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Comment by ermir | Hacker News Reader

Iron is not widely available in nature as a ready-to-use element, it must be processed into elemental iron, which takes a lot of energy as input. Therefore this can't be really considered as fuel, more like energy storage. You still need fossil fuels or nuclear power to turn iron ores into iron, then you have iron available for the process described in the article.

I'm not criticizing the process, but it's not accurate to call it "fuel" like it could be the solution to replacing fossil fuels.

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The article says this. It wraps up with:

"If these problems can be overcome, you could use renewable electricity to produce iron, store it as long as necessary, transport it there and then burn it for power when needed, says Bergthorson. “Places that have excess energy could make iron, and others can buy it. This way, you could commodify renewable energy so it can be globally distributed without the need for transmission lines. Metals can solve a big problem in the renewable energy transition: long-duration energy storage.”"

Sure you could use renewables to make iron. But that thought process also extends to other methods too. You could use renewables to make other non renewable fuels.

Why not just skip the middleman? Use renewables?

I think this is likely more of an energy storage project, rather than an energy production one (which seems to be the stance the article takes).

At grid-level, battery tech is challenging, requiring technologies like pumped storage that require particular environments (e.g. damming a river) and can't really be transported.

If this works out you could use excess solar during the day to deoxidize the rust produced, and then run the iron reactor overnight, or on cloudy, windless days.

How does that battery/production distinction work? How is it a battery if it is consuming/burning a fuel? More as a stable fallback or something?

Well, if you can burn it to produce energy + spent fuel

and then put back energy in the spent fuel to make new fuel again

then you have really a battery. That's how li-ion batteries work. The issue is the efficiency: how much of the energy you used to recharge the "battery" (iron) is going to be available when you discharge (burn) it

Thanks that makes sense

Non-rechargeable batteries are also consuming a fuel. The products just stay in the same enclosed container. Same with rechargable batteries, just that there the process is easily reversible.

It is a bit of a fuzzy distinction. Batteries are typically simple chemical reactions that cause electrons to move around. But viewed from the outside a hydrogen fuel cell behaves the same; so why not call this one a battery too (especially since the process is reversible).

A useful distinction seems to be that batteries are solid state and don't use high process heat, else something would be seriously wrong. Of course, the underlying reactions are probably very similar if you look at them with a chemist's eye.

Well, it ties into the storage issue that we see with renewable. We still need energy when there is no wind at night. Burning iron at night and regenerating during the day could be a solution. It needs to prove that it can be competitive with the other methods (compressed air, li-ion batteries, flow batteries, molten salts, flywheels...).

> It needs to prove that it can be competitive with the other methods.

I think the one thing is that iron storage would be a potential long term form of storage, while all those other methods that you mentioned are really short term, designed primarily just to deal with the daily peaks and troughs of renewable production, but not as much the "it's been completely overcast for 3 weeks" problem. The only other form of storage I'm aware of that is also long term like that is pumped water storage, and that is obviously very geographically limited.

If using Fe why not iron batteries? Keep the redox, remove the energy from the system via eletrical current instead of low efficiency heat, boiler and steam engine combo.

Great point. Fe batteries are very new so I'm not aware of the cost/benefit or if Fe batteries still slowly discharge over time, but yeah in both cases you're just oxidizing iron, so why not take the more direct route to generate electrical current directly.

There are also applications where the desired output is heat, not electricity. In that case, iron fuel would be useful.

Here’s an out of the box thought. Can we wrap the globe in undersea cables or does transmission losses kill the idea? Reason being that time zones and hemispheres make the “renewable is not always on” problem go away. It’s always on somewhere, so if there was a global grid you don’t really need storage?

Thank you.

They mention that with hydrogen. It's cheaper to produce hydrogen but much harder to transport it. Fortunately, hydrogen can reduce iron oxide, which turns out to be a great complement. Their analysis is that the system cost of burning iron and renewing it at electrolysis plants is lower cost (and safer) than using hydrogen directly.

Because renewables are intermittent and unevenly located. This could potentially solve those problems.

There could be a space for it. Or maybe batteries will just always be better. Depends on the full costs of each and the use case. Burning fuel to make electricity is pretty inefficient, but burning fuel for heat compares better.

Renewables are exceedingly bad at storing energy for times when sun or wind isn't blowing so you always need a mix.

That's not a wind or sun problem, that's a battery and transmission problem.

This is actually the same principle as BTC. High volume cheap electricity is used to process random numbers and the value is stored as BTC allowing it to be freely transferred once first mined.

The green economics of this need some serious consideration as i'd be really aware if you can reprocess it and get a second reaction for less energy than it cost you to turn the rust back into free iron metal.

There's a pretty big difference between BTC and a burnable fuel. It is not possible to turn BTC back into electricity directly, it is only possible to turn it into electricity by first turning it into money, which then buys more electricity (from any, renewable or non renewable) power source. You can't ship someone a container of memory sticks containing BTC and then they get power out of them without burning more fuel or building more solar panels/other renewables. The much better comparison would be hydrogen, which can be produced using readily available water and renewable electricity, shipped, then burned. The difference is that hydrogen doesn't really produce much in the way of by products when burned.

> the value is stored as BTC

What value? Where did any value originate in this process?

The maniacs who claimed that something had a price on a market and cost to create claim that this means value was created. From an ecological perspective, nonsense. Economically, somewhat sound.

Misappropriated rare resources cause destroyed nature for the reason that capitalism said it was sound.

Every joule can only be spent once, but and as long as there is no moral coercion, there is a profit to be made from pillaging it from the supply.

Not sure I agree, on one hand you have actual, physical potential energy, on the other hand you have numbers on a computer that could become worthless depending on unpredictable economic factors.

If a power plant has sufficient store of Iron, with a complete cycle, from burning iron to recovering iron, then it is no longer a consumable.

I can imagine a solar plant, making iron in the day and burning it in the night and essentially act as a base load plant, the holy grail of renewable energy.

The definition of the word "fuel" does not include the requirement that it was originally found laying around in the environment.

Yeah but it pretty much requires that producing the fuel requires less energy than the fuel provides, otherwise itd be like trading a quarter for a dime.

But also don't underestimate how huge it would be if we could store energy efficiently as elemental iron. E.g., produce it using solar, burn it for grid energy. Of course that depends on the efficiency of the whole process.

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