Most solar cookers work on the basic principle: Sunlight warms pots and/or food, which is used for cooking. A solar cooker lets the UV light rays in and then converts them to longer infrared light rays that cannot escape. Infrared radiation has the right energy to make the water, fat, and protein molecules in food vibrate vigorously and heat up. It is not the sun’s heat that cooks the food, nor is it the outside ambient temperature, though this can somewhat affect the rate or time required to cook, but rather it is the sun’s rays that are converted to heat energy that cooks the food, and this heat energy is then retained by the pot and the food by the means of a covering or lid. This occurs in much the same way that a greenhouse retains heat or a car with its windows rolled up. An effective solar cooker will use the energy of the sun to heat a cooking vessel and efficiently retain the energy (heat) for maximum cooking effectiveness.
The salient features of the solar cooker are:
• No requirement of cooking gas or kerosene, electricity, coal, or wood.
• No need to spend on fuel, as solar energy is available free.
• Food cooked in a solar cooker is nutritious. About 10-20% of protein retention is more as compared to that in conventional cooking. Vitamin thiamine retention is about 20 to 30% more whereas vitamin A is retained 5 to 10% more when food is cooked in the solar cooker.
• Solar cooking is pollution-free and safe.
• Solar cookers come in various sizes. Based on the number of family members, the size of the cooker can be chosen.
• All cooking activities (like boiling, roasting) can be done using a solar cooker.
• There are government schemes that offer subsidies to purchase solar cookers.
Four Basic Types of Solar Cookers
There are four basic types of solar cookers – panel cookers, box cookers (sometimes called box ovens), parabolic cookers, and tube cookers. Each of these basic types of solar cookers meets a specific need and a specific type of cooking.
Panel cookers resemble an open, three-sided box. The bottom and side panels of the box are covered with shiny material creating reflectors. The sun rays hit the shiny panels and are redirected into the center of the box.
A “heat trap” is used in the center of the box to capture the sun rays. Heat traps can be made from anything that is clear and allows the UV rays to pass through. Common heat traps are clear cooking bags used to cook turkeys; large glass bowls with one turned upside down on top of the other; and a small, clear jar placed inside of a larger clear jar.
The dark cooking container is placed inside the heat trap. When the redirected UV rays hit the pot, the molecules begin vibrating which creates heat. The heat trap prevents the heated molecules from dissipating, creating a superheated vessel. Temperatures reach 250° F (121° C) – 300°F (149°C). This type of cooker is good for the general cooking of soups, meats, vegetables, casseroles, and desserts.
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| All Season Solar Cooker (ASSC) |
Box Oven Solar Cookers
The box oven is the most well-known type of solar cooker. It is very much like the panel cooker above, except that the open side is covered by clear glass or plexiglass, creating an air-tight heat trap or oven in the center of the box. Commercial brands, as well as homemade models, have a layer of insulation between two walls that hold in the heat. Also, the inside of the box is usually painted black to create a heat sink as well. Finally, most box oven cookers also have large shiny panels to redirect the UV rays down into the heat trap.
Because the center cavity of the oven is usually larger than the heat trap found in the panel cooker, the box oven can hold a larger cooking pot. Because the center cavity of the oven is well insulated, it can reach higher temperatures than a panel cooker. Temperatures reach between 250° F (121°C) – 400°F(204°C).
By and large, even with all of the differences, panel cookers and box ovens are very much the same. Because the solar oven gets hotter, it will of course cook faster. However, given a little bit of extra time, the panel cooker will produce the same amazing results.
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| Solavore Sport Solar Cooker |
Parabolic Solar Cookers
Parabolic solar cookers are shaped like parabolic satellite dishes. The dish is covered with a shiny material that makes the entire surface reflective. In short, sunlight comes into the dish and is reflected back up to a center focal point. A cooking vessel is placed above the reflective surface at the focal point. The concentrated UV rays reach extremely high temperatures of 500°F ( 260°C) – 700°F (371°C) that are capable of frying, and grilling.
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| Sun Chef Parabolic Solar Cooker |
Evacuated Tube Cookers
Evacuated tube cookers are fairly new on the market, but are quickly becoming everyone’s favorite. Made from a large evacuated glass tube, surrounded by shiny reflector panels, the glass tube can reach temperatures of 550°F (290°C) or greater. The cooker gets hot enough to cook meat, bread, vegetables, and dessert.
Evacuated tube cookers are still solar cookers and need the sunlight to cook, however, the tube cookers does well even under cloudy skies.
A note of caution: Glass is glass and all normal precautions regarding heated glass must be observed. DO NOT pre-heat the glass tube prior to cooking. DO NOT put cold food into a hot glass cooker. DO NOT leave an empty tube cooker focused to the sun.
Disadvantages of a solar cooker
- Adequate sunshine is required for cooking.
- Takes a longer time to cook food than the conventional cooking methods.
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