This area has few days over 100 but does see relatively cool nights. It is an ideal area for this. I would say from southernmost california to southernmost texas, this basic setup is pretty workable and that includes something around 50 million americans. Regulator hurdles in some places make it impossible though. Costs are going to scale up mostly in line with the heating/cooling requirements and cloudiness of your area.

My panels are ground mounted and pointed in the ideal direction. I think this contributes to their efficiency because the ground helps cool them during the hottest periods but it is a tricky thing to nail down. On a previous home I had roof mounted panels and they seemed to perform much worse, difficult to identify the exact reason though.