The article discusses a case study in Austria focusing on the integration of renewable energy sources (RESs) like photovoltaic (PV) and wind to generate hydrogen for various applications, particularly seasonal energy storage. Process modeling was applied to analyze the complexities of designing integrated wind–PV–electrolyzer underground hydrogen storage (UHS) projects. The study highlighted the significance of sizing RESs relative to electrolyzer capacity, the impact of different wind-to-PV ratios, and the benefits of selling both electricity and hydrogen. Results showed that oversizing RES capacities could significantly reduce the levelized cost of hydrogen (LCOH), especially when including electricity sales revenues. Dynamic adjustments to the RES-to-electrolyzer capacity ratio based on market developments were also suggested to optimize costs. The analysis demonstrated the feasibility of such integrated projects in regions like Austria, where systems can be flexibly adapted to market conditions. Key cost components identified included compression, gas conditioning, wells, and cushion gas, with the levelized cost of underground hydrogen storage (LCHS) estimated at 0.80 €/kg for the Austrian project. Overall, the article emphasizes the role of hydrogen in achieving CO2 emission targets and the importance of utilizing RESs efficiently for hydrogen production and seasonal energy storage.