If we rely on solar, we need a massive overcapacity. In large parts of the world the output of a solar panel is 50% in the winter compared to the summer, and in addition, we use significantly more power during the winter. And that will be even further exaggerated if fossils do not heat water for district heating in addition to the power produced - but perhaps that is offset by AC usage in the summer. Either way, we would need a significant overcapacity to meet demand, not to mention huge investments in battery infrastructure.
And that does not even take predictable peaks into account (think the pause of a national event with lots of viewers, where people make coffee/tea/snacks at the same time), which needs fossil peaker plants, or even more battery capacity.
