New York Times: Where nightfall once meant only darkness in the tiny Tanzanian island of Tumbatu, now there are 200 points of light. And Majuba Mohammed, a high school teacher, is the proud owner of one of them. He is talking excitedly by cellphone about the tiny solar panel on his roof that now charges that phone, and powers the lamp that lets his family read indoors at night. "The project is very beautiful and helpful, and it goes well,“ says Mohammed. Nearly 200 solar panels like his have …