> Of course in reality you want a
grid with many power plants so that when one is down the rest probably aren't.
Which is the reason batteries can't make for a reliable grid by themselves. There is a strong correlation for every battery being unable to provide power at the same time because they all start discharging instead of charging when demand exceeds supply and the longer that continues the fewer batteries you have that still have any charge, and therefore the higher the withdrawal rate on the remaining ones to extract the same number of total watts, until you have none.
> "Probably" does some work though, for example: https://www.bloomberg.com/news/articles/2022-04-29/half-of-f...
This is why you want a diverse set of generation sources so that you don't get correlated outages. It's better to have nuclear and renewables than just one or the other. France is unique in the world for having more than the optimal amount of nuclear. And it's really more like nuclear is concentrated in France and connected to a European grid containing several other things, but then you can't say that 50% of generation was offline because of this.
Also notice that even the "unplanned" reduction in output was still pretty planned. They find an issue that requires mitigating at multiple plants, so more than the usual number have to be taken offline at some point in the same year, but they get to choose when and can do most of them outside the period of peak seasonal demand, instead of letting the weather choose when.
> Excess dispatchable power helps make up for when that probably doesn't turn out in your favor.
Suppose you had enough battery storage to run the whole grid for 24 hours instead of for 4 hours. Then you unexpectedly discover that half of your power plants (regardless of what type they are) have to be taken offline for two months for repairs/maintenance. How much good are you getting out of 20 hours when you essentially need 30 days?
> If we're banning CO2 emissions then up until the last couple of years in most places your only option would be to overbuild nuclear until the point that it was dispatchable and not base load power.
Hydro is even older than nuclear and there are places where it's close to 100% of generation. If you don't have enough dam sites for that but still have some then using nuclear for base load and hydro for load following has been a solid option with zero fossil fuels since nuclear became available.
But nobody is even proposing to use nuclear as dispatchable power. Its purpose is base load regardless of what form of dispatchable power you use, and the purpose of base load is to reduce the amount of dispatchable power that you need.