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An open-source flow battery kit

dualpower.supply

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Re: An open-source flow battery kit

#11

Post by Workaccount2 »

heeton wrote: post #7
Workaccount2 wrote: post #2

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…

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 noth…

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.

Re: An open-source flow battery kit

#12

Post by ajford »

Workaccount2 wrote: post #11
heeton wrote: post #7

Earlier quoted context omitted.

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 noth…

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 i…

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.

Re: An open-source flow battery kit

#13

Post by Workaccount2 »

marcosdumay wrote: post #9
Workaccount2 wrote: post #2

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…

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.

Re: An open-source flow battery kit

#14

Post by KennyBlanken »

Workaccount2 wrote: post #2

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…

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.

Re: An open-source flow battery kit

#16

Post by Workaccount2 »

ajford wrote: post #12
Workaccount2 wrote: post #11

Earlier quoted context omitted.

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 i…

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.

Re: An open-source flow battery kit

#17

Post by KennyBlanken »

I've been watching ESS (they make a non-toxic iron flow battery system) for years and been really frustrated that they have made essentially zero progress deploying the technology, with less than half a dozen deployments.

The technology looks great, but they seem annoyingly incompetent at marketing/selling their product...or are just holding out for "whale" customers, refusing to work with anyone except microgrid (ie college campus) and utility scale customers.

So many promising products and technologies die because the inventors/developers hold out for huge customers while ignoring the huge demand from retail/small/medium corp customers.

"We won't talk to anyone except corporations with deep pockets. Once we find a couple of those, we'll be filthy stinking rich!" instead of "if we sell the components at a price that undercuts LiFePO4, we'll have as many customers as we can handle, and there's plenty of margin for distributors and retailers, so we don't have to be B2C."

Re: An open-source flow battery kit

#18

Post by KennyBlanken »

kleton wrote: post #15

What is the Coulombic efficiency? A paper membrane probably leaks a lot, but a state of the art ion exchange membrane probably runs $1k/m2.

It's in the blog. The author mentions finding that matte inkjet paper worked fairly well.

There are much cheaper membranes; ESS for example uses a membrane that is used by lithium ion batteries (I think) and thus is commonly available and very inexpensive.

Re: An open-source flow battery kit

#19

Post by Workaccount2 »

Tade0 wrote: post #6
Workaccount2 wrote: post #2

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…

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.

Re: An open-source flow battery kit

#20

Post by _alex_ »

I dont know anything about flow batteries, but some quick searching leads me to believe that there are two tanks of electrolytes with pumps that pump them along a membrane and then you get power across the membrane. In this small battery kit, is the idea that the battery provides enough power to both operate all its own pumps/electronics, and then output usable power? Does anyone know how much power you'd be able to get out of a small setup like this?

Looks like a cool project!

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