Does car sharing reduce greenhouse gas emissions? Life cycle assessment of the modal shift and lifetime shift rebound effects

Car-sharing platforms provide access to a shared rather than a private fleet of automobiles distributed in the region. Participation in such services induces changes in mobility behaviour as well as vehicle ownership patterns that could have positive environmental impacts. This study contributes to the understanding of the total mobility-related greenhouse gas emissions reduction related to business-to-consumer car-sharing participation. A comprehensive model which takes into account distances travelled annually by the major urban transport modes as well as their life-cycle emissions factors is proposed, and the before-and-after analysis is conducted for an average car-sharing member in three geographical cases (Netherlands, San Francisco, Calgary). In addition to non-operational emissions for all the transport modes involved, this approach considers the rebound effects associated with the modal shift effect (substituting driving distances with alternative modes) and the lifetime shift effect for the shared automobiles, phenomena which have been barely analysed in the previous studies. As a result, in contrast to the previous impact assessments in the field, a significantly more modest reduction of the annual total mobility-related life-cycle greenhouse gas emissions caused by car-sharing participation has been estimated, 3-18% for three geographical case studies investigated (versus up to 67% estimated previously). This suggests the significance of the newly considered effects and provides with the practical implications for improved assessments in the future.Comment: 10 pages, 4 figures (in the end of the file

Consistent Incorporation of Multiple Background Scenarios Into One Background Database: Proposition of a New Approach

When analyzing future impacts of emerging technologies, one has to account for future developments in the background system to ensure temporal consistency between the foreground and background system. This can be achieved by incorporating scenarios into a background database, such as ecoinvent. Combining multiple scenarios can cause conflicts if several scenarios adapt the same process, and can result in an intransparent generation of scenario databases. We propose an approach which enables a transparent and reproducible incorporation of multiple scenarios into a single background database. It builds on and extends already existing brightway libraries, such as wurst and the superstructure. The recently developed brightway library wurst allows to systematically incorporate electricity scenarios from one source, i.e., the integrated assessment model of IMAGE. Incorporating additional scenarios, e.g., with higher regional resolution or for more sectors, such as greener steel production, extends the scope and accuracy of future background databases. An example for regional conflicts would be the incorporation of both average electricity scenarios for Europe and specifically for Germany. Our approach builds on the superstructure principle which produces one scenario database combining the background database with the processes and flows required for the scenarios. Secondly, it generates excel sheets which specify the values of flows for all scenarios. The scenario database and scenario excel sheets can be imported into the activity-browser, the graphical user interface for Brightway. The activity-browser enables a scenario-based LCA calculation and interpretation, which is easy-to-use also for nonpythonic LCA practitioners. Moreover, the generated superstructure database along with the scenario excel sheets can be easily shared. Our approach provides an extension to the superstructure principle to resolve conflicts caused by different scenario sources. We aim at creating a reliable and reproducible workflow to transparently generate a superstructure database which consistently combines scenarios from multiple sources. The goal is to make this approach available to the LCA-community as an open-source tool. Thus, our proposed approach contributes to the usability of background scenarios, and facilitates the cooperation as well as the exchange of scenarios between LCA practitioners

Prospective LCA to provide environmental guidance for developing waste-to-PHA biorefineries

Polyhydroxyalkanoates (PHA) production from waste streams using mixed microbial cultures (MMC) can unlock the potential of PHA to substitute oil-based plastics. However, these processes are still at low technology readiness level (4–6). Demonstrating a better environmental performance would boost their deployment at industrial scale. Hence, including environmental guidance during their development, when there are still opportunities for major alterations, is essential. To the best of our knowledge, this work elucidates for the first time how waste-to-PHA biorefineries could develop in the future by combining prospective LCA with scenario methodology and where the attention of stakeholders should be focused. Four future scenarios were derived considering both surrounding (e.g., scale, environmental or bioeconomy policies) and technological parameters (e.g., acidification yield, PHA content in biomass or recovery yield). Those scenarios derived under ambitious environmental and bioeconomy policies shop up to 50% lower environmental impacts than those under business-as-usual policies. These differences are caused by the different background processes’ environmental burdens (e.g., electricity mix with low renewable energies share) and the higher consumption of chemicals and utilities. However, the environmental impacts caused by lower yields can be partially mitigated by valorizing the intermediate waste streams into biogas. Sensitivity analysis results pointed out recovery yield and PHA content as the parameters that influence most the environmental performance, being responsible for up to 60% of variance in environmental performance. These parameters determine the chemicals and utilities consumption in PHA downstream processing, which is confirmed as the main environmental hotspot. This work goes beyond previous LCA studies on PHA production and quantifies the influence of different parameters on the environmental performanceS

An environmental optimization model for bioenergy plant sizes and locations for the case of wood-derived SNG in Switzerland

Bioenergy from woodfuel has a considerable potential to substitute fossil fuels and alleviate global warming. One issue so far not systematically addressed is the question of the optimal size of bioenergy plants with regards to environmental and economic performance. The aim of this work is to fill this gap by modeling the entire production chain of wood and its conversion to bioenergy in a synthetic natural gas plant both with respect to economic and environmental performance. Several spatially explicit submodels for the availability, harvest, transportation and conversion of wood were built and joined in a multi-objective optimization model to determine optimal plant sizes for any desired weighting of environmental impacts and profits. We find a trade-off between environmental and economic optimal plant sizes. While the economic optima range between 75 – 200 MW, the environmental optima are with 10 – 40 MW significantly smaller. Moreover, the economic optima are highly location specific and tend to be smaller if the biomass resource in the geographic region of the plant is scarcer. The results are robust with regards to the effect on global warming as well as with respect to the aggregated environmental impact assessment methods Ecoindicator ’99 and Ecological Scarcity 2006

Future greenhouse gas emissions of automotive lithium-ion battery cell production

Understanding the future environmental impacts of lithium-ion batteries is crucial for a sustainable transition to electric vehicles. Here, we build a prospective life cycle assessment (pLCA) model for lithium-ion battery cell production for 8 battery chemistries and 3 production regions (China, US, and EU). The pLCA model includes scenarios for future life cycle inventory data for energy and key materials used in battery cell production. We find that greenhouse gas (GHG) emissions per kWh of lithium-ion battery cell production could be reduced from 41 to 89 kg CO2-Eq in 2020 to 10-45 kg CO2-Eq in 2050, mainly due to the effect of a low-carbon electricity transition. The Cathode is the biggest contributor (33%-70%) of cell GHG emissions in the period between 2020 and 2050. In 2050, LiOH will be the main contributor to GHG emissions of LFP cathodes, and Ni2SO4 for NCM/NCA cathodes. These results promote discussion on how to reduce battery GHG emissions

The ecoinvent database version 3 (part II): analyzing LCA results and comparison to version 2

Industrial Ecolog

Analysis of the Availability of Bioenergy and Assessment of its Optimal Use from an Environmental Perspective

This thesis addresses the availability and environmentally optimal use of bioenergy. A life cycle perspective is adopted to consider the supply, the technical conversion, and the final use of bioenergy as well as its use for the substitution of fossil energy. In order to determine the sustainable energetic biomass potential in Switzerland, which is the geographic focus of this thesis, a bioenergy potential assessment is conducted using a sustainability constraints approach. Life cycle assessment (LCA) is performed to analyse the suitability of the conversion of wood to synthetic natural gas (SNG). However, individual technology LCAs are not sufficient to provide answers to the question of "how energetically available biomass resources can be used optimally for bioenergy from an environmental perspective". Instead, more comprehensive trans-sectoral assessments are required including all relevant bioenergy technologies and end-uses, as well as fossil energy technologies that can be substituted. To enable such analyses, an LCA-based system optimization (LCA-SO) framework is developed and applied to the Swiss and European cases. Finally, also spatial aspects need to be considered to determine optimal plant sizes. Therefore, a spatially explicit bioenergy value chain model was developed for the case of SNG plants in Switzerland. One of the main findings of this thesis is that 82 PJ of biomass is available in Switzerland, which corresponds to approximately 7% of its primary energy demand. Half of this potential has yet to be realized. By 2035, when optimally used in the business as usual scenario defined by the Swiss Energy Perspectives, biomass could mitigate about 5 megatons of CO2, which would be equal to 13% of Switzerland's total emissions. Simultaneously, the demand of fossil energy for heat, electricity, and transportation would be reduced by 13%, 3%, and 2%, respectively. In the European Reference Scenario (2030) 9%, 13%, and 1%, respectively, of fossil heat, electricity, and transportation could be replaced and 600 Mt of CO2, equal to about 15% of the EU's total emissions, could be avoided. To achieve these goals, woody biomass should be used mainly for heating and combined heat and power (CHP) generation. The production of SNG from wood to substitute fossil energy has been found environmentally beneficial from the GHG, Ecological Scarcity, and Eco-indicator 99 perspectives. However, the production of transportation fuel from woody biomass is, at the current technological development state, associated with important efficiency losses and is therefore not considered an optimal solution. For non-woody biomass (by which we refer to agricultural residues, manure, bio- and food industry wastes, and sewage sludge) the optimal use is to a large degree determined by the substitution of fossil energy and varies according to the environmental indicator applied. For all biomass, it is vital that a high substitution efficiency is achieved, which implies an efficient conversion of biomass and the choice of optimal substitutions. Finally, the spatially explicit bioenergy modelling conducted in this work indicates that smaller bioenergy plant sizes are slightly preferable in terms of overall environmental benefits, mainly due to reduced transportation distances. However, further analyses would be required to generalise this finding

Die Ökobilanz der energetischen Holzverwertung: Faktoren für einen hohen ökologischen Nutzen

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