Exponential
Battery prices plummetting, and V2G from EVs, is a path for near tropical regions to get to 90% solar energy. Robotics based manufacturing shifting to those regions is also a likely shift. Northern lattitude quality of life from global warming, is still a nice source of population attractiveness. Hydrogen made from solar is the path to 100% renewables and solar everywhere. Canada is a decent place for solar because of extremely long summer days. Canada can both make H2 in summer, and use H2 in winter. Even near tropical locations would have large spring and fall surpluses to cover near full summer demand from solar. They also need to make H2 from those surpluses.
I'm not sure of the validity of model, though I appreciate the effect of cooling at night.
Without solar, ground, usually fairly dark, absorbs solar heat at 100%. Solar panels cover 75%-80% of this heat to electricity, and while they get hotter than lighter shaded ground, the heat capacity of dirt is much higher, and the heat is lost quicker from air/wind contact. Similarly a building that has a solar cover with a slight airgap, will be cooler during the day than without solar, and using less AC, produce less warming surrounding the building.
For cold areas, snow cover actually retains warmth in soil. With bifacial panels, increases winter production significantly. No airgap over buildings, is path to keeping more heat for building, but using an airgap to help preheat air or water pipes for heat pump is just another path of using environmental heat to focus on useful heat. Heat pumps for heating (vs cooling) in general reduce outside temperatures.