Introduction to solar cooking

Last edited: 7 July 2024

Solar_Cooking_in_Africa_-_A_Remarkable_Technology_Transfer

Below you will find an introduction to solar cooking. The Solar Cooking Wiki also provides an individual page for 146 different countries where you will find news, NGOs, manufacturers, and individuals working on solar cooking projects in that country. Links to possible funders are also available:

Depending on where you live and how you cook, solar cooking can save you time, effort, and fuel. It is also an environmentally friendly and fun way to prepare your meals. All foods can be cooked in some type of solar cooker.

Cooking with a solar box cooker or solar panel cooker is similar to using a slow cooker (crock-pot). Typically, cooking times for these types of cookers are twice that of conventional cooking methods, however, slower cooking also has its advantages. These cookers provide a moderate, even heat, are only reoriented once towards the sun over several hours of cooking, and the food does not have to be stirred during cooking. This frees the cook up to do other useful tasks while the food cooks independently.

Parabolic solar cookers offer another approach to solar cooking by being able to reach higher temperatures and perform more like a traditional stovetop. As such, they require more attention while cooking to avoid burning the food and they need to be turned periodically to follow the sun, depending on cooking time.

For areas in the world experiencing deforestation and limited access to clean water, solar cooking is a valuable part of the solution, by providing a safe, smoke-free alternative method of cooking and pasteurizing water.

Buy or build a solar cooker?

The CooKit is an example of a simple solar panel cooker, probably best suited to locations close to the equator

If you are interested in trying solar cooking for the first time, you may be wondering whether you should build your own solar cooker, or to buy one from a manufacturer. There are advantages to both options:

Building your own solar cooker can be a fun and cost-effective way to get started.
A wide variety of solar cookers are available for purchase, and you will often receive a higher-quality cooker than one you might build yourself.

If you would like to build a cooker, visit the build a solar cooker page to choose a design that's right for you. You will find information there comparing the characteristics of each style of cooker.

If you would like to purchase a cooker, check out the list of manufacturers and vendors on the buy a solar cooker page. Commercial cookers are typically durable and efficient, and offer an easy way for new users to experience solar cooking. As cookers are manufactured globally, consider potential shipping costs when selecting a design.

How do solar cookers work?

Solar cookers work on this basic principle: Sunlight is converted to heat energy, that is retained for cooking.

Many solar panel cookers and solar box cookers are capable of reaching 150 °C (302 °F), or higher. The captured solar radiation passes through a greenhouse enclosure enclosing a dark colored cook pot. As it hits the dark surface, the solar radiation is converted to heat, which is contained within the glazing enclosure, and cooking temperatures are achieved. The same principle is often experienced by drivers returning to a hot car that has been parked in the sun.

Visible light is converted to heat, and reradiated as longer wavelength infra-red light. These longer wavelengths have difficulty passing back through glass or other greenhouse materials, and are relfected back at the cook pot and other black surfaces within the cooking chamber. The efficiency of these cookers is typically determined by the amount of reflector area available of the solar cooker to gather sunlight, and the ability of the greenhouse enclosure to receive the available light and help insulate the hot cook pot. Double Pyrex bowls have been shown to work well as greenhouse enclosures for solar panel cookers. See: Glazing for additional enclosure ideas.

	Fuel: Sunlight Sunlight is the fuel. A solar cooker needs an outdoor spot that is sunny for several hours and protected from strong wind, and where food will be safe. Solar cookers don't work at night or on cloudy days.
Convert sunlight to heat energy Dark surfaces get very hot in sunlight, whereas light surfaces don't. Cooking is typically best done with dark, shallow, thin metal pots with dark lids to hold in heat and moisture. The thin metal cook pots heat up quickly, but thicker pots will retain heat longer and should be preheated before adding the food.
Retain heat A transparent heat trap around the dark pot lets in sunlight, but keeps in the heat. This is a clear, heat-resistant plastic bag or large inverted glass bowl (panel cookers) or an insulated box with a glass or plastic window (box cookers).
Capture extra sunlight One or more shiny surfaces reflect extra sunlight onto the pot, increasing its cooking potential.

Parabolic solar cookers use a bowl shaped reflector to focus the light directly onto the cook pot, usually from below. Typically they do not require a greenhouse enclosure to retain the heat. They reach much higher temperatures than the other styles of solar cookers, usually above 200 °C (392 °F), and also have the ability to fry and broil foods.

SolSource Solar Stove with Cookware — SolSource is an example of a parabolic solar cooker shown with cookware. The light is focused at the bottom of the cook pot.

Industrial scale cooking, Solare Brucke, 6-10-15 — Institutional solar cooking can employ many large parabolic reflectors to generate steam, and cook for thousands of people daily. A number of these systems are in use in India. This example, was built with technology from Solare Brücke.

Main article: How solar cookers work

Solar cooker types

The three most common types of solar thermal cookers are box cookers, panel cookers, and parabolic cookers. Hundreds — if not thousands — of variations on these basic types exist. Evacuated tube cookers and trough cookers are two lesser known styles of cooker design. The two approaches are often combined, as the geometry of each is suited to the other. Additionally, several large scale solar cooking systems have been developed to meet the needs of cooking for lerge numbers of people.

Box cookers

Solar box cookers typically cook food at temperatures between 90 °C (194 °F) and 200 °C (392 °F). They can often accommodate multiple pots, and usually take between one and three hours to cook various foods. The sides and bottom are insulated to retain cooking heat. Worldwide, they are the most widespread. There are several hundred thousand in India alone.

Main article: Solar box cooker designs

Panel cookers

Panel cookers incorporate elements of box and parabolic cookers. They often have a large reflector area and the cook pot has some form of clear enclosure to retain heat. Panel cookers are capable of cooking at approximately 170 °C (338 °F). They are the easiest style to make and relatively inexpensive to buy.

Main article: Solar panel cooker designs

Parabolic cookers

The AlSol 1.4 parabolic cooker demonstrates how the cook pot is supported to receive the focused light from below from the reflector.

Parabolic solar cookers use a bowl shaped reflector to focus the light directly onto the cook pot, usually from below, and typically do not require a greenhouse enclosure to retain the heat. The parabolic name refers to the shape of the curve of the reflector cross-section.

They require more frequent reorientation to the sun, possibly every fifteen minutes, but they cook food more quickly at higher temperatures compared to other solar cookers, often reaching temperatures over 200 °C (392 °F). They also have the ability to fry and broil foods. Generally parabolic solar cookers will need to be attended to more than box or panel cookers to avoid possibly burning the food at the bottom of the cook pot. They are especially useful for large-scale institutional solar cooking systems.

Main article: Parabolic solar cooker designs

Trough cookers

Early GoSun cooker, 2-29-16 — The GoSun is an example of a trough solar cooker that also uses an evacuated tube cooking chamber.

For capturing sunlight, trough solar cookers use a reflector with a curved parabolic cross-section, that continues as a straight trough in the other direction. Instead of focusing the light at one spot like a typical bowl-shaped parabolic solar cooker, the light is reflected along what is known as a focal line. These reflectors are easier to fabricate than a parabolic dish, but require a long fairly narrow cooking tray, which is why they work well with evacuated tube enclosures.

Main article: Trough solar cooker designs

Evacuated tube cookers

SLiCK SM70 photo, 8-19-15 — The SLiCK SM70 is an example of an evacuated tube style solar cooker.

Evacuated tube literally means that the cooking chamber is constructed of two layers of blown glass in the shape of a sealed tube, where the air has been removed between the layers.

Heat loss often happens by conduction through a medium or by and convection through the air. With no air between the layers of glass, the chamber is nicely insulated, and well suited for retaining cooking heat. The chamber is so effective at insulating it often does not require a large reflector to capture sunlight. A slender cooking tray can be inserted from one end. The opposite end is either sealed with a stopper, or has been sealed during the manufacturing process. Improvements in glass technology is allowing for larger diameter tubes to be fabricated, which will allow larger cooking trays to be inserted inside.

Main article: Evacuated tube solar cooker designs

Other types

Beyond performance ratings

Various methods of testing are available to evaluate the performance of solar cookers. Solar Cookers International responded to requests from cooks, manufacturers, and organizations to create an objective, scientific process to evaluate the cooking potential of different cookers, and developed the Performance Evaluation Process (PEP). A number of solar cookers have been tested with this method, and can be seen at PEP tested solar cookers.

Beyond cooking performance, other factors should be considered when designing, purchasing, or building a solar cooker.

Cost: The cost of all supplies needed for the solar cooker - including estimated replacement parts needed within five years, compared to the cost of alternative cooking methods and the fuel used in them over five years. Also to consider: Environmental benefits of solar cooking
Convenience: The cooker either needs little or no attention during cooking or, the instructions address how often adjustments are needed during a cooking period (for example with parabolic cookers, frequent turning to track the sun or stirring to prevent burning). If movable, is the cooker easy to move and easy to store? What is required to check on the cooking food, and remove it from the cooker when done?
Safety: The cooker should be incapable of starting an accidental fire inside or outside the cooker. A warning included that the reflectors remain at ambient temperature, but the cook pots become quite hot. In the case of concentrator cookers, warn of risk for accidentally damaging eyes or burning hands at the focal point. Modern designs usually incorporate a deep parabolic reflector to avoid these types of accidents. See also: Health benefits of solar cooking
Cooking capacity: Can the cooker prepare a meal for at least a small family, and/or specify size of family it is intended to cook for? In some cultures it may be important for the cooker accommodate a variety of covered pots and pans to prepare the local cuisine.
Durability, maintenance: Repairs should be infrequent, and/or possible to do without special equipment, with replacement parts readily available or easily made DIY. Instructions included for ordinary maintenance or repair as needed (such as wiping off dust from windows and reflective surfaces). Information should indicate expected durability under various weather conditions, and/or guides for protecting it when weather may damage it.
Wind stability: The cooker should be reasonably stable in wind to avoid spilling food, or should include instructions to easily make it so (for example; tie-downs or placing rocks in specified places).
Instructions: Clear guides for estimated length of cooking time and variables that influence cooking time (food quantity, wind, etc.) See: Guidelines and cooking tips

Using your solar cooker

The golden rule for solar cooking is get your food on early, and do not worry about overcooking. Most people starting to solar cook will be using a solar panel cooker or solar box cooker. These cookers are oriented to the sun and typically don't need to be turned to follow the sun during a 2-4 hour cooking period, though cooking time can be shortened if the cooker is turned.

Once you have decided on a cooker, you will need to find appropriate cookware. Thin-walled dark enameled metal cook pots work well. They are good at heating up quickly. Glass jars can also be used, either clear or preferably painted on the outside. Please note that all cooking vessels need to have a lid, but not be completely sealed to avoid steam pressure build-up. Pots that reflect light, such as silver aluminum pots, will not work as well. Paint these first.

When using a solar panel cooker the pot is normally placed inside some sort of clear glass or plastic enclosure to retain heat and make use of the greenhouse effect.

Main article: Guidelines and cooking tips

Introductory manuals

Solar Cookers: How to Make, Use, and Enjoy (There are also detailed versions in Arabic (Standard, Variation), French, Spanish, and English for Kenya, and Galician.)

Solar Cookers-How to Make, Use, and Enjoy

Construction of solar cookers and driers - Christelle Souriau & David Amelin (This is an excellent overview of solar cooking basics and simple solar cooker and dryer construction methods.)

Solar orientation, Construction of solar cookers and driers, Souriau & Amelin, 6-9-15 — Solar orientation, Construction of solar cookers and driers, *Souriau & Amelin*

Learn more

Audio and video

November 2020:

Virtual_Café_Sci-_DARE_to_Solar_Cook_-_The_Physics_of_Cooking_with_Sunshine — Virtual Café Sci- DARE to Solar Cook - The Physics of Cooking with Sunshine

DARE to Solar Cook - The Physics of Cooking with Sunshine - *Dr. Alan Bigelow, Mary Buchenic, and Jennifer Gasser*

June 2015:

Star_Tides_4_Solar_Cookers — Star Tides 4 Solar Cookers

Our last series on the STAR-TIDES expo in Washington, DC continues with technology available for emergency crisis and disaster relief. VOA’s Carolyn Turner talked with Solar Cookers International about their exhibit displaying how to cook with only the sun - *Voice of America*

External links

The Expanding World of Solar Box Cookers - Barbara Kerr (This is the full-text of the book by this solar cooking pioneer)
Construction of solar cookers and driers - Christelle Souriau & David Amelin (This is an excellent overview of solar cooking basics and simple solar cooker and dryer construction methods.)
Three part series by Sharon Cousins on practical, humanitarian, and environmental aspects and potential uses for solar cooking: Solar Cooking: Clean, Bright and Accessible, Out of the Smoke, Into the Sun, and Cleaner Cooking, Healthier Planet