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      10-13-2011, 06:38 PM   #60
carve's Avatar

Drives: 335i
Join Date: Feb 2009
Location: usa

iTrader: (0)

What is the REx module? Like a small gasoline generator?

Also, hydrogen is no more a source of energy than batteries- it's an energy storage medium, and not a very efficient one for a car.

Making H2 or charging a battery both start with electricity. A good electrolysis process is between 50-80% efficient. We'll be kind and call it 75% efficient. Liquifying 1kg of H2 takes the energy equivelent of about 1/3 kg of H2, so now we have 50% of the energy we started with. H2 isn't suitable for use in pipelines, so it'll have to be moved around in ENORMOUS trucks, since the tanks need to be so huge. These will be hydrogen powered trucks, so lets say we have about 40% of the initial energy once it reaches the fuel station. Hydrogen is kept liquid by boiling it off. It's also the smallest molecule, so it tends to leak. A big industrial, stationary tank might lose 1-3% per day...a smaller car tank might be more like 5%. So, figure that by the time we're ready to use the hydrogen, we have about 33% of the energy we started with.

Now we run it through a fuel cell. They're about 50% efficient (not to mention EXPENSIVE- exotic materials), so by the time we're ready to feed electricty to the motor we have 17.5% of energy we started with.

Now lets look at electric. Power grid losses are about 7%, so our charger has 93% to work with. Figure a 12% loss in the charger, so we're looking at 82% remaining. The battery is 85% efficienct at charging and discharging. .82*.85*.85= 59%

17.5% efficient vs. 59% efficient. The future indeed. Even if my estimates are off slightly, these two systems are nowhere remotely close to each other in efficiency. My transportation and handling charges involve a lot of guess work, but hydrogen is already behind batteries after merely producing and liquifying it. Figure batteries are about 300% as efficient as H2.

The ONLY advantages of H2 are it's much quicker to refuel, and for now the tanks have better energy density, although that advantage is shrinking fast.

Last edited by carve; 10-14-2011 at 01:35 PM.