Review and Evaluation of Automated Charging Technologies for Heavy-Duty Vehicles

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Summary of paper: This study analyzes automated charging technologies for electric heavy-duty vehicles (HDVs), critical for electrifying heavy road freight transport and integrating with autonomous driving. It covers static and dynamic charging methods, assessing each for advantages, challenges, and readiness levels. Static conductive charging, like charging robots and pantographs, shows promise, with pantographs being the most mature. Static wireless charging faces implementation challenges. Dynamic conductive charging, particularly overhead contact lines, suits high-traffic routes. Dynamic wireless charging has integration potential but faces efficiency issues. Battery swapping reduces charging downtime, with varied readiness levels. Further standardization is crucial for large-scale deployment. Continuous research is necessary to enhance efficiency and integration. Success in these areas will greatly benefit the creation of an efficient, automated, and environmentally friendly transport sector. This paper is less technical and provides more of the current status of the high level market/product view. It is an interesting summary of the multiple pathways underdevelopment for EV charging.

Issue to be addressed:

1. Line 49/50 appears to have a typo in the middle of the sentence

2. The paragraph beginning at Line 51 asserts that all automated HDVs must be electrified. However, this assertion may not hold true and warrants reconsideration within the paper's context. Establishing this hypothesis is not essential for the validity of the rest of the paper.

3. Lines 73-102 should be discussed before the paper structure discussion on line 71.

4. MCS line 122 needs a reference (SAE J3271)

5. Section 2.1 - consider other options such as https://www.greencarcongress.com/2019/07/20190723-staublil.html

6. Section 2.4 - No mention of technology progress beyond currnet status (such as R&d at ORNL, Purdue University, and others). This comment is also noted for the other subsections of section 2.

7. Line 486 - Please confirm that the definitions are not swapped.

8. Table 5 - No mention of issues with different aged batteries or chemistries that need to be maintained and shared between different users, unless this is intended by the generalized use of the word standards.

9. Section 2.6 - Issues with exposure to weather events is not addressed. May also be careful with a TRL 9 designation for Trolley buses, which while true is not the same operating domain as the main space of heavy duty vehicles.

10. Section 2.8 - consider the challenges with dynamic vehicle alignment for energy exchange. Tolerance to this is being considered as one of several mitigation strategies.

11. Section 2.8 - may also sider the work that HEVO is doing.

12. There is very little by way of meaningful discussions of the investigations conducted. The paper, while informative of the current state of some of these systems, would gain significnat value if it could get into where or how this may need to evolve for future alignments, international use (beyondbroad comments such as  "common standards"), interoperability and inter-modalities.

13. It is noteworthy that the authors recommeded high TRLs don't imply that the issues (some technical or aligned technical i.e. issues with adjacent systems) have been sorted out. This is somewhat misleading. Example, swappable battery technology TRL 9 still has several open issues several indicated by the authors. But there are adjacent tech issues such as the impact to the battery performance and durability (e.g. contactors, plumbing and cooling system wear, etc.) over time that have not be sufficiently investigated. This should be addressed by the authors.

Comments on the Quality of English Language

English needs minor edits.

Author Response

Dear Reviewer,

Thank you for your valuable feedback and many helpful suggestions!
We addressed the following issues:

01: We corrected the typo (depends à depend) and wrote out “i. a.” in full (line 38 f.).

02: We re-formulated the sentence to prevent the understanding that all automated HDVs must be electrified (line 46 ff.).

03: We re-structured the introduction accordingly (line 99 f.).

04: We added a reference (line 125).

05: Following additional research, we added a section on the charging system developed by the company Stäubli (line 196 ff.). Additionally, we included it in our TRL assessment (line 210 ff.). Thank you for your suggestion!

06: We thought about your suggestion to include R&D examples for the charging technologies. However, as we derive the TRLs from the examples, we decided to focus on the technologies being developed by companies for market launch, which exhibit the highest TRLs. For technologies, which are not as intensively being developed by companies, such as the dynamic wireless and the battery swap technology, we included R&D examples. Additionally, we included a note stating that our list of examples is not exhaustive (line 114).

07: We confirm that the definitions were not swapped. However, to prevent misunderstanding we added explanations (line 498 ff.).

08: We added an additional paragraph on the need for standards for the charging stations, including their equipment, which determines whether a battery is installed in a vehicle (line 553 ff.). We added a corresponding bullet point to the table. 

09: We added a paragraph on the charging infrastructure’s sensitivity to strong winds and gusts (line 687 ff.). We added a corresponding bullet point to the table. We separated the TRL evaluations of the HDTs and trolley buses (line 708).

10: We added a paragraph on the importance of tolerance to horizontal misalignment for dynamic wireless charging technologies (line 878 ff.). Additionally, we added a corresponding bullet point to the table.

11: Following additional research, we added the dynamic wireless charging technology being developed by the Purdue University as another example for charging heavy-duty vehicles dynamically and wirelessly (line 900 ff.). We have included this technology in our TRL assessment (line 914 ff.). Thank you for your suggestion!

12: In our "Conclusions" chapter, we have already addressed many of the points you suggested. Perhaps the choice of the chapter title was misleading, which is why we have renamed it to "Discussion and Conclusions." Additionally, we have added several paragraphs to better contextualize the technologies and clarify recommendations for development and policy actions. These paragraphs are: 929ff; 934f; 948ff.

13: We thought about your comment. However, we are of the opinion that a TRL 9 does not imply that all issues with the technology have been overcome but that the technology is proven in an operational environment (see line 395). In our opinion this does not exclude further R&D and optimization. In the case of battery swapping, we really see to completely different situations in China and Australia where the technology is on the way to mass deployment and the rest of the world, especially Europe, where only one single prototype exists.

Thank you again for the feedback. We hope that we have been able to respond to your criticism with the changes mentioned.

Best Regards

The authors

Reviewer 2 Report

Comments and Suggestions for Authors

The authors provide a summary of charging technologies. The paper is well written.

1.    Please list the research questions addressed in this paper. These should address a research gap which you should illustrate based on a literature review of recently published papers.
2.    Please clearly state what new knowledge or new conclusions your paper offers. It seems as if most parts of the paper are just an illustration of (soon) available technology.
3.    If you would like your paper to go beyond merely summarizing (soon) available technology, I would recommend adding a discussion section where you compare and contrast the future development needs of the technology, and which reconditions you are giving or anything else that could add knowledge to the research instead of summarizing it.
4.    You use references in the tables such as “in contrast to 1”. While the links work, I feel that it is a bit annoying to always have to check which number refers to which technology. These numbers don´t correspond to any table number. Hence people who read a printed version of the paper, or don´t want to constantly jump back and forth between the paper won´t know which numbers refer to which technology. Please also consider that using these links as you did will make it difficult for blind people to “listen” to the paper.
 

Author Response

Dear Reviewer,

Thank you for the time you took to review our work and for the valuable feedback.

We have addressed your points wherever possible. Below, you will find our answers to your comments and, where applicable, what we have changed in the paper.  

1 & 2: In lines 49ff, we have added a brief section to delineate the paper’s objectives and research question more clearly. However, this work does not constitute original research on this topic but rather serves as a review of existing technology, aiming to consolidate current knowledge and thus lay a foundation for further research. To our knowledge, there are currently no meta-analyses in the field of automated charging for heavy-duty vehicles. We therefore believe that a list of comparable reviews on, for example, non-automated charging infrastructure or contactless charging infrastructure offers no added value to the reader and the scientific knowledge gain. Relevant scientific literature on the individual technologies is, of course, referenced in the corresponding chapters.

3: In our "Conclusions" chapter, we have already addressed many of the points you suggested. Perhaps the choice of the chapter title was misleading, which is why we have renamed it to "Discussion and Conclusions." Additionally, we have added several paragraphs to better contextualize the technologies and clarify recommendations for development and policy actions. These paragraphs are: 929ff; 934f; 948ff.

4: Thank you very much for this comment. You are absolutely right that the numbers hinder the flow of reading and comprehending. And we must admit that we have not paid enough attention to making this document as barrier free as possible.  Even though the numbers should correspond to the table numbers, otherwise this would be an error in formatting. Now in the current document this should work.

We have added abbreviations of the respective technologies both in the respective table and whenever they are mentioned and referenced. We hope this will help in making the paper more readable and easier to listen to.

Thank you again for the feedback. We hope that we have been able to respond to your criticism with the changes mentioned.

Best Regards

The authors

Reviewer 3 Report

Comments and Suggestions for Authors

The study offers a thorough examination of automated charging technologies for electric heavy-duty vehicles, encompassing static and dynamic approaches and evaluating their advantages, challenges, and readiness levels. It underscores the need for ongoing research, development, and standardization efforts to enhance efficiency, reduce costs, and ensure seamless integration into existing infrastructures for the advancement of an automated and sustainable transport sector. The paper makes a significant scientific contribution and is suitable for publication. A few minor suggestions include restructuring some sections for better clarity, such as dividing the extensive subsections in Section 2 into separate sections. Additionally, Figure 11 could be relocated before the conclusion, aligning it with the relevant section for improved coherence.

Comments on the Quality of English Language

good

Author Response

Dear Reviewer,

Thank you for your encouraging words, valuable feedback, and helpful suggestions!

We subdivided Section 2 into Section 2.1 Static Charging Technologies (Subsections 2.1.1 to 2.1.5) and Section 2.2 Dynamic Charging Technologies (Subsections 2.2.1 to 2.2.3) for better clarity. As the final figure serves as a summary of the TRL assessments and can not be assigned to just the static or the dynamic charging technologies, we decided to keep it in Section 3.

Best Regards

The authors

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for addressing my points from the previous review. My key suggestion (following up from my previous review) is to provide better clarity when TRL 8/9 is suggested as the scoring. I appreciate the comments in your reviewer feedback that this high TRL does not mean that there aren't any challenges. I recommend that this view be better highlighted in the paper. There is a significant difference between product introduction as small scale versus at wide scale. Both may be at a TRL 9 but the challenges and work efforts going forward are quite different. 

Comments on the Quality of English Language

Well writen with minor corrections needed.

Author Response

Dear Reviewer,

Thank you for your feedback!
For better clarity we added a paragraph to each TRL assessment concluding a TRL 9. In this paragraph we point out that a TRL 9 does not rule out further development to address potential challenges (see line 396 ff. as an example). 

Best regards

The Authors

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed my comments.

Author Response

Dear Reviewer,

Thank you for taking the time evaluate our revised work.

Best regards

The Authors