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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 e

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?

overfeed 8mo ago
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.
- xxs 8mo ago
  Yet, most of the world has had 3 phase (400V phase to phase) for ages. At the wall.
  - overfeed 8mo ago
    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.
    - xxs 8mo ago
      >with "Yet" when I clearly spelt out the trade-offs It was with regard that 800V was the driving factor, it'd be possible to have 'fast' charging earlier with existing infrastructure, even home. >be safely charged with the said 3 phases? The limiting factor for charging would be charging current in lots of cases. Getting 60% of 75kWh battery, it's 45kWh to charge in 20mins, the output should be ~150kW (90% efficiency) or 325A (on 400v), 4x 12-15mm wires. Note about 'home' charging - three phase 32A is widely available domestically or around 6-8h to fully charge
  - Symbiote 8mo ago
    North America has 3 phase power for any necessary purpose (factory, DC rapid charging station etc). It's 480V/227V.
- crote 8mo ago
  The faster fill-up time of hydrogen was mostly a lie. It could fuel a single vehicle at that speed, but then the filling station would need a significant time to build up enough pressure for the next one. Turns out having to fill vehicles at 350 to 700 bar (5,000 to 10,000 psi) is a massive pain - especially when you can't keep it cryogenically cooled as a liquid in your storage tanks.
somat 8mo ago
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.
Manuel_D 8mo ago
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).
- dotancohen 8mo ago
  The Toyota Mirai is a passenger vehicle, not an airplane nor a transatlantic container ship.
  - solatic 8mo ago
    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.
    - Manuel_D 8mo ago
      Is suspect large trucks may eventually move to hydrogen, but smaller passenger vehicles will stay on batteries. The nature of hydrogen containment favors larger capacity, on account of better volume to surface area ratios.
      - throwaway473825 8mo ago
        Hydrogen was marketed as a stopgap until batteries are good enough. Well, batteries are good enough for trucks now: https://www.electrive.com/2026/01/23/year-end-surge-electric-trucks-outsell-diesel-for-the-first-time-in-china/ https://www.electrive.com/2026/01/23/year-end-surge-electric... Once you go battery electric, you never go back. It's the most efficient way to move vehicles.
      - MaKey 8mo ago
        >Is suspect large trucks may eventually move to hydrogen [...] They won't, why would they? The number of hydrogen gas stations is going down and the price is going up. Batteries are good enough already - the Mercedes eActros 600 with its 600 kWh battery has a range of 500 km.
rswail 8mo ago
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.
- throwaway473825 8mo ago
  Liquid hydrogen loses 1% of its volume per day due to boil-off. Hydrogen is incredibly difficult to move without huge energy losses.
  - pfdietz 8mo ago
    It would be moved by pipeline as a compressed gas, not as LH2. The US already has > 1000 miles of H2 pipelines.
    - closewith 8mo ago
      All between co-located industrial generators and consumers. H2 pipelines are DOA due to the absurd compression costs.
      - pfdietz 8mo ago
        A BTU of hydrogen requires more energy to compress to a given pressure than a BTU of natural gas, but hydrogen also has lower viscosity, so less recompression is needed. The point you raise does not rule out hydrogen pipelines.
        closewith 8mo ago
        It does, definitively.
        pfdietz 8mo ago
        If it does, then it also rules out long distance transmission of electrical power, as that is even more expensive. And the hydrogen advantage is even greater when one considers one can piggyback storage onto this system, as is done in natural gas pipelines. The electrical system would need additional batteries which are much more expensive per unit of storage capacity.
ben_w 8mo ago
> 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-reality-versus-projections-of-the-international-energy-agency/ 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.
- roryirvine 8mo ago
  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!"...
graemep 8mo ago
> 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 https://en.wikipedia.org/wiki/Toyota_Mirai It looks like a reasonable idea, but it needs infrastructure.

overfeed 8mo ago

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.

xxs 8mo ago
Yet, most of the world has had 3 phase (400V phase to phase) for ages. At the wall.
- overfeed 8mo ago
  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.
  - xxs 8mo ago
    >with "Yet" when I clearly spelt out the trade-offs It was with regard that 800V was the driving factor, it'd be possible to have 'fast' charging earlier with existing infrastructure, even home. >be safely charged with the said 3 phases? The limiting factor for charging would be charging current in lots of cases. Getting 60% of 75kWh battery, it's 45kWh to charge in 20mins, the output should be ~150kW (90% efficiency) or 325A (on 400v), 4x 12-15mm wires. Note about 'home' charging - three phase 32A is widely available domestically or around 6-8h to fully charge
- Symbiote 8mo ago
  North America has 3 phase power for any necessary purpose (factory, DC rapid charging station etc). It's 480V/227V.
crote 8mo ago
The faster fill-up time of hydrogen was mostly a lie. It could fuel a single vehicle at that speed, but then the filling station would need a significant time to build up enough pressure for the next one. Turns out having to fill vehicles at 350 to 700 bar (5,000 to 10,000 psi) is a massive pain - especially when you can't keep it cryogenically cooled as a liquid in your storage tanks.

somat 8mo ago

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.

Manuel_D 8mo ago

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).

dotancohen 8mo ago
The Toyota Mirai is a passenger vehicle, not an airplane nor a transatlantic container ship.
- solatic 8mo ago
  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.
  - Manuel_D 8mo ago
    Is suspect large trucks may eventually move to hydrogen, but smaller passenger vehicles will stay on batteries. The nature of hydrogen containment favors larger capacity, on account of better volume to surface area ratios.
    - throwaway473825 8mo ago
      Hydrogen was marketed as a stopgap until batteries are good enough. Well, batteries are good enough for trucks now: https://www.electrive.com/2026/01/23/year-end-surge-electric-trucks-outsell-diesel-for-the-first-time-in-china/ https://www.electrive.com/2026/01/23/year-end-surge-electric... Once you go battery electric, you never go back. It's the most efficient way to move vehicles.
    - MaKey 8mo ago
      >Is suspect large trucks may eventually move to hydrogen [...] They won't, why would they? The number of hydrogen gas stations is going down and the price is going up. Batteries are good enough already - the Mercedes eActros 600 with its 600 kWh battery has a range of 500 km.

rswail 8mo ago

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.

throwaway473825 8mo ago
Liquid hydrogen loses 1% of its volume per day due to boil-off. Hydrogen is incredibly difficult to move without huge energy losses.
- pfdietz 8mo ago
  It would be moved by pipeline as a compressed gas, not as LH2. The US already has > 1000 miles of H2 pipelines.
  - closewith 8mo ago
    All between co-located industrial generators and consumers. H2 pipelines are DOA due to the absurd compression costs.
    - pfdietz 8mo ago
      A BTU of hydrogen requires more energy to compress to a given pressure than a BTU of natural gas, but hydrogen also has lower viscosity, so less recompression is needed. The point you raise does not rule out hydrogen pipelines.
      - closewith 8mo ago
        It does, definitively.
        pfdietz 8mo ago
        If it does, then it also rules out long distance transmission of electrical power, as that is even more expensive. And the hydrogen advantage is even greater when one considers one can piggyback storage onto this system, as is done in natural gas pipelines. The electrical system would need additional batteries which are much more expensive per unit of storage capacity.

ben_w 8mo ago

> 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-reality-versus-projections-of-the-international-energy-agency/ 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.

roryirvine 8mo ago
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!"...

graemep 8mo ago

> 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 https://en.wikipedia.org/wiki/Toyota_Mirai It looks like a reasonable idea, but it needs infrastructure.