I enlisted the support of the entire family for this one. One egg outside in full sunlight, the other inside the car on the dashboard. Both on lightly oiled silver plates (not real silver, the tinny ones you get in the supermarket to do naice veg sticks on for parties). Both plates left out for about 90 minutes before cracking the egg.
Results are in:
Egg 1, full sunlight outside. Began at an ambient 30C and swiftly climbed to 50 on the thermometer. Egg did not cook so much as shrivel, slowly, into a desiccated mess. The yolk cooked quite quickly, while the white just dried up. On recovery some hours later, crystalline egg white scattered from the plate like ovine dandruff.
Verdict: Effective in that the egg was no longer raw, but 0/10 for eatability.
Egg 2, inside car on dashboard. Thermometer gave up entirely and the needle vanished, so well over 50C. Cracked the egg about 90 minutes later. The white began to set instantly, which was quite impressive. The yolk cooked quickly but the white took another hour or so, but we did end up with a set white, and even a little curlicue of crispy brown at the edge. When I washed the bastard plate up and dislodged the egg yolk, it actually bounced off the sink.
Verdict: Better. It wasn't exactly appetising but it did look more or less like a fried egg. The yolk however was pustulous. 2/10 for eatability. You could, but you wouldn't want to.
Conclusions: the relatively flimsy silver plates were not the ideal base for the fried egg. Ideally we would have used a thicker piece of metal with more thermal mass, which would have retained more heat and cooked the egg from below using conduction heat as per a traditional frying pan, rather than relying on the heat of the sun to cook it from above, heating it with convection heat from the hot air which ultimately dried it out rather than cooking it.
However, the hypothesis, which was "it really is quite unusually hot outside" was proved.
Thank you for coming to my Egg Talk.