No amount of overprovisioning is going to help you at 2am with solar (or during a really bad storm), and wind has similar but even less predictable issues.
Either way, overprovisioning, storage, etc. add significant costs and it isn't clear what those costs would actually need to be to avoid serious problems with high frequency if we actually take fossil fuels out of the equation.
We have experience with fossil fuels enough to say 'store x amount of diesel (or natural gas) onsite so you can handle a 100 year storm' or similar. We have no such experience with solar, battery storage, wind, etc.
Also keep in mind, California has pretty much the ideal climate for 'green' energy - almost all it's population is in temperate, sunny climates, and it has huge sunny deserts and wind generating mountains all nearby. Most electrical usage will be air conditioners, and in that climate those are near ideal solar loads.
And they're the ones that just pushed to keep their major nuke plant online they were shutting down.
It's going to be a lot harder for almost everyone else.
Demand side only goes so far - sometimes people do actually need that energy now, and it tends to be when there are real issues that need that energy to address. Like emergencies, storms, cold snaps in the winter, etc.