Well, nuclear works better on a planning indeed. And you can definitely plan for demand according to previous years. The issue with solar and wind is that sometimes it just doesn't work at all, like at night or when there is no wind. It works well but it's intermittent. The ideal mix would be, for the time being, 50/50 at least to phase out fossil fuels, then lowering the part of nuclear should be within reach. Personally I don't believe in 100% wind and solar year long, but a 60/40 or 70/30 mix (plus hydro, geothermal and such depending on the region of the world) should be achievable.