Comparison of the Gaussian Wind Farm Model with Historical Data of Three Offshore Wind Farms
Round 1
Reviewer 1 Report
I have just a few comments:
- The novelty with respect to the existing literature is not well established and should be better highlighted.
- Many figures are too small, especially to read the fonts to appreciate the details of the figures itself.
- In section 4: I miss some statement on uncertainty of the data, possibly also in earlier section.
- I find the explanations of the deviations seen in Figs. 18 and 19 rather thin and this should preferably be improved for validation purposes.
Author Response
Dear reviewer,
We sincerely thank you for taking the time to read and revise the manuscript. We appreciate your comments and believe they will further the scientific relevance and readability of our manuscript. Specifically,
"The novelty with respect to the existing literature is not well established and should be better highlighted."
We agree with this statement and have extensively revised the literature and expanded our introduction. We have also better positioned our contributions with respect to the state of the art.
"Many figures are too small, especially to read the fonts to appreciate the details of the figures itself."
We understand the reviewer's concern and have reformatted and enlarged each figure in the article.
"In section 4: I miss some statement on uncertainty of the data, possibly also in earlier section."
We appreciate this comment and wholeheartedly agree. We have expanded Section 4 with a brief paragraph on the uncertainty in the historical data.
"I find the explanations of the deviations seen in Figs. 18 and 19 rather thin and this should preferably be improved for validation purposes."
We understand the reviewer's concern for the energy ratio plots and comparisons for the OWEZ wind farm. We have rephrased some of our explanations and emphasize that, due to the inconsistency in model agreement/disagreement and due to the relatively small discrepancies, we cannot pinpoint the exact source(s) for the found model discrepancies.
I have separately uploaded the revised manuscript and the marked-up document demonstrating the changes made. I hope this finds you well. Thank you for your time.
Best,
Bart
Reviewer 2 Report
The authors computed the energy ratio from SCADA data of three offshore wind farms and compared it with the predicted result of the Gaussian wake model in FLORIS framework. The data preprocessing was thorough and well defined, therefore reducing the uncertainty in further analysis. Edge cases with model deficiencies were exanimated in detail and two sources were spotted in the result, namely the deep-array effect and inflow heterogeneity. The paper can be considered for publication as it is.
One comment on the energy ratio equation: The reference power is defined as the average power production of a set of upstream wind turbines. Is it a mean average or weighted average? If it’s a mean average, given a wind direction, presumably the wakes from all five reference turbines will have the same portion of contribution on the power deficit of the test turbine. I am merely curious if this is the case for the farms of interest. For instance, given a wind direction of [225, 228] in the Anholt wind farm, it seems that turbine 40 will ’dominate’ the power losses of turbine 54 rather than the first-row turbines 15, 16 and 17. Will the reference power captures this near wake interaction?
Author Response
Dear reviewer,
We sincerely appreciate the time and effort you have invested in reviewing our manuscript. Thank you for your compliments and your approval of the manuscript.
Concerning your question:
"The reference power is defined as the average power production of a set of upstream wind turbines. Is it a mean average or weighted average?"
We indeed take a non-weighted average of the power productions of a set of upstream turbines. Since they are all operating in freestream flow, they are expected to produce an equal amount of power (assuming no heterogeneity in the inflow). This essentially is meant to increase the confidence on what we select as the reference power production. If we were to just take that single upstream turbine's power production, it is likely to be more sensitive to noise or transients in the atmospheric conditions. For the test turbine's power production, we only look at a single turbine. Hence, we do not make any implicit assumptions on the wake effects of upstream turbines. Essentially, we are dividing the power production of a single, waked turbine by the power that that same turbine would have produced had there been no wake losses. That latter quantity is best determined by taking the average of the power productions of multiple upstream turbines that are in close proximity to the waked turbine.
I hope this clarifies your question. Feel free to reach out to me if it does not.
Thank you again for your time. I have uploaded a revised manuscript and also a marked-up document demonstrating the changes made based on the other reviewers' comments. I hope this finds you well.
Best,
Bart
Reviewer 3 Report
The paper addresses a topic of interest, related to the development and use of wake and wind farm models, which has been the subject of research since the mid-1980s. The paper is well written and of some interest, which makes it possible to recommend its publication if some of the following, mostly relatively minor, points are clarified. The aspect on which some doubts may be raised concerns the novelty and originality of the methods and contributions of this paper with respect to previous works, which the authors should emphasize to make it clearer that the contributions made are not merely incremental.
The literature review should be improved. Citations to early wake and wind farm models are scarce. The reference [12] is not sufficiently representative, considering that the basic ideas of the models contemplated in the present work do not differ very substantially from those of the models proposed in the mid-1980s. It would also be convenient to explain briefly and more precisely the improvements introduced recently with respect to those initial models.
The main motivation for the work given in the Introduction section relates to aspects of wind farm control, which requires the use of appropriate wind farm models to define the control strategy. Thus, in the introduction, reference is made to the "development of control-oriented wind farm models" (by the way, it might not be superfluous to briefly indicate what the type of wind farm control based on wake steering consists of). However, the article does not deal with wind farm control, so this mention may be misleading at first glance. This should be stated more explicitly from the beginning. It is also somewhat imprecise what is indicated in lines 43 to 44 since it seems to imply that the model of reference [12] was proposed as a control-oriented wind farm model when at that time there were no control issues in mind but only wind farm efficiency estimation.
The authors have published numerous articles closely related to the same subject (even some more than those included in the reference list), which does not make it easy to specify in detail the contributions made in the present one. The authors state in lines 81 to 87 the differences with respect to [27]. It seems that the main difference is to have extended the analysis to unsteady atmospheric conditions. The use of the energy ratio method does not seem novel, although it has been used here in a fairly systematic procedure of data calibration.
The results seem satisfactory and generally relevant. Perhaps there is more merit in the filtering of the data used for the validation of the code than in the predictive capability of the models included in the code, which obviously have limitations. These limitations, partly due to the uncertainty of some parameters, are perhaps the weakest aspect of the paper, and perhaps it would be appropriate to discuss them in a little more detail. The statement made at the end of the penultimate paragraph of the conclusions on the possible applicability of the model in wind farm control applications seems to be somewhat speculative for the moment, although it may be interesting to study it in the future.
Author Response
Dear reviewer,
We sincerely thank you for taking the time to read and revise the manuscript. We appreciate your comments and believe they will further the scientific relevance and readability of our manuscript. Specifically,
"The literature review should be improved [...]" , and , "The authors have published numerous articles closely related to the same subject (even some more than those included in the reference list)",
We wholeheartedly agree with these statements and have extensively revised the literature and expanded our introduction. Note that, in our literature review we focus on literature that has previously compared engineering models to historical data, rather than focusing on the underlying mathematics of the engineering models themselves. We believe that the latter better belongs in the articles in which the models are published, or in a review paper on wind farm modeling. We have also better positioned our contributions with respect to the state of the art.
"[...] the article does not deal with wind farm control [...], misleading at first glance.", "[...] concerns the novelty and originality of the methods and contributions of this paper [...]", and "specify in detail the contributions made in the present one"
We understand and agree with the reviewer's concerns. The article was initially written with a strong focus on wind farm control, while realistically the paper is a comparison of a wind farm flow model in a non-wake-steered and non-induction-controlled to historical data. The link that we tried to make is that the "GCH" model is commonly used in wind farm flow control experiments, while it has received limited validation in the literature, also in non-wind-farm-controlled operation. That is the scientific gap we are aiming to tackle, in addition to the novelties in how we approached the data analysis. Accordingly, we have clarified these scientific gaps and our article's contributions in the introduction.
"[...] limitations, partly due to the uncertainty of some parameters, are perhaps the weakest aspect of the paper, and perhaps it would be appropriate to discuss them in a little more detail", and "The statement made at the end of the penultimate paragraph of the conclusions on the possible applicability of the model in wind farm control applications seems to be somewhat speculative for the moment [...]"
We understand and agree with the reviewer's concern. In the text, we have clarified the application of these parameters in a more practical setting. We have also added a brief paragraph on data uncertainty in Section 4. Finally, we have rephrased the conclusions to better reflect the findings in the article.
" It is also somewhat imprecise what is indicated in lines 43 to 44 [...]"
We have clarified the definition of an "engineering wind farm model" as part of the expanded literature review, in the introduction.
I have separately uploaded the revised manuscript and the marked-up document demonstrating the changes made. I hope this finds you well. Thank you for your time.
Best,
Bart
