Hydrogen fuel cells begin to show off in the world of competitive racing

[intaglio]

21. And if the energy is free, what happens to your calculations?

Technically oil is also thermodynamically inefficient because you have to ignore the amount of energy used to produce the original plants and bacteria.

Then let us look at the ridiculous amount of pollution produced by the oil industry and the nonsensical amount of energy involved in the clean-up and the stupid amount of CO2 that has never been cleaned-up and is part of the source of AGW. This too is not included in your efficiency calculations.

I agree that no energy source can be totally carbon neutral but you have to try and the closest to C neutral is likely to be solar, wind and tidal. Energy storage is an important element of a near neutral energy economy and, at present that problem has not been cracked (no pun intended). Likely elements of the energy storage solution are:
1) Hydrogen from water, disadvantage bulk storage (low mass per volume);
2) Hydroelectric pumped storage, disadvantage limited suitable sites;
3) Pneumatic pumped storage, disadvantage limited sites (void oil fields, salt caverns);
4) Chemical battery; problems low energy density, scaling and noxious byproducts;
5) Mechanical battery (gyroscopic), problem bulk;
6) Heat storage (molten salts), limited to thermal solar power stations and noxious byproducts.

Hydrogen storage is likely to be partially resolved by the use of clathrate type nanostructures