Green Hydrogen Driven by Wind and Solar—An Australian Case Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper hydrogen as electricity storage for South Australia is investigated. The paper would be interesting and relevant for publication in Wind. I have the following comments for the paper that should be addressed before considering publication:

1.       The paper and study seem to only have a focus on the electricity system, and this is risky as it limits the potential options available for securing system balancing, e.g. electric vehicles and chillers could provide flexibility (Smart energy system). Please discuss.

2.       There is also a focus on Carnot batteries in research. You decided to exclude these, due to?

3.       The numbered list on page 4 starts number at 3.

4.       The term “RRP” in Figure 2 needs to be explained.

5.       Does your method include effects on electricity price when buying and selling? Meaning that you increase prices when buying and reduces prices when selling.

6.       Please elaborate on how you identified the buy and selling price points (manual optimization).

7.       Figure 8 is low quality.

8.       I am unable to find what efficiency you assume of the PEM and hydrogen storages. These are quite important as hydrogen as electricity storage is very inefficient.

9.       It would be good for the reader to see how much of the revenue comes from spot and how much from FCAS in Table 8.

10.   How do your LCOEs look compared with other similar studies for other areas?

11.   Please elaborate risks related to using historical data to investigate a potential future solution. E.g. forecasting demands and potential competition (batteries, flexible demands, grid extensions, etc.) on the investigated markets and what that could mean for your results.

Author Response

1. The paper and study seem to only a focus on the electricity system, and this is risky as it limits the potential options available for securing system balancing, e.g. electric vehicles and chillers could provide flexibility (Smart energy system). Please discuss.-----.........----there are many options for flexibility, but this research was focused on the hydrogen system services and not on the broader flexibility service sector.
2. There is also a focus on Carnot batteries in research. You decided to exclude these, due to?----...........the battery research drew on the government-funded ARENA research that chose to exclude Carbot batteries, and we accepted that choice.
3. The numbered list on page 4 starts number at 3………this has been corrected
4. The term “RRP” in Figure 2 needs to be explained………….. Figure 2 has been removed
5. Does your method include effects on electricity prices when buying and selling? Meaning that you increase prices when buying and reduces prices when selling.-..........---We assume this hydrogen plant has minimal effect on electricity prices, and this minimal effect has not been included in our method.
6. Please elaborate on how you identified the buy and selling price points (manual optimization).............---this was using historical averages for electricity prices, and we tested a number of possible buy and sell points and came up with an optimum through iteration.
7. Figure 8 is low quality……….- I have replaced this figure (which is now figure 7)
8. I am unable to find what efficiency you assume of the PEM and hydrogen storages. These are quite important as hydrogen as electricity storage is very inefficient.--.........- the PEM efficiency is shown at line 221 as 51% and the storage cost in a salt cavern includes the cost of compression (OPEX), and I have made this more specific in Table 4. By adding OPEX to the heading
9. It would be good for the reader to see how much of the revenue comes from the spot and how much from FCAS in Table 8.----.....-FCAS is set as 15% of the arbitrage revenue (Equation 5)
10. How do your LCOEs look compared with other similar studies for other areas?----.........--the cost of the produced electricity is relatively high in the Australian wholesale market, and there are no public LCOEs to compare
11. Please elaborate risks related to using historical data to investigate a potential future solution. –this can go in DISCUSSION E.g. forecasting demands and potential competition (batteries, flexible demands, grid extensions, etc.) on the investigated markets and what that could mean for your results………… this has been added at lines 655 to 659.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper analyzes, through modeling, the possibility of storing excess renewable power in the form of hydrogen as a means of providing long duration energy storage in Australian context. The hydrogen assumed to be stored in a salt cavern. It is an interesting topic and paper. However, I have some questions/suggestions to improve the paper before publication:

1-      Have you considered the cost of H2 compressor? What is the storage pressure in salt cavern? H2 compressor could be as expensive as H2 gas turbine.

2-      Why a H2 turbine with a 800 MW size is chosen? What is the justification for it?

3-      What is the lifetime of the plant that you considered?

4-      Have you considered the lifetime of PEM electrolyzers in your calculations and their replacement costs?

5-      Table 8 reports the LCOE ($/MWh) ranging from $ 442 to 921$. Do you think having a storage system with this high produced cost of electricity makes sense. Please elaborate.  

6-      Table 8: why the revenue is assumed constant in all years. Please elaborate. 

7-      Correct numbers in lines 148 to 154.

8-      Line 159: re-electrification

9-      Please explain RRP in the text before using it in Figure 2.

10-  Please mention figure 2 in the text.

11-  Figure 7: One of the “No Turbine Operation” seems to be redundant.

12-  Line 272: It is mentioned: “as though the system had been used throughout the previous four calendar years”. Can you further explain why this assumption is made (i.e. 4 years).

13-  Line 305 and also Line 559, regarding “sea water electrolysis”: Please consider that sea water electrolysis has both practical and technical challenges compared to using pure water. The presence of salts and impurities in sea water can lead to issues such as corrosion of electrodes and the formation of by-products, etc.. Additionally, energy requirements for sea water electrolysis may be higher compared to using pure water due to the higher conductivity of sea water, etc.

14-  Table 2: Please define FCAS before using it in the table.

15-  Equation 1 in Line 358: How did you get this equation, is it through interpolation, etc. ? and what is the unit of 1937.3?

16-  Line 368: Are all costs reported in $A? please make it clear in the paper.

17-  Line 415: Figure 9 is correct.

18-  Line 417: The “CI 90%” is not explained in the paper before.

19-  Lines 338, 377, 661: Please correct the references, they are not in format.

20-  Table 7 and Figure 10: Why a 5000 tonneH2 storage size is chosen given that the minimum amount of stored electricity would be about 15000 MWh according to figure 10. What would be the impact of using a smaller storage size?

21-  Figure 10: The orange line is more important than the blue line. Therefore, the orange line should be more visible.  

22-  Line 661: reference for Homer.

23-  There is no need to have both titles and captions in figures 2, 4, 9, 10, and 11.

Author Response

Thank you for your review. I have included all your suggestions.

1-      Have you considered the cost of H2 compressor? What is the storage pressure in salt cavern? H2 compressor could be as expensive as H2 gas turbine.-..........-the pressure is shown at line 663 as 250 bar, and the h2 compressor cost is shown in Table 4 as per Gerwen Figure 5

2-      Why a H2 turbine with a 800 MW size is chosen? What is the justification for it?-.......... the model was optimised to an 800 MW size. So this is an output of the research.

3-      What is the lifetime of the plant that you considered?........- the lifetimes are now shown at line 221 and 224 (20 years for the PEM fuel cell and 25 years for the turbine as per Gerwen

4-      Have you considered the lifetime of PEM electrolyzers in your calculations and their replacement costs?...........- yes, the calculation assumed a life of 20 years on the plant

5-      Table 8 reports the LCOE ($/MWh) ranging from $ 442 to 921$. Do you think having a storage system with this high produced cost of electricity makes sense. Please elaborate-.............. the conclusion is that this is an expensive form of storage and does not make sense without subsidy

6-      Table 8: why the revenue is assumed constant in all years. Please elaborate. …..…the revenue is assumed constant as there is no clarity about future prices, so current prices were used.

7-      Correct numbers in lines 148 to 154……………, those numbers have been corrected

8-      Line 159: re-electrification-............. this term is now defined

9-      Please explain RRP in the text before using it in Figure 2…...I have removed Fig 2

10-  Please mention figure 2 in the text…...I have removed Fig 2

11-  Figure 7: One of the “No Turbine Operation” seems to be redundant…..thank you for picking that up; that is now corrected

12-  Line 272: It is mentioned: “as though the system had been used throughout the previous four calendar years”. Can you further explain why this assumption is made (i.e. 4 years)..........the assumption is to use real electricity prices and not assume future prices.

13-  Line 305 and also Line 559, regarding “sea water electrolysis”: Please consider that sea water electrolysis has both practical and technical challenges compared to using pure water. The presence of salts and impurities in sea water can lead to issues such as corrosion of electrodes and the formation of by-products, etc.. Additionally, energy requirements for sea water electrolysis may be higher compared to using pure water due to the higher conductivity of sea water, etc.-...... thank you, and I have added notes to caution on seawater at line 300

14-  Table 2: Please define FCAS before using it in the table……thank you, I’ve added that definition

15-  Equation 1 in Line 358: How did you get this equation, is it through interpolation, etc. ? and what is the unit of 1937.3?..............- yes, equation 1 is through interpolation of the two papers 44 and 45

16-  Line 368: Are all costs reported in $A? please make it clear in the paper….thank you, I have changed the notation to $A throughout

17-  Line 415: Figure 9 is correct….yes, this figure (now Fig 8) is correct

18-  Line 417: The “CI 90%” is not explained in the paper before.----.................thank you. I have defined that as a confidence interval 90%

19-  Lines 338, 377, 661: Please correct the references, they are not in format.--................. references have been put into the format

20-  Table 7 and Figure 10: Why a 5000 tonneH2 storage size is chosen given that the minimum amount of stored electricity would be about 15000 MWh according to figure 10. What would be the impact of using a smaller storage size?- …………………the design optimal shows as 5000 Tonne H2, which relates to 63,840 MWH as per line 451.

21-  Figure 10: The orange line is more important than the blue line. Therefore, the orange line should be more visible………..- clarity of the image improved by resizing

22-  Line 661: reference for Homer………. I have removed the reference to Homer

23-  There is no need to have both titles and captions in figures 2, 4, 9, 10, and 11…….this has been corrected

Reviewer 3 Report

Comments and Suggestions for Authors

The article “Green Hydrogen Driven by Wind and Solar- An Australian Case Study” contributes to addressing the multiple issues of energy transition, and in this case, from the territorial perspective of a country (Australia).

However, in reading the document, a series of issues have been detected which, in my opinion, need to be corrected so that the final version can be considered for publication:

 

-Introduction: (page 2) the objectives of the research are not clearly and fully explained. Is the objective to analyze the financial viability of green hydrogen? Or is it to see its incorporation into the Australian electricity grid?. The wording is confusing. Moreover, the authors are aware that the characterization as "green hydrogen" depends on the supporting technology. Perhaps the advantages of green hydrogen over blue hydrogen, for example, or grey hydrogen should be assessed comparatively. I would like to say that the scientific debate lacks a certain degree of depth. Furthermore, the limitations of the research, which always help to understand the final results, are not mentioned either.

 

-Literature review: (pages 3 and 4) the format of figure 1 and table 1 should be revised, and in particular in table 1, the bibliographic references should be part of the source. I.e. "authors' elaboration from .....".

Recent literature references should also be included, especially in sub-section 2.2, e.g. on mixed or hybrid installations developed in Norway (wind and hydrogen).

But what I don't understand is the reason for including the sub-section "Summary". I have never seen anything like this before. It is not necessary, as the abstract should concisely summarize the most relevant aspects of the whole article.

 

-Method: this section should explain the research methodology in detail, by typology, by phases, the data used, the case study.

However, it seems that the authors have focused on explaining a model of green hydrogen expansion, rather than a scientific research method underpinning the creation/definition of such a green hydrogen model. Considering the proposed text, it seems that the authors have used a descriptive approach to the situation in Australia, supported by a set of figures and graphs that illustrate this reality.

And once again the sub-section on Summary.

 

-Results: The main results are presented by category, which gives a sense of order to the research.

On page 12 and page 13 there is information that could help to draft Section 3 (Method) more correctly and completely. And once again the sub-section on Summary.

 

 

-Discussion: the discussion of results presents a solid contrast with bibliographical references, although the authors should go further by adding to the discussion other references they have cited in the literature review.

Author Response

Thank you for your review. I have included all your suggestions and, in particular, have followed your ideas on removing the summary sections and improving the introduction, method, and discussion to better follow the academic structure.  To help you I have included your statement, and then put a series of dots, and then my response.

1. Introduction: (page 2) the objectives of the research are not clearly and fully explained. Is the objective to analyze the financial viability of green hydrogen? Or is it to see its incorporation into the Australian electricity grid?. The wording is confusing. Moreover, the authors are aware that the characterization as "green hydrogen" depends on the supporting technology. Perhaps the advantages of green hydrogen over blue hydrogen, for example, or grey hydrogen should be assessed comparatively. I would like to say that the scientific debate lacks a certain degree of depth. Furthermore, the limitations of the research, which always help to understand the final results, are not mentioned either……………thank you for your excellent points. We have worked on clarity in the introduction, focusing on analysing the financial viability in the context of the incorporation into the grid.
2.  -Literature review: (pages 3 and 4) the format of figure 1 and table 1 should be revised, and in particular in table 1, the bibliographic references should be part of the source. I.e. "authors' elaboration from ………….....".this advice helped us reform the text to clarify how we used the bibliographic references.
3. Recent literature references should also be included, especially in sub-section 2.2, e.g. on mixed or hybrid installations developed in Norway (wind and hydrogen)...... thank you, we have made a reference to this research in Norway by Damman et al. and pointed out our focus is on electricity system and not hydrogen transport in this research.
4. But what I don't understand is the reason for including the sub-section "Summary". I have never seen anything like this before. It is not necessary, as the abstract should concisely summarise the most relevant aspects of the whole article……the summary has been removed from the literature review
5.  Method: this section should explain the research methodology in detail, by typology, by phases, the data used, the case study. However, it seems that the authors have focused on explaining a model of green hydrogen expansion, rather than a scientific research method underpinning the creation/definition of such a green hydrogen model. Considering the proposed text, it seems that the authors have used a descriptive approach to the situation in Australia, supported by a set of figures and graphs that illustrate this reality…………………..Thank you for you key point, and we have followed your tips to clarify our method, which was to develop a case study at Port Augusta, South Australia. Hence we have considered of the jobs and skills of the people in Port Augusta, as well the electricity, water, salt cavern and land supply.
6. And once again the sub-section on Summary………….. this Summary heading has been removed and incorporated in the text.
7. Results: The main results are presented by category, which gives a sense of order to the research.On page 12 and page 13 there is information that could help to draft Section 3 (Method) more correctly and completely……….….the structure from on pages 12 and 13 that are now in a numbered list in the Method Detail section 3.2.
8. And once again the sub-section on Summary.article……the summary has been removed from the method
9. Discussion: the discussion of results presents a solid contrast with bibliographical references, although the authors should go further by adding to the discussion of other references they have cited in the literature review………….thank you, I have added more of the references from the literature review.

 

 

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

This new version of the document largely incorporates the corrections and recommendations provided in the first revision.

The change in the quality and clarity of the document is more than notable, allowing for an understanding of the problems to be analysed and described. However, the authors are advised to pay special attention to the wording, as some sentences may lead to misinterpretation (e.g. page 5, lines 157-160).

Author Response

Thank you again. Your careful review has given useful advice. In terms of line 157, I have improved clarity by changing the sentence to read "explored the literature" instead of "extrapolated the literature".