In 2002, teenaged William Kamkwamba had a vision in the very poor African nation of Malawi: A little bicycle generator that powers a light, if connected to a windmill, could allow him to read his schoolbooks at night. As he went further with his plans, he began to see how such a windmill might actually bring the 20th century to his own village. Out this week is “The Boy Who Harnessed the Wind,” a book that tells Kamkwamba’s story. We talked with William Kamkwamba and Bryan Mealer, the book’s co-authors.