Solar cooker

Principles

1) Concentrating sunlight: A mirrored surface with high specular reflectivity is used to concentrate light from the sun on a small cooking area. Depending on the geometry of the surface, sunlight can be concentrated by several orders of magnitude. For most household solar cooking applications, such high temperatures are not really required. Solar cooking products, thus, are typically designed to achieve temperatures of 150 ° F (65 ° C) (baking temperatures) to 750 ° F (400 ° C) (grilling / searing temperatures) on a sunny day.

2) Converting light energy to heat energy: Solar cookers concentrate sunlight onto a receiver such as a cooking pan. The interaction between the light energy and the receiver material converts light to heat. This conversion is maximized by using materials Pots and pans used on solar cookers should be matte black in color to maximize absorption.

3) Trapping heat energy: It is important to reduce convection by isolating the air inside the cooker from outside the cooker. Simply using a glass lid is Enhances your pot light absorption from the top of the pan and Provides a greenhouse effect That Improves heat retention and Minimizes Convection loss . This “glazing” transmits incoming visible sunlight but is opaque to escaping infrared thermal radiation. In resource constrained settings, a high-temperature plastic bag can be used for a similar function, trapping air inside and making it possible to reach temperatures on cold and hot days.

Operation

Different types of solar cookers are used, but most follow the same basic principles.

Food is prepared as if for an oven or stove top. However, because food cooks are more expensive, it is usually smaller than it is otherwise. ^[3] For example, potatoes are usually cut into bite-sized pieces rather than roasted whole. ^[4] For very simple cooking, such as melting butter or cheese , may not be needed and the food may be placed on an uncovered tray or in a bowl. If several foods are to be cooked separately, then they are placed in different containers.

The container of food is placed inside the solar cooker, which can be elevated on a brick , rock, metal trivet , or other heat sink , and the solar cooker is placed in direct sunlight. ^[3] Foods that cook can be added to the solar cooker later. Rice for a mid-day meal may be started early in the morning, with vegetables, cheese, or in the middle of the morning. Depending on the size of the solar cooker and the number of cooked foods, a family may use one or more solar cookers.

A solar oven is turned towards the sun and left until the food is cooked. Controlling a stove or a stove, it can not be controlled, it can not be controlled escape and thereby slows the cooking process. If wanted, the solar oven May be checked every one to two hours, to turn the oven to face the sun more PRECISELY and to Ensure That shadows from nearby buildings or plants-have not blocked the sunlight . If the food is to be left untended for many times during the day, then the solar oven is in the process of becoming more efficient. ^[5]

The cooking time depends primarily on the equipment being used, the amount of sunlight at the time, and the quantity of food that needs to be cooked. Air temperature , wind, and latitude also affect performance. Food cooks faster in the two hours before and after the local solar noonthan it does in the early morning or late afternoon. Large quantities of food, and food in large pieces, take longer to cook. As a result, only general figures can be given for cooking time. With a small solar panel cooker, it may be possible to melt butter in 15 minutes, to bake cookies in 2 hours, and to cook rice for four people in 4 hours. With a high performance parabolic solar cooker, you can be able to grill a steak in minutes. However, depending on the local conditions and the solar cooker type, these projects could take a long time.

It is difficult to burn food in a solar cooker. ^[4] Food that has been cooked even though it is usually indistinguishable from minimally cooked food. The exception to this rule is some green vegetables, which quickly changes from a perfectly cooked bright green to an olive drab , while still retaining the desirable texture.

For most foods, such as rice, the typical person would be unable to tell the truth. There are some differences, however: Bread and cakes brown on their tops instead of on the bottom. Compared to cooking over a fire, the food does not have a smoky flavor.

Box and Panel designs

A box cooker has a transparent glass or plastic top, and it may have additional reflectors to concentrate sunlight into the box. The top can usually be removed to allow dark pots containing food to be placed inside. One or more reflectors of shiny metal or foil-lined material may be to the bounce extra light into the interior of the oven chamber. Cooking containers and the bottom of the cooker should be dark-colored or black. 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 box should have insulated sides. Thermal insulationfor the solar box cooker must be able to withstand temperatures up to 150 ° C (300 ° F) without melting or out-gassing. Crumpled newspaper, wool, rags, dry grass, sheets of cardboard, etc. can be used to insulate the walls of the cooker. Metal pots and / or bottom trays can be darkened with flat-black paint spray (one that is non-toxic when warmed), black tempera paint, or soot from a fire. The solar box cooker typically has a temperature of 150 ° C (300 ° F). This is not a hot oven, but still hot enough to cook food over a somewhat longer period of time.

Panel solar cookers are inexpensive solar cookers that use reflective panels to direct sunlight to a cooking pot that is enclosed in a clear plastic bag.

Solar Oven science experiments are regularly done in high schools and colleges, such as “Solar Oven Throwdown” at the University of Arizona . ^[6] These projects are able to achieve high temperatures and high temperatures using mathematical models.

Parabolic reflectors

Parabolic solar cookers concentrate sunlight to a single point. When this point is focused on the bottom of a pot, it can heat the pot quickly to the temperatures that can be compared with the temperatures achieved in gas and charcoal grills. These types of solar cookers are widely used in several regions of the world, most notably in China and where most of the time is spent cooking and cooking. Some parabolic solar cooker projects in China abate between 1-4 tones of carbon dioxide per year and receive carbon credits through the Clean Development Mechanism (CDM) and Gold Standard .

Some parabolic solar cookers with cutting edge materials and designs which lead to solar energy efficiencies> 90%. Others are large enough to feed thousands of people each day, such as the Auroville in India, which makes 2 meals per day for 1,000 people. ^[7]

If a reflector is axially symmetrical and shaped, its cross-section is a parabola , it has the property of bringing parallel rays of light (such as sunlight) to a point focus . If the axis of symmetry is aimed at the sun, it is located at the focus of the sunlight, and becomes very hot. This is the basis for the use of this kind of reflector for solar cooking.

Paraboloidal reflectors

Paraboloids are compound curves , qui are more difficulties to make with a simple equipment than single curves . Although paraboloidal solar cookers can cook more or less than a conventional stove, they are difficult to construct by hand. Frequently, these reflectors are made up of many small segments that are all

Although paraboloids are difficult to make, they can be made quite simply by rotating open-topped containers which hold liquids. The top surface of a liquid which is being rotated at a constant speed around a vertical axis of a naturally occurring paraboloid. Centrifugal force causes material to move outward of the axis of rotation until a deep enough depression is formed in the surface for the force to be balanced by the levelling effect of gravity . It turns out that the depression is an exact paraboloid. (See Liquid mirror telescope .) If the material solidifies while it is rotating, the paraboloidal shape is maintained after the rotation stops, and can be used to make a reflector. ^{[citation needed ]}This technical Sometimes rotation is used to make paraboloidal mirrors for astronomical telescopes, and HAS aussi beens used for solar cookers. Devices for constructing such paraboloids are known asrotating furnaces.

Paraboloidal reflectors generate high temperatures and cook quickly. Several hundred thousand exist, mainly in China . ^{[ citation needed ]} They are particularly useful for individual household and large-scale institutional cooking.

A Scheffler cooker (named after its inventor, Wolfgang Scheffler ) uses a large ideally paraboloidal reflector which is rotated around an axis that is parallel to the earth’s using a mechanical mechanism, turning at 15 degrees per hour to compensate for earth’s rotation. The axis passes through the reflector’s center of mass, allowing the reflector to be easily. The cooking vessel is located on the axis of rotation, so the mirror concentrates sunlight onto it all day. The mirror has to be compared with a perpendicular axis to compensate for the seasonal variation in the sun’s declination. This perpendicular axis does not pass through the cooking vessel. Therefore, if the reflector were a rigid paraboloid, its focus would not remain stationary at the cooking vessel as the reflector tilts. To keep the focus stationary, the reflector’s shape has to vary. It remains paraboloidal, but its focal length and other parameters change as it tilts. The Scheffler reflector is therefore flexible, and can be bent to adjust its shape. It is often made up of a large number of small sections, such as glass mirrors, joined together by flexible plastic. A framework that supports the reflector includes a mechanism that can be used appropriately. The mirror is never exactly paraboloidal, but it is always close enough for cooking purposes. ^{[ quote needed ]}

Sometimes the rotating reflector is located outdoors and the sunlight passes through an indoor kitchen, often a large communal one, where cooking is done. ^{[ quote needed ]}

Paraboloidal reflectors that have their centers of mass coincident with their focal points are useful. They are able to turn to the sun’s motions in the sky. Two perpendicular axes can be used, intersecting the focus, to allow the paraboloid to follow both the sun’s daily motion and its seasonal one. The cooking pot stays stationary at the focus. If the paraboloidal reflector is axially symmetrical and is made of material of its thickness, its center of mass coincides with its focus if the depth of the reflector, measured along its axis of symmetry from the vertex to the plane of the rim, is 1.8478 times its focal length. The radius of the rim is 2.7187 times the focal length. The angular radius of the rim, as seen from the focal point, is 72.^{[ quote needed ]}

Parabolic troughs

Parabolic troughs are used for sunlight for solar-energy purposes. Some solar cookers have been built that use them in the same way. ^{[ citation needed ]} Generally, the trough is aligned with its horizontal and east-west focal line. The food to be cooked along this line. The trough is pointed to its axis of symmetry at the sun at noon. This requires the trough to be tilted up and down as the seasons progress. At the equinoxes, no movement of the trough is needed during the day to track the sun. ^[9]At other times of year, there is a period of noon when no tracking is needed. Usually, the cooker is used only during this period. This simplicity makes the design attractive, compared with using a paraboloid. Also, being a single curve , the trough is simpler to construct. However, it suffers from lower efficiency.

It is possible to use two parabolic troughs, curved in perpendicular directions, to bring a paraboloidal reflector. ^{[ citation needed ]} The incoming light strikes one of the troughs, which sends it to a line focus. The second trough intercepts the converging light and focuses on a point. ^{[ quote needed ]}

Compared with a single paraboloid, using two partial troughs has important advantages. Each trough is a single curve , which can be made simply by bending a flat sheet of metal. Also, the light that reaches the target of cooking, which reduces the risk of damage to the eyes of anyone nearby. On the other hand, there are disadvantages. More mirror material is needed, increasing the cost, and the light is reflected by two surfaces instead of one, which inevitably increases the amount that is lost.

The two troughs are held in a fixed orientation relative to each other by being both fixed to a frame. ^{[ citation needed ]} The whole assembly of frames and troughs has been moved to the sky. Commercially made cookers that use this method are available.In practical applications (like in car-headlights), concave mirrors are of parabolic shape

Spherical reflectors

Spherical reflectors operate much like paraboloidal reflectors, such that the axis of symmetry is pointed towards the sun so that it is concentrated to a focus. However, the focus of a spherical reflector will be limited because it suffers from a known spherical aberration . Some concentrating dishes (such as satellite dishes) that do not require a specific focus for a spherical curvature over a paraboloid. If the radius of the rim of spherical reflector is small compared with the radius of curvature of its surface (the radius of the sphere of the sphere of the reflector is a part), the reflector approximates a paraboloidal one with focal length equal to half of the radius of curvature. ^[10]

Vacuum Tube Technology

Evacuated tube solar cookers are essentially a vacuum sealed between two layers of glass. The vacuum allows the tube to act both as a “super” greenhouse and an insulator. The central cooking tube is made from borosilicate glass, which is resistant to thermal shock, and has a vacuum beneath the surface to insulate the interior. The inside of the tube is lined with copper, stainless steel, and aluminum nitrile to better absorb and conduct heat from the sun’s rays. Some vacuum tube solar cookers allow lightweight designs such as those of the GoSun range. ^[11]Portable vacuum tube cookers such as the GoSun allow users to cook a freshly caught fish on the beach. ^[12]

Advantages and disadvantages

advantages

• High-performance parabolic solar cookers can reach temperatures above 290 ° C (550 ° F). They can be used to grill meats, stir-fry vegetables, make soup, bake bread, and boil water in minutes.
• Conventional solar box cookers installed temperatures up to 165 ° C (325 ° F). They can sterilize water or prepare for a meal.
• Solar cookers use no fuel. This saves cost as a result of environmental damage caused by fuel use. Since 2.5 billion people cook on open fires using biomass fuels, solar cookers could have reduced economic and environmental benefits by reducing deforestation. ^[13]
• When solar cookers are used outside, they do not contribute inside heat, Any type of cooking can evaporate grease, oil, and other material into the air, so there may be less cleanup.

Disadvantages

• Solar cookers are more useful in the cloudy world (where the sun is low in the sky or below the horizon), so an alternative cooking source is still required in these conditions. Solar cooking advocates suggests three devices for an integrated cooking solution: a) a solar cooker; b) fuel-efficient cookstove ; c) an insulated storage container such as Very hot food can continue to cook for hours in a well-insulated container. With this three-part solution, the oil is minimized while still providing hot meals at any hour, reliably.
• Some solar cookers, especially solar ovens, take a long time to cook a conventional stove or oven. Using solar cookers may require food preparation. However, it requires less hands-on time during cooking, so it is often considered a reasonable trade-off.
• Cooks may need to learn special cooking techniques to fry common foods, such as fried eggs or flatbreads like chapatis and tortillas . It may not be possible to safely or completely cook such foods, such as large roasts , loaves of bread, or pots of soup , particularly in small panel cookers; the cook may need to divide these into smaller portions before cooking.
• Some solar cooker designs are affected by strong winds, which can slow the cooking process, cool the food due to convective losses, and disturb the reflector. It may be necessary to anchor the reflector, such as with string and weighted objects like bricks.

Projects

Cardboard, foil foil, and solar collectors have been donated to the refugee camp and Touloum refugee camps in Chad by the combined efforts of the Jewish World Watch , the Dutch KozonFoundation , and Solar Cookers International . The refugees construct the cookers themselves, using the donated supplies and locally purchased Arabic gum . ^[14] It has also become more prevalent than ever before, with the result that they are more likely to grow up for their families and make handicrafts for export. ^[14] By 2007, the Jewish World Watchhad trained 4,500 women and had provided 10,000 solar cookers to refugees. The project has also reduced the number of attacks by as much as 70 percent, thus reducing the number of attacks. ^{[ quote needed ]}

Some Gazans have started to make solar cookers. About 40 to 45 Palestinian households reportedly started using these solar cookers. ^[15] , including some made with mirrors.

Bysanivaripalle, a silk-producing town That Is 125 km (78 mi) northwest of Tirupati in the Indian state of in Andhra Pradesh , is the first of icts kind: an Entire Village That uses only solar cooking.

Thousands of parabolic solar cookers produced by One Earth Designs are used on the Himalayan Plateau in China to reduce dependence on biomass fuel like wood and yak dung. ^[16]

See also

References