Assessing Uncertainties of Life-Cycle CO2 Emissions Using Hydrogen Energy for Power Generation

Hydrogen and its energy carriers, such as liquid hydrogen (LH2), methylcyclohexane (MCH), and ammonia (NH3), are essential components of low-carbon energy systems. To utilize hydrogen energy, the complete environmental merits of its supply chain should be evaluated. To understand the expected environmental benefit under the uncertainty of hydrogen technology development, we conducted life-cycle inventory analysis and calculated CO2 emissions and their uncertainties attributed to the entire supply chain of hydrogen and NH3 power generation (co-firing and mono-firing) in Japan. Hydrogen was assumed to be produced from overseas renewable energy sources with LH2/MCH as the carrier, and NH3 from natural gas or renewable energy sources. The Japanese life-cycle inventory database was used to calculate emissions. Monte Carlo simulations were performed to evaluate emission uncertainty and mitigation factors using hydrogen energy. For LH2 , CO2 emission uncertainty during hydrogen liquefaction can be reduced by using low-carbon fuel. For MCH, CO2 emissions were not significantly affected by power consumption of overseas processes; however, it can be reduced by implementing low-carbon fuel and waste-heat utilization during MCH dehydrogenation. Low-carbon NH3 production processes significantly affected power generation, whereas carbon capture and storage during NH3 production showed the greatest reduction in CO2 emission. In conclusion, reducing CO2 emissions during the production of hydrogen and NH3 is key to realize low-carbon hydrogen energy systems.