Forced to drop out of school at age 14 because his family could no longer afford tuition, William Kamkwamba of Malawi set out to study energy and build windmills on his own. “Energy poverty” limits development, economies and jobs in the world’s poorest nations, explains Sarah Childress for the Wall Street Journal. Kamkwamba, now 20, built his windmill, by lashing blue-gum tree trunks together for...