Yesterday morning I went out the front door to get the mail. I detected the faint smell of smoke. I didn't think much about it figuring it was my neighbor burning some branchs that washed up on the beach. A while later I was walking past a window and I noticed a faint wisp of smoke drifting past my field of view. Beings it was right next to the house I figured it would be wise to investigate. On the yard below was an area 18" by 3' wide that was charred and smoldering. The only cause I could think of was combustion caused by the heat. Today as I went out to get the mail--about the same time as yesterday--I had a thought.
On the back of the house is one of those all glass solariums. I went out and looked and the sun was just getting to the point that is was going thru the curved glass portion where the roof meets the wall.
I looked down and sure enough the sunlight was striking the ground where the scorch mark from yesterday was. In the pic you can see that the sun coming thru, or reflected off, of the solarium is hitting the ground at the end of the mark where the fire started as determined by wind direction.
Just thought this might be mildly interesting.