The Features and Qualities Necessary for the Acceptance, Manufacture and Distribution of Large Quantities of Solar Cookers.

by Richard C. Wareham, 10/1/99

Past successes and failures are the keys to establishing a format for a successful solar cooker program and to determine the ideal features of a solar cooker.  There is no question that solar cookers work -- hundreds of different designs and models have cooked for years in many countries.  By reviewing these programs and designs answers can be found to build the "best" unit and to develop the best format for a successful solar cooker program.

The largest solar cooker programs were developed and subsidized by the governments of China and India.  Smaller programs have been and are still being operated by various charities, service organizations, NGO's, etc.  There is one common thread in most of these projects -- the solar cookers have been either given away or heavily subsidized.  When the sponsor stopped funding, the program stopped or stalled.  Also, most commercial manufacturing of solar cookers has been discontinued due to financial losses.

Point one.  Solar cookers must be profitable for a business or self-supporting for a non-profit organization to be manufactured on a permanent basis.

When selling a solar cooker to a potential user the first question asked is:  "What does it cost?"  A good, low price cooker isn't the everything, it is the only thing.   Since the mass market for solar cookers is the poor in underdeveloped countries, time payment programs for the user and initial consignments or support for the local distributors are necessary.  Governments and sponsors are needed to supply this initial support.  NGO's, service organizations and religious groups are needed to use, approve and demonstrate the cooker.  However, the most successful distributors have been farmer coops and businesses who have displayed the unit and sold it for a profit.

Point two.  The price of a quality solar cooker must be as low as possible and must include a profit for the seller. 

 "What will it cook?" is the next question.  In Africa the average person eats one Kg of food per day.  The basic food is cornmeal with a vegetable side dish.  Families of five or more are common, therefore a unit should large enough to cook five or more Kg in two to four hours.  Areas with 4kw/sq. meter per day of solar energy are the most successful for solar cooking.

Point three.  A large cooker is desirable but the size will be limited by the cost and weight.  Cost increases faster than size.  The cooker must be light weight so that one person can move it, adjust it or hang it in his/her home.

 "How do I use it?" is also asked.   This varies with the type of solar cooker.  Parabolic cookers require almost continuous adjustment.  Cookers with four external reflectors require frequent focusing to reach their high temperatures.  Box cookers should be adjusted every hour.  Panel cookers require the least adjustment but they collect and retain the least solar energy.  Continuous attention is difficult since most people have other work or demands on their time.

Point four.  The cooker must be user friendly, i.e. require the minimum attention and adjustment.

Other features for an acceptable, successful solar cooker are:  l.  Good quality and long life.  2.  Rugged enough to withstand the frequent handling. 3.  Easily cleaned.  4.  Economical and easy to ship even for a short distance.  The cookers should stack or nest so that it can be moved and easily stored by the user or selling organization.

POINT FIVE.   The final and most important condition for a successful program is:  The solar cooker must be built in the country where it is used and the materials must be locally available (preferably made in that country).

The market and the greatest need for solar cookers occur in underdeveloped countries who have limited domestic materials and few manufacturing facilities.  Most countries in the world do not have extruders, molders, laminators, etc. and they do not manufacture cardboard, sheet metal, plywood, aluminum foil, Fiberglas, mineral wool, felt, widow glass and plastic sheet, film or bags.  These materials and the other items must be purchased from overseas companies with "hard" currency.  The cost of materials, freight and duties make importing solar cookers or the materials to build them, expensive and difficult. 

There are some exceptions where the market, materials and manufacturing facilities are available to mold or fabricate almost any solar cooker in the same country, i.e., the SUNSTOVE® is molded and assembled in South Africa and Calcutta, India.  It had been hoped that these non-profit groups could supply the neighboring countries.  However, for eight (8) years the SUNSTOVE Organization has tried to export.  Some success was achieved where Rands or Dollars were available but because of "hard currency" requirements, import duties, and freight costs, exports to most of their neighbors had limited success.

For the vast majority of countries the answer is to use local materials to produce a solar cooker of reasonable quality.  Materials normally available in all countries are scrap aluminum off-set (lithograph) printing plates for the reflectors, exterior and interior; scrap textile cuttings, wool, cotton, hemp, jute, sisal, carpet, rug, blanket, etc. for insulation;  and wood for a frame.  The glass, plastic sheet or film used for the solar window are not normally manufactured locally but are commonly stocked.  If scrap is available, use it.

A fabricated "SUNSTOVE®" has been manufactured for seven (7) years with these local materials by Mazahua Mission in Mexico.  However, this unit and the molded units in India and South Africa require metal pots.  Pots add to the cost of the unit.  When it is necessary to import the pots they are expensive. 

As a companion for the fabricated SUNSTOVE® a new design, the "SunPan", was developed specifically for those countries with limited materials, facilities and expensive pots.

The "SunPan" solar cooker and its pans (pots) are designed to be built with the local materials by a domestic manufacturer.   The amazing aluminum, lithograph printing plate seems destined to be the solar cooker's best friend.  Rectangular pans (pots) and the solar cooker can be hand fabricated from these plates.  The cost of scrap printing plates is about $1.25 per kilogram.  Four 2.5 liter pans, designed to hold and cook 1 Kg of food each, can be cut from a one kilogram printing plate.  The total cost of the materials for the "SunPan" solar cooker (including the pans) is less than $10.00.  This unit can be a profitable cottage industry.  Manufacturing only requires hand tools: i.e., hammer, saw, screwdriver, paint brush, hand riveter and tin snipes plus nails, rivets, screws and black paint.  The "SunPan" can be mass-produced on a manual production line.

Lithograph printing plates are available in every country at the government printing office, the local printer or the local newspaper.  Used printing plates are sold as scrap.  In semi-developed and developed countries these aluminum plates are available in almost any quantity.  All of our data and drawings for the "SunPan" solar cooker are based on the Heidelberg #102 printing press plate, 770mm x 1030mm, which is common throughout the world.  Printing plate sizes from other presses can be used but may have to be riveted together or trimmed to size.  All printing plates must be cleaned on one side for reflection and to be suitable to touch food.  Do not clean the side away from the sun or food -- the ink makes a good primer for those areas you want to paint: i.e., the lids (tops) of the cooking pans.

We at the SUNSTOVE Organization are available to assist you in designing a cooker using these materials.  The molded "SUNSTOVE®' can be purchased fob Johannesburg or Calcutta----copy it and mold your own.  Your local international shipping agent must make all financial and shipping arrangements since the non-profit groups in these countries do not have export or shipping departments and cannot finance other potential manufacturers.  The metric drawings to hand fabricate the "SunPan" are on this Web site.  The design and name are free for all to copy and use.  Use the registered name, "SunPan", when manufacturing and selling the "hometown solar cooker" to identify this solar cooker construction and design.

Good luck on your projects.

Tip of the day.  When using any solar cooker, place it next to a brick, adobe or concrete  wall that faces the Sun at noon.  The wall will give some protection from the wind, reflect solar energy to the cooker and absorb (store) solar energy.  All of these will improve your cooker's performance.

Sunstove Organization is a Section 21 non-profit organization (Reg. No. 93/03638/00) devoted to the dissemination of information that will improve the living conditions of the poor.  All inquiries and suggestions may be directed to: info@SunGravity.com.