The NG Solar Cooker has been designed by Neelaratna Geekiyanage. Neelaratna has been researching increasing the efficiency of solar box cookers by comparing various approaches to cooking utensils. Typically, a lightweight blackened pot is used with solar cookers. He has tried covering a conventional shiny pot with a black cloth, as well as a more form-fitting black velvet covered pot. According to his observations, the velvet covered pot performed better than the typical dark colored pot, or the loosely covered shiny pot.
It could be that a tight fitting velvet cover provides the necessary heat sink for cooking, as well as offers some insulation to the cook pot itself to help retain some of the heat. With the cover in place, heat is conducted directly to the pot by touching, which is probably why a loose cover does not work as well. And with the cover, a portion of the heat is retained from being reradiated away from the pot, like with a simple black pot. Usually this lost heat is captured by the air in the box cooker and redirected back at the pot in a convective heat transfer fashion. Retaining the heat is more efficient than first losing it, and then recapturing it. A heavily insulated jacket may have diminishing desirable results however. The amount of heat retained or lost needs to be balanced with practical cooking methods, and if it is worth the trouble of adding the cooking jacket to the pot, which may be easily stained with cooking liquids, and add complexity to checking on the cooking food..
The design is also addressing the issue of losing heat through the box envelope. Most box cookers have modest approaches to insulation, and the NG Solar Cooker uses high-performing rigid foam insulation for the box structure itself. A reflective surface has been applied to the inside of the foam surface, to redirect heat back at the pot. A black painted cooking tray supports the cook pot. He found that a double layer of Perspex plastic has worked the best for the transparent box cover. Adding better quality insulation to box cookers will add to their construction cost and complexity, but research is pointing to greater cooking potential.