This working paper provides an overview of current data sources for off-grid renewable energy systems. The authors suggest methodological improvements to help categorize such systems, evaluate and aggregate data and measure progress in deployment. The aim of the paper is to identify key methodological challenges for data collection and analysis of the current status of off-grid renewable energy systems. The authors list these challenges and propose some definitions and classifications to improve data collection. The paper also provides a global overview of available data organized by country and statistical resources. It concludes with several steps to improve methodology development and data collection in the future.