Green hydrogen production in Brazil: an exergetic analysis of the rational use of energy between export and domestic consumption

Green hydrogen has been promoted as a vector for the global energy transition, especially in countries with high availability of renewable energy sources. In this context, Brazil has been consolidating itself as a destination for major investments aimed primarily at the production of green hydrogen and ammonia for export, driven by its vast renewable potential, port infrastructure, resources, and favorable geographical position. However, analyses that critically evaluate this strategy from the perspective of the rational use of energy quality are still scarce. This study evaluates the thermodynamic efficiency of the green hydrogen production chain, comparing the export strategy, domestic use of hydrogen, and the direct use of electrical energy within the Brazilian National Interconnected System (SIN). The methodology is based on exergy analysis and the calculation of the energy return on investment (EROI), considering the entire production chain of a plant with a capacity of 1,000 t of NH3g per day. The system analyzed consists of seawater desalination via reverse osmosis, SOE electrolysis for H2g production, cryogenic air separation to obtain N2, Haber–Bosch synthesis for production of NH3g, and an offshore wind farm dedicated to electrical energy supply. Based on the results of the exergy efficiency and the overall EROI of the ammonia export chain, it is observed that the process consumes more energy than it delivers at the destination. In contrast, the direct use of offshore wind energy through the SIN presents higher exergy efficiency and EROI than the export chain. When intended for domestic use, diesel in heavy-duty transport and mineral coal in heat generation, green hydrogen shows a greater thermodynamic advantage compared to other conventional energy vectors, as it allows the substitution of fossil fuels in specific applications with better utilization of the available energy quality. Therefore, although the export of green hydrogen is economically attractive, it results in significant destroyed exergy. From the perspective of rational energy use, thermodynamics, and national energy security, it is better to prioritize the domestic use of hydrogen and direct renewable electrical energy. Thus, it is recommended that green hydrogen production prioritize non-dispatchable surplus energy and its use in domestic sectors, preserving exergy for national socioeconomic development.