Originally posted by: Mark R
Originally posted by: destrekor
here's the thing about water. It can be considered an energy source, because relatively little energy is needed to to get energy out of hydrogen. But it can also be classified as a storage medium, because you cannot directly access the hydrogen in it. Here's the kicker though: what if we discover a more convenient way to extract hydrogen from water? What if we use only a little energy in extracting the hydrogen, and then a little more in igniting the hydrogen, and end up gaining a large amount of energy?
what if we make it sustainable? as in, once you ignite the hydrogen, you keep a steady line of hydrogen being fed into the fire that is created and contained.
But here's the kicker. You cannot get more energy out of the hydrogen than you put in to separate it; you will always lose. There is no way around it. At least, that is what is stated in the fundamental laws of physics.
If you split the water into hydrogen, with perfect efficiency (not actually achievable), and then recombine it perfectly (again, not actually achievable) the best you can do is break even. In practice, you have to accept losses.
In fact, current techniques for seperating hydrogen and then using it, are horribly inefficient - you'd be lucky to get 50% of your energy back. This is one of the fundamental problems of building a 'hydrogen economy' for cars - by the time you've generated the hydrogen, transported it, packaged it in a form suitable for cars, and then converted it back to energy, you've barely got 25% of your energy left.
While it is very convenient and relatively efficient to convert electricity into hydrogen, generating electricity is a massive loser. It comes down to the fact that most electricity is generated by burning a fuel to produce heat and then somehow using the heat from the fire to turn a generator. Converting heat to mechanical energy is inefficient, and there is no way round this (again, it's a law of physics - specifically it's due to entropy); that said, current technology is still a fair way from the limit, so there is room for improvement - but even with impossibly perfect technology you're still onto a serious loser with this approach.