after building a more detailed simulation than prior models that solar panels increase urban temperature variations, causing the five simulated cities to be hotter during the day and colder during the night.
Important bit here seems to be its a simulated city, fwiw. Though I can see the logic
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.