The World Bank has sought to advance the diffusion of solar photovoltaic (PV) technology for off-grid applications in the developing world. As these systems are fundamentally different to centralised power stations and conventional rural electrification, the World Bank has been learning how best to lend for such technology. This study seeks to highlight the lessons learnt from the World Bank＇s first loans for off-grid PV to India, Indonesia, and Sri Lanka. It uses lifetime cost analysis to justify continued intervention in this sector, and it draws on theories of innovation diffusion to guide analysis and ultimately policy recommendations. Because of the special role of entrepreneurial start up companies in the rural PV sector, the paper also uses a company cash flow model to demonstrate the efficacy of various supply-side policies. Finally, the study concludes with a checklist of policy lessons and a consideration of the role of the International Finance Corporation in this sector.