The "problem" with renewables is that they are not dispatch-able, meaning you will never be 100% sure that tomorrow or a week for now there will be sun or wind in a specific region. On the other hand, a nuclear or a coal powered plant, know months in advance if they will be available for peak load or not.

Yes, if it is sunny or windy, they can be scaled in minutes, but only if conditions are met. The inverse is true for nuclear/coal - they cannot be scaled up & down in minutes.