History repeating itself

[Robert Myers]

At 06:54 PM 3/15/02, you wrote:

---snip---


 >And what about cars that run on hydrogen? The only bi-product of the
 >combustion is water vapor! The only reason noone has fully developed the
 >hydrogen engine is the deep pockets of the gas companies, and the esistance
 >by automakers to foot the development bill!

Use of hydrogen as a non-polluting fuel is presently something of a red 
herring, Mike.  The old rule, "you can't get something for nothing", still 
applies.  As Isaac Asimov would say, "TANSTAAFL - There ain't no such thing 
as a free lunch."  True, use of hydrogen to power a car (or anything else 
for that matter) results in only water being formed - 
_at_that_particular_location_.  Now, where do we get the hydrogen?  One 
typical source would be from electrolysis of water.  How much electrical 
energy do we need to use to generate enough hydrogen to run that car?  The 
absolute minimum amount is the energy produced by the hydrogen when it is 
being used to run the car.  Unfortunately, these processes, while rather 
efficient, are not 100% efficient.  There are losses at each step and 
therefore more starting energy is required to end up with the desired 
result at the end.

Where do we get the electricity to generate that hydrogen?  From burning 
fossil fuels?  If so then the use of the hydrogen as an auto fuel is 
intimately connected with the generation of greenhouse gases and 
consumption of fossil fuels.  All that has been accomplished is to convert 
the source of the greenhouse gases from being multiple smaller individual 
sources (a fleet of automobiles, let's say) to a single point source (the 
generating plant).  How about the total quantity of greenhouse gases?  It 
depends on just how efficient each of the intervening step is and how many 
of those intervening steps there are.

Suppose that the infernal (sic) combustion engine is (what?) 75% 
efficient.  I have no clue here.  (I'm sure the information is available 
but I haven't made the effort to look it up.)  That would mean that it 
converts 75% of the total available energy in the fuel it consumes to 
produce useful work and wastes the remaining 25%.  OK, now let's look at 
the use of hydrogen.  The generating plant has an efficiency factor.  Let's 
be generous and say it's 80% (meaning that the plant produces 80 units of 
energy as output from every 100 units of energy it gets in the form of coal 
or oil or natural gas or whatever).  The electrolysis of water will also 
have an efficiency of something less than 100%.  Pick a number.  95%?  The 
hydrogen engine in the automobile also will have an efficiency 
factor.  Pick another number.  90%?  If these numbers are more or less 
accurate then from the initial energy source, some fossil fuel, the 
hydrogen engine will have an overall efficiency of 0.80 * 0.95 * 0.90 = 
0.684 or a ~68% overall efficiency.

The two numbers 75% for a gasoline engine vs. 68% for a hydrogen engine are 
not all that far apart.  Other assumed efficiency factors for the various 
steps would, of course, give different numbers.  The actual numbers would 
certainly give differing calculation results from what I have here.  It is 
noteworthy, however, that introducing additional steps in any process often 
results in an overall decrease in the efficiency of whatever is being 
done.  My point is that the use of hydrogen as an auto fuel does little, if 
anything, to preserve the environment when compared to using either 
gasoline or diesel. It sounds nice but the overall effect isn't much 
benefit to the environment.

Now, OTOH, if you have some other non-polluting source for your hydrogen 
then a hydrogen engine make environmental sense.  Photovoltaic energy would 
be one such possibility.  Wind powered generators would be another.  At 
present such facilities are a rarity rather than the norm.

Bob
*****
  Robert L. Myers   304-574-2372
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