Ralph Sims began his career in Sustainable Energy at Massey University, New Zealand in 1971 making and testing biodiesel from animal fats. After 4 years based at the IEA (International Energy Agency) in Paris (2006-2009) as a senior analyst working on renewable energy and climate change mitigation, he returned to his position of Professor of Sustainable Energy, and Director, Centre for Energy Research. He has had numerous post-graduate students and produced many international reports on on energy and climate. Having "retired", he is now Emeritus Professor.
He consulted for the OECD on energy and rural development, for 7 years was a member of the Science and Technical Advisory Panel of the Global Environment Facility (GEF) of the World Bank, wrote policy sections of REN21 Global Status Reports, researched on distributed energy systems with a 2019 report for UNFCCC, was a Fellow of the Institute of Professional Engineers and of the UK Institute of Agricultural Engineers, a Companion of the Royal Society of New Zealand and received the 2010 Outstanding Achievement Award from the NZ Energy Efficiency and Conservation Authority (EECA) of which he was a ministerial Board Member appointee for 3 terms. For the IPCC he has led chapter teams covering Energy Supply (2007), Renewable Energy Integration (2011), Transport (2014) and is currently Review Editor for the forthcoming 6th Assessment Report, Mitigation.