Hydrogen powered cars

[Llamatron]

Apparently the only emission from a hydrogen fueled car is water. Does that mean that when/if we're all driving these cars we'll just end up drowning the world in water rather than warming it up with greenhouse gases?

[jake-the-peg]

No because you will be obtaining the hydrogen by splitting water into Oxygen and Hydrogen in the first place.

You will however probably need electricity to do this

[Llamatron]

Oh right, so they get the hydrogen from water.
Do hydrogen fuelled cars produce as much water as was used in the production of its fuel?
I mean, is there a water in/water out imbalance?

[jake-the-peg]

Yes, water is two molecules hydrogen and 1 oxygen - hence H2O.

You split the Oxygen off and then when you burn the Hydrogen you are effectively adding an O to the H2 to make H2O again.

In a sence you can think of it as a rechargable battery

[Llamatron]

I remember that bit from school chemistry classes.

This process can't be totally 'green' can it?
How is the hydrogen actually used to generate power? Surely only a fraction is wasted as water. So more water goes into the whole process than goes out.

[rja211077]

you should start here
http://people.howstuffworks.com/hydrogen-econo my.htm

[jake-the-peg]

There are a number of ways to 'burn' the hydrogen that you've extracted from water but even if you don't burn all of the hydrogen, then releasing minute problems into the atmosphere is not a problem.

How can I be sure of this?because hydrogen is so small and light that it can slowly escape the Earths gravity and leak into space.

The point is that whilst burning Hydrogen is "green" obtaining it is not - you need an energy source to split water to get the hydrogen in the first place. Obviously (hopefully it's obvious) you can't do that by burning the hydrogen.

Hydrogen also has a number of potential safety issue that need examining, it's very explosive - check out the Hindenburg on Wikipedia.

It is however a good potential long term replacement for a mobile fuel source when there's no petrol left.

But you do need to get the power in the first place from fossil fuels or nuclear (either fission or fusion) or renewables.

Long term (> 50 years I'd think a mixture of fusion and renewables with hydrogen cars is most likely) but other battery cars are with us now - things like this

www.teslamotors.com

[Gef]

To answer the original question - no.

[Clanad]

I realize it's entirely pedantic JTP, but in your second post, I'm sure you meant to say "... water has two atoms hydrogen and 1 oxygen..." didn't you?

[Mortartube]

obtaining hydrogen cpuld be green if it was extracted from the sea using electricity generated by offshore wind farms.

[jake-the-peg]

yes thank Clanad.

This is exactly right motartube Hydrogen as a fuel is only as green as the method used to obtain the electricity to produce it.

Pretty much the problem with all the renewables is it sounds great unti you do the maths and then you tend to find that you have to cover half the country with windfarms to make up for the days when there's little wind and the sea's flat..

Which is why I say I think you'll probably find we still need some nuclear in 50 years or so.

However there is some interesting work going on with bacteria that can be made to produce hydrogen - if we can genetically modify them to get a good rate of production they could be a real runner

Have a look here if you're interested

http://www.fao.org/docrep/w7241e/w7241e0g.htm

or here for one with more pictures and less technical detail

http://www.energycooperation.org/bioproduction H2.htm