Panels are effectively part of the earth. It’s one closed system.

You do have a point: a black body radiates more heat than a high-albedo one so at night, the panels can cool down below ambient temperature. Overall, low albedo (reflectivity) and small thermal mass causes higher temperature differences between day and night – and it’s daytime when people want cooler temperatures.

But yes, any shade will help people living below solar panels feel cooler on sunny days, which is why I advocate for building a solar roof over just about every parking lot.