A Probabilistic Approach to Analyze Wind Energy Curtailment in Non-Interconnected Greek Islands Based on Typical Wind Year Meteorological Data

Round 1

Reviewer 1 Report

The fluids-798821 manuscript deals with the problem of wind energy curtailments in non-interconnected islands (NIIs), focusing on the area of the Aegean Sea-Greece. The subject of investigation is of high interest for the given area, especially within the context of ongoing interconnection projects  of NIIs to the Greek mainland.

Towards this direction, the authors proceeded to the development of a planning exercise concerning wind energy installations, looking at a total of 20 NII systems and measuring the impact of four main components (PV capacity, dynamic penetration limit, technical minima, system flexibility) on the anticipated levels of wind energy curtailments. Although the paper offers significant insight on the structural limitations of NIIs to support large-scale RES penetration, presentation of the methodology and results produced could be improved considerably.

More specific comments are given in the following:

Language:

The paper could benefit from a thorough language/phrasing review. Some instances are given below: 

# Line 49: ...is drawing towards

# Line 74: accents the fact

# Line 77: …and then upgrade

# Line 132: contiguous islands

# Line 153: This figure permits / a comparative visual assessment

# Line 175: the antiquity

Introduction:

# The introduction is quite extensive. Maybe parts of it could be removed, or taken to the discussion-conclusions part, e.g. discussion on storage.

# The paper lacks also discussion on interconnection plans and projects, and how these relate to the results of the authors (more suitable for the discussion-conclusion part as well)

# Some of the information included needs to be updated, e.g. some of the islands have been interconnected.

# Table 2: Could there be an attempt to rank/group islands in terms of flexibility?

# Table 2: Are summer units transported to certain islands considered? Data refers to 2016. Are there more recent information available? Same applies for the entire paper dataset. - Line 232: If I am not mistaken, there is a wind park of ~1.3MW on Sifnos.

#Figure 3: Is the figure used to support a conclusion in the results / discussion section ?

# Line 234: Reference is made to permitted wind capacity – including relevant numbers could be of added value for making a point at a later stage.

Methodology:

# Wind-data:

• The authors mention that each month was selected separated from a 10 years period. Further explanation could enhance undestanding.
• How is the 50m selected relating to the average tower height for Aegean Sea wind parks?
• Capacity factors of Table 5 seem a bit high for the given Weibull values. What is the wind power curve used? Do Weibull values correspond to 10m or 50m of elevation?

# PV-data: Have the authors used a standard, real-world PV generation profile which was adjusted to different solar potential regimes? Could this lead to non-realistic solar irradiance / PV generation values?  

# Load-demand data: Are all time series referring to a common year? Would be nice to include a figure with the actual, hourly load demand time series used, in normalized form.

# Same applies for the rest of time series – wind CF and PV CF in order to also assess the complementarity between the different profiles.

# Is there a common unit commitment strategy considered for all islands? Can the authors analyze this in detail? Are spinning reserve requirements taken into account?

Results

# Figures presented are somewhat hard to follow. Could be of value to define a reference scenario and present curtailment results in the form of difference with the reference scenario.

 # The authors imply that in certain instances, wind energy curtailments are reduced, owing to higher PV integration. An explanatory figure could support a better understanding of their argument.   

# Estimated wind energy curtailments for Astypalaia reach 50%, even for 10% of normalized wind capacity. How do similar estimated results relate to actual wind energy curtailments in representative Aegean islands with existing wind park installations?

#Figure 13: Vertical axis could start at 80%.

# 4.2: Wind penetration limit: Is this component independent from the component of flexibility?

# 4.5: The authors make some strong, generic quantitative points on the effect of e.g. technical minima on wind energy curtailments (lines 590-92). Could such boundaries be visualized concerning the variation of main components and their impact on wind energy curtailments in general, maybe in the form of a contour plot?

Conclusions:

Conclusions could be expanded by making reference to storage and interconnection developments in the given area, prospective offshore wind projects etc, as well as with the inclusion of some more quantified policy recommendations on the margins for extra wind capacity on the examined islands. 

Author Response

Thank you for your time and your comments. Most of your comments have been taken into consideration in the revised version. 

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents a probabilistic calculation procedure for estimating the wind energy curtailments in non-interconnected islands. Although the paper is interesting and the presentation of the procedure and the results are clear, the paper by no means falls into the scope of Fluids Journal. I don't think that the Fluids Journal readers would be interested in the specific research, as it is not in their interests. The authors should seek for a more relevant Journal to publish their work.

Author Response

The paper presents a probabilistic calculation procedure for estimating the wind energy curtailments in noninterconnected islands. Although the paper is interesting and the presentation of the procedure and the results are clear, the paper by no means falls into the scope of Fluids Journal. I don't think that the Fluids Journal readers would be interested in the specific research, as it is not in their interests. The authors should seek for a more relevant Journal to publish their work.

- Thank you for time and your valuable comments on my work. I agree with you, but there is a special issue in Fluids Journal on the topic of “Wind and Wave Renewable Energy systems”. So together with other more technological papers on this topic, maybe a more technical paper which brings up the issues of non-interconnected power systems could be of interest…

Reviewer 3 Report

In this paper, the authors analyze the effect of different factors on wind energy curtailment in non-interconnected Greek islands. In general, this paper is well-written. However, there are still some minor parts requiring modification. 

1. Please double-check the gramma and some possible error, such as row 226, there is no unit for 319.7
2. On row 190. the definition of wind capacity factor is not clear. 
3. Figure 2 is unreadable. More explanation is required to demonstrate the meaning of each section in one bar.
4. In Table3, based on row 168, smaller unit Should be minimum unit and larger unit should be maximum unit.
5. On row 452, the authors mentioned "Based on the described methodology, PV energy curtailment will occur only in case of high PV penetration and especially in case that PV power output is greater than the load demand." However, this kind of situation only happens with residential PV panel. With this kind of situation, the curtailment of wind will almost always be done at first. However, If we consider about the large size of solar farm and wind farm, the curtailment of PV or wind should have no priority. Therefore, PV production should be separated from the load data.

Author Response

Thank you for time and your valuable comments on my work. Please find my responses and actions undertaken on your comments.

In this paper, the authors analyze the effect of different factors on wind energy curtailment in non-interconnected Greek islands. In general, this paper is well-written. However, there are still some minor parts requiring modification. 

1. Please double-check the gramma and some possible error, such as row 226, there is no unit for 319.7

• MW (added)

1. On row 190. the definition of wind capacity factor is not clear. 

• Wind turbines power curves were added

1. Figure 2 is unreadable. More explanation is required to demonstrate the meaning of each section in one bar.

• The main concept is to provide the overview of conventional power units structure than the details…

1. In Table3, based on row 168, smaller unit Should be minimum unit and larger unit should be maximum unit.

• Done

1. On row 452, the authors mentioned "Based on the described methodology, PV energy curtailment will occur only in case of high PV penetration and especially in case that PV power output is greater than the load demand." However, this kind of situation only happens with residential PV panel. With this kind of situation, the curtailment of wind will almost always be done at first. However, If we consider about the large size of solar farm and wind farm, the curtailment of PV or wind should have no priority. Therefore, PV production should be separated from the load data.

• This is the reality in Greek islands. There is a constraint about the maximum capacity per PV plant. Then there are only small PV solar farms. Less than 80kW in most of the islands. Less than 150kW in Crete. So we discuss about small PV power plants installed in the load centers. This is the reason, that PV curtailment is not established. However, if we consider really high PC integration, then PV curtailment have to be established in case that PV output will be greater than load. This concept was used in the simulation / methodology.  

Round 2

Reviewer 1 Report

The revised version of  the manuscript reflects the efforts of the authors for improvement and sufficiently addresses the review comments provided. As such, I recommend for its acceptance and publication. 

Minor issue: Please check reference numbering due to changes made in the text. 

Author Response

Dear Reviewers,

Thank you for time and your valuable comments on my work. Please find my responses and actions undertaken on your comments.

Regards,

George

Minor issue: Please check reference numbering due to changes made in the text. 

• Done

Reviewer 2 Report

The authors with their revised version have responded adequately to the reviewers' comments. Nevertheless, there are some minor details that I believe need to be clarified before publishing it.

1. A thorough check of the reference numbering is needed.
2. A final language review should be done, since minor mistakes still exist e.g. line 81, line 143 (strange use of word 'representation'), line 253,  also there are sentences referring in the past and a present form is used e.g. lines 135-136, 222, etc, and the use 'paragraph' instead of 'section' in lines 513,545, and probably more.
3. In Fig. 2 there are lines inside the bars which are not explained in the caption or the text. There is also a ref to Fig. 2 in the text (lines 142-148) where the authors assume that the reader understands from the fig. the flexibility of the power systems, but it is not obvious. If this is combined with the lines in the bars (probably represent convention power units) I would recommend having a different color for the same type of units (still with the lines separating each unit) and a legend explaining the colors.
4. In Fig. 3 it would be better to use solid dots to also distinguish the sign for the very small islands.
5. Do the authors believe that their results would be very different if they had used for their calculation a different pitch control wind turbine with the same or similar rated power? Are the models of wind turbines used the only suitable for their analysis?
6. References are missing from the paragraph between lines 224-238.
7. In line 256, what do you mean by 'safe side assumption'. Could you please explain more about it?
8. In line 396, why did you have to adjust the actual measurements to the PVGIS data? What is this adjustment consists of?
9. In Table 7, and generally the solar radiation used, was in the horizontal plane or at which angle?
10. Line 419-420 is missing a reference.
11. I don't think that in Fig 14 both charts are necessary. I believe that the bottom one is enough.
12. In line 524, do you have an explanation for the change of the order in the top-5 islands? 

Author Response

Please check the uploaded file with my actions to your comments/suggestions. 

Author Response File: Author Response.pdf