Solar Funnel Cooker

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Last edited: 13 December 2018

The Solar Funnel Cooker is safe and low cost, easy to make, yet very effective in capturing the sun's energy for cooking and pasteurizing water.

In the mid 2000's, Steven Jones woke up to the fact that half of the world's peoples must burn wood or dried dung in order to cook their food. It came as quite a shock to him, especially as he learned of the illnesses caused by breathing smoke day in and day out, and the environmental impacts of deforestation; not to mention the time spent by people (mostly women) gathering sticks and dung to cook their food. And yet, many of these billions of people live near the equator, where sunshine is abundant and free. Ergo...

As a University Professor of Physics with a background in energy usage, Steven set out to develop a means of cooking food and sterilizing water using the free energy of the sun. First, he looked at existing methods.

While studying this problem, Steven thought again and again of the great need for a safe, inexpensive yet effective solar cooker. It finally came to him at Christmastime in the mid 2000's, a sort of hybrid between the parabola and a box cooker. It looks like a large, deep funnel, and incorporates what he believes are the best features of the parabolic cooker and the box cooker.

The first reflector was made at his home out of aluminum foil glued onto cardboard, then this was curved to form a reflective funnel. Steven and his children figured out a way to make a large card-board funnel easily (explained later).

Later, Steven did extensive tests with students (including reflectivity tests) and found that aluminized Mylar was good too, but relatively expensive and rather hard to come by in large sheets. Besides, cardboard is found throughout the world and is inexpensive, and aluminum foil is also easy to come by. And individuals can make their own solar cookers easily, or start a cottage-industry to manufacture them for others.

Prototypes of the Solar Funnel Cooker were tested in Bolivia, and performed well. Brigham Young University submitted a patent application, mainly to ensure that no company would prevent wide distribution of the Solar Funnel Cooker. BYU makes no profit from the invention. Steven later learned that a few people had had a similar idea, but with methods differing from those developed and shown here. Steven has works to disseminate this design so it can be used to capture the free energy of the sun - for camping and for emergencies, yes, but also for every day cooking where electricity is not available and even fuel wood is getting scarce.

How it Works

The reflector is shaped like a giant funnel, and lined with aluminum foil. (Easy to follow instructions will be given soon.) This funnel is rather like the parabolic cooker, except that the sunlight is concentrated along a line (not a point) at the bottom of the funnel. You can put your hand up the bottom of the funnel and feel the sun's heat, but it will not burn you.

Next, paint a jar black on the outside, to collect heat, and place this at the bottom of the funnel. Or one can use a black pot, with a lid. The black vessel gets hot, fast. But not quite hot enough to cook with... We need some way to build up the heat without letting the air cool it. So, I put a cheap plastic bag around the jar -- voila, the solar funnel cooker was born! The plastic bag, available in grocery stores as a "poultry bag", replaces the cumbersome and expensive box and glass lid of the solar box ovens.

Steven tested a bag used for fruits and vegetables, nearly transparent and available free at American grocery stores, that works great. This is stamped "HDPE" for high-density polyethylene on the bag (ordinary polyethylene melts too easily). A block of wood is placed under the jar to help hold the heat in. (Any insulator, such as a hot pad or rope or even sticks, will also work.)

A friend of Steven's who is also a Physics Professor did not believe that he could actually boil water with the thing. Steven showed him that with the "solar funnel cooker," he was able to boil water in Utah in the middle of winter! He laid the funnel on its side since it was winter and pointed a large funnel towards the sun to the south. Steven also had to suspend the black cooking vessel -- rather than placing it on a wooden block. This allows the weaker sun rays to strike the entire surface of the vessel.

Steven thought that a pressure cooker would be great. But the prices in stores were way too high for him. Wait, how about a canning jar? These little beauties are designed to relieve pressure through the lid -- a nice pressure cooker. And cooking time is cut in half for each 10º C we raise the temperature (Professor Lee Hansen, private communication). He used one of his wife's wide-mouth canning jars, spray-painted (flat) black on the outside, and it worked great. Food cooks faster when you use a simple canning jar as a pressure cooker. However, you can also put a black pot in the plastic bag instead if you want. But don't use a sealed container with no pressure release like a mayonnaise jar -- it can break as the steam builds up! (I've done it.)

Reports

• January 2017: Instructions and Analysis of Solar Funnel Cookers - Bernhard Müller

See also

• Windshield Shade Solar Cooker

External links

• Construction plans for the Funnel Cooker (also in French, Portuguese, and Spanish)
• Tests of the Funnel Cooker in 2001