[roenxi]

The solar panels do have to be fabricated. That probably doesn't have the same scaling potential as nuclear given how much power/m2 nuclear can reach.

Also, at a guess the energy in solar panels drop with the square of distance to the sun. It is unlikely to be a good choice for interstellar travel if 'advance[ing] as a species' heads in the more fantastic directions.

[epistasis]

If we are getting to the point where W/m2 is an important win for nuclear, we are going to start to have serious problems with the rejected heat.

A fundamental limitation of thermal steam engines is that they can only ever be 50% efficient, and you have to dump that waste heat in order to maintain power.

Already, heat mitigation systems for some existing nuclear plants are starting to fail during heat waves as the climate warms. And these are expensive systems: at Diablo Canyon in California, it's cheaper to replace an entire, functioning reactor with renewables than it is to simply build a new cooling system.

Which is all to say that nuclear won't scale tremendously well unless we 1) figure out fusion, and 2) figure out direct conversion of energy to electricity rather than using steam turbines to mechanically drive a generator.

For the ultimate goal that many people have for nuclear, as a power source when not on earth, these sorts of advancements are also likely also necessary. Cooling in space is not a trivial matter.