The point is that, without storage, no matter how much solar you install you don't lower the required amount of fossil fuel plant capacity at all because the peak occurs when solar is at 0.

The yearly peak, in summer, occurs when solar is running.

The daily peak, on spring and autumn days, falls outside the solar peak, but also well below the yearly peak.

So solar does help displace the least efficient and most expensive part of your gas fleet.

But it's not the peak that's the point of the duck curve, it's the solar falling faster than gas can switch on and that difference is very amenable to being fixed by even a small amount of battery storage.

> it's the solar falling faster than gas can switch on

Is "switch on" really the problem? As Germany showed during the solar eclipse (https://www.dw.com/en/german-power-net-survives-solar-eclips...), as long as it's a predictable event, you can have the necessary generation already "switched on" and running at a low power, and the limit becomes only how fast you can ramp up their power. Which is still an issue, but not as much as it would be if they had to turn on all the gas generators with zero notice.

Yeah, it's just the ramp up, it's predictable in advance.

Also the worst case scenario is curtailing some solar because you need to bring the gas plants online a little earlier.

Storing it would help reduce the peak in the evenings.