Demand varies, supply follows. Peaker plants run only a few hours/day, but are the costliest per kwh. The fuel for peaker plants is natural gas. You can think of natural gas as one-time batteries (ancient, chemical storage).

Instead of one time batteries that you burn and dispose, this will be replaced by EVs and BESS. EVs and BESS are rechargeable. With free fuel. From Sunlight.

Production window can also be increased by vertical solar, adds ~4 hours. Production window can be further extended in most locations by adding East-West transmission capacity. If you are a large country (China, US, Australia ...), you can easily do this and do this with your neighbors, where free sunlight can flow in both directions. Think about natural gas pipelines going through many countries. But this is WAYY better, because you don't pay for fuel, just build the transmission network. But transmission networks are not cheap or quick, the best bet might be BESS, and of course EVs everywhere.

The legacy grid which is just wealth extraction for the super rich (Warren Buffett) is going to die.