9 ms·

Iron as an inexpensive storage medium for hydrogen

160 points by bornelsewhere 2y ago

teruakohatu 2y ago
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?
- jl6 2y ago
  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 it all up.
  - zdragnar 2y ago
    They're storing the hydrogen as water, though. The only reason to produce it in the summer from excess production via electrolysis is to be able to reduce iron oxide to pure iron rather than just buying the pure iron to start with.
  - londons_explore 2y ago
    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.
    - outop 2y ago
      Isn't it possible that such a system will over-produce 99% of the year and that therefore, the marginal cost will almost always be $0? 'Take my energy and allow me to stop accelerating my flywheels which regulate production' seems more plausible than 'someone would always like more heat for something' (what?) Or possibly 'take my energy and I'll cut off some of the people using spare energy to do low priority, low value computation for free'?
      - londons_explore 2y ago
        I think electricity use is far more elastic than you're imagining. Plenty of big users can turn up/down production and already do so based on prices. If wide price swings got more frequent, more stuff would get dynamic. You can imagine home appliances having an 'eco' setting which runs the appliance like the washing or the dishwasher at the cheapest time in the next 12 hours. Or the water heating systems which heat more water when prices are cheap. Or heaters which switch between natural gas and heat pump based on price. Or electric car chargers which charge during the cheapest hours. (all of these already exist, but none are yet common). Over the long term there is also plenty of elasticity. If electric heating is expensive, people will install gas/oil heaters when they renovate. If electricity is cheap, more people buy electric cars. With cheap electricity, maybe fewer people decide to add more insulation to their houses. Businesses don't upgrade energy inefficient equipment to be more energy efficient, etc. Plenty of demand elasticity in both the short and long term. End result: As long as the market is unconstrained, prices won't hit zero more than say ~5% of the time.
        outop 2y ago
        I disagree that this argument makes it less likely to have very low prices much of the time. I think it makes it more likely. If peak to trough is a large gap, say 60% of peak, this tends to make it less likely that peak will be met by overproduction, since that would involve very large capital costs. The picture you paint above would suggest a very small gap between peak and trough, say 2% of peak. This means that almost certainly there would be enough over capacity to more than meet peak demand. Therefore the total daily demand would be more than met by capacity, leading to some energy being thrown away. So at all times except the peak, the marginal cost would be zero. You have given an accurate argument for why demand would be elastic at trough. But you haven't given any reason why overall demand would be very elastic.
- brazzy 2y ago
  Energy production from solar is lower in winter, but it's not zero. And other forms (notably wind) are not reduced. It's a non-problem, really. Especially at scale.
- zdragnar 2y ago
  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.
  - MadDemon 2y ago
    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.
    - mark-r 2y ago
      The difference depends on your latitude. On the equator the seasons won't make a difference, above the arctic circle you'll get diddly-squat from your panels in the winter during the endless night. Switzerland is at 47 degrees, not quite arctic circle but far enough north to see a huge difference.
- adrian_b 2y ago
  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 advantage is the very low cost even for very large storage capacities.
  - moffkalast 2y ago
    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 2y ago
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    - DrNosferatu 2y ago
      I hear peroxide conversion efficiency can be as low as 30%, and concentrated peroxide is quite dangerous.
      - moffkalast 2y ago
        > Efficiency Admittedly, the current, non-optimized, technical trial-level efficiency of the here-built system was very low, with an overall storage efficiency of 11.4%, So far their is even lower, though they claim a theoretical max of 79%. Storing large amounts of energy that's ready to be used is rarely not dangerous in any case. Except maybe potential energy of a tank of water on a mountain.
  - mark-r 2y ago
    There's an advantage to pure hydrogen vs. synthetic hydrocarbons, the lack of carbon means no greenhouse gas production when you use it.
- johndough 2y ago
  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.
- jillesvangurp 2y ago
  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 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.
  - DoctorOetker 2y ago
    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?
    - jillesvangurp 2y ago
      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.
- toast0 2y ago
  If this is intended to support a grid, rather than be grid forming or isolated, then you'd sequence that somehow. 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.
jval43 2y ago
Actual publication linked is very readable: https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se01228j https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se0...
- johndough 2y ago
  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/d3se01228j-f6_hi-res.gif https://pubs.rsc.org/image/article/2024/se/d3se01228j/d3se01...
  - erickj 2y ago
    I believe most Swiss scientific investigations are legally required to involve Cervelat
    - HeatrayEnjoyer 2y ago
      What is it?
      - micwag 2y ago
        The national sausage of Switzerland: https://en.wikipedia.org/wiki/Cervelat https://en.wikipedia.org/wiki/Cervelat
    - lta 2y ago
      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
  - pfdietz 2y ago
    Fires are one of the risks of so-called Direct Reduced Iron. The product has high surface area which leads to fast oxidation. https://www.metallics.org/dri.html 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.
ttflee 2y ago
Looks like a variant of iron-air battery project to me.
w-m 2y ago
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.
- 7952 2y ago
  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.
  - deleted 2y ago
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  - rini17 2y ago
    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.
    - micwag 2y ago
      This is for seasonal energy storage with only 1 charge and discharge per year. It competes with water reservoirs not with batteries.
miohtama 2y ago
Is this same as rust batteries earlier? https://www.scientificamerican.com/article/rusty-batteries-could-greatly-improve-grid-energy-storage/ https://www.scientificamerican.com/article/rusty-batteries-c...
- aDyslecticCrow 2y ago
  I thought the same thing, but no, the chemical process is different. Iron-air batteries are traditional flowcell batteries (with some extra complications). 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.
dest 2y ago
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?
- ben_w 2y ago
  I've seen claims up to 300 Wh/kg for batteries, but yes this is still more than that.
  - AtlasBarfed 2y ago
    Is that lithium iron or for sulfur chemistries? And for good batteries their density doesn't really matter. Sodium ion batteries will be fantastic grid storage simply because they're just going to be dirt cheap
Temporary_31337 2y ago
production and conversion are inefficient compared to other sources of energy, as up to 60 percent of its energy is lost in the process.
- nomercy400 2y ago
  Lost, as in turned into heat? Is it possible to capture that heat during production and conversion, and use it to run a turbine?
  - tonfa 2y ago
    In winter I think the plan is to use the heat for district heating. (which is also kinda interesting since in parts of Switzerland district heating through waste management facilities starts to be a problem due to a reduction of the amount of waste available)
  - dredmorbius 2y ago
    This is the concept behind combined-cycle generation, where an initial stage (direct natural gas combustion) runs a turbine whose cooling (water) drives a second-stage steam turbine. These can push total efficiency to ~60+%, with an ultimate efficiency of ~90+% possible where a tertiary thermal application which uses low-grade heat (anywhere from ~100--180°C / 212--356°F) can be used for some industrial, food-process, or space-heating applications, called cogeneration. <https://en.wikipedia.org/wiki/Combined_cycle_power_plant https://en.wikipedia.org/wiki/Combined_cycle_power_plant> <https://en.wikipedia.org/wiki/Cogeneration https://en.wikipedia.org/wiki/Cogeneration> Seimans has a good video 'splainer: <https://yewtu.be/watch?v=eeiu-wcyEbs https://yewtu.be/watch?v=eeiu-wcyEbs> GE also has numerous offerings in this space, and I've seen trade articles describing this in the past, though I'm not finding any presently. There isn't some majyckal process by which all thermal energy can be converted to motion (or by extension, electrical generation), but it is possible, with additional complexity and capital equipment, to extract much of it.
- kitd 2y ago
  Energy efficiency is only one part of the equation. There are economic and social efficiencies in using simple, eco-friendly components that are easy to build/transport/store/run/scale up. Those can easily offset any energy losses over the lifetime of the technology.
DrNosferatu 2y ago
Efficiency is quite low: 40%-60%. I would say it's only worth it if the marginal cost of producing the hydrogen is close to 0.
- DrNosferatu 2y ago
  Isn’t a more viable economic “battery” to just turn on your LLM training massive data center, or Aluminum smelter (or any other high-consumption, low-urgency industrial process) when there’s excess electric production?
- goodpoint 2y ago
  This not a problem at all when using PV. Plus, the generated heat can be used.
  - rini17 2y ago
    It is, water electrolysis is surprisingly fickle process.
  - crote 2y ago
    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 - so you don't even need the battery at all. You'd essentially just be turning a huge amount of power into heat for nothing.
    - goodpoint 2y ago
      The mechanism you described is tautological. If you assume people will install infinite PV than the problem is solved. In reality, the battery is needed when the battery is needed. It might be a long cold winter, or maybe just few evenings after rainy days, but a cheap long lasting battery is still useful.
    - 2y ago
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samatman 2y ago
When I was a child, we would play a game called "the floor is lava". It's a simple game: you have to get around, but not touch the floor. Jumping on the furniture and such. Fine for a pastime, when you're small, but to get places, you use the floor. A certain faction of the project to decarbonize the electrical grid likes to play a similar childish game: "nuclear power is lava". It causes them to come up with whimsical and absurd epicycles, which make no sense at all unless you're playing that game. Seasonal storage of 2GWh? Please. A 2GW plant produces 2GWh every hour, with 90% uptime. And it doesn't involve losing more than 90% of the photovoltaic energy, I will eat my whole hat if the ray-to-electricity pipeline for this boondoggle exceeds 10% efficiency. Can we please stop wasting time and effort, and invest in the buildout of a substantial nuclear fleet to provide baseline power?
- ComputerGuru 2y ago
  China seems to be working towards that goal. Everyone else, not so much.
- AtlasBarfed 2y ago
  Are you totally ignorant of how much nuclear costs? Go ahead and look at the lazard lcoe numbers, and this year was an odd increase for solar wind that will basically be the best that nuclear can hope for. If nuclear could provide a cheap scalable easily approved rapidly deployed safe and low waste reactor that could be price competitive with solar and wind, then they be in the game. That is not happening without probably 10 to 20 years of research and development with billions of dollars of funding. Old nuclear was solid rods and gigantic domes and all of that stuff simply is not price competitive, and even if you dropped everything and started attempting to get approvals and construction for hundreds of nuclear plants, they won't come online for 10 to 20 years themselves. When's going to get cheaper solar? Certainly going to get cheaper with perovskites. Stores will get cheaper with lfp and sodium ion improvements, solid state and hopefully someday sulfur chemistries. The nuclear industry needed to get its act together decades ago. In my opinion, it made a huge error in abandoning msr in the 70s (which has all the features of a competitive nuclear plant if they could figure out the materials science) and other breeder reactors. A solid fuel rods reactor is simply not reliably safe in all disaster scenarios (Fukushima).
fredgrott 2y ago
This solution is better and no toxicity https://www.pnnl.gov/news-media/baking-soda-solution-clean-hydrogen-storage https://www.pnnl.gov/news-media/baking-soda-solution-clean-h...
kimmk 2y ago
For seasonal grid-level storage, I wonder if simple compressed hydrogen storage (around 350 bar) is the most reasonable solution. AFAIK doesnt require any high-tech materials, avoids most embrittlement caused by LH2 and boil-off rates are reasonable.
- msandford 2y ago
  The most efficient seasonal battery is probably synthetic hydrocarbons. By the time you get to propane (3 carbons) the pressures for liquid are super super reasonable (400psi including a giant safety factor) and there's zero embrittlement. Further is that vehicles can use propane so you don't even have to idle the plants during the winter so long as there's some PV from the southern states. They might be running at 100% capacity in summer and 40% capacity in winter but that's way better than 0%. It's a lot easier to keep people employed to operate the plants if they're needed year round.
credit_guy 2y ago
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 are probably bigger energy losses bringing the reactant mass at the required temperature (400 degrees C). Unfortunately, I don't see this making any sense for large scale energy storage. Storage tanks for compressed hydrogen enjoy the square-cube law. The larger they are the less expensive they are proportional to the mass of hydrogen they hold. With this iron oxide method, you need 27 tons of iron oxide for one ton of hydrogen. You can procure right now tanks that can hold 2.7 tons of hydrogen and weigh 77 tons empty [1], the ratio is 28 to 1. But the round-trip efficiency of the tank is virtually 100%. The efficiency of the iron-based storage is only 50%. The tanks are not very expensive. I can't see the niche that this idea can apply to. [1] https://www.iberdrola.com/press-room/news/detail/storage-tanks-green-hydrogen-puertollano https://www.iberdrola.com/press-room/news/detail/storage-tan...
- paulsutter 2y ago
  Hydrogen is difficult to store and transport, you really want natural gas or jet fuel
- kilotaras 2y ago
  27 tons of iron oxide have a volume of 5m^3 and can be stored in pretty much a hole in the ground. 2.7 tons of hydrogen have a volume of almost exactly 30000 m^3, requiring storing it under high pressure in specialized containers. Hydrogen is famous for being hard to store without losses. For long-term storage storage and losses are a problem. > But the round-trip efficiency of the tank is virtually 100%. The efficiency of the iron-based storage is only 50% Maybe I'm missing something, but why? As you mentioned it takes 29kj to restore 3 moles of H2 out of (3 moles of H20 + 1 mole of Fe2O3). Where does 50% comes from?
  - kilotaras 2y ago
    i.e. the paper[0] states that first "discharging" produced 7.09kg of H2 out of 8.71 theoretically possible the efficiency is super low, but again, according to the paper, "most of the energy input was due to thermal losses at the reactor surface (83.9%)", which also benefits from square/cube law. [0] https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se01228j https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se0...
paulsutter 2y ago
You really want to store excess energy as natural gas or jet fuel because of all the existing infrastructure. Especially since excess power is available at so many solar sites, we’re so good at transporting these fuels, and the cost of photovoltaic will keep going down The vast, cheap power that photovoltaic will provide is a giant opportunity. Please review the links below https://terraformindustries.com/ https://terraformindustries.com/ Terraform industries converting sun and air into natural gas: https://techcrunch.com/2024/04/01/terraform-industries-converted-electricity-and-air-into-synthetic-natural-gas/ https://techcrunch.com/2024/04/01/terraform-industries-conve... The solar industrial revolution is the biggest investment opportunity in history: https://caseyhandmer.wordpress.com/2024/05/22/the-solar-industrial-revolution-is-the-biggest-investment-opportunity-in-history/ https://caseyhandmer.wordpress.com/2024/05/22/the-solar-indu...
shikon7 2y ago
Why would you use hydrogen to extract the energy of the iron? Wouldn't it be more efficient to burn the iron directly? Likewise, is there no better way to reduce iron oxide to iron than by creating hydrogen first?
- yxhuvud 2y ago
  There may be, but now you are assuming energy is what is needed and not the hydrogen itself. Hydrogen is used in lots of industrial processes and is really hard to store in bulk.
dredmorbius 2y ago
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 stretch, diesel fuel). It stores forever (proved to 300 million years), it is drop-in compatible with extant infrastructure and equipment, it's infinitely miscable with present fuels, it doesn't leak out of storage, it doesn't embrittle metals (and in fact generally lubricates and protects them). Yes, the round-trip storage efficiencies are low (as low as ~15--20% recovery based on thermal electrical generation, roughly the same as the solution named here), but that's in exchange for something that can readily provide weeks to months of storage capacity in a stable, low-risk form. Where you need storage that's long-term stable, dense, safe, and instantly dispatchable, your options are few. The technology has been demonstrated in numerous experimental trials, and is similar to processes run at national scale for decades in Germany and South Africa. US-based research has been conducted at Brookhaven National Laboratory, M.I.T., and the US Naval Research Lab, amongst others. The stumbling block to date has been that fossil fuel prices are sufficiently low[1] that synfuels simply are not competitive presuming market-based mechanisms which fail to account for externalities and other market failures. I've be aware of this for about a decade and have written about the technology, Fischer-Tropsch fuel synthesis, multiple times on HN: <https://hn.algolia.com/?dateRange=all&page=0&prefix=true&query=by%3Adredmorbius%20fischer-tropsch&sort=byPopularity&type=comment https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...> ________________________________ Notes: 1. A market failure of staggering proportions, as the under-pricing is on the order of a million-fold. See: Jeffrey S. Dukes, "Burning Buried Sunshine", <https://core.ac.uk/download/pdf/5212176.pdf https://core.ac.uk/download/pdf/5212176.pdf> (PDF)
- mglz 2y ago
  How much incoming solar power ends up in the methane? And how do you get the energy back out?
  - deleted 2y ago
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zahlman 2y ago
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 had. Rather, it's using the energy to deoxidize rust. Then on the recovery side, why use this steam process? Apparently (because the thermodynamics work out so that this whole thing has efficiency > 0) you get energy out of the process of putting the oxygen back into the iron. So why not just, well, burn (i.e. rust) the iron directly? What exactly is the dissociation and re-combination of the steam accomplishing?
- usrusr 2y ago
  > "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 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)
- kortex 2y ago
  > 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.
czierleyn 2y ago
Is this the same idea as? https://teamsolid.org/ https://teamsolid.org/
ano-ther 2y ago
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 https://doi.org/10.1039/D3SE01228J ).
kragen 2y ago
or you can maybe skip the hydrogen intermediary on one end and burn the iron in an iron-air battery. then you get much higher efficiency. electrowinning of iron in alkali is also feasible, eliminating the hydrogen on both ends
- hollerith 2y ago
  But then you have to keep on adding iron, which might be costlier than hydrogen. And you have to keep on removing iron oxide.
  - kragen 2y ago
    well, adding iron and removing iron oxide is what electrowinning iron does, but i think i added that part of my comment after you made yours. but you can still add iron and remove iron oxide with the hydrogen smelting furnace the ethz researchers devised if you like that better

160 points by bornelsewhere 2y ago

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?

jl6 2y ago
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 it all up.
- zdragnar 2y ago
  They're storing the hydrogen as water, though. The only reason to produce it in the summer from excess production via electrolysis is to be able to reduce iron oxide to pure iron rather than just buying the pure iron to start with.
- londons_explore 2y ago
  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.
  - outop 2y ago
    Isn't it possible that such a system will over-produce 99% of the year and that therefore, the marginal cost will almost always be $0? 'Take my energy and allow me to stop accelerating my flywheels which regulate production' seems more plausible than 'someone would always like more heat for something' (what?) Or possibly 'take my energy and I'll cut off some of the people using spare energy to do low priority, low value computation for free'?
    - londons_explore 2y ago
      I think electricity use is far more elastic than you're imagining. Plenty of big users can turn up/down production and already do so based on prices. If wide price swings got more frequent, more stuff would get dynamic. You can imagine home appliances having an 'eco' setting which runs the appliance like the washing or the dishwasher at the cheapest time in the next 12 hours. Or the water heating systems which heat more water when prices are cheap. Or heaters which switch between natural gas and heat pump based on price. Or electric car chargers which charge during the cheapest hours. (all of these already exist, but none are yet common). Over the long term there is also plenty of elasticity. If electric heating is expensive, people will install gas/oil heaters when they renovate. If electricity is cheap, more people buy electric cars. With cheap electricity, maybe fewer people decide to add more insulation to their houses. Businesses don't upgrade energy inefficient equipment to be more energy efficient, etc. Plenty of demand elasticity in both the short and long term. End result: As long as the market is unconstrained, prices won't hit zero more than say ~5% of the time.
      - outop 2y ago
        I disagree that this argument makes it less likely to have very low prices much of the time. I think it makes it more likely. If peak to trough is a large gap, say 60% of peak, this tends to make it less likely that peak will be met by overproduction, since that would involve very large capital costs. The picture you paint above would suggest a very small gap between peak and trough, say 2% of peak. This means that almost certainly there would be enough over capacity to more than meet peak demand. Therefore the total daily demand would be more than met by capacity, leading to some energy being thrown away. So at all times except the peak, the marginal cost would be zero. You have given an accurate argument for why demand would be elastic at trough. But you haven't given any reason why overall demand would be very elastic.
brazzy 2y ago
Energy production from solar is lower in winter, but it's not zero. And other forms (notably wind) are not reduced. It's a non-problem, really. Especially at scale.
zdragnar 2y ago
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.
- MadDemon 2y ago
  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.
  - mark-r 2y ago
    The difference depends on your latitude. On the equator the seasons won't make a difference, above the arctic circle you'll get diddly-squat from your panels in the winter during the endless night. Switzerland is at 47 degrees, not quite arctic circle but far enough north to see a huge difference.
adrian_b 2y ago
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 advantage is the very low cost even for very large storage capacities.
- moffkalast 2y ago
  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 2y ago
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  - DrNosferatu 2y ago
    I hear peroxide conversion efficiency can be as low as 30%, and concentrated peroxide is quite dangerous.
    - moffkalast 2y ago
      > Efficiency Admittedly, the current, non-optimized, technical trial-level efficiency of the here-built system was very low, with an overall storage efficiency of 11.4%, So far their is even lower, though they claim a theoretical max of 79%. Storing large amounts of energy that's ready to be used is rarely not dangerous in any case. Except maybe potential energy of a tank of water on a mountain.
- mark-r 2y ago
  There's an advantage to pure hydrogen vs. synthetic hydrocarbons, the lack of carbon means no greenhouse gas production when you use it.
johndough 2y ago
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.
jillesvangurp 2y ago
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 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.
- DoctorOetker 2y ago
  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?
  - jillesvangurp 2y ago
    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.
toast0 2y ago
If this is intended to support a grid, rather than be grid forming or isolated, then you'd sequence that somehow. 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.

jval43 2y ago

Actual publication linked is very readable: https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se01228j https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se0...

johndough 2y ago
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/d3se01228j-f6_hi-res.gif https://pubs.rsc.org/image/article/2024/se/d3se01228j/d3se01...
- erickj 2y ago
  I believe most Swiss scientific investigations are legally required to involve Cervelat
  - HeatrayEnjoyer 2y ago
    What is it?
    - micwag 2y ago
      The national sausage of Switzerland: https://en.wikipedia.org/wiki/Cervelat https://en.wikipedia.org/wiki/Cervelat
  - lta 2y ago
    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
- pfdietz 2y ago
  Fires are one of the risks of so-called Direct Reduced Iron. The product has high surface area which leads to fast oxidation. https://www.metallics.org/dri.html 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.

ttflee 2y ago

Looks like a variant of iron-air battery project to me.

w-m 2y ago

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.

7952 2y ago
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.
- deleted 2y ago
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- rini17 2y ago
  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.
  - micwag 2y ago
    This is for seasonal energy storage with only 1 charge and discharge per year. It competes with water reservoirs not with batteries.

miohtama 2y ago

Is this same as rust batteries earlier? https://www.scientificamerican.com/article/rusty-batteries-could-greatly-improve-grid-energy-storage/ https://www.scientificamerican.com/article/rusty-batteries-c...

aDyslecticCrow 2y ago
I thought the same thing, but no, the chemical process is different. Iron-air batteries are traditional flowcell batteries (with some extra complications). 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.

dest 2y ago

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?

ben_w 2y ago
I've seen claims up to 300 Wh/kg for batteries, but yes this is still more than that.
- AtlasBarfed 2y ago
  Is that lithium iron or for sulfur chemistries? And for good batteries their density doesn't really matter. Sodium ion batteries will be fantastic grid storage simply because they're just going to be dirt cheap

Temporary_31337 2y ago

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

nomercy400 2y ago
Lost, as in turned into heat? Is it possible to capture that heat during production and conversion, and use it to run a turbine?
- tonfa 2y ago
  In winter I think the plan is to use the heat for district heating. (which is also kinda interesting since in parts of Switzerland district heating through waste management facilities starts to be a problem due to a reduction of the amount of waste available)
- dredmorbius 2y ago
  This is the concept behind combined-cycle generation, where an initial stage (direct natural gas combustion) runs a turbine whose cooling (water) drives a second-stage steam turbine. These can push total efficiency to ~60+%, with an ultimate efficiency of ~90+% possible where a tertiary thermal application which uses low-grade heat (anywhere from ~100--180°C / 212--356°F) can be used for some industrial, food-process, or space-heating applications, called cogeneration. <https://en.wikipedia.org/wiki/Combined_cycle_power_plant https://en.wikipedia.org/wiki/Combined_cycle_power_plant> <https://en.wikipedia.org/wiki/Cogeneration https://en.wikipedia.org/wiki/Cogeneration> Seimans has a good video 'splainer: <https://yewtu.be/watch?v=eeiu-wcyEbs https://yewtu.be/watch?v=eeiu-wcyEbs> GE also has numerous offerings in this space, and I've seen trade articles describing this in the past, though I'm not finding any presently. There isn't some majyckal process by which all thermal energy can be converted to motion (or by extension, electrical generation), but it is possible, with additional complexity and capital equipment, to extract much of it.
kitd 2y ago
Energy efficiency is only one part of the equation. There are economic and social efficiencies in using simple, eco-friendly components that are easy to build/transport/store/run/scale up. Those can easily offset any energy losses over the lifetime of the technology.

DrNosferatu 2y ago

Efficiency is quite low: 40%-60%. I would say it's only worth it if the marginal cost of producing the hydrogen is close to 0.

DrNosferatu 2y ago
Isn’t a more viable economic “battery” to just turn on your LLM training massive data center, or Aluminum smelter (or any other high-consumption, low-urgency industrial process) when there’s excess electric production?
goodpoint 2y ago
This not a problem at all when using PV. Plus, the generated heat can be used.
- rini17 2y ago
  It is, water electrolysis is surprisingly fickle process.
- crote 2y ago
  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 - so you don't even need the battery at all. You'd essentially just be turning a huge amount of power into heat for nothing.
  - goodpoint 2y ago
    The mechanism you described is tautological. If you assume people will install infinite PV than the problem is solved. In reality, the battery is needed when the battery is needed. It might be a long cold winter, or maybe just few evenings after rainy days, but a cheap long lasting battery is still useful.
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samatman 2y ago

When I was a child, we would play a game called "the floor is lava". It's a simple game: you have to get around, but not touch the floor. Jumping on the furniture and such. Fine for a pastime, when you're small, but to get places, you use the floor. A certain faction of the project to decarbonize the electrical grid likes to play a similar childish game: "nuclear power is lava". It causes them to come up with whimsical and absurd epicycles, which make no sense at all unless you're playing that game. Seasonal storage of 2GWh? Please. A 2GW plant produces 2GWh every hour, with 90% uptime. And it doesn't involve losing more than 90% of the photovoltaic energy, I will eat my whole hat if the ray-to-electricity pipeline for this boondoggle exceeds 10% efficiency. Can we please stop wasting time and effort, and invest in the buildout of a substantial nuclear fleet to provide baseline power?

ComputerGuru 2y ago
China seems to be working towards that goal. Everyone else, not so much.
AtlasBarfed 2y ago
Are you totally ignorant of how much nuclear costs? Go ahead and look at the lazard lcoe numbers, and this year was an odd increase for solar wind that will basically be the best that nuclear can hope for. If nuclear could provide a cheap scalable easily approved rapidly deployed safe and low waste reactor that could be price competitive with solar and wind, then they be in the game. That is not happening without probably 10 to 20 years of research and development with billions of dollars of funding. Old nuclear was solid rods and gigantic domes and all of that stuff simply is not price competitive, and even if you dropped everything and started attempting to get approvals and construction for hundreds of nuclear plants, they won't come online for 10 to 20 years themselves. When's going to get cheaper solar? Certainly going to get cheaper with perovskites. Stores will get cheaper with lfp and sodium ion improvements, solid state and hopefully someday sulfur chemistries. The nuclear industry needed to get its act together decades ago. In my opinion, it made a huge error in abandoning msr in the 70s (which has all the features of a competitive nuclear plant if they could figure out the materials science) and other breeder reactors. A solid fuel rods reactor is simply not reliably safe in all disaster scenarios (Fukushima).

fredgrott 2y ago

This solution is better and no toxicity https://www.pnnl.gov/news-media/baking-soda-solution-clean-hydrogen-storage https://www.pnnl.gov/news-media/baking-soda-solution-clean-h...

kimmk 2y ago

For seasonal grid-level storage, I wonder if simple compressed hydrogen storage (around 350 bar) is the most reasonable solution. AFAIK doesnt require any high-tech materials, avoids most embrittlement caused by LH2 and boil-off rates are reasonable.

msandford 2y ago
The most efficient seasonal battery is probably synthetic hydrocarbons. By the time you get to propane (3 carbons) the pressures for liquid are super super reasonable (400psi including a giant safety factor) and there's zero embrittlement. Further is that vehicles can use propane so you don't even have to idle the plants during the winter so long as there's some PV from the southern states. They might be running at 100% capacity in summer and 40% capacity in winter but that's way better than 0%. It's a lot easier to keep people employed to operate the plants if they're needed year round.

credit_guy 2y ago

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 are probably bigger energy losses bringing the reactant mass at the required temperature (400 degrees C). Unfortunately, I don't see this making any sense for large scale energy storage. Storage tanks for compressed hydrogen enjoy the square-cube law. The larger they are the less expensive they are proportional to the mass of hydrogen they hold. With this iron oxide method, you need 27 tons of iron oxide for one ton of hydrogen. You can procure right now tanks that can hold 2.7 tons of hydrogen and weigh 77 tons empty [1], the ratio is 28 to 1. But the round-trip efficiency of the tank is virtually 100%. The efficiency of the iron-based storage is only 50%. The tanks are not very expensive. I can't see the niche that this idea can apply to. [1] https://www.iberdrola.com/press-room/news/detail/storage-tanks-green-hydrogen-puertollano https://www.iberdrola.com/press-room/news/detail/storage-tan...

paulsutter 2y ago
Hydrogen is difficult to store and transport, you really want natural gas or jet fuel
kilotaras 2y ago
27 tons of iron oxide have a volume of 5m^3 and can be stored in pretty much a hole in the ground. 2.7 tons of hydrogen have a volume of almost exactly 30000 m^3, requiring storing it under high pressure in specialized containers. Hydrogen is famous for being hard to store without losses. For long-term storage storage and losses are a problem. > But the round-trip efficiency of the tank is virtually 100%. The efficiency of the iron-based storage is only 50% Maybe I'm missing something, but why? As you mentioned it takes 29kj to restore 3 moles of H2 out of (3 moles of H20 + 1 mole of Fe2O3). Where does 50% comes from?
- kilotaras 2y ago
  i.e. the paper[0] states that first "discharging" produced 7.09kg of H2 out of 8.71 theoretically possible the efficiency is super low, but again, according to the paper, "most of the energy input was due to thermal losses at the reactor surface (83.9%)", which also benefits from square/cube law. [0] https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se01228j https://pubs.rsc.org/en/content/articlelanding/2024/se/d3se0...

paulsutter 2y ago

You really want to store excess energy as natural gas or jet fuel because of all the existing infrastructure. Especially since excess power is available at so many solar sites, we’re so good at transporting these fuels, and the cost of photovoltaic will keep going down The vast, cheap power that photovoltaic will provide is a giant opportunity. Please review the links below https://terraformindustries.com/ https://terraformindustries.com/ Terraform industries converting sun and air into natural gas: https://techcrunch.com/2024/04/01/terraform-industries-converted-electricity-and-air-into-synthetic-natural-gas/ https://techcrunch.com/2024/04/01/terraform-industries-conve... The solar industrial revolution is the biggest investment opportunity in history: https://caseyhandmer.wordpress.com/2024/05/22/the-solar-industrial-revolution-is-the-biggest-investment-opportunity-in-history/ https://caseyhandmer.wordpress.com/2024/05/22/the-solar-indu...

shikon7 2y ago

Why would you use hydrogen to extract the energy of the iron? Wouldn't it be more efficient to burn the iron directly? Likewise, is there no better way to reduce iron oxide to iron than by creating hydrogen first?

yxhuvud 2y ago
There may be, but now you are assuming energy is what is needed and not the hydrogen itself. Hydrogen is used in lots of industrial processes and is really hard to store in bulk.

dredmorbius 2y ago

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 stretch, diesel fuel). It stores forever (proved to 300 million years), it is drop-in compatible with extant infrastructure and equipment, it's infinitely miscable with present fuels, it doesn't leak out of storage, it doesn't embrittle metals (and in fact generally lubricates and protects them). Yes, the round-trip storage efficiencies are low (as low as ~15--20% recovery based on thermal electrical generation, roughly the same as the solution named here), but that's in exchange for something that can readily provide weeks to months of storage capacity in a stable, low-risk form. Where you need storage that's long-term stable, dense, safe, and instantly dispatchable, your options are few. The technology has been demonstrated in numerous experimental trials, and is similar to processes run at national scale for decades in Germany and South Africa. US-based research has been conducted at Brookhaven National Laboratory, M.I.T., and the US Naval Research Lab, amongst others. The stumbling block to date has been that fossil fuel prices are sufficiently low[1] that synfuels simply are not competitive presuming market-based mechanisms which fail to account for externalities and other market failures. I've be aware of this for about a decade and have written about the technology, Fischer-Tropsch fuel synthesis, multiple times on HN: <https://hn.algolia.com/?dateRange=all&page=0&prefix=true&query=by%3Adredmorbius%20fischer-tropsch&sort=byPopularity&type=comment https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...> ________________________________ Notes: 1. A market failure of staggering proportions, as the under-pricing is on the order of a million-fold. See: Jeffrey S. Dukes, "Burning Buried Sunshine", <https://core.ac.uk/download/pdf/5212176.pdf https://core.ac.uk/download/pdf/5212176.pdf> (PDF)

mglz 2y ago
How much incoming solar power ends up in the methane? And how do you get the energy back out?
- deleted 2y ago
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zahlman 2y ago

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 had. Rather, it's using the energy to deoxidize rust. Then on the recovery side, why use this steam process? Apparently (because the thermodynamics work out so that this whole thing has efficiency > 0) you get energy out of the process of putting the oxygen back into the iron. So why not just, well, burn (i.e. rust) the iron directly? What exactly is the dissociation and re-combination of the steam accomplishing?

usrusr 2y ago
> "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 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)
kortex 2y ago
> 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.

czierleyn 2y ago

Is this the same idea as? https://teamsolid.org/ https://teamsolid.org/

ano-ther 2y ago

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 https://doi.org/10.1039/D3SE01228J ).

kragen 2y ago

or you can maybe skip the hydrogen intermediary on one end and burn the iron in an iron-air battery. then you get much higher efficiency. electrowinning of iron in alkali is also feasible, eliminating the hydrogen on both ends

hollerith 2y ago
But then you have to keep on adding iron, which might be costlier than hydrogen. And you have to keep on removing iron oxide.
- kragen 2y ago
  well, adding iron and removing iron oxide is what electrowinning iron does, but i think i added that part of my comment after you made yours. but you can still add iron and remove iron oxide with the hydrogen smelting furnace the ethz researchers devised if you like that better