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Home : FOOD : Cooking : Solar Cooking |
| Every day, the earth is bombarded with enough solar energy to power the planet for centuries. This amount of energy, of which we use an insignificant amount, is almost unimaginable. We could be taking greater advantage of an almost limitless energy supply! One of the easiest ways to use solar energy is to convert it into thermal energy or heat. Heat can be used for several things, including generating electricity, refrigeration, mechanical power and cooking. To cook with solar heat, you need specific system components including a reflector, absorber and heat trap. Solar cookers are extremely environmentally friendly, as they produce Zero green-house emissions during operation, reduce deforestation and desertification, reduce your house cooling requirement, and are normally made from discarded materials. Their operation is simple: put the food in and forget about it. Most cookers can be made is a few hours and require very little maintenance. There are three main types of solar cookers: box, parabolic and panel. Their main difference is how they use the components to convert the solar energy (light) into thermal energy (heat). Box cookers These are basically insulated boxes with a transparent top. They use small reflectors to direct light into a large heat trap (box) that is closed and insulated. Within the heat trap, there is a metal plate that is colored black to absorb the heat. This heat is then used to cook the food. Their advantages are that they are moderately cheap and simple to construct. They can also be built to last. However, because of the large size of the heat trap and small size of the reflectors, they rarely exceed 250 degrees F and they are fairly bulky. The best application for a box cooker would be for cooking food slowly at low temperatures or for pasteurizing water, especially when you want the cooker to be left outside. Parabolic cookers Parabolic cookers have a large reflector surface that focuses light to a small heat absorber. Because they use such a large and precise reflector, they do not need a heat trap, and the food container itself usually serves as this component. They are very efficient at converting the light into heat. However, because of this efficiency and precision, they must track the sun fairly closely, which increases the difficulty and cost of such a system. The can reach temperatures of over 500 degrees F, and can easily burn food, so they must be tended to fairly closely. Parabolic cookers are excellent for electrical and steam production, as well as fast cooking of food. The advantages are high temperatures and fast cooking times, but the disadvantages are that they need tracking mechanisms for efficient operation, are bulky, and difficult to construct. Panel cookers These are somewhat of a hybrid design. They use large reflector surfaces and medium sized absorbers and heat traps. The reflectors are not precisely directed, so they don't require complicated tracking mechanisms. Because the heat trap and absorber areas are small, they are easy to make and can achieve higher temperatures than box designs. Panel cookers are the most widely used type of solar cooker mainly because of their cheap and easy construction. Many designs use cardboard and aluminum foil as the reflector, an oven bag as the heat trap, and a black metal pot as the absorber and food container. They are available in a wide variety of configurations, but we will focus on the simple, but effective “funnel-style” Panel Cooker. Windshield Shade Cooker This design is based on Kathy Dahl-Bredine's design (link - http://solarcooking.wikia.com/wiki/Windshield_shade_solar_funnel_cooker), made simply from a windshield sunscreen and some Velcro tabs. The design is very versatile, but is somewhat fragile in winds. It is also fairly small, but can cook 2 meals for 2 people in 6 hours. It could also easily pasteurize a gallon of water a day. Sew velcro to each side of the arc on the long side of the shade. Now, join these side, and you have a funnel. Place this funnel in a box or in a bucket, and place a grill inside the funnel, but allow it to rest on the rim of the bucket. Your food container goes on this grill, but put it inside an oven bag to provide a heat trap. To increase the capacity of the cooker design, you will need a larger reflector. We recommend using cardboards pieces and aluminum foil to start with and later, you can build a model using plastic cardboard, sheet metal or any other durable material. You want a rectangle that is twice as long as it is wide. A good size would be 2 pieces of cardboard 3ft by 3ft joined to make a large piece, 6 ft by 3 ft. In the center of one of the long sides, draw a half-circle arc. This arc should have a radius equal to the diameter of your food container. Cut out the arc, and then join the cardboard at either side of this arc. You may have to fold the cardboard slightly to make the sides meet, but you should end up with a funnel, with a round hole at the bottom. Lay the cardboard out again and cover it with foil. Use velcro or another fastening method to connect the sides. Place your food container in the oven bag and in the center of the funnel. You can now leave the food to cook, and adjust the angle of the cooker every hour or two. << Back to Cooking |
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