At the 2016 AT course we had a solaroven challenge. I took an old box, unfolded it and cut the biggest circle I could out of it, maybe 3 feet. Slit it so I could roll it into a cone. Covered it in tinfoil glued down with homemade flour glue. At the base of the cone maid a cardboard platform to insulate The platform where I was going to set my bottle from the cone surface. On that platform set a black Metal stove pipe end cap where I set a dark beer bottle full of water . Everything except the cardboard and cap was sealed in an oven bag to prevent convection heat loss. In June, on a sunny day, maybe 60°, pointing it about 25° in front of the sun, the empty bottle was too hot to touch after five minutes and boiled a bottle full of water in about 45 minutes. I won the challenge and the prize was A large organic chocolate bar that I ended up sharing with everyone. Which was fine...because the chocolate bar was organic and lived up to my organic rule: costs twice as much for half the quality... organic charcoal is in that category too
I am not sure I would call it intense heat. It obviously got to 212 F to boil the water. I think crock pots get right about to that temp to cook. I was going to build a oven, but I broke down and bought a solar oven for myself for Christmas but I have not tried it yet. It is a Solavore Sport Solar Oven as I liked the compact design and reviews. It was a bit pricey but I don't think I could build anything as nice for the money. I am hoping I can get it to at least 300 F for more baking kinds of things.
I know when I BBQ that I am shooting for around 220 F. Some people cold smoke around 180 F but it takes forever for stuff to get done at that temp. Like I said I shoot for around 220 to 250 (as it is hard to be exact with fires). If you heat the meat above the boiling point of water it renders the fat and connective tissue to give you that low and slow tender goodness. I will do pork ribs (smoker full) for 6 hrs and a typical 7-9 lb Boston butt (fat side up to self baste) for ~ 8 hrs and a 15-17 lb brisket (untrimmed, fat side up to self baste) for ~14 hrs.
This looks like a job for .... legal tender! It says so right in this tiny ad: