How to build a homemade solar oven

Constructing a homemade or handmade solar oven is a possible alternative to enjoy the benefits of solar cooking. But to achieve good results, the following guidelines must be taken into account:

  • Start from a good design.
  • Use appropriate materials.

Have the technological resources to carry out the construction

The growing interest in living healthier habits and the need for conventional energy savings have turned the possibility of having an artifact that cooks food with the energy of the sun, into something very attractive for many people.

Homemade solar oven build

The homemade solar oven made for didactic purposes, recycling a pizza box

It is easy to find in various sources, especially on the Internet, guides, and tutorials that offer information on how to build a homemade solar oven. Using various materials, with special preference in those recycled and/or almost zero cost. However, in the vast majority of these publications are often omitted data relating to temperatures, cooking times, the durability of the device and other important aspects relating to what can be expected from the device once it is finished and in operation. If you are thinking about building a homemade solar oven, the first thing you have to define is the use that the device you are going to make will have. If it is for didactic or experimental purposes, such as a science project at school or to experiment with solar thermal energy, it will surely be enough to build a simple design device at the lowest possible cost. On the contrary, if your goal is to build an artifact to cook in a habitual way and in acceptable times using the sun’s energy, you must necessarily start from a good design, use appropriate materials and follow a careful construction process.

Something you may not know is that most of the kitchens and solar ovens made with recycled materials have been designed with the premise of pasteurizing water in those areas of the world where drinking water for a number of circumstances is very difficult. Most of the places I mention are close to the Earth’s equator, where the available solar energy is higher and therefore the performance of any solar device is higher. Pasteurizing water from wells, streams or other natural sources, represents the difference between health and illness for many human beings who lack a drinking water network and this is achieved by heating the water to temperatures above 65 ° C, therefore a device that accomplishes this and also without the need for fuel, Firewood or other conventional energy source is really of enormous utility. However, for many people who live within an urban context, the need to pasteurize water is irrelevant and what they really want is to build a solar oven by hand to cook them and for this, the level of 65 ºC is quite insufficient.

To ensure the cooking of the food in a solar oven, it must be able to reach a working temperature above 90 ° C, so that is the barrier to overcome if you want to make a useful appliance. In the Spanish latitudes, the simple designs of homemade solar ovens made with cardboard and aluminum foil, usually reach temperatures around 80 ºC, so it will be necessary to improve aspects of the design and/or use more appropriate materials to achieve higher temperatures. In general, homemade equipment begins to have practical utility to cook as usual to achieve about 120 ºC, below this value the cooking is quite slow and limited to some very simple preparations.

With the above I do not intend to discourage anyone in the self-construction of homemade solar ovens , what I try is to give information so that it is done properly and not generate false expectations in people who still do not know about the subject, making them believe that you can cook perfectly using any contraption that does not meet a minimum of conditions.

How to build a homemade solar oven – Plans and designs

The first step to build a solar oven is to choose a suitable design, many websites of environmental trend offer information to make them, however, it should be noted that although you can find quite optimal designs, there are others that lack technical criteria at all.

As the idea of this section is to guide people who have recently come into contact with solar cooking, and therefore still do not have the elements of judgment to know if a design is good or not to build a solar oven , I think the most successful is to recommend a place where they can safely find valid information. On the website of the Organization Solar Cookers International you can find many guides and plans to make kitchens and solar ovens, among them the so-called “Minimum Solar Cooker” is highly recommended, it is a team that brings together the essence of the solar oven, it can be manufactured with very basic materials if it is needed for an experimental use and it adds indications to improve its efficiency and durability from the use of more appropriate materials and some modifications of the original design. In the link below, you can download the above information in Spanish and pdf format to print it later and make it more comfortable to use when building your homemade solar oven.

Materials to build a homemade solar oven

Different materials can be used to build a solar oven. But your choice must be made according to the use you are going to give and the benefits you want to obtain from the resulting device. Let’s analyze the possible options for each of the solar oven parts :

Homemade solar oven built with wood

Structure or housing:

A large majority of publications on home solar ovens, recommend making the cooking area. That is the casing with waste materials such as shoe boxes, pizzas, etc. From the point of view of recycling and its null economic cost, these materials may be fine. But cardboard is not the most appropriate material in many cases. The cardboard has little mechanical resistance. It fatigue quickly is not resistant to weathering or moisture that occurs in the oven as a result of the evaporation of water from food. Neither is it a hygienic material, it retains odors. And it is very difficult to clean in case of spills or splashes. If you are going to build a solar oven for experimental use and you will only use it a few times. Using cardboard boxes can be an affordable and inexpensive option. But if your intention is to make a device for regular use, cardboard boxes are not optimal materials to build a solar oven. Depending on the budget and the available tools, there are much more recommendable alternatives such as agglomerated wood panels, fiber, sheet metal or other materials that are more stable, hygienic and of good mechanical resistance.

Mineral wool – Optimal material to build a solar furnace

Thermal insulation: For thermal insulation of the cooking area there are several options. The idea is to place between the inside and outside walls of the housing, some material with high thermal resistance, there are several alternatives. It ranging from not using anything or use newspaper, cardboard, wood, vegetable fibers, etc. If the construction of the apparatus obeys to perform a school experiment or similar, leave a vacuum or use newspaper or cardboard as insulation material. It is cheap, easy and to some extent help to retain heat. If you want to build a homemade solar oven for continuous use, it is advisable to use materials with better characteristics in order to achieve reasonable efficiency. The use of insulation for conventional ovens or mineral wool is the most successful. The cork panels are easy to work with and are also good insulation. In no case should plastic foams or artificial sponges be used, since they produce toxic vapors when heated, which can leak into the cooking zone?

Aluminum mirror sheets to build a solar oven

Interior walls of the cooking zone:

To improve the efficiency of the solar oven, it is advisable to cover with some reflective material. It is the cooking zone, in this way part of the solar rays. It is conveniently redirected to the base of the cooking zone.

In most of the publications, the use of aluminum foil is recommended, better known in Spain as albal paper. If you are going to build a solar oven to experiment or fulfill some didactic objective. Sticking aluminum foil on the side walls is an economical solution and will relatively fulfill the reflection function for some time. If you want to make a solar oven that has practical utility. I do not recommend using aluminum foil and even less in the interior of the cooking area, as it is a disposable material. Designed for another purpose and that deteriorates quickly with repeated exposure to heat and humidity. After a few uses, it will begin to take off, to break and also lose much of its brightness and consequently its poor reflective qualities.

The most advisable to cover the walls of the cooking area. If you want to build a solar oven of reasonable performance. It is the aluminum sheets of mirror type because they are durable. It has little weight and resists exposure to heat without deterioration.

Materials for the roof

Normally in all cases, it is recommended to use glass, although some methacrylates with good transparency can also be used with acceptable results. You must disregard those greenish crystals, always use crystals with the greatest possible transparency. If the homemade solar oven is designed to generate high temperatures. It is advisable to use glass or tempered glass (resistant to heat) and also provide this cover with some system. It capable of allowing the expansion of the glass caused by heat. Otherwise, it will fracture once it reaches a certain temperature rise.

Materials for the absorber plate

In the simplest designs, the need for an absorber plate. It can be replaced by the same cooking vessel, which must necessarily be metallic and matte black. In case of planning for normal use and with better performance, it is necessary to incorporate an absorber plate in the bottom of the cooking box. A suitable material for this improves the performance of the device. A sheet or tray of metal and black, which provides thermal mass and greatly improves the performance of the device.

Materials for reflectors

The use of external reflectors in a homemade solar oven is optional. But certainly very convenient since it increases the solar energy collection area and directs more radiation into the cooking zone.

Material to build reflectors of a homemade solar oven

The usual recommendation in numerous sources reiterates the use of aluminum foil as material to build the external reflectors. From here, I insist again that the use of this material, will be relatively valid depending on the use. That is going to have the device that is thought to build. If it is a very simple construction you can use it, but in case of equipment in which you want higher yields is not recommended. Aluminum foil or “albal” paper is not a material of high durability. It has not been conceived to reflect light in solar artifacts of any kind. Its application is to serve as a wrap for food and is disposable (use and throw). Although it has certain reflective properties, these are not ideal at all.  It has a reflection rate of approximately 60%, which means that it reflects adequately that the percentage of sunlight, the other 40% is lost. The mechanical resistance of this material is very poor, easily broken by any action. It even more after being exposed to the weather for a long time. When degraded by ultraviolet rays and becomes increasingly opaque and fragile. There are special sheets for solar use with reflection rates above 90% and also have good mechanical strength, weathering and UV rays, which are appropriate materials to build a homemade solar oven with reasonable performance.

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