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Discussion Starter #1
I've been doing some research on typical emissions for BEV, ICE and FCV, and had some questions about the latter that I was hoping someone might answer.

95% of hydrogen fuel comes from steam reforming, and apparently this produces 9-12 tons of CO2 per 1 ton of hydrogen (http://www.aidic.it/CISAP4/webpapers/7Collodi.pdf). Unless I'm missing something, this puts Toyota Mirai CO2 emissions on par with a Leaf charged from the average British grid mix.

So, questions -

1. Am I missing something there? Methane emissions? Additional energy for compression or liquefaction?

2. Is H2 from steam reforming actually suitable for use in fuel cell cars? I normally hear electrolysis referred to as the method for producing FCV fuel (which uses at least double the electricity of an EV), and am wondering if it's because steam reforming doesn't result in a sufficiently high level of purity.

3. Is any hydrogen typically lost between processing and pumping into the car?


(If anyone's thinking "hydrogen is an energy carrier not a fuel", thanks, have an invisible cookie.)
 

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I'd need to recheck the data I collected some time back but the production of the hydrogen is only the first step in the chain and steam reformation needs a considerable energy input although considerably less than electrolysis. It also needs to be compressed or if travelling any long distance liquified in a cryogenic facility. It needs transport to a filling station which is usually by tanker although quite a few of the filling stations are being set up to generate hydrogen onsite.

One of the big issues is that hydrogen gets past seals with reasonable ease so the losses in distribution and in car storage can be large especially for low mileage vehicles. A few years back I remember the test FCEVs would empty their tanks over a two week period sat in a car park - presumably that loss rate has been reduced.

Another factor is powertrain efficiency. A BEV typically has a propulsive efficiency of 80-90%, an FCEV 35-40% so when you count everything in it's not a great solution. It does have the potential advantage of delivering more range although the Marai is not far off a Tesla Model S, and of course the fill up is faster.
 

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I don't think you are missing anything there.

Right now H2 production is very inefficient and produces lots of CO2 in the process. The thing about H2 is that it has the potential to get much, much better. Once a way of producing H2 more efficiently is developed then H2 will then start to look much better.
 

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Hydrogen is the future. Always will be probably. Buck Rogers in the 25th Century will probably have an affordable one first.
I have to say that I'm unconvinced. For spaceflight in the foreseeable future, yes, but for road transport I'm not so sure. The losses in the chain are quite frightening and FCEVs have a number of question marks over long term reliability and cost.
 

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If the goal is zero CO2 emissions then electrolysis is the only viable way to produce Hydrogen. The problem is that electrolysis not a particularly efficient process. It also takes quite a lot of energy to compress hydrogen for transportation and even just to pump it into the car.

If your electricity comes from renewable sources then it can be argued that efficiency is less important. Just build more windmills and use those to produce Hydrogen. The problem (for hydrogen) is that it is much more efficient and therefore cheaper to use that electricity to just charge a battery.

It will always be cheaper to run a battery car than a hydrogen car if the energy comes from renewable sources.
 

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It just doesn't seem a practical, environmental or cost effective solution -
1. Enormously wasteful to generate the hydrogen in the first place, either by fossil fuel extraction or electrolysis.
2. Storage and distribution needs to be very tightly controlled to avoid accidents and explosions.
3. A typical EV charge point is around £50,000, a typical hydrogen fuel station is in the millions of pounds.
4. We already have a good start on an EV charge infrastructure and only one or two hydrogen stations.
5. Customers are unlikely to be permitted to pump the hydrogen themselves, thus adding cost by having an attendant at the pumps.

Batteries, although they do have a major environmental impact to produce initially have little impact long term and also make "fuelling" as simple as plugging in. Charge times are coming down and range is going up on BEV, it just doesn't make sense to go fuel cell unless it's the oil and gas industry pressuring government to keep their businesses alive.
 

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Discussion Starter #8
Thanks guys. @pbceng I take it that H2 fuel generated at the filling station is done by electrolysis?

If anyone's interested, this morning's research has yielded findings of the energy required for compression and cooling: https://www.hydrogen.energy.gov/pdfs/9013_energy_requirements_for_hydrogen_gas_compression.pdf

Typically, it's 3.1 kWh per kilo of 700-bar hydrogen. The page also states energy requirements for liquefying rather than compressing, in which case it's around 10 kWh per kilo. This is all in addition to the emissions from the H2 production itself (be it steam reforming or electrolysis).

Car efficiency in terms of miles per kg is easy to find out, so I guess the only really significant data I'm missing now is:
  • How much H2 is typically lost while the fuel is being distributed, and the rate at which it's lost while sat in the car's tank (I'd assume the latter would be negligible for a modern FCV?).
  • How much CO2 is typically emitted by fuel transport - ie. how many H2 kilos carried per truck, the average miles of that truck per payload, and the CO2 output of that truck. This is also one of the main factors that's eluding me for calculating ICE emissions.
  • Emissions spent obtaining the natural gas etc. from which the hydrogen is obtained (assuming H2 generation process isn't electrolysis). This also applies to ICEs and possibly EVs - I'm not sure if the Carbon Trust's CO2 estimates per electricity source include materials acquisition - and I'm not expecting to ever find hard data on it.
 

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I wouldn't eliminate the seal loss - hydrogen is the smallest molecule and as such is devilishly tricky to seal against. I suspect the rate of loss has been reduced but the higher pressure systems are only likely to make matters worse I suspect. I don't have any up to date figures unfortunately.

Transportation costs are difficult to locate, but if I find any I'll post them. I think I found some extraction costs for the natural gas somewhere but I've only concentrated on oil of late and the producers stopped supplying so much detailed information in about 2012.
 

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The losses in the chain are quite frightening
Losses will become irrelevant if it is green and nearly free!

It just doesn't seem a practical, environmental or cost effective solution
No... not now... you are right but those issues will be cracked.
 

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Losses will become irrelevant if it is green and nearly free!
The problem with being inefficient with the use of power is that you have to produce more power to compensate.
You then have to use more power to make the extra wind turbines, tidal generators, solar panels etc. and that in turn leads to more pollution making and maintaining those things and everything spirals out of control.
Just reduce things to the simplest and most efficient way of doing it, that's the "green" way. That means using batteries instead of an inefficient hydrogen generation plant, all the losses in the shipping and storage and all the extra paraphernalia to keep people safe.
 

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Discussion Starter #13
Right, well in the absence of data on fuel materials acquisition, fuel distribution and hydrogen leakage, I've finished my little spot of amateur research and polished it into a vaguely legible format.

Page 1: Tables
CarRunning_Tables.jpg

Page 2: Detailed results
CarRunning_Results.jpg

Page 3: Findings
CarRunning_Findings.jpg

Page 4: Methodology
CarRunning_Methods.jpg

Page 5: Reasons for models compared
CarRunning_ModelsUsed.jpg

Page 6: Global values cross-referenced in results page
CarRunning_Variables.jpg
 

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Discussion Starter #14
^ The full-sized versions still look squeezed on my screen, but you can see the proper resolution by opening in a separate tab/window or downloading.

And for anyone really curious, attaching the original spreadsheet (had to zip because the forums won't attach the .xlsx format).

If anyone can be arsed to read this stuff, I'd love to hear what you think!
 

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