Environmental performance for hydrogen locally produced and used as an energy source in urban buses

Abstract

Different economies are adopting various strategies to achieve the greenhouse gas reduction targets established during the 21st Conference of Parties. Regarding urban transportation, the Brazilian government launched the Hydrogen-bus Project (BHP) that, although the pilot project has shown high technological efficacy, is missing environmental-related studies from a systemic perspective. This work aims to assess the environmental performance of an expansion scenario for the BHP, which is small-scale and locally producing hydrogen from water electrolysis. The expansion scenario covers the entire São Paulo Metropolitan region (22 million inhabitants), modeled from a ‘well to wheel’ boundaries by including hydrogen production and use in 4076 buses, yearly traveling 265,000 km. Emergy synthesis (with ‘m’) and life cycle assessment (LCA) are applied to obtain complementary environmental indicators. LCA results show that the expansion scenario's implementation phase contributes most to fossil energy depletion (94%), acidification potential (94%), and particulate matter (70%) impact categories, while the operational phase reaches 63% of total global warming potential. Compared with diesel, electricity, liquefied petroleum gas, and biodiesel energy alternatives, the studied hydrogen scenario showed the worst figures for fossil energy depletion (4.61E-06 MJeq./km person) but the best performance for global warming (4.35E-06 kgCO2-eq./km person), acidification potential (2.40E-09 kgSO2-eq./km person), and particulate matter between 2.5 and 10 μm (8.32E-11 kgPM2.5-10/km person). From an emergy viewpoint, the operational phase demands about 96% of the invested emergy in the evaluated scenario, mostly from electricity for water electrolysis (51%) and human labor (44%). No emergy contribution for societal development as expressed by the emergy yield ratio (EYR of 1.0) is available for the evaluated scenario. Still, compared to biodiesel and diesel options, hydrogen has higher renewability (m-%R of 42%), lower environmental loading ratio (ELR of 1.4), and slightly higher emergy sustainability (m-ESI of 0.71). Generally, the hydrogen-based evaluated scenario proved to be the best option compared to diesel and biodiesel. In addition to discussing alternatives energy sources to break the addiction to fossil fuel, this work highlights the importance of considering a conceptual model supporting method and indicator choice, as well as providing a consistent, updated, and detailed calculation procedure, which will be useful for future similar studies and support scientific-based public policies.