Proposing a multi-generation system to convert geothermal energy to LH2

Liquid hydrogen is a solution for storing and transmitting electricity that is produced by renewable energy sources such as geothermal energy. In this paper, a Rankine cycle with a proton exchange membrane electrolyzer, an ammonia absorption refrigeration cycle, and a hydrogen liquefaction cycle are simulated and analyzed for storing geothermal energy as liquid hydrogen. The power generated by the Rankine cycle is used to produce hydrogen gas in the electrolyzer. Additionally, the cooling obtained from the absorption refrigeration cycle is used to pre-cool the hydrogen gas to a temperature of -9.26 ℃, and then the hydrogen is liquefied at -253 ℃ by a mixed refrigeration cycle. The innovation of this study is based on using the cold energy obtained from the absorption refrigeration cycle in the liquid hydrogen production cycle and integrating the liquid hydrogen production process with the geothermal energy system. By using energy, exergy, and economic analysis, the final cycle efficiency was improved compared to the initial system. The special energy consumption of the liquefaction unit is 81.8 kWh per kilogram of hydrogen. In a three-year payback period, using economic analysis, the minimum selling price is calculated to be $2.11, which is lower than a similar liquid hydrogen production cycle presented in the past.