Evaluation of the Lifecycle Environmental Benefits of Full Battery Powered Ships: Comparative Analysis of Marine Diesel and Electricity

Round 1

Reviewer 1 Report

A paper discussing an interesting topic via a sound approach/methodology.

Content is absolutely fine and well supported; a few minor language improvements (see attached file for clarification) are needed before proceeding to the publishing stage.

Comments for author File: Comments.pdf

Author Response

Thank you very much again for your kindest view on our research work. Also, we do very appreciate your editorial comments which have enhanced the quality of this paper with no doubt. We have reflected all your comments into the manuscript. We hope all our responses and actions to your comments make sense.

 

Comments and Suggestions for Authors

A paper discussing an interesting topic via a sound approach/methodology.

Content is absolutely fine and well supported; a few minor language improvements (see attached file for clarification) are needed before proceeding to the publishing stage.

 

We have amended the manuscript in response to all comments in the attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper is on an interesting topic, but is very poorly written, with important content describing methods and assumption missing and some content that is seemingly irrelevant.

The results presented are not supported by the paper. For example, how emissions during fuel and electricity transport were estimated is not described, but the emissions are reported to be a significant fraction of the total emissions. Testing on engine fuel consumption and emissions is inadequately described. No validation of the simulations of the electric ship were described.

Additional related studies could be citied.

Some non-standard English and some awkward sentences.
Many references are missing or are invalid.
Without major revisions to add the missing content, streamline the irrelevant details, fixing references, and editing the language, I cannot recommend publishing this paper.

Section 2.1.2.

Figure 4 shows no electric load, while Figure 5 does. Is there no electric load or generator consuming fuel on the diesel ship? What is the electric load on the electric ship?

Is there any emission control or exhaust aftertreatment on the diesel ship?

The assumed relationship between allowable depth of discharge and number of cycles is based on an old reference (Buchmann, 2001). Is this relationship valid for current batteries?

The description of the control system on p 9 will be confusing to most readers of this journal, as will the schematics in Figure 6, 7, and 8. What details are needed for supporting the LCA? What energy losses are there in the system? How do these depend on the propulsion power (linear, non-linear)?

Section 2.1.3, Was the PSIM model validated? Can the authors provide any evidence that the model gives realistic results?

Section 2.2.1 The reference cited for the electric generation mix for South Korea is cited as EIA, but the source is the BP Statistical Review of World Energy. Please fix the reference or the source cited.

Please provide a valid reference for the energy production modeling.

Section 2.2.1 What was assumed about electrical losses between delivery of power to the port and the energy delivered to the battery onboard the electric ship?

In Figure 12, what does “AMP” mean?

Section 2.2.2. Gives no results. Were energy consumption and emissions during fuel transport and electricity transmission and distribution neglected? The last sentence in Section 2.2.2 is incomplete. Perhaps text is missing.

Section 2.2.3. The authors cite references on the discrepancy between actual and calculated emissions (Bauer et al., 2015; Tietge et al., 2016), but the works cites address highway passenger vehicles. Are there any references discussing discrepancies between calculated and actual emissions from marine vessels?

It is good that the authors present results of fuel consumption and emission measurements, but more details need to be provided. What engine was tested? Under relevant compression ratios and temperatures? What laboratory was testing performed in? Were standard test procedures followed? What standard procedures? What fuel was used in the test? How was fuel consumption measured? How were engine emissions measured? Were these engine-out measurements or downstream of emission aftertreatment equipment?

Were particulate emissions measured?

In Table 4, what do “Inlet” and Return” mean?

The table after Table 4 should be numbered Table 5. In this table, does the electricity represent the electricity from the battery? Or is it the electricity supplied to the ship during charging, or the electricity supplied to the port for charging?

In Section 3, why weren’t particulate matter emissions not calculated?

Section 3.2.1. Insufficient information is provided about the six electricity generation scenarios. How were emissions estimated for electricity generation?

 

Author Response

We are very grateful for your detailed and specific comments which we might have missed or caused some confusion to readers. Your comments helped us to have carefully revisited our paper and strived to make enhancement. Once again thank you for your detailed review and worthful comments and we hope all our responses make sense to you.

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This is an interesting paper which investigates the effect of using a hybrid battery system on marine emissions.

Remarks:

1) All the cross-references of the document should be checked.

2) Figure 6 is unreadable. Quality should be improved.

3) FIgure 7,8 looks like a simulink model. Do they add value to the paper? Maybe move to appendix.

4)Table 4: remove photos, keep only measurements.

5) In discussion: It is in customary to include questions in the manuscript.

Author Response

Thank you very much for your correct understanding on the research aim and direction. All your remarks were carefully responded. We hope all our responses make sense to you.

 

This is an interesting paper which investigates the effect of using a hybrid battery system on marine emissions.

 

Remarks:

 

1) All the cross-references of the document should be checked.

 

Thank you. We revisited our manuscript and checked the cross references (the error have been caused by the file conversion during the process. But, we corrected all properly.)

 

2) Figure 6 is unreadable. Quality should be improved.

 

Yes. Corrected as below.

 

3) FIgure 7,8 looks like a simulink model. Do they add value to the paper? Maybe move to appendix.

 

Thank you for your comments. We agree so that we move the whole simulation part into Appendix.

 

 

4)Table 4: remove photos, keep only measurements.

 

Yes, we did it.

 

5) In discussion: It is in customary to include questions in the manuscript.

 

 

In the last part of the Discussion, we added an open question for the future study as below:

 

“Last but not least, the results of LCA have shown it may be more difficult to achieve zero emission in the shipping industry than it was thought. It is because the shipping is not a single and isolated business but interconnected with various activities associated with other fields, in particular of energy industry. What cleaner concepts, ideas, systems and practices are necessary for the marine industry to truly- achieve zero emissions for both short route and ocean going vessels? The follow-up research should pursue answering this question.”

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The paper was improved slightly in this revised version (v2), but serious deficiencies remain. The analysis is fraught with specious or unsupported assumptions, and the system boundary of the analysis is not clear. These deficiencies make it impossible for me to recommend publication without major revision.

The paper is rife with grammar and usage problems, so much so that it is difficult to read the paper.

In the Abstract, please define “roro-passenger ship”. And “PSIM”. Is there a reference that describes PSIM? Can the authors cite a reference for the GaBi software?

In the Introduction, there is a reference to “Energy, 2019); this is not a valid citation.

In the first paragraph of Section 2.1, it says, “… battery models are not directly associated with the LCA.” However, the results of the simulations of battery operation were presumably used in the LCA, otherwise, why is this modeling included in the paper?

Section 2.1.1 has more invalid references, e.g., “Association, 2017” should be “Korean Shipping Association, 2017”.

My question about the validity of the assumption of constant propulsion load was not addressed:

How realistic is the assumption of constant power, as shown in Figure 3? Won’t the speed vary somewhat and the power vary with speed, loaded weight of the ship, wind and other weather conditions, and other traffic in the area? When the3 ship maneuvers close to the port, aren’t the engine load and speed highly dynamic?

Is there any emission control or exhaust aftertreatment on the diesel ship?

My comment about the electric load on the vessel was partially addressed in Section 2.1.2, but there are still methodological issues. The revised version says “For diesel ships … the electrical load is covered with independently arranged diesel generator sets.” And that “ … this paper disregards the energy consumption associated with the electrical load (for auxiliary and hotel) for the simple reason that it is the very same for both ship types …”. However, the emissions from diesel generator sets are different from emissions from electricity generated to charge the battery powered ship, the emissions will differ even if the electricity consumed is the same. If, however, the electric load is orders of magnitude smaller than the energy consumed for propulsion, the electric load and associated emissions can be neglected. Can the authors support this approximation by giving the approximate magnitude of the auxiliary electric load and comparing with the propulsion energy? If the auxiliary loads are in fact negligible, perhaps they should not be shown in Figure 5.

In Section 2.1.2, can the authors cite a reference to a source describing PSIM and give some results of validation testing to provide confidence in the simulation results?

Section 2.2.2 Can the authors describe Alternative Marine Power, shown in Figure 10? Do emissions from AMP differ from those of electricity supplied by the Korean electrical grid? If so, this seems to be a major oversight.

In Table 4, CO2 emissions are given, but GHG-equivalent would be more appropriate, especially for natural gas and hydroelectric power, since thee can have methane emissions.

In Section 2.2.3, some of my questions were partially addressed, but not these questions:

What engine was tested? Under relevant compression ratios and temperatures?

What laboratory was testing performed in?

Were standard test procedures followed? What standard procedures?

What fuel was used in the test?

How were engine emissions measured? Were these engine-out measurements or downstream of emission aftertreatment equipment?

Author Response

Thank you again for your detailed comments. We have taken your comments seriously and strived our best to present clear explanation on helping your understanding. We hope all our response to your comments are relent.

Please see the attachment!

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The paper was improved significantly in this revised version (v3).

In the cover letter, the authors responded to my comment suggesting a reference to a source describing PSIM and gave some results of validation testing to provide confidence in the simulation results, but they did not add any information to the paper; it was only in the cover letter. Can the authors at least cite the PSIM user manual in the paper? As the authors say in the cover letter, some readers are interested in battery system models for actual applications.

The authors provided information about the testing facilities in their cover letter, but not in the paper. Perhaps the test lab can be mentioned in the paper. In the cover letter, it in unclear whether the engine testing was performed at the Vessel Exhaust Gas Test Research (Located in Sacheon city, South Korea) or at KOMERI (Korea Marine Equipment Research Institute). Perhaps these are the same.

Also in their cover letter, the authors revealed that the engine tested was the same type of engine as the target ship, and KOLAS standards were applied to test. I strongly suggest adding this information to the paper.

The authors also provided information about the emissions testing in their cover letter, but the paper would be improved by including some of this information.

Author Response

For Reviewer #2

Thank you very much again for your continual devotion to guiding us into ways to improve the quality of this paper. Indeed, we have to admit that your comments have enhanced several aspects of this paper, which had not been properly presented in the earlier version. We have reflected all your comments (Version 3); all of them were to add some relevant contexts into the manuscript.

Thank you once again for your detailed questions, comments and advice. We think all those have undoubtably taken the significance of your time and efforts.

The paper was improved significantly in this revised version (v3).

1. In the cover letter, the authors responded to my comment suggesting a reference to a source describing PSIM and gave some results of validation testing to provide confidence in the simulation results, but they did not add any information to the paper; it was only in the cover letter. Can the authors at least cite the PSIM user manual in the paper? As the authors say in the cover letter, some readers are interested in battery system models for actual applications.

Thank you very much for your worthy comments. In reflection of your comment, we added the following context with references into the manuscript.

“The proposed battery system has been simulated using PSIM program which is specifically designed for modelling and simulating power electronics, motor drives, and power conversion systems. With fast simulation speed and friendly user interface, PSIM is recognized as a provider of a powerful simulation environment (Powersim Inc, 2019). In case of using PSIM program, as long as the input parameters related to inverter, motor, and other elements are correct, the simulation results based on the numerical computations will be always the very same to the actual performance. As a result, current studies tend to ignore the validation process because the matter is the reliability of parameters not models; our analysis fully rely on the manufacturers information (Guena and Leblanc, 2006; Lee et al., 2016; Ning and Popov, 2004; Zhang and Chow, 2016). Regarding the validation, one of good example can be found in Zhang and Chow (2016) who have compared the results between the PSIM and actual tests for power managements of a hybrid electric propulsion system for a ship.”(P10).

 

2. The authors provided information about the testing facilities in their cover letter, but not in the paper. Perhaps the test lab can be mentioned in the paper. In the cover letter, it in unclear whether the engine testing was performed at the Vessel Exhaust Gas Test Research (Located in Sacheon city, South Korea) or at KOMERI (Korea Marine Equipment Research Institute). Perhaps these are the same. Also in their cover letter, the authors revealed that the engine tested was the same type of engine as the target ship, and KOLAS standards were applied to test. I strongly suggest adding this information to the paper.

The Vessel Exhaust Gas Test Research is the name of the test bed and KOMERI is the institute who is in charge of this test facility.

In reflection of your comment, we added the following context with references into the manuscript.

“The test bed was designed in Vessel Exhaust Gas Test Research (VEGTR) located in Sacheon city, South Korea, which is operated by Korea Marine Equipment Research Institute (KOMERI). The same capacity of engine as the target vessel were tested and the fuel consumption and emissions of the diesel engine mounted on the test bed were measured at each operation section as shown in Figure 11. A dynamometer was installed to set-up and monitor the equal load as the actual operation profile, and two sets of flowmeters were fitted to the inlet and the outlet of the engine fuel piping system. The difference between the inlet flow and the outlet flow represents actual fuel consumption in the engine.

Engine simulations were conducted in accordance with the National Certified Test (KOLAS) guidelines which is in the same line with ISO/IEC 17025:2017.”(P19)

3. The authors also provided information about the emissions testing in their cover letter, but the paper would be improved by including some of this information.

In reflection of your comment, we added the following context with references into the manuscript.

“The emissions were measured at the exhaust gas piping line of the engine (no emission aftertreatment is applied). As a device that measures the concentration of exhaust gas emitted from a ship, a portable analyzer (GASMET, DX-4000) convenient for on-site measurement was used: the analyzer can identify over 350 types of gases, and up to 50 types gases can be analyzed simultaneously. It adopts Fourier Transform Infrared Spectroscopy (FT-IR) sampling method where the exhaust gas is directly exposed to the infrared (IR) beam of the analyzer. As this beam pass through the exhaust gas, the transmitted emission types are measured. The exhaust gases were measured 50 times for 10 seconds, and the average value was adopted.” (P20).

Author Response File: Author Response.pdf