Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Iron as an inexpensive storage medium for hydrogen

ethz.ch

Post reply on HN
Print view View original

71–80 of 107 posts

Re: Iron as an inexpensive storage medium for hydrogen

#71

Post by rini17 »

micwag wrote: post #48
rini17 wrote: post #41

Earlier quoted context omitted.

If it has 33% net efficiency that sets it back 3 times compared to batteries right from the outset. With stainless steel pressure vessels needed here and hydrogen precautions, not holding my breath.

This is for seasonal energy storage with only 1 charge and discharge per year. It competes with water reservoirs not with batteries.

That means it has only 1 chance per year to recoup the investment. And that requires exorbitant energy spot selling price, which too rarely happens to rely on. The economics just isn't there.

Re: Iron as an inexpensive storage medium for hydrogen

#72

Post by lta »

erickj wrote: post #23
johndough wrote: post #10

Earlier quoted context omitted.

I'd like to point out row 3 of the excellent Fig. 6 where the authors evaluate the risk of fine iron powder being exposed to air, which heats up to about 600°C due to oxidation. https://pubs.rsc.org/image/article/2024/se/d3se01228j/d3se01...

I believe most Swiss scientific investigations are legally required to involve Cervelat

This is one of the most absurd comment I've read in a while. I love it, thank you.

Fwiw, cervelat is also very common in France, I grew up eating that stuff. Maybe that's why I liked the article so much. There's something to dig up there

Re: Iron as an inexpensive storage medium for hydrogen

#73

Post by rini17 »

7952 wrote: post #49
rini17 wrote: post #41

Earlier quoted context omitted.

If it has 33% net efficiency that sets it back 3 times compared to batteries right from the outset. With stainless steel pressure vessels needed here and hydrogen precautions, not holding my breath.

But there comes a point where battery storage has all been used and prices go even higher. You sell at a x6 profit margin. And are able to sell at x3 profit margin for longer than the battery operators. And that assumes that 100% of the fuel would need to come from storage.

You are betting against batteries? That's becoming risky, Na-ion has the potential to be literally as cheap as dirt. And they are not flammable.

Re: Iron as an inexpensive storage medium for hydrogen

#75

Post by 7e »

crote wrote: post #38
goodpoint wrote: post #32

Earlier quoted context omitted.

This not a problem at all when using PV. Plus, the generated heat can be used.

The issue is that it's a self-defeating mechanism. PV doesn't produce zero energy during wintertime, they just produce less . You're going to be building additional PV to charge the Season Battery, but those additional panels will also be providing power during the winter. If your battery's efficiency gets bad enough the added winter power from those extra panels is going to be enough to cover the winter shortage - s…

There will always a use for surplus energy. Are you really going to curtail surplus solar in the summer when you could just build storage for it? That’s the profit maximizing solution, even if the efficiency isn’t high. It just needs to be cheap.

Re: Iron as an inexpensive storage medium for hydrogen

#76

Post by thargor90 »

derriz wrote: post #47
crote wrote: post #38

Earlier quoted context omitted.

The issue is that it's a self-defeating mechanism. PV doesn't produce zero energy during wintertime, they just produce less . You're going to be building additional PV to charge the Season Battery, but those additional panels will also be providing power during the winter. If your battery's efficiency gets bad enough the added winter power from those extra panels is going to be enough to cover the winter shortage - s…

A good point. Depending on the latitude/weather/etc, the difference between winter PV production can see a reduction of between 40% and 85% compared to summer output (sampling from [0]). Panel prices have dropped so much, it's far more likely that, at least with places where summer output is double that of winter or less, that simply doubling the number of panels solves the problem. Batteries and PV are cheap and get…

The biggest problem is heating in winter, which requires way more energy than cooling in summer. So for colder areas doubling Panels will not be enough.

Re: Iron as an inexpensive storage medium for hydrogen

#77

Post by mppm »

credit_guy wrote: post #56

This is a pretty elegant idea. It takes 826 kJ to split a mole of iron oxide (Fe2O3) and it takes 855 kJ to split 3 moles of water (H2O). So if you take H2 and blow over one mole of Fe2O3 you can strip the O3 for the cost of 826 kJ but then by burning the hydrogen in oxygen you get 855 kJ, for a net exothermic effect of 29 kJ, which is a rounding error. The opposite reaction requires 29 kJ, again negligible, there ar…

> Storage tanks for compressed hydrogen enjoy the square-cube law.

Not really. Wall thickness is roughly proportional to diameter, and surface area to the square, so you don't gain anything in terms of storage mass ratio by building bigger tanks.

> But the round-trip efficiency of the tank is virtually 100%

This is oversimplifying quite a bit. Compressing hydrogen, the lightest gas, is very energy intensive per unit of mass, and this energy is not fully recoverable upon decompression (due to general pump efficiency and thermal losses in the intercooler).

Re: Iron as an inexpensive storage medium for hydrogen

#78

Post by kortex »

credit_guy wrote: post #56

This is a pretty elegant idea. It takes 826 kJ to split a mole of iron oxide (Fe2O3) and it takes 855 kJ to split 3 moles of water (H2O). So if you take H2 and blow over one mole of Fe2O3 you can strip the O3 for the cost of 826 kJ but then by burning the hydrogen in oxygen you get 855 kJ, for a net exothermic effect of 29 kJ, which is a rounding error. The opposite reaction requires 29 kJ, again negligible, there ar…

Iron oxide is completely inert. You can store it in piles, under the elements. Iron powder less so, you need to keep it dry, but again you can just pile it up. The only tricky part is moving dense dry solids around at the huge scales required.

Edit: wait I forgot that direct reduced iron powder exothermically reacts with oxygen and water in the air, that's how single-use instant hand warmers work. So yeah you gotta isolate the iron powder a bit more than stick it under a tarp.

I've been playing too much Factorio lately so of course my mind goes towards rail systems (could repurpose coal plants) in combination with pneumatics.

Re: Iron as an inexpensive storage medium for hydrogen

#79

Post by wffurr »

mglz wrote: post #66
dredmorbius wrote: post #64

We have a cheap, stable, infrastructure-friendly, high-density storage formula for hydrogen. Or better, since the application here isn't hydrogen-specific but is simply looking to find a fuel-storage solution: energy storage. It's hydrocarbons. In this case, synfuel hydrocarbons as direct analogues of fossil-fuel based compounds of chain-lengths 1 (methane) to around a dozen or so (kerosene / aviation fuel, at a stre…

How much incoming solar power ends up in the methane? And how do you get the energy back out?

>> How much incoming solar power ends up in the methane?

As in how many power to gas plants are operating currently? I would guess not many due to the price vs fossil methane, but as the GP notes this is a major market failure due pricing the externalities of fossil methane.

>> And how do you get the energy back out?

Easy, burn it. For heat, or with a turbine, electricity. Zero carbon impact because it started out as atmospheric CO2.

Re: Iron as an inexpensive storage medium for hydrogen

#80

Post by usrusr »

zahlman wrote: post #65

I don't think I understand the idea here properly. When storing energy, the idea is to split water into hydrogen and oxygen, and then let the hydrogen recombine with the oxygen from iron oxide... to make water again. Meanwhile the oxygen from the original water is just released (since it's everywhere anyway)? That doesn't really seem to me like "storing hydrogen", since you just get the water back that you already ha…

> "So why not just, well, burn (i.e. rust) the iron directly? What exactly is the dissociation and re-combination of the steam accomplishing?"

Direct use of reduced iron as an energy carrier has been discussed here:

https://news.ycombinator.com/item?id=24996153

Oxodizing iron gives rather low intensity heat, comparable, iirc, to burning lignite. That might be good for some combined cycle applications (but still a logistics nightmare?), but it's not a drop-in replacement for anything. Hydrogen on the other hand is good for an extremely wide range of applications, from fuel cells to e-fuel production (and all kinds of other chemical processes) to flying Neil Armstrong to the moon.

To succeed in decarbonization we will need an entire "cache hierarchy" to solve the intermittency problem, a single storage solution will never be enough. Batteries to make hydrolyzers able to run around the clock during high availability seasons, hydrogen storage to make converters further down the pipeline run continuously during surplus seasons and not only on the best days.

What will definitely not get us to decarbonization is any of the following three approaches:

(a) building enough production capacity that we don't need storage (most production would be idle most of the time for lack of a buyer)

(b) focusing on one kind of storage (same problem again, now with conversion capacity)

Post reply on HN