by Doug Coulter » Wed Aug 25, 2010 9:48 am
Well, sort of. It would not really be running on water (the energy of splitting it is a cost, not a benefit), but on oxidizing aluminum. Pretty poor cycle efficiency considering aluminum ore is reduced in molten bath by electricity input made at sub 50% thermal efficiency to begin with. I'd have to go search again, but a guy in the semi fab business patented (worst kind, a submarine patent filed early and modified till the time was right to make it public) on using Gallium-Aluminum with water to do this. The Gallium dissolves the aluminum enough to spoil the protective oxide coating, and let aluminum show just how reactive it is at valence 3. Very good power to weight ratio, the gallium is not consumed, and the by product is alumina to go back to the refinery (and be converted back at very-sub 40% net energy efficiency using electricity made usually from fossil fuels).
Note that the reaction of Al with anything is very exothermic itself (example:thermite!), and when that something is water based, nearly all that energy is wasted as well. It's quite easy to get an HCl solution boiling with more than hydrogen output by putting Al into it. Or for that matter, an NaOH solution. Schemes that only recover the hydrogen miss out on a lot of that.
I see all this as probably a waste of net energy -- see the numbers -- with the big deal being stored power to weight ratio being really good compared to batteries, something I'm quite familiar with having run on solar PV panels since 1979 and having built a couple small electric cars. To paraphrase Churchill, batteries are the worst thing there is -- except when compared to everything else. My work in engineering body worn electronics (prosthetics usually) has taught me that they truly stink -- all kinds I've used so far; haven't done sodium sulfer or vanadium redox, the latter of which look interesting for solar systems where weight doesn't matter...
Boy, when those plug-in hybrid cars get a little life experience like I've had -- there's going to be the backlash from hell on them when people find out how optimistic those cycle lives are in real life. Decades of actual, honest testing here show that the manufacturers claims for *all* battery cycle lives are total marketing baloney -- and that's putting it very nicely. Anyone who owns battery powered tools -- did you get anything like the number of recharge cycles claimed for that battery tech? Did you get half that? At half that, did you get full capacity, or maybe more like 20% of the new? I know the answer....most don't keep track, but if you use them such that you're recharging once a week, do you have to buy fresh ones yearly, or nearly so? Eg in 50-70 cycles, not the 300-700 claimed for the technology?
That's the beauty of either the Al based schemes or the vanadium redox batteries -- if you accept a high loss factor, at least they don't degrade over time so badly, because the battery itself is inert, and is basically a fuel cell.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.