Life Cycle Assessment of buses with alternative powertrain and fuel options for low carbon public transportation in the city of São Paulo

Type de publication:

Conference Proceedings

Source:

Gerpisa colloquium, Bordeaux (2024)

Résumé:

Life Cycle Assessment of buses with alternative powertrain and fuel options for low carbon public transportation in the city of São Paulo

The impacts of human activities on the environment are one of today's most significant challenges, especially climate change and global warming, caused by the accumulation of greenhouse gases (GHG) in the atmosphere. The effects of these changes are felt with increasing intensity year after year, causing thousands of deaths and financial losses in the billions (UNFCCC Secretariat, 2023). The emergence of the issue has been gaining importance globally since the signing of the Kyoto Protocol in 1995. Still, it was only in 2015 that a broad consensus on the need to control GHGs was established by 196 countries under the Paris Agreement, whose general objective is to limit the increase in global temperature to a maximum of 1.5°C compared to pre-industrial levels. Since then, public and private stakeholders have been multiplying their efforts to mitigate and eliminate sources of GHGs (UNFCCC Secretariat, 2020). One of these sources is the transport sector, which, like the energy sector, seeks to reduce its dependence on fossil fuels in favor of less emitting alternatives, such as biofuels and electric vehicles (UNFCCC Secretariat, 2018).

Over the last decade, there has been an increase in studies and research into the environmental impact of different types of engines and fuels. Despite this trend, these works focus more on North America, Europe and China (Aichberger & Jungmeier, 2020). Many factors that affect the assessment of the environmental impacts of these engines and fuels, such as the impact of the global supply chain on vehicle manufacturing and land use change in fuel production, are far from a consensus in the literature. In Brazil and the Global South, only some studies address this topic, and even fewer adopt the scope of public transportation in the analysis (Emodi et al., 2022).

Intending to contribute to formulating urban mobility public policies to mitigate GHG emissions in the transportation sector in the city of São Paulo (SVMA, 2022), this article evaluates the emissions of buses operated with different powertrain technologies and fuels, considering their entire life cycle. In addition to the environmental sphere, the alternatives were compared from an economic-financial point of view according to their total cost of ownership, to better assist the municipal administration in the transition of the bus fleet.

To achieve the objective of the study, an introduction and contextualization of the problem are presented, highlighting the municipal regulatory framework on the subject (ANP, 2023; Câmara Municipal de São Paulo, 2018; IBAMA, 2021; Prefeitura do Município de São Paulo, 2021), followed by a review of the primary studies in the literature. Next, a Life Cycle Assessment of the different bus types is carried out using the GREET database and software (Argonne National Laboratory, 2023) to evaluate GHG emissions on a cradle-to-gate basis. The GREET model is an automotive LCA tool developed by Argonne National Laboratory and has been used extensively to carry out automotive LCAs (Wang et al., 2021). Local data from municipal public transport operators, industry associations and national public agencies was used to model the use and end-of-life phases.

The scope of this work considers internal combustion, hybrids and electric buses. The fuels analyzed were diesel, biodiesel, vehicular natural gas, biomethane and ethanol. The environmental impact assessment of the electric bus was carried out considering the electricity generation's carbon intensity (CI) (Climate Transparency, 2022). In addition, essential but often overlooked parameters for LCA, such as the LCA inventory analysis and the effect of land use change (Esteves et al., 2016; Guarenghi et al., 2023), were included, adopting local conditions.

The results show that hybrid engines reduce GHG emissions by 20% compared to conventional engines. The benefits of electric and biofuel buses in reducing GHG depend on the CI of the energy sources used in their production. In São Paulo's operating conditions, the electric vehicle proved to be the least emitting alternative. This is the case for electrical matrices with a carbon intensity of up to 126 g CO2 eq./kWh, above which the biomethane bus becomes the best option. For electricity generation with a CI above 830 g CO2 eq./kWh, the electric bus becomes more emitting than the diesel hybrid. When land use changes are included in the evaluation of the quantification of the CI of ethanol (Guarenghi et al., 2023) and biodiesel (Esteves et al., 2016), based on agricultural feedstock, these become more or less emitting than their fossil substitutes, depending on the change in the carbon stock of the productive area over time. The use phase (estimated based on Dallmann, 2019) accounts for the majority of GHG emissions, with the exception of the electric bus, whose production phase dominates emissions. It was found that the total cost of ownership of clean technologies is almost always lower than that of conventional ones, which indicates that the decarbonization of São Paulo's public transport sector can be achieved while preserving the economic and financial balance of the municipal administration.

 

References

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