Simultaneous Optimisation of Cable Connection Schemes and Capacity for Offshore Wind Farms via a Modified Bat Algorithm
Round 1
Reviewer 1 Report
Review of the paper
Title: Simultaneous Optimisation of Cable Connection Scheme and Capacity for Offshore Wind Farm via a Modified Bat Algorithm
By: Yuanhang Qi, Peng Hou, Liang Yang, Guangya Yang
Submitted to: Applied Sciences
Manuscript ID: applsci-416021
This paper presents a numerical study on optimisation of cable connection scheme and capacity for offshore wind farm using a modified Bat algorithm. The topic is interesting. The paper provides useful information of this topic. The scope of the journal fully covers this research subject. I recommend the paper for publication after revision. The comments below will guide the authors.
1. Please clarify the novelty of the submitted manuscript and refer to previous frameworks and guidelines.
2. In Section 2, list the main assumptions pertaining to the proposed models (Eqs. 1-8).
3. Same as above, in Section 3, list the main assumptions pertaining to the optimization algorithm (Eqs. 9-14). Provide also the main input parameters and constraints.
4. In Section 3, provide some details on the numerical solutions, schemes and other settings. Which software was used?
5. Model validation or verification is missing.
6. I would recommend a conclusion section where the main findings resulting from the study should be clearly identified.
7. Run the spelling tool for grammar/typing mistakes; revise the nomenclature section and add the abbreviations and acronyms, improve the quality/presentation of the figures and equations, some are not readable.
Author Response
Response to Reviewer 1 Comments
Point 1: Please clarify the novelty of the submitted manuscript and refer to previous frameworks and guidelines.
Response 1: Thanks for your useful comment. The novelty of our work compared to previous works has been highlighted in the introduction and marked with yellow as follows:
Despite the power losses cost (PLC) were considered in the objective function in [14]-[16], its impact on the cable sectional area was not modeled in [14][15] while ref. [16] neglects the influence of PLC on the cable selection by using the cables with the same sectional area. In addition, the uncrossed cable connection layout was studied in [18] whereas the PLC’s influence was neglected. Through the literature study, it can be seen that the power losses impacts’ on the cable sectional area selection and cable connection layout formulation was not well studied. Thus, an OWFCCLP model was proposed in this paper. Compared to the above works, the PLC’s impact on the cable connection layout formulation as well as the cable sectional area selection were both considered in the optimization model and the uncrossed cable connection layout was ensured during the layout formulation process. The internal array cable and its laying costs are considered as the CAPEX while the revenue losses due to power losses are regarded as the operational cost (OPEX). To solve the problem an updated bat algorithm (BA) is adopted and the proposed model was validated via a case study.
Point 2: In Section 2, list the main assumptions pertaining to the proposed models (Eqs. 1-8).
Response 2: Thanks for your useful comments. According to your suggestions, we added this part into the paper and marked with yellow. The revised part is in the following.
2.3. Assumptions
In this simulation, some assumptions are made as follows.
1) The number and positions of the OS and WTs are given.
2) All cables are assumed to be 3-core cross-linked polyethylene (XLPE) AC cable.
3) The cables’ length is selected according to the geometrical distance without considering detailed practical situations, such as the barriers, restriction in the sea, and the length from WT foundation to the sea bottom.
4) The cost of cable laying and purchasing is linearly proportional to the cable length.
5) The power factor is assumed to be 0.75.
6) All WTs are assumed to be operated at 1 p.u. voltage.
Combining with the assumptions above, the OMTSP model is modified and thus well suitable for solving the OWFCCLP. To help get an optimized solution, a BA algorithm is adopted in this paper, which is introduced in the next section.
Point 3: In Same as above, in Section 3, list the main assumptions pertaining to the optimization algorithm (Eqs. 9-14). Provide also the main input parameters and constraints.
Response 3: Thanks for your useful comments. According to your comments, the assumption of bat position and velocity is added into the paper. The main input parameters are also specified in section 4. All revised parts are marked with yellow in the paper as follows:
Assuming is with w dimensions, the corresponding velocity. and are both positive integers and, ], .
The input parameters of BA are identical for each model, that is Q=400, θ=150, α=0.999, γ=0.001.
Point 4: In Section 3, provide some details on the numerical solutions, schemes and other settings. Which software was used?
Response 4: Thanks for your detailed comments. The numerical solutions and the details of the optimized cable connection schemes are shown in Appendix, table A4-5 respectively while the settings are shown in table A2. The program is compiled using the C++ language and the simulation software is Visual Studio 2010. All revised parts are highlighted with yellow in section 4 of the paper.
Point 5: Model validation or verification is missing.
Response 5: Thanks for your comment. In this paper, an optimization method is proposed for optimizing the cable connection layout of the offshore wind farm in the planning stage. The proposed optimization model is validated in the case study via simulation. We only compared the performance of the proposed BA with standard BA and found that the adopted BA outperformed standard BA in finding a better solution. In future, the present algorithm will be compared with other metaheuristic algorithms such as PSO to validate its performance, this part has been added into the future work in the paper and highlighted with yellow as follow:
To solve such large optimization problem, the performance of the metaheuristic algorithm is critical and thus more algorithms will be compared and implemented to solve the OWFCCLP in our future work.
Point 6: I would recommend a conclusion section where the main findings resulting from the study should be clearly identified.
Response 6: Thanks for your helpful comment. According to your suggestion, the original conclusion and future work section has been reorganized into two separated sections to identify the findings resulting from the study in the revised paper.
Point 7: Run the spelling tool for grammar/typing mistakes; revise the nomenclature section and add the abbreviations and acronyms, improve the quality/presentation of the figures and equations, some are not readable.
Response 7: Thanks for your careful comments. According to your comments, some changes have been made in the following. All revised parts have been highlighted with yellow in the paper.
1. All the spelling and grammar errors have been corrected by running the spelling tool, ‘grammarly’.
2. More explanations have been added into the nomenclature section. Besides, the abbreviations and acronyms are also added.
3. The original figures are all replaced with high quality figures, some explanations are added below the equations to make the work more readable.
Author Response File: 
Author Response.docx
Reviewer 2 Report
In the manuscript “Simultaneous Optimisation of Cable Connection Scheme and Capacity for Offshore Wind Farm via a Modified Bat Algorithm”, the author wanted to answer a very important question on optimal cable connection in offshore wind farm. This is an interesting work. It should be published with minor revision. Here are some of the comments:
1) The reference numbers are not consistent.
2) In the introduction, the author has given a nice literature review. The author also presented the novel contribution of the present work. It will be better if the author mentions their contribution in the context of the literature review. That will emphasize the perspective of the present work.
3) Explanation is needed for the higher purchase cost for MBA than BA_FREE in case of Scenario II.
4) The author has applied a metaheuristic algorithm for the solution. What did the author do to ascertain global solution? If not, how the solution presented is justified should be mentioned clearly.
Author Response
Response to Reviewer 2 Comments
Point 1: The reference numbers are not consistent.
Response 1: Thanks for careful comment. According to your comment, the reference numbers are checked and corrected in the revised paper and highlighted with yellow.
Point 2: In the introduction, the author has given a nice literature review. The author also presented the novel contribution of the present work. It will be better if the author mentions their contribution in the context of the literature review. That will emphasize the perspective of the present work.
Response 2: Thanks for careful comments. According to your comment, the contribution part is rewritten to emphasize the perspective of the present work. The revised part is highlighted with yellow in the paper as follow:
Despite the power losses cost (PLC) were considered in the objective function in [14]-[16], its impact on the cable sectional area was not modeled in [14][15] while ref. [16] neglects the influence of PLC on the cable selection by using the cables with the same sectional area. In addition, the uncrossed cable connection layout was studied in [18] whereas the PLC’s influence was neglected. Through the literature study, it can be seen that the power losses impacts’ on the cable sectional area selection and cable connection layout formulation was not well studied. Thus, an OWFCCLP model was proposed in this paper. Compared to the above works, the PLC’s impact on the cable connection layout formulation as well as the cable sectional area selection were both considered in the optimization model and the uncrossed cable connection layout was ensured during the layout formulation process. The internal array cable and its laying costs are considered as the CAPEX while the revenue losses due to power losses are regarded as the operational cost (OPEX). To solve the problem an updated bat algorithm (BA) is adopted and the proposed model was validated via a case study.
Point 3: Explanation is needed for the higher purchase cost for MBA than BA_FREE in case of Scenario II.
Response 3: Thanks for your helpful comment. According to your comment, the explanation is added into the section 4.2.3. The revised part has been marked with yellow in the paper as follow:
It can be seen that higher cable purchasing cost, with 13.17 kEUR increase, is required for the layout obtained by the MBA compared to the layout obtained by BA_FREE in Scenario II. This is because the layout found by the BA_FREE is with crossed cables. To ensure an uncrossed cable connection layout as shown in Figure 10 (a), another layout is selected by the MBA and thus increase the overall cable purchasing cost.
Point 4: The author has applied a metaheuristic algorithm for the solution. What did the author do to ascertain global solution? If not, how the solution presented is justified should be mentioned clearly.
Response 4: Thanks for your comment. To approach a global optimal solution, an updated version of BA is introduced in this paper. However, the global optimal solution can never be obtained due to the nature of metaheuristic algorithm. Thus, to get a better solution further, each algorithm (MBA, BA_FREE, BA_MIN) is run for 10 times and the best solution within 10 trials is selected as the final solution.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Authors addressed my comments in the revised version of the paper. The paper can now be accepted for publication in Energies Journal .
