I have been very impressed to read, in SBJ #17, that the solar panel cooker (SPC) idea, as publicized by Barbara Kerr and myself in the preceding issue, had met with an abundant response. Even negative results can be of interest when we seek to understand them. For instance, in the comment, "I used a "turkey -size" oven cooking bag and a dark ceramic teapot. Nothing!", there are two interesting clues. First the ceramic teapot was not a good choice because ceramic can be a bad conductor of heat [depending on its density, Ed.]. Food can remain lukewarm, even if the pot is very hot on the outside. And secondly, a turkey is an enormous bird, and using a bag appropriate to hold it may mean that the quantity of food could have been too big for the cooker.
Let us not forget that the SPC was designed as a substitute for the traditional box for small quantities of food. The dimensions given for my prototype in SBJ #16 are appropriate only when cooking for one person.
During the 1994 summer, I somewhat improved the SPC's convenience and efficiency by introducing two changes: a new system for creating the greenhouse effect and a more compact design.
Undoubtedly, oven bags are unbeatable for their lightness, but in my city (Lyon, 500,000 inhabitants) there are no oven bags available in the supermarkets. On the other hand, Pyrex salad bowls are very easy to find everywhere in France--even in small towns. Their price (about $4 US) is ten times the price on an oven bag, but they can be used hundreds of times for solar cooking as well as for other purposes in the kitchen. For traveling, however, they are relatively heavy and cumbersome.
This can be done by placing the dark pot into a glass dish whose diameter is slightly larger than that of the pot.
Obviously the advantages of such a system are partially offset by extra heat loss from the uninsulated lid. By raising the pot off the ground a further gain is achieved. In fact, my experiments have shown that cooking times with this new system are no longer than with the original design with a salad bowl up-turned over the pot.
In order to improve stability, I reduced the number of panels from five to four. A pleasant surprise was that the removal of the central back panel not only resulted in a more compact and stable cooker, but also improved the efficiency of the reflective surfaces, by permitting multiple reflections between the two remaining vertical panels. This peculiar assembly I propose to call a "reflective open box" (ROB) to distinguish it from the original solar panel cooker (SPC).