The ingeniously simple design uses two cardboard boxes, one inside the other, and an acrylic cover that lets in the sun's rays and traps them.

Black paint on the inner box, and silver foil on the outer one, help concentrate the heat. The trapped rays make the inside hot enough to cook casseroles, bake bread and boil water.

What the box also does is eliminate the need in developing countries for rural residents to cut down trees for firewood. About 3 billion people around the world do so, adding to deforestation and, in turn, global warming.

By allowing users to boil water, the simple device could also potentially save the millions of children who die from drinking unclean water.

Bohmer's invention on Thursday won the FT Climate Change Challenge, which sought to find and publicize the most innovative and practical solution to climate change.

"A lot of scientists are working on ways to send people to Mars. I was looking for something a little more grassroots, a little simpler," Bohmer said Thursday.

Bohmer, a Norwegian-born entrepreneur based in Kenya, said he also had been looking at solutions "way too complex, for way too long."