> What you want is dispatchable power.

That's the most expensive one, especially if you both need it to be reliable (can't be a battery that can run out) and need it to not emit CO2 (can't be natural gas peaker plants). So what you want is to minimize the amount of dispatchable power that you need.

Which is what baseload does up to the point that it's generating the "base" (i.e. typical daily minimum) amount of load, because then you don't need any of that portion of the load to be dispatchable since the baseload plants will handle it ~100% of the time.

If baseload is half of peak load then you only need 50% of peak load to be dispatchable because baseload sources handle the other half. If you have no baseload sources then you need enough dispatchable sources to handle 100% of the peak load in case that's the only thing available some days/times, e.g. when peak load is after sunset and solar output is zero.

The difference gets even more significant when you consider the possibility of reducing demand through pricing. Suppose raising the price by a moderate amount can lower the daily average demand by 25%; past that you start hitting inelastic demand and would need unrealistically high prices. If you have baseload as 50% of generation then you now only need dispatchable sources to handle 25% of peak load because the other 25% can be achieved through pricing. Without baseload sources you need 75% -- three times as much instead of twice as much.

More than that, it reduces to 25% the amount of long-term dispatchable power you need, i.e. things that cost a fixed amount to have and are also expensive to use but can't run out of capacity. Things you might only use two weeks out of two years, like hydrogen fuel cells or expensive flow batteries; you don't want to need three times as much of those.

Meanwhile you can use short-term dispatchable power (i.e. normal batteries) to do things like handle the peak demand in the early evening while charging them using solar during the day. The period after sunset but before the load falls off is only a few hours long, so you only need 50% of total capacity for ~15% of the hours in the day, i.e. having only 7.5% of daily capacity would mean that you don't have to use demand suppression through pricing unless you have an extended supply shortfall from renewables. Whereas if you don't have baseload then you need enough batteries for ~50% of daily capacity because now you need enough batteries to handle the entire peak demand in the early evening instead of half and the entire demand late at night instead of none. On top of the long-term storage in case the batteries run out.