Gardening

How to build a solar oven

Before starting to build a solar oven, it is necessary to consider some variables such as the use that is going to be given, the availability of Sun in the region where it is going to be used, the number of diners that it will have to feed, etc. It is also important to assess the availability of materials in the region where it is going to be built. Cooking in countries with abundant solar radiation, where a solar cooker will give excellent results, is not the same as cooking in regions where sunny days are scarce for a good part of the year. In the latter case, the oven must incorporate a double glass, more reflectors and the possibility of directing it more finely towards the Sun. The design of a solar cooker depends largely on the imagination and possibilities of each one. It could be said that there are as many solar cookers as there are users of them, since,

National Geographic in its December 2009 issue discovered a self-built solar oven as a “great invention”. This avant-garde American society proved with this article to be very outdated and little informed about the world of solar cooking, and that in the United States resides the headquarters of the main international driving force behind solar cooking (unheard of!). In Spain, this “novel” invention, always according to National Geographic, has been the subject of school and educational activities for decades.

Building your own solar cooker is one of the attractions of cooking in the sun. The simplest solar cooker in terms of construction and handling is the box type, usually called a solar oven.

 

Materials for the construction of a solar oven

The essential materials for the construction of a solar oven are:

For the structure :

The materials used for the box to have and maintain its shape can be very varied: cardboard, wood, plywood, bamboo, metal, cement, bricks, stones, glass, fiberglass, woven reeds, plastic, papier-mâché, clay, etc. trodden earth, tree bark, etc.

Two cardboard boxes of different sizes can be used – to insert the insulating material in the middle – which can be obtained in any establishment, provided that there are no toxic contents.

To achieve a higher temperature inside the box, the inside sides of the box are lined with aluminum foil or other reflective material, and outside reflective sheets can be arranged to bounce additional light into the solar box. These can be used as a kitchen cover when not in use.

Insulators:

The walls and bottom of the box must have a high insulation value to achieve high enough temperatures for cooking. Good insulators are considered: aluminum foil, feathers, cellulose, wool, straw, and even crumpled newspapers.

It is important that the insulating materials surround the interior of the cooking cavity on all sides except for the glazed side (receiving solar radiation).

Transparent material :

Any transparent material that allows solar radiation to enter the box and fits on the upper face of the solar oven would do. Clear, solid or flexible glass or plastic is generally used.

In addition to the boxes, insulation and glass, you will also need: carpenter’s glue, a cutter, some pliers and a piece of wire.

A common size is 50 cm wide, 50 deep and about 35 cm high, but these measurements will vary depending on the size of the pots or containers that are going to be used. If you intend to cook several dishes at the same time, it should be taken into account, but it is not advisable to make the oven very high because it would produce shadows that reduce its effectiveness.

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Let’s do it!

Step 1 : build the structure

To build the structure we need two boxes. One of the boxes must be larger than the other because it will contain it. To do this, a square-shaped hole is cut in the base of the larger box, so that the other can be inserted, as indicated in the drawing. In addition, the small box is cut by its opening to form four flaps that fold out and that will serve to glue both boxes.

This diagram shows how to build the solar oven with two cardboard boxes separated by a layer of insulating material.

Step 2: line the boxes

Now they must be lined with the aluminum foil, the small one on its four internal faces plus the flaps and the outside. And the big one throughout its interior, including the background.

Step 3: fill with insulating material

When inserting the small box into the large one, there is an empty space that must be filled with an insulating material, such as crumpled paper, old wool, feathers, corrugated cardboard, etc. By closing the large box with duct tape, the space will be closed.

Step 4: build a lid for the glass

To build the lid, you can start from a smooth cardboard surface, to which four flaps are folded and glued as indicated in the drawing (step 1). You can use a strong plastic instead of glass, but it is not recommended, since it will have to be replaced since it tends to deform in the heat of the sun. To locate the glass, just cut out a square on the lid which, in turn, will be lined with aluminum foil to act as a reflector when opening the box (step 2). The glass will be attached to the cardboard with the silicone (step 3).

Here are the steps to follow to form the lid that contains the glass or plastic that will serve to trap the heat inside the solar oven.

Step 5: system to hold the lid

All that remains is to incorporate a system so that the lid remains raised. Wires can do the trick. To do this, small pieces of cardboard can be glued on the same side of the cover and the reflector where the bent ends of the wire will be inserted, as indicated in the drawing.

A black metal tray with curbs can be located in the back of the kitchen so that the box does not get wet if there are spills. Containers should also be black to capture incident solar radiation as much as possible. With this model, it is possible to reach more than 100 ºC, with which it is possible to prepare a wide variety of meals. This is a simple box model to which you can apply all the accessories you can imagine.

 Here you can find more information on how to cook with a solar cooker and oven

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