|Fig. 1: Schematic of a box-style solar cooker.|
Solar cookers are essentially what they sound like, solar-powered contraptions for cooking food. Solar cookers are one of the earliest attempts by humans to harness solar energy for practical purposes. Although not cooking, an early sect of Jews called the Essenes warmed grains on rocks heated by the desert sun and is an early demonstration of harnessing solar power.  The first known constructed solar cooker was the "hot box" style solar cooker created by Horase de Saussure in 1776, which was able to reach temperatures of about 190 degrees Fahrenheit and cook fruits. [1-3] In 1869 Mouchot developed the first parabolic style solar cooker, which was later used by Napoleon III for French colonial troops in Africa. It was also demonstrated at the world Exhibition in Paris by cooking a pound of beef in 20 minutes.  Seven years later (1876) in India, W. Adams developed one of the first mirror, or panel style solar cookers, which could cook vegetables and meat.  These three solar cookers developed within a hundred years of each other remain the basic types of solar cookers, and although the technology has become significantly more complicated, the basic type remains the same today.
Box-style cookers, as mentioned, are the first known solar box cooker, but are also the most commonly used style. In general, they are insulated boxes that have a transparent top and a reflective lid.  Box-style cookers take advantage of three basic ideas. First, when sunlight hits a dark surface, it is partially transformed into infrared radiation, or heat. Secondly, when light hits shiny or reflective surfaces, the light bounces off the surface at particular angles, which can be used to direct sunlight. Finally, transparent materials allow sunlight to pass, but traps heat.  Thus box cookers are generally a box with internal dark surfaces, reflective pieces to direct sunlight into the cooker, and a transparent lid that allows light in, but traps the heat in the box. Today, these box cookers often reach temperatures of about 200 to 300 degrees Fahrenheit. [3,4] One focus of technological improvements are materials, specifically the materials used for the inner box, the insulation layer, and the transparent layer in an attempt to increase the heat absorbed, minimize heat loss, and increase light transparency and heat trapping. 
|Fig. 2: Schematic of a parabolic-style solar cooker.|
The parabolic style solar cookers use parabolic surfaces, or curved mirrors, to concentrate the sunlight to a focal point.  The major advantage of parabolic style cookers is that they tend to be much more efficient, and are able to reach much higher temperatures (400 degrees Fahrenheit) and cook food faster than other types. [2,4,5] However, these advantages often are unable to compete with the major disadvantage that the parabolic style requires frequent adjustment and more instructions for use. [2,4] Parabolic style cookers work because parabolic mirrors focuses the light parallel to its axis to a single point, and thus focusing the heat, but this requires the mirror to be adjusted so that the incident sunlight is parallel to the axis. 
The panel style cooker involves multiple reflectors that are arranged to focus sunlight onto a pot or other device.  The major advantage to panel cookers is that they can be constructed from cheap materials, such as cardboard and aluminum foil, and can be constructed in less than an hour. [5,7] Panel style cookers are often looked at as a mixture of parabolic cookers and box cookers, and have some of the most variation between designs. [1,2,5]
Although there is a lot of variation between designs of solar cookers, in general they all fall under three categories: box, parabolic, and panel. The box style is the most prolific, due to its decent efficiency, ease of use, and price. The parabolic style tends to be more effective, reaching higher temperatures and faster cook times, but is expensive and requires frequent adjustments. The panel style cooker can be very cheap and easy to build, but often are not as effective as the other models.
© Michelle Nii. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 J. M. Radabaugh and B. Root, Heaven's Flame: A Guidebook to Solar Cookers (Home Power, 1998)
 H. P. Garg Advances in Solar Energy Technology: Volume 1: Collection and Storage Systems (Springer, 1987).
 B. P. Kerr, The Expanding World of Solar Box Cookers (Barbara P. Kerr, 1991).
 S. Anwar and B. L. Capehart, eds., Encyclopedia of Energy Engineering and Technology (CRC Press, 2007).
 D. S. Chauhan, Non-Conventional Energy Resources (New Age Intl., 2006).
 A. Williams, How It Works (FQ Books, 2009).
 V. Nelson, Introduction to Renewable Energy (CRC Press, 2011).