this post was submitted on 04 Aug 2023
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Is hydrogen more energy dense than other net zero fuels such as methenol?
It depends on whether you mean by weight or by volume.
By weight, hydrogen has an almost unbeatable energy density. It's much higher than methanol or even gasoline.
By volume, hydrogen has a horrible energy density, several orders of magnitude lower than any modern type of battery, for example.
So if you have infinite space, hydrogen is great. But a plane does not have infinite space. So you try to compress the hydrogen or cool it down to increase the energy density. However, this will still come out at much worse than gasoline or jet fuel.
The big issue for aircraft is weight more so than volume. You can add a section and stretch an airplane without too much issue. Whereas the ability to lift is limited by weight and engine power.
Weight is definitely the most important issue for a plane, but at some point volume also becomes a limiting factor. Yes, you can stretch an airplane, but that also makes it heavier. With jet fuel, they're currently using every available space, storing most of it in the wings and some also in the fuselage. That's much harder to do with hydrogen, because the pressure containers can't just take on any shape. They have to withstand absolutely insane pressures, so they have to be either cylindrical or spherical.
Yeah, I was thinking volume. Wasn't aware that energy density was also calculated by weight. It makes me wonder tho, is this more "hydrogen economy" hype, or is it worth it
Hydrogen has often been called the champagne of fuels, because it's so expensive and most likely will be for the foreseeable future. So I don't think we'll ever have a "hydrogen economy" in the sense that most things are powered by hydrogen like they now are by fossil fuels.
Electrifying things directly will always be cheaper and much more efficient, even if you have to use batteries. I'm sure hydrogen will play a role somewhere, but it will always be a niche fuel.
That being said, the world uses gigantic amounts of hydrogen already as a chemical substance for industries such as fertilizer production or hydrocarbon cracking. This hydrogen is almost completely made from fossil fuels and this causes huge amounts of carbon dioxide emissions (more than the entire country of Germany). The first thing we should do is to replace this fossil hydrogen with green hydrogen, because it will directly cause lower CO2 emissions. Once we've done that and we still have the option to produce more hydrogen, we can start looking for other application such as flight, shipping or energy storage.