Temperature of the panels does affect solar panel efficiency though. It is measurable, but comes in second to total daylight in terms of total daily output. It is significant enough that there are now Hybrid PV-Thermal Panels which generate both electricity and hot water. The water loop cools the panels which increases efficiency (up to 15% more electricity generated) while also turning the waste heat into usable hot water for your home. They are more efficient because they turn more of the solar energy into useable stuff for your home than just electricity or thermal panels separately.