Layout Optimization Process to Minimize the Cost of Energy of an Offshore Floating Hybrid Wind–Wave Farm

Round 1

Reviewer 1 Report

In this paper authors presents a study to develop a tool integrated by various (technical, mathematical and decision) processes that allows minimize the average lifetime cost with respect to the energy generation of an offshore farm compose of the Floating Power Plant´s hybrid wind and waves P80 concept. In general, the paper is very interesting and current to optimize the costs of marine hybrid parks, a barrier of great importance of the wind sector. But it is necessary to improve some aspects and has some gaps that would need to be solved in order to be published.

The main objective of the paper is very clearly defined in the first paragraph of the conclusions (lines 530-535), but it is not so much in the abstract and in the introduction. This aspect should be improved. The structure of epigraph 2 Materials and methods misleads the reader. Figure 1 model diagram is not clearly explained. According to the model this is composed of 4 modules and each one should be an item even if they do not have the same importance as optimization. For the paper´s objective, authors propose to use meta-heuristic methods such as evolutionary algorithms. Have not the authors considered any other possibility? This should be clarified. In the literature, the location problem in Renewable Energy has been studied in several works. Perhaps the use of multi-criteria decision methods (with the inclusion or not of fuzzy logic for the modelling of the many uncertainties involved) could have been considered for this phase of the work, and subsequently the use for the optimization phase of layout of the platforms where constraints and penalties were considered Conclusions: They should be a little more synthesized, aspects of the analysis of the results are repeated.

Figures:

Figure 1 should be improved. Lines above methods, colors too striking between the background and modules. Figure 2: Included in figure d.var1, d.var6, d.var7 and d.var8. Figure 4: Do not appear the 16 possible sites. 1, 2, and 3 are missing. Six discarded a priori could be marked in another color. Figure 5 and 6 should show units on the axes. Figure 9 is 40Km scale, and Figure 3 is 50 Km scale but both look the same. The scales should be review. Figure 10 Missing a platform in the first row of five. What type of wind rose does it refer to (speed rose, frequency, energy)? That should be clarified

Minor observations:

In line 48, the reference [46] appears that is not in the list of references. In the first line of results (line 490) appears the word “chapter”, when it would be better to indicate section or epigraph Review format of table 5 and 6

 

Author Response

In this paper authors presents a study to develop a tool integrated by various (technical, mathematical and decision) processes that allows minimize the average lifetime cost with respect to the energy generation of an offshore farm compose of the Floating Power Plant´s hybrid wind and waves P80 concept. In general, the paper is very interesting and current to optimize the costs of marine hybrid parks, a barrier of great importance of the wind sector. But it is necessary to improve some aspects and has some gaps that would need to be solved in order to be published.

ANSWER: Thank you very much for your appreciation and for your suggestions, which have helped very much improve the paper.

 

Q1: The main objective of the paper is very clearly defined in the first paragraph of the conclusions (lines 530-535), but it is not so much in the abstract and in the introduction. This aspect should be improved.

ANSWER: Thank you very much for your observation. We have rewritten the corresponding sentences in Abstract and Introduction.

Q2: The structure of epigraph 2 Materials and methods misleads the reader. Figure 1 model diagram is not clearly explained. According to the model this is composed of 4 modules and each one should be an item even if they do not have the same importance as optimization.

ANSWER: Thank you for the observation. As the paper focus on a part of a more global study, perhaps some restructuring used for the paper was not conveniently performed. In this version, on the one hand, we have made clear that the focus of the paper is mainly the optimization process, and we have referred the original work to know more about the wind and wave energy generation models, which are not the focus of this paper. We have explained the diagram more clearly and changed the name of section 2.1 to “the costs model”, and that of figure 1 to “Diagram of the tool”.

Q3: For the paper´s objective, authors propose to use meta-heuristic methods such as evolutionary algorithms. Have not the authors considered any other possibility? This should be clarified.

ANSWER: Thank you for your question. At the beginning of Section 2.2 we state that classical analytical or gradient based optimization are not (as in most real-world optimization problems) useful because of a number of reasons. These reasons include: the wide range of variables involved in the model; the nature of many of the parameters (discrete, not easily described by explicit functions, involving specific processes for their calculation); the spatial constraints; and the lack of convexity. So, as, in addition, we thought of this paper to contribute to a Special Issue devoted to Optimization systems, processes and complex networks using multi-agent based approaches, we decided to use PSO. The authors have worked in the past with several other evolutionary algorithms (EAs), specifically, Genetic Algorithms and Ant Colony Optimization, although most of our work uses PSO. This is the reason why we decided to keep on using this swarm-based EA. As mentioned in the same paragraph, other authors within the field of windfarms have also used EAs. In addition, as mentioned in the first paragraph of Conclusions, one of our future research lines include using other types of meta-heuristic algorithms, most likely multi-objective ones such as the ASO. Please, let us know if you consider this would be further clarified.

Q4: In the literature, the location problem in Renewable Energy has been studied in several works. Perhaps the use of multi-criteria decision methods (with the inclusion or not of fuzzy logic for the modelling of the many uncertainties involved) could have been considered for this phase of the work, and subsequently the use for the optimization phase of layout of the platforms where constraints and penalties were considered

ANSWER: thank you very much for the observation, which is very relevant for the entire complex process addressed in this paper. In fact, as we have observed in the Introduction and then stressed further along the paper, the entire path of selecting the optimal layout of the farm encompasses several processes, some of them involving uncertainties. In the paper, we have mainly focused on the numerical optimization of the position and the layout of the farm. However, a number of decisions have been made in other stages of the process, which have been mentioned in the paper, and which have used multi-criteria decision-making (MCDM) methods. Examples are the selection of the wind and waves models (merely mentioned in Section 2 of the paper, despite their fundamental weight in the global study), the qualitative study developed to previously locate more appropriate sites for the farm (mentioned in Section 3), the decisions about discarding some sites (addressed in subsection 3.2), etc. In the Introduction we explicitly speak about an entire decision-making process “based on engineering and project management foundations”. This, obviously, include MCDM methods. The authors have wide experience in MCDM methods in various industrial contexts, having used such methods as AHP, TOPSIS, various method of the ELECTRE family, and DEMATEL, some of them both in their crisp and fuzzy versions. However, in this case, the length of the paper advised us to omit the description of such decisions. To compensate this possible lag, we decided to include a last paragraph in the conclusions section, summarizing the sensitivity study and the uncertainty analysis performed in [16]. Please, let us know if you see here room for improvement, without compromising the length of the paper.

Q5: Conclusions: They should be a little more synthesized, aspects of the analysis of the results are repeated.

ANSWER: Thanks again. Done

Q6: Figures

Q6.1: Figure 1 should be improved. Lines above methods, colors too striking between the background and modules.

ANSWER: Done. We hope to have interpreted your suggestion suitably.

Q6.2: Figure 2: Included in figure d.var1, d.var6, d.var7 and d.var8.

ANSWER: Thanks. Done.

Q6.3: Figure 4: Do not appear the 16 possible sites. 1, 2, and 3 are missing. Six discarded a priori could be marked in another color.

ANSWER: Thank you for the observation. All the sites have been added.

Q6.4: Figure 5 and 6 should show units on the axes.

ANSWER: Thank you. They were specified in the caption, but not in the graph. Done.

Q6.5: Figure 9 is 40Km scale, and Figure 3 is 50 Km scale but both look the same. The scales should be review.

ANSWER: although at first sight it may look like the scale should be the same in both pictures, the length of the scale with respect to the map size is different. The scale was obtained directly from Google Earth when extracting the image, so a manual mistake cannot have been made.

Q6.6: Figure 10 Missing a platform in the first row of five. What type of wind rose does it refer to (speed rose, frequency, energy)? That should be clarified

ANSWER: Thank you very much. The missing platform has been added. The wind rose indeed measures the frequency; to clarify, we have included this information in the figure caption.

 

Minor observations:

In line 48, the reference [46] appears that is not in the list of references. In the first line of results (line 490) appears the word “chapter”, when it would be better to indicate section or epigraph. Review format of table 5 and 6

ANSWER: [46] is [20], done; “chapter” replaced with “section”; tables’ format reviewed.

 

Thank you very much again.

Reviewer 2 Report

Authors develop a tool to minimize the levelized cost of offshore energy generated by a Floating Power Plant`s hybrid wind and wave concept.
This tool is composed of wind and waves energy generation models and cost models. Although the study is carried out for a specific wind- wave farm known as P80 hybrid wind-wave concept designed by Floating Power Plant A/S company and for a specific location, the study case is very interesting.
In addition, the text is well exposed and described.
For all the above mentioned, I recommend this paper for publication in Processes.

Finally a couple of minor points:

line 142, define EI

line 287, Change "to shallow" for "too shallow"

Figure 4. The quality of this figure could be improved. In addition, sites of stations 1, 2 and 3 do not appear in the figure because, I suppose, they were not considered. For coherence, I suggest removing stations 14, 15 and 16 from the figure since they were not also considered. Another possibility is to put the 16 possible sites.

Author Response

Authors develop a tool to minimize the levelized cost of offshore energy generated by a Floating Power Plant`s hybrid wind and wave concept.

This tool is composed of wind and waves energy generation models and cost models. Although the study is carried out for a specific wind- wave farm known as P80 hybrid wind-wave concept designed by Floating Power Plant A/S company and for a specific location, the study case is very interesting.

In addition, the text is well exposed and described.

For all the above mentioned, I recommend this paper for publication in Processes.

ANSWER: Thank you very much for your appreciation.

 

Finally a couple of minor points:

Q1: line 142, define EI

ANSWER: thank you for the observation. We have written in full ‘electrical infrastructure’ as in other two places, to avoid the definition of an almost not used and not very relevant abbreviation.

Q2: line 287, Change "to shallow" for "too shallow"

ANSWER: thanks again. Done.

Q3: Figure 4. The quality of this figure could be improved. In addition, sites of stations 1, 2 and 3 do not appear in the figure because, I suppose, they were not considered. For coherence, I suggest removing stations 14, 15 and 16 from the figure since they were not also considered. Another possibility is to put the 16 possible sites.

ANSWER: Thank you very much again. Unfortunately, it is not possible to improve the quality of the color scale, as it was obtained directly from the source website (EMODnet) as an image. They were contacted but they replied that they cannot provide raw data that can be processed. Following another reviewer’s advise we have included all the sites in the Figure, as also suggested by you.

 

Thank you very much again.

Reviewer 3 Report

The analysis and content that are included in this paper are very interesting. Some minor remarks include:

1. What are the criteria for choosing the proposed technology for the wind energy converter in the offshore hybrid system?

2. Although ref [16] is mentioned in the manuscript, it would be helpful if a Table that includes the main considerations of costs and parameter values is added in Section 2.1.

Author Response

The analysis and content that are included in this paper are very interesting.

ANSWER: Thank you very much for your appreciation.

 

Some minor remarks include:

What are the criteria for choosing the proposed technology for the wind energy converter in the offshore hybrid system?

ANSWER: Thank you for your relevant question, which we can answer openly. Regarding the WTG (what we understand for wind energy converter) used in the P80, the company (FPP) currently considers the use of a WTG of about this size since the floater’s structural, stability and control systems are currently designed for a WTG of this size (the bigger the WTG, the more economically feasible the system is, but the more technologically challenging it is to implement; currently, offshore WTGs reach up to 12 MW).

As for the specific model used in the study, it was chosen given the availability of all the data needed to model its energy generation (power curve, thrust coefficient curve, height…)

Although ref [16] is mentioned in the manuscript, it would be helpful if a Table that includes the main considerations of costs and parameter values is added in Section 2.1.

ANSWER: We understand your point. However, due to confidentiality reasons, we were required by the company (FPP) to keep the costs components hidden. However, in several parts of the paper it is mentioned the relevance of some of these specific components. And, in any case, should you be interested in specific details, please feel free to contact the first author.

 

Thank you very much again.

Round 2

Reviewer 1 Report

The revision version of the paper has take into consideration all the suggestions and replied and explained one by one. This paper has improved significantly through the review process and I think the clarifications now are enough to be published in Process Journal at MDPI editorial