Best to think of fossil fuels as a shot in the arm of the development of human civilization. On that timescale, It was always going to be temporary, whether due to climate change or simply the limits of availible fuel. We were always going to need to use it to bootstrap onto something else within a couple hundred years of the invention of the steam engine. The math is reasonable and yes, total solar power isnt a problem (storage and distribution is, but total availability isnt hard).