It gets a great deal of media coverage and typing hydrogen economy into an internet search engine will see over 1.5 million page returns, but the enthusiasm for the subject does not reflect the technological reality. The myth of hydrogen is that it is a clean fuel, with no emissions when used to generate power, and is an alternative to our hydrocarbon sources of energy. None of this is correct.
First of all you cannot obtain hydrogen by simply drilling a hole in the ground and then with some refinement, burning it in an engine.
You can with oil and gas. A lot of energy has to be expended to gain the hydrogen. It will be extracted, largely, from oil and gas. Only water and biomass (biological matter) are alternative sources.
But it takes less energy, and is technically easier, to obtain hydrogen from oil and gas. So we are still dependent upon oil and gas. Something to think about the next time a politician proposes hydrogen, as an alternative to oil and gas. It isn't.
And what of the energy source to extract hydrogen? Well that could come from coal or gas or nuclear power stations or perhaps the new wind farms.
Advocates of the hydrogen economy like to argue for extracting the gas from water using what they term renewable energy, meaning wind, wave, and solar.
Why wave, wind or solar is renewable is beyond me. How can it be renewed? But in any case none of these technologies can provide energy as cheaply as coal, gas, or nuclear power stations.
Wind power is only competitive with oil above a barrel price of $35 in 2003 dollars. Admittedly we are now seeing prices well above that but that can't be guaranteed, and that's no basis for a total socio-economic changeover.
Finally the myth that a hydrogen power plant has no emissions.
A fuel cell produces water vapour and the direct burning of hydrogen produces water and nitrogen oxides. The oxides aside water vapour itself can be considered a greenhouse 'gas' and this is why hydrogen aircraft would have to fly lower.
This is to ensure that the vapour becomes rain and does not stay in the upper atmosphere to trap solar radiation.
But flying lower in the atmosphere increases drag and therefore more fuel needs to be used.
However these problems should not be seen as insurmountable, these technical obstacles could be overcome. But the solutions are a long, long way off.
The idea of a hydrogen economy has become almost a religious concept, a technological nirvana. Societies should be careful not to adopt scientific theories as religious absolutes.
Doubt is at the core of science and all theories, however tried and tested, must be the subject of questioning.
To exalt a theory or technology is to return us to an age of religious tyranny but with a handful of scientists setting down the truth instead of Popes, Imams or Patriarchs.
The reality of the future is that societies will have a fuel mix. Some solar, some biomass, some wind, some oil, some gas, some hydrogen and, if we are serious about tackling global warming, a lot of nuclear. But that's not an aviation issue.