A National and Regional Greenhouse Gas Breakeven Assessment of EVs across North America
Round 1
Reviewer 1 Report
The authors attempt to answer a major question whether promoting electric vehicles (EVs) is an effective policy to mitigate GHG emissions in North America based on two major metrics: distance of intersection point (DIP) and emissions disparity (ED). The study benchmarks the environmental performance of the EVs against internal combustion engine vehicles (ICEVs) powered by petrol and diesel at national, regional, and state levels. The study method and data are generally well detailed, explained and cited.
However, the whole study is just an extended case study of the pervious study published by some of the authors who applied exactly the same methodology that previously used to address similar policy question but for different geographic areas. In addition, the assumptions made on the future emissions performance of supply chain, technology, efficiency and recycling are not enough to address all factors that may influence the outcome of the benchmarking. For example, the electricity used to charge the EVs might be produced at a time where clean energy share in the grid is high or low depending on the time of use. Moreover, the study links the changes in environmental performance across the states to only the grid emission intensity, ignoring the emissions pertaining to petrol and diesel delivery which vary based on how far each state is from the supply source and also ignoring the spatial and temporal ambient temperature variations on the EV performance. Too, it ignores the expected scaling up of CO2 capture and storage technologies in the oil industry which may substantially reduce emissions at the source. All of these factors may change the outcome of this study.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This paper evaluates the breakeven of greenhouse gas emissions in the life cycle of electric vehicles in North America, and studies the impact of potential national electricity grids evolutions on emissions of electric vehicles in different regions, which has good research significance. It is recommended to revise the following questions before being accepted.
1. Further explain the innovation of this research.
2. The current data calculation details should be tabulated, and what is the basis for forecasting future data should be stated.
3. How to predict the vehicle type distribution and market penetration rate in 2035? For example, the electrification transformation process of passenger cars and commercial vehicles.
4. What are the hypothetical scenarios for grid decarbonization in 2035? It is suggested to add uncontrollable influencing factors, or to explain the uncertain factors in the development process.
5. The article has great potential to be accepted, and there is relevant literature that deserves to be cited: 'Comparative study on fuel saving potential of series-parallel hybrid transmission and series hybrid transmission. Energy Conversion and Management', 'Practical application of energy management strategy for hybrid electric vehicles based on intelligent and connected technologies: Development stages, challenges, and future trends. Renewable and Sustainable Energy Reviews'.
Author Response
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1 |
Further explain the innovation of this research. |
Please see that to address this comment we have added a contribution statement after the research questions. Text shown below in Italics:
This research makes the following contributions. First, this work performs the first spatial assessments of EV environmental performance across North America which in-corporates electricity trading. This approach has been taken in Europe [29]. Woody et al. [30] performed a spatial LCA of EVs, but their study did not include regional electricity trade and was largely focused on the electrification of heavy-duty vehicles. And (Onat, Kucukvar and Tatari, 2015) had performed a comparative carbon footprint analysis in the US, but, they also did not include interstate trading and published in 2015, making the rapidly developing EV data likely outdated. Mexico and Canada were also not included in their study, making cross-country comparisons difficult, particularly surrounding the varying decarbonization commitments made by each country, as shown in (Shafique and Luo, 2022). The inclusion of Mexico addresses (Onat and Kucukvar, 2022)’s call for in-creased representation of developing country case studies.
We have also addressed additional research gaps in the paragraphs before the research questions, eg lines 104-106 |
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2 |
The current data calculation details should be tabulated, and what is the basis for forecasting future data should be stated. |
The sources for all future predictions are included in the paper, these have been made clearer and are now referenced multiple times, to make the basis for forecasting more visible. E.g. lines 310-312.
Furthermore, since the first manuscript was created, Mexico has released an updated Sustainable Development Programme. While the renewables targets do not change, the projections have and this has been accounted for in lines 446-452. |
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3 |
How to predict the vehicle type distribution and market penetration rate in 2035? For example, the electrification transformation process of passenger cars and commercial vehicles. |
Please note that we in this study we only consider mid-size vehicles and we do not do any fleet level analysis and thus we have not considered the impact of various penetration levels nor vehicle type distribution, as this was not the focus of the study. We certainly think that this is an interesting and important avenue of study however. To improve clarity, in lines 151-154 we have added a clarifying text making clear the scope of the study |
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4 |
What are the hypothetical scenarios for grid decarbonization in 2035? It is suggested to add uncontrollable influencing factors, or to explain the uncertain factors in the development process. |
In our work we benchmark against the decarbonization plans as well as actual projections for each country. However, it is certainly recognized that plans and reality do not always coincide. We have thus added lines 574-576 in the limitations section to reflect these considerations. |
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5 |
The article has great potential to be accepted, and there is relevant literature that deserves to be cited: 'Comparative study on fuel saving potential of series-parallel hybrid transmission and series hybrid transmission. Energy Conversion and Management', 'Practical application of energy management strategy for hybrid electric vehicles based on intelligent and connected technologies: Development stages, challenges, and future trends. Renewable and Sustainable Energy Reviews'. |
Please see that we have greatly updated the literature review, and have added the suggested articles. |
Reviewer 3 Report
These are the comments to enhance the quality of work:
1) Provide some numerical data in the Abstract, what authors have achieved.
2) Critical literature review is required (what you have achieved from review).
3) Enhance literature review section more and incorporate recent references as;
https://doi.org/10.1049/gtd2.12439; https://doi.org/10.1080/15325008.2022.2139870
4) Mention three contributions in point form.
5) Rewrite conclusion section with more informative manner.
Author Response
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1 |
Provide some numerical data in the Abstract, what authors have achieved. |
Please see that both of these points have been added to the abstract |
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2 |
Critical literature review is required (what you have achieved from review). |
Please see that we have greatly updated the literature review in the introduction. From this review, we recognized the need for an EV study which considered the impacts from electricity trade in North America, particularly one which considered the impacts in a developing country context (Mexico). Lastly, from these comments we have further expanded the results to consider ambient temperature impacts on EV performance which are relevant were identified as needed in national level study. Our contribution statement clarifies our identification of these research gaps (see our response to Reviewer 2 comment 1 in this sheet). |
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3 |
Enhance literature review section more and incorporate recent references as;
https://doi.org/10.1049/gtd2.12439; https://doi.org/10.1080/15325008.2022.2139870 |
Please see that these articles have been added to the text in the discussion to strengthen the text. We have further expanded the literature review, adding 24 new references to the study. |
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4 |
Mention three contributions in point form. |
Please see that we have added a contribution statement after the research questions which clearly labels point by point the contributions. |
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5 |
Rewrite conclusion section with more informative manner. |
Please see that the conclusion section has been edited to be more succinct and speak more to the results of the paper |
Round 2
Reviewer 1 Report
The revised version has substantially improved the quality and significance of the conducted research.
Reviewer 3 Report
Comments for author File: Comments.pdf
Author Response
1- For the convenience of the reader, put a table of abbreviations at the beginning of the article and add your abbreviation there.
Please see that we have added such a table before the Introduction.
2-After the introduction, the literature review section should be added to the article.
We thank you for this comment, but the Sustainability format does not include a literature review section, and in line with typical academic paper style, the literature is embedded in the Introduction and Discussion to put such a review in context. If the reviewer feels that there needs to be greater citing within this text, we encourage them to let us know, but we note that in just the Introduction we already have 45 sources, and thus we do not think it is under-researched
3- In part 2.2.1, there is a formula that requires numbering and defining parameters, for example, what does CEF represent.
Please see that we have now added numbering and definition for the parameters
4- In part 2.4.1 and 2.4.2 you can expand the sources
In this section we are stating/explaining the parameters used in the model, so it is not clear the benefit of extra sources as they could potentially confuse the reader in terms of which sources were used for what.
5- In the conclusion, the work done is not bold, please rewrite
Please see that we worked to make the work done within the paper more clear. If it is meant that the work done should be in bold text, we are slightly confused as this is not typical of academic papers.
