Live data from Hacker News

Iron as an inexpensive storage medium for hydrogen

ethz.ch

81–90 of 107 posts

Re: Iron as an inexpensive storage medium for hydrogen

#81
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…

> Rather, it's using the energy to deoxidize rust.

Exactly, really what they are storing is electrons.

Rusting the iron directly releases heat, which limits your efficiency to the delta-T of the process. Reducing steam to hydrogen and then converting the hydrogen in a fuel cell allows higher efficiency to produce electricity.

Re: Iron as an inexpensive storage medium for hydrogen

#82
post #66

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?

The usual way—boiling water.

Re: Iron as an inexpensive storage medium for hydrogen

#83
Despite the cycle losses, this seems like a good idea for easy to maintain storage. And they plan to use the heat as well, so that will step up efficiency.

Will be interesting to see how their campus power project works out in the next years.

Also, innovative “sausage safety test” for the Fe powder reacting with air (figure 6: https://doi.org/10.1039/D3SE01228J ).

Re: Iron as an inexpensive storage medium for hydrogen

#84
post #66

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?

[deleted]

Re: Iron as an inexpensive storage medium for hydrogen

#85

Earlier quoted context omitted.

The right question is what the efficiency of this process is. End to end, not just the charging/discharging. Both charging and discharging seems to require a lot of heat. Waste heat is essentially lost energy that is released in the form of heat. I assume the discharge reaction is exothermic. That would be the energy stored in the summer months. Heating up a lot of tons of iron during charging is also not going to be…

would you mind explicitly listing the 4 conversions? I see: 1) generation 2) storage efficiency (energy while storing divided by energy upon release) what are the other 2 you had in mind?

1) generate hydrogen 2) store hydrogen in iron oxide 3) discharge hydrogen again 4) convert it into something useful (electricity, heat, movement, etc.).

All those steps lose energy. And there's stuff that happens in between involving pipes, leaky valves, tanks, compression, etc.

Re: Iron as an inexpensive storage medium for hydrogen

#86
post #77

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…

Also hydrogen loves to leak through tank walls, and can make metals brittle (this was covered in the article)

Re: Iron as an inexpensive storage medium for hydrogen

#87
post #75
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…

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.

Of course there will always be a use for surplus energy. It's basically free, so we'll probably see whole new industries pop up to make use of it.

For example, an aluminium smelter might use free summer energy to turn alumina into aluminium, and turn the plant off in the winter - at which time the labor force can do extended maintenance and do post-processing on the aluminium produced during the summer.

Although finding an industry where such seasonal turnovers are viable isn't trivial, if you find one it's going to be far more profitable than very lossy storage.

Re: Iron as an inexpensive storage medium for hydrogen

#88
post #79
post #66

Earlier quoted context omitted.

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…

This.

Synthesis efficiency is on the order of 60%. Combustion efficiency, driven by Carnot's Law, ~30--50%, possibly a bit higher for combined and/or power-to-thermal. But the overall round-trip efficiency, based on both synthesis and generating losses will be low, 15--25%, perhaps as high as 30%.

The goal of such a system isn't efficient storage so much as it is persistent and dispatchable. It's possible to store large quantities of liquid fuels for long periods of time and tap into them within seconds or minutes as generating, or other fuel-based energy applications, are required. Other storage/release options either don't have the long-term storage capability, or cannot be ramped up as quickly.

Other storage options range from the exceedingly short-lived but responsive (supercapacitors, kinetic flywheels) which can respond on a sub-second to second basis, but aren't viable for long-term storage at all, to options which work over a few hours, daily supply-demand inconsistencies, etc., such as pumped hydro and high-termperature thermal storage (e.g., molten salt), to seasonal thermal storage (hot water, ground geothermal where geology supports this).

Fuel synthesis makes sense where there's exceedingly high seasonality in energy generating capacity (e.g., summer vs. winter for PV / solar), or where there are longer-term highly-variable generating trends (e.g., wind, with higher and lower output over the course of days or weeks). Or where communities are highly isolated and cannot readily be connected to a grid to balance consumption and generation over time (remote islands, arctic communities), or where a region has a very high generating potential but low domestic demand (say, northwest Australia, with sun-drenched deserts and low electrical demand from sheep and roos).

Banking summer-time / high-production capacity as fuel, and drawing down those fuel reserves or shipping them to areas of high demand could be the shape of a future energy economy. It should dramatically rewrite energy geopolitics.

Re: Iron as an inexpensive storage medium for hydrogen

#89
post #78

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 i…

single-use instant hand warmers are catalyzed by salt and a little water. iron powder is indeed hazardous by itself but not like that
Post reply on HN