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Old 07-15-2017, 04:00 AM   #11 (permalink)
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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.

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Old 07-15-2017, 04:15 AM   #12 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
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.
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.

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Originally Posted by oil pan 4 View Post
Don't worry about how much energy it takes to compress hydrogen, it's nothing compared to what it takes to make it.
That too is in the post mentioned. I would be using cheap electrolysers for this. I think they're reasonably efficient.
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Old 07-15-2017, 11:37 AM   #13 (permalink)
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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.
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Old 07-15-2017, 12:50 PM   #14 (permalink)
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Originally Posted by smallscaleH2 View 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 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?
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Old 07-15-2017, 04:20 PM   #15 (permalink)
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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.
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Old 07-16-2017, 07:56 AM   #16 (permalink)
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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

Last edited by smallscaleH2; 07-16-2017 at 08:07 AM..
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Old 07-16-2017, 01:00 PM   #17 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
Batteries are much more efficient.
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.

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That's why everyone is using them.
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.
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Old 07-16-2017, 01:26 PM   #18 (permalink)
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Quote:
Originally Posted by jamesqf View Post
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.
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.

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14 liter of hydrogen = 1 kg of hydrogen @ 1 bar
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.
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Old 07-17-2017, 05:04 AM   #19 (permalink)
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Originally Posted by samwichse View Post
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

Last edited by smallscaleH2; 07-17-2017 at 07:07 AM..
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Old 07-17-2017, 12:53 PM   #20 (permalink)
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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.

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