The picture in my mind was: You have overbuilt solar charging nearby batteries (lithium ion, sodium ion, whatever) to cover the 4-hour busy period at night, and

The picture in my mind was: You have overbuilt solar charging nearby batteries (lithium ion, sodium ion, whatever) to cover the 4-hour busy period at night, and smaller amounts of longer duration storage like pumped hydro to cover the quieter periods after 10pm. I'm not sure if that'd work out to be cheaper than doing the proposed 60% wind/45% solar mix with inter-state transmission. It would reduce the need for new transmission lines, though.