Cooking for large groups
From Solar Cooking
The basics of the system are like this. One or more very large parabolic reflectors are built next to the kitchen, outside in the bright sun. These reflectors are equipped with motors that cause the reflectors to track the sun and focus the reflected light through a hole in the wall of the kitchen. The powerful beam of focused light is directed onto a reservoir that holds a liquid such as water or vegetable oil, making it very hot. Pipes distribute the heated fluid (in some cases as steam for steaming rice and vegetables) to various cooking stations in the kitchen, where the heat is used to cook food. If several of these large reflectors are used, it seems likely to me that you would need several holes in the wall and several places where the beams of light could heat up the reservoir containing the fluid. These systems are not cheap, and people have to be trained to maintain the reflectors and the equipment for tracking the path of the sun.
Also, as we understand it, Dr. Deepak Gadhia of India is India's leading, or one of her leading, experts on the Scheffler approach.
Sun Ovens International makes a giant solar box cooker with propane back-up, which it markets as a village bakery. I think several hundred of these have been installed in various parts of the world. Some members of Rotary International have formed a project that seems to specialize in buying these cookers to donate to selected villages. The company is called Sun Ovens International, and the giant box cooker is called the "Villager" or Villager Sun Oven. They are large capacity solar cookers. The cost is somewhere around 11 thousand USD.
I can only recall one other solar cooking system that was designed to serve larger sized groups. Like the Scheffler system, the idea was to heat a medium such as water or vegetable oil in a piping system. The oil heated in the pipe by solar energy would be piped indoors where the heat would be utilized at indoor cooking stations or to heat a large oven for baking--if I recall correctly. I only saw photos of the cooker with very little additional information, but my impression was that it was a smaller scale community kitchen operation than the Scheffler system. Instead of a parabolic dish that focuses light into a point, this design used a parabolic trough, which focuses light onto a line. The pipe with the oil in it ran through the cooker right where this focal line was, so that the pipe received powerful amounts of sunlight, and the liquid heat transferring medium inside the pipe would be well heated. The people who developed this idea were based in Lesotho. The website I had for them stopped working several years back, and I am not sure if they are still in the field, but if you want to try contacting them, this is the last information I had:
Ivan Yaholnitsky's broad-based poverty alleviation work includes solar energy uses, like solar cooking. Make 3 sizes of box cookers. Designed/built parabolic trough bread baker--it bakes 10 loaves in 40 minutes.
That line about baking 10 loaves of bread in 40 minutes gives you some sense of the capacity of the cooker.
All three of the above possibilities would represent a substantial investment. If you want to work on a smaller scale, or build up the solar cooking capacity in increments, you would probably have to choose from the more standard types of cookers and acquire several. For example, three or four fairly large solar box cookers would be enough on sunny days in the tropics to cook rice and lentils for 25 children or more. Because there is so little work involved, one cook could operate three or four or five or six box cookers without much of a problem if there is room in a sunny spot for that many cookers. Preparing the food for the cooker would involve much more labor than the actual cooking would require. If local food preferences include breads that require rapid cooking over high heat (such as tortillas, naan bread or injera bread), then you might want to include a parabolic cooker in the mix of cookers acquired. If your groups are larger, you could expand by adding more cookers, and at some point, more cooks.
No matter what system you use, it is essential that the cooks who will use it a) want to learn the new skills, b) receive thorough training and have a source of help if they encounter problems, and c) will be diligent in using their new skills and equipment and in doing the necessary maintenance.
I provided information to allow you to pursue the Scheffler systems, the Villager Sun Oven, and, perhaps, the Solar Soft parabolic trough bakery. If you decide you want to take the more modest approach of using a small fleet of more conventional solar cookers, your possibilities for acquiring the cookers multiplies a lot. So, if you want me to point you to sources of box cookers, parabolic cookers, or build-it-yourself instructions, let me know.
