A visit to a small hospital in northern Ghana changed Mahama Nyankamawu’s life forever. “It was dark, they had no electricity and the medicines they had had all gone bad,” recalled the 40-year-old, who went to the hospital after a car accident in 2014. The experience inspired Nyankamawu to create Volta, a company that builds solar power projects for health clinics, schools and farms across Ghana. Volta’s customers pay for 25% of the capital costs…