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Alaska: theoretically, Heat Retention Solar Oven may work even in Alaska (in the summer). Modify the design specs so that the floor and sides and the cover each have an R-value of R90. Leave the oven uncovered (in summer) for about 8 to 9 hours each sunny day. Use large reflector panels. Cover the oven at night, and on cloudy days. Use four panes of glass (preferably with anti-reflective coating) and at least a 1/4 inch between each pane, to acheive an R-value of R4 for the window.
Ideal Solar Oven Shape:
In order to maximize the efficiency of the oven, one needs to minimize the surface area of the walls and floor and maximize the area of the window. Heat enters through the window and it exits the solar oven through the walls and floor. (Of course, heat also exits through the window, but any successful design will have more heat entering than leaving through the window, so the net effect is that heat enters.)
A rectangular shaped solar oven has five surfaces, (four walls and a floor), with a net heat loss. But a triangular shaped solar oven has only four surfaces with a net heat loss (three walls and a floor). This triangular arrangement decreases the overall heat loss of the oven, improving efficiency. Another shape with lowered net heat loss is the "pizza box" shape, i.e. having a very low height. Adding height to a rectangular oven decreases efficiency and increases het loss. The lower the oven the better.
Also, in order to maximize the effectiveness of the reflectors, without constant readjustment, the solar oven should be a long shape, with one end facing east and the other facing west. The logitudinal axis of the oven would then allow the longest reflectors to align with the solar declination. Thus, the longest reflectors would not need to be readjusted. The end reflectors would be smaller and could be set up with the western end reflector at 90 degrees and the eastern reflector down, in the morning. Then, at about solar noon, the western reflector would be taken down and the eastern end reflector would be at 90 degrees from horizontal.
In areas of the word 25 degrees of latitude or less, the rectangular oven shape, with a low height would be most efficient. However, above 25 degrees latitude, the triangular shape would be best, with the window tilted towards the South. The angle of tilt should be the same as the latitude plus ten degrees (when used year round). If the oven is only used in the spring, summer, and fall, then the angle of tilt should be the same as the latitude.
Solar Oven Size and Cultural Considerations:
Most solar oven designs come from developed, industrialized nations. The culture in those nations generally favors small family size or even individuals living completely on their own. People in these cultures like independence and mobility. The solar ovens designed in these nations reflect the culture. They are small ovens designed for a "family of four" or fewer. They are light and easily transportable. But they don't feed very many people. They have design limitations caused by cultural blind spots.
In other areas of the world, and in other cultures, family size is much larger and people live in a more communal setting, such as a small town or a village. The best design for such a culture would be a larger solar oven that could cook a large meal for a dozen or more persons, and one which had perhaps more than one oven compartment. A very large solar oven could be built with 2, 3, or even 4 separate oven compartments, for use by an extended family or a small village. Such a design would be more fitting to many areas of the world.
A Heat Retention Solar Oven could be made large enough to have four oven compartments within a single solar oven. One oven compartment could be on each side of the oven. A large enough solar oven should be able to supply enough heat for all four ovens (about 1500 watt-hours per oven per day, or 6 kW-hours per day total). One of the main weaknesses with the typical solar oven design is that it only cooks enough food for a few people. But, in areas of the world where solar ovens are most useful, such as in small villages, people live in extended families and they live and work cooperatively together as a village. They need a large solar oven capable of cooking for an extended family or for a good portion of the village itself. A large Heat Retention Solar Oven would fit their needs better than the typical solar ovens they are offered.
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Disclaimer: The drawings, procedures, and words on this site are for information purposes only. No claims are expressed or implied as to the safety, usefulness, or accuracy of this information. This site does not contain recommendations or actual plans for building a Heat Retention Solar Oven. This particular solar oven design is theoretical and experimental.