The head of the Australian energy market operator AEMO, Daniel Westerman, has rejected nuclear power as a way to replace Australia’s ageing coal-fired power stations, arguing that it is too slow and too expensive. In addition, baseload power sources are not competitive in a grid dominated by wind and solar energy anyway.
There are historical accounts of volcanic activity blocking the sky, I think in Europe, for a few years. For all we know it was the whole planet. That would definitely disrupt solar energy collection without being an extinction level event.
Diversity is a genuine factor of fossil fuel free energy generation.
Literally no sun for years would mean no crops which means everyone and all their animals would be dead