This is what many people should grasp what renewables and nuclear are about. The real electricity world operates with an energy mix. In many places there is open electricity trading, and if you introduce new sources to the marketplace, it affects the buying of other sources. So if you have lots of coal and gas, introducing wind power, even when the wind doesn’t blow constantly, can reduce the usage of the coal and gas power.
So here is a rough sketch how fossil fuels might be eliminated gradually in some mythical place with lots of solar and hydro power. This is not an accurate description of reality, more of a demonstration of principle. Now I’m really in a hurry and have to go, I probably don’t have time to review things for a few days, so can’t respond immediately to comments.