One third of the world's population depends on diminishing supplies of firewood to cook their food. This is not sustainable. It leads to deforestation, which leads to less oxygen and more global warming. It also cuts into quality family time as women have to spend time searching for the firewood.
Most of these people do not have safe drinking water.
With solar cookers, there wouldn't be the need to cut down trees, and there could be more quality family time. It would also pasteurize the water. Solar cookers can be provided inexpensively ($25 per family) by Solar Cookers International.