Around 1870, another Frenchman named Augustin Mouchot designed a box / oven heat trap and concave mirrors to create a solar oven, a solar still, a solar pump and ultimately the first solar steam engine. He saw great commercial potential for this invention in the sun-rich, fuel-poor French colonies of North Africa and Asia.
In the mid-1940s, Dr. Charles G. Abbot, secretary of the American Smithsonian Institution, was the first recorded inventor of solar cookers in which the heat collector was outside in the sun but the cooker itself was inside a house, with heat transported from the collector to the cooker by circulating oil. A solar boiler pumped hot oil into an insulated tank and the stored heat made it possible to cook in the evening.
Working with the concept of solar cooking comes and goes and the evolution continues. Today, flat panel stoves and parabolic stoves are distributed in many third world countries by various aid agencies. Boiling water and milk pasteurization are two of the main uses of solar cookers. Solar ovens are very capable of boiling water and milk to kill bacteria.
In places where they have a lot of sun and intense sun, solar cookers have their place. In very poor parts of the world where populations are large and compete for any available fuel source, solar cookers can make a big difference.
The biggest disadvantage of a solar cooker is the time it takes to cook a meal. Two hours is about the minimum. For most meat dishes, cooking something like a roast will take six hours or more.