Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This research is very interesting and worth of study. I suggest it being accepted with minor revision as detailed below:

1. English needs to improve. They are some typos and grammar issues. It is suggested to have either native English speaker or experienced researchers to proofread it.

2. The explanation for the results need to improve. The authors just presented their results in figures, but the explanation on the figure is very brief. It needs to be improved.

3. The error range is too large. It might be better to classify the car range for similar capacity cars such as small car, medium car, large car. Currently, they put all these cars together which leads to large range of errors. 

4. it is suggested to clearly specify the way of labelling? 

Comments on the Quality of English Language

English is good, but it needs to improve as there are many typos and grammar issues.

Author Response

Comment: This research is very interesting and worth of study. I suggest it being accepted with minor revision as detailed below.

Response: We thank the reviewer for the positive evaluation.

 

Comment: English needs to improve. They are some typos and grammar issues. It is suggested to have either native English speaker or experienced researchers to proofread it.

Response: Following the reviewer’s comment, we have carefully checked the entire text for typos, and for the correct use of English. Two of our four co-authors are native speakers. They provided critical feedback and helped improve the manuscript.

 

Comment: The explanation for the results need to improve. The authors just presented their results in figures, but the explanation on the figure is very brief. It needs to be improved.

Response: We thank the reviewer for the comment and have carefully reviewed, once more, the entire results section. We think it now presents the most important empirical findings in an informative, yet concise, manner. We would like to maintain a clear separation between the presentation of results in Section 3 and the discussion of results in Section 4 and therefore abstain from discussing, e.g., implications or limitations of our results, in more detail in Section 3.

            However, following the reviewer’s comment, we have identified one place, where the results could benefit from a longer explanation. On P4-5, we now write in relation to Figure 2: “Yet, drawing conclusions from Figure 2 about the powertrain efficiency is not straightforward. First, the number of available models differs between manufacturers. Some offer one or a few models in certain market segments, whereas others offer models in virtually all market segments. Second, the technical characteristics and attributes of models vary between individual manufacturers. We see in Section 4.2 how differences, e.g., in mass, frontal area, or battery capacity incur considerable efficiency trade-offs.”

 

Comment: The error range is too large. It might be better to classify the car range for similar capacity cars such as small car, medium car, large car. Currently, they put all these cars together which leads to large range of errors. 

Response: The reviewer raises an important point. The purpose of Figure 2 is to show differences in the efficiency of models between individual manufacturers. The results highlight that the energy consumption of vehicles can vary considerably within and between manufacturers. This implies that other attributes such as mass, front area, or battery capacity indeed incur important efficiency trade-offs, which are analyzed in Section 3.2. We think the large error margins make this fact transparent, rather than disguising it. As the article already presents myriad figures and analyses, we prefer to abstain from disaggregating Figure 2, e.g., for several vehicle classes. This choice may be justified because the related information is to some extend already visible in Figures 4 and 5. Furthermore, it might not be straightforward to distinguish vehicle classes, which then lead to smaller error ranges in each class. For example, vehicles could be classified by their length. However, such a classification would not account for different chassis types such as SUVs, crossovers, sedans, or light-duty vehicles, which, in turn, causes similarly large error margins in the individual classes. Likewise, separating vehicles by price, mass, or battery capacity would necessarily disregard the many other factors that introduce variability into the energy consumption of electric vehicles.

Yet, the reviewer’s comment highlights another weakness of Figure 2. It does currently not show readers how many vehicles compose the data samples for individual manufacturers. We have therefore adapted the figure in this respect and provide on the y-axis information about the respective sample sizes. Together with the additional text in response to the previous comment, this modification makes Figure 2 more transparent, without unduly extending the manuscript.

 

Comment: It is suggested to clearly specify the way of labelling? 

Response: We thank the reviewer for this comment and have carefully reviewed the manuscript in this respect. At the end of the introduction, we now provide more background information on labelling in the European Union. On P1 we have clarified: “While energy labelling could address this situation, Europe lacks a dedicated energy label that classifies the energy consumption of electric vehicles in a transparent and easily understandable manner.”

On P2, we now explain at the end of the introduction: “Energy labels have long helped consumers to identify efficient products, and they have motivated manufacturers to innovate. Following their introduction for household appliances in 1994 [20], Europe has updated and expanded the labelling scheme to include tires [21], space heaters [22], electronic displays [23], as well as smartphones and tablets [24]. Including electric vehicles would ultimately cover a technology whose electricity consumption may soon exceed that of any other labelled product.”

 

Comment: Comments on the Quality of English Language - English is good, but it needs to improve as there are many typos and grammar issues.

Response: In line with our response above, two of our authors are native English speakers, who have carefully checked the entire manuscript for typos and correct use of English.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper may be accepted for publication, but with minimal changes in the following:

      (i)            Check the title. Did you mean the European Union instead of Europe?

   (ii)            The proposal is to exclude specific values within the abstract.

   (iii)            As part of the introduction, the sentence (The market for electric vehicles is booming) should be reformulated.

  (iv)            Any debate about electric vehicles should, among other things, be complemented by real facts. It is a well-known fact that electricity for batteries on electric vehicles is mainly obtained from dirty technologies/fuels, i.e. burning coal and oil. Therefore, when talking about the zero emissions of electric vehicles, it is necessary to include the emissions that occur during the production of electricity. As a temporary solution, the use of hybrid vehicles should be noted. In that case, natural gas is used as fuel for the internal combustion engine that drives the electric current generator on the vehicle. Natural gas is cleaner than oil and coal. Electric drive makes sense only if the electricity for charging the batteries is obtained from renewable energy sources, such as water and wind energy, geothermal energy, etc.

    (v)            The aforementioned facts should be integrated within the existing introductory analysis. For this purpose and for the sake of a more complete comparison, it is necessary to analyze and refer to the research carried out in the following scientific works: https://doi.org/10.3390/su11184948  and

https://doi.org/10.3390/atmos15020184  

  (vi)            For each researched vehicle, it is necessary to enter the following data: (MY), fuel type (diesel or gasoline engine), etc.

 (vii)            Please state the version number of the used software for models forming and programming. State the name of the manufacturer, city, and country from where the equipment was sourced.

(viii)            Show the concept of a mobile or home charging station for electric-powered vehicles. Show the network of chargers on highways. Point out problems and needs.

  (ix)            The contents of some figures are not legible. Please replace the images with one of a sufficiently high resolution (min. 1000 pixels width/height, or a resolution of 300 dpi or higher).

    (x)            Expand the list of references and the introductory part of the work.

  (xi)            For the purpose of comparison, as example, look the difference between zero emission targets and curent situation regarding to various electric grid and EV.

 (xii)            Check the complete material, especially the terminology, abbreviations, and units of measurement.

(xiii)            Expand the discussion of the achieved research results in accordance with the set research goals. Clearly state the contribution of the research.

Author Response

The paper may be accepted for publication, but with minimal changes in the following.

Response: We thank the reviewer for the positive evaluation.

 

Comment: Check the title. Did you mean the European Union instead of Europe?

Response: The reviewer addresses an important point. Our data sample comprises electric vehicles that are available in Germany, the Netherlands, and the United Kingdom. The discussion of energy labelling focuses more explicitly on the European Union (EU) but it is relevant for many more countries, since EU legislation (e.g., type approval of motor vehicles but also energy labelling) is implemented explicitly or implicitly in the national laws of non-EU countries (examples are the United Kingdom that was a EU Member State until 2020, but also Norway, Switzerland, Iceland, as well as the current EU candidate countries). To emphasize this more general scope and relevance of the paper, we prefer to refer in the title to ‘Europe’.

 

Comment: The proposal is to exclude specific values within the abstract.

Response: To address this comment, we need to consider the objective of this paper, which is 1) to analyze the technical characteristics of electric vehicles, and 2) to provide researchers and policy makers with empirical data regarding energy efficiency and related trade-offs. This objective requires the presentation in the abstract of key numerical results of our analysis. We therefore would like to abstain from excluding specific values from the abstract. This approach is in line with the general recommendation for writing scientific abstracts, which should provide readers with a synthesis of the research rather than metainformation about the research (see, e.g., Eckhoff, J. (2019): How to write an abstract. Springer Nature. Source: https://communities.springernature.com/posts/how-to-write-an-abstract; Alexandrov, A.V., Hennerici, M.G. (2007): Writing good abstracts. Cerebrovasc Dis (2007) 23 (4): 256–259).

 

 

Comment: As part of the introduction, the sentence (The market for electric vehicles is booming) should be reformulated.

Response: We agree with the reviewer. Since this sentence does not contain any tangible information, we have deleted it from the manuscript.

 

Comment: Any debate about electric vehicles should, among other things, be complemented by real facts. It is a well-known fact that electricity for batteries on electric vehicles is mainly obtained from dirty technologies/fuels, i.e. burning coal and oil. Therefore, when talking about the zero emissions of electric vehicles, it is necessary to include the emissions that occur during the production of electricity. As a temporary solution, the use of hybrid vehicles should be noted. In that case, natural gas is used as fuel for the internal combustion engine that drives the electric current generator on the vehicle. Natural gas is cleaner than oil and coal. Electric drive makes sense only if the electricity for charging the batteries is obtained from renewable energy sources, such as water and wind energy, geothermal energy, etc.

Response: We agree in essence with the reviewer’s comment, as we had investigated and confirmed these findings in earlier LCA projects (Helmers, Dietz, Weiss, 2020). However, we also think it is to some extent out of scope of the current paper. It is clear from the introduction and method sections that we focus on the certified and real-world energy consumption of electric vehicles, i.e., the electricity consumed while vehicles are driven on the road.

The system boundary of our research is now explained in a very transparent manner in Section 4.1. The bullet point on ‘System boundary’ we now state that: “We focus here on the energy consumption during vehicle use. It is beyond the scope of this research to evaluate the overall energetic and environmental impacts of electric vehicles, which requires holistic life cycle assessment […]”.

The expression ‘zero-emission vehicles’ is only used in the introduction in reference to pertinent policy documents. These documents refer to ‘zero-emissions’ to mean vehicles that do not have any tailpipe emissions. Since this terminology is generally used and understood in this way by a broad audience, and since the terminology is not relevant for the actual research of this article, we prefer to abstain from discussing and clarifying it in greater detail.

 

Comment: The aforementioned facts should be integrated within the existing introductory analysis. For this purpose and for the sake of a more complete comparison, it is necessary to analyze and refer to the research carried out in the following scientific works: https://doi.org/10.3390/su11184948  and

https://doi.org/10.3390/atmos15020184 

Response: To account for the reviewer’s request, we now address the relevance of environmental impacts from electricity generation in Section 4.1 (P13L409). The bullet point explaining the system boundary of our research also includes the proposed reference to the paper https://doi.org/10.3390/su11184948 and reads as follows: “System boundary: We focus here on the energy consumption during vehicle use. It is beyond the scope of this research to evaluate the overall energetic and environmental impacts of electric vehicles, which requires holistic life cycle assessment, including vehicle production, end-of-life treatment, and electricity generation (e.g., [36-38,56]).”

            We have critically assessed the paper https://doi.org/10.3390/atmos15020184 and found it to be out of scope for this research.

 

Comment: For each researched vehicle, it is necessary to enter the following data: (MY), fuel type (diesel or gasoline engine), etc.

Response: Our research focuses on fully-electric vehicles; any other vehicles equipped with internal combustion engines are excluded. We clarify this point now upfront in the methodology section. On P2L86, we write: “This article covers fully electric passenger cars and light-duty vehicles powered by an electric motor that draws electricity exclusively from an externally rechargeable battery. We include vehicles classified in the European Union as categories M1 and N1 [13]. We exclude: i) fuel-cell vehicles running on hydrogen, as well as ii) hybrid, plug-in hybrid, and any other vehicles equipped with an internal combustion engine.”

 

Comment: Please state the version number of the used software for models forming and programming. State the name of the manufacturer, city, and country from where the equipment was sourced.

Response: Following the reviewer’s comment, we now state the version of the software used for our data analysis. On P 4, we write: “All analyses are conducted with R version 4.4.0 […].”. Other equipment, such as laboratory apparatuses, was not used for this research. Hence, we cannot ‘state the name of the manufacturer, city, and country from where the equipment was sourced’.

 

Comment: Show the concept of a mobile or home charging station for electric-powered vehicles. Show the network of chargers on highways. Point out problems and needs.

Response: Although these are critical aspects for the adoption of electric vehicles, they are beyond the scope of this research. Our focus is here on the energy consumption and related efficiency trade-offs in electric vehicles.  We prefer neither to address mobile and home charging stations and nor charging networks on highways, given that this is both out of scope and a fast-evolving landscape.

 

Comment: The contents of some figures are not legible. Please replace the images with one of a sufficiently high resolution (min. 1000 pixels width/height, or a resolution of 300 dpi or higher).

Response: We have checked the resolution and size of all figures and have provided the journal with high-resolution pdf files of all diagrams.

 

Comment: Expand the list of references and the introductory part of the work.

Response: The reviewer is correct in pointing out that our introduction is short. However, this brevity is a deliberate choice. The article presents data and analyses and is therefore empirical, rather than conceptual. We think such an article can be introduced by briefly stating the motivation, research question, and political implications of the research.

However, to address the reviewer’s concern, we think readers may indeed benefit from a few words, and references, about the history of energy labelling in Europe. Such information is relevant for our research because it indicates that energy labelling has been gradually expanded in past decades to include new products. Thus, extending the label to electric vehicles will not require a fundamental shift in the labelling approach, but would rather be in the spirit of the labelling philosophy. On P2L75, we now write: “Energy labels have long helped consumers to identify efficient products, and they have motivated manufacturers to innovate. Following their introduction for household appliances in 1994 [20], Europe has updated and expanded the labelling scheme to include tires [21], space heaters [22], electronic displays [23], as well as smartphones and tablets [24]. Including electric vehicles would ultimately cover a technology whose electricity consumption may soon exceed that of any other labelled product.”

 

Comment: For the purpose of comparison, as example, look the difference between zero emission targets and current situation regarding to various electric grid and EV.

Response: This comment addresses important aspects, which are, however, beyond the scope of our research. We do not attempt to analyze emission targets, nor do we assess or scrutinize pathways for the transition towards certain policy goals. All we do is to analyze the energy consumption of electric vehicles (as certified during type approval and as experienced by vehicle users on the road). To avoid distracting the discussion, we prefer not to address the mentioned issues in greater detail. Also, we like to indicate that we have published 6 scientific papers addressing the relevance of the carbon footprint of electricity production when it comes to the life cycle impact of electric vehicles. This research confirmed the points the reviewer raised, but again, here we focus solely on the electricity consumption.

 

Comment: Check the complete material, especially the terminology, abbreviations, and units of measurement.

Response: Following the reviewer’s comment, we have checked the text, as well as the terminology, abbreviations, and units to the best of our ability. Abbreviations and units are now explained upon first use. We think the revised manuscript is free of errors, but please let us know if you spot any issues in this respect.

 

Comment: Expand the discussion of the achieved research results in accordance with the set research goals. Clearly state the contribution of the research.

Response: To address the reviewer’s comment, we have scrutinized once more the results, discussion, and conclusions sections. More specifically, on P4-5, we now write in relation to Figure 2: “Yet, drawing conclusions from Figure 2 about the powertrain efficiency is not straightforward. First, the number of available models differs between manufacturers. Some offer one or a few models in certain market segments; others offer models in virtually all market segments. Second, the technical characteristics and attributes of models vary between individual manufacturers. We see in Section 4.2 how differences in, e.g., mass, frontal area, or battery capacity, incur considerable efficiency trade-offs.”

Furthermore, we now link in a more transparent manner the discussion of results with the stated research objections. The comparison of results with other studies (Section 4.2) and the discussion of implications for policy makers (Section 4.3) were carefully reviewed in this respect. The last bullet point of the conclusions on P17L530 now clearly states how our results can be used by policy makers: “The large variability in energy consumption values suggests there is a need to inform consumers about the energy use, energy-related costs, and efficiency trade-offs of electric cars.”

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript gathers relevant information that could be useful for other research related to the characteristics of electric vehicles. It also proposes that vehicles be classified primarily in terms of efficiency. I believe this is an appropriate and pertinent manuscript, and the information obtained will be useful for future researchers.

I consider it essential to expand the state of the art, as the introduction is very brief. Avoid repeating the results in the conclusions. The conclusions should mention relevant aspects of the research without making unnecessary repetitions.

Author Response

Comment: The manuscript gathers relevant information that could be useful for other research related to the characteristics of electric vehicles. It also proposes that vehicles be classified primarily in terms of efficiency. I believe this is an appropriate and pertinent manuscript, and the information obtained will be useful for future researchers.

Response: We thank the reviewer for this positive evaluation. The intended purpose of our paper is precisely as summarized by the reviewer.

 

Comment: I consider it essential to expand the state of the art, as the introduction is very brief.

Response: In line with our response to Reviewer 2, we would like to highlight that our research presents data and analyses and is therefore empirical, rather than conceptual, in nature. We think such research can be briefly introduced by stating the motivation, research question, and any political/societal implications.

In line with our responses above, we think readers may indeed benefit from a few words about the history of energy labelling in Europe. Such information is relevant for our research because it indicates that energy labelling has been gradually expanded in past decades to include new products. Thus, extending the label to electric vehicles will not require a fundamental shift in the labelling approach but it would rather be in the spirit of the energy label. On P2L77, we now write: “Energy labels have long helped consumers to identify efficient products, and they have motivated manufacturers to innovate. Following their introduction for household appliances in 1994 [20], Europe has updated and expanded the labelling scheme to include tires [21], space heaters [22], electronic displays [23], as well as smartphones and tablets [24]. Including electric vehicles would ultimately cover a technology whose electricity consumption may soon exceed that of any other labelled product.”

 

Comment: Avoid repeating the results in the conclusions. The conclusions should mention relevant aspects of the research without making unnecessary repetitions.

Response: We thank the reviewer and agree with this comment. In response, we now present only in the first bullet point numerical results on energy consumption. All other numerical values have been removed from the conclusions. We think it is justified to repeat energy consumption values in the conclusions because this finding is central to our analysis and to the discussion of energy labelling.