The system we use is nothing like that. It also uses a black enameled-steel pot and an oven roasting bag like the kind you buy at the store to roast your Thanksgiving turkey in. It can bake potatoes easily in about three hours, and can even bake breads and cakes if used in a bright noonday sun. Our rule of thumb is that if there's enough sun to cast a shadow, you can use the cooker. The biggest advantage of solar cooking is that once the food is cooked, it stays warm without overcooking.
Solar cookers operate on the principle of the slow cooker.
It typically heats up to around 200-250 degrees, which is plenty hot enough to cook most things. In areas where the water supply is contaminated, it's also used to pasteurize water for drinking. To use our cooker, we put the food into a black enameled-metal pot. This pot goes into the roasting bag, with a little rack or trivet to keep the pot from touching the bag on the bottom. The bag is then sealed with a twist-tie, or clothespin, or whatever, and the whole assembly is placed into the reflector.