Sustainable evaluation of different water sources to produce reen hydrogen

Abstract

Producing hydrogen from water electrolysis using renewable energy sources is essential to decarbonize the economy. Some studies show that the need for hydrogen would be 2.3 Gt per year in a renewable future. However, if the global economy achieves this hydrogen amount, the water requirement for electrolysis would be near 1x1014 kg per year (1.8% of present global water consumption). As a result, water ecosystems can be under significant pressure if not well managed. Thus, water scarcity, both in quality and quantity, requires assessing the adequacy of the sources. Therefore, this work aims to develop a model to evaluate water sources from economic, environmental, and social perspectives for use in electrolyzers. The methodology includes adapting and applying the Sustainable Value (SV) model and developing a Multi-Criteria Decision Making (MCDM) model. Two models are discussed; the first model uses 12 criteria, with different weights, to evaluate the water sources; it is applied in 2 study cases, a 1MW green hydrogen cluster and a 60 MW hydrogen plant in a petroleum refinery. The available water sources were groundwater, industrial wastewater, seawater, rainwater, and water grid (applicable only for case 1). Cost calculations considered all steps of water supply (collection, transport, treatment (including disposal), and storage). The evaluation demonstrated the low cost associated with water compared to the total cost of electrolysis (1.6%); thus, the social and environmental dimensions must have a leading role compared to the economic dimension. This consideration, in addition to the concern with water scarcity, was applied in the development of the second model (MCDM model), which considers the level of water scarcity in the region where the electrolysis plant is implemented in the form of the water exploitation index (WEI+), in which the weights of the dimensions vary according to water availability. In addition, 2 new criteria were added to improve the model (14 criteria). This MCDM model was applied in 3 study cases in an industrial park (case 1), a petroleum refinery (case 2), and clusters across the state of Bahia (case 3). Groundwater, industrial wastewater, seawater, rainwater, water grid (applicable for cases 1 and 3), surface water, and urban wastewater (applicable only for case 3). The results indicate variations in the suitability of water sources, influenced by factors such as location, treatment costs, and socio-environmental considerations. It is concluded that a multifaceted approach is essential in selecting water sources for green hydrogen production, aligned with global sustainability and energy transition objectives. Overall, rainwater is the most suited WS for small scale in locals with water available, and industrial wastewater is suited for bigger scales and scarcity scenarios.