[Schroedingersat]

The difference is a solar farm consists of 4 million identical modules and a quarter billion identical cells. If a cell is faulty, it decreases output of that module by 2%. If a module is faulty it either decreases the string output by 5% or costs $80 and 15 minutes to replace. If many modules are found to have a long term fault later, repowering comes at a cost penalty of about 1c/kWh. Building terawatts of solar involves trillions of identical cells, and trillions of trials to practise making them cheaply with zero penalty for iteration.

A nuclear reactor consists of many thousands of bespoke parts. If one is faulty, at the very least the whole thing is shut down while millions are spent replacing it, or possibly it kills a lot of people. Building terawatts of nuclear involves making each part thousands of times, and the penalty for iteration is thousands of man hours for validation as well as potentially shutting down every power plant with that part. If there is a major systematic flaw you are out 5-20c/kWh and years of output.