Increased demand won't change the fact that you need a good sunny location and a bit of area for any solar plant. Siting the solar/thermal plants in Arizona doesn't do much good for Montana, if you let me bring up those pesky transmission issues again.
I haven't followed solar/thermal technology, so maybe they can build them in Montana, but I'd doubt that it work too well in the Montana winter.
Actually, solar thermal plants will work quite nicely in Montana. You just need more collector area. Summer/winter have very little to do with it, as long as you have sufficient days with clear skies. I live in Western Washington (west of the Cascades), and it's cloudy here for many days out of the year. But right across the mountains EAST of the Cascades, we have a "rain shadow desert" around Yakima and Hanford, that has high insolation most of the days of the year (300 clear days/year in Yakima), and in easy transmission distance to the population centers.
"I haven't followed solar/thermal technology, so maybe they can build them in Montana, but I'd doubt that it work too well in the Montana winter."
I didn't follow solar/thermal for a long time, either (too low tech for my taste), but right now, it looks like much the best long-term bet. Windmills are WAY too variable, with unpredictable variability. Solar varies too, but the variability is largely predictable, and can be "built in" for the specific location. And with the new addition of "thermal storage", solar CAN "do it all".
I think the coming option will be a solar thermal/natural gas hybrid system, with the percentage of each resource used depending on local conditions.
Don't get me wrong. I would FAR prefer the nuclear option. But if we aren't allowed to do that, we do NOT have to give up a "high-energy" civilization. The entire energy usage of the United states can be collected with two plots of land, 100 miles by 100 miles (and that includes day/night and seasonal variability, and a collection efficiency equaling today's solar thermal plants). Of course, any such system would actually be built of many smaller units.
If I were designing such a system, I would make the highway system (especially the Interstates) the "transmission grid". Start at I-10 in Los Angeles, and every 100 miles (or half the distance between population centers if less than 100 miles), start building solar power plants. Run the transmission lines along the highway rights of way. Expand the system eastward along I-10, and then north as mass production drives down the cost of mirrors.
This also fixes the problem of energy for transportation, whether that turns out to be electric battery cars, or hydrogen fuel cell cars. And it also fixes the "transmission" problem.
Heinlein predicted something like this in his short story "The Rolling Roads". In this case, the roads wouldn't actually roll, but they WOULD be solar powered, as they were in his story.