Current, Projected Performance and Costs of Thermal Energy Storage

Round 1

Reviewer 1 Report

The manuscript requires a major revision before considering it for publication. The author should revise the manuscript as per the comments given below.

1. Authors should include some quantitative results in the abstract and the the present abstract is too general.

2. It is difficult for the authors to follow and understand the introduction section. There is a lack of continuity.

3. In this study, the technical depth is totally missing and the author should revise the manuscript in depth.

4. The manuscript is found to be lengthy with less significant and the author should revise the full manuscript in a brief way.

5. The entire manuscript should be revised with respect to language and grammatical mistakes.

Author Response

.Authors should include some quantitative results in the abstract and the the present abstract is too general.

Thank you for the comment. The authors added that information in the abstract. It is difficult for the authors to follow and understand the introduction section. There is a lack of continuity.

Thank you for the comment. The authors try to revise the introduction section in line with the comment and the comment of other reviewers. Some redundance sentences were eliminated.

In this study, the technical depth is totally missing and the author should revise the manuscript in depth.

Thank you for the comment. Based on this comment, the authors understand that the aim of the paper Is not clear. Therefore, the focus of the paper is highlighted in the introduction section as follows:

“In this framework, the presented work presents a first-of-its-kind review specifically on the current, projected performance and costs of thermal energy storage. And this study gives a relevant contribution to this latter. Starting from a previous work developed by the same authors [32], this study allows the reader to draw an overview of the main challenges and future directions of the TES systems in Europe. The paper is structured in four sections, section 2 described the main TES typologies; section 3, the core of the paper, investigated the market penetration of each technology and the project performance and cost. Last but not least, the potential and barriers to TES application, especially in Europe, are reported in section 4 followed by the conclusion paragraph.”

In other words, this review is not related to the technical aspect, but on the performance and cost (current and projected) of TES. The authors provide in section 2 an overview of the main TES to give to the reader the opportunity to recall them and understand the following sections of the manuscript.

The manuscript is found to be lengthy with less significant and the author should revise the full manuscript in a brief way.

Thank you for the comment. The authors try to revise the manuscript to reduce the lengthy of the paper, eliminating some redundance sentences and some figures that represent common information (e.g. Figure 1, 3,6,7). However, the authors reported the main information from those figures and explain them in text. 

 The entire manuscript should be revised with respect to language and grammatical mistakes

Thank you for the comment. The authors revised the manuscript in terms of English language.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have conducted an extensive review of thermal energy storage. The work is very well focused and the conclusions are relevant to achieve a greater use of these technologies that allow to reduce their high costs and increase their performance.

However, some points need to be reviewed.

Page 4 line 136: 550ºC<T>250ºC might be better as:

T>250º; (high) T>500ºC (very high)

Page 4 Table 3: Cost units are not included in the table

page 6 line 226: ..., three types of PCMs "pesos". What does "pesos" mean?

page 10 line 353 calcium hydroxide is not CaCO2 is (Ca(OH)2.

page 11 Table 10 KPI3 and KPI4 should be deleted

page 12 lines 416-418: . The gross annual electricity generation of the CSP plant divided by NCOTES is used to calculate ¿¿¿¿NCOTES ??? This sentence should be revised.

Author Response

Comments and Suggestions for Authors

The authors have conducted an extensive review of thermal energy storage. The work is very well focused and the conclusions are relevant to achieve a greater use of these technologies that allow to reduce their high costs and increase their performance.

However, some points need to be reviewed.

Page 4 line 136: 550ºC<T>250ºC might be better as:

T>250º; (high) T>500ºC (very high)

Thank you for the comment. The authors changed the previous sentence with the one suggested by the reviewer.

Page 4 Table 3: Cost units are not included in the table

Thank you for the comment. The authors solved this problem.

page 6 line 226: ..., three types of PCMs "pesos". What does "pesos" mean?

Thank you for the comment. The authors fixed the typing error (“pesos” was a typing error).

page 10 line 353 calcium hydroxide is not CaCO2 is (Ca(OH)2.

Thank you for the comment. The authors solved this problem.

page 11 Table 10 KPI3 and KPI4 should be deleted

Thank you for the comment. The authors solved this problem.

page 12 lines 416-418: . The gross annual electricity generation of the CSP plant divided by NCOTES is used to calculate ¿¿¿¿NCOTES ??? This sentence should be revised.

Thank you for the comment. The authors revised the sentence in line whit the suggestion. In this way, the meaning of the sentence is clear. For your convenience, we report the modified sentence in the text:

“Therefore, to take into account the costs and benefits of electricity generation from CSP plants, they suggest adopting “a normalized TES cost”- NCOTES, which normalizes the cost of storage systems with regards to their annual electricity generation capacity. [44].”

 

Author Response File: Author Response.docx

Reviewer 3 Report

Paper entitled: Current, Projected Performance and Costs on thermal energy storage

 

The authors have reviewed the various types of thermal energy storage systems, especially latent heat thermal storage ones, from performance, current, and cost point views. They have reviewed more than 80 papers published in recent years.

General speaking, the manuscript has covered a large portion of the papers in the related literatures. However, it could have a better organization to present them. The following comments can help in reaching this purpose. So, please consider them and attempt to remove all of them. After handling the comments, publication of the manuscript in the reference journal can be feasible.  

 

1.      Each abbreviation in the text should be introduced completely at the first appearance. For instance, the authors could define "thermal energy storage" as TES before showing it in the abbreviation form.

2.      Please refer to the comprehensive view of the technology provided at the end of the abstract section.

3.      Around the nomenclature list, it had better to organize the list based on alphabetical order. Please consider it.

4.      About table 1, please add the obtained results from each reference to the mentioned table. Just speaking about the applied technology cannot be acceptable.

5.      The applied number for the caption of the figures is not correct. Please modify them since the first figure has been started from 2.

6.      Visual quality of the figures is not proper. It seems these are a cropped view from the other references until provided by the authors. So, please provide them stand- lonely.

7.      If possible/ as a suggestion, please utilize different types of the charts instead of some of the applied tables to better distinguish the results obtained in the reviewed references.

8.      More referring to the "Numerical" and "Experimental" words in the text of the manuscript can be useful. Please consider it.

9.      The following studies investigated the latent heat thermal energy storage and can be considered and explained: (a) Dynamic melting in an open enclosure supported by a partial layer of metal foam: A fast thermal charging approach; (b) Melting process of the nano-enhanced phase change material (NePCM) in an optimized design of shell and tube thermal energy storage (TES): Taguchi optimization approach.

10.  Using sentences dependent on the other papers at the conclusion section is not suitable. Please omit them and try to speak about those gained in the present study.

11.  At the final part of the conclusion section, the authors have referred to the cost and performance limitations for LH-TES systems. By reviewing more than 80 references, it is suitable to provide some suggestions to remove the mentioned limitations. So, append them at the end of the conclusion section.    

Author Response

The authors have reviewed the various types of thermal energy storage systems, especially latent heat thermal storage ones, from performance, current, and cost point views. They have reviewed more than 80 papers published in recent years.

General speaking, the manuscript has covered a large portion of the papers in the related literatures. However, it could have a better organization to present them. The following comments can help in reaching this purpose. So, please consider them and attempt to remove all of them. After handling the comments, publication of the manuscript in the reference journal can be feasible.  

1. Each abbreviation in the text should be introduced completely at the first appearance. For instance, the authors could define "thermal energy storage" as TES before showing it in the abbreviation form.

Thank you for the comment. The authors solved this problem.

2. Please refer to the comprehensive view of the technology provided at the end of the abstract section.

Thank you for the comment. The authors accept this suggestion.

3. Around the nomenclature list, it had better to organize the list based on alphabetical order. Please consider it.

Thank you for the comment. The authors organized the nomenclature list in alphabetical order.

4. About table 1, please add the obtained results from each reference to the mentioned table. Just speaking about the applied technology cannot be acceptable.

Thank you for the comment. First, Table 1 was moved at the end of the literature investigation. In fact, all the refences cited in Table 1 are described in the text. Moreover, it was added a new column “potentiality” of each technology based on the reference’s experiences. 

5. The applied number for the caption of the figures is not correct. Please modify them since the first figure has been started from 2.

Thank you for the comment. The authors solved this problem.

6. Visual quality of the figures is not proper. It seems these are a cropped view from the other references until provided by the authors. So, please provide them stand- lonely.

Thank you for the comment. The authors increase the quality of the imagines as you can see especially in Figures 1 and 2.

7. If possible/ as a suggestion, please utilize different types of the charts instead of some of the applied tables to better distinguish the results obtained in the reviewed references.

Thank you for the comment. The authors transformed some tables into schemes/charts (see new Figures 1). Moreover, some figures (Fig. 1,3,6,7) were eliminated because they collect common information and make the paper lengthier. The authors reported the main information from those figures and explain them in text. 

8. More referring to the "Numerical" and "Experimental" words in the text of the manuscript can be useful. Please consider it.

Thank you for the comment. The authors try to consider this suggestion in the text as “track changes” function reported.

9. The following studies investigated the latent heat thermal energy storage and can be considered and explained: (a) Dynamic melting in an open enclosure supported by a partial layer of metal foam: A fast thermal charging approach; (b) Melting process of the nano-enhanced phase change material (NePCM) in an optimized design of shell and tube thermal energy storage (TES): Taguchi optimization approach.

Thank you for the comment. The authors added those two papers in the introduction section.

10. Using sentences dependent on the other papers at the conclusion section is not suitable. Please omit them and try to speak about those gained in the present study.

Thank you for the comment. The authors eliminated the citation from the conclusion section. Moreover, all the citation are well described in the introduction and methodology sections.

11. At the final part of the conclusion section, the authors have referred to the cost and performance limitations for LH-TES systems. By reviewing more than 80 references, it is suitable to provide some suggestions to remove the mentioned limitations. So, append them at the end of the conclusion section.    

Thank you for the comment. The authors added some suggestions to remove the mentioned limitations in the conclusion section as follow:

“Based on this review, some gaps could be fulfilled in improving the heat exchange be-tween heat transfer fluid and storage medium through the adoption of appropriate conductivity systems. Also increasing the thermal properties of the storage medium, specifically its thermal diffusivity, through the adoption of nanotechnologies (Nano-Enhanced-PCM) could be a relevant path. In this way, it is possible to better exploit the storage medium by reducing the extension of the heat exchange surface and, therefore, increasing the compactness and reducing the cost of LH-TES systems..”

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have addressed all the comments. It can be accepted