Capt. Geoffrey Thorpe wrote:
If we don't have the energy to extract the hydrogen, then what makes it "the
future"? I've never understood that angle - "we will need hydrogen for when
we run out of oil" - but we need oil to extract the hygrogen, eh?

Seems to me like we need "something" as an energy source for when we run out
of oil, and what kind of fuel one would generate for transportation would
depend a lot on what that "something" is. Might be H2, very possibly won't.

Hydrogen isn't an energy source, just a way of storing energy in a
transportable form, same as battery or biofuel.

It has a few disadvantages too - when you combine electrolysis to get H2
with fuel cell efficiency the overall efficiency is around 66%. Thats
good compared with an IC engine's typical 25-35%, but other storage
methods, e.g. Li-poly batteries, which have a charge/discharge
efficiency of around 85%. The proof of this is that direct drive (no
storage) solar electric UAVs and those using Li-poly storage have
already flown successfully but no solar fuel cell system has, AFAIK, yet
flown.

Now consider that liquid H2, which is what cars will probably run on.
This needs cryogenic storage (if you don't cool it to liquid you either
need heavy HP gas cylinders or you adsorb it in a carrier and that
material isn't all that light either). In practice cryogenic tanks boil
off hydrogen to cool the remainder, which reduces the overall efficiency
by 15% if you immediately drive until the tank is empty and by up to
100% if you just park the car.

I think some other liquid fuel, such as ethanol, would be a lot less
hassle, but, like hydrogen, it needs to be manufactured industrially
using solar or nuclear power if enough is to be produced to entirely
replace fossil vehicle fuels.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |