Evaluating Hydrogen-based Electricity Generation using the Concept of Total Efficiency

The popularity of hydrogen has been increasing globally as a promising sustainable energy source. However, hydrogen needs to be produced and processed before it can be used in the energy sector. This paper uses total efficiency to evaluate the lifecycle of hydrogen-driven power generation. Total efficiency introduces the energy requirement of fuel preparation in conventional efficiency and is a reliable method to fairly compare different energy sources. Two case studies in Spain and Germany, with nine scenarios each, are defined to study different hydrogen-preparation routes. The scenarios include the main colors of hydrogen production (grey, turquoise, yellow and green) and different combinations of processing and transportation choices. In most cases, the highest energy penalty in the overall preparation process of the fuel is linked to the production step. A large difference is found between fossil fuel-based hydrogen and green hydrogen derived from excess renewable energy, with fossil fuel-based hydrogen resulting in significantly lower total efficiencies compared to green hydrogen. The use of natural gas as the primary source to generate hydrogen is found to be a critical factor affecting total efficiency, particularly in cases where the gas must be transported from far away. This shows the value of using excess renewable energy in the production of hydrogen instead of grid power. Even in the most efficient scenario of green hydrogen studied, total efficiency was found to be 7 % lower than the respective conventional efficiency that does not account for hydrogen generation. These results emphasize the importance of considering the impact of fuel preparation stages in comparative thermodynamic analyses and evaluations.