Quantifying the System Benefits of Ocean Energy in the Context of Variability: A UK Example

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper studies the system benefits of ocean energy in the context of variability, using the UK as a case study. The innovations are clearly defined, and the technical approach is reasonable; however, the conclusions are somewhat vague. Overall, the quality of the paper is high and meets the standards for publication, so I recommend acceptance after minor revisions. The specific suggestions for modification are as follows:

(1) Since this paper primarily focuses on the UK, I suggest including “UK” in the title.

(2) Chapter 1 clearly presents the innovations of this study, but I recommend further emphasizing the value of the current research. Additionally, it would be helpful to include a section outlining the structure of the paper to facilitate reader comprehension.

(3) In Chapter 3, I suggest separating the Results and Discussion into two distinct sections. The current combination makes it difficult for readers to identify which parts are based on existing data and which parts involve predictions.

(4) Sections 3.3 and 3.4 should be moved to a separate Discussion chapter.

(5) The conclusion section is too vague and lacks a summary. I recommend further refining it and presenting the conclusions in a bullet-point format for clarity.

Author Response

We thank the reviewers for their thorough comments, and have amended the manuscript accordingly. Responses to the specific comments are given below in green. We have also made some minor amendments to improve the wording and grammar.

This paper studies the system benefits of ocean energy in the context of variability, using the UK as a case study. The innovations are clearly defined, and the technical approach is reasonable; however, the conclusions are somewhat vague. Overall, the quality of the paper is high and meets the standards for publication, so I recommend acceptance after minor revisions. The specific suggestions for modification are as follows:

(1) Since this paper primarily focuses on the UK, I suggest including “UK” in the title.

Thank you for the suggestion, ": a UK example" has been added to the title to make this clearer

(2) Chapter 1 clearly presents the innovations of this study, but I recommend further emphasizing the value of the current research. Additionally, it would be helpful to include a section outlining the structure of the paper to facilitate reader comprehension.

The structure of the paper has been clarified at the end of the introduction. The motivation has also been stated more clearly.

(3) In Chapter 3, I suggest separating the Results and Discussion into two distinct sections. The current combination makes it difficult for readers to identify which parts are based on existing data and which parts involve predictions. (4) Sections 3.3 and 3.4 should be moved to a separate Discussion chapter.

In response to (3) and (4), we felt it was clearer to discuss the results in the same section, particularly as the results are split into two broad areas and separating the discussion could become repetitive. Other reviewers have noted the paper is well-structured, albeit needing signposting in introduction as you also suggest.

(5) The conclusion section is too vague and lacks a summary. I recommend further refining it and presenting the conclusions in a bullet-point format for clarity.

Following feedback from multiple reviewers, the conclusion has been reworked to hopefully improve the clarity, highlighting the novelty and key results.

 

Reviewer 2 Report

Comments and Suggestions for Authors

Please see the PDF attached.

Comments for author File: Comments.pdf

Author Response

We thank the reviewers for their thorough comments, and have amended the manuscript accordingly. Responses to the specific comments are given below in green. We have also made some minor amendments to improve the wording and grammar.

This paper investigates the wave energy on annual/sub-annual timeframes by considering the variability of solar photovoltaic, onshore and offshore wind, wave, and tidal stream over multiple years, and their ability to match with electricity demand. The present study also focuses on the importance of considering multiple years of input data when assessing power system impacts by highlighting their quantitative analysis. This work aligns with the current trend of research and has an interest in wave energy systems. However, some points need to be addressed and clarified in the manuscript for wider readability. The following issues and comments are outlined as:

1. Introduction: A robust motivation paragraph must be provided at the beginning of the Introduction, as it is not clear to the readers.

The motivation has been made clearer in the introduction.

2. Introduction: Last paragraph: difficult to grasp by the reader, to understand exactly what was done section-wise. Therefore, it is suggested to discuss a flowchart of the work or discuss it by indicating sections.

The structure of the paper, focusing on methodology and results and including section numbers has been clarified at the end of the introduction, and a flowchart has been added as suggested.

3. Section 2: The authors must provide the basic modelling framework instead of referring to [27] as this review could not understand the methods the way presented.

The modelling framework is described in section 2.3, which has been clarified in the text. Additional detail has also been added on the modelling framework; however some references are still made to the [27] for specific details.

4. In Tables 1 & 2, do they not have units for the quantities provided?

Table 1 is noted as being in GW, but this has been clarified in the caption. Table 2 is normalised, therefore has no units.

5. Results and Discussions: How do the authors check or quantify their results in terms of accuracy and confirm their applicability for future applications?

The model validation is described in the modelling methodology paper, which has been clarified it the manuscript. These results build on potential future pathways developed by the grid operator in the UK, which are therefore of interest for future power system planning. It has been clarified in the manuscript that these are not intended to be predictions of the future, but scenario analysis of what could happen in future.

6. In Figures 4 & 5, the length of the captions should be reduced by moving the texts to their respective discussions.

We note the reviewer’s concern with the length of the captions; however these are complex figures and detail is required in the caption to aid the reader’s understanding without having to read the full manuscript. However the caption for Fig. 4 has been shortened as suggested.

7. Conclusion: Although the future scope of the present analysis is discussed but the

Following feedback from multiple reviewers, the conclusion has been reworked to hopefully improve the clarity, highlighting the novelty and key results.

8. What is the computational cost of the simulations?

The paper has been clarified to note that the PyPSA model runs take minutes on a modern laptop, however significantly more data processing is required for the input resource data for each year. Some of this input data is provided by external sources, so the computational cost of this is unknown.

9. The following references may be of interest to the present work as a new wave energy system is developed recently. 

   https://link.springer.com/article/10.1007/s11804-025-00696-3

   We thank the reviewer for highlighting this new wave energy technology, and we are aware there are a broad spectrum of concepts being developed. Therefore, we have clarified in the limitations that a scenario has been developed from one of many devices, but we expect the trends to be similar for others. It was not within the scope of the work to investigate the sensitivity to multiple types of wave energy converter, which would have added significant additional data processing effort.

Reviewer 3 Report

Comments and Suggestions for Authors

This study provides valuable insights into the potential of diverse renewable energy portfolios for both annual and sub-annual supply–demand balancing. To strengthen the robustness of its conclusions and enhance its practical relevance, the authors should extend the data series, incorporate projected climate‐change impacts, integrate storage system coupling, account for network constraints, address technological and policy uncertainties, and include a life-cycle carbon‐emissions assessment. I therefore recommend acceptance pending major revisions.

1. The study relies on a five-year dataset (2015–2019), yet its own conclusions highlight the necessity of a longer time frame—such as seven years—to better capture fluctuations in the correlation between renewable energy resources and electricity demand. A shorter sampling period may fail to include extreme weather events or anomalous years, potentially resulting in biased estimates of the correlations between different renewable resources and demand.
2. While the study assumes that the temporal characteristics of each renewable resource will remain consistent with historical patterns, it remains unclear whether the authors have accounted for potential long-term changes in wind conditions, wave dynamics, or tidal patterns driven by climate change.
3. Although the variability of renewable energy sources is acknowledged in the text, energy storage systems are not adequately incorporated or discussed in the modeling framework.
4. The cost and availability of wave and tidal energy in 2030 in the study relies on literature projections or vendor claims, and lacks uncertainty analyses of capex changes, O&M costs, and technology maturity.
5. The study relies on a purely cost-optimal economic dispatch approach, without accounting for electricity price fluctuations, carbon pricing dynamics, changes in subsidy policies, or the evolving design of electricity markets.
6. The study considers carbon emissions only during the operational phase, while overlooking the embedded carbon footprint associated with equipment manufacturing, transportation, installation, and decommissioning. It is recommended that the authors either incorporate these lifecycle emissions into the analysis or provide a clear scientific rationale for their exclusion.
7. It is recommended that the authors expand the conclusion section with more detailed insights and reflections, which could better engage readers and encourage further exploration of the topic.
8. Although the research presented in the paper is focused and coherent, it is recommended that the authors include a flowchart illustrating the structure of the study. This would enhance the overall readability and help guide the reader through the research process more effectively.
9. The quality of the figures in the article should be further improved. In particular, the text, numerical values, and mathematical symbols within the images should be standardized using Times New Roman font to maintain consistency and enhance readability.

Author Response

We thank the reviewers for their thorough comments, and have amended the manuscript accordingly. Responses to the specific comments are given below in green. We have also made some minor amendments to improve the wording and grammar.

This study provides valuable insights into the potential of diverse renewable energy portfolios for both annual and sub-annual supply–demand balancing. To strengthen the robustness of its conclusions and enhance its practical relevance, the authors should extend the data series, incorporate projected climate‐change impacts, integrate storage system coupling, account for network constraints, address technological and policy uncertainties, and include a life-cycle carbon‐emissions assessment. I therefore recommend acceptance pending major revisions.

We thank the reviewer for their detailed comments and suggestions. As with all modelling, certain assumptions need to be made around aspects that are not central to the main analysis. It would not be possible to model all aspects of the energy system nor report them in a single paper. We have attempted to clarify in the manuscript the boundaries of the current work, and have expanded upon the limitations. 

1.    The study relies on a five-year dataset (2015–2019), yet its own conclusions highlight the necessity of a longer time frame—such as seven years—to better capture fluctuations in the correlation between renewable energy resources and electricity demand. A shorter sampling period may fail to include extreme weather events or anomalous years, potentially resulting in biased estimates of the correlations between different renewable resources and demand.

We appreciate the reviewer’s comments on the fact that five years of data may not fully capture all correlations between renewable resources and is unlikely to capture extreme weather events or anomalous years, which we have highlighted in the limitations of this work. However, the computational cost of generating additional years of availability data for the wave and tidal resource also needs to be considered.

2.    While the study assumes that the temporal characteristics of each renewable resource will remain consistent with historical patterns, it remains unclear whether the authors have accounted for potential long-term changes in wind conditions, wave dynamics, or tidal patterns driven by climate change.

The manuscript has been clarified to highlight that any long-term changes in the resource, such as wind or wave conditions, resulting from climate change were not modelled in this work. This would introduce significant additional uncertainty, making the results more difficult to interpret.

3.    Although the variability of renewable energy sources is acknowledged in the text, energy storage systems are not adequately incorporated or discussed in the modeling framework.

A representation of energy storage is included within the model, which has been clarified in the manuscript. This includes both batteries and PSHE, plus interconnectors and demand-side response, all in line with projections in the Future Energy Scenarios. However, it was not the focus of this work to investigate the implications or uncertainties around future changes to energy storage.

4.    The cost and availability of wave and tidal energy in 2030 in the study relies on literature projections or vendor claims, and lacks uncertainty analyses of capex changes, O&M costs, and technology maturity.

It is acknowledged that the future costs of tidal stream and wave energy is uncertain, however it is beyond the scope of the current work to assess this. The CAPEX and OPEX of any of the generation technologies is not directly modelled in this work. The manuscript has been clarified to reflect this, and note that one wave technology has been used to provide a scenario of future generation.

5.    The study relies on a purely cost-optimal economic dispatch approach, without accounting for electricity price fluctuations, carbon pricing dynamics, changes in subsidy policies, or the evolving design of electricity markets.

The reviewer highlights many interesting aspects which could be investigated in future research, but were beyond the scope of the current work. These areas have however been highlighted in the discussion.

6.    The study considers carbon emissions only during the operational phase, while overlooking the embedded carbon footprint associated with equipment manufacturing, transportation, installation, and decommissioning. It is recommended that the authors either incorporate these lifecycle emissions into the analysis or provide a clear scientific rationale for their exclusion.

Lifecycle carbon emissions are of course an important topic for investigation, but were not within the scope of the work presented in this paper. Fully accounting for these would have required significantly more time and effort than was available, and modelling this in a simplified way could be very misleading. 

7.    It is recommended that the authors expand the conclusion section with more detailed insights and reflections, which could better engage readers and encourage further exploration of the topic. 

Following feedback from multiple reviewers, the conclusion has been reworked to hopefully improve the clarity, highlighting the novelty and key results.

8.    Although the research presented in the paper is focused and coherent, it is recommended that the authors include a flowchart illustrating the structure of the study. This would enhance the overall readability and help guide the reader through the research process more effectively.

The structure of the paper has been clarified at the end of the introduction, together with a flowchart showing the main steps schematically.

9.    The quality of the figures in the article should be further improved. In particular, the text, numerical values, and mathematical symbols within the images should be standardized using Times New Roman font to maintain consistency and enhance readability.

The figures in the manuscript all use Open Sans which “is characterized by its wide apertures on many letters and a large x-height, making it highly legible on screens and at small sizes.” There is no mathematical notation in any of the figures, just positive & negative numbers in percentage terms. We will take guidance from the editors if further revision to the figure are required.

Reviewer 4 Report

Comments and Suggestions for Authors

This manuscript presents a well-structured and comprehensive study assessing the role of ocean energy (wave and tidal stream) in enhancing the resilience and performance of future power systems in Great Britain. Using five years (2015–2019) of consistent, hourly time series data for electricity demand and renewable availability, the authors demonstrate the sensitivity of dispatch modeling to interannual variability and explore the benefits of integrating 1–10 GW of ocean energy.

Here are some comments.

• The abstract includes lengthy and wordy opening sentences. The authors should revise them.
• More results should be added to the abstract. Moreover, the authors didn’t present any sentence describing the conclusions remarks.
• Consider adding a short paragraph at the end of the introduction summarizing the research objectives.
• The Introduction touches briefly on demand flexibility and electrification (lines 35–38). More details may be useful.
• Clarify what specific assumptions were made in the scaling and how well they reflect expected demand-side changes. Consider referencing sensitivity from related literature.
• The manuscript notes that 2016 is a leap year and the extra day introduces <0.3% error. While the impact is indeed minor, clarify whether this was handled by truncation, normalization, or direct inclusion to avoid confusion.
• The results present interannual variability using descriptive statistics (mean, range, IQR), but no statistical tests or confidence intervals are applied to assess significance. Include statistical significance testing (e.g., ANOVA or t-tests) for key metrics (dispatch cost, emissions) to verify whether observed differences across years or scenarios are robust.

Author Response

We thank the reviewers for their thorough comments, and have amended the manuscript accordingly. Responses to the specific comments are given below in green. We have also made some minor amendments to improve the wording and grammar.

This manuscript presents a well-structured and comprehensive study assessing the role of ocean energy (wave and tidal stream) in enhancing the resilience and performance of future power systems in Great Britain. Using five years (2015–2019) of consistent, hourly time series data for electricity demand and renewable availability, the authors demonstrate the sensitivity of dispatch modeling to interannual variability and explore the benefits of integrating 1–10 GW of ocean energy.

Here are some comments.
•    The abstract includes lengthy and wordy opening sentences. The authors should revise them.
•    More results should be added to the abstract. Moreover, the authors didn’t present any sentence describing the conclusions remarks.

In response to the first 2 points, the abstract has been revised based on feedback from multiple reviewers, including splitting some longer sentences, hand highlighting the main conclusions.

•    Consider adding a short paragraph at the end of the introduction summarizing the research objectives.

The motivation for the research has been clarified in the introduction.

•    The Introduction touches briefly on demand flexibility and electrification (lines 35–38). More details may be useful.

Additional detail on the representation of storage, flexibility, and future electrification in the modelling have been added to the paper, however this is not the main focus of this work, and has been investigated by other literature. 

•    Clarify what specific assumptions were made in the scaling and how well they reflect expected demand-side changes. Consider referencing sensitivity from related literature.

The manuscript has been updated to clarify the scaling was linear to match both total (GWh/yr) and peak (GW) demand. Demand side response and other forms of storage were included in the model in line with the projected future capacities in the FES LTW 2030 scenario, which has been clarified in the manuscript. An erroneous statement about allowance for demand-side response being included as part of the demand profile has been removed; this relates to other (unpublished) work not in this study. 

•    The manuscript notes that 2016 is a leap year and the extra day introduces <0.3% error. While the impact is indeed minor, clarify whether this was handled by truncation, normalization, or direct inclusion to avoid confusion.

The manuscript has been revised to make it clearer this extra day was handled by inclusion.

•    The results present interannual variability using descriptive statistics (mean, range, IQR), but no statistical tests or confidence intervals are applied to assess significance. Include statistical significance testing (e.g., ANOVA or t-tests) for key metrics (dispatch cost, emissions) to verify whether observed differences across years or scenarios are robust.

While it is acknowledged that the limited data available means it is not possible to robustly quantify using detailed statistical tests the magnitude of the changes to the key metrics. However, a simple paired Student’s t-test has been used to assess significance at the 5% level, with details added to the manuscript.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have revised the paper by incorporating the suggestions and clarifying the comments. No more further comments.