Solar cooker

ΩSolar cookers are devices that heat food using only solar energy.Since they use no fuel and they cost nothing to run, humanitarian organizations are promoting their use worldwide to help slow deforestation and desertification caused by the need for firewood used to cook. Solar cookers are also sometimes used in outdoors cooking, especially in situations where minimal fuel consumption or fire risk are considered highly important.

Types of Solar Cookers

There are many different types of Solar cookers. All solar cookers are based on a small pool of ideas to heat food with the sun's heat and light. The basic principles of solar cookers are:

• Concentrating Sunlight: Some device, usually a mirror, is used to concentrate light and heat from the sun into a small cooking area, making the energy more concentrated and therefore more potent.
• Converting Light to Heat: Any black on the inside of a solar cooker, as well as certain materials for pots, will improve the effectiveness of turning light into heat. A black pan will absorb almost all of the sun's light and turn it into heat, substantially improving the effectiveness of the cooker. Also, the better a pan conducts heat, the faster the oven will work.
• Trapping Heat: Isolating the air inside the cooker from the air outside the cooker makes an important difference. Using a clear solid, like a plastic bag or a glass cover, will allow light to enter, but once the light is absorbed and converted to heat, a plastic bag or glass cover will trap the light inside using the Greenhouse Effect. This makes it possible to reach similar temperatures on cold and windy days as on hot days.

Alone, each of these strategies for heating something with the sun is fairly ineffective, but most solar cookers use two or all three of these strategies in combination to get temperatures sufficient for cooking.

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 conventional oven. However, 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. However, a thick pan that conducts heat slowly (such as Cast Iron) will lose heat at a slower rate, and that combined with the insulation of the oven can be used to keep food warm well into the evening.

Solar Box Cookers

File:Minimum-Solar-Box-Cooker.jpeg

The "Minimum" Solar Box Cooker

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 trays 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 much 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 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.

CooKit

In Ghana, Zouzugu villagers like this woman prevent dracunculiasis and other waterborne diseases by pasteurizing water in CooKits.

Panel solar cookers are the first solar cookers that are truly affordable to the world’s neediest. In 1994, a volunteer group of engineers and solar cooks associated with Solar Cookers International developed and produced the CooKit. Elegant and deceptively simple looking, it is an affordable, effective and convenient solar cooker. It requires a dark, covered pot and one normal plastic bag per day or one high-temperature plastic bag per month. With a few hours of sunshine, the CooKit makes tasty meals for 5-6 people at gentle temperatures, cooking food and preserving nutrients without burning or drying out. Larger families use two or more cookers. The CooKit weighs half a kilogram, folds to the size of a big book for easy transport. CooKits are now produced independently in 25 countries from a wide variety of materials at a wholesale cost of $3-7 US. We expect that the new hand-assembled CooKits will outlast the manufactured CooKits which last for two years. [Adapted from a more extensive article on the CooKit from the Solar Cooking Archive Wiki]

HotPot

The HotPot cooking vessel consists of a dark pot suspended inside a clear pot with a lid

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 tea kettle, Norbulingka, Tibet

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 only need diffused sunlight to work and needs no Sun tracking.

Hybrid solar oven

A hybrid solar oven is a type of solar oven that uses both the regular elements of a solar box cooker as well as a conventional electrical heating element for cloudy days or nighttime cooking. Hybrid solar ovens are therefore more dependable. However, they lack the cost advantages of some other types of solar cookers, and so they have not caught on as much in third world countries.

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.

Trials in Lesotho

Diffusion of innovations theories, discussed in the book of the same name by Everett Rogers, discusses adoption of solar ovens in Lesotho. Although solar ovens were safer and cheaper to use than oil burning ovens, Lesotho women resisted using them. A similar negative conclusion was reached by a reviewer, who after the clouds rolled in had to wait many hours for lunch, and decided to return to conventional ways of cooking ^[1].

Despite these negative test results, agencies such as the Peace Corps have tried to use change agents to influence the women. But these change agents have differed from the women in class and norms and were not effective in spurring change. Researchers have found that the diffusion process works better if the change agent trains a local aide who belongs to local social networks and can better influence locals.

A German man named Michael Hönes has been establishing solar cooking in Lesotho, enabling small groups of women to build up community bakeries using solar ovens [2].

Use in Darfur Refugee Camps

Well over 10,000 solar cookers have been donated to the Iridimi and Touloum refugee camps in Chad by the combined efforts of the Jewish World Watch and Dutch foundation KoZon. This was done so that the Darfuri women wouldn't have to leave the relative safety of the camp to gather firewood, exposing them to a high risk of being raped, kidnapped, or murdered.

See also

• Farrington Daniels
• Solar forge
• Solar furnace
• Solar still
• Solar water disinfection

External links

• The Solar Cooking Archive Wiki
• The Solar Cooking Archive
• Solar Cookers International (NGO)
• Compendium of Solar Cooker Designs - by Dr Ashok Kundapur.
• Sun Ovens
• Solar Ovens
• Solar Cooking
• Cook With the Sun
• Solar Funnel
• Energy Information Administration
• Solar Ovens in Lesotho
• Infinitely large solar furnace
• ^ Solar Oven test review
• Photo of our in earth solar cook
• The Solar Bowl at Auroville
• Hybrid solar oven
• Cornell University ESW Solar Oven Project
• Documentary of Nepal organization FoST promoting Solar Cookers - by Edwin van Gorp.