If solar panels can be turned off, why are utility companies having to sell excess power at a loss? Why can’t they tell the solar farms to reduce their output by the required amount?
What harm on scale is the variable output especially from small p.v. utilities built out of incentives NOT personal power plants, the grid is sized with some large power plants serving a large set of customers, their absorption vary but if the grid is vast (and not too vast) enough variation tend to be slow on average, let's say 50MW PP experience 100-200kW demand variation in very short time. They can compensate easily keeping the grid frequency stable. With a significant amount of grid injecting p.v. variation might be MUCH bigger creating significant stability issues where injection goes up too quickly making the frequency skyrocketing and large PP can't decrease their output fast enough risking disconnection witch in turn might put large p.v. plants offline suddenly creating a cascading effect of large blackouts.
That's the real issue with grid-connected and tied renewables and another reason why we need to go toward self-consumption NOT injection.