Correlations of power output fluctuations in an offshore wind farm using high-resolution SCADA data

Seifert, Janna Kristina; Kraft, Martin; Kühn, Martin; Lukassen, Laura J.

doi:https://doi.org/10.5194/wes-6-997-2021

Articles | Volume 6, issue 4

https://doi.org/10.5194/wes-6-997-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/wes-6-997-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 6, issue 4

Research article

|

23 Jul 2021

Research article |

| 23 Jul 2021

Correlations of power output fluctuations in an offshore wind farm using high-resolution SCADA data

Janna Kristina Seifert, Martin Kraft, Martin Kühn, and Laura J. Lukassen

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Final revised paper (published on 23 Jul 2021)
Preprint (discussion started on 29 Sep 2020)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Referee report', Anonymous Referee #1, 15 Nov 2020
RC2: 'WES 2020-96', Mark Kelly, 30 Nov 2020
AC1: 'Authors response to RC1 and RC2', Janna Kristina Seifert, 23 Jan 2021

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Janna Kristina Seifert on behalf of the Authors (23 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (19 Feb 2021) by Andrea Hahmann

RR by Anonymous Referee #1 (03 Mar 2021)

Suggestions for revision or reasons for rejection

Overall I believe this line of work is important and relevant for the community and based on this I believe this work is suitable for publication in Wine Energy Science. The authors have replied in detail to the comments of the referees and the corresponding changes have improved the manuscript. Obviously, the analysis of the field data is a challenging task as articulated by the authors. I believe that in various places, as indicated below, the presentation in the manuscript can be further clarified.

Regarding some of points mentions in the previous review round as commented on by the authors.

Referee 1:
* RC4: So to clarify; the data on U is provided to you (and is based on Power signal) and you did not calculate it yourself.
* RC6: The slight asymmetry is mentioned in the conclusions (line 340), but I am not sure it is mentioned clearly in the body of the text, please double check.
* The information provided as response to RC11 is very useful, but I could not find this information in the manuscript. I think the answer can be summarized shortly in the manuscript, and the authors can refer to the graph provided in the response document, which is already available online. So the graph itself does not need to be incorporated in the manuscript. But it is useful to inform the reader of the main manuscript that it is available.
* RC20: the provided answer does not really answer my question. The provided answer states the general benefit of the approach, but I am wondering whether the authors can clarify the specific new insights obtained for the case considered here.

Referee 2:
The authors state “The 20° interval is the result of the 10-degree tolerance in the wind direction measurements of the wind turbines”. I think this information is very important and it should be incorporated in the main text.

I also read the manuscript again. In various places the authors could be more precise on the formulation, i.e. making clear to what case, data, parameter is exactly referred. Or the English grammar should be removed. I provided a list of some of the main instances below, but please check the entire manuscript, especially the abstract, on this.

Abstract:
* "Space-time correlations of wind turbine pairs" ==> the power output is correlated; not the turbine pairs
* "Such information plays an important role for the control" ==> Can provide important insights for controls, i.e. information obtained from the analysis you presented is not yet used in wind farm control
* which overcomes the challenge of highly variable flow conditions within the wind farm ==> make this a new sentence. New it refers to the SCADA data. However, this statement is on your analysis approach.
* Wind direction investigations show ==> More effect of the wind direction.
* line 21 ==> average size of [new]? Wind farms
* line 44: "Furthermore, the variance of the wind velocity and the mean velocity turned out to be important parameters in the modelling set up." ==> Please clarify to which modeling setup you are referring.
* line 58: "includes unstable inflow conditions," ==> please be more precise. LES and wind tunnel data also include unsteady effects. However, typically LES and wind tunnel have constant wind directions, while wind direction varies in field data, etc.
* line 70: "relevant wind turbine statistics" ==> statistics on the power production of the turbines not statistics of the turbines themselves.
* line 95: Please be more precise on what wind direction fluctuations you refer to. Fluctuations around some mean value? The average wind direction does namely matter.
* line 109-110: "All these factors multiply to an order of unpredictable variability" ==> please clarify your formulation.
* line 135: As mentioned before, these effects have a limited ==> sentence is not complete.
* line 186: why do you have the reference of 13ms^-1?
* Figure 2 /3: For certain wind directions you have less measurements. The gap seems to be at slightly different wind directions in figure 2 and 3 (left / right of the 0/360 degree line). I guess it has to do with the way you defined your measurement intervals, but please make sure this is clarified to the reader.
* line 224: "are ideal compared to free field measurements" ==> I agree. Can you clarify to the reader what specific aspects you believe are the main reason for the observed differences between field data and LES and wind tunnel data?
* line 337: "more defined averaged correlations" ==> please clarify
* line 339: "introduced parameters" ==> please clarify what parameters you refer to.
* line 343: "more defined" ==> please clarify what you mean
* line 349: "turbine pairs in the same row are affected by the same flow conditions," ==> please clarify
* line 354: "clearly distinguishable parameters" ==> What parameters do you mean?
* line 361: "The remaining clusters were not as significant as the other but also showed" ==> In this sentence it is not so clear to which clusters you refer.

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RR by Mark Kelly (07 Apr 2021)

ED: Publish subject to minor revisions (review by editor) (12 Apr 2021) by Andrea Hahmann

AR by Janna Kristina Seifert on behalf of the Authors (30 May 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (16 Jun 2021) by Andrea Hahmann

ED: Publish as is (17 Jun 2021) by Jakob Mann (Chief editor)

AR by Janna Kristina Seifert on behalf of the Authors (25 Jun 2021) Manuscript

Short summary

Fluctuations in the power output of wind turbines are one of the major challenges in the integration and utilisation of wind energy. By analysing the power output fluctuations of wind turbine pairs in an offshore wind farm, we show that their correlation depends on their location within the wind farm and their inflow. The main outcome is that these correlation dependencies can be characterised by statistics of the power output of the wind turbines and sorted by a clustering algorithm.