In this paper, the authors elaborated on the conversion of excess electricity, generated from renewable energy sources by water electrolysis, into chemical energy and on its underground storing. Specifically, one of potential solutions in the function of transition and decarbonization of the energy sector is a project of conversion and storage of wind and solar energy, that is, underground storage of chemical energy (hydrogen). In the primary cycle of producing and storing hydrogen, underground storing of hydrogen (UHS) in geological formations is a crucial factor in storing large volumes of energy for a theoretically longer, or an indefinite period. The paper presents possibilities of using the stated technology in Croatia by using a small standard underground gas storage facility (UGS). The article presents technical-technological process of producing and underground storing of hydrogen: from generating electricity through renewable energy sources or other industrial processes generating waste energy, the production of hydrogen and its compression, transport and storage in underground geological formations. In this paper, the authors will also elaborate on the status of the EU States´ regulations, which present the main factor for the previously mentioned activities, as well as on the necessary changes that the relevant regulations need to undergo.