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View Diary: Recent DOE Break-Through with Hydrogen Fuel Cells, should make them Affordable (275 comments)

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  •  Made-up numbers are wrong (3+ / 0-)
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    jamess, Quicklund, Egalitare

    "The energy needed to manufacture enough fuel energy to operate 100,000 autos would be enough to power 400,000 autos if that energy could be used directly in the autos.  (The numbers are made-up just to illustrate the idea.)"

    As I recall, the energy efficiency of converting CH4 to H2 et al. is pretty good if done on an industrial scale. The big difference is that the thermodynamic efficiency of heat engines is very low -- with automobile engines it's around 20% (although large high-efficiency engines in ships have achieved 50% efficiencies). Thus, the net energy efficiency of natural gas is higher when it is used in fuel cells rather than burned in internal combustion engines.

    The problem with using solar cells to hydrolyze water is that they're still too expensive. And you definitely do NOT want to hydrolyze seawater -- all that salt will really screw up your equipment. Fresh water is much better. Distilled water even better.

    •  Heat the water first makes it far easier (2+ / 0-)
      Recommended by:
      jamess, Quicklund

      to break the chemical bonds. Solar systems could use the sun to both super heat the water vapor and provide the electrical energy to split the H2 from O2. The hardest part and most energy consuming is separating the two gases and compressing the hydrogen.

      Really don't mind if you sit this one out. My words but a whisper -- your deafness a SHOUT. I may make you feel but I can't make you think..Jethro Tull

      by RMForbes on Sun Apr 24, 2011 at 10:22:23 AM PDT

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      •  Er... (1+ / 0-)
        Recommended by:

        Assuming that you're talking about natural gas conversion to hydrogen, you're quite right that heating up the water could be done by solar -- but only by solar heating, not solar electricity, and even then it would be a pre-heating process only. As soon as you bring solar PV into the picture, the prices go through the roof. There's reason to hope that the cost of solar PV will go down, but it's definitely not there yet.

        •  I've been working on a system (0+ / 0-)

          that uses the waste heat that would normally flow out the exhaust of a standard ICE to heat additional water vapor plus a small amount of new fuel before the heated gases are reformed in a catalytic reaction chamber just prior to intake. We call this pre-ignition catalytic conversion. Exhaust gases from a modern ICE are over 600 degrees and it does not take much additional external energy to reform all the gases down to smaller more reactive units.

          Water spits into H2 and O2 at 1200 degrees which is why we were taught not to use water on jet fuel fires in the Navy. The water becomes fuel when the temps are high enough. Why can't we apply the same principles to Solar, use solar energy to super heat the water vapor to as close as we can to 1200 degrees and use the electricity produced by the solar panels to complete the separation of H2 from O2 and compress the gases.

          Really don't mind if you sit this one out. My words but a whisper -- your deafness a SHOUT. I may make you feel but I can't make you think..Jethro Tull

          by RMForbes on Sun Apr 24, 2011 at 03:39:33 PM PDT

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    •  It would be astounding were they correct. (0+ / 0-)

      That is why I posted the disclaimer.  The point was illustrated though, I think.

      You are right.  The overall efficiency of one process must be compared to the overall efficiency of another process. This applies to energy usage and greenhouse gas production. That includes the ecological impact of materials extraction.  (Which is why the platinum is such a killer.)  It is not clear at this point which system wins that comparison.

      I am fairly certain that seawater can be distilled.  The reason I typed the word seawater and not freshwater is because fresh water is also a dwindling resource.  If fuel cells require surface fresh water, IMO this too will kill the technology.

      Stop. Stand up. Make a sign. Walk around in public. Be polite and orderly and the rest takes care of itself. Want to shake up the Plutocrats? Demonstrate your attention to politics.

      by Quicklund on Sun Apr 24, 2011 at 01:01:55 PM PDT

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