A solar cooker, or solar oven, is a device which uses the energy of sunlight to heat food or drink to cook it or sterilize it. High-tech versions, for example electric ovens powered by solar cells, are possible, and have some advantages such as being able to work in diffuse light. However at present they are very unusual because they are expensive. The vast majority of the solar cookers presently in use are relatively cheap, low-tech devices. Because they use no fuel and cost nothing to operate, many nonprofit organizations are promoting their use worldwide to help reduce fuel costs for low-income people, reduce air pollution and slow deforestation and desertification, caused by use of firewood for cooking. Solar cooking is a form of outdoor cooking and is often used in situations where minimal fuel consumption is important, or the danger of accidental fires is high.
Low-Tech Solar Cookers
There are a variety of types of solar cookers: over 65 major designs and hundreds of variations of them. The basic principles of solar cooker design are:
- Concentrating Sunlight: A reflective mirror of polished glass, metal or metallised film is used to concentrate light and heat from the sun into a small cooking area, making the energy more concentrated and increasing its heating power.
- Converting Light to Heat: A black or low reflectivity surface on a food container or the inside of a solar cooker will improve the effectiveness of turning light into heat. Light absorption converts the sun’s visible light into heat, substantially improving the effectiveness of the cooker.
- Trapping Heat: It is important to reduce convection by isolating the air inside the cooker from the air outside the cooker. A plastic bag or tightly sealed glass cover will trap the hot air inside. This makes it possible to reach similar temperatures on cold and windy days as on hot days.
- Greenhouse Effect: Glass transmits visible light but blocks infrared thermal radiation from escaping. This amplifies the heat trapping effect.
Types of Solar Cooker
The available designs of solar ovens fall into three main categories: the box, parabolic, and panel designs. The feature common to each oven design is the shiny reflective surface that directs the sun’s rays onto a dark cooking vessel. Each category has advantages when compared on their heating ability, ease of construction, ease and safety of use.
1. Box Cooker Solar Ovens
2. Reflective Panel Solar Cookers
3. Parabolic Solar Cookers
Box Solar Cooker
Box cookers are the most common type made for personal use. There are over several hundred thousand in India alone. Despite the name “box” cooker, they are made in both circular and rectangular shapes. They consist of an enclosed inner box covered with clear glass or plastic, a reflector, and insulation. There is a wide variety of patterns and plans for the box cooker. While they do not heat quickly, they do provide slow, even cooking and are extremely cheap to make. Box cookers are very easy and safe to use, and fairly easy to construct.
Panel Solar Cooker
Panel cookers are flat reflective panels which focus the sunlight onto a cooking vessel without the inner box common in box cookers. Panel cookers are the easiest and least costly to make, requiring just four reflective panels and a cooking vessel, but they are unstable in high winds and do not retain as much heat when the sun is hidden behind clouds. The diagram shows a panel cooker with a dark cooking vessel and thermometer all wrapped in a plastic oven bag.
Parabolic Solar Cooker
Reflective materials are used to concentrate light and heat from the sun into a small cooking area, making the Sun’s energy more concentrated and therefore more powerful, resulting in the fastest cooking times of all Cooker designs.
Parabolic cookers require more precision to focus the sunlight on the cooking vessel and are therefore the most complex design to build. If the sunlight is not focused exactly on the cooking vessel, the food will not cook efficiently.