Estimation of Energy Storage Requirements in an Independent Power System from an Energy Perspective

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript estimates the energy storage requirements for the most extreme day of electricity consumption in a year in Taiwan and forecasts the annual power generation from renewable sources. The paper, using the power load during the Spring Festival of 2023 as a benchmark and assuming an annual electricity consumption growth rate of 2%, takes into account wind, solar, and coal-fired power generation to calculate the unused power generation. This study holds certain guiding significance for the future adjustment of Taiwan's energy structure.

 

I suggest the paper needs a major revision as there are a few things to be checked and/or corrected

 

1. Why the growth rate is 2% in line 54? Please add some explain.
2. Section 2.1 denotes the necessity to investigate the day with the highest storage demand. Admittedly, holiday load requirements are diminished, but how is the maximum renewable generation determined? To my understanding, the discrepancy in wind generation between winter and spring is negligible, whilst solar power peaks in spring. The selection of the Spring Festival, which occurs in winter, as the period of maximum generation is not agreement with the findings presented in this study.
3. The manuscript employs a total cost objective function, with the ultimate goal of minimizing it. A contradiction arises in that when the total cost is at its minimum, the power generation also decreases to its lowest. In other words, commonly utilized metrics such as the payback period or cost per unit of electricity generated should be considered.
4. The formulas presented in the manuscript should be substantiated with references. Furthermore, the connection between the listed formulas and the ensuing discussion appears tenuous at best.
5. There are formatting errors in the manuscript, including incorrect figure numbering. A meticulous examination of the entire document is warranted.
6. The images in the manuscript are indistinct. Please provide clear illustrations.

 

Comments on the Quality of English Language

The author demonstrates a satisfactory level of proficiency in English. The manuscript is generally well-written and the ideas are communicated effectively. There are minor areas for improvement, but they do not significantly hinder the understanding of the research. I appreciate the effort put into ensuring the language quality of this paper.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript entitled “Estimation of Energy Storage Requirements in an Independent Power System from an Energy Perspective” introduces a method to estimate the energy storage requirement for the day.

1) All figures are in poor resolution, and it is hard to read the figures. All figures must be re-plotted;

2) References should be added into Table 1 and 2.

3) The contribution of this paper is not clear, and it is difficult to tell which method is employed to make the estimation.

4) No literature review section is found in this paper, the authors just introduce some basic energy background of Taiwan Province in China. The authors would like to see the state-of-the-art methods to estimate the energy storage requirement.

 

5) The reviewer highly suggest the authors add a figure to the overall architecture of the energy system investigated in this paper, since there are so many component in this system such as Gas-Fired Generation Units , Energy Storage, it is difficult to finger out the overall picture of the system.

6) In the mathematical model, the authors do not introduce renewable generators, from the reviewer’s point of view, PV and wind turbine are also important.

7）The authors just introduce the constraints of the system, but what the method employed to make the estimation? The reviewer feels very confused.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This article presents a novel and comprehensive approach to estimating the energy storage requirement for the day with the most extreme electricity consumption behavior in a year, without energy curtailment, in an isolated grid that prevents the export of surplus energy. The authors used the installed capacity and actual power generation of renewable energy sources in 2022, the electrical load during a Festival as a baseline, the annual electricity consumption growth rate of 2%, and the minimum gas power output of approximately 6 GW as the main inputs for their analysis. They also provide an open-source code that can provide updated results with new planning data input.

The article has several strengths, such as:

It addresses a relevant and timely problem of optimal integration of renewable energy sources and energy storage systems in an isolated grid, which has implications for energy security, sustainability, and resilience.

It uses a rigorous and transparent methodology that is based on realistic and verifiable data and assumptions and that can be easily replicated and updated by other researchers or practitioners.

It provides clear and concise results and findings, such as the unused power generation, which represents the pumped-storage hydroelectricity and battery energy storage systems requirements for that day under a no-curtailment scenario, and the forecast of the annual power generations of renewable sources based on the government’s annual installation capacity plans.

It offers insightful and practical recommendations for the optimal design and operation of the isolated grid, such as the need to consider the variability and uncertainty of renewable energy sources, the trade-offs between energy storage and curtailment, and the potential benefits of demand response and smart grid technologies.

The article also has some areas for improvement, such as:

It could provide more details and justification for some of the assumptions and parameters used in the analysis, such as the annual electricity consumption growth rate of 2%, the minimum gas power output of approximately 6 GW, and the electrical load during a Festival as a baseline. Also, the authors should give more context on how and when the "Green Energy Go First" policy (Line 47) will be applied in order for the non-Taiwan natives to capture the impact of such policy.

Line 106, the authors should justify or explain this assumption, which will have an impact on the results: “The generation cost is assumed to be proportional to the square of the power output…” The potential impact on the costs of such an assumption should also be discussed.

Figures 2, 3, 5, 6 and 8 should be redesigned to allow for bigger fonts.  They are important but quite difficult to interpret because of the difficulty of reading them.  Please note that the second Figure 5 should be titled Figure 6.

The article should add a few more references for comparable works to improve the context and also the comparison with existing studies. It could compare and contrast the results and findings with other studies or scenarios that have different assumptions or inputs, such as different renewable energy sources mix, different energy storage technologies, different demand patterns, or different grid configurations. Some examples:

·       Sahebkar Farkhani J, Zareein M, Najafi A, Melicio R, Rodrigues EMG. The Power System and Microgrid Protection—A Review. Applied Sciences. 2020; 10(22):8271. https://doi.org/10.3390/app10228271

·       Zahraoui Y, Alhamrouni I, Mekhilef S, Basir Khan MR, Seyedmahmoudian M, Stojcevski A, Horan B. Energy Management System in Microgrids: A Comprehensive Review. Sustainability. 2021; 13(19):10492. https://doi.org/10.3390/su131910492

In the 4.3. Discussion of Simulation Results (Line 260) could further discuss the limitations and challenges of the no-curtailment scenario, such as the technical and economic feasibility, the reliability and efficiency of energy storage systems, and the impacts on the power quality and stability of the isolated grid.

The conclusion focuses on recommendations to Taiwan decision-makers, but the (international) readers would benefit from the author's perspectives on extrapolating the results.  They could briefly explore the implications and generalizability of the results and findings for other isolated grids or regions that have similar or different characteristics, such as size, geography, climate, resources, policies, or regulations.

 

Overall, this article is a valuable contribution to the literature and practice of energy systems planning and operation in isolated grids. It provides a novel and comprehensive approach to estimating the energy storage requirement for the day with the most extreme electricity consumption behavior in a year, without energy curtailment, in an isolated grid that prevents the export of surplus energy. It also provides an open-source code that can provide updated results with new planning data input. The article has several strengths, such as the relevance and timeliness of the problem, the rigor and transparency of the methodology, the clarity and conciseness of the results and findings, and the insightfulness and practicality of the recommendations. The article also has some areas for improvement, such as the details and justification of some of the assumptions and parameters, the comparison and contrast with other studies or scenarios, the discussion of the limitations and challenges of the no-curtailment scenario, and the exploration of the implications and generalizability of the results and findings.

Comments on the Quality of English Language

The language quality is clear and sound. Some very typos that a quick spell-check could resolve are present, but a few items need a second look. For example,

In lines 14 and 16, “power generations,” should be corrected to “power generation”.

Lines 101-103, this sentence should be rewritten “To achieve the goal of the energy storage system discharging energy during peak demand and charging when needed, this study modifies traditional power generation scheduling methods by utilizing Mixed Integer Linear Programming (MILP).”, because the study will not “achieve” the goal of EES discharging… The study is not the system, but rather this study will “simulate,” make mathematical modeling, test, etc. modified (traditional) power generation scheduling method.

 

Line 202, maybe the words “In conclusion” should not be used while we’re still in the middle of the article.  Others could be chosen or insisting on the fact that this is a partial conclusion if need be.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

accept