Solution: Solar Stoves Edit

Overview Edit

Firewood is the traditional energy source for cooking in the majority of countries of the developing world. The FAO estimated that 2 billion people worldwide, experience serious problems with their cooking fuel supply. High population density, deforestation and soil erosion cause severe environmental degradation. The use of fossil fuels for cooking also aggravates poverty and impacts negatively on local economies. Solar cooking as an environmentally friendly technology could contribute to the solution – provided that the technology is accepted by end-users and that the solar stoves are both appropriate and affordable.

A solar cooker or solar oven is a way of harnessing the sun's power to cook food. A metal box forms the simplest solar cooker. A set of large mirrors or a large Fresnel lens to focus sunlight to a single point may also be added. On a sunny day a black baking tray or cooking pot can convert hundreds of watts of light into heat, in addition to any infra-red. Temperatures in a typical oven can reach 200 °C (400 °F).

Apart from the obvious need for sunlight and the need to aim the solar oven before use, using a solar oven is not substantially different from a regular oven. However since they use no fuel they are free to run, humanitarian organizations are promoting their use worldwide to help slow deforestation and desertification caused by the need for firewood with which to cook. The first known western solar cooker was built by Horace de Saussure in 1767.

A solar box cooker is an insulated box with a transparent top and a reflective lid. It is designed to capture solar power and make use of the greenhouse effect to cause heat to accumulate inside. The top can usually be removed to allow dark pots containing food to be placed inside. The box usually has one or more reflectors with aluminum foil or other reflective material to bounce extra light into the interior of the box. Cooking containers and the inside bottom of the cooker should be dark-colored or black. The inside walls should be reflective to reduce radiative heat loss and bounce the light towards the pots and the dark bottom, which is in contact with the pots. A good example of this type of cooker is the "Minimum" Solar Box Cooker.

The inside insulator for the solar box cooker has to be able to withstand temperatures up to 150° C (302 °F) without melting or off-gassing. Crumpled newspapers, wool, rags, dry grass, sheets of cardboard, etc. can be used to insulate the walls of the cooker, but since most of the heat escapes through the top glass or plastic, very little insulation in the walls is necessary. The transparent top is either glass, which is durable but hard to work with, or an oven cooking bag, which is lighter, cheaper, and easier to work with, but less durable. If dark pots and/or bottom tray cannot be located, these can be darkened either with flat-black spray paint (one that is non-toxic when dry) or black tempera paint.

The solar box cooker typically reaches a temperature of 150 °C (302 °F); not as hot as a standard oven, but still hot enough to cook food over a somewhat longer period of time. It should be remembered that food containing moisture cannot get hotter than 100 °C (212 °F) in any case, so it is not necessary to cook at the high temperatures indicated in standard cookbooks. Because the food does not reach too high of a temperature, it can be safely left in the cooker all day without burning. It is best to start cooking before noon, though, depending on the latitude and weather, food can be cooked either early or later in the day. The cooker is also used to warm food and drinks but can also be used to pasteurize water or milk.

Solar box cookers can be made of locally available materials or be manufactured in a factory for sale. They range from small cardboard devices, suitable for cooking a single meal when the sun is shining, to wood and glass boxes built into the sunny side of a house. Although invented by Horace de Saussure, a Swiss naturalist, as early as 1767, solar box cookers have only gained popularity since the 1970s. These surprisingly simple and useful appliances are seen in growing numbers in almost every country of the world.

Threats Addressed Edit

Pros Edit

  • Potential for unlimited pollution free cooking
  • No fuel needed
  • Clean
  • Cheap to make and free to operate
  • Pasteurize water (65° C or 150° F x 20 minutes) without fuel
  • Won't burn food

Cons Edit

  • Weather dependent
  • Some versions tend to be very slow to cook
  • Can't cook at night
  • Must cook in the open away from shade
  • Improper use or accidents can result in serious eye damage or fire - always use eye UV protection

Products Edit

  • Solar Household Energy Solar Stove
  • Lehmans Deluxe Sun Oven Solar Stove

Resources Edit

  • A comprehensive study on the social acceptance of solar stoves in Africa
  • A study on the diffusion of solar cookers among the Basotho of Lesotho
  • Solar cooking as a solution to a fuel wood crisis in Burkina Faso
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