Young Kennedy is astonished. His face lights up in the single room in the straw-thatched house. So does the book he is reading with his friend, Nellie. The two excited nine-year-olds from the village of Gumbi in western Malawi have just done what about 600 million others in sub-Saharan Africa have never been able to do – switch on an electric light in their homes to read a book in the dark. There is a…