Hydrogen as large-scale seasonal storage option: its potential role in the Italian decarbonised energy system

The global energy sector is facing a deep transformation, as it is rapidly moving from fossil fuel sources towards a strong decarbonization in the coming decades. Renewable energy sources will lead to a deep electrification of the system, but their variability has to be managed on a daily and seasonal scale. In this Master Thesis Project Hydrogen Seasonal Storage is investigated as a possible solution for enhancing the flexibility of the electricity system with high shares of renewables, considering the Italian case. The surplus electricity produced from renewable energy sources during summer months is used to produce hydrogen, which is stored and then re-converted into electricity through fuel cells, when the renewable generation is not sufficient to meet the demand, namely during winter months. The COMESE model has been used in this study, a section for the analysis of seasonal storage systems has been added to the code and some scenarios of the Italian electricity system by 2050 with hydrogen as a seasonal storage option has been simulated, starting from a Reference Scenario estimated following the Italian long-term strategy for greenhouse gas emissions reduction guidelines. The addition of the seasonal storage reduced the annual energy waste of 27% compared to a scenario without seasonal storage technologies, reducing also the amount of installed solar power and batteries capacity required. For a system in which the generation from variable renewable energy sources is more than 85% of the total generation, the seasonal storage capacity should be at least 10% of the demand, in order to optimally exploit the surplus from the renewable generation during summer months. The dispatchable generation plays a fundamental role in energy systems with high shares of vRES, in particular the percentage of dispatchable generation on the total, should be at least 18%, in order to have a value of energy waste lower than 15% of the annual demand. The cost of the electricity produced in the scenarios presented varies between 9.64 c€/kWh and 13.08 c€/kWh and for scenarios with a seasonal storage capacity higher than 1% of the annual demand, the cost of the storage tanks has the biggest influence on the total cost of the system and on the increase of the electricity produced cost.