Hydrogen's Dirty Little Secret.... - Toyota Prius Forum : Prius Online Toyota Forums
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#1 (permalink) Old 04-28-2004, 09:59 PM
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Default Hydrogen's Dirty Little Secret....

....no, not that it's ...er EXPLOSIVE! Nope, I'm not really concerned about that at all.

Maybe you engineer-types can help me, a lowly programmer-type with some high and mighty energy concepts. I would greatly appreciate any assistance you could offer.

Let's see, as I understand it, hydrogen comes from one of two main sources:

1) Petroleum. It gets removed from oil as part of the refining process.
2) Water. We "split" the water molecule, to produce hydrogen and oxygen.

In either case, the hydrogen, when used in a "fuel cell" car to generate energy for electricity, only produces electrical energy by way of the hydrogen and oxygen atoms bonding. And water is the only byproduct. Sounds like utopia!

Okay.....help me understand something. If it generates energy when bonding, then....doesn't it follow that it requires energy when breaking that bond (ie; when "making" the hydrogen via #2 above)?

Are we using great quantities of electricity to "make" hydrogen? If so, are we spending more energy to "make" the hydrogen than the hydrogen offers in electrical power in our hydrogen fuel-cell cars?

My concern is this:

What's the biggest fuel source for electrical power in the United States? Isn't it....oil? And then coal? And maybe a smattering of natural gas and nuclear? But mostly, it's oil, right?

Okay, if my logic is right, would I be correct to posit that the dirty little secret of hydrogen-powered vehicles is that they would continue to require the same (or possibly a greater) amount of fossil fuel as the cars they're supposedly going to replace?

I'm sure there's an engineer out there who could explain this little problem to me, and authoritatively tell me that I'm wrong, and that in fact, nirvana does exist, and the road to it is through hydrogen technology.

Thanks!
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#2 (permalink) Old 04-28-2004, 10:31 PM
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The latest Scientific American (May 2004 issue) has a full article on just this topic! How timely

Very quick summary (go read the article, I'm not doing it justice at all): Using electricity to make hydrogen is foolish if the electricity comes from burning hydrocarbons. Steam reforming of hydrocarbons to make hydrogen for a fuel cell is actually more efficient overall than gas/diesel electric hybrids. Naturally, this is all theoretical, assuming a practical fuel cell vehicle can be developed.

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#3 (permalink) Old 04-28-2004, 10:49 PM
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Thanks for the reference! I will go read the article, maybe this weekend when I'm doing homework.
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#4 (permalink) Old 04-28-2004, 10:58 PM
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DON'T read if not interested in how to separate water! Boring if you do.
The way it "splits" the molecules of water into hydrogen and oxygen is using a very simple step called Electrolysis. Electrolysis can be used with very little power and all it is, is putting two wires, + and - , into water and allowing the electricity to separate the molecules. Then you must collect the + end if you want the hydrogen. The way it separates the molecules is that Hydrogen is a very study molecule that is polar. When you charge that polar state is doesn't allow the hydrogen to adhere, another thing that relates to polar, to the oxygen molecule. If it can't adhere to the oxygen then the two split and form into their gas form and are both lighter than air, so they float up through the water. Water is made up of H2O, which means that there will be 2 parts hydrogen to every one-part oxygen. So making hydrogen makes allot.
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#5 (permalink) Old 04-28-2004, 11:05 PM
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Default Hydrogen Stores Energy Like a Battery only Better

Here is the deal, Hydrogen is not a source of energy, it is a vehicle for storing energy. Energy is taken (from natural gas, the sun, wind, but never from a nuclear power plant*) and used to produce hydrogen (from natural gas or water). This creates potential energy that is stored in the form of hydrogen gas. (Just like the energy from breaking is stored in the battery of your Prius).

The hydrogen is then passed though a fuel cell which releases this potential energy and converts it into an electrical charge that can do work. Thermodynamics predicts that there will be an energy loss at each step.

Engineering and practical experience tells us that the total process is more efficient (on both net energy and total pollution scale) than any other process (e.g. drill for oil, make gas, transport gas, burn in ICE; etc.)

If you want the complete story, check this link: http://www.rmi.org/images/other/E-20HydrogenMyths.pdf
http://www.rmi.org/images/other/Trans/T ... oTrans.pdf

*Nuclear power will never be used to produce Hydrogen because it is the most expensive power there is. The advantage of Hydrogen is that you can use a cheap source of power like wind to generate the energy and then use the hydrogen to store that energy until you need it. Nuclear power would never exist without the core industry of making Nuclear Weapons. Anywhere there are Nuclear power plants, there are weapons being made, the energy is just a by-product.
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#6 (permalink) Old 04-29-2004, 05:03 AM
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The whole hydrogen 'economy' can be summed up very simply.

Imagine a power station making electricity somewhere. In the states, that comes mostly from burning coal.

1 kilowatt hour used to make hydrogen by electrolysis, then compressed, transported and burned in a fuel cell car provides a range of about 0.8 miles.

1 kilowatt hour used in a battery-electric vehicle provides a range of about 4 miles.

As I've pointed out on here before, the simple economics are that any country running fuel cell vehicles will have to produce 5 times more electricity for transport than a country using battery-electric vehicles. This isn't something policy makers in the states are overly concerned with, however, as you guys are sitting on at least 200 years worth of coal. (Which, incidentally, can also be converted into petrol for cars - if a little more expensively than drilling it out of middle eastern countries).
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#7 (permalink) Old 04-29-2004, 09:54 AM
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Default It doesn't quite work that way

It doesn't quite work that way. Read the 20 Hydrogen Myths.
http://www.rmi.org/images/other/E-20HydrogenMyths.pdf
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#8 (permalink) Old 04-29-2004, 03:53 PM
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Quote:
It doesn't quite work that way. Read the 20 Hydrogen Myths.
It would be more useful for us if you told where exactly to read in the 49 pages, wizardbill... However, I noticed on page 18 some characteristics of a "Hypercar" prototype that say :
Quote:
330-mile / 530-km range on 7.5 lb / 3.4 kg of hydrogen safely stored in commercial 5-kpsi (350-bar) tanks
I will not discuss the overall design of the car, which sounds like science-fiction compared to currently available fuel cell cars :
Quote:
47% of RX300s curb mass (1,889 lb / 857 kg), but carries a similar load (1,014 lb / 460 kg), even up a 44%
grade
and will start from your figures. 3.4 kg hydrogen for 530 km (330 miles) makes the car need 6.4 g hydrogen for 1km, or 10,3 g for 1 mile. Now the usable energy content of 1g of hydrogen is 33.2 Wh (see here), so 1 mile driving the "Revolution" car would cost 10.3 * 33.2 = 342 Wh if the fuel cell and the hydrogen production were 100% efficient, which is of course not the case. Or to turn the things into clett's way, 1 kWh would (before correcting the calculation !) provide a 2.9 mile range. Now some people involved in fuel cell stuff, namely Toyota Company, claim the well-to-wheel efficiency of their fuel cell cars is 22% without hybridation, or 29% with hybrid technology, as you can see here. Now you come out with (in the best case) a 0.85 mile range, pretty close to clett's figure (I'm writing this comment live, without any preconceived idea, so that's really cool ! ).Actually, this calculation is WRONG ! I've posted it almost one month ago and nobody corrected me... are you sleeping ? See page 3 for something better...

And what about current available gasoline hybrids ? My "old" Prius gets easily 50 MPG (US gallons!) or less than 5 liter / 100 km. According to this document the gasoline energy content is around... 19000 BTU / lb ? What are these f.....g units ? Let me translate : OK, 1 BTU = 0.293 Wh, and 1 lb = 0.454 kg so that means around 12.3 kWh / kg, or 16.4 kWh / liter. WRONG ! see correction on page 3 (thanks to Arms) Using 5 l for 100 km, I'm burning 82 kWh of energy, hence 1 kWh gives me a 1.22 km range, or 0.76 mile range. Pretty much the same. But with my present vehicle, not a science-fiction project. OK, that's only tank-to-wheel efficiency and not well-to-wheel, but well-to-tank efficiency for gasoline is around 0.9. Last week-end, driving in ideal conditions I even achieved more than 60 MPG for my 150 km round trip. That translates into a one mile range per kWh. Not too bad for an "old" car.

Quote:
Energy is taken (from natural gas, the sun, wind, but never from a nuclear power plant*) and used to produce hydrogen (from natural gas or water).
A nuclear engineer just told me the opposite recently : for him, future generation nuclear plants are the only affordable way to produce hydrogen in massive amounts at reasonable cost. OK, he is (and I am) living in a country where more than 3/4 of the electricity comes from nuclear plants... but some other people in Australia have the same opinion.
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#9 (permalink) Old 04-30-2004, 07:04 AM
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Default Re: It doesn't quite work that way

Quote:
Originally Posted by wizardbill
It doesn't quite work that way. Read the 20 Hydrogen Myths.
Maybe I should have qualified such claims!

First the EV mileage. This information is widely available as EVs have been on the road (in the hands of enthusiasts if not the wider population) for a long time now. The Solectria Force EV, for example can achieve 5-6 miles per kWhr, as can AC propulsions Tzero. So 4 miles per kWh is a relatively conservative estimate for mid-size EV efficiency. (Today, at least, with some proper R&D thrown at them by the big auto companies this would likely improve).

Whats much less well publicised (for obvious reasons) is the range per kilowatt-hour provided by electrolysis derived hydrogen powered fuel cell vehicles. First, the hydrogen has to be extracted from water by electrolysis. This process is only 85% efficient. Then to compress the hydrogen and get rid of the waste heat that generates takes a lot more energy. In fact, this is hydrogens biggest downfall as a potential energy carrier. If it were a liquid, then it would be a much better proposition. These two steps means that it takes about 60 kilowatt-hours to make and compress 1 kilogram of hydrogen (see page 9 here). Imagine we could take this hydrogen and put it directly into one of todays latest fuel cell vehicles (which, for arguments sake, is sitting right next to the electrolysis plant). Burning it in a PEM fuel cell is at best only 50% efficient (when the fuel cell has the chance to work at peak efficiency), so at least a further half of all the energy contained in the hydrogen is lost (to heat, which is why fuel cell vehicles have enormous radiators).

Now lets examine two actual examples of fuel cell vehicles. Admittedly, things have improved since I last did the calculations the range of the best FCV has improved by about 20%, mainly because of the addition of hybridisation (ie allowing regenerative braking etc a la Prius).

First, Fords Focus based FCV. This can store 2.8kg of hydrogen on board, and has a (reported) range of 125 miles. As it takes 60kWh to make a kg of hydrogen, this equates to 0.74 miles per kilowatt hour.

Then, Toyotas FCV. It has the best mileage efficiency of any FCV so far, using hybridisation to achieve 64 miles per kg. This is equivalent to 1.07 miles per kWhr.

However, can you see the missing link in this calculation? I havent included any of the energy costs of transporting the hydrogen from point of manufacture to the filling stations! Its not like oil where you can stick a huge amount in one tanker - in fact youd probably need something like ten times as many tankers to do the same job, and its been estimated that with a hydrogen economy 7% of all road haulage would have to be hydrogen tankers taking fuel to filling stations! This increases the amount of energy used by FCVs again, while EVs can be charged anywhere.

Heres a simple visual comparison of why fuel cell vehicles are so inefficient:

1) EV: wall socket -> battery -> motor

2) FCV: wall socket -> electrolysis -> compression -> storage -> transportation -> vehicle fuel tank -> fuel cell -> motor

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#10 (permalink) Old 04-30-2004, 05:23 PM
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Default Re: It doesn't quite work that way

Quote:
Originally Posted by clett
However, can you see the missing link in this calculation? I havent included any of the energy costs of transporting the hydrogen from point of manufacture to the filling stations! Its not like oil where you can stick a huge amount in one tanker - in fact youd probably need something like ten times as many tankers to do the same job, and its been estimated that with a hydrogen economy 7% of all road haulage would have to be hydrogen tankers taking fuel to filling stations! This increases the amount of energy used by FCVs again, while EVs can be charged anywhere.
Just transport it in blimps!

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