Hybrid Energy Solutions for Enhancing Rural Power Reliability in the Spanish Municipality of Aras de los Olmos
, Carlos Roldán-Blay, Carlos Roldán-Porta, Guillermo Escrivá-Escrivá and Daniel DasÃ-Crespo
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe peer-reviewed manuscript addresses the issue of achieving reliable access to energy while taking into account the unique needs of the local community. In particular, two cases were analyzed: the first optimizing the existing configuration and the second introducing a biomass generator. Below are comments, the inclusion of which may help to improve the quality of the final article.
Comment 1. The study uses the HOMER simulation environment. The manuscript notes that access to the full input data sets is limited due to privacy concerns. However, it is worth describing the physical structure of the input data in more detail.
Comment 2. Section 2 seems too extensive. It is worth excluding the mathematical model issues (especially for the HOMER environment) into a separate section. In the Materials and Methods section, the research methodology should be precisely defined. In particular, it is crucial to define the research problems, research objectives (main and specific objectives), as well as methods, techniques and research tools. It is also worth presenting the general research algorithm, e.g. in a diagram.
Comment 3. The names of the sections cannot be only two letters (sections 2.3.2, 2.3.3, 2.3.5).
Comment 4. In the conclusion section it is worth emphasizing directions for further research.
Comment 5. In the English language, some sentences are too long and it is worth splitting them into several shorter sentences. This will improve the readability of the document.
Best Regards
Comments on the Quality of English LanguageLong sentences should be divided into several smaller ones.
Author Response
Comment 1. The study uses the HOMER simulation environment. The manuscript notes that access to the full input data sets is limited due to privacy concerns. However, it is worth describing the physical structure of the input data in more detail.
Response to Comment 1: We thank the reviewer for this important observation. Indeed, due to privacy restrictions, the complete raw data cannot be publicly shared. However, to improve transparency and replicability, we have expanded the description of the input data structure used in the study.
Specifically, in Section Input Data, we now provide additional details on:
The load demand and meteorological datasets consist of hourly records for one calendar year, resulting in 8,760 data points. Load demand data were collected through direct measurement at the site, reflecting actual hourly energy consumption for one year. Solar irradiance, wind speed, and air temperature data are sourced from NASA’s POWER database as monthly average values and then interpolated within HOMER software to yield hourly estimates for accurate simulation.
Biomass data reflect a constant daily availability of 27.07 tonnes/day throughout the year, derived from livestock waste production statistics in the region. The biomass data include costs (38.65 USD/tonne), lower heating value (28 MJ/kg), carbon content (60%), and gasification ratio (0.70 kg biogas/kg biomass).
We have clarified these points within the manuscript to provide readers and researchers with a clear understanding of the dataset structures, enhancing the interpretability and reproducibility of our results.
Please look at the lines 331-353, 355, 360-363, 367, 373, 377-379, 384-386.
Comment 2. Section 2 seems too extensive. It is worth excluding the mathematical model issues (especially for the HOMER environment) into a separate section. In the Materials and Methods section, the research methodology should be precisely defined. In particular, it is crucial to define the research problems, research objectives (main and specific objectives), as well as methods, techniques and research tools. It is also worth presenting the general research algorithm, e.g. in a diagram.
Response to Comment 2: We sincerely thank the reviewer for this valuable suggestion. We agree that Section 2 (Materials and Methods) was extensive and could benefit from clearer structuring. To address this comment, we have reorganized Section 2 as follows:
- Site Description and Existing Energy Challenges
- Proposed Solutions and Scenarios
- Brief Review of Input Data, Technical Aspects, and Economic Considerations
- Problem-Solving Algorithm
These modifications significantly enhance readability and structure, addressing the reviewer's valuable feedback.
Please look at the lines 268-273, 277-279, 292-310, 311-329, 374-375, 398-406, 409-413, 423-439, 473-492, 521-522.
Comment 3. The names of the sections cannot be only two letters (sections 2.3.2, 2.3.3, 2.3.5).
Response to Comment 3: We thank the reviewer for highlighting this formatting issue. Following the reviewer’s suggestion, we have revised the section titles to provide more descriptive names rather than using abbreviations. Specifically, we modified the section titles as follows:
- "PV Panel" → "Photovoltaic (PV) Panel"
- "WT" → "Wind Turbine (WT)"
- "BG" → "Biogas Generator (BG)"
- "BES" → "Battery Energy Storage (BES)"
These changes enhance clarity and readability, ensuring each section conveys its content.
Please look at the lines 497, 520, 548, 616.
Comment 4. In the conclusion section it is worth emphasizing directions for further research.
Response to Comment 4: We thank the reviewer for this valuable recommendation. We fully agree and have expanded the conclusion section to explicitly outline future research directions and potential improvements clearly:
Advanced Energy Storage Technologies: Future studies could investigate advanced storage solutions, such as lithium-ion batteries, redox flow batteries, or supercapacitors, to enhance reliability, economic efficiency, and operational flexibility compared to traditional lead-acid battery storage.
Demand-Side Management Strategies: An in-depth exploration of DSM approaches, including energy efficiency measures, load shifting, and smart demand response strategies, could significantly align energy demand with renewable energy generation, further optimizing operational efficiency and reducing costs.
Diversification with Complementary Renewable Sources: Additional studies could consider integrating complementary renewable energy resources, such as small-scale wind turbines or micro-hydropower systems, depending on local resource availability, to diversify energy supply and minimize grid dependency.
Real-Time Energy Management Systems: Investigating advanced control systems, including artificial intelligence and machine learning-based forecasting tools, could facilitate more precise management of system components, optimizing generator dispatch schedules and improving overall energy efficiency.
Economic Sensitivity and Uncertainty Analysis: A comprehensive sensitivity analysis of input data uncertainty, including biomass cost variability, fluctuation in renewable resource availability, and fuel price changes, would provide valuable insights into hybrid system deployment's robustness and financial risks.
Pumped Hydro Storage: Given the mountainous geography of Aras de los Olmos, future research could explore the feasibility and economic potential of implementing pumped hydro storage systems. These systems could offer significant advantages by addressing renewable intermittency, providing seasonal storage capacity, and enhancing long-term reliability and sustainability.
Life Cycle and Sustainability Assessment: A full life cycle assessment would offer deeper insights into environmental sustainability, encompassing material sourcing, recycling, ecological impacts, and long-term system performance.
These additions will help clarify future research pathways, accounting for uncertainties and geographical suitability and enhancing the overall comprehensiveness of hybrid energy solutions.
Please look at the lines 1290-1297 and 1307-1309.
Comment 5. In the English language, some sentences are too long and it is worth splitting them into several shorter sentences. This will improve the readability of the document.
Response to Comment 5: We appreciate the reviewer’s suggestion and agree that improving sentence structure can significantly enhance readability. Following this recommendation, we have carefully revised the manuscript to identify and split excessively long sentences into shorter, clearer sentences. Specifically, we have addressed readability issues primarily in the Abstract, Introduction, Results, Discussion, and Conclusion sections, aiming to improve clarity and coherence.
These adjustments ensure better readability, facilitating a clearer understanding of the paper’s contributions and findings. All revised sentences have been highlighted in the manuscript for easier identification during review.
Please look at the lines 22-29, 32-37, 64-68, 80-90, 189-194, 414-417, 961-966, 1187-1192, 1250-1255, 1300-1306.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis study explores the application of a Hybrid Energy System (HES) in enhancing the power supply reliability of the rural area of Aras de los Olmos, Spain. The HOMER software is used for the techno-economic optimization analysis. My comments are as follows:
The data sources and processing methods regarding the energy load, meteorological data, and biomass resources in the article need to be further elaborated in detail. It is recommended to add detailed descriptions of data acquisition, preprocessing, and comparative analysis to improve the credibility of the data.
It is advisable to supplement the specific assumptions, constraints, and key parameters (such as capacity factor, failure rate, etc.) of the HOMER modeling to enhance the reproducibility of the study.
It is recommended to conduct a sensitivity analysis to explore how the changes in key economic parameters affect the research conclusions.
The article does not adequately discuss the current energy policies in Spain and their impacts on the deployment of hybrid energy systems.
The article mentions the comparison of emissions of carbon dioxide, nitrogen oxides, and sulfur oxides, but lacks a life cycle emission assessment of biomass utilization. It is suggested to add a Life Cycle Assessment (LCA) or refer to relevant literature to provide a more comprehensive environmental impact analysis.
It is recommended to optimize the design of the charts to improve the intuitiveness of data visualization, and add explanations of the key charts in the main text to enhance the readability of the paper.
It is recommended to supplement the following literature (not mine) 10.1109/TCSI.2024.3523339
10.1109/TII.2024.3495785
Comments on the Quality of English LanguageThis study explores the application of a Hybrid Energy System (HES) in enhancing the power supply reliability of the rural area of Aras de los Olmos, Spain. The HOMER software is used for the techno-economic optimization analysis. My comments are as follows:
The data sources and processing methods regarding the energy load, meteorological data, and biomass resources in the article need to be further elaborated in detail. It is recommended to add detailed descriptions of data acquisition, preprocessing, and comparative analysis to improve the credibility of the data.
It is advisable to supplement the specific assumptions, constraints, and key parameters (such as capacity factor, failure rate, etc.) of the HOMER modeling to enhance the reproducibility of the study.
It is recommended to conduct a sensitivity analysis to explore how the changes in key economic parameters affect the research conclusions.
The article does not adequately discuss the current energy policies in Spain and their impacts on the deployment of hybrid energy systems.
The article mentions the comparison of emissions of carbon dioxide, nitrogen oxides, and sulfur oxides, but lacks a life cycle emission assessment of biomass utilization. It is suggested to add a Life Cycle Assessment (LCA) or refer to relevant literature to provide a more comprehensive environmental impact analysis.
It is recommended to optimize the design of the charts to improve the intuitiveness of data visualization, and add explanations of the key charts in the main text to enhance the readability of the paper.
It is recommended to supplement the following literature (not mine) 10.1109/TCSI.2024.3523339
10.1109/TII.2024.3495785
Author Response
Comment 1: The data sources and processing methods regarding the energy load, meteorological data, and biomass resources in the article need to be further elaborated in detail. It is recommended to add detailed descriptions of data acquisition, preprocessing, and comparative analysis to improve the credibility of the data.
Answer to Comment 1: We sincerely appreciate the reviewer's valuable suggestion. We have revised the manuscript by elaborating on the data sources and processing methods used for the energy load profiles, meteorological conditions, and biomass resource estimations. Specifically, the following details have been added clearly to the Materials and Methods section of the revised manuscript:
(1) Load Data Acquisition and Processing: The community's hourly load data were obtained from local electricity distribution meters installed at major distribution points within Aras de los Olmos. These datasets were collected continuously for a year, providing accurate hourly measurements of aggregated residential, commercial, and public infrastructure electricity demand. Raw data were quality-checked for missing or abnormal values, then averaged and aggregated to produce representative daily and monthly load profiles used in HOMER modeling.
(2) Meteorological Data Sources and Preprocessing: Hourly solar irradiance (Global Horizontal Irradiance, GHI) and wind speed data were sourced directly from the NASA POWER database, an established and reliable source of global meteorological data. Raw meteorological data were reviewed carefully for completeness and consistency, and standard preprocessing procedures—such as interpolating missing hourly data points—were applied when necessary. This ensured accurate and reliable renewable energy modeling inputs.
(3) Biomass Resource Estimation: Biomass availability was estimated based on detailed agricultural residue production data specific to the local area, thoroughly documented in a previous local agricultural biomass assessment (reference [20]). Annual agricultural productivity reports and standardized residue-generation ratios (mass of residue per unit of crop yield or livestock number) were used to quantify monthly biomass availability. These estimates were then cross-validated against local agricultural and livestock production reports, accurately representing seasonal variations and practical resource availability.
These detailed clarifications on data acquisition, preprocessing, and validation methods significantly enhance our study's transparency, credibility, and replicability.
Please look at lines 331-353.
Comment 2: It is advisable to supplement the specific assumptions, constraints, and key parameters (such as capacity factor, failure rate, etc.) of the HOMER modeling to enhance the reproducibility of the study.
Answer to Comment 2: We appreciate the reviewer’s valuable comment and fully agree on the importance of explicitly clarifying assumptions, constraints, and key parameters used in the HOMER modeling to ensure the reproducibility and transparency of our results.
To address your concern, we have expanded the Materials and Methods section to include clear explanations and specific details of the modeling assumptions and constraints applied in HOMER, as well as key input parameters such as:
Technical assumptions: including system component efficiencies, operational lifetimes, and reliability metrics such as failure rates or downtime assumptions.
Economic parameters: clearly stated discount rate, inflation rate, and detailed cost assumptions (capital, replacement, O&M) for each system component.
Operational constraints: including constraints on renewable penetration, grid sales, battery state of charge (SOC) limits, and biomass availability.
Performance metrics: clearly defined parameters such as capacity factors, minimum renewable fraction, and reliability requirements (allowed shortage or unmet load).
We explicitly added these clarifications in a concise subsection within the revised manuscript, significantly enhancing reproducibility and methodological rigor.
Please look at lines 768-782.
Comment 3: It is recommended to conduct a sensitivity analysis to explore how the changes in key economic parameters affect the research conclusions.
Answer to Comment 3: We sincerely thank the reviewer for highlighting this valuable recommendation. We fully acknowledge the importance of sensitivity analysis and agree that exploring the impacts of variations in key economic parameters—such as discount rates, capital costs, and biomass feedstock prices—could significantly enhance our study's conclusions' robustness and practical feasibility.
Although our current study did not explicitly include such sensitivity analyses, we have highlighted this as an important limitation of our current work. Additionally, we have expressly recommended by the revised manuscript that future research incorporate detailed sensitivity analyses or uncertainty modeling methods (e.g., Monte Carlo simulations) to rigorously evaluate how uncertainties and variations in key economic parameters affect system performance and economic viability.
We believe explicitly recognizing this limitation and providing a clear recommendation for future work adequately addresses the review and strengthens the transparency and applicability of our findings.
Please look at lines 1243-1249.
Comment 4: The article does not adequately discuss the current energy policies in Spain and their impacts on the deployment of hybrid energy systems.
Answer to Comment 4: We sincerely thank the reviewer for this insightful comment. Indeed, the role of current energy policies in Spain significantly influences the deployment of renewable and hybrid energy systems, and their inclusion will enhance the context and relevance of our study.
In response, we have expanded the Introduction section of the revised manuscript to explicitly discuss relevant aspects of current Spanish energy policy and their potential implications for deploying hybrid renewable energy systems. Specifically, we have included a concise overview of:
The Integrated National Energy and Climate Plan (PNIEC 2021–2030) aims to increase renewable energy generation and reduce emissions in Spain significantly.
Relevant regulatory frameworks and incentives support decentralized renewable energy systems, including self-consumption regulations (Real Decreto 244/2019), feed-in tariffs, and subsidy schemes to promote local energy autonomy and community-based renewable energy projects.
Implications of these policies on the economic viability, regulatory feasibility, and practical implementation of hybrid systems, particularly those combining photovoltaic (PV), biomass, and storage solutions in rural and semi-remote areas.
These additions strengthen the manuscript by clearly situating our research within Spain's broader policy landscape, providing readers with essential context regarding how current national energy policies support or influence the deployment of the hybrid energy solutions proposed in this study.
Please look at lines 218-228.
Comment 5: The article mentions the comparison of emissions of carbon dioxide, nitrogen oxides, and sulfur oxides, but lacks a life cycle emission assessment of biomass utilization. It is suggested to add a Life Cycle Assessment (LCA) or refer to relevant literature to provide a more comprehensive environmental impact analysis.
Answer to Comment 5: We sincerely appreciate the reviewer's insightful comment regarding the comprehensive environmental assessment of biomass utilization through Life Cycle Assessment (LCA). We fully acknowledge that evaluating emissions solely based on direct combustion products (COâ‚‚, NOâ‚“, SOâ‚“) provides only a partial view of the environmental impact.
While performing a full Life Cycle Assessment is beyond this specific study's defined scope and limitations, we agree with the reviewer's suggestion about the importance and relevance of LCA in thoroughly evaluating biomass-based hybrid systems. Thus, we have addressed this point in the revised manuscript by explicitly highlighting this limitation and adding relevant references to existing literature that provide detailed life cycle emissions assessments for biomass-based energy generation.
Specifically, we have referenced credible studies in the revised manuscript that explore comprehensive LCA analyses of biomass utilization, covering emissions from feedstock production, transportation, anaerobic digestion, biogas combustion, and digestate management. These references provide readers with deeper insights into the broader environmental implications associated with biomass-based systems, enhancing the robustness and completeness of our ecological impact discussion.
Please look at lines 1175-1183.
Again, we thank the reviewer for raising this crucial point, as it significantly improves the comprehensiveness and transparency of our environmental assessment.
Comment 6: It is recommended to optimize the design of the charts to improve the intuitiveness of data visualization, and add explanations of the key charts in the main text to enhance the readability of the paper.
Answer to Comment 6: We sincerely appreciate the reviewer’s valuable suggestion regarding the intuitiveness and readability of data visualizations in our manuscript. Due to the current stage of manuscript revision and certain practical limitations, significant redesign or modification of existing charts is not feasible. However, we fully acknowledge the importance of clear visual representation and have attempted to enhance readability by providing clearer and more informative textual explanations in the revised manuscript.
Specifically, brief but informative interpretations of key figures have been integrated directly into the main text, guiding readers through the main analytical insights and implications.
We recognize that there remains scope for further improvements in visualization quality and clarity, and we explicitly suggest optimizing chart designs as a critical consideration in future research or extended studies based on this work.
We appreciate the reviewer’s helpful comment, which will improve future dissemination of our findings.
Comment 7: It is recommended to supplement the following literature (not mine) 10.1109/TCSI.2024.3523339
10.1109/TII.2024.3495785
Answer to Comment 7: We thank the reviewer for providing these valuable references, which are indeed relevant to our study. As suggested, we have reviewed and cited the recommended literature within the revised manuscript to strengthen the theoretical context further and support key methodological aspects of our study.
Specifically, the following references have been integrated into the manuscript:
- Reference 1: DOI: 10.1109/TCSI.2024.3523339
- Reference 2: DOI: 10.1109/TII.2024.3495785
These references were cited to enhance the discussion on hybrid renewable energy system design, optimization techniques, and control strategies, providing readers with deeper insights into current trends and state-of-the-art research in this field.
We appreciate the reviewer's valuable suggestions, which have significantly enriched our manuscript's theoretical background and methodological rigor.
Please look at lines 210-217.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsSee the attached report
Comments for author File: Comments.pdf
See the review report
Author Response
Comment 1. The authors should be cautious when framing the benefits of a biogas plant as renewable with potential to reduce GHG: Note that biogas is associated with methane emission which is more detrimental to ozone that C02. Therefore, this benefit should be carefully worded in the revision.
Response to Comment 1: We sincerely thank the reviewer for this valuable point. We fully agree and acknowledge that biogas production, although renewable and potentially beneficial for reducing fossil-fuel dependency, is associated with methane emissions. Methane is a potent greenhouse gas with a significantly higher global warming potential than COâ‚‚. Therefore, we have revised the manuscript to reflect this nuanced understanding.
Specifically, we clarified in the manuscript that the benefits of biogas depend strongly on proper management and system design. We explicitly mentioned that the environmental advantages of biogas depend on effective control of methane emissions, ensuring minimal leakage and efficient combustion. We have carefully rephrased related sentences, emphasizing that biogas only contributes to GHG emission reductions when methane leakage is appropriately managed and mitigated.
This revision provides a balanced perspective, accurately conveying both the potential benefits and the critical importance of methane management in biogas systems.
Please look at the lines 94-98, 1125-1127, 1202-1204, 1287-1289.
Comment 2. The authors have unnecessarily written a lot about HOMER, which does not add value to the manuscript. All writings from lines 116-167 specific to HOMER is irrelevant and must be deleted. Instead, the literature review should focus on optimization studies related to the study under consideration.
Response to Comment 2: We appreciate the reviewer's valuable feedback. Following your recommendation, we have significantly revised the manuscript. Specifically, we removed the extensive HOMER-related content (lines 116–167) from the manuscript, as we agree it was overly detailed and did not directly add value to the central objective of our study.
In its place, we have introduced a focused literature review emphasizing optimization studies relevant to hybrid renewable energy systems in rural and semi-remote areas, especially those integrating biogas generation, PV systems, and energy storage. This revision clearly situates our research within the existing body of knowledge, highlighting the contributions of similar optimization approaches and identifying gaps addressed by our study.
Please look at the lines 135-187.
Comment 3. The novelty and rationale of this study is not clearly articulated. It is not enough for the authors to just carry out a basic HOMER pro study; a work worth publishing in this journal must go beyond this. What is new in this work? How does this work advance existing research in hybrid energy systems?
Response to Comment 3: We sincerely appreciate the reviewer's valuable and constructive comment. We fully acknowledge the importance of clearly articulating our study's novelty, contributions, and rationale beyond simply performing a fundamental HOMER Pro analysis.
In response to this comment, we have thoroughly revised the Introduction section, replacing a previously general paragraph with a newly formulated, comprehensive statement explicitly highlighting this work's novelty, rationale, and specific contributions.
The revised paragraph addresses the following novel aspects and research advancements:
Context-specific optimization: Our study explicitly targets semi-remote rural communities experiencing persistent power outages despite grid connectivity—an essential but often overlooked scenario. Although hybrid renewable energy systems have been widely studied, very few works specifically examine locally sourced livestock waste as a primary dispatchable fuel alongside photovoltaic (PV) systems to address reliability challenges practically.
Integrated multi-objective approach: We explicitly integrate economic costs, environmental impacts, and system reliability into a unified optimization framework. Unlike previous research addressing these dimensions separately, our study evaluates trade-offs, providing decision-makers with balanced, actionable insights into optimal hybrid energy configurations.
Critical evaluation of biomass sustainability: Our research explicitly highlights the importance of properly managing methane emissions from biogas systems. We emphasize that biogas-based systems only offer genuine greenhouse gas emission reductions when effective methane leakage control and efficient combustion management practices are implemented. This critical issue, often overlooked in the literature, represents a notable contribution and provides a realistic environmental sustainability perspective.
Structured, replicable methodology: Our proposed optimization methodology is designed to be replicable globally in other semi-remote or rural settings. We clearly outline the systematic research process, enabling policymakers and rural energy planners worldwide to apply these methods effectively for sustainable regional development.
By incorporating these specific points, the revised introduction emphasizes our study's novelty, highlighting how this research advances existing knowledge and offers practical, actionable insights beyond standard HOMER analyses. We believe these revisions significantly strengthen the manuscript's contribution and clarify its value to the academic community.
Please look at the lines 229-255.
Comment 4. Some of the figures and descriptions under Materials and Methods are not relevant. What is the evidential value of Figures 2,3 and 4? If necessary, they should be placed in the appendices, otherwise they should be deleted.
Response to Comment 4: We appreciate the reviewer’s valuable observation regarding Figures 2, 3, and 4. Upon reassessment, we agree that these figures do not directly enhance the manuscript's core arguments or evidential value. Instead, their presence may distract readers from the main narrative and key findings.
To address this issue clearly, we have made the following revisions:
Figure 2 (screenshot of HOMER interface): This figure has been removed from the manuscript since it only illustrated a general software interface without a specific analytical value.
Figure 3 and Figure 4 (screenshots and generic interface diagrams): These figures have also been removed due to their limited evidential and analytical value in supporting our study's specific findings and conclusions.
The text referring to these figures has likewise been removed or appropriately revised. These modifications significantly streamline the manuscript, sharpen the focus of the Materials and Methods section, and ensure each figure contributes explicitly to the analysis or discussion of our study’s outcomes.
We believe these changes effectively address the reviewer’s concerns, enhancing the clarity and relevance of the manuscript.
Please look at the lines 355-356, 364-365, 368, 380-381, 386-390.
Comment 5. Equations (1) and (2), describing wind speed models are not referenced. The authors must cite the sources for these equations.
Response to Comment 5: We thank the reviewer for highlighting this oversight. Indeed, equations presented in the manuscript (specifically Equations 1 and 2 describing the wind speed modeling) were not properly cited. We have clearly added relevant references for these equations to address this issue in the revised manuscript.
Specifically, the equations describing the wind speed models are standard approaches commonly employed in renewable energy studies and are widely referenced in HOMER and renewable energy optimization literature. We have now explicitly cited authoritative sources from the literature (e.g., HOMER official documentation, established references such as [NREL, 2005], and related peer-reviewed studies) to ensure proper attribution and facilitate readers’ access to further details.
These citations have been added directly below the equations in the revised manuscript to establish the evidential basis and enhance our methods' scientific rigor and traceability.
Please look at line 402.
Comment 6. The case study description is unclear: Is it a residential neighborhood or a single entity/residence? On line 306-308, the authors give an average daily load demand f 3516.1kWh/day with an average daily and monthly power given in Figure 5 and Figure 6. The case study should be well and clearly described, including the sources of the load profile.
Response to Comment 6: We appreciate the reviewer’s valuable comment and acknowledge the need for a clearer case study description. To address your concern, we have revised the case study description (in Section 2: Materials and Methods), clearly specifying the scale, composition, and context of the studied load profile.
Specifically, the following changes have been made:
Clearly stated that the case study represents a rural residential community (the village of Aras de los Olmos) rather than a single entity or individual household. We explicitly clarified that the provided average daily energy demand of 3,516.1 kWh/day corresponds to the aggregated electricity consumption of the entire residential community (including residential buildings, small local businesses, public facilities, and communal infrastructure).
Added clear and concise textual explanations accompanying Figure 5 and Figure 6, clarifying that these figures illustrate typical hourly, daily, and monthly variations in energy consumption for the whole community, thus representing realistic and practical load profiles.
Clearly state the source of the load profile data (e.g., direct measurements from local utility meters or community-wide data provided by local energy authorities).
These revisions significantly enhance the clarity of the case study description, making the scope and applicability of our findings more transparent.
Please look at the lines 440-450.
Comment 7. What is the evidential value of Figure 7?
Response to Comment 7: We thank the reviewer for pointing this out. Figure 7 provides essential evidential value by clearly illustrating the hourly distribution and seasonal variability of actual measured load consumption in the studied community through a heat map visualization. Specifically, the figure provides:
Visual evidence of real-world consumption patterns: It demonstrates daily and seasonal load variability, highlighting peak load periods, seasonal fluctuations, and periods of low demand, which directly inform our optimization scenarios and renewable energy system sizing.
Justification for renewable energy and storage system design: By identifying when peak loads occur and their frequency throughout the year, Figure 7 supports the necessity and sizing of energy storage (battery or biomass generation) and renewable capacity (solar PV) to effectively manage variability and reduce outages.
Enhanced reader understanding: The heat map format provides intuitive insight into energy-use patterns, enabling policymakers and stakeholders to easily interpret consumption trends and the rationale behind our recommended hybrid configurations.
Thus, Figure 7 directly supports our system optimization choices, demonstrates data-driven analysis, and provides clear evidence underpinning the practical relevance and accuracy of our study’s findings.
Please look at the lines 467-469.
Comment 8. In Figure 8, the authors give the monthly biomass flow of their case study location: How is this flow estimated? Where does it coming from? This should be clearly explained in the case study.
Response to Comment 8: We appreciate the reviewer’s valuable observation regarding biomass sources. Indeed, the monthly biomass flow represents the estimated availability of biomass derived from local agricultural residues within the community of Aras de los Olmos. This estimation is based on actual local agricultural production data, thoroughly documented and validated in previous research conducted specifically for this region, as described in reference [20].
To clarify this point explicitly in the manuscript, we have now added a concise explanation in the case study description section (Materials and Methods) specifying clearly:
The source of biomass: The biomass used is obtained from locally produced agricultural residues, as detailed and validated in reference [20].
The estimation method: The biomass flow was calculated using local agricultural production statistics and residue generation factors provided in the referenced study ([20]). These calculations represent realistic monthly biomass availability, accounting for seasonal agricultural patterns and harvest schedules in Aras de los Olmos.
This revision enhances the transparency, clarity, and evidential value of biomass estimation, ensuring readers fully understand its basis, relevance, and direct relationship to our research outcomes.
Please look at the lines 473-492.
Comment 9. The equations for solar PV and wind generation are not sufficiently referenced (not cited at all):
- A wind power model is well characterized in: Sichilalu, S., Wamalwa, F. & Akinlabi, E.T., 2019. Optimal control of wind-hydrokinetic pumpback hydropower plant constrained with ecological water flows. Renewable Energy, 138, pp.54-69.
- The solar PV model is characterized in: Wamalwa, F. & Ishimwe, A., 2024. Optimal energy management in a grid-tied solar PV-battery microgrid for a public building under demand response. Energy Reports, 12, pp.3718-3731.
Response to Comments 9, 10, and 11: We sincerely thank the reviewer for highlighting these points and providing specific references for the wind and solar PV generation models. We agree entirely with these comments. Accordingly, we have now explicitly cited the provided references in the revised manuscript to clearly support and validate the presented equations:
Wind Power Generation Model: We have cited the suggested reference:
Sichilalu, S., Wamalwa, F. & Akinlabi, E.T. (2019). Optimal control of wind-hydrokinetic pump back hydropower plant constrained with ecological water flows. Renewable Energy, 138, 54–69.
Solar PV Generation Model: Similarly, we have cited the suggested reference:
Wamalwa, F. & Ishimwe, A. (2024). Optimal energy management in a grid-tied solar PV-battery microgrid for a public building under demand response. Energy Reports, 12, 3718–3731.
These references have been explicitly integrated into the manuscript immediately following the corresponding equations, ensuring complete transparency and rigorous documentation of our modeling methods.
Please look at the lines 501, 524.
Comment 12. What is the value of Figure 9? This should be removed.
Response to Comment 12: We appreciate the reviewer’s valuable feedback. Upon careful reconsideration, we agree with the reviewer’s viewpoint regarding Figure 9. Indeed, this figure does not provide additional evidential or analytical value to the manuscript and may instead distract from the main arguments and results presented.
Accordingly, we have removed Figure 9 entirely from the manuscript and adjusted the corresponding text accordingly. This revision further enhances manuscript conciseness and clarity in line with previous comments.
Thank you for bringing this to our attention.
Please look at the lines 541, 545-548.
Comment 13. The authors should also provide the literature sources and citations for the written information about biomass plants and conversion process, given in 2.3.3. Also write the sub-heading in full: not BG.
Response to Comment 13: We sincerely thank the reviewer for highlighting this important issue. We fully agree and have made the following corrections and enhancements in the revised manuscript:
(1) The subsection title previously abbreviated as "BG" has now been fully expanded to "Biogas Generator (BG)" for clarity.
(2) To ensure proper documentation and evidential rigor, we have explicitly added literature sources and citations supporting the information regarding biomass plants and their conversion processes in Section 2.3.3. Specifically, we referenced reputable and peer-reviewed sources detailing biomass conversion technologies, biogas production processes, and plant operational parameters, clearly citing them in the revised text.
These revisions clarify the source of the presented information and significantly strengthen the manuscript’s scientific accuracy and traceability.
Please look at the lines 552-555.
Comment 14. What is the value of Figure 10 and where is it sourced from? Also Figure 11 and 12, what are their relevance? What are their sources?
Response to Comment 14: We thank the reviewer for highlighting this concern. Upon reconsidering Figures 10, 11, and 12, we recognize that these figures do not add significant analytical or evidential value to the main arguments or findings in the manuscript. These figures were initially included to illustrate general configurations and operational principles related to the hybrid energy systems studied based on generic representations commonly provided by HOMER software. Thus, their inclusion does not directly enhance the evidential value of our study.
Considering your valuable feedback, we have removed Figures 10, 11, and 12 from the revised manuscript and correspondingly removed references and descriptions related to these figures in the main text. Instead, concise textual descriptions supported by relevant literature sources have been maintained in the manuscript, ensuring a more streamlined and focused narrative.
These revisions substantially enhance the manuscript's readability, clarity, and overall coherence, directly addressing your concerns regarding the relevance, sources, and evidential contribution of these figures.
Please look at the lines 583-585, 586, 593-594, 598, 600, 606-607.
Comment 15. Refer to the following source on technical modeling of the BES:
- Wamalwa, F. & Ishimwe, A., 2024. Optimal energy management in a grid-tied solar PV-battery microgrid for a public building under demand response. Energy Reports, 12, pp.3718-3731.
Response to Comments 15 and 16: We thank the reviewer for this valuable suggestion. As recommended, we have explicitly cited the suggested reference regarding the technical modeling of the Battery Energy Storage System (BES): Wamalwa, F. & Ishimwe, A. (2024). Optimal energy management in a grid-tied solar PV-battery microgrid for a public building under demand response. Energy Reports, 12, 3718–3731.
We have referenced this source when describing the battery energy storage (BES) modeling and its technical parameters within the revised manuscript. This ensures proper documentation, aligns our methodological approach with established literature, and enhances transparency and scientific rigor.
Please look at the lines 680-681.
Comment 17. Similarly, the literature citations on the economic model are lacking. The sources from where the equations (21) to (26) must be provided, including the sources for the numbers in Table 1.
Response to Comment 17: We sincerely appreciate the reviewer’s valuable and constructive comment, and we fully agree that the manuscript should explicitly reference the sources for the economic equations and parameters used, specifically Equations (21) to (26) and the values in Table 1.
To address this, we have revised the manuscript as follows:
Explicit Citations for Economic Equations: We clearly state that the economic equations (21)–(26) employed in our analysis are taken directly from the HOMER user manual and follow established literature [21,44]. These equations represent widely adopted approaches for economic modeling in hybrid renewable energy system optimization studies.
Clarification of Parameter Sources: We note that the parameters presented in Table 1—covering capital costs, O&M costs, replacement costs, and lifetimes—are derived from the generic examples provided by HOMER. These values are consistent with typical market conditions and current practices, ensuring alignment with recognized standards and data sources outlined in the official HOMER documentation. For further rigor, we have cross-referenced additional references such as relevant peer-reviewed publications and institutional reports (e.g., NREL, IRENA) to confirm the plausibility and consistency of these values.
By incorporating these clarifications, we ensure the traceability, scientific rigor, and replicability of our economic analyses. All relevant sources are now explicitly cited both in the main text and directly under Table 1.
Please look at the lines 763-767.
Comment 18. Figures 13 and 14 should come right after section 2.1 so that the authors have an idea of the system components that you are describing in 2.2 and 2.3.
Response to Comment 18: We sincerely thank the reviewer for this helpful suggestion. We completely agree that positioning Figures 13 and 14 earlier in the manuscript provides readers with an essential overview and enhances the clarity of subsequent sections.
In the revised manuscript, we have repositioned Figures 13 and 14 immediately after subsection 2.1 (Problem Definition and Research Objectives), within a new subsection (2.2: General Description of the Proposed System). A brief descriptive text has been added to explicitly state the purpose and relevance of these figures. This clearly introduces readers to the overall system configuration before delving into detailed descriptions and mathematical modeling in subsequent subsections.
We believe this revision significantly enhances the manuscript's readability and structural coherence.
Please look at the lines 311-329 and 783-798.
Comment 19. The results presentation is horrible. First, most of the figures, such as Figure 27, 28,29, 30, and 31, are not relevant at all. These should be deleted. Secondly, the results presentation should not just be about explanation of the Figures but a discussion on the implications of these findings.
Response to Comment 19: We sincerely appreciate the reviewer’s clear and constructive comments, and we fully agree that the original presentation of results required significant revision.
First, upon careful reconsideration, we have completely removed Figures 27, 28, 29, 30, and 31 from the revised manuscript. We acknowledge that these figures offered limited analytical and evidential value, and their removal significantly improves the clarity, conciseness, and overall readability of the results section.
Secondly, we agree that results should go beyond simply describing figures. Therefore, we have significantly revised the Results section. Rather than merely describing the figures, the revised results section now emphasizes the implications and significance of the study's key findings. Specifically, we:
Clearly discuss the practical implications of the optimized scenarios (e.g., the impact on operational reliability, economic viability, environmental sustainability, and social benefits).
Explicitly analyze and interpret the significance of the obtained results in the context of rural energy planning.
Highlight how the proposed scenarios improve resilience against frequent outages, reduce emissions effectively, and balance initial investment with long-term cost savings.
These adjustments ensure that our results are presented analytically and comprehensively, enhancing the manuscript’s scientific contribution, clarity, and overall coherence.
We appreciate this valuable feedback and believe these improvements significantly strengthen the manuscript.
Please look at the lines 816-825, 913-949, 1045-1099.
Comment 20. How sensitive are the results to changes in system variables and parameters, such as uncertainties in discount rates (cost of capital) and system component costs? It is important to note that the model performance cannot be captured correctly using single numbers as used in this study.
Response to Comment 20: We sincerely thank the reviewer for highlighting this crucial point. We agree that single-value analyses may not fully capture uncertainties and sensitivity to critical system variables. We have revised the manuscript by explicitly acknowledging and addressing this issue. Specifically:
Sensitivity to discount rate (cost of capital): We explicitly acknowledge that changes in the discount rate significantly affect the Net Present Cost (NPC) and Levelized Cost of Energy (LCOE). Even slight variations in discount rate assumptions can alter the economic attractiveness of hybrid energy systems. Thus, a clear statement about this sensitivity has now been included in the revised discussion, highlighting the necessity of cautious interpretation when generalizing results.
Sensitivity to system component costs: We clarify that component cost fluctuations, such as variations in PV panel prices, biogas generator capital costs, biomass feedstock prices, or battery costs, directly influence economic feasibility and system optimization outcomes. We explicitly mention that future price reductions or increases can substantially alter the comparative advantage between the proposed scenarios and traditional grid reliance.
Recommendation for future work: Given these sensitivities, we explicitly recommend performing detailed sensitivity analyses or uncertainty modeling (e.g., Monte Carlo simulations or probabilistic sensitivity analyses) in future research to provide a robust decision-making framework, accounting comprehensively for parameter uncertainty and variability.
By explicitly adding these clarifications and recommendations to the revised manuscript, we ensure readers understand the sensitivity of the results, acknowledging the limitations of single-value analyses and highlighting directions for future research.
Please look at the lines 1220-1229.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsThe reviewer commends the authors for addressing all the raised concerns and comments within a short time. The manuscript can be accepted for publication in its current form, with minimal language and formatting edits.
Comments on the Quality of English LanguageThe reviewer commends the authors for addressing all the raised concerns and comments within a short time. The manuscript can be accepted for publication in its current form, with minimal language and formatting edits.
