The Solar Panel Cooker was invented by Roger Bernard and described by him in Solar Box Journal #16, February 1994. The solar panel cooker introduces a transparent greenhouse enclosure around the cooking pot, replacing the insulated box of a Kerr-Cole solar box cooker.
The reflective panels of the panel cooker surround the pot and its greenhouse, bathing the pot in concentrated sunlight, thereby heating the pot. The pot then heats both the food in the pot and the air trapped between the greenhouse and the pot. Because the air is held in place by the greenhouse, it insulates the pot, reducing heat loss from the pot and food to a rate which is initially lower than the rate at which the sunlight delivers heat to the pot. The resulting accumulation of heat cooks the food.
In Solar Box Journal #16, Bernard describes an inverted glass salad bowl as the greenhouse enclosure. In an associated article in the same issue of SBJ, Barbara Kerr suggests a transparent plastic oven bag, which is now widely used. Both these forms of greenhouse enclosure suffer from condensation of cooking vapors, and require periodic drying. Since the pot and its lid are sealed in the greenhouse, it is awkward to stir the food, or test for doneness.
Bernard solved these problems (see Solar Box Journal #18, October 1994 ) by suspending the black cooking pot by its lip inside a glass vessel. This arrangement exposes the top of the pot, giving easy access to the food, and venting cooking vapors directly to the atmosphere, rather than into the greenhouse airspace. Placing the uninsulated top of the pot into direct contact with the atmosphere, however, increases heat loss from the pot.
This proposal elaborates on Bernard's arrangement, introducing an additional
greenhouse enclosure for the lid of the pot, and packaging both greenhouse
enclosures as integral parts of an easily handled assembly. For the
cook, the greenhouse enclosure is no longer a distinct object;
the combination of two greenhouse enclosures and pot is the
pot. This integration should add substantial convenience to solar
panel cooking.
Fig. 1 shows a cross section of the pot in use.
A transparent stand supports the pot, admits sunlight to heat the pot,
and contains an insulating airspace. It forms a greenhouse enclosure
for all but the top of the pot. Handles on the stand make it a convenient
accessory for handling the pot, which has no handles. When the pot
is removed from the stand, it is awkward to handle when full of hot food.
The design encourages the cook to keep the pot in the stand while preparing
food before cooking, and while serving food after cooking. The lid of the
pot has an integrated greenhouse enclosure, including an inner black
heating surface. Cooking vapors are unlikely to invade either of
the greenhouse air spaces, removing the problem of condensation.
Glass is an obviously suitable material for the transparent parts. A plastic with suitable thermal and optical properties could be used, and would be lighter, thinner, and might have more easily accessible manufacturing facilities. I have not sufficiently investigated the technical and economic aspects of the use of plastic to have an opinion as to its relative desirability. Either kind of material requires fabrication by molding. This design sketch pays attention to keeping the tooling costs of the molds as low as possible. In particular, the transparent parts shown here can each be formed with a two part mold. See Fig. 7.
Aluminum is an ideal material for the pot and the bottom of the lid.
Each of these parts would be formed from a single piece of material by
processes available to any pot manufacturer. Again, tool development
is required. The pot is straight forward. The lid bottom does have
a slight "negative draft" required to form the shape that retains the press
fit transparent lid top. See Fig 3.
The top surface of the lower element of the lid (the pan of the lid) is, of course, black. The pan is in contact with cooking vapors but not food. Since it is much hotter than the food, but is not in contact with the food, the pan will radiate its heat to the food more effectively if its bottom surface is also black.
This design tapers the sides of the pot and stand to allow each to be
stacked with itself, as shown in Fig. 4.
Stacking the components of multiple pots in this way greatly reduces the
space needed for storage or transportation. My intuition says that
the taper should not produce an unacceptable reduction in the amount of
energy that reaches the pot, but this needs checking.
David Delaney
ddelaney@sympatico.ca
142 Waverley Street
Apartment 2A
Ottawa, Ontario, K2P 0V4
Canada
