The panels presumably are isolated from the roof with an air gap, thus their lower temperature. They passed some of the heat on to the air. The thermal-generating effect would depend on the flow of heat to the air, not the temperature of the sun-illuminated object. In a steady state equilibrium, that flow equals the solar input, minus the reflected light, and minus any power siphoned off in other forms (whether electricity from the PV panels, or evaporation of water from green plants).