Research topics

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Last edited: 30 December 2011

Whether you're planning a science project or are just a solar cooking enthusiast, the Solar Cookers International Network (SCInet) wants you to know that your research can help extend the world's knowledge of solar cooking and be of great help to people around the world. You should be aware that it's easy to build a high-performance solar cooker if you have access to modern materials. However, the more than a billion poor people in the world, who could really benefit from having a solar cooker, don't have access to such materials. This means that your research will be most useful if it concentrates on the simplification of cooker design or on the use of low-tech, local materials.

Here are some ideas for areas of research. We will post your findings on this page if you let us know what you found out. We are also interested in adding new areas of research to this list. Please edit this page to add your results or to pose new questions.

General Cooker Features / Improvements Needed

• Better means of heat storage, longer cooking after sunset
• More efficient usage of space
• Going longer without needing to be turned (largely a matter of cooker geometry)
• Water resistance, general durability

General topics

In-the-ground solar cookers

Instead of building a cooker out of scarce materials that needs to hold its shape above ground in the wind and weather, might it be better to dig a hole in the ground of a certain shape that could act as the solar cooker? A Space Blanket or other reflective tarp could line the hole and a dark pot inside a plastic bag would be placed inside the hole. Possibly the plastic bag could be replaced by a clear plastic tarp over the top of the entire hole.

See In-the-ground solar cooker designs.

What is the simplest way to indicate that pasteurization temperature has been reached?

Throughout the world it is mistakenly believed that unsafe water needs to be boiled for 20 minutes to make it safe to drink. Bacteriological tests in the field have confirmed that it is only necessary to bring the water to 65° C (149° F) to make it safe to drink (see: Water pasteurization). It is easy to see when water is boiling so no temperature measurement in needed. However, it is not easy to see when water gets to 65° C. What is needed is a simple method that is available to poor people around the world to indicate when this temperature has been reached.

• Solar Cookers International has designed the Water Pasteurization Indicator (WAPI) for this purpose, but this design makes use of a high-tech wax to indicate temperature.
• Tom Sponheim suggests that you can simply take boiling water and mix it with a given quantity of cold water. As long as the mix is correct, then the water will still be above the water pasteurization temperature and will thus be safe to drink. See Boil 3, Add 1 Method.
• It might be possible to use beeswax to indicate this temperature in place of the wax used in the WAPI.
• Matthew Collier has adapted an idea by Galileo here.
• A document explaining various methods to make thermometers from simple materials is here.
• Philip Guest has this suggestion: Woods metal is an alloy of Bi (50%), Pd (25%), Sn (12.5%), and Cd ( 12,5%). This has a melting point of 346° Kelvin, (70°C). Sounds complex, but a lot of modern golf club drivers contain the alloy for its mass, encapsulated in a strong sealed vile it should be safe, e.g. Pyrex. Recycle those clubs, find an ethical manufacturer, and were away, costs should be small, and can be started in most developed countries. Logistic problems, storage and distribution but this could be coordinated. A test tube and a bung could suffice.
• Philip Guest had another suggestion: Methanol boils at 65°C. One could design a vial that is dynamically unstable so that it would fall over if the methanol in it goes above its boiling point.
• William Nix suggests a Thermometer using egg yolk to indicate temperature.

Could you use solar energy to melt together shredded plastic bottles to make a waterproof panel that could be used to construct a CooKit or other solar cooker?

• This might be easily done with some plastics but not others. What type of plastic bottle is in mind? Does it have to be shredded or can it be cut into a few larger pieces? If polyethylene, polycarbonate, PMMA, or polypropylene, this should be easy. Polystyrene, on the contrary, gives off the worst smell imaginable when hot, and has a fairly difficult-to-reach melting point of 240^oC. Unfortunately, polyethylene terephthalate is even worse, and many plastic bottles are made of it. A basic design for melting "good" plastic could be the Solar Pocket.

• SolarCycle has developed a technology to convert waste plastic bags into panels that are then lined with reflective material from the inside of potato chip bags.

Could fiber optic cables be used to transfer the power of the sun to a cooker inside the house?

The main issue is a means to transfer heat to inside the house-or to a conivinient distance/place. A different approach woud to use of a heat pipe. A heatpipe is an efficient heat transfer device with no maintenanace. A standard one for the temperatures we are dealing with (for cooking) would consist of a copper tube with water as the transfer media. This are readily from several manufactures.

Box Cookers

How does a sheet of plastic film (like an oven cooking bag) compare with a sheet of glass for the glazing? Does a double sheet of plastic film equal a single sheet of glass? Do windy conditions effect plastic film more than glass?

• Here are the findings of Ajit Kumar N Shukla.

• It should be mentioned that most oven cooking bags are substantially less transparent than that. As a rule, if things look noticeably dimmer, foggy or off-colored when viewing through 2-3 layers of the plastic, it is not good. Plexiglass works, if it will not go above 120^oC (248^oF). For many other types of solar cookers, such as panel cookers, oven cookings bags work reasonably well.

How does cooking in a clear jar compare with cooking in a jar that has been painted black?

• Michael Michalowicz found that painting the jar black increased efficiency by 6%.

• Arthur Stamey-Mills performed a side-by-side test where he heated water in a black pot and in a clear pot. The black pot heated the water to a temperature that was 18% higher than in the clear pot.

How can you make a dark paint that poor people around the world can make using simple materials (ash, egg white, sap, wheat paste, etc.).

• Shannon Cox suggests blackening the outside of the pots over a fire. She has aluminum army mess kits and they turned black the first time she used them cooking over a fire. We are aware that this can work. It would be nice to know how long this takes and if there are ways of quickening the process.

• Håkon Kjernli writes, "As a kid, I read an advice for blackening metal: dip it in linen seed oil and hold it into a fire. The oil burns and leaves a solid black color, similar to what you get on an old open-fire cooking pan. I guess any kind of oil or fat will do the job. Do this a few times and as I recall, you should have a very durable black coating which does not insulate or crack. I have not tried it for 30 years, but I will the next time I sit by a fire with a piece of metal and some fat or oil nearby."

How could a simple mechanism be designed that would automatically turn the cooker after a few hours?

Main article: Solar tracking

Should the walls inside the cooker be foiled to reflect the light, or should they be painted black?

• Ethan discovered in his science project that an empty oven with shiny walls and a steel plate on the bottom got 8% hotter than the others he tried.

• A Minimum Solar Box Cooker without foil but with a white surface was able to pasteurize water at 47°N latitude.

How can you waterproof cardboard (beeswax, oil, etc.)?

• One participant found that using gelatin worked very well to water-proof cardboard.

Panel Cookers

Is it possible to create a pot assembly with a dark inner pot, a clear outer pot, and a vacuum in between

Using this configuration, the sunlight would be able to enter, but the heat would be stopped from escaping by the vacuum. This could greatly improve cooking efficiency. For information on this, watch this video.

Does it help to raise the pot off the ground? If so, what should you use to lift it? Should the lifters be place inside the plastic bag or outside?

Dr. Steven Jones found that raising the pot on a wire frame improved cooking greatly.

How should you arrange it so multiple pots could be used (stacking, side-by-side, etc.)?

• Ravindra Pardeshi sent the results of his testing and it is posted here.

Does the bag have to go all the way around the pot, or could it fitted with a frame to keep it open and just be lowered over the pot like a dome?

A more Durable Solar Cooker for Desert Refugee Camps

With millions of people forced by drought, famine and war into desert refugee and displaced person camps, the need for a cheap, durable solar cooker that will allow people to cook with sunlight during the day and save their scarce wood for use at night and on cloudy days, has become urgent and critical. This video outlines the durability issues of current solar cookers used in desert refugee camps and shows some of the research that has been conducted by volunteers around the world. Funding is needed to move this effort forward and help these women and children who must walk miles to find wood, but have easy access to abundant, free sunlight for cooking and boiling water.

Other needs

1. Unbreakable lightweight metal pressure vessel, similar to glass “canning” jars
2. Vessels designed for use with parabolic concentrators, including shapes, surfaces and glazing.
3. Inexpensive durable high performance reflective materials. Example: metalized Mylar®.
4. Develop a long-lasting bag for the CooKit and other panel cookers.

Out-of-the-box topics

Using fiber optic cables to transmit solar energy to a solar cooker located inside a structure

• Harvey Sherback writes that a hybrid solar lighting system that has been under development may be modifiable to power an indoor solar cooker. The present design consists of an exterior concentrating collector which focuses sunlight into fiber optic cables which then distribute it to light fixtures throughout a building. The present design purposefully strips away the UV and IR components of the sunlight because they add heat not light. If this system was re-engineered, it may be feasible to operate a solar cooker inside the building. Video clip here of hybrid solar lighting system

See also

• Conference papers