Even before renewables/green energy, we've had problems with surplus power in the grid. It's actually one of the biggest issues for infrastructure to solve in moving away from fossil fuels. We simply don't have the storage capacity, and nobody has any real plan or path toward a solution as of yet, as far as I know.

For probably a century or so now, power companies have been paying manufacturing industries to run their heaviest equipment with nothing in them just to bleed extra power out of the grids during lows in demand because power stations can't change their outputs fast enough, especially things like nuclear energy. Even stuff like coal or natural gas plants have a spool up or down time that can't keep pace with the changes in demand.