I must report a big huge failing grade on my solar oven design. A couple days ago I 'cooked' potatoes after Conrad from greenedmonton's left an excellent link to one of his posts on cooking with his solar oven.
Into the black pot went the new garden potatoes. Into the oven went the pot at about 9:30 am. To be doubly sure I'd catch the solar rays, I tilted the oven more significantly south and ensured the inside tin foil and reflectors were properly arranged.
At 6 pm I proudly removed the pot's lid to discover tepid potatoes that looked more ready for the still than my dinner plate. The solar oven seemed to have advanced the potatoes' fermentation process; brown spots and sour smell have dashed my high hopes for this experiment with solar.
I'm afraid I need to start over with my design. Perhaps after some success next year I'll be able to report what was wrong with our garage-junk set up... but until then, if you've any wisdom, I'd love to hear it!