This report describes what is meant by the "energy deficit," which represents a barrier to inclusive growth and poverty reduction. Without major changes to the way people access and use energy, almost one billion people will still be without electricity in 2030, according to the authors. The report traces the common features of some of the most promising disruptive technologies and business solutions that have the potential to deliver socio-economic, health and environmental benefits at scale—decentralized energy solutions that provide safe, reliable and affordable power to low-income consumers in under-served areas.