They will eventually need huge battery banks to store energy until it can be used.
Or else creating all that wind and solar power will cause more problems than it solves.
It hasn't been a major problem yet becuase solar and wind power have been such a small percentage of the total power produced.
Or maybe there are other ways that can be created to get around the problem: Utilities could pay a factory to shut down when the wind isn't blowing enough to support its electrical draw.