyte in the neighbourhood of $100 per KWh. Or $10k for a ~100KWh battery.

All this is nothing definitive, but it’s not showing any 10x or 100x differences that would rule out an interesting idea.

In order to really make a determination though you need to know what the internal resistance characteristics looks like.

18kWh becomes near useless if it can only source enough current to power your TV at any given time. Or to put that another way: 18kWh doesn't do you much good if you can only draw 200W from it at a time.

Given that flow batteries are known for their virtually zero self-discharge, and this project is aiming for a cheap/easy membrane, it seems very likely that internal impedance will kill most use cases here.

Mind you I don't think flow batteries themselves are useless to pursue. It's just that I believe a viable flow battery is almost certainly going to be something that requires complex chemistries and advanced manufacturing. In the same way you can build an open source EV from scratch, but you really wouldn't want to ever take that thing on the street.

Why wouldn't you take a scratch-build EV on the road? People build kit-cars all the time, and an EV has a much simpler control system.

This is a very simplified project to prove the concept and provide a test bed for further exploration, not an end-product by any stretch. This seems like the perfect project to test various membranes and electrolyte solutions.

>Why wouldn't you take a scratch-build EV on the road?

Because you don't want to snap your spine in a minor fender bender.

Scratch built is not the same thing as an EV conversion kit, where all the hard stuff (like a frame and body panels) was already made by commercial manufacturers.

This flow battery is from scratch (well except for the pumps and electronics, but the cell itself is). They are not using off the shelf electrolyte and electrochemical cells like a flow battery kit would.

It's a neat project and would teach a lot, but I just cannot find a scenario in my head where I would want this (even a scaled up version) over another solution.

Every other year, (solar-)electric cars scratch-built by high school students drive on public roads from Texas to (usually) California. This is considered a reasonable level of challenge, and something which insurers will cover (entrants are required to have vehicle liability insurance).

https://www.solarcarchallenge.org/challenge/about.shtml

https://www.solarcarchallenge.org/challenge/docs/rules2023.p...

Or from Darwin to Adelaide in Austrlia, where they have road trains to contend with. DIYing cars is very doable.

And you would daily drive one of those?

You would be ok getting into an accident with one the same as you would get in an accident driving a civic?

Or maybe those are just learning vehicles meant to teach, and not meant to be car replacements? Just like this flow battery project?

Ironically your post validates my whole point: This is a student project at best, and likely worthless as a "democratization of energy storage". The same way those EV's would never be considered "democratization of EV cars".

C'mon...

I take your criticism, but as for your comment that it's "a student project at best"... we do have PhDs (mine in flow batteries !) and manage this project in our spare time, at our homes...

Our small team is fully qualified to work at any flow battery company. Just give us some time and let us work on it full-time for a bit (which will happen soon). The linked post on top was a blogpost I cranked out in a few minutes one night, not something I ever expected to be on HN.

> ~100KWh lithium batteries are around the $20-30k. (Used Tesla pack for reference)

Nitpick: that seems high, and probably very specific to high capacity Model S packs. A brand new 75kWh Tesla pack for a Model 3 is around $10K installed these days.

Flow batteries are optimized for cost and capacity. Not weight, nor volume/energy density, nor instantaneous power delivery. In the case of some iron flow designs, add in "dirt-cheap, non-toxic materials."

A pair of 55 gallon drums equals 7.4kWh, and I'm guessing a lot of us could easily find that much space in our basements. That's enough to power 300W of load 24x7 (a modern fridge is about 60W. 100W will get you really far in terms of LED lighting given that most "60W" bulbs are well under 10W these days.)

One "car battery" sized LiFePO4 battery is about 1400Wh, and costs anywhere from $100 to $500+ depending on the manufacturer/reseller.

I'm a little mystified why they didn't go with a simpler iron-flow design as it is very cheap, and can be nearly completely non-toxic.

The actor I'm mildly paying attention to is Lockheed-Martin, who have an energy systems group that's working on flow batteries. Judging by patents, their flow battery likely uses various transition element ions that are kept in solution with any of a variety of organic ligands. The wide variety of chemistries is the attractive part, since they present many knobs to twiddle for optimization.

Iron plating is a hydrogen evolution nightmare. It's interesting for sure, but not feasible for a simple demonstration system, due to pH issues and oxidation state drift from hydrogen evolution. We do plan to explore it in the future, and move onto larger cells/stacks that offer practical amounts of storage.

There are two key details you are missing:

1) Its scalable to dishwasher size, ( enough to power a tiny house )

2) If you shot it with a bullet, it would just leak salt water. That is all. Lithium Ion will explode:

Now here is the quiz: If you have a cell phone that is inflating, do you A) Dunk it in water? or B) Toss it in a full document safe? or c) Quickly empty your document safe, and toss it in?

If a flow battery leaks, you can toss in a chicken into the delightful brine.

Since you cannot scale this easily to Utility sized batteries easily, the D.O.E. is not interested. i.e. if you are looking to scale this to a couple of hundred megawatts, just stop reading and thinking about this now. This is NOT mobile. Its not useful for cars or cities. Its right sized for homes.

   … if you are looking to scale this to a couple of hundred megawatts, just stop reading and thinking about this now

I thought that was one huge appeal of flow batteries is that you can basically infinitely scale them. China has a 100MW installation (potentially more since this 2022 report)

https://www.pv-magazine.com/2022/09/29/china-connects-worlds...

These guys in the US make a 500kwh version, that can run at 75kw of discharge power across 3 phases, and its a single shipping container: https://essinc.com/energy-warehouse/

It doesn't seem like it would take up that much space to have 200 shipping containers sitting somewhere, i'm pretty sure the Home Depot distrubution center in our town already is close to that in their parking lot (yes, you would want them not on wheels, and farther apart)

That’s incredible. I wonder what are the costs relative to a grid scale battery of equivalent size.

I only wish they made one that were barrel sized and fit for consumers. Worst case, you have a leak vs a home battery fire.

> Worst case, you have a leak vs a home battery fire.

Battery fires are an EV (and then, only certain models) and laptop/phone thing. Only a few home batteries use the really flammable electrolytes (mostly Tesla Powerwalls, I'd bet). Most people are using LFP for home, which is less expensive and doesn't have the fire problem.

"But that's not what happened. Instead of the batteries becoming the next great American success story, the warehouse is now shuttered and empty. All the employees who worked there were laid off. And more than 5,200 miles away, a Chinese company is hard at work making the batteries in Dalian, China.

The Chinese company didn't steal this technology. It was given to them — by the U.S. Department of Energy. First in 2017, as part of a sublicense, and later, in 2021, as part of a license transfer."

https://www.npr.org/2022/08/03/1114964240/new-battery-techno...

> Explode

Not all Lithium Ion chemistries react this way. LFP does not explode:

https://youtu.be/D8xNjz73p80?si=LA4iGdI6sTJ_C9kJ

"For some scientists doing flow battery experiments in their respective homes/apartments, we’ve got some solid preliminary results"

Obviously it's a research project not a commercial product. What do you expect?

Personally I would find it useful for applications where there needs to be little to no self-discharge and fire safety - like a remote shed with some kind of sensor.

You still need something to power the pumps. And we already have long term low power batteries. And solar + battery has filled this role for decades.

The pumping cost constitutes a 1-2% total penalty on round-trip energy efficiency for a well-designed flow battery.

This is awesome!

Obviously we’d need a real ion exchange membrane and put 40 of them in series, but it looks pretty scalable even in its present form. This looks very practical to me, once a few more years of tinkering is done.

I’d love to have more information about electrode fluid cost, life and reconditioning/reprocessing, as well as power densities for membrane area.

I’d love to be able to add capacity just by adding tanks and electrode fluid! For microgrids like ours, this is a longstanding goal.

> I just don't see what this is trying to do outside being a learning experience for students.

Perhaps one of those students will figure out how to make a useful large scale flow battery? I have solar, and the missing piece is being able to store electricity for the winter.

Perhaps the person who figures it out learned something from a project like this?

This website is called hacker news. I think you are missing the point of this post.

Reply on news.ycombinator.com