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Comment by the8472 | Hacker News Reader

As long as you don't get your hydrogen from natural gas it's just energy storage like batteries. You can make it from electricity or directly via solar-powered reactions.

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That's pretty much irrelevant, though. The infrastructure for energy distribution is decoupled from its production. Even if hydrogen is split from water via gas today, it can be done by solar or wind tomorrow with no changes to the distribution network.

Current hydrogen production is largely from cracking methane, where natural gas is the feedstock (and also energy source) - it is much cheaper than production from electrolysis.

>As long as you don't get your hydrogen from natural gas (...)

And that's the problem: hydrogen production is a huge waste of energy. Well to wheel efficiency of fuel cells is 22% vs 73% for battery EV (source: https://twitter.com/transenv/status/899976235794788352/photo...)

But BEV cannot really use intermittent energy sources. Not without severely inconveniencing drivers and that's impossible. Hydrogen could be made from intermittent energy sources.

I can't speak to well to wheel, but at the very least current research tech electricity to hydrogen to electricity round trips are 75% efficient.

https://www.nature.com/articles/s41560-019-0333-2

How efficient is hydrogen as an energy storage medium compared to e.g. Li-Ion batteries?

Hydrogen is 3x more energy dense than diesel, and diesel is about 5 to 10x more energy dense than lithium ion batteries.

By mass or volume?

trying to split the difference between https://en.wikipedia.org/wiki/Toyota_Mirai https://en.wikipedia.org/wiki/Tesla_Model_S https://en.wikipedia.org/wiki/Tesla_Model_3

I mean different shaped/sized cars and all but probably a bit worse? range vs weight seems about on par with the S but worse HP?

but also https://en.wikipedia.org/wiki/Fuel_cell#Theoretical_maximum_... so ?

Efficiency as in energy/kg?

Tesla batteries: 207 watt-hours per kilogram (per google search)

Hydrogen: 120-142 MJ per kilogram (per google search)

Conversion from MJ to watt-hours: 277.778 watt-hours per MJ

120*277.778/207 ~ 161 more compact. Assuming energy conversion losses are equal.

Efficiency in terms of watts out from the medium divided by watts into the medium over a normal duty cycle.

As I said in another comment with some napkin calculations is about 30%. Another user gave a 22% number compared to 73% for batteries. The difference is hugely in favour of batteries.

Mining and processing Lithium isn't that clean either.

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