I was wrong about solar power. Solar power is not subject to thermodynamic limits based on heat sources and heat sinks because the photovoltic process is not a heat cycle; it is a combination of quantum physics and semiconductors. Photons from the sun are converted to electrical current directly. It appears that current theoretical efficiencies are around 33% and practical efficiencies are around 20%.
There is talk of theoretical efficiencies being up to 60%, but those studies seem to be pretty pointy-headed. One potentially significant concept is a technique to convert solar power into hydrogen gas. This would be important because hydrogen gas could be bottled and used for transportation fuel via a fuel cell.
But I remain skeptical of solar power for two reasons:
(1) Solar power in its current form, developed through decades of research, is still a very expensive way to produce electricity. Meaning to me, that if (when) the SHTF, mankind will abandon it because it is relatively inefficient.
(2) We have discussed how wind energy can provide between 15% and 20% of the electrical grid. Solar power is competing with wind power to provide that portion of our electrical power. Perhaps the addition of solar power could bring the ‘renewable’ portion of our electricity to 25 or 30%.
If the world goes to fuel cells, the most efficient way to provide transportation would probably be:
(1) Nuclear power to create electricity;
(2) Electricity to create hydrogen;
(3) Hydrogen to power fuel cells;
(4) Fuel cells to power transportation