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production and conversion are inefficient compared to other sources of energy, as up to 60 percent of its energy is lost in the process.
Is it possible to capture that heat during production and conversion, and use it to run a turbine?
production and conversion are inefficient compared to other sources of energy, as up to 60 percent of its energy is lost in the process.
Actual publication linked is very readable: https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se0...
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...
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?
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?
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 free. It doesn't matter whether you do it slowly or quickly.
Creating the hydrogen is also not a loss free process. Nor is doing something useful with it like using it in a fuel cell (0.85), burning it (0.45), etc. These inefficiencies multiply.
All that lost energy comes out of the original budget of energy that came out of the solar panels.
Even if you use some wildly optimistic numbers, they multiply to something well below 0.5 pretty quickly even before you consider charging & discharging.
But lets do something silly and unrealistic and just do the math for an average step efficiency at 0.7, 0.8, and 0.9. We're talking four conversions here so that's 0.7^4 =0.24 vs. 0.41 and 0.66. And forget about getting anywhere near average 0.9 efficiencies with all of those steps. I'm assuming 0.7 would already be on the high side. Add more steps to the process and it only gets worse. Pipes aren't perfect. If you need to pressurize the hydrogen before you use it (like in a car), that isn't free either.
Basically, this takes a system that was already quite inefficient end to end and adds two more steps that sound like they involve some pretty significant energy losses to it (i.e. probably well below 0.5 when combined), thus making the system as a whole a lot more inefficient. Hydrogen as a battery already sucked with normal storage. This doesn't improve things.
There's a good reason that most hydrogen produced is used at or close to its site of production: it minimizes the energy losses and producing hydrogen is really expensive so it's not really desirable to lose 80-90% of the energy unless you really need to.
I would say it's only worth it if the marginal cost of producing the hydrogen is close to 0.
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?
Somewhere with lots of solar on the grid probably has excess energy, even during winter, during the day, so you'd plan to put in the input energy to start the reaction during the afternoon peak, and if you miss that for some reason, some sort of coordinated startup procedure would likely be used.
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.
Is this same as rust batteries earlier? https://www.scientificamerican.com/article/rusty-batteries-c...
This paper uses hydrogen as an intermediary, which has advantages but also adds some questionable margins in efficiency. But I don't know the efficiency of the suggested iron-air batteries either.
This may be nicer if you want hydrogen rather than an electric battery. But if you turn that hydrogen into a fuel cell... the efficiencies of producing and consuming that hydrogen add up.
Actual publication linked is very readable: https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se0...
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...
https://www.metallics.org/dri.html
> Being a highly reduced material, DRI has a tendency to re-oxidise, an exothermic reaction. Thus, without appropriate precautions being taken in its handling, transport and storage, there is a risk of self-heating and fires. The International Maritime Organisation's International Maritime Solid Bulk Cargoes Code classifies DRI - Direct Reduced Iron (B) - as Group B (cargo with chemical hazard) and class MHB (material hazardous only in bulk) and requires that DRI be shipped under an inert atmosphere, usually nitrogen.
It would be nice if the iron could be in an alloy that, in addition to being oxidized/reduced, could further absorb hydrogen when in the reduced state. FeTi absorbs hydrogen, but I don't think the titanium would withstand repeated oxidation/reduction cycles. The Ti would go to the +4 oxidation state and stay there.