The main load is during the day when the sun shines anyway, and then the seasonally changing periods before and after, basically ramping when people are getting up, then dropping off while people are going to bed. On the west side of a continent, the power for the ramp can come from the east because the sun shines earlier there; on the west the sun shines later and the east can get power. At night, there are still nuclear and other plants, and it is very foreseeable that installations of ground battery technology will have been in place well before twentieth century plants are retired.

High load in the day during sunlight is mostly true for summer heat, but in the winter you have cold evenings which requires base load or storage, combined with solar angle/efficiency being worse in the winter.