I flew a lot above big PV plants in southern France, also above the mentioned new ones on the plateau of Valensole. I didn't find more or better thermals there than elsewhere. A big factor in the development of a thermal is moisture, and there is for sure more of that in the surrounding forest than in the PV area.

I'm also not promoting PV but Bert is right about the energy payback being about 2 years. Of course that depends a lot on the region. Electric cars and gray energy is a different story...