Erasmus Wambua, a schoolboy, left, studies at home using a book illuminated by a single electric LED lightbulb, powered by M-Kopa solar technology, in Ndela village, Machakos county, in Kenya, on Wednesday, July 22, 2015. Customers agree to pay for the solar panel with regular instalments which M-Kopa, a Nairobi-based provider of solar-lighting systems, then monitors for payments that are made using a mobile-phone money-transfer service. Photographer: Waldo Swiegers/Bloomberg via Getty Images