I´ve spent the past several weeks designing a couple versions of a retained heat cooker (RHC) -- an inexpensive device that cooks food by retaining the heat that has been stored in the food after boiling it for a very short period of time. Essentially it´s just an insulated and sealed box or bag or basket. It takes up to twice as long to cook some foods, like beans or whole potatoes, but no fuel is consumed during the cooking process, the food can´t be burned by an inattentive cook, the kids can´t burn their hands on the pot or the fire, and the cook can leave the kitchen and go do something productive while the food is cooking.
The first RHC that I designed was for the women´s club, where they cook for 120 people every day. It´s a big plywood box in two parts, with 4 inches of styrofoam walls and a reflective plastic lining. It had to be rugged to survive daily use with pots of food weighing more than 100 pounds. Last week I installed it and trained them to use it. They´re now using it daily to cook about 40 pounds of rice. After bringing the rice to a boil for 5 minutes, they lift the pot into the RHC (luckily, it's a pot with four handles, because it takes more than two people to lift it!) They leave it for two hours, and the rice is done. At that time it´s still at 199 degrees F, so it stays nice and hot even if the rest of the meal isn´t ready for another hour or more. The women say that the rice is more evenly cooked than when they cook it over the gas stove. They proudly show off their new tool to all of the customers who come to buy their meals.
Several of the women and some of my neighbors asked me to design a smaller version for use in their homes, so I´ve built a much cheaper version from just styrofoam slabs and a plastic liner. The cost of materials is about $8, so someone could earn a living making a couple of them each day and selling them for $12 each.