January 10, 2005

Hydrogen Craze 

Another new entry in my links list, Alternative Energy Blog: it's a well-done blog dealing specifically with alternative energy sources and the like, with a particular focus on practical projects. I think it's worth reading.

I may look very skeptical on alternative energy sources, but it's not really true. I just want to moderate the excessive enthusiasm of some people about alternative energy, and the most misunderstood idea of these days, that is the "Hydrogen Economy".

Hydrogen is a highly flammable gas, lighter than air. In the reasearch and industrial environment, people are righteously wary of hydrogen: its use is dangerous, and maximum attention is required to avoid serious accidents. Hydrogen molecules are very small, and that means that hydrogen will escape from the tiniest holes and cracks in a tank or line.
The flammability of hydrogen was one of the causes of the Hindenburg airship tragedy. There is also another tricky issue about hydrogen: usually, if a compressed gas expands through a small orifice (like a leak from a line, or a punctured vessel), its temperature will decrease. But not hydrogen: this gas, and helium, will instead heat up upon expansion (it depends from their molecular properties) and eventually reach the auto-ignition temperature, thus causing a fire or even an explosion. The widespread use of hydrogen as a fuel (especially for automobiles) poses serious safety problems. Cars would explode in case of accident like you see in bad action movies, and refilling stations need special features to ensure safety. I think hydrogen may be suitable for trains, buses, ships, this sort of larger vehicles with a lower risk of accident.

Not to mention the fact that there are no distribution and refilling structure and facilities for hydrogen, and while they can be built, it will take at least several years and a lot of money - if the NIMBY sindrome does not kick in.

But the crux of the issue is that hydrogen is not an energy source, but just a fuel. It is less polluting (and potentially more efficient) than hydrocarbons, but it still has the same function, that is moving chemical energy from one place to another. There are no natural sources of hydrogen, apart from a small concentration in natural gas. Hydrogen must be produced, and the most efficient way is to react steam with a carbon-containing fuel (gas, oil, coal, biomass etc) in a steam reformer. With this process, we obtain hydrogen but also carbon dioxide, plus ashes if coal or biomass are used as fuel, and the problem of carbon dioxide emissions is not resolved - if such a problem is really so serious, something that we do not know yet. However, this process has the benefit of reducing the diffuse pollution from vehicles, which will emit only water vapour (maybe a little of nitrogen oxides). The steam reforming plants will be only a few, localized and easier to control and run properly. The overall pollution will probably be reduced this way, but at a considerable cost.

Another way to produce hydrogen is water electrolysis, but it needs huge amounts of electricity, and thus we return to the problems of energy production. A vision is a photovoltaic cell farm used to electrolize water, but such a process may very well be too inefficient to be of any interest. Nucular energy will not be appreciated by many enviro-folks, who instead crazily love hydrogen. Other systems have been proposed, from photoelectrolysis (a cell that will electrolize water simply exposing it to sunlight in presence of an appropriate catalyst) to hydrogen-producing bacteria, but none of them is commercially available now (things may change, however).
There are huge scientific and enegineering problems to solve before hydrogen will become a fuel of widespread use, and my take is that it will remain too dangerous to be used in cars.

Still, I think that alternative energy sources have a good potential, especially for developing and under-developed areas, where something like a 300 W water turbine can make the difference between some electricity and none at all. See, we in the West are used to have plenty of electricity at our disposal, but in a place where people still use oil lamps, a sinlge electrical lightbulb makes a big difference. But the for the bulk of electricity production in developed countries, I think we'll have to rely on conventional sources for many more years.


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