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.