How to make a solar oven
Posted by Solar energy guru | Filed under Solar thermal solutions
A solar oven uses a reflector to focus sunlight onto a cooking container enclosed in an insulated box. It is also called a box cooker, and is one of the three main types of solar cooker, the others being the panel and parabolic. The process of making a solar oven is simple enough that most people can make one in a few hours. The materials required are readily available at low cost and most can be found around the home. A solar oven works similar to a conventional oven by retaining most of the heat generated, and this allows for shorter cooking times. However, solar ovens still take a considerable amount of time to cook anything, and are mostly used on camping trips and in places that have limited fuel supplies.
The solar oven box is actually two boxes separated by a small gap and filled with insulating material. They are usually made from cardboard or wood, with the inner box just large enough to hold the cooking container when the oven lid is on. The cardboard won’t catch fire because the temperature inside is about half that required to set paper on fire. Cooking time is reduced if the container is supported by wooden blocks that allow reflected sunlight to reach its underside, and they also allow heated air to completely surround the container. The insulating material can be made from shredded newspaper, wool, fiberglass, or cutoffs from roof and wall insulation. Supports should be placed between the gap to keep the boxes separated, and the top gap between the two boxes sealed to prevent heated air from escaping. The inside of the cooking space can be lined with aluminum foil to reflect more sunlight onto the cooking container.
The lid of the solar oven must allow reflected sunlight into the box but it also must prevent heated air from escaping. A sheet of glass is often used for the lid, but the temperatures inside the solar oven are low enough that acrylic glass can also be used. The reflector panels can be made from cardboard or wood, and lined with aluminum foil. Painting the panels with silver paint is another option but it doesn’t provide the same amount of reflected light. Mirrors and sheets of polished metal can also be used for reflectors, but these add extra weight which is undesirable if the solar oven is to be carried long distances. The reflectors are placed around the edge of the lid and angled towards the sun with the help of support rods.
The outside of the cooking container should be painted black to increase the amount of sunlight absorbed because other colors reflect part of the sunlight away, and this helps increase the amount of heat generated. The container should also also be placed inside a clear oven-proof bag to help retain more heat. Normal plastic bags can be used but probably won’t last longer than one or two uses because of the temperature. Even with a large reflector and a well insulated box, the heat generated is small by comparison to a conventional oven and cooking times can be well over an hour. The time taken is even greater when there are clouds, and also when the outside temperature is low.
It is a simple task to make a solar oven but it requires several hours and a considerable amount of material. Panel cookers are easier to make but do not work nearly as well, and while parabolic cookers work best of all, they require good workshop skills to make one. The cooking time of a solar oven is long even when the outside conditions are perfect, but is acceptable when there are few other options. A lightweight and portable solar oven makes a good choice for camping when compared to heavy gas cookers and the effort required to collect firewood. Most importantly, they use free non-polluting energy provided by the sun, which never runs out and is accessible just about everywhere on Earth.
