Comment by kumarski | Hacker News Reader

Comment by kumarski | Hacker News Reader

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Okay, going to chime in here because this is categorically wrong on so many fronts.

Tldr: Impossible for civilization to make an instantaneous non-gradual switch to hydrogen fuel cells.

People like Hydrogen because they're hyped about how it is:

- Clean

- Plentiful

- Emission-less

Hydrogen is difficult to handle.

- Unwieldy as a gas

- Boils at 20 degrees F/ - 6 degrees C / ~420 Kelvins

- Tough to maintain at a high pressure.

To go 300+ miles or ~480km or more on hdyrogen is ugh tough.

H - 120 MJ/kg

Gasoline - 44 MJ/kg

Volume wise, ugh.

H- 8 MJ/L

Gasoline - 32 MJ/L

You need ~5-10 kilograms of H2 to deal with light duty vehicles.

Compressing the stuff is annoying.

Training and retraining all the gas station attendants to deal with cryogenic materials is no small undertaking.

There's 100K gasoline/diesel stations in the USA.

Very special handling for hydrogen.

Hydrogen penetrates metals.

Makes metals the enemy and things can wear down unexpectedly. Scary stuff. Preventative maintenance is complicated.

Gasoline has ~4x-8x the kwh per a gallon to compressed hydrogen fuel. (my calculation might be a bit off, but not that far off.)

Pumping hydrogen into a vehicle is done slowly from my recollection.

Hydrogen's explosion risk is extreme, the spark from the leak could cause it. eekkkkk.

Hydrogen's flames are invisible. It's a pale blue flame that's difficult to see during the day.

People might come back and say there's progress with magnesium adn/or carbon nanotubes or other things, but they're all meh and don't scale.

Hydrogen has a shitty power to mass ratio. It escapes independently/leaks out easily without you knowing. It's dangerously explosive!

It emits lots of CO2 to make the stuff. CH4+O2 = CO2+2H2 Makes the whole thing seem like a pointless exercise.

The efficiency of manufacturing hydrogen for fuel usage is probably like 10% to 30%. Can't imagine it being more than that.

I'm not a Chem E though.

To make a cryogenic pipeline system in the USA for H2 would cost $1T+

Every year I get asked about Hydrogen, it's all BS.

Any scientist that says it's highly viable has me wondering how much money they wasted on their degree.

> Volume wise, ugh. H- 8 MJ/L, Gasoline - 32 MJ/L

In practice, hydrogen @10 kpsi/70 MPa is currently a bit over 1 MJ/L when including the tanks. Gasoline is misleading as well, because a fuel cell is easily twice as efficient as a gas engine and up to 3x.

Li-ion batteries are anywhere from .5 to 2.5 MJ/L, for reference. Thing is, volumetric efficiency is all but irrelevant for most applications. Even airplanes have huge amounts of empty space that could accommodate tanks; container ships would be less efficient but that's about it.

> You need ~5-10 kilograms of H2 to deal with light duty vehicles.

5 kg will take a Toyota Mirai over 300 miles.

> Training and retraining all the gas station attendants to deal with cryogenic materials is no small undertaking.

This is not a thing. Attendants don't need to do anything with cryogenic anything.

> Hydrogen penetrates metals. Makes metals the enemy and things can wear down unexpectedly. Scary stuff. Preventative maintenance is complicated.

This is an issue when you're trying to build electron microscopes, not when you're fueling cars. The diffusion rate of hydrogen is negligible for everyday purposes like safety. Certain parts need to be designed to avoid embrittlement, but it's a minor problem- embrittlement is only really an issue at VERY high temperatures. If the steel isn't glowing, it's a minor issue, and for most other metals it's even less of an issue.

> Pumping hydrogen into a vehicle is done slowly from my recollection.

It's as fast as a highway pump, and often slightly faster. It's pretty hard to pump slowly when 10 kpsi is involved, after all.

> Hydrogen's flames are invisible. It's a pale blue flame that's difficult to see during the day.

Typically it just explodes, unfortunately. Hydrogen is always at such high pressure that it spreads out rapidly and sustained flames are very unlikely, and then there's the fact that the energy density causes things to break.

> The efficiency of manufacturing hydrogen for fuel usage is probably like 10% to 30%. Can't imagine it being more than that.

Commercial processes are ~60% and non-commercial are above 80%.

Hydrogen might make some sense for long haul trucks. Then you need fewer refueling stations on only the major routes. You could also generate the hydrogen locally by using electricity.

Alternatively you could equip the trucks with batteries and connect them to the electrical grid via overhead lines similar to trains for recharging. Combined with autonomous driving those trucks could go non-stop and leave the highway with full batteries.

Do we really need to convert long distance trucks to fully electric? Why not just work on hybrid trucks to increase efficiency and allow them to operate with zero emissions while in urban areas.

2nd option exists and is called rolling highway ;)

Hydrogen boils at 20 degrees Kelvin, not Fahrenheit. That's -423 degrees Fahrenheit. If it boiled at 20 F, it would be a LOT easier to store and handle.

What is your opinion of Toyota’s hydrogen storage system for cars? It seems to tick all the boxes.

(I just assume Toyota isn’t going big on the Mirai for the same reason Ford and GM still only pay lip-service to BEVs: they don’t want to upset their dealer network too much)

Why does it need to be instantaneous? Who is even asking for instantaneous?

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