Preprints
https://doi.org/10.5194/wes-2023-145
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wes-2023-145
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
07 Nov 2023
| 07 Nov 2023
Status: a revised version of this preprint was accepted for the journal WES and is expected to appear here in due course.
Combining wake redirection and derating strategies in a wind farm load-constrained power maximization
Abstract. Power derating and wake redirection are two wind farm control techniques proposed in the last decade as means for increasing the overall wind farm power output. While derating operations are associated with a limited gain in terms of farm energy harvesting and with a decrease in turbine loading levels, farm controls based on wake redirection proved, both in silico and experimental tests, to entail significant increases in the overall wind farm power output. However, according to wake redirection strategies, the upstream wind turbines may typically operate at large yaw misalignment angles, and the possible increase in loads that the machines may experience in such conditions represents a source of concern when it comes to testing this control on existing farms that are not specifically designed for prolonged misaligned operations. In this work, it is first demonstrated that a suitable derating level can compensate for the increase in the rotor loads associated with large misalignment angles. Secondarily, two load-constrained wind farm controls based on a combination of wake redirection and derating are proposed with the aim of maximizing the overall farm output while maintaining unaltered the design load envelope of the wind turbines operating within the controlled wind farm.
How to cite. Croce, A., Cacciola, S., and Isella, F.: Combining wake redirection and derating strategies in a wind farm load-constrained power maximization, Wind Energ. Sci. Discuss. [preprint], https://doi.org/10.5194/wes-2023-145, in review, 2023.
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Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
RC1: 'Comment on wes-2023-145', Anonymous Referee #1, 17 Dec 2023
The comment was uploaded in the form of a supplement: https://wes.copernicus.org/preprints/wes-2023-145/wes-2023-145-RC1-supplement.pdf
- AC1: 'Reply on RC1', Alessandro Croce, 15 Mar 2024
-
RC2: 'Comment on wes-2023-145', Daan van der Hoek, 20 Dec 2023
General comments
The paper proposes a novel approach to wake redirection that includes derating yawed turbines to operate within a ‘safe envelope’ for turbine loading. The effect of yawed and derated operation on turbine loading was simulated using BEM, while the effect on wake characteristics was evaluated with the steady-state wake model FLORIS. Based on the acquired simulation results, the proposed method shows great promise and hence the results are suitable for publication. The writing in the paper is mostly clear, with some minor errors that are detailed below. Furthermore, a small change in the structure of the paper is suggested. Additional comments can also be found in the list below.
Specific comments
- The paper contains many instances where one-sentence paragraphs could easily be combined with the preceding or following paragraph.
- Ln 13: Power maximization and cost minimization are interconnected and should not be regarded as two separate aspects.
- Ln 22: Please add a reference supporting this statement.
- Ln 32: Please specify whether this concerns the yawed turbine, downstream turbines, or both.
- Ln 45: Please specify how derating is achieved in this paper.
- Ln 182-185: Similarly, wake redirection is only employed for a limited range of wind directions. This could also be considered during the load-constrained optimization, as the safe region corresponds to average fatigue loads, correct?
- Ln 220: Can you be more specific on how the optimization is limited to a smaller number of turbines? For example, by making the yaw misalignments of downstream turbines a function of the upstream turbines.
- Ln 279-281: Not only will derating the turbine result in lower power output, but the decrease in thrust will also make wake steering less effective. Please also comment on this aspect of the combined control approach.
- Section 3.1 does not present any results and would fit better in the methodology section. This would also prevent some questions that arise after reading the current section 2 on how the combined control strategy is implemented.
- Ln 323: Which wake deflection model is employed within FLORIS?
- Figure 3: While the 3d bar plots clearly show the results of some of the edge cases, it is not possible to distinguish the effects of yaw misalignment and derating in the center of the plots. Please switch to a 2D contour plot, or 2D bar plot, or make the current bars uniform in color (no gradient). The same applies to Fig. 5.
- Figure 6: Is this constraint function independent of wind speed? Please specify if this is not the case.
- Ln 390: Rated speed of the 10MW turbine is set at V=11.4 m/s and not 14 m/s.
- 16: When considering the test cases, we see that most wind speeds are above-rated. What is the reasoning behind this parameter choice, given that wake redirection is most effective at below-rated conditions (if at all effective above-rated)?
- Figure 7: Would it not make more sense to refer to spacing s as the vertical between the turbines, and not the absolute distance between turbines as is used at the moment?
- Figure 11: Please increase font size. Furthermore, I suggest changing the axes to express distance as a function of rotor diameter D.
- Ln 455: The second case should refer to 45 deg instead of 90 deg.
- While the results with the 9 turbine farm demonstrate the effectiveness of the proposed control methods, the symmetry of the layout results in some redundant results (as also indicated in the table captions). Therefore, it would be interesting to consider a more complex/less uniform layout.
- The constrained optimization currently only considers blade root moments and blade tip deflection. Are these also the most critical components to consider, or will including other structural components further decrease the performance gain of wake redirection with derating?
- While the choice of a steady-state wake model to demonstrate the proposed combined wind farm controller is understandable, these models are prone to overestimating the effects of derating on the wake statistics. Please comment on this in the paper in the discussion of the simulation results with 3D distance.
Technical corrections
- Title: “load-constrained wind farm power maximization”
- Ln 10: “… while maintaining an unaltered design load envelope …”
- Ln 20: “Among all …, wake redirection (WR) has proved to be highly effective for increasing wind farm energy harvesting.”
- Ln 21: “… deflect its wake away from downstream rotors.”
- Ln 23-24: Single sentence paragraph, combine with subsequent paragraph.
- Ln 27: incomplete reference “Services (2004)”.
- Ln 36: “misaligned” instead of “misalignment”.
- Ln 45: “… integrated in load-constrained wind farm control.”
- Ln 60: “increased design loads”.
- Ln 74: Two consecutive sentences starting with “moreover”.
- Ln 94: Rewriting the sentence is suggested, for example: “Clearly, to keep every turbine operating below or at its design loads, a wind farm controller should maximize power output within the safe envelope of each turbine in a farm, thereby combining derating and wake redirection.”
- Ln 182: “… seldom considered problematic.”
- Ln 186: “That being said, …”
- Ln 186-189: For clarity, please rewrite into multiple smaller sentences.
- Ln 193: “ … a wind farm controller …”
- Ln 200: “steady-state wind farm controller”
- Ln 201: “… consists of …”
- Ln 202: “… yaw angle \phi …”
- Ln 205: Break in two sentences. “Similarly, the ambient characteristics are collected into an array p …”
- Ln 224: “…, an optimal load-constrained controller is proposed …”
- Ln 251: “… in Eq. (5).”
- Ln 276: “On that plot, …”. I assume this is referring to Fig. 2, but please specify which plot.
- Ln 287: “… define the turbines’ operative setpoints through a simpler sub-optimal optimization algorithm without a …”
- Ln 304: “The LQR, being model-based, …” Please rewrite the sentence for clarity.
- Ln 339: Missing reference for “Standards”.
- Ln 342: Capital letter “in order …”
- Ln 354: I believe there is a typo here, blade tip deflection is highest for positive misalignment angles (Fig. 3b).
- Ln 351: “As in the previous analyses, the positive impact of derating on loads can be clearly noticed.”
- Ln 391: “…, with D being the rotor diameter, …”
- Ln 407: “However, the gain increment in the sub-optimal case (i.e. 3.8%), appears to be only marginally lower than that of the combined control approach equal to 3.9%.”
- Ln 410: “…, especially in farms containing a large number of turbines.”
- Ln 423: “To this end, Fig. 9 and Tab. 5 report …”
- Ln 439: “… for 60% of the cases, … for 85% of the cases, … for 95% of the cases.”
- Ln 514: typo “analyze”
Citation: https://doi.org/10.5194/wes-2023-145-RC2 - AC2: 'Reply on RC2', Alessandro Croce, 15 Mar 2024
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
RC1: 'Comment on wes-2023-145', Anonymous Referee #1, 17 Dec 2023
The comment was uploaded in the form of a supplement: https://wes.copernicus.org/preprints/wes-2023-145/wes-2023-145-RC1-supplement.pdf
- AC1: 'Reply on RC1', Alessandro Croce, 15 Mar 2024
-
RC2: 'Comment on wes-2023-145', Daan van der Hoek, 20 Dec 2023
General comments
The paper proposes a novel approach to wake redirection that includes derating yawed turbines to operate within a ‘safe envelope’ for turbine loading. The effect of yawed and derated operation on turbine loading was simulated using BEM, while the effect on wake characteristics was evaluated with the steady-state wake model FLORIS. Based on the acquired simulation results, the proposed method shows great promise and hence the results are suitable for publication. The writing in the paper is mostly clear, with some minor errors that are detailed below. Furthermore, a small change in the structure of the paper is suggested. Additional comments can also be found in the list below.
Specific comments
- The paper contains many instances where one-sentence paragraphs could easily be combined with the preceding or following paragraph.
- Ln 13: Power maximization and cost minimization are interconnected and should not be regarded as two separate aspects.
- Ln 22: Please add a reference supporting this statement.
- Ln 32: Please specify whether this concerns the yawed turbine, downstream turbines, or both.
- Ln 45: Please specify how derating is achieved in this paper.
- Ln 182-185: Similarly, wake redirection is only employed for a limited range of wind directions. This could also be considered during the load-constrained optimization, as the safe region corresponds to average fatigue loads, correct?
- Ln 220: Can you be more specific on how the optimization is limited to a smaller number of turbines? For example, by making the yaw misalignments of downstream turbines a function of the upstream turbines.
- Ln 279-281: Not only will derating the turbine result in lower power output, but the decrease in thrust will also make wake steering less effective. Please also comment on this aspect of the combined control approach.
- Section 3.1 does not present any results and would fit better in the methodology section. This would also prevent some questions that arise after reading the current section 2 on how the combined control strategy is implemented.
- Ln 323: Which wake deflection model is employed within FLORIS?
- Figure 3: While the 3d bar plots clearly show the results of some of the edge cases, it is not possible to distinguish the effects of yaw misalignment and derating in the center of the plots. Please switch to a 2D contour plot, or 2D bar plot, or make the current bars uniform in color (no gradient). The same applies to Fig. 5.
- Figure 6: Is this constraint function independent of wind speed? Please specify if this is not the case.
- Ln 390: Rated speed of the 10MW turbine is set at V=11.4 m/s and not 14 m/s.
- 16: When considering the test cases, we see that most wind speeds are above-rated. What is the reasoning behind this parameter choice, given that wake redirection is most effective at below-rated conditions (if at all effective above-rated)?
- Figure 7: Would it not make more sense to refer to spacing s as the vertical between the turbines, and not the absolute distance between turbines as is used at the moment?
- Figure 11: Please increase font size. Furthermore, I suggest changing the axes to express distance as a function of rotor diameter D.
- Ln 455: The second case should refer to 45 deg instead of 90 deg.
- While the results with the 9 turbine farm demonstrate the effectiveness of the proposed control methods, the symmetry of the layout results in some redundant results (as also indicated in the table captions). Therefore, it would be interesting to consider a more complex/less uniform layout.
- The constrained optimization currently only considers blade root moments and blade tip deflection. Are these also the most critical components to consider, or will including other structural components further decrease the performance gain of wake redirection with derating?
- While the choice of a steady-state wake model to demonstrate the proposed combined wind farm controller is understandable, these models are prone to overestimating the effects of derating on the wake statistics. Please comment on this in the paper in the discussion of the simulation results with 3D distance.
Technical corrections
- Title: “load-constrained wind farm power maximization”
- Ln 10: “… while maintaining an unaltered design load envelope …”
- Ln 20: “Among all …, wake redirection (WR) has proved to be highly effective for increasing wind farm energy harvesting.”
- Ln 21: “… deflect its wake away from downstream rotors.”
- Ln 23-24: Single sentence paragraph, combine with subsequent paragraph.
- Ln 27: incomplete reference “Services (2004)”.
- Ln 36: “misaligned” instead of “misalignment”.
- Ln 45: “… integrated in load-constrained wind farm control.”
- Ln 60: “increased design loads”.
- Ln 74: Two consecutive sentences starting with “moreover”.
- Ln 94: Rewriting the sentence is suggested, for example: “Clearly, to keep every turbine operating below or at its design loads, a wind farm controller should maximize power output within the safe envelope of each turbine in a farm, thereby combining derating and wake redirection.”
- Ln 182: “… seldom considered problematic.”
- Ln 186: “That being said, …”
- Ln 186-189: For clarity, please rewrite into multiple smaller sentences.
- Ln 193: “ … a wind farm controller …”
- Ln 200: “steady-state wind farm controller”
- Ln 201: “… consists of …”
- Ln 202: “… yaw angle \phi …”
- Ln 205: Break in two sentences. “Similarly, the ambient characteristics are collected into an array p …”
- Ln 224: “…, an optimal load-constrained controller is proposed …”
- Ln 251: “… in Eq. (5).”
- Ln 276: “On that plot, …”. I assume this is referring to Fig. 2, but please specify which plot.
- Ln 287: “… define the turbines’ operative setpoints through a simpler sub-optimal optimization algorithm without a …”
- Ln 304: “The LQR, being model-based, …” Please rewrite the sentence for clarity.
- Ln 339: Missing reference for “Standards”.
- Ln 342: Capital letter “in order …”
- Ln 354: I believe there is a typo here, blade tip deflection is highest for positive misalignment angles (Fig. 3b).
- Ln 351: “As in the previous analyses, the positive impact of derating on loads can be clearly noticed.”
- Ln 391: “…, with D being the rotor diameter, …”
- Ln 407: “However, the gain increment in the sub-optimal case (i.e. 3.8%), appears to be only marginally lower than that of the combined control approach equal to 3.9%.”
- Ln 410: “…, especially in farms containing a large number of turbines.”
- Ln 423: “To this end, Fig. 9 and Tab. 5 report …”
- Ln 439: “… for 60% of the cases, … for 85% of the cases, … for 95% of the cases.”
- Ln 514: typo “analyze”
Citation: https://doi.org/10.5194/wes-2023-145-RC2 - AC2: 'Reply on RC2', Alessandro Croce, 15 Mar 2024
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Alessandro Croce
CORRESPONDING AUTHOR
Department of Aerospace Science and Technology, Politecnico di Milano, Milano, Italy
Stefano Cacciola
Department of Aerospace Science and Technology, Politecnico di Milano, Milano, Italy
Federico Isella
Department of Aerospace Science and Technology, Politecnico di Milano, Milano, Italy
Short summary
For a few years now, various techniques have been studied to maximize the energy production of a wind farm, that is, from a system consisting of several wind turbines. These wind farm controller techniques are often analyzed individually and can generate loads higher than the design ones on the individual wind turbine. In this paper we study the simultaneous use of two different techniques with the goal of finding the optimal combination that at the same time preserves the design loads.
For a few years now, various techniques have been studied to maximize the energy production of a...
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