H2 equivalent to 1 liter of gasoline
 

A question I had was how much hydrogen gas (and at what pressure !) equals 1 liter of gasoline. Wikipedia mentions gasoline has 33,41 kWh per gallon (or hence 125 kWh per liter) and (idealhy.eu mentions that) hydrogen gas contains 0,003 kWh per liter (at a pressure of 1 bar). I would thus assume that to attain a same amount of energy (125 kWh per liter), I'd need to use a 41666 bar compression on that 1 liter tank.

Is this actually correct ? I don't see where I made a mistake, yet such kind of pressures are not used in everyday life (the biggest compression rate used is some 700 bar).

Can anyone verify whether my calculation is correct or not ?

I think you will find that the hydrogen is stored at 350 or 700 bar, therefore to hold 1 litre petrol equivalent you require a far greater volume than 1 litre.

I gallon of gas equivalent is about 2kg.
So a liter would be about half a Kg.
Forget volume, do calculations in mass any time possible.

I think that is correct.

What are you trying to do with hydrogen exactly?

Your conversion is backward. 33.41kWh/gal / 3.78541 L/gal = 8.83 kWh/L

So your calculations following that point are off by a factor of about 14x.

I knew something looked wrong in there but I just couldn't figure it out. Thanks for pointing it out for me and we'll the OP I guess. 3 1/2 hours of sleep got me a little fuzzy.

Re: thanks for noticing this samwichse; updated the calculation:

1 liter of gasoline= 33,41 kWh per gallon (or hence 8,83 kWh per liter)
hydrogen gas contains 0,003 kWh per liter (at a pressure of 1 bar). I would thus assume that to attain a same amount of energy (8,83 kWh per liter), I'd need to use a 2943 bar compression on that 1 liter tank.

This still seems huge (the biggest compression rate used is some 700 bar). I guess it's doable if I am to use a 10 liter tank pressured at 294,3 bar but still that's a relatively large tank for just 1 liter of gasoline equivalent.

The other thing I've been wondering about: does this take into account the size the gas still takes in after compression (I would assume that 1 liter of hydrogen, after compression to say 294 bar only takes in about 1/294th of the space (so 0,003397 liter). Or well, about that amount of space ...
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The other calculation I did actually used weight rather than volume (as oil pan 4 suggested). It went as follows:

1 liter of gasoline = 0,26 gallon of gasoline
14 liter of hydrogen = 1 kg of hydrogen @ 1 bar (see uigi.com/h2_conv.html )
1 kg of hydrogen = energy in 1 gallon of gasoline (see heshydrogen.com/hydrogen-fuel-cost-vs-gasoline )
0,26 kg hydrogen = 3,64 liter of hydrogen (compressed at 1 bar) -0,26 X 14-
So in this latter calculation, it looks as if a mere 3,64 liter tank with hydrogen, without any compression at all would do

This obviously doesn't seem correct, but I don't see the mistake here either.

I think 1kg hydrogen is equivalent to a gallon of gasoline. And 1 gallon of gas = 33.7kWh.

The real problem with compressed H2 is the tank. From a quick search, the air in a typical scuba tank weighs about 6.5 lbs. Firgure H2 is about 1/14 as dense as air, and you get about 1/2 lb of H2 in a tank that weighs 30 libs or so.

Then there's the energy needed to compress it to 3000 psi...

3,000? How about 10,000PSI?

Have you read my other post ?

I calculated out you could get about 6,95 kWh in a SCUBA.
Haven't tried it in practice though, so if you have, let me know.

I got the SCUBA tank idea from USH2. If it won't work, I guess I could always change it for a CNG tank, but I don't see any structural difference between the 2, so I assume both should work.

As for the energy needed and the compression used (3000 instead of 10 000 psi): using less compression means less energy needed (and less energy loss as well). Obviously it still remains inefficient from this standpoint, but on the other hand it has no (polluting) exhaust gases and you could use renewable electricity to make the hydrogen.

Only problem is the most efficient way to get hydrogen is steam reformation of natural gas.
Do you know how much electrical energy it takes to get hydrogen?
The idea of hydrogen sounds clean but it's unbelievably wasteful. Wastefulness is the opposite of anything you could call clean.
Don't worry about how much energy it takes to compress hydrogen, it's nothing compared to what it takes to make it.

You could save a ton of time and energy and just use natural gas or batteries.

There are plenty of reasons why everyone has moved away from hydrogen as motor and rocket fuel.

Again, read my other post

The idea is to circumvent being dependant on others for the hydrogen supply and rather make it yourself. Then, there's no possibility that the hydrogen was produced by steam reformation of natural gas, or made using electrolysis but from non-renewable energy sources.

It will be costly to do it yourself, but for small enterprises with many vehicles, it may be financially doable.

That too is in the post mentioned. I would be using cheap electrolysers for this. I think they're reasonably efficient.

If you can do high temperature, high pressure electrolysis at high voltage then the process may get up to 50% efficient.
That means several hundred degrees F and 200 to 300 psi minimum.

At normal temperature and pressure it's only around 10% efficient.

An electric vehicle can be refueled with renewable power too and not suffer the horrific inefficiencies of electrolysis.

I haven't worked out the energy you could store as H2 in a scuba tank, just did a "back of the envelope" calculation of the weight of H2 vs tank weight. But that leads to another interesting question: figuring all the various ineffiencies in getting energy in and out, would it be more weight-efficient to store energy as H2, or as electricity in a lithium battery?

Batteries are much more efficient.
That's why everyone is using them.
Hydrogen conversation from electrolysis, maybe 50% efficient some day with tech that does not exist beyond lab experiments. That's at least a 50% loss just to convert the H2O into H2 and O.
Charging and using a lithium Battery to get power to the wheel, worst case scenario is around 70%. That's power grid to wheel.

Getting back to the other calculation in which there was a mistake; ie this one:
"1 liter of gasoline = 0,26 gallon of gasoline
14 liter of hydrogen = 1 kg of hydrogen @ 1 bar (see uigi.com/h2_conv.html )
1 kg of hydrogen = energy in 1 gallon of gasoline (see heshydrogen.com/hydrogen-fuel-cost-vs-gasoline )
0,26 kg hydrogen = 3,64 liter of hydrogen (compressed at 1 bar) -0,26 X 14-
So in this latter calculation, it looks as if a mere 3,64 liter tank with hydrogen, without any compression at all would do "

jamesqf said you would get about 1/2 lb of H2 in a SCUBA tank: that's 0,45 kg of H2.
1 kg H2 = energy in 1 gallon of gasoline = 33,41 kWh (see heshydrogen.com/hydrogen-fuel-cost-vs-gasoline )
0,45 kg H2 x 33,41 kWh = 15,03 kWh
That's far more than what I calculated in my other calculation (I calculated a maximum of 6,95 kWh).
6,95 kWh / 33,41 kWh = 0,208 kg of H2
0,208 kg of H2 would be 2,9 liter of hydrogen (according to uigi.com/h2_conv.html )
So 2,9 liter, whereas in my other calculation I had 11,25 liter.
In this other calculation I calculated it using a pressure of 206 bar; so in this calculation I would have a pressure of 799 bar
--> 11,25 x 206 = 2317,5
--> 2317/ 2,9 = 799 bar

Energy efficient, yes. I was thinking about weight efficiency, though. That is, you can store a lot of energy in a gas tank that doesn't weigh a whole lot. Compress H2 or CNG to 3000 psi, and you need a heavy tank to store not nearly as much energy.

Likewise batteries: you might have a 99.9% efficient battery, but if one that holds the energy equivalent to a gallon of gas weighs several tons, it's not much practical use.

Not the only reason. We also have a pretty good electric infrastructure. Fast chargers are a luxury item: many people could get by with a good extension cord.

Current tech batteries are about 80-85lbs for the actual usable energy in a gallon of gasoline.

Assumptions:
33,700 wh per gallon of gasoline.
250 wh/kg of good lithium batteries
25% actual thermal efficiency of the ICE (about right for a normal car)

33700/250=134.8kg
134.8kg*0.25=33.7kg
33.7kg=74 lbs

Add a bit for motor/motor controller losses.

This is incorrect. Look at your source again. That's 1 liter of liquid hydrogen. Good luck carrying that around. 1kg of hydrogen gas at 1 atmosphere is 11.126m^3, or 11,126 literally.

Aaah, there was the mistake I was looking for, and the reason why this part of my calculation above didn't measure out:

0,208 kg of H2 would be 2,9 liter of hydrogen (according to uigi.com/h2_conv.html )
So 2,9 liter, whereas in my other calculation I had 11,25 liter.
In this other calculation I calculated it using a pressure of 206 bar; so in this calculation I would have a pressure of 799 bar
--> 11,25 x 206 = 2317,5
--> 2317/ 2,9 = 799 bar

Thanks for finding it.
Then much does 1 kg of H2 equal in terms of liter of hydrogen (at 1 bar of pressure) ? I calculated this yet another way:

energy in 1 gallon of gasoline (33,41 kWh) = 1 kg H2
33,41 kWh = 1 bar x 0,003 kWh/l x 11136 l
or 33,41 kWh = 250 bar x 0,003 kWh/l x 44,54 l
So you need about 12 x 4 gallon CNG tanks (with H2 compressed @250 bar) for the energy in 1 kg H2

The weight of the protective structure for 10,000PSI hydrogen tanks, and the battery it carries, and the cooling system, and the fuel cell itself. Compare the weights of say the Toyota Mirai vs the Chevy Bolt EV: 4,078 pounds vs 3,563. The Mirai has (in theory) more range, but it carries 1 less person.

A kilogram of hydrogen is almost exactly the same energy content as a gallon of gasoline.

The 60kWh Bolt battery holds the equivalent of 1.78 gallons of gasoline. (33.7kWh / gallon), and the Mirai can carry 5kg of hydrogen.

Mostly irrelevant, though, since most cars seldom carry more than one person.