Seasonal Energy Storage via Underground Hydrogen: A Regional-Scale Assessment for Friuli Venezia Giulia (Italy)

ABSTRACTSeasonal and long-duration energy storage is essential for electricity systems with high shares of variable renewable generation. This study evaluates the technical feasibility of seasonal electricity balancing based on underground hydrogen storage (UHS) in the Friuli Venezia Giulia (FVG) region of northeastern Italy. A monthly energy balance model is used to quantify hydrogen storage capacity requirements, storage volumes, and round-trip efficiency constraints, with photovoltaic (PV) surplus electricity serving as the energy input. The electricity-hydrogen-electricity pathway is modeled assuming a literature-based round-trip efficiency of 38.4%, including electrolysis, underground storage, and power reconversion losses. Results show that offsetting a winter electricity deficit of approximately 1.28 TWh requires the seasonal storage of about 5.9 × 108 Nm3 of hydrogen (≈ 53 kt), corresponding to a summer surplus generation of roughly 3.32 TWh. This storage-driven balance implies the installation of approximately 6.8 GWp of PV capacity (≈ 12.3 × 106 panels) and a land occupation of ~42 km2 (≈ 0.5% of the regional area). A ±10% variation in round-trip efficiency results in a ±7.5% change in both storage volume and associated generation capacity. Overall, the results highlight the potential and limitations of hydrogen-based seasonal energy storage, particularly in terms of efficiency losses and infrastructure scale, and provide an order-of-magnitude benchmark for underground hydrogen storage as a long-duration energy storage solution in regions with limited alternative renewable resources.