## 4 Discussion
Taking all of the criteria into consideration, a case could be made for any of the water electrolysis processes, but SOE powered by renewable electricity appears to be an especially worthwhile technology to focus on in the future. The source of renewable electricity that should be utilized depends on the characteristics of the region in which the electrolyzer is built. While wind energy showed greater energy efficiency and lower production cost in the literature review, this does not necessarily mean it is the most optimal option everywhere. Also, an important alternative that was not in the scope of this research is the possibility of utilizing multiple sources of renewable electricity in conjunction with, or integrating them into, the electricity grid mix. A hybrid configuration can ensure a more stable and reliable electricity supply, particularly in the case of wind and solar PV, which are known to be intermittent sources. * The literature review also revealed some encouraging data about the emerging H\({}_{2}\) production technologies. Biomethane pyrolysis, ESMR, supercritical water gasification of sewage sludge [76], industrial CO-to-H\({}_{2}\) via water-gas shift reaction [77], solar thermal thermochemical decomposition, nuclear thermochemical decomposition, biophotolysis, and ammonia thermal decomposition were herein investigated, all of which are in the late research and early development stages, except for ammonia thermal decomposition via fixed-bed reactors, which exhibits a TRL of 9. Because these technologies are mostly laboratory-scale or small-scale, data rely heavily on simulations and models. Out of the emerging technologies, currently biomethane pyrolysis, ESMR, and bio-photolysis predict the lowest hydrogen costs, with minimum costs of USD 1.36-1.53 per kg H\({}_{2}\). Nuclear thermochemical decomposition is not far behind, at USD 2.24-4.11/kg H\({}_{2}\), with the price varying by almost USD 2 depending on the cycle type. Solar thermal thermochemical decomposition and ammonia thermal decomposition are currently not competitive and will need a lot of technological development and improvements to become viable options for hydrogen production. However, ammonia decomposition via fixed-bed reactors or PSA membranes can produce H\({}_{2}\) at a high energy efficiency with close-to-zero carbon emissions while utilizing ammonia as a renewable feedstock. Therefore, more so than solar thermal decomposition, which has a low energy efficiency, the strategic integration of ammonia thermal decomposition technologies has fairly high prospects as long as production costs are lowered [56; 57; 58; 60; 62; 64; 67; 70; 71; 73; 74; 76; 77]. * Out of the rest of the H\({}_{2}\) production technologies, nuclear thermal thermochemical decomposition and biomethane pyrolysis appear to be the most promising. The production of \"turquoise\" H\({}_{2}\) via biomethane pyrolysis has low energy requirements and has a negative global warming potential due to utilizing an otherwise high-emitting feedstock. Thermochemical decomposition with nuclear power has an energy demand similar to that of SMR and produces zero carbon emissions. The most promising cycles are S-I, HyS, and Cu-Cl. The energy efficiencies of the two technologies are 40-56%, which could be improved upon with more research and design optimization. The other technologies exhibit some advantages, such as ESMR's high energy efficiency and the potentially low production cost of bio-photolysis, but due to their higher GWPs, they are more practical as transitional technologies rather than as long-term solutions [75; 78].