240 General: Electric power

[stephend]

Originally Posted by Volvodrivingbiker

I remember watching a Equinox documentry called it runs on water where this boffin had come up with a way of converting water into Hydrogen and oxygene before it entered the engine so he just put water in the tank .
found it heres the link http://www.youtube.com/watch?v=vghjGwvmrqE

I haven't watched the video (I'm up to my broadband limit!) so I don't know what said boffin's particular shtick is. But... bottom line is that if (1) you split water to form hydrogen and oxygen, then (2) you react hydrogen and oxygen to make water, then the energy you get out in step 2 is exactly equal to the energy you have to put in in step 1. So you don't - indeed can't - get any net energy out of it. In reality, no practical process is ever 100% efficient, so you'd waste some energy on each cycle, and end up putting more energy in than you take out.

If you harness the energy liberated in step 2 to drive the vehicle, then you need some other source of energy for step 1. That would most likely come either from burning some sort of fuel (petrol, methanol etc) or from battery power - in which case you're back to exactly the same problems as with standard ICE or electric vehicles. The only way that you could really be zero-carbon would be if you used onboard solar cells to generate the energy for step 1 - but then it's not obvious that this method is better than using onboard solar cells to charge the batteries of an electric vehicle. On the basis that all energy conversions are wasteful (i.e. not 100% efficient), it's almost inevitably better to skip step 2 and just use the source of energy that you're using for step 1 to power the vehicle directly.

Bottom line, unfortunately, is that hydrogen is not a fuel in the conventional sense, it's more a way of storing energy that you generate by other means (it's an "energy vector" in the technical jargon). If you want to be pedantic, that's true of oil as well, solar energy being the original source of the energy locked up in the oil - but it was all done millions of years ago, so it's "free" to us...

Here endeth the chemistry lesson.