Neither - just production-level economies of scale. Operating costs of solar are way below that of coal, and setup and manufacturing costs have dropped signific

Neither - just production-level economies of scale. Operating costs of solar are way below that of coal, and setup and manufacturing costs have dropped significantly with volume. Note the comparison is for new installations - coal power is only cheap now because the massive construction expenses were sunk long ago. Constructing a coal plant is a huge expense, particularly as it has to be centralized because it makes no sense below a certain size. Whereas with solar you can have very small installations closer to point of use that are still financially sensible. You win on capex, you win on operating costs, and you win on transmission losses. Capital expense used to be much much higher a decade ago for solar, and emission standards for coal plants were not rigorously enforced for old installations, making coal appear cheaper. Of course, if you count the expenses related to the pollution and health damage done by coal plants, coal was always more expensive.