Solar cooking systems

Solar box cooker

A solar cooker is a way of using the sun’s power to cook. They are mainly two types of solar cookers: Concentrating and solar box cookers (usually known as solar oven because the way they are used). 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.
One disadvantage of solar cooking is that it provides the hottest food during the hottest part of the day, when people are less inclined to eat a hot meal.

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A solar box cooker is an insulated box with a transparent top and a reflective lid. 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.
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 can be used to warm food and drinks and 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. An index of detailed wiki pages for each country can be found here.

Solar panel cooker

The solar panel cooker is the simplest form of solar cooker yet developed. Solar panel cookers have multiple simple reflectors arranged to focus solar radiation onto a covered black pot enclosed in a clear heat-resistant plastic bag or other clear enclosure. The original design by Dr. Roger Barnard of France used an open, foiled box with a dark, lidded pot of food in the focal point insulated by an inverted glass salad bowl. From Dr. Barnard’s basic design, Barbara Kerr, an Arizonan, developed a foldable model suitable for backpacking. Working from that model, Bev Blum, the director of Solar Cookers International, joined with volunteer engineers to develop a mass-producible solar panel cooker, the CooKit, which has found acceptance in refugee camps as well as for recreational and teaching uses and in households in the United States. Thousands of families in the Kakuma Refugee Camp in Kenya and the Aisha Refugee Camp in Ethiopia have taken up this form of solar cooking to save both firewood and money.

HotPot

A recent development is the HotPot developed by US NGO Solar Household Energy, Inc. The cooking vessel in this cooker is a large clear pot with a clear lid into which a dark pot is suspended. This design has the advantage of very even heating since the sun is able to shine onto the sides and the bottom of the pot during cooking. An added advantage is that the clear lid allows the food to be observed while it is cooking without removing the lid.

Solar Kettles

Solar kettles are devices which allow water to be heated to boiling point through the application of solar energy alone. Typically they use evacuated(or vacuum) solar glass tube technology to capture, accumulate and store solar energy needed to power the kettle. Besides heating liquids, since the stagnating temperature of solar vacuum glass tubes is a high 220 degrees Celsius, Solar Kettles can also deliver dry heat and function as ovens and autoclaves. Morever, since solar vacuum glass tubes work on accumulated rather than concentrated solar thermal energy, Solar Kettles need just diffused sunlight to work and needs no Sun tracking.

Environmental advantages

Solar ovens are just one part of the alternative energy picture, but one that is accessible to a great majority of people. A reliable solar oven can be built from everyday materials in just a few hours or purchased ready made.
Solar ovens can be used to prepare anything that can be made in a conventional oven or stove—from baked bread to steamed vegetables to roasted meat. Solar ovens allow you to do it all, without contributing to global warming or heating up the kitchen and placing additional demands on cooling systems. Nearly 75 percent of US households prepare at least one hot meal per day; one-third prepare two or more. Some of those meals could be made in an environmentally responsible way, using a solar oven.

The World Health Organization reports that cooking with fuel wood is the equivalent of smoking two packs of cigarettes a day. Inhalation of smoke from cooking fires causes respiratory diseases and death. One of the solutions advocated to address this problem is solar cooking which makes no smoke at all. It just uses free and abundant solar energy.