Once again, we put a small black bread pan full of water into our oven. We set it out at 8:30 a.m., and left it out until 5:00 p.m. (by which time a heavy cloud cover had rolled in). Our oven stayed pretty steadily at about 270 degrees Fahrenheit throughout most of the day, but it never got any hotter than that. We did notice that we had condensation leakage between the bowl and the lip of the pan it was sitting on - it is possible we were losing heat as well.
The next time we try this oven, I think we'll return to using an oven bag, but this time a smaller size. In the meantime, we will begin preparing another model to try. At this point, I'm glad I'm not relying on the sun for all my cooking needs. I'm afraid we'd be eating a lot of raw food. My hat is off to the people who come up with the simple ideas for these ovens (so simple I never would have thought of them). I'm also in awe of the people who are making them work! Inspired by their success stories, and the fact that they are using their successes to help other people around the world, we'll keep pressing on.
It's great to homeschool - even when we fail.