Latest revision as of 17:40, 26 January 2021

Abstract

The transport and electricity sectors are in the midst of major changes in an attempt to limit climate change and air pollution problems. In the coming decades conventional fossil fuelled vehicles are expected to be replaced with electric powertrain vehicles, resulting in increased electricity demand by the transport sector. At the same time, the electricity sector is also in upheaval due to policy decisions to move away from fossil and, in many locations, nuclear energy sources towards renewables such as hydro, wind, and solar. Rightfully so, many questions have been raised in the scientific literature and media regarding the environmental benefits of these new vehicle technologies and how the different energy chain and vehicle options compare. The goal of this thesis is to analyse the environmental burdens of current and future (2050) passenger transport technologies in Switzerland while taking into account future developments of the Swiss and global electricity sectors. I use the methodology of Life Cycle Assessment (LCA) to quantify the environmental burdens from current and future passenger transportation by motorcycle (Chapter 3), aircraft (Chapter 4), urban bus (Chapter 5), and passenger car (Chapters 6 and 7) for different refuelling/ recharging energy chains. Vehicle performance is modelled using a consistent framework across powertrain types to ensure fair comparison. Road vehicle energy consumption is calculated using a physics-based model that simulates operation using internationally harmonised driving cycles. This model is calibrated with real energy consumption data for each vehicle and powertrain type. This allows prediction of future vehicle performance by estimating the potential future changes for each input parameter, such as internal combustion engine efficiency or lithium ion battery cell energy density. In Chapter 6 I extend this model to enable Monte Carlo analysis and global sensitivity analysis to show that the electricity used for charging electric vehicles is the largest source of global variability of the environmental burdens of electric cars, though vehicle size, lifetime, driving patterns and battery size also strongly contribute to variability. I also further adapt the model using exponential smoothing of driving cycles and wind tunnel measurement results to show that future autonomous and connected vehicles could consume roughly 10% less energy per kilometer than comparable human driven vehicles. I also incorporate future developments of the electricity sector into the calculations by integrating scenario results from the IMAGE integrated assessment model into the ecoinvent LCA database using the open source software package Wurst that I helped to create. Two scenarios from the IMAGE model are used for the development of the future electricity sector for 26 global regions: Baseline may be considered a business as usual type scenario, while ClimPol represents the aggressive decarbonisation that would be consistent with a likely probability of achieving the 2°C target. This is a significant development in the field of prospective LCA and I am able to show that without these changes to the background database, future climate burdens could be overestimated by up to 75% in the ClimPol scenario. In Chapter 8 I compare different passenger transport modes for the Baseline and ClimPol electricity scenarios in the year 2050. Results are generally quite consistent across vehicle types. The introduction of battery electric vehicles is found to provide clear climate benefits compared to conventional combustion vehicles for all vehicle types as long as the electricity used for charging has carbon content similar to or less than that of a modern natural gas power plant. Switzerland’s current and future electricity mix for all likely scenarios easily meets this requirement, so a robust conclusion may be drawn that battery electric vehicles of all types should be supported in Switzerland from a greenhouse gas (GHG) emission point of view. When other environmental impact categories are considered the superiority of battery electric vehicles is less clear, though hard conclusions cannot yet be drawn due to methodological limitations. I also develop a simple fleet model to estimate the total life cycle emissions caused by the Swiss passenger transport sector. Fleet model results for 2050 show that if all road vehicles are powered by battery electric powertrains the total Swiss domestic passenger transport related life cycle GHG emissions are 47% lower in the Baseline scenario and 72% lower in the ClimPol scenario compared to 2017 emissions. Similar model results for fleets of fuel cell vehicles show 34% and 66% improvement respectively, while a fleet of hybridized combustion vehicles would enable reductions of 31% and 41% respectively. When international air transport is also included in the future fleet assessment it is found to dominate the results in some categories, especially climate change and cumulative energy demand. Future growth in air transportation demand is expected to negate all climate change reductions made in ground transportation, leaving total sector emissions in 2050 roughly similar to current emission levels. If air transport demand continues to grow according to historic rates and future projections, it will become one of the most important sources of greenhouse gases in the future, as technical improvements are expected to be outpaced by growth in demand. The only remaining solutions appear to be shifting continental transport demand to electric train, which has comparatively low impacts, or curbing demand growth. There are three main outcomes of the thesis. The first is the wealth of data published as extensive supporting information in each of my publications. These models and results should be used as inputs by energy and transport modellers as well as fed into life cycle assessment databases. The second is the open source software package Wurst that can be used to create modified versions of the ecoinvent database. This methodology has the potential to greatly improve the quality of prospective LCA. The third outcome of this thesis is the report (Chapter 7) that I helped to prepare for the Swiss Federal Office for Energy. The summary of this report is expected to reach the highest level of decision makers in the country and help inform Swiss policy regarding the energy transition.

Original document

The different versions of the original document can be found in:

• http://dx.doi.org/10.3929/ethz-b-000276298

• http://hdl.handle.net/20.500.11850/276298