Contents I. INTRODUCTION
According to Widera [1], the Paris Agreement has made it clear that creating sustainable energy technology is essential to halting climate change. The future of renewable hydrogen as a form of energy storage seems promising. It can therefore be used to guarantee the stability of the energy system and to meet demand during periods when variable renewable energy (VRE), such as wind and solar energy, is less easily accessible [1]. The decarbonization of several industries, including transportation and the building industry, is aided by appropriate energy storage techniques that address the intermittent nature of RES. Hydrogen-to-gas conversion systems offer a practical alternative for switching from fossil fuels to renewable energy sources (RES), balancing volatile renewable sources, notably at the local and regional level. The focus of the paper will be on the co-production of hydrogen using solar energy and water electrolysis, with the possibility of using hydrogen for stationary applications like combined heat and power (CHP) plants or fuel cell electric generators as well as energy storage and transportation. In the past years, most of the scientific literature was devoted to methods for producing hydrogen sustainably [2]. Only a few authors have addressed hydrogen energy storage, according to the review of the literature. The combination of hydrogen production, storage, delivery, and use for low carbon heat, power, and mobility is only very rarely discussed in the literature. Due to the interest in the topic, the electrolysers have been put to the test in about 50 pilot and demonstration facilities across the world for the integrated production of alternative energy sources (such as hydrogen or synthetic methane) and renewable energy. The majority of test locations have installed 1 MW electrolysers or greater. The use of electrolysis-produced hydrogen for stationary, sustainable transportation, and combined energy storage, however, is uncommon and site-specific [1]. Some of the biggest non-technological challenges are caused by laws and regulations that are not tailored to the particular needs of hydrogen use. Because of this, the pilot projects work to better understand the advantages and disadvantages of the hydrogen technology, such as electrolyser operation, plant selection, necessary approvals and regulations, links to the power and gas grids, and required approvals and regulations. This essay's goal is to investigate how the energy transition could be made more successful and efficient utilizing examples from the three case studies that were selected. While the other two are located in Europe, one of them is located in the United States of America. The most recent continuing project, chosen by the Fuel Cells and Hydrogen Joint Undertaking, sought to create a completely integrated model of hydrogen production, storage, transit, and use for low carbon heat, electricity, and transportation (Orkney-Archipelago, UK) is among the European projects that have been examined [3]. The American demonstration scenario is the National Wind Technology Center's (Boulder, Colorado) Wind-to-Hydrogen Project, which was developed by the National Renewable Energy Laboratory (NREL). It is the first full-scale wind power and hydrogen plant in the world, located on Utsira in Norway. Its objective is to serve as a demonstration project for the integration of solar and wind turbines, as well as hydrogen generation in an electrolyzer. The analysis that is being presented considers the current state of hydrogen generation, and more specifically "green" hydrogen, as well as potential developments in the most industrialized countries and the accompanying costs [4].
