Iron as an inexpensive storage medium for hydrogen • Hacker News Board

Re: Iron as an inexpensive storage medium for hydrogen

#11

Post by johndough » Sat, Aug 31, 2024, 7:10 AM UTC

teruakohatu wrote: post #2

At scale, what I don’t get is this requires a lot of energy to kickstart the reaction (heating the iron ore to 400 degrees). Where is that energy coming from when energy production is constrained in winter. Or would the plan be to slowly heat over fall?

Heat losses at the surface of a sphere scale with the square of the radius, while the energy density scales with the cube of the radius, so you can just scale it up until the heat loss is relatively small.

In the paper, the authors mention 11.4% efficiency for this system and a theoretical maximum efficiency of 79% if scaled up, so it might take a lot of scale.

Re: Iron as an inexpensive storage medium for hydrogen

#12

Post by MadDemon » Sat, Aug 31, 2024, 7:17 AM UTC

zdragnar wrote: post #5

teruakohatu wrote: post #2

At scale, what I don’t get is this requires a lot of energy to kickstart the reaction (heating the iron ore to 400 degrees). Where is that energy coming from when energy production is constrained in winter. Or would the plan be to slowly heat over fall?

The article says they're currently powered from a grid connection but hope to be fully solar powered soon. What I'm not getting is how this process produces more energy than the solar input to power the process. Unless they're getting solar collectors to try to generate 400 degree temperatures rather than PV solar to electricity, but that seems like a sketchy proposition at best in winter.

It does not, but they are storing the energy for winter. Solar produces a lot more energy in summer, which is especially true in Switzerland or Europe in general.

Re: Iron as an inexpensive storage medium for hydrogen

#13

Post by moffkalast » Sat, Aug 31, 2024, 7:39 AM UTC

adrian_b wrote: post #8

teruakohatu wrote: post #2

At scale, what I don’t get is this requires a lot of energy to kickstart the reaction (heating the iron ore to 400 degrees). Where is that energy coming from when energy production is constrained in winter. Or would the plan be to slowly heat over fall?

Even most internal-combustion engines require energy stored in a battery to kickstart them, so this is not different. Obviously the energy efficiency of this process based on iron is modest. It is likely that the energy efficiency is even lower than for the process of storing energy by making synthetic hydrocarbons (e.g. synthetic gasoline), which are much easier to use once energy is stored in them. The only advanta…

My immediate thought is, why not store it as peroxide? It takes more energy to make too, but at least it's liquid rocket fuel instead of gaseous rocket fuel.

Re: Iron as an inexpensive storage medium for hydrogen

#14

Post by londons_explore » Sat, Aug 31, 2024, 8:12 AM UTC

jl6 wrote: post #3

teruakohatu wrote: post #2

At scale, what I don’t get is this requires a lot of energy to kickstart the reaction (heating the iron ore to 400 degrees). Where is that energy coming from when energy production is constrained in winter. Or would the plan be to slowly heat over fall?

They mention using waste heat from the reaction to minimize the energy cost of discharge. As long as they still get some power out of it, it could be a win even if it’s quite inefficient. When the input hydrogen is “free” in the summer (due to excess production), inefficiency can be tolerable. I do wonder if “free” will actually pan out, or whether someone will find a way to demand-shift from winter to summer and use…

I suspect in the next 50 years electricity will end up globally transportable via undersea cables, like the internet does for data today.

At that point, it's always summertime somewhere and it's always daylight somewhere, and if prices were to fall to zero there is always someone who would like more heat for something.

Therefore I suspect zero-priced energy will stop existing.

Re: Iron as an inexpensive storage medium for hydrogen

#15

Post by w-m » Sat, Aug 31, 2024, 8:15 AM UTC

This seems to be the most important problem to be solved for a green, future grid. So I’m happy there’s a new solution shown every other month.

It’s annoying that they always seem to contain some hand-wavy efficiency calculations. I think this one didn’t even consider the losses from hydrogen production? Is there a benchmark out there, of these long-term electricity storage solutions? Like: you get 1 MWh at 25 deg C, and 6 months later, it’s measured how much your system restores. Everything taken from the grid during storage for upkeep or kickstarting the process is subtracted as well.

Re: Iron as an inexpensive storage medium for hydrogen

#16

Post by [deleted] » Sat, Aug 31, 2024, 8:21 AM UTC

moffkalast wrote: post #13

adrian_b wrote: post #8

Earlier quoted context omitted.

Even most internal-combustion engines require energy stored in a battery to kickstart them, so this is not different. Obviously the energy efficiency of this process based on iron is modest. It is likely that the energy efficiency is even lower than for the process of storing energy by making synthetic hydrocarbons (e.g. synthetic gasoline), which are much easier to use once energy is stored in them. The only advanta…

My immediate thought is, why not store it as peroxide? It takes more energy to make too, but at least it's liquid rocket fuel instead of gaseous rocket fuel.

[deleted]

Re: Iron as an inexpensive storage medium for hydrogen

#17

Post by miohtama » Sat, Aug 31, 2024, 8:28 AM UTC

Is this same as rust batteries earlier?

https://www.scientificamerican.com/article/rusty-batteries-c...

Re: Iron as an inexpensive storage medium for hydrogen

#18

Post by dest » Sat, Aug 31, 2024, 8:30 AM UTC

The energy density of the system is surprisingly high (in my modest perspective). It looks like 800kWh per ton of iron. Isn't it ~five times as much as the batteries we have in cars?

Re: Iron as an inexpensive storage medium for hydrogen

#19

Post by Temporary_31337 » Sat, Aug 31, 2024, 8:50 AM UTC

production and conversion are inefficient compared to other sources of energy, as up to 60 percent of its energy is lost in the process.

Re: Iron as an inexpensive storage medium for hydrogen

#20

Post by 7952 » Sat, Aug 31, 2024, 8:51 AM UTC

w-m wrote: post #15

This seems to be the most important problem to be solved for a green, future grid. So I’m happy there’s a new solution shown every other month. It’s annoying that they always seem to contain some hand-wavy efficiency calculations. I think this one didn’t even consider the losses from hydrogen production? Is there a benchmark out there, of these long-term electricity storage solutions? Like: you get 1 MWh at 25 deg C,…

The focus on efficiency can be short sighted though. The whole point of storage is that the energy you sell is more expensive than the energy you buy. If the profit margin is high enough then you can afford to waste energy through inefficiency. And grids with lots of renewables will naturally have times where energy is cheap and times when it is expensive.

Also, I doubt this will exist in isolation. It will probably be built in places that already have demand for hydrogen, available land, have accessible energy, a good grid connection, and existing iron-ore infrastructure. It will be built in such a way to minimise costs and maximise available customers.