Offshore Power Plants Integrating a Wind Farm: Design Optimisation and Techno-Economic Assessment Based on Surrogate Modelling
Round 1
Reviewer 1 Report
The paper describes the use of optimization and surrogate modeling to conduct conceptual design of a combined cycle power plant for offshore oil and gas platforms that also rely upon offshore wind power. The article is well-laid out and makes an solid, incremental contribution to the literature. However, there are a some holes in the analysis that, if addressed, would make the conclusions more forceful. Also, the writing is in need of professional English editing.
Specific comments:
Section 2.1:
- Would be helpful to see the wind power curve
- Fig 1: Might be helpful to show an external input from wind power
- Please expand the acronyms in Fig 1 in the caption (GT, WHRU, SC, OTSG)
Section 2.2:
- Need to see all of the independent variables in the surrogate model here. Table 2 is a start, but is incomplete. Maybe Table 3, but with variable descriptions, not just symbols, and design variable bounds used in the optimization
- Need to see all of the dependent variables used in the surrogate model. Maybe like Table 5, but again with descriptions.
- Is there a different Kriging surrogate for each dependent variable?
- Need to see a list of the off-design conditions.
Section 2.3
- The CO2 metric looks like a sum over operating conditions but the text says it is a lifetime emissions metric. If it is a lifetime metric, then there must be a distribution of off-design conditions and the sum is a weighted sum. Please clarify this point both in text and Eqn 3.
- Eqn 6 looks a lot like NPV, but later NPV is described separately from the cost in Eqn 4. Having multiple cost metrics, but only optimizing on one of them is confusing and could potentially be misleading. Is the cost here just the final NPV summation in the time series?
Section 4
- 25 generations in a GA seems like a low number. Are you sure the results are converged? If you ran for 50 generations would you get a different answer?
- The Pareto fronts in Figures 5-6 are nearly impossible to see. Figure 7 is much better. I suggest just showing Figure 7 and coloring the symbols by their Weight metric for a 3-D view. Also, the diamond and circle are too similar to distinguish A vs B where they overlap. Maybe choose a different symbol for one of them?
- Figure 8 is good and helps make a strong argument!
- The conclusion that wind only help CO2 and only hurts cost may be true, but seems premature here because the wind turbine was not included in the optimization. The CC plant was optimized with the wind turbines in mind, but the wind turbines were not optimized with the CC plant in mind. I would be much more convinced if the wind turbines were optimized too.
Section 5
- The GT and GW+W designs are really controls or baselines, but are not presented as such in the tables or text. It might be helpful to start with their performance upfront in Section 4. Then they can be a basis for comparison when seeing later results.
Section 5.2
- NPV is brought in here as a cost metric, but how is it different from the cost in Eqn 6? Is cost just the final NPV in the timeseries?
Section 5.3
- Figure 14 y-axis should be labelled as relative to Design A CC-W. Is that correct?
- Should the discount rate be included in the sensitivity analysis? Are the results significant?
Nomenclature
- U & A should be also be described separately.
Author Response
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This is a good work. However, thorough revisions are needed. Some of them are listed below:
1) The nomenclature is not complete
2) there is inconsistency in symbols
3) how the hyperparameters in kriging model is obtained may be described in details
Author Response
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper deals with the possibility to integrate a wind farm into an offshore power plant constituted of a combined cycle. The main concept of paper seems good, and analysis are tested through simulations, which are convenient. However, some serious concerns exist for this reviewer which needs to be addressed by the authors. I hope these comments will be helpful to you.
1. What are the contributions of the model proposed in this paper over the other existing models? Please justify it by adding some items at the end of your introduction. The authors are invited to improve the introduction section by adding some advantage and/or disadvantages of the proposed model in comparison with other models in the literature. It will be great if this comparison is also made in the results section.
2. It is not clear if the previously compared method had the same objectives as this study. If not how the other presented objectives are evaluated. If yes what the new part of study is.
3. The authors did not provide a clear overview of the progress beyond the state of the art that is achieved by the proposed methodology. Some example are: Reserve Allocation of Photovoltaic Systems to Improve Frequency Stability in Hybrid Power Systems (Energies 11 (10), 2583), Load-frequency control in a multi-source power system connected to wind farms through multi terminal HVDC systems (Computers & Operations Research 96, 305-315). Kumar, P.; Kothari, D.P. Recent philosophies of automatic generation control strategies in power systems. IEEE Trans. Power Syst. 2005, 20, 346–357. Crossland, A.F.; Jones, D.; Wade, N.S.; Walker, S.L. Comparison of the location and rating of energy storage for renewables integration in residential low voltage networks with overvoltage constraints. Energies 2018,11, 2041. Please include these papers in your references list, and discuss in details in literature review.
Author Response
Author Response File: Author Response.pdf
Reviewer 4 Report
Review of the paper
Title: Offshore power plants integrating a wind farm: design optimisation and techno-economic assessment based on surrogate modelling
By: Luca Riboldi, Lars O. Nord
Submitted to: Processes (MDPI)
Manuscript ID: processes-380896
The paper is suitable for publication in the Processes Journal. It is about the design optimisation and techno-economic assessments using surrogate modelling approach for offshore power plants integrating a wind farm. The paper is well written and provides useful and up to date information on these complex systems and processes. The scope of the journal fully covers this research topic. Appropriate terminology is applied. I recommend the paper for publication in this journal.
Round 2
Reviewer 1 Report
Thank you for addressing my comments
Reviewer 3 Report
I am not convinced by the author's response regarding the novelty and main contribution of this paper over the other existing model!
