Hydrogen is being pushed as the 'clean' power source of the future, particularly for road transport. Though this future is possible in some respects, the idea as normally presented is highly misleading.
Seen in isolation, hydrogen has some clear advantages over current transport fuels. It's main advantage is that it burns (or reacts in the case of fuel cells) very cleanly leaving only water as a byproduct. This means that it produces no carbon dioxide, greenhouse gases or any other dirt or pollutants. Apparently it also allows higher energy efficiency.
However, one fallacy that never seems to be corrected in public is this: hydrogen is not a primary energy source. Unlike coal, gas, oil, wind, tides etc. it does not occur naturally in any great quantity (on earth at any rate). This means that for commercial use it must be processed from other sources, normally hydrocarbons (oil and gas) or water.
If hydrogen is made from fossil fuels (oil or gas) then, quite apart from them being a limited resource anyway, we are left with all the carbon that was removed in the conversion process. This carbon represents a large amount of energy, but if used (i.e. burned) we would end up with a large quantity of carbon dioxide on our hands. Since every process has its inefficiencies, this looks as though it could actually be worse than just using the original hydrocarbon.
If hydrogen is made from water (by electrolysis, by the way), we do not have the carbon problem. However, you may have noticed that you make it out of water, burn it, and you get water back. This cycle, predictably, is not 100% efficient. We have to put more energy in to make the hydrogen than we get out when we use it. Not only that, but where do we get the electricity for making the hydrogen? From power stations that are currently mainly fossil fueled.
Better than a battery?
The point of all this is that hydrogen must be considered as a storage medium, rather than an energy source. As such, it really could have some reasonable benefits. Vehicles could then be powered (if indirectly) from any energy source - even nuclear or wind.* Thus power produced cleanly and efficiently on a large scale could be used to power individual vehicles. But possibly even more importantly, couldn't hydrogen be used to power aeroplanes? Ah, no I'm not the first to think of it - a short search brings up this.
Another thing to consider is that if vehicles are, in the future, being powered by hydrogen made using electricity, all the energy previously supplied as petrol and diesel will have to come though the National Grid. This will be a significant increase in electricity demand at a time when (with current trends) the supply will dwindling.
So, politically speaking, three things come from the above:
- Hydrogen is energy storage and as such cannot be considered a power source.
- To have any chance of creating a 'Hydrogen Economy' we need to build more power stations ASAP.
- We need to invest in hydrogen powered aircraft?!
Just a little piece of interest to end with: if nuclear fusion becomes commercial at any stage, the power obtained from hydrogen would be more than it takes to make. Many times more in fact - making power literally as abundant as water...
*This could be said of batteries as well, but it looks likely that hydrogen will have greater range and faster refuelling for the foreseeable future.