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I always wonder if hydrogen is a side-step without any real practical use or will somehow create a niche where the high-density requirements of long range trave

I always wonder if hydrogen is a side-step without any real practical use or will somehow create a niche where the high-density requirements of long range travel are needed. I.e. airplanes and cargo ships. Hydrogen is awful to store and has no existing infrastructure around it, and you only get efficiency gains if you use fuel cells, otherwise it's back to Carnot's law. Compare this to synthetic biofuels. They are already the market, as an example I can go fill up my diesel car right now with it, certified to work by the manufacturer, and can be transported and used by existing infrastructure. Why isn't this talked about more? Are the land usage requirements making it unfeasible for a global switchover in the aviation and maritime industries requiring converting CO2 from the air making it much more expensive? Or is it simply not flashy enough?

m4rtink 6y ago
I'm not sure hydrogen can be really said to be high density - at least as rocket popelant it is notoriously low density, even in liquid form.
- WJW 6y ago
  Compared to battery packs (the main competitor for "green" vehicles) it has a very high energy density.
  - masklinn 6y ago
    It has a higher energy density but not "very high". Lithium-ion tops out around 2.4 MJ/L, LOH 8~10. Maybe one order of magnitude difference when you use less dense li-ion. Plus that energy density of LOH doesn't take in account the absolute hell that it is to keep stored. Fossil fuels are in the mid-30s by comparison. What LOH does have compared to batteries and even fossil fuels is very high specific energy (energy per kg), it's about triple fossil fuels and a good 2 orders of magnitude better than li-ion. That's why it's been used a lot in rocketry, where mass is a much bigger concern than volume.
- pa7x1 6y ago
  There is two densities to care about when talking about energy sources. Energy density per volume unit and energy density per mass unit. Hydrogen has a very high energy density per mass unit (the highest of the chemical reaction energy sources). But lower energy density per volume than Li. The two figures matter for different use cases, cargo-ships and aviation want to optimize for energy density per mass, while small passenger transport (e.g. scooters, cars...) wants to optimize for energy density per volume. Energy density per mass graph: https://en.wikipedia.org/wiki/Energy_density#/media/File:Energy_density.svg https://en.wikipedia.org/wiki/Energy_density#/media/File:Ene...
baybal2 6y ago
If you have tons of near free energy, and hydrogen, making other synthetic fuels, which are way more storable is not a problem, a ton of other avenues will open in chemical industry for "direct synthesis" Fuel cells can also use synthetic fuels, including hydrocarbons, and ammonia.
masklinn 6y ago
> Hydrogen is awful to store and has no existing infrastructure around it, and you only get efficiency gains if you use fuel cells, otherwise it's back to Carnot's law. Plus the hydrogen production pipeline is mostly from hydrocarbon so it's no gain at all. AFAIK hydrolysis is currently rather expensive and mostly for situations where you need very pure hydrogen (e.g. scientific application).
- regularfry 6y ago
  Part of the discussion in the UK at the moment is around the feasibility of reusing existing natural gas infrastructure (good luck with that) and building explicitly green hydrogen plants as opposed to generating from hydrocarbons. The problem is the scale you'd need to make a dent. It's being proposed as a serious solution to road and rail transport hydrocarbon use, and the power requirements are bigger than anyone I've seen addressing. The last-mile distribution problem is also not inconsiderable, but it pales in comparison to having to copy and paste a chunk of our existing renewable energy fleet.

m4rtink 6y ago

I'm not sure hydrogen can be really said to be high density - at least as rocket popelant it is notoriously low density, even in liquid form.

WJW 6y ago
Compared to battery packs (the main competitor for "green" vehicles) it has a very high energy density.
- masklinn 6y ago
  It has a higher energy density but not "very high". Lithium-ion tops out around 2.4 MJ/L, LOH 8~10. Maybe one order of magnitude difference when you use less dense li-ion. Plus that energy density of LOH doesn't take in account the absolute hell that it is to keep stored. Fossil fuels are in the mid-30s by comparison. What LOH does have compared to batteries and even fossil fuels is very high specific energy (energy per kg), it's about triple fossil fuels and a good 2 orders of magnitude better than li-ion. That's why it's been used a lot in rocketry, where mass is a much bigger concern than volume.
pa7x1 6y ago
There is two densities to care about when talking about energy sources. Energy density per volume unit and energy density per mass unit. Hydrogen has a very high energy density per mass unit (the highest of the chemical reaction energy sources). But lower energy density per volume than Li. The two figures matter for different use cases, cargo-ships and aviation want to optimize for energy density per mass, while small passenger transport (e.g. scooters, cars...) wants to optimize for energy density per volume. Energy density per mass graph: https://en.wikipedia.org/wiki/Energy_density#/media/File:Energy_density.svg https://en.wikipedia.org/wiki/Energy_density#/media/File:Ene...

baybal2 6y ago

If you have tons of near free energy, and hydrogen, making other synthetic fuels, which are way more storable is not a problem, a ton of other avenues will open in chemical industry for "direct synthesis" Fuel cells can also use synthetic fuels, including hydrocarbons, and ammonia.

masklinn 6y ago

> Hydrogen is awful to store and has no existing infrastructure around it, and you only get efficiency gains if you use fuel cells, otherwise it's back to Carnot's law. Plus the hydrogen production pipeline is mostly from hydrocarbon so it's no gain at all. AFAIK hydrolysis is currently rather expensive and mostly for situations where you need very pure hydrogen (e.g. scientific application).

regularfry 6y ago
Part of the discussion in the UK at the moment is around the feasibility of reusing existing natural gas infrastructure (good luck with that) and building explicitly green hydrogen plants as opposed to generating from hydrocarbons. The problem is the scale you'd need to make a dent. It's being proposed as a serious solution to road and rail transport hydrocarbon use, and the power requirements are bigger than anyone I've seen addressing. The last-mile distribution problem is also not inconsiderable, but it pales in comparison to having to copy and paste a chunk of our existing renewable energy fleet.