The peak in places like California is not midday, but always in the evening. And the challenge with solar is that the sun has frequently set by then. The chart that describes this problem is called the duck chart: https://www.caiso.com/Documents/FlexibleResourcesHelpRenewab...
The yearly peak for California, is in the afternoon, on particularly sunny days in July or August. The peak is slowly moving later because solar is shaving that peak and saving everyone lots of money.
Your document shows January and March, which is when the duck issue is at its worst. The peaks in these months are two or three times lower than the yearly peak, when the system has to work at its most stretched.
And remember this is net load, as those lines go lower, the actual demand is rising slightly, it's just being provided by solar rather than the utility.
