They don’t reflect a lot of light which ordinarily means a material is absorbing all the energy and turning it to heat, but in the case of solar panels you’re turning maybe 20% of it into electricity instead
Your figure for asphalt seems off. I think the more pertinent comparison would be between solar cells and undisurbed land, which have similar albedo. But thermal mass is probably even more important: ground beneath solar panels receive less thermal radiation than unshaded ground, and while solar cells get hot during the day they cool down quickly at night. Simplifying greatly, they should re-emit about half of the heat they capture to the sky, and half to the ground.
>I think the more pertinent comparison would be between solar cells and undisurbed land, which have similar albedo.
No, that's a terrible comparison. We're talking about Phoenix here: the whole place is basically covered in asphalt, either roads or parking lots. There's no "undisturbed land" there at all.