I read an article that suggested that cars in future will be fuelled with hydrogen. So I have written up my doubts about this. I am no expert, but some of my arguments may be useful for other non-experts.
My younger daughter recently bought a (used) car driven by natural gas, proud to be doing something for the climate. She was surprised when I told her this fuel is little better than diesel, if at all. Hydrocarbons have similar calorific value per gram, and the weight is largely carbon. And diesel motors are rather efficient.
I see little sense in fuelling cars with hydrogen. The energy from burning hydrogen is about 2½ times as much as from the same weight of hydrocarbons. But this advantage is wiped out by the difficulty of light compact storage. For instance one car manufacturer (according to Wikipedia) is investigating use of NaBH4. But the hydrogen in this comprises about 10% by weight. So hydrocarbon fuel effectively weighs a quarter as much.
Surely it makes more sense to produce hydrocarbons, and continue to use them. This continues to use highly developed motors and the current infrastructure. Using a suitable power source, (the sun, or perhaps eventually thermonuclear power), it is possible to have a cycle producing diesel (and oxygen) from water and carbon dioxide, which are recycled via the atmosphere when the diesel is burnt. Of course such diesel fuel is much more expensive than when the hydrocarbons come almost for free from underground.
There is already research using algae to produce hydrocarbons. One problem is that green plants store only about 3% of the solar energy. Other ways of producing transportable fuel from solar energy, (including use of batteries), are hardly better. Of course diesel is already produced “commercially” from solar energy using maize or sugar-cane. But this wastes fertile land that is needed for food production, (assuming we want to continue to overpopulate the world). We need to produce diesel rather more efficiently on the oceans or deserts.
Some energy is lost when CO2 is concentrated out of the atmosphere. How significant is this?
Perhaps I am missing some other point. Is less energy needed to get a hydrogen atom from NaBH4 than from H2?
But I suspect that the neglect of diesel production has other reasons. It is in too direct competition with current diesel. It is competitive only paying full attention to climate change and limited resources. The oil companies would be best positioned to get involved in this, but can hardly get enthusiastic about it.
Electric power and hydrogen seem an attractive alternative to diesel, as long as one ignores where they come from, mainly cheap oil, gas, coal, and nuclear power. They give the car firms a chance to sell new products, if only in small numbers, and to seem to be doing something about oil shortage and climate.
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