> the variation you get between Summer and Winter levels of insolation

The obvious thing to do is just size the solar array for the winter insolation levels, since the solar part is likely to be so much cheaper than the storage part.

Also, don't forget wind, which is also super cheap at the good sites. It will balance out some of the seasonal shift, and also a good amount of the night time needs.

This all depends on cross-continent interconnects, and energy markets. The entrenched interests are going to resist mightily to anything that might cost them even a cent, and they control the laws to lock out competition.

I view interconnects as important an issue as the interstate system. It will enable so much innovation and drive down costs quite a bit.