@
LeeH,
For my previous job developing covert cameras to be mounted on the outside of vehicles in Afghanistan, I ran a quick test. I took an available extruded aluminum enclosure from our lab's bone yard.
We put it in the parking lot (black asphalt, we thougt it close enough to the balck Chevy Suburbans that would have our cameras)
The enclosure had heat sink fins (not a smooth box). Fins are good to shed heat from inside to outside.
On a 70F day in Seattle (not direct sun angle), our thermocouples measured 130F inside the enclosure.
Sure, the heat sink fins could be blamed. They increase surface area, to aid heat transfer from inside (hot) to outside (cooler).
But the increased black surface area on the outside increased the solar heating effect. We had a ~60F delta. Conclusion: In direct sun, "cooling fins" turn into "heating fins"
Re-Reading the above, it sounds obvious. LOL. Maybe us electrical folks weren't up to the thermodynamic aspect....
Bottom Line: Solar heat is real. Electronics generate their own heat, which needs to leave the enclosure. If sun is hitting the box, the heat may travel INTO the box, instead of OUTSIDE the box. And we all know, heat is a mortal enemy of electronics! Leads to premature demise, dropouts, etc.