When famine struck William Kamkwamba’s village in Malawi, he had to quit school. Determined to improve his family’s life, he pored over science books in the library. After learning about windmills, the 14-year-old boy built one out of scraps of junk, bringing electricity to his home. Kamkwamba, now a student at Dartmouth College, teamed up with journalist Bryan Mealer to tell his story in “The Boy Who Harnessed the Wind,’’ published in 2009. Now the co-authors have collaborated with artist Elizabeth Zunon on a powerful, gorgeously illustrated children’s book, published by Penguin, with the same title.