Comparison of hydro-pumped and green hydrogen as energy storage processes: A case study on Kefalonia Island, Greece

The present research work investigates the performance of two large-scale energy storage technologies: hydro-pumped storage (HPS) and green hydrogen production, within a hybrid renewable energy system (HRES) developed for Kefalonia Island, Greece. Given the island's seasonal water and electricity shortages driven by summer demand and limited infrastructure, the goal is to identify which storage option better supports local autonomy. Two scenarios, differing only in storage method, were simulated using identical wind input and desalination setup. Performance was evaluated based on climate and demand data, focusing on water and electricity needs. Both scenarios achieved 99.9 % potable water coverage. The HPS system exhibited notably higher energy efficiency (67 %) compared to hydrogen (33 %), and produced slightly more desalinated water, reaching 18,157,791 m 3 versus 17,986,544 m 3 respectively. Electricity demand coverage reached 77.8 % with HPS and 76.0 % with hydrogen, while irrigation demand was met by 80.2 % and 79.4 %, respectively. Seasonal storage analysis revealed pronounced summer depletion in both cases due to high demand and low wind availability, with HPS recovering faster and maintaining higher storage levels owing to lower energy losses. The comparison underscores the need for storage strategies adapted to island-specific water and energy dynamics. HPS is more efficient for short-to-medium-term needs, while green hydrogen offers potential for long-duration storage and deeper decarbonization. • Novel hybrid renewable system comparing hydro-pumped and green hydrogen storage. • Hydro-pumped storage achieved 67 % energy efficiency vs 33 % for hydrogen. • Potable water coverage reached 99.9 % in both storage scenarios. • Hydro-pumped storage covered 80.2 % of irrigation and 77.8 % of electricity demand. • 250,232 MWh/year produced from 19 wind turbines integrated with desalination.