Renewables obviously enable us to mostly stop using fossil fuels, fossils have just been too cheap because of unpriced externalities. (replace is the wrong word because some of the fossils use can and should just be stopped and not replaced by other energy)

There isn't anything mysterious we expect to empirically discover through demonstrations approaching 100%, though of course engineering does incrementally improve and progress.

Relevant: https://en.wikipedia.org/wiki/List_of_countries_by_renewable...