Comment by dotancohen
16 hours ago
I had to Google what is green hydrogen. It is hydrogen produced by electrolysis.
If you've already got the electricity for electrolysis, would it not be more efficient and mechanically simpler to store it in a battery and power an electric motor?
> If you've already got the electricity for electrolysis, would it not be more efficient and mechanically simpler to store it in a battery and power an electric motor?
The Mirai uses the hydrogen in a fuel cell so it is an EV: https://en.wikipedia.org/wiki/Toyota_Mirai
It looks like a reasonable idea, but it needs infrastructure.
The value proposition of hydrogen is energy density. Batteries have low energy per unit of volume and awful energy density by unit of mass. You will never, ever, fly across the Pacific on a battery powered aircraft. Transoceanic shipping is also not feasible with batteries (current and proposed battery powered shopping lanes are short hops of a couple hundred kilometers or less).
The Toyota Mirai is a passenger vehicle, not an airplane nor a transatlantic container ship.
Sure, but if the economics of hydrogen motors worked out for planes and shipping, the argument is that it would also economically work out for cars.
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True, but it is a good first step. Start small, increment to larger solutions.
> If you've already got the electricity for electrolysis, would it not be more efficient and mechanically simpler to store it in a battery and power an electric motor?
Yes, if you actually have the batteries.
Between around 2014-2024, the common talking point was "we're not making enough batteries", and the way the discussions went it felt like the internal models of people saying this had the same future projections of batteries as the IEA has infamously produced for what they think future PV will be: https://maartensteinbuch.com/2017/06/12/photovoltaic-growth-...
I've not noticed people making this claim recently. Presumably the scale of battery production has become sufficient to change the mood music on this meme.
To be fair, there are still plenty of people on HN talking about lack of battery capacity as a reason to delay solar/wind rollout; I suspect it'll take a bit more time for the new reality to sink in fully.
The fossil industry was always suspiciously keen on green hydrogen - partly because the path to green hydrogen would likely have involved a long detour through grey and blue hydrogen, and partly because it gave them an excuse to lobby against phasing out natural gas for domestic heating/cooking ("we need to retain that infrastructure to enable the hydrogen economy!").
You can see the same thing happening in their support for Carbon Capture and Storage - "we're going to need the oil producers to enable carbon sequestration, so we might as well keep drilling new wells to keep their skills fresh!"...
I think that is the way it is headed. But you never know. Sometimes when comparing it helps me to reduce these things down to lower levels.
What is a battery? A chemical cell to store hydrogen and oxygen(true, it does not "have" to be hydrogen and oxygen but it usually is) to later get energy out of. For example lead-acid(stores the oxygen in the lead-sulfate plates and the hydrogen the the sulfuric acid liquid) or nickle-metal(charges into separate oxygen and hydrogen compounds, discharges into water) the lithium cell replaces hydrogen with lithium. Consider a pure hydrogen, oxygen fuel-cell, it could be run in reverse(charged) to get the hydrogen and oxygen and run forward(discharged) to get electricity out of it. So it is a sort of battery, a gas battery. Gas batteries are generally a bad idea, mainly because they have to be so big. Much time and effort is spent finding liquids that can undergo the oxidation/reduction reactions at a reasonable temperature. But now consider that there is quite a bit of oxygen in the air, if we did not have to store the oxygen our battery could be much more efficient, This is the theory behind free-air batteries. But what if our battery did not have to run at a reasonable temperature. We could then use a heat engine to get the energy out. And thus the Mirai. They are shipping half of the charged fluid to run in a high temperature reaction with the other half(atmospheric oxygen) to drive a heat engine that provides motive power.
As opposed to having the customer run the full chemical plant to charge and store the charged fluids to run in a fuel cell to turn a electric motor for motive power. Honestly they are both insane in their own way. But shipping high energy fluids tend to have better energy density. Perhaps the greatest problem in this case is that it is in gaseous form(not very dense) so has no real advantage. Unfortunately one of the best ways to retain hydrogen in a liquid form is carbon.
Before the introduction of 800V charging architectures, long charge-time for EVs was a big con. Hydrogen Cell vehicles were supposed to be EVs with drastically faster fill-up times. The tradeoff was more complex delivery infrastructure.
Yet, most of the world has had 3 phase (400V phase to phase) for ages. At the wall.
I don't know why you prefixed with "Yet" when I clearly spelt out the trade-offs and contrasts in distribution between H2 and electricity.
The Mirai goes from empty to full in 5 minutes or less - which compares very well with fossil-fuel burners. Now that every OEM has abandoned battery-swapping, how fast can EV batteries be safely charged with the said 3 phases? How long were the charging time when the Mirai was debuted? That was the trade-off Toyota was hoping to fall on the good side of, nevermind the Japanese government bet on hydrogen and whatever incentives are available for Toyota.
North America has 3 phase power for any necessary purpose (factory, DC rapid charging station etc). It's 480V/227V.
Green hydrogen is a way to ship solar power elsewhere that doesn't have it, similar to a battery, but with the advantage of being able to be piped/pumped/liquified etc.
For that purpose and for long-term storage of energy and for aircraft/spacecraft, synthetic hydrocarbons are much better.
Making synthetic hydrocarbons was already done at large scale during WWII, but it was later abandoned due to the availability of very cheap extracted oil.
So when oil was not available, the economy could still be based on synthetic hydrocarbons even with the inefficient methods of that time (it is true however that at that time they captured CO2 from burning coal or wood, not directly from the air, where it is diluted).
Today one could develop much more efficient methods for synthesizing hydrocarbons from CO2 and water, but the level of investment for such technologies has been negligible in comparison with the money wasted for research in non-viable technologies, like using hydrogen instead of hydrocarbons, or with the money spent in things like AI datacenters.
Liquid hydrogen loses 1% of its volume per day due to boil-off. Hydrogen is incredibly difficult to move without huge energy losses.
It would be moved by pipeline as a compressed gas, not as LH2. The US already has > 1000 miles of H2 pipelines.
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