Hybrid hydrogen energy storage systems are increasingly considered for renewable integration in rural and weak-grid contexts, yet much of the literature remains simulation-based, site-specific, or insufficiently explicit about control and operational performance. This paper examines a hybrid hydro–PV–battery–hydrogen system operated at the Agkistron Living Lab in Northern Greece and assesses the role of layered storage in renewable surplus valorization and resilience-oriented operation. This study combines a system architecture description, a supervisory energy management strategy based on Hybrid Automata, and analysis of field data under both grid-connected and intentional off-grid conditions. The installation integrates hydropower, photovoltaics, battery storage, alkaline electrolysis, hydrogen storage, and PEMFCs. The results show that during on-grid operation, the EMS prioritizes battery charging and then hydrogen production, enabling high renewable utilization and low curtailment while preparing reserves for outages. During a 48 h intentional islanding event, the battery and hydrogen pathway operated sequentially, achieving an autonomy index of 82%, compared with 36% for the battery-only benchmark. Although the hydrogen pathway showed lower round-trip efficiency than battery-only storage, it substantially extended off-grid autonomy and continuity of supply. The findings support hybrid battery–hydrogen storage as a transferable operating concept for rural systems where renewable surplus and resilience requirements coexist.
Kafetzis et al. (2026) studied this question.