Techno-economic analysis of inter-annual energy storage and overcapacity in 100 % renewable energy systems for 145 regions globally

In this study, a comprehensive analysis of inter-annual storage requirements for 100% renewable energy systems is presented for the world, structured in 145 regions. This research provides the first global assessment of solar and wind resources on multiple sectors, including power, heat, transport, and desalination. Inter-annual storage options include hydrogen, methane, and liquid fuels. Using high-resolution weather data from NASA from 1984 to 2005, storage requirements, overcapacity for renewable electricity generation, and economic implications across different regions are analysed. The results reveal substantial regional variations in storage requirements, with hydrogen re-electrification systems showing the widest range of storage needs across different global regions. Cost analyses for two scenarios are presented to minimise either curtailment or cost. The study reveals that optimal storage solutions are highly region and demand-specific, challenging the one-size-fits-all approach often assumed in energy system planning. The curtailment-optimised scenario requires 1.4% overcapacity in wind and solar photovoltaics electricity generation, complemented by significant storage capacity of 417.4 TWh_H2,LHV, 0.8 TWh_CH4,LHV, and 4.2 TWh_th,LHV of hydrogen, methane, and liquid fuels, respectively, adding an on demand-weighted average of 103.1% to the baseline cost of a 100% renewable energy system in 2050. In contrast, the cost-optimised scenario requires 5.0% generation overcapacity with no additional inter-annual storage, increasing costs by 3.3%. This core finding reveals that increasing the overcapacity is a significantly more impactful and economically viable pathway than a primary reliance on building large-scale storage. These findings provide crucial insights for policymakers and system planners working towards the resilience of 100% renewable energy systems.