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Saturday, June 21, 2008


The plug-in hydrogen hybrid, part 4

I was pretty sure locating a hydrogen generator on the car would be a bad idea, even if you powered it with battery packs instead of trying to drive it from the car's electrical system (after all, an alternator that demands 50 hp is going to put a big dent in your gas mileage). But I wanted to find out just how bad an idea it was, whether it was something that you could build but would be inadvisable, or some sort of monstrosity that wouldn't be able to move under its own power. When I calculated what size battery pack the hydrogen generator would need, it came out as something that looks like it would be technically possible but definitely not practical. Because an internal combustion engine isn't as efficient as an electric motor, this thing would have worse battery issues than an electric car.

The problem is that you're trying to plug it in before the hydrogen generator instead of after. Put the hydrogen generator in your basement and you might have something. So here's a few calculations to find out what it is you might have.

Gasoline has an energy density of 34.8 MJ/liter, according to Wikipedia. Some math turns that into 132 MJ/gallon, to 36.6 kilowatt-hours per gallon. So if you were making the hydrogen at home from household current, your cost for the equivalent of a gallon of gasoline would work out to this:

Price of a "gas gallon equivalent" = (Cost per kilowatt-hour) * (36.6 kilowatt-hours per gallon)/(Generator Efficiency)

Don't forget to factor in the energy needed to compress the hydrogen into the generator efficiency. You'd want to generate the hydrogen and oxygen separately, since you'll need to compress it in order to carry enough hydrogen to make a difference. So if you're paying 12 cents per kilowatt-hour and your generator's total efficiency is 50% including the power needed to run the compressor, you'd be paying the equivalent of $8.78 for a gallon. By the way, you'd also be stuck with similar costs on the plug-in hydrogen hybrid, although your generator efficiency would be up because you wouldn't need to compress the hydrogen nearly as much.

Still not good, but bring the price of gas up and the efficiency up and you might have something...

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Agreed. I see many people building their own hydrogen generators to save money on gas bills. Seems like the trend is gonna rise soon and most of us would be running our cars on water.
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