Towards Sustainable Energy Independence: A Case Study of Green Hydrogen as Seasonal Storage Integration in a Small Island

Tilos, a Greek island in the Mediterranean Sea, hosts a pioneering hybrid energy system combining an 800-kW wind turbine and a 160-kWp photovoltaic (PV) field. The predominance of wind power makes the energy production of the island almost constant during the year, while the consumption peaks in summer in correspondence with the tourist season. If the island wants to achieve complete selfsufficiency, seasonal storage becomes compulsory. This study makes use of measured production data over 1 year to understand the best combination of renewable energy generation and storage to match energy production with consumption. A stochastic optimization based on a differential evolution algorithm is carried out to showcase the configuration that minimizes the levelized cost of required energy (LCORE) in different scenarios. System performance is simulated by progressively increasing the size of the storage devices, including a combination of Lithium-ion batteries and power-to-gas-topower (P2G2P) technologies, and the PV field. An in-depth market review of current and forecasted prices for RES and ESS components supports the economic analysis, including three time horizons (current and projections to 2030 and 2050) to account for the expected drop in component prices. Currently, the hybrid storage system combining BESS and P2G2P is more cost-effective (264 €/MWh) than a BESS-only system (320 €/MWh). In the mid-term (2030), the expected price drop in batteries will shift the optimal solution towards this technology, but the LCORE reached by the hybrid storage (174 €/MWh) will still be more economical than BESS-only (200 €/MWh). In the long term (2050) the expected price drop in hydrogen technologies will push again the economic convenience of P2G2P and further reduce the LCORE (132.4 €/MWh).