Management of Railway Power System Peaks with Demand-Side Resources: An Application to Periodic Timetables

Round 1

Reviewer 1 Report

The paper entitled as "Management of Railway Power System Peaks with Demand Side Resources: An Application to Periodic Timetables" is an interesting paper to the audiences of transportation, urban development and energy. The paper aims at analysing Railway Power Systems Demand.

The following should be corrected and adressed by the authors.

1) In the abstract "some models" term should be extended. Which models, what are the contributions comparing the analysis in the paper to the conventional techniques? These should be stated. 

2) The overall investigation shows that the concept of sustainability is not adequately discussed and referenced. I see that the paper is linked to it, however, authors did not clarify it. Considering that the paper is submitted to Sustainability Journal, the paper should be revised with this respect in various places: 

abstract: underline the relation to sustainability

introduction: introduce papers or already existent literature with emphasis on sustainability

policy recommendation and discussion section.

Conclusion.

3) Policy recommendations: Authors should introduce a discussion and policy recommendation section in this paper before conclusion. Discuss findings by relating them to sustainability. On the managerial side, policies are stated. However, environmental impacts should be discussed. What are the suggestions to societies? Policy makers? following the findings of the paper? I suggest to emphasize the implications on emvironmental sustainability by relating the findings and analysis to energy demand. Note that the paper already has a comprehensive results section with subheadings. Therefore, this suggested section can be a similar subheading with a similar size of two paragraphs.

4) Various cities and regions are covered in the study. By referencing to statistical agencies such as IEA, can you discuss the ratio of fossil fuel and nonrenewable energy use in total energy with reporting in-text statistics in these countries? With this way, I suggest adding another bridge to energy and environmental sustainability nexus.  After, I suggest underlining your contribution in this paper with respect to energy efficiency by also linking it to environmental sustainability. I suggest this discussion in the results section's relevant places. Also, a short summary can be presented in the discussion section. 

 5) the concept of renewable is used in the abstract, however, it is used only in one place in the paper. By careful revision with regards to critique above, I also ask you to discuss what you wanted to introduce in terms of renewable again in the paper. 

Author Response

Thanks for all your valuable comments and the time you have used in the review process. We enclose an overall document pdf with responses (answer to reviewers from page 1 to 14) and the changes in the R1 version of the document (sustainability_COLORED form page 15).

Author Response File: Author Response.pdf

Reviewer 2 Report

1.       the abstract needs to reduce general information but focus on the method and results. For example, the last sentence “which improves the 19 social and economic benefits of railway transportation on the overall energy and environmental 20 objectives for 2050.” Some data needs to be used to support the benefits.

2.      In figure 2, “Train losses (5-7%” it needs some clarifications about the train losses, are these losses due to system friction (mechanical losses?) or due to rolling resistance. It is noted that mechanical friction losses have already, to some extend, been considered in rolling resistance function.

3.      “These resistance forces can be examined in detail with different models [20, 21] but they are not the objective of this paper.” It is understandable that rolling resistance is not the focus of the paper, however, it is key for energy calculations. It is noted that train starting resistance is significantly higher than the resistance formula Equation (3) as discussed in the paper “Hill-starting a heavy haul train with a 24-axle locomotive”. Some discussions and acknowledge of the starting resistance can be useful. Meanwhile, curving resistance formula is also regarded as in accurate as discussed in “Curving resistance from wheel-rail interface” some discussions and acknowledgment is also useful.

4.      Figure 8 a seems to be incomplete, please adjust the figure. Meanwhile, it is better to explain the notations used in this figure in the captions. Or replace the notations but text descriptions. Otherwise, it is inconvenient to read the figure. Also, Figure 8b probably not contributing a lot to the paper. You can mention that the couch studies is Talgo VI coaches, this is sufficient. Figure 8c also looks incomplete.

5.      In figure 9 a, measured data and simulated data have general agreement. However, there are some obvious differences near 35 min and after 45 min. explanations need to be added about the reasons behind the differences. One of the possible reason can be your air brake model, it seems your braking is shaper than the measured date. In realty air brake acts slowly due to pressurised air.

6.      “increment of mass due to rotating inertia, a coefficient in the range [0, 0.30] depending on the type of vehicle. Usually in the range [0.06, 0.10] for a complete train.” it is better to be more accurate about the parameter as presented by equation (1) and discussed in “Train braking simulation with wheel-rail adhesion model”. this parameter would have significant influences  on your results, for example 0.06 and 0.10 would give you 4% differences in your final results, this is considered to be quite obvious difference.

7.      The starting resistance is also important for your acceleration and braking energy calculations in Table 4. Therefore some discussions about the starting resistance is needed.

8.      Some numbers, values are needed in your conclusions to show the significance of your statements.  

9.      In figure 10, it is good to see that you’ve considered fuel cell, batter and supercapacitors. However, it is not clear what are the percentages of these ESS, different ESS have different characteristics, the final combined characteristics are also different.

10.   “However, hybrid units DHMEU, in the diesel mode of operation, have several advantages to be discussed later in this work, for example, a high traction effort (figure 5b).”  an example application of ESS locomotive can be found in “Comparison of locomotive energy storage systems for heavy-haul operation”.

11.   Examples need to be given for hotel loads, what are the typical types of hotel loads.

Author Response

Thanks for all your valuable comments and the time you have used in the review process. We enclose an overall document pdf with responses (answer to reviewers from page 1 to 14) and the changes in the R1 version of the document (sustainability_COLORED form page 15).

Author Response File: Author Response.pdf

Reviewer 3 Report

The introduction of new technologies in railways is entailed and simulated. The Smart Grids DER policies in PPS, have been identified and simulated for RPS to make easier the implementation of periodic timetables. Train models, “hotel load” models and ESS models have been revisited and linked to improve the usefulness of simulations results. Braking energy can therefore be harvested by ESS and energy efficiency improved both in the RPS and PPS. This is an interesting and comprehensive study, which should give a guideline for the improvement of the social and economic benefits of railway transportation on the overall energy.

I would like to recommend it for publication after minor revision.

1)     The full names of the abbreviations appeared for the first time should be provided, such as “HVAC” in the Abstract part.  

2)     I note that is mainly based on theoretical predication. Have the authors ever put it practical study and case study?

Author Response

Dear reviewer;

Thanks for all your valuable comments and the time you have used in the review process. We enclose an overall document pdf with responses (answer to reviewers from page 1 to 14) and the changes in the R1 version of the document (sustainability_COLORED, from page 15).

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

I see that the papers is greatly updated following review comments. Thanks for careful work. My decision is accept. 

Reviewer 2 Report

thanks for the revision.