The Potential Impact of Climate Change on the Efficiency and Reliability of Solar, Hydro, and Wind Energy Sources

Round 1

Reviewer 1 Report

In this paper, the author investigated the impact of climate change on the supply of renewable energy. The subject of the manuscript falls within the scope of the journal. This manuscript represents a good contribution to this area of research. The following issues should be addressed to improve the quality of this paper:

 

a. The current literature review on this topic is almost inexistent.

b. The authors considered the precipitation data relevant to hydro plants. It is recommended that also air temperature data to be considered because higher air temperature would increase surface evaporation, reducing water storage and power output.

c. The authors considered only the wind speed data relevant to wind plants. It is recommended that also air temperature data to be considered because increasing air temperatures will lead to slight declines in air density and power output.

d. The authors considered only surface solar radiation to be directly related to the solar power production. It is recommended that also air temperature data to be considered because an increase in global temperature would negatively affect the efficiency of the cells and therefore the power output. Also, a precipitation increase would reduce efficiency.

e. Discussion of results is incomplete. Authors should compare the findings of this research with the findings of other authors.

f. Impersonal writing needs to be used consistently throughout the manuscript.

g. All the terms used in the mathematical formulas should be properly described.

h. In Figure 16, the two locations need to be specified.

Author Response

 Review 1

Review Report Form

Open Review

(x) I would not like to sign my review report
( ) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
(x) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style

 

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	( )	( )	(x)	( )
Are all the cited references relevant to the research?	( )	(x)	( )	( )
Is the research design appropriate?	( )	(x)	( )	( )
Are the methods adequately described?	( )	(x)	( )	( )
Are the results clearly presented?	( )	(x)	( )	( )
Are the conclusions supported by the results?	( )	(x)	( )	( )

Comments and Suggestions for Authors

In this paper, the author investigated the impact of climate change on the supply of renewable energy. The subject of the manuscript falls within the scope of the journal. This manuscript represents a good contribution to this area of research. The following issues should be addressed to improve the quality of this paper:

We heartily thank the reviewer for the time and effort to construct insightful comments and suggestions. We have addressed each point in our revisions and the responses to each comment are below in blue italics.

 

1. The current literature review on this topic is almost inexistent.

 

We have restructured the text to more clearly convey our story and added references on the climate change signal [20] and the impact of extreme climate on renewables [11,12] and on renewables and the electrical grid [17] to better represent past work. In addition, references on risk and reliability metrics were added [22-24].

 

 

1. The authors considered the precipitation data relevant to hydro plants. It is recommended that also air temperature data to be considered because higher air temperature would increase surface evaporation, reducing water storage and power output.

 

A note has been added to the effect that air temperature data (which as shown is a modest relative change) is a second or third order effect in water storage.

 

1. The authors considered only the wind speed data relevant to wind plants. It is recommended that also air temperature data to be considered because increasing air temperatures will lead to slight declines in air density and power output.

 

Same comment as above in item b.

 

 

1. The authors considered only surface solar radiation to be directly related to the solar power production. It is recommended that also air temperature data to be considered because an increase in global temperature would negatively affect the efficiency of the cells and therefore the power output. Also, a precipitation increase would reduce efficiency.

 

Same comment as above in b.

 

1. Discussion of results is incomplete. Authors should compare the findings of this research with the findings of other authors.

 

A paragraph was added to the discussion section to highlight the novel aspects of this work.

 

1. Impersonal writing needs to be used consistently throughout the manuscript.

 

While we understand that this has been the standard in science journals in the past, we do not believe this is required for MDPI journals and prefer to follow the trend in many science journals by using some first-person language in order to improve the readability. Making the material easier to access is paramount when working across disciplines such as this study.

 

1. All the terms used in the mathematical formulas should be properly described.

 

We agree, thank you. We have added a few definitions that were missing.

 

 

 

1. In Figure 16, the two locations need to be specified.

 

Thanks for noticing this error. The legend has been fixed to identify the associated stations.

 

 

Reviewer 2 Report

The topic is of paramount interest, the approach is interesting, and the intermittency parameter seems to be a valid indicator.

Coming to solar, hydro and wind, first of all I would have expected to see the trend of the resource anomaly itself (solar irradiation, rainfall, wind speed), like for air temperature, for the two locations considered. Are these resources increasing or decreasing?

Only after I would have focused on their intermittence. The apparent finding  (why no linear regression is shown in fig. 2?) is that intermittence is practically constant for solar; its trend is uncertain for hydro in Palma, slightly decreasing in Cordova and slightly increasing in Lake Oroville. Finally, wind intermittence is constant based on daily data (of little interest) and increasing for hourly data in both locations. I can't say if these findings are really meaningful...

As for the evaluation of power and energy storage, both appear awkward to me. The definition of "power produced" P(t) is mysterious. P(t) is in the order of 10⁶-10⁷ kW for Solar, 10^-3 kW for hydro and from 10³ (Palma) to 10⁶ kW (Cordova) for wind. How are these power values are calculated? Are they referred to a unit area? 

Sentences like "P(t) is the Solar power (or Wind power) produced every day and P_F(t) is the power flow" (lines 129-30) or "The power flow out P_F(t) is the one that minimizes the maximum of R with the condition R > 0 for all times" (line 132) need to be clarified. The first definition seem to refer to energy rather than power, unless you assume that P(t) is the daily average power produced. The resulting storage (MaxR) has values in the order of 10⁷ kWh for solar, 10^-1 for hydro, and 10⁵ to 10⁷ for wind. The error bar is all over the same... How is it calculated?

Furthermore, the storage needs for a plant seems to be calculated for a 5 years base. This period is too long and rather unrealistic for any plant whatsoever. 

Author Response

Review 2

Open Review

( ) I would not like to sign my review report
(x) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
(x) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style

 

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	(x)	( )	( )	( )
Are all the cited references relevant to the research?	(x)	( )	( )	( )
Is the research design appropriate?	( )	( )	(x)	( )
Are the methods adequately described?	( )	( )	(x)	( )
Are the results clearly presented?	( )	(x)	( )	( )
Are the conclusions supported by the results?	( )	(x)	( )	( )

Comments and Suggestions for Authors

The topic is of paramount interest, the approach is interesting, and the intermittency parameter seems to be a valid indicator.

We heartily thank the reviewer for the time and effort to construct insightful comments and suggestions. We have addressed each point in our revisions and the responses to each comment are below in blue italics.

Coming to solar, hydro and wind, first of all I would have expected to see the trend of the resource anomaly itself (solar irradiation, rainfall, wind speed), like for air temperature, for the two locations considered. Are these resources increasing or decreasing?

We agree this was not clear.  The Pout plots are the change in the resource itself.  We have added some sentences to hopefully make this more clear for the three variables of interest.

 

Only after I would have focused on their intermittence. The apparent finding  (why no linear regression is shown in fig. 2?) is that intermittence is practically constant for solar; its trend is uncertain for hydro in Palma, slightly decreasing in Cordova and slightly increasing in Lake Oroville. Finally, wind intermittence is constant based on daily data (of little interest) and increasing for hourly data in both locations. I can't say if these findings are really meaningful...

We do the intermittence first because we are building toward the storage needs as a metric.  Though the referee is correct that most often the trends in the resource are stressed, because the intermittence is fundamental to this analysis we want the reader to see it stressed first and then see the trends on the resources.  

As for the evaluation of power and energy storage, both appear awkward to me. The definition of "power produced" P(t) is mysterious. P(t) is in the order of 10⁶-10⁷ kW for Solar, 10^-3 kW for hydro and from 10³ (Palma) to 10⁶ kW (Cordova) for wind. How are these power values are calculated? Are they referred to a unit area? 

The arbitrary scaling that goes into these numbers is now made hopefully more clear with additional explanation added.  The numbers themselves do not matter for these calculations, but what is more important is their relative values.

Sentences like "P(t) is the Solar power (or Wind power) produced every day and P_F(t) is the power flow" (lines 129-30) or "The power flow out P_F(t) is the one that minimizes the maximum of R with the condition R > 0 for all times" (line 132) need to be clarified. The first definition seem to refer to energy rather than power, unless you assume that P(t) is the daily average power produced. The resulting storage (MaxR) has values in the order of 10⁷ kWh for solar, 10^-1 for hydro, and 10⁵ to 10⁷ for wind. The error bar is all over the same... How is it calculated?

Thank you, the referee is correct is it the daily averaged Power flow.  We have fixed this error.  The error bars are not actually error bars they as stated in the figure captions they represent the time interval over which the calculation is done (this is a problem with the fact that the convention is to call those types of bars on the figure error bars, even when they do not represent error.

Furthermore, the storage needs for a plant seems to be calculated for a 5 years base. This period is too long and rather unrealistic for any plant whatsoever. 

 Storage needs are not storage for 5 years rather the storage needed to maintain the optimal daily Pf calculated over a 5 year period.  Arguably this should be more then 5 years but to balance good statistics against secular trends, 5 years was chosen.

 

Author Response File: Author Response.docx

Reviewer 3 Report

The Potential Impact of Climate Change on the Efficiency and Reliability of Solar, Hydro, and Wind Energy Sources After reading the manuscript I have some comments to improve the quality of the paper

C1: The implications should be strengthened, in light of the obtained findings.

C2. Add the limitation of the study

C3: Improve the conclusion section and focus on the main contribution of the current research.

C4Add more discussion to the empirical sections.

 

C5- The introduction needs some improvement regarding climate change. The citations are not exhaustive. Further, the researcher(s) can enrich the introduction by considering the following manuscripts. 

Author Response

Review 3

 

Open Review

( ) I would not like to sign my review report
(x) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
(x) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style

 

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	( )	(x)	( )	( )
Are all the cited references relevant to the research?	( )	(x)	( )	( )
Is the research design appropriate?	( )	(x)	( )	( )
Are the methods adequately described?	( )	( )	(x)	( )
Are the results clearly presented?	( )	(x)	( )	( )
Are the conclusions supported by the results?	( )	(x)	( )	( )

Comments and Suggestions for Authors

The Potential Impact of Climate Change on the Efficiency and Reliability of Solar, Hydro, and Wind Energy Sources After reading the manuscript I have some comments to improve the quality of the paper

We heartily thank the reviewer for the time and effort to construct insightful comments and suggestions. We have addressed each point in our revisions and the responses to each comment are below in blue italics.

C1: The implications should be strengthened, in light of the obtained findings.

Some sentences added in abstract and conclusion (and discussion) to strengthen this.

C2. Add the limitation of the study

Sentences added to the discussion to reiterate the limitations

C3: Improve the conclusion section and focus on the main contribution of the current research.

Some sentences added and conclusion (and discussion) to strengthen this.

C4 Add more discussion to the empirical sections.

 We have tried to add some clarifying sentences in the results

C5- The introduction needs some improvement regarding climate change. The citations are not exhaustive. Further, the researcher(s) can enrich the introduction by considering the following manuscripts. 

The manuscripts suggested by the reviewer were not included in the review document we received so we were not able to include them in the revisions.

 

Author Response File: Author Response.docx

Reviewer 4 Report

This article proposes "The Potential Impact of Climate Change on the Efficiency and Reliability of Solar, Hydro, and Wind Energy Sources." Please consider the following comments for improvements. 

1. There are many climate change issues (variables). Impact of which issues are addressed in this study? Please describe in Abstract and in the remainder of the paper.

2. The authors consider two locations. However, the analytical results found from these two regions are missing in the abstract section.

3. The Introduction section somehow failed to show the literature review of the similar works. Although the authors listed and discussed many papers, they are not focused. Please discuss more about the related papers, find the gaps, and write your contributions. 

4. It's is true that the climate change impacts the size of energy storage devices. However, there are many technical and operation issue in power system which greatly impact the size. Those should be discussed in section 2.1.2. If possible, please reformulate the mathematical model.

5. The results (Fig. 3, 4 and so on)  show a linear relationship over several years . Will this relationship satisfy, if the number of years increases? 

6.  One possible measure of the efficiency of highly variable renewable energy power  plants is the ratio of the energy storage needed to the averaged energy production  in one day. This is considered in this study. However, technically, the efficiency of a solar cell is determined as the fraction of incident power which is converted to electricity.

7. Reliability has not been discussed mathematically.

Overall, the paper needs significant improvements for further considerations. 

 

Author Response

Review 4

 

Open Review

( ) I would not like to sign my review report
(x) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
(x) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style

 

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	( )	( )	(x)	( )
Are all the cited references relevant to the research?	( )	( )	(x)	( )
Is the research design appropriate?	( )	(x)	( )	( )
Are the methods adequately described?	( )	( )	(x)	( )
Are the results clearly presented?	( )	( )	(x)	( )
Are the conclusions supported by the results?	( )	( )	(x)	( )

Comments and Suggestions for Authors

This article proposes "The Potential Impact of Climate Change on the Efficiency and Reliability of Solar, Hydro, and Wind Energy Sources." Please consider the following comments for improvements. 

We heartily thank the reviewer for the time and effort to construct insightful comments and suggestions. We have addressed each point in our revisions and the responses to each comment are below in blue italics.

 

1. There are many climate change issues (variables). Impact of which issues are addressed in this study? Please describe in Abstract and in the remainder of the paper.

 

Added in abstract and a few more words in introduction.

 

2. The authors consider two locations. However, the analytical results found from these two regions are missing in the abstract section.

 

Added clarification about the main results in the abstract.

 

3. The Introduction section somehow failed to show the literature review of the similar works. Although the authors listed and discussed many papers, they are not focused. Please discuss more about the related papers, find the gaps, and write your contributions. 

 

We have restructured the text to more clearly convey our story and added references on the climate change signal [20] and the impact of extreme climate on renewables [11,12].

 

4. It's is true that the climate change impacts the size of energy storage devices. However, there are many technical and operation issue in power system which greatly impact the size. Those should be discussed in section 2.1.2. If possible, please reformulate the mathematical model.

 

A comment in section 2.1.2 was added about the details of storage devices.  The model used explicitly is designed to calculate the needed storage but not including the technical details of the storage devises. Reformulating the mathematical model is beyond the scope of this work.

 

5. The results (Fig. 3, 4 and so on) show a linear relationship over several years . Will this relationship satisfy, if the number of years increases? 

 

The linear fits shown over ~60 years are not meant to imply that the actual functional form of the change is linear, rather that there is a secular trend. Since this is the extent of the data available globally we can not say what the trend will be in the future though in subsequent work we will be looking in to the future with global climate model results.

 

6. One possible measure of the efficiency of highly variable renewable energy power  plants is the ratio of the energy storage needed to the averaged energy production  in one day. This is considered in this study. However, technically, the efficiency of a solar cell is determined as the fraction of incident power which is converted to electricity.

 

As we said in the text we are intentionally not including the details of the solar cell power conversion (or the wind or hydro) some words were added to reiterate this in section 3.1.  The efficiency value we have constructed is quite different from the devise power conversion efficiency, rather it is a plant efficiency as described relative to the storage. A sentence clarifying this was added to section 3.1.

 

7. Reliability has not been discussed mathematically.

 

Discussion of the details of the mathematical quantification of the risk and reliability are outside the scope of this paper however three additional references have been added in the introduction which describe risk and reliability metrics in citations [22-24].

 

Benjamin A. Carreras, David E. Newman, and Ian Dobson, North American Blackout Time Series Statistics and Implications for Blackout Risk, IEEE TRANSACTIONS ON POWER SYSTEMS, DOI: 10.1109/TPWRS.2015.2510627, Nov 2016 

 

10. A. Carreras, D. E. Newman, and I. Dobson, “Does Size Matter?,” Chaos 24, 023104 (2014); doi: 10.1063/1.4868393

 

DE Newman, BA Carreras, NS Degala, I Dobson, Risk metrics for dynamic complex infrastructure systems such as the power transmission grid, 2012 45th Hawaii International Conference on System Sciences, 2082-2090

 

 

Overall, the paper needs significant improvements for further considerations. 

We have revised the structure to more clearly communicate the research.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Thank you for the revised manuscript. The revised paper may be considered for publication.

Reviewer 3 Report

 Accept in present form

Reviewer 4 Report

Thanks for addressing the comments.

 

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.