Understanding the macro-level trends in energy conversion, including the use of energy forms, efficiency limits for conversion steps and the length of conversion pathways, both historically and as we move to a low-carbon energy future. The methods will involve the acquisition and reconciliation of historical data related to energy conversion steps and technological innovation; calculation of theoretical and practical energy efficiency limits, using exergy analysis; and morphological analysis of energy conversion steps. The expected outcome is a holistic framework for analysing energy forms, conversion efficiencies and pathways, which makes sense of historical trends in energy use and reveals the technology options (and limitations) for transitioning to a net-zero emission society. This project has national and international importance for understanding future energy infrastructure and directing actions towards emissions mitigation options which can make a difference.