## 1 Introduction  
Recently, the adverse effects of climate change have become more and more obvious [1]. The reason behind this development is identified in the global energy-related greenhouse and CO\({}_{2}\) gas emissions. Although these are periodically flattening out, they have increased by an average of 1% per year over the last ten years [2]. In order to counteract this development, constructive approaches are needed to implement a global transformation of the energy systems dominated by fossil fuels. By an intelligent combination of wind, solar, as well as bio energy with efficient energy storage along with an effective power recovery system, a decentralized \"green\" energy supply can be realized. Hereby, different energy sectors of industrial plants and urban residential areas can be supplied with \"green\" energy [3, 4]. Hydrogen as an energy carrier offers ideal conditions for such a cross-sectoral \"green\" energy supply, since in addition to stationary energy applications, it can also contribute to the decarbonization of the transport sector [4, 5]. Furthermore, hydrogen, as a clean energy carrier, has the potential to provide the much-needed flexibility to power systems, acting as a buffer to non-dispatchable renewable energy generation, and can, therefore, play a key role in seasonal balancing of renewable generation by storing large amounts of hydrogen [2]. Indeed, the efficient and safe storage of hydrogen is still a technical challenge. Problems here include the embrittlement and diffusion with a variety of constructions materials,including most plastics and mild steel. In addition, hydrogen requires special safety regulations and has a low volumetric energy storage density (ESD). The gravimetric chemical ESD of hydrogen, of 33.3 kWh/kg, is, however, the highest of all gases, but under normal conditions, it has only 30% of the volumetric ESD of natural gas (\(\approx\)10 kWh/m\({}^{3}\)); namely, 3 kWh/m\({}^{3}\)[4]. The most common H\({}_{2}\) storage technologies, to increase its volumetric ESD, are compression and the liquefaction. For compressed gas storage of hydrogen (CGH2), the gas is usually compressed to pressures between 20 and 35 MPa, in the mobility range up to 70 MPa [5]. This increases the ESD from 0.8 kWh/L (25 g/L) at 35 MPa to 1.3 kWh/L (40 g/L) at 70 MPa [5,6]. However, approximately 9 to 12% of the final energy provided is consumed for the compression of hydrogen from atmospheric pressure to 35 MPa or 70 MPa, respectively [7]. For the seasonal long-term storage of large quantities of hydrogen via pressure storage, various concepts with underground caverns are being investigated and implemented [4,8,9]. Depending on the specifications and technical feasibility, they can be constructed at depths until 2000 m, having geometric volumes of up to 1,000,000 m\({}^{3}\), typical heights of 300 to 500 m, and diameters of 50 to 100 m. They can be operated at pressures of up to or even above 20 MPa, depending on the depth [8]. This technology is simple and inexpensive, but there are limitations due to the low volumetric ESD and the high risk of accidents. In case of an accident, hydrogen is released instantaneously over time, which remarkably enhances the risk of explosion [10]. Another H\({}_{2}\) storage technology is the liquefaction of hydrogen. Using cryogenic systems, the gas is cooled down to 20 K at \(\approx\)0.1 MPa. Thereby, ESDs of up to 2.3 kWh/L (70 g/L) are achieved ([6,9]). The required energy to liquefy H\({}_{2}\) lies, however, between 20% and 50% of the lower heating value of hydrogen, depending on the plant size [11]. A combination of the compression and liquefaction techniques is the cryo-compressed hydrogen (CcH2) storage. Hydrogen is stored in an insulated tank that can resist cryogenic temperatures (20 K) and high pressure (at least 30 MPa). The fact that the tank, in contrast to LH2, is able to withstand high pressures extends the time until evaporation losses begin.