Sustainability analysis of hydrogen production processes

Hydrogen is a versatile energy carrier and storage medium that is expected to have a key role in the energy transition, as it can be employed in a variety of applications. Hydrogen can be produced from different feedstocks and using different processes. Based on the production technology used, hydrogen is conventionally identified by a color. In this work, we compare different hydrogen generation processes: (i) green hydrogen, obtained by electrolysis of water using electricity from floating photovoltaic platforms, (ii) grid hydrogen, also obtained by electrolysis but using grid electricity, (iii) grey hydrogen, produced from natural gas using steam reforming and (iv) blue hydrogen, which is similar to grey hydrogen, but uses hot potassium carbonate as the solvent for carbon capture and storage. The paper considers the production of hydrogen necessary for 2 trips per day of a medium size ferryboat to navigate full electric for 7 h in the Adriatic Sea. Process simulation is applied to solve material and energy balances for each process investigated, as well as for the evaluation of capital and operating costs. Process simulation outcomes are then used to estimate three key performance indicators focused on energetic, economic, and environmental sustainability issues: the energy return on energy invested, the levelized cost of hydrogen, and the life cycle assessment. The energy indicator for grid and green hydrogen has a value of 13.39–14.29, versus a value of 4.59–5.48 for other hydrogen production methods from natural gas. The cost for green hydrogen is slightly higher (8.76) compared to the blue hydrogen (5.50) however green hydrogen has a much lower impact to the environment. Considering the combined results obtained by all the indicators, it is concluded that the most sustainable hydrogen production method is green hydrogen.