Chapter 2

An aluminized-mylar Solar Funnel Cooker was also tested in Bolivia, during the Bolivian winter. Water pasteurization temperature was reached in 50 minutes, boiled eggs cooked in 70 minutes, and rice cooked in 75 minutes. The Bolivian people were pleased by the performance. So were we! (La Paz, Bolivia, August, 1996).

I also donated two dozen solar funnel cookers for people in Guatemala. These were taken there by a group of doctors going there for humanitarian service. The people there also liked the idea of cooking with the sun's free energy! For an aluminized-Mylar Solar Funnel Cooker kit, please contact CRM (licensed manufacturer) at +1 (801) 292-9210.

[Image: 10.jpg -- Photo description: This photo shows what looks like the same style of funnel as in the above pictures except that it doesn't look homemade but something produced by a factory. The photo shows something which looks like a machined metal/shiny plastic funnel.]

VII. Water and Milk Pasteurization

Contaminated drinking water or milk kills thousands of people each day, especially children. The Word Health Organization (WHO) reports that 80 percent of illnesses in the world are spread through contaminated water. Studies show that heating water to about 65 degrees to 70 degrees Celsius (150 degrees Fahrenheit) is sufficient to kill coliform bacteria, rotaviruses, enteroviruses and even Giardia. This is called pasteurization.

Pasteurization depends on how hot and how long water is heated. But how do you know if the water got hot enough? You could use a thermometer, but this would add to the cost, of course. When steam leaves the canning jar (with lid on tight) and forms "dew" on the inside of the cooking bag, then the water is probably pasteurized to drink. (The goal is to heat to 160 degrees Fahrenheit for at least six minutes.) With a stripe of black paint scraped off the jar, one can look through the bag and into the jar and see when the water is boiling - then it is safe for sure.

Think of all the lives that can be saved simply by pasteurizing water using a simple Solar Cooker!

VIII. Safety

Safety was my first concern in designing the Solar Funnel Cooker, then came low cost and effectiveness. But any time you have heat you need to take some precautions.

-The cooking vessel (jar) is going to get hot, else the food inside won't cook. Let the jar cool a bit before opening. Handle only with gloves or tongs.

-Always wear dark glasses to protect from the sun's rays. We naturally squint, but sunglasses are important.

-Keep the plastic bag away from children and away from nose and mouth to avoid any possibility of suffocation.

IX. Cooking with the Solar Funnel Cooker

What do you cook in a crock pot or moderate-temperature oven? The same foods will cook about the same in the Solar Funnel Cooker --without burning. The charts below give approximate summer cooking times.

The solar cooker works best when the UV index is 7 or higher. (Sun high overhead, few clouds.)

Cooking times are approximate. Increase cooking times for partly- cloudy days, sun not overhead (e.g., wintertime) or for more than about 3 cups of food in the cooking jar.

Stirring is not necessary for most foods. Food generally will not burn in the solar cooker.

VEGETABLES (Potatoes, carrots, squash, beets, asparagus, etc.) Preparation: No need to add water if fresh. Cut into slices or "logs" to ensure uniform cooking. Corn will cook fine with or without the cob. Cooking Time: About 1.5 hours

CEREALS AND GRAINS (Rice, wheat, barley, oats, millet, etc.) Preparation: Mix 2 parts water to every 1 part grain. Amount may vary according to individual taste. Let soak for a few hours for faster cooking. To ensure uniform cooking, shake jar after 50 minutes. CAUTION: Jar will be hot. Use gloves or cooking pads. Cooking Time: 1.5-2 hours

PASTA AND DEHYDRATED SOUPS Preparation: First heat water to near boiling (50-70 minutes). Then add the pasta or soup mix. Stir or shake, and cook 15 additional minutes. Cooking Time: 65-85 minutes

BEANS Preparation: Let tough or dry beans soak overnight. Place in cooking jar with water. Cooking Time: 2-3 hours

EGGS Preparation: No need to add water. Note: If cooked too long, egg whites may darken, but taste remains the same. Cooking Time: 1-1.5 hours, depending on desired yolk firmness.

MEATS (Chicken, beef, and fish) Preparation: No need to add water. Longer cooking makes the meat more tender. Cooking Time: Chicken: 1.5 hours cut up or 2.5 hours whole; Beef: 1.5 hours cut up or 2.5-3 hours for larger cuts; Fish: 1-1.5 hours

BAKING Preparation: Times vary based on amount of dough. Cooking Times: Breads: 1-1.5 hours; Biscuits: 1-1.5 hours; Cookies: 1 hour

ROASTED NUTS (Peanuts, almonds, pumpkin seed, etc.) Preparation: Place in jar. A little vegetable oil may be added if desired. Cooking Time: About 1.5 hours

MRE's AND PREPACKAGED FOODS Preparation: For foods in dark containers, simply place the Container in the cooking bag in place of the black cooking jar. Cooking Times: Cooking time varies with the amount of food and darkness of package.

X. How to Use the Solar Funnel as a Refrigerator/Cooler

A university student (Jamie Winterton) and I were the first to demonstrate that the BYU Solar Funnel Cooker can be used--at night --as a refrigerator. Here is how this is done.

The Solar Funnel Cooker is set-up just as you would during sun-light hours, with two exceptions:

1. The funnel is directed at the dark night sky. It should not "see" any buildings or even trees. (The thermal radiation from walls, trees, or even clouds will diminish the cooling effect.).

2. It helps to place 2 (two) bags around the jar instead of just one, with air spaces between the bags and between the inner bag and the jar. HDPE and ordinary polyethylene bags work well, since polyethylene is nearly transparent to infrared radiation, allowing it to escape into the "heat sink" of the dark sky.

During the day, the sun's rays are reflected onto the cooking vessel which becomes hot quickly. At night, heat from the vessel is radiated outward, towards empty space, which is very cold indeed (a "heat sink").

As a result, the cooking vessel now becomes a small refrigerator. We routinely achieve cooling of about 29 degrees Fahrenheit (10 degrees Celsius) below ambient air temperature using this remarkably simple scheme.

In September 1999, we placed two funnels out in the evening, with double-bagged jars inside. One jar was on a block of wood and the other was suspended in the funnel using fishing line. The temperature that evening (in Provo, Utah) was 78 degrees Fahrenheit. Using a Radio Shack indoor/outdoor thermometer, a BYU student (Colter Paulson) measured the temperature inside the funnel and outside in the open air. He found that the temperature of the air inside the funnel dropped quickly by about 15 degrees, as its heat was radiated upwards in the clear sky. That night, the minimum outdoor air temperature measured was 47.5 degrees--but the water in both jars had ICE. I invite others to try this, and please let me know if you get ice at 55 or even 60 degrees outside air temperature (minimum at night). A black PVC container may work even better than a black-painted jar, since PVC is a good infrared radiator--these matters are still being studied.

I would like to see the "Funnel Refrigerator" tried in desert climates, especially where freezing temperatures are rarely reached. It should be possible in this way to cheaply make ice for Hutus in Rwanda and for aborigines in Australia, without using any electricity or other modern "tricks." We are in effect bringing some of the cold of space to a little corner on earth. Please let me know how this works for you.

XI. Conclusion: Why We Need Solar Cookers

The BYU Funnel Cooker/Cooler can:

-Cook food without the need for electricity or wood or petroleum or other fuels.

-Pasteurize water for safe drinking, preventing many diseases.

-Save trees and other resources.

-Avoid air pollution and breathing smoke while cooking.

-Use the sun's free energy. A renewable energy source.

-Cook food with little or no stirring, without burning.

-Kill insects in grains.

-Dehydrate fruits, etc.

-Serve as a refrigerator at night, to cool even freeze water.

(Try that without electricity or fuels!)

The burden for gathering the fuel wood and cooking falls mainly on women and children. Joseph Kiai reports from Dadaab, Kenya: "Women who can't afford to buy wood start at 4 am to go collecting and return about noon... They do this twice a week to get fuel for cooking... The rapes are averaging one per week." From Belize: "Many times the women have to go into the forest dragging their small children when they go to look for wood. It is a special hardship for pregnant and nursing mothers to chop and drag trees back to the village... they are exposed to venomous snakes and clouds of mosquitoes." (Anna K.) (Quoted by Solar Cookers International from a newsletter.)

And the forests are dwindling in many areas. Edwin Dobbs noted in Audubon Magazine, Nov. 1992, "The world can choose sunlight or further deforestation, solar cooking or widespread starvation..."

Americans should be prepared for emergencies, incident to power failures. A Mormon pioneer noted in her journal: "We were now following in their trail traveling up the Platte River. Timber was sometimes very scarce and hard to get. We managed to do our cooking with what little we could gather up..." (Eliza R. Snow) Now there's someone who needed a light-weight Solar Cooker!

Here's another reason to use a solar cooker. Many people in developing countries look to see what's being done in America. I'm told that if Americans are using something, then they will want to try it, too. The more people there are cooking with the others will want to join in. A good way to spread this technology is to encourage small local industries or families to make these simple yet reliable solar cookers for others at low cost. I've used this cooker for three summers and I enjoy it. Cooking and making ice with the funnel cooker/cooler will permit a significant change in lifestyle. If you think about it, this could help a lot of people. The BYU Solar Funnel Cooker uses the glorious sunshine -- and the energy of the sun is a free gift from God for all to use!

XII. Answers to commonly-asked questions

Will the cooker work in winter (in the United States)?

As the sun moves closer to the southern horizon in the winter, the solar cooker is naturally less effective. A good measure of the solar intensity is the "UV index" which is often reported with the weather. When the ultraviolet or UV index is 7 or above--common in summer months--the solar cooker works very well. In Salt Lake City in October, the UV index was reported to be 3.5 on a sunny day. We were able to boil water in the Solar Funnel Cooker during this time, but we had to suspend the black jar in the funnel so that sunlight struck all sides. (We ran a fishing line under the screw-on lid, and looped the fishing line over a rod above the funnel. As usual, a plastic bag was placed around the jar, and this was closed at the top to let the fishing line out for suspending the jar.)

The solar "minimum" for the northern hemisphere occurs on winter solstice, about December 21st each year. The solar "maximum" occurs six months later, June 21st. Solar cooking works best from about March 20 to October 1 in the north. If people try to cook with the sun for the first time outside of this time window, they should not be discouraged. Try again when the sun is more directly overhead. (One may also suspend the jar in the funnel, which will make cooking faster any time of the year.)

It is interesting to note that most developing countries are located near the equator where the sun is nearly directly overhead all the time. Solar Cookers will then serve year-round, as long as the sun is shining, for these fortunate people. They may be the first to apply fusion energy (of the sun) on a large scale! And they may accomplish this without the expensive infrastructure of electrical power grids that we take for granted in America.

How do you cook bread in a jar?

I have cooked bread by simply putting dough in the bottom of the jar and placing it in the funnel in the usual way. Rising and baking took place inside the jar in about an hour (during summer). One should put vegetable oil inside the jar before cooking to make removal of the bread easier. I would also suggest that using a 2-quart wide-mouth canning jar instead of a 1-quart jar would make baking a loaf of bread easier.

What is the optimum "opening angle" for the funnel cooker?

A graduate student at Brigham Young University did a calculus calculation over two years ago to assess the best shape or opening angle for the Solar Funnel. Jeannette Lawler assumed that the best operation would occur when the sun's rays bounced no more than once before hitting the cooking jar, while keeping the opening angle as large as possible to admit more sunlight. (Some sunlight is lost each time the light reflects from the shiny surface. If the sunlight misses on the first bounce, it can bounce again and again until being absorbed by the black bottle.) She set up an approximate equation for this situation, took the calculus- derivative with respect to the opening angle and set the derivative equal to zero. Optimizing in this way, she found that the optimum opening angle is about 45 degrees, when the funnel is pointed directly towards the sun.

But we don't want to have to "track the sun" by turning the funnel every few minutes. The sun moves (apparently) 360 degrees in 24 hours, or about 15 degrees per hour. So we finally chose a 60-degree opening angle so that the cooker is effective for about 1.2 hours. This turned out to be long enough to cook most vegetables, breads, boil water, etc. with the Solar Funnel Cooker. We also used a laser pointer to simulate sun rays entering the funnel at different angles, and found that the 60-degree cone was quite effective in concentrating the rays at the bottom of the funnel where the cooking jar sits.

XIII. Recipe for wheatpaste

Prepare 1 cup (2.4 dl) of very hot water. Make a thin mixture of 3 tablespoons (45 ml) of white flour and cold water. Pour the cold mixture slowly into the hot water while stirring constantly. Bring to a boil. When it thickens, allow to cool. Smear on like any other glue. For slightly better strength, add 1 tablespoon (15 ml) of sugar after the glue is thickened. After using a portion, reheat the remaining in a covered jar or container to sterilize it for storage or keep refrigerated. If wheat flour is not available, other flours will work.

XIV. Updates [compiled by transcribists]

Rabbit-wire base

In later experiments Steven E. Jones and Christopher McMillan of Brigham Young University tested different bases for the cooking pot used in the Solar Funnel, published on the web in the article "Tests of the Solar Funnel and Bowl Cookers in 2001. According to Jones, the rabbit-wire stand they tested has proven to be much better than the wooden block detailed in this article.

"We found immediately that raising the vessel off the bottom of the cooker using a rabbit-wire stand provided more rapid and even heating than the wooden block used previously. Placing the jar or pot on a wire stand allows as much reflected light onto the cooking vessel as possible. This allows even the bottom of the cooking container to absorb thermal energy that is reflected off the lower portion of the funnel."

[Image: 11.jpg -- Photo Description: This photo shows two different sized cylinders, made of rabbit wire -- fencing material for rabbits, made of crossed wires tacked together, so to make a single sheet. A black pot is being lowered into the cylinders, and will come to rest on a wire cross, inside the cylinder, made from wires going from one side of the cylinder to the other.]

Reduced angle

The original report describes a large solar funnel, having a 60-degree opening angle. Our ongoing experiments show that a reduced angle of approximately 45 degrees allows about 10% faster solar cooking. Such a funnel is shown in the photograph. Start with the funnel described in the original report, then simply bring the sides A and B together with a 20-cm overlap at the top of the funnel. This makes a funnel with steeper sides.

Save-heat cooker (a retained heat cooker for canning jars heated using the sun or fire)

The photograph shows the Save-Heat Cooker which we have designed and built. The box is made from a polystyrene cube, 30 cm on a side. We have drilled 4 holes each about 10 cm in diameter into this block, so that each holds a canning jar. Then a lid fits over the top to hold in the heat.

When a jar is placed in the solar funnel cooker, a maximum temperature of about 110 degrees C is reached in approximately 45 minutes (depending on solar conditions). Then steam is released around the rim of the canning jar, which becomes an inexpensive pressure cooker. But the jar will not get hotter, so one takes the jar out of the cooker (with a gloved hand) and places it into the Save-Heat box. Our experiments show that the temperature drops slowly in this box, about 5 degrees C per hour, so that cooking continues for 4 hours or so, without a heat source. In this way, one can prepare up to four quarts of food per Save-Heat Cooker at mid-day, and have the food cooked and hot for the evening meal! Or, if desired, the food will keep in the box overnight and be ready for eating the next morning. Thus, a solar cooker can supply food for mid-day, evening and the next morning, as desired. (Another design of the Save-Heat Cooker holds up to seven quart-sized canning jars.)

The Save-Heat Cooker is particularly useful for foods such as beans which take a long time to cook. Food heated using a wood fire could likewise be placed in a jar, and then this jar placed in the Save-Heat Box, in order to save fuel-wood consumption, and cooking time and effort. The box can be cheaply molded out of polystyrene or styrofoam or other material, so long as it is a good insulator and capable of withstanding temperatures of around 110 degrees centigrade.

Funnel-cooling during the day

We noted in the original report that the funnel works as a cooler at night, by reflecting heat out of the canning jar and up to the cold sky. We have found that this works during the day also, when the funnel is pointed to a region of the sky away from the sun (and buildings, etc.). We found cooling of about 12 degrees F., compared with about 20 degrees cooling at night. To achieve this, the jar was placed on a rabbit-wire support as described above, and housed in two cheap, clear polyethylene bags, such as used for vegetables in the United States.

Hot-and-cold running water.

By placing a large funnel around a water barrel, it will be solar-heated during the day, or cooled at night. Thus, having two barrels each with a funnel-like reflector around it, and covering one when not sunny and the other whenever it is sunny, one can have hot and cold water. These barrels could be placed on a platform or roof to provide hot-and-cold running water!

Conclusion

We are hopeful that these developments will help many people, especially those in areas of the world where electricity or even wood or gas are in short supply, if available at all. These ideas are offered freely to all.

Prof. Steven E. Jones, Colter Paulson, Jason Chesley, Will Shakespeare and Jacob Fugal.

For questions regarding the complete Solar Funnel Cooker kit using aluminized Mylar and a jar for the cooking vessel, please contact CRM at +1 (801) 292-9210.

Recent updates to this project can be found at http://physics1.byu.edu/jones/rel491/solarbowl.htm.