How renewable is the global electricity system An assessment of the evolution of renewability between 1900-2050

The global electricity system depends on fossil fuels and other non-renewable energies, not only for the direct use of fuels, but also for the manufacture of the materials required to build the energy infrastructure. The importance of infrastructure will increase due to the large amount of materials needed in renewable energy technologies capable of capturing the free renewable energy available in nature. Based on this context and on the IEA’s Net-Zero Emissions (NZE) scenario, this study applies the novel renewable exergy return on investment (RExROI) metric to assess the evolution of the global electricity system for the 1900-2050’s period. RExROI measures the amount of renewable exergy returned by investing one unit of non-renewable exergy, both as fuel and embodied in the infrastructure materials. The results indicate that from 2027 onwards the RExROI begins to be greater than zero, i.e. the global electricity system becomes renewable. RExROI from this year onwards grows strongly due to the energy transition to reach 7.18 MJ/MJ in 2050, i.e. 7.18 MJ of renewable exergy is captured for each non-renewable MJ invested. However, considering only non- renewable infrastructure due to renewable technologies, the RExROI would increase to 31.75 MJ/MJ. The RExROI concept can be considered as a Renewation Index (RI), applicable to any energy system and even to society as a whole. Thus, societies with a negative RExROI or close to zero are not guaranteed to endure in the long term because they destroy non-renewable resources that will eventually become depleted. Increasing RExROI is therefore of vital importance for the sustainability of any society.