 "Households at lower levels of income and development tend to be at the bottom of the energy ladder, using fuel that is cheap and locally available but not very clean nor efficient.According to the World Health Organization, over three billion people worldwide are at these lower rungs, depending on biomass fuels—crop waste, dung, wood, leaves, etc.—and coal to meet their energy needs.A disproportionate number of these individuals reside in Asia and Africa