Life-cycle assessment of diesel, natural gas and hydrogen fuel cell bus transportation systems

Abstract

The Sustainable Transport Energy Programme (STEP) is an initiative of the Government of Western Australia, to explore hydrogen fuel cell technology as an alternative to the existing diesel and natural gas public transit infrastructure in Perth. This project includes three buses manufactured by DaimlerChrysler with Ballard fuel cell power sources operating in regular service alongside the existing natural gas and diesel bus fleets. The life-cycle assessment (LCA) of the fuel cell bus trial in Perth determines the overall environmental footprint and energy demand by studying all phases of the complete transportation system, including the hydrogen infrastructure, bus manufacturing, operation, and end-of-life disposal. The LCAs of the existing diesel and natural gas transportation systems are developed in parallel. The findings show that the trial is competitive with the diesel and natural gas bus systems in terms of global warming potential and eutrophication. Emissions that contribute to acidification and photochemical ozone are greater for the fuel cell buses. Scenario analysis quantifies the improvements that can be expected in future generations of fuel cell vehicles and shows that a reduction of greater than 50% is achievable in the greenhouse gas, photochemical ozone creation and primary energy demand impact categories.

Introduction

The Sustainable Transport Energy Programme (STEP) is an initiative to examine alternative transport fuels for Western Australia (WA). The project includes three buses manufactured by DaimlerChrysler, which operate with fuel cell engines from Ballard Power Systems, and a raw hydrogen supply provided by the BP Kwinana oil refinery. The STEP trial is in partnership with the Clean Urban Transport for Europe (CUTE) trial, the Ecological City Transport System (ECTOS) trial in Iceland, and the Global Hydrogen Bus Platform (HyFLEET:CUTE) [1].

Recent work has evaluated the potential for the establishment of a hydrogen economy in Australia [2] and current activities in the field [3]. These studies have presented a qualitative overview. A policy framework for hydrogen has yet to be established. There is a recognized need for detailed quantitative analysis and testing [4].

The Government of Western Australia, through the Department for Planning and Infrastructure (DPI), has commissioned several research projects to develop academic knowledge and expertise from the fuel cell bus trial. The life-cycle assessment (LCA) is one such project, that is aimed at evaluating the hydrogen infrastructure and fuel cell buses in relation to the existing diesel and natural gas transportation systems. Based at Path Transit's Morley Bus Depot in the Malaga suburb of Perth, the fuel cell buses are operating in regular service alongside the conventional Transperth natural gas and diesel bus fleets.

The life-cycle models are designed to be flexible and thereby allow for future scenario analysis that examines different primary energy sources, fuel production processes, and expected improvements in technology. Concepts for sustainable bus transportation can be incorporated using the methodologies and boundary conditions defined during the project. Continued efforts to develop and refine these models can identify industry opportunities, as the entire product life-cycle moves towards optimization, and important problems are resolved in the early stages of the emerging hydrogen economy. The knowledge gained from this research may be used to define the direction of future programmes and policies.

The application of LCA and similar well-to-wheels (WTW) methods to hydrogen fuel cell vehicles has become an active field of research. A precursor and important basis for this study is the research conducted by Faltenbacher et al. [5], [6] as part of the CUTE trial evaluation. The preliminary results from the CUTE trial, reported in [5], [6], provided a base of methodology for the subsequent LCA work on the CUTE, ECTOS and STEP trials. In a recent literature review [7], several common deficiencies in the hydrogen futures literature were raised. Many studies lack participation from stakeholders and use a top-down theoretical approach with little discussion of the issues experienced by technology on the ground. These issues are categorically addressed by this study through the use of data provided by the participating companies and collected from the field results of the STEP fuel cell bus trial.

Research on the capabilities of hydrogen fuel cell technology in relation to conventional and other alternative transport solutions has been undertaken in the LCA context using a variety of methods. The Comparison of Transport Fuels conducted by Beer et al. [8] referenced the GREET model and examined a very broad range of transport fuel alternatives. The only hydrogen pathway examined was production from steam reforming of natural gas, which is just one of the many possible pathways. Colella et al. [9] evaluated the change in emissions and energy use from an instantaneous change to a hydrogen fuel cell vehicle fleet. Granovskii et al. [10] conducted an LCA of hydrogen fuel cell and gasoline vehicles using a first-principal methodology, which was based on theoretical calculations of the required economic and energetic data. Zamel and Li [11] performed an LCA of fuel cell and internal combustion engine vehicles in Canada, with fuel-cycle calculations carried out using GREET [12] and vehicle cycle data derived from published literature. General Motors conducted two WTW studies [13], [14], one based in North America and the other in Europe, of which the latter examined a total of 88 fuel supply pathways including 14 hydrogen-based pathways. The GM studies did not include hydrogen sourced as a by-product of petroleum refining, which is the case in the STEP project. Pehnt [15] made an LCA of fuel cell stacks in accordance with ISO methodology and included discussion of allocation rules regarding Platinum Group Metals (PGM's) and recycling concerns. Ahluwalia et al. [16] and Schäfer et al. [17] have reported performance expectations for future fuel cell vehicles, together with a range of results due to the large uncertainty associated with both this developing technology and the specific boundary conditions chosen for each study.

There is a need for present-day LCA results, which adhere to internationally accepted methodology standards, to indicate the current state of the technology and highlight the issues from an operational trial. The LCA research conducted in Perth aims to address this need and to develop a set of validated models that can be used for scenario and sensitivity analysis.