Hydrogen 15x more power dense than diesel?

[Journeyman]

Just read an ad for a very very high end new catamaran that will feature hydrogen storage for electrical needs.

The CEO is quoted as saying "hydrogen is 15 times more power dense than diesel".

Can anybody rationalize how that could be true?

Thanks,
J

[MartinR]

By weight, yes, but definitely not by volume, not even if it is liquefied. I think they are talking power cells. Methanol would be a much more accessible option for this. Hydrogen is a very tough gas to store, leaks through basically everything.

[44'cruisingcat]

Yep, difficult to stop it from leaking, and if it does leak, it's the most flammable substance there is. Can explode when mixed with air in ratios from about 5% to 75%.

[Paul L]

Here's the early testing on the energy in hydrogen

[Dockhead]

Originally Posted by 44'cruisingcat

Yep, difficult to stop it from leaking, and if it does leak, it's the most flammable substance there is. Can explode when mixed with air in ratios from about 5% to 75%.

Hydrogen is also extremely light and rises and dissipates almost instantly if leaked in small quantities. Our lead-acid batteries produce a lot of hydrogen which is just released into our cabins. I don't think it's very dangerous if handled in a reasonable way.


Hydrogen could be a very cool energy storage medium, but the problem is there is no supply infrastructure. I think that one thing kind of kills it for us. Would be interesting to see how the makers of that "very high end cat" propose to deal with that.

[44'cruisingcat]

Actually your lead acid batteries produce quite small amounts of hydrogen.

The amounts you'd require if it was to be used as a propulsive fuel would be incomparably larger.

[Dockhead]

Originally Posted by 44'cruisingcat

Actually your lead acid batteries produce quite small amounts of hydrogen.

The amounts you'd require if it was to be used as a propulsive fuel would be incomparably larger.

I doubt if leaks from such a system (for electrical power generation anyway, not propulsion) would be greater than the amount freely vented from lead acid batteries.



The problem is incomparably easier to deal with, than dealing with propane leaks.

[Journeyman]

Originally Posted by MartinR

By weight, yes, but definitely not by volume, not even if it is liquefied. I think they are talking power cells. Methanol would be a much more accessible option for this. Hydrogen is a very tough gas to store, leaks through basically everything.

He is taking power cells.

The idea being once the ship's batteries are charged during times of abundant solar and wind power, any excess power is used to make hydrogen with an electrolyzer, so the fuel cell can then charge the batteries during times of less available solar and wind.

OK, but fuel cells do not store energy other than in their hydrogen tank, no?

So the statement that hydrogen is "15x more power dense than diesel" seems both a nonsequitor and erroneous, no? I have read liquid hydrogen volumetrically is only about 1/4 the power density of diesel.

The high profile article is in this month's Yachting World page 78.

[Peregrine1983]

Originally Posted by Journeyman

So the statement that hydrogen is "15x more power dense than diesel" seems both a nonsequitor and erroneous, no? I have read liquid hydrogen volumetrically is only about 1/4 the power density of diesel.

1/4 of the power sounds about right if this table this table is accurate - which lists diesel at 35.8 MJ/L and hydrogen at 700 atmospheres as 9.17 MJ/L.


BUT as MartinR said, they're probably talking power cells.

[Journeyman]

Peregrine, as in my reply to
Martin, power cells (fuel cells) do not store energy.

[Peregrine1983]

Originally Posted by Journeyman

Peregrine, as in my reply to
Martin, power cells (fuel cells) do not store energy.

I believe you're confusing the energy released by burning hydrogen versus using it with a catalyst and oxygen in an electrochemical reaction - a fuel cell - to generate electricity.

The Wikipedia table I linked to that lists hydrogen being about 1/4 the energy density of diesel is (I believe) talking about the energy released by burning hydrogen vs burning diesel.

And yes a fuel cell doesn't store electricity, it generates it.

[NPCampbell]

3x more dense ...

Compressed hydrogen has more way more energy per weight (~140MJ/kg) than gas or diesel (~45-50 MJ/kg) but way less energy per volume even if liquified (1:4). Additionally, compressing hydrogen to a liquid to reduce storage size consumes around 50MJ/kg negating 1/3 of it's efficiency over gas. Then there's the boom factor. Hydrogen is 10 times more flammable than gasoline.

[sailormed]

There is a reason Elon Musk chose kerosene over liquid hydrogen for his rockets

[44'cruisingcat]

Originally Posted by Dockhead

I doubt if leaks from such a system (for electrical power generation anyway, not propulsion) would be greater than the amount freely vented from lead acid batteries.



The problem is incomparably easier to deal with, than dealing with propane leaks.

Wrong. Have you actually worked on a hydrogen plant?

The molecules are so small it's extremely difficult to stop it from leaking. Also, if you're going to condense it, you need very high pressures. VERY HIGH. We spent weeks leak testing, replacing expensive spiral wound gaskets, and still never got that plant gas tight. And that wasn't at condensing pressures.

By comparison propane is easy.

Then there's the flammability of hydrogen. It'll burn explosively in concentrations far weaker than propane would. And far richer too.

[MartinR]

They have tried to develop hydrogen as car fuel for decades now, and have not been able to make it work reliable. Neither for direct combustion nor for fuel cells.

Fuel cells for stationary applications are in use, though.
Perfect fuel from an environmental point of view otherwise.