This box cooker is not for the faint of heart! It's a two person lift or four determined children. It was built a couple years ago in the mountains of eSwatini (Swaziland).
The main cooking chamber is too big and causes shadows as it was a 45 gallon drum cut for a BBQ. The reflectors were built from galvanized flat sheet riveted together and polished with automotive wax. They need to come in a little for better solar gain but at this angle help reduce the shadows inside the oven. Six large lava rocks were placed inside to hold a conventional oven grate. This allowed three large oven pans to fit inside.
When I used it we pre heated the oven for 30 minutes and baked two very large corn bread cakes for 60+ people, they took an hour and a half. In a test to boil water we got nowhere as I was not permitted to paint the large pot. I based the cooker off plans from SolarFreedom and Craig Shearer from Saskatchewan and he was okay with my build as it was not for profit. The Freedom Solar Cooker much smaller with a 500mm or ~20 inch oven.
Some problems I created building it, when I wrapped the outer sheet metal into the barrel to secure it a thermal bridge was created. The sheet metal should have been cut at the sides. I used blocks of wood as standoffs for the outer layer for insulation, metal or a combination of the two may have been better. I also did a bad job of cutting the glass and had to rebuild the reflector frame/oven door with plywood as the first wooden door was not up to holding the reflector. Handles also had to be added to move it around.
We measured 215°F so not bad for a beast of an oven. And with a thick blanket placed over the glass it can be used as an insulated heater to continue cooking after the sun has set.