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Comment by philipkglass | Hacker News Reader

Unfortunately, there were no details about the proposed battery chemistry in the video either.

From memory, nickel-iron batteries have the following limitations for stationary storage:

- Relatively high self-discharge rate (though this isn't a big problem if you're buffering renewable electricity on a daily basis)

- Comparatively low energy efficiency, ~70%

- Hydrogen evolution by water electrolysis during charging -- a potential hazard, and one of the main loss paths driving the low efficiency

- Electrolyte water loss from electrolytic evolution of hydrogen during charging requires regular compensation with additional water

There have been a number of approaches to improve efficiency/suppress hydrogen evolution in nickel-iron batteries by the addition of organosulfur compounds. I don't think that any of those approaches are on the way to commercialization yet, though.

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You're true on all of your points. But there's other factors that make them very interesting.

1. Since the electrolyte is a base (Sodium/Potassium hydroxide) you can make it out of wood ash in a pinch.

2. The batteries can handle all sorts of catastrophic damage - have a charged battery and run a gutter nail through every plate? It'll fizzle and discharge in the nail.

3. You can severely overcharge and undercharge with no ill effect. Our current NiMH, Lithiums and the like all have really bad effects when you under/over charge them. Blowing up is one such... err, "feature"

4. These batteries are known to last over 100 years. They were some of the first ones that Ford and Edison put in cars. Chalk this up to longevity (and no acid eating consumable lead plates).

Oh, and for your electolyte losses- true that you do need to top off with distilled water. But 'regular changing' is actually around 6 months to 1 year. I wouldn't be listing that as a major downside. I'd much rather add a few pellets of NaOH and some distilled every 6 months than pay for a new lead-acid battery every 2-3 years.

> "- Hydrogen evolution by water electrolysis during charging -- a potential hazard, and one of the main loss paths driving the low efficiency"

On that point...

https://www.youtube.com/watch?v=GZ8IcoHjFdk

Also, it's worth noting that this is a research project. Test cells have been produced, but experiments are ongoing, so the final design is not set in stone.

Oh, great! I see that the separate YouTube channel's videos discuss the chemistry though the fund raising page's video doesn't. That won me over -- $100 donated. It looks like I have a bunch of videos to watch this weekend :-)

Can you just store the hydrogen? Or is it just so inefficient as to be useless?

Seems like batteries to cover 95%+ of your use case then having hydrogen backup for for covering rare weather conditions might work well for off grid setups.

That's the "battolyser" concept -- store and use the hydrogen from nickel-iron unit charging instead of wasting it. But round-trip storage efficiency is lower via hydrogen (if you want electricity as the end form of energy) and it increases complexity/cost to add systems for hydrogen. So the economics may not be improved even though the energetic efficiency would be.

I think the main issue with hydrogen is just that it's crazy dangerous and sort of hard to work with safely. It's highly flammable, and becomes violently explosive when mixed with oxygen.

It's easy to make - just pass current through water - but while all batteries are basically bombs, a key factor in their design is that they should go off very slowly.

How about burning it as it is produced?

Okay, but now you just have some steam and heat floating around.

It's gonna dissipate pretty quickly, not a great way to store power for the medium-long term. Hydrogen separated from Oxygen is where the useful potential energy difference is.

The idea behind hydrogen fuel cell batteries is that you spend your cheap clean renewable energy to split H2O slowly when energy is available, and burn the hydrogen when you need bursts of power. If you burn the hydrogen right away, you're just un-doing the water-splitting reaction and you won't have anything to use for power when the cheap clean renewable energy is not available, like during the night for solar power.

I think that the usual way to get energy back out of the hydrogen is just to burn it and let the hot pressurized gas power a steam turbine, but don't quote me on that. Or try it at home; scalding and flash burns are good things to avoid.

Could you use the steam to drive a turbine to recharge the batteries? You'd not recover nearly everything clearly but I'd imagine it's more than nothing.

You reallllly don't want to store H2 gas.

On second thought, you realllllllllllly dont want to store H2 gas.

Having worked some in welding (I considered doing it instead of programming for a while), the problems with H2 are numerous. Firstly, it seeps out of any container you put it in. And I do mean any. Hell, even glass ampules in the chemistry have a hard time sealing H2.

Another major issue, is that H2 does "fucky" things with metal. Ever heard of hydrogen embrittlement? (1) You have cracks in your metal. Well, hydrogen, being as tiny as it is, also can bond with the metal. Gets in there, makes cracks bigger. Creates weird metal acids (H2FeCO4) and they attack more metal.

And if you're storing H2 gas in a regular container, you just made a time detonating fuse, and.... you don't know the time.

But yeah, H2 gas creation may be easy, but storage is super hard and really dangerous. And unless you can get H2 in liquid form, it's pretty low power density compared to things like octane.

(1) https://en.wikipedia.org/wiki/Hydrogen_embrittlement

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