If there is no wind or sun, we're facing a global apocalypse. There's always wind or sun. You just need to capture it. Nuclear is not on demand either, most plants aren't designed to be. Nuclear is designed to be baseload energy, which, for decades, has fallen out of favour in lieu of more flexible doctrines. Octopus Energy is doing quite a bit of work with AI and energy demand, using incentives to control public energy consumption, which reduces the backup you would need for renewables. Also, that study I referenced, presumes about a 25% decrease in cost of nuclear. Again, best case scenario for nuclear.