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I think there is some potential for hydrogen fuel cell powered planes since the energy density of hydrogen is significantly better than batteries.

bdamm 7y ago
But not economic on any known horizon. For some reason fuel cells have repelled good economy (in dollars) for 15 years now.
tengbretson 7y ago
The fact that H2 can't be stored as liquid, even under pressure makes me pretty doubtful. I suspect ethanol or plant-derived oil will beat out hydrogen for as long as batteries aren't up to the task.
- jeffreyrogers 7y ago
  Yeah, I think that's more likely. But for all electric I think hydrogen makes more sense than batteries, since improving batteries enough for real applications requires new chemistries, while I think the obstacles for hydrogen are more about economics.
  - ecpottinger 7y ago
    No, look at the prices and requirements for a hydrogen storage tank, you either need a high pressure tank or one that can handle very low temperatures. Neither is cheap or simple.
    - Hypx 7y ago
      For aviation purposes, it's cheap enough.
- davedx 7y ago
  H2 can be stored as a liquid, it’s more difficult. Check out AeroDelft who are building a liquid hydrogen plane: https://aerodelft.nl/ https://aerodelft.nl/
- sa1 7y ago
  There was some news about metal sponges earlier that may be able to hold high volumes of H2 under low pressure. https://www.bbc.com/news/science-environment-52328786 https://www.bbc.com/news/science-environment-52328786
  - mannykannot 7y ago
    You got me thinking, so I looked for some numbers. Hydrogen has a specific energy of 120 MJ/kg, while Kerosine has 46 MJ/kg. According to the abstract of the paper being discussed here, the new material has a deliverable capacity of 14% by weight, corresponding to about 17 MJ/kg - only a bit better than 1/3 that of kerosine, but considerably better than lithium ion batteries, which apparently achieve less than 1 MJ/kg, while the best-performing lithium-sulfur batteries are at about 1.8 MJ/kg. In addition, we must deal with this material only losing 14% of its weight as its hydrogen is used up, while kerosine loses all of its weight - a combustion-powered airplane becomes more efficient as its fuel is consumed. Furthermore, to get that 14% deliverable capacity, you have to start with it at 100 bar, so the tank containing it will have a substantial weight. So we have progress here, but not yet a substitute for liquid hydrocarbons.
- Hypx 7y ago
  LH2 is a liquid. It's likely airplanes will use liquid hydrogen as a fuel.
snovv_crash 7y ago
I think we're more likely to get working Lithium Sulphur batteries first, which would effectively relegate fuel cells to the garbage can. Between the fuel and the cells, batteries are just so much easier to operate once they're out in the field, there's no comparison.
- Hypx 7y ago
  Lithium sulfur still has a tiny fraction the energy density of hydrogen. It's very unlikely, probably impossible, to ever beat hydrogen on energy density with a battery. Also, Li-S still has too low of energy density for airplanes, and given the long recharge time problem batteries fundamentally are a no-go in aviation.
  - snovv_crash 7y ago
    LiS is only 10x below gasoline. When you account for the difference in efficiency, and the the difference in weight for the motors, and then reliability and redundancy, it is roughly a factor of 2 away. That is fine for shorter routes. Recharging time isn't an issue, just have the batteries swappable.

bdamm 7y ago

But not economic on any known horizon. For some reason fuel cells have repelled good economy (in dollars) for 15 years now.

tengbretson 7y ago

The fact that H2 can't be stored as liquid, even under pressure makes me pretty doubtful. I suspect ethanol or plant-derived oil will beat out hydrogen for as long as batteries aren't up to the task.

jeffreyrogers 7y ago
Yeah, I think that's more likely. But for all electric I think hydrogen makes more sense than batteries, since improving batteries enough for real applications requires new chemistries, while I think the obstacles for hydrogen are more about economics.
- ecpottinger 7y ago
  No, look at the prices and requirements for a hydrogen storage tank, you either need a high pressure tank or one that can handle very low temperatures. Neither is cheap or simple.
  - Hypx 7y ago
    For aviation purposes, it's cheap enough.
davedx 7y ago
H2 can be stored as a liquid, it’s more difficult. Check out AeroDelft who are building a liquid hydrogen plane: https://aerodelft.nl/ https://aerodelft.nl/
sa1 7y ago
There was some news about metal sponges earlier that may be able to hold high volumes of H2 under low pressure. https://www.bbc.com/news/science-environment-52328786 https://www.bbc.com/news/science-environment-52328786
- mannykannot 7y ago
  You got me thinking, so I looked for some numbers. Hydrogen has a specific energy of 120 MJ/kg, while Kerosine has 46 MJ/kg. According to the abstract of the paper being discussed here, the new material has a deliverable capacity of 14% by weight, corresponding to about 17 MJ/kg - only a bit better than 1/3 that of kerosine, but considerably better than lithium ion batteries, which apparently achieve less than 1 MJ/kg, while the best-performing lithium-sulfur batteries are at about 1.8 MJ/kg. In addition, we must deal with this material only losing 14% of its weight as its hydrogen is used up, while kerosine loses all of its weight - a combustion-powered airplane becomes more efficient as its fuel is consumed. Furthermore, to get that 14% deliverable capacity, you have to start with it at 100 bar, so the tank containing it will have a substantial weight. So we have progress here, but not yet a substitute for liquid hydrocarbons.
Hypx 7y ago
LH2 is a liquid. It's likely airplanes will use liquid hydrogen as a fuel.

snovv_crash 7y ago

I think we're more likely to get working Lithium Sulphur batteries first, which would effectively relegate fuel cells to the garbage can. Between the fuel and the cells, batteries are just so much easier to operate once they're out in the field, there's no comparison.

Hypx 7y ago
Lithium sulfur still has a tiny fraction the energy density of hydrogen. It's very unlikely, probably impossible, to ever beat hydrogen on energy density with a battery. Also, Li-S still has too low of energy density for airplanes, and given the long recharge time problem batteries fundamentally are a no-go in aviation.
- snovv_crash 7y ago
  LiS is only 10x below gasoline. When you account for the difference in efficiency, and the the difference in weight for the motors, and then reliability and redundancy, it is roughly a factor of 2 away. That is fine for shorter routes. Recharging time isn't an issue, just have the batteries swappable.