Energy demand in the twenty-first century will be driven by the needs of three billion people in the emerging world and three billion new inhabitants to our planet. To provide them with a renewable and sustainable energy supply is perhaps the greatest challenge for science in the twenty-first century. The science practiced to meet the energy needs of the twentieth century responded to a society of wealth, and energy systems were designed to be large and centralized. However, the inability of the emerging world to incur large capital costs suggests that a new science must be undertaken, one that does not rely on economy of scale but rather sets as its target highly manufacturable and distributed energy systems that are affordable to the poor. Only in this way can science provide global society with its most direct solution for a sustainable and carbon-neutral energy future.