Hydrogen is currently considered one of the most promising “green” fuel, owing to the fact that its staggering energy content of 142 MJ kg-1 exceeds that of petroleum by a factor of three and that the product of its combustion is water vapour. However, it should be remembered that hydrogen is not an energy source, but a secondary energy carrier. It means that hydrogen must be produced, and exactly the same amount of energy needed in the production process is subsequently released during its use in fuel cells. Consequently the advantage of hydrogen for energy must be carefully considered with respect to other carriers, such as electricity.