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by
  • César Berna-Escriche,
  • Carlos Vargas-Salgado * and
  • Alberto Escrivá-Castells
  • et al.

Reviewer 1: Oleg V. Zhdaneev Reviewer 2: Anonymous

Round 1

Reviewer 1 Report

This paper describes the current progress of hydrogen production from surplus electricity generated by an autonomous renewable system in Spain. Several optimized scenarios using demand management techniques have also been explored. 

1.    It is recommended that the authors thoroughly check grammar and spelling errors to improve the overall clarity of the paper. For example, “bottles under high pressures” should be renamed to "reservoirs", "vessels" or "containers", etc. Typos should also be removed ("heavy heavy-duty vehicles", "study.. ", etc.)

2.    Section 3. The Renewable Generation should be supplemented with the technological characteristics of the planned solar panels and wind turbines.

3.    Authors need to discuss more about hydrogen productıon technology vıa water electrolysis. More detaıled economıc analysis need to be ıncluded.

4.    Authors have to provide the latest cost of the mentioned technologies for 2022.

5.    Low or high pressure vessels can be used to store hydrogen. If there are sufficient areas, it is advisable to store hydrogen in low-pressure vessels. In this case, there is no need for additional costs for compressor equipment, energy for compression and expensive cylinders. We recommend reflecting this information in the calculations and in Figure 10.

6.    Compare your results with others from the literature and discuss them if it is possible. Give more detailed information for the validation procedures.

Author Response

Please find attached the response to reviewer.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript covers an interesting R&D topic and fits the scope of the Journal. Hydrogen production from renewable energies is a prolific research field. Nonetheless, the paper requires extra efforts to improve its quality and presentation. A set of comments are expounded hereafter.

- The manuscript is, in general, well organized. However, there are some mistakes or improvements to introduce regarding the format of the document, as commented below.

The type of paper should be indicated, chosen from the offered by the Journal. For instance, in this case, it probably corresponds to Article.

In line 154, there is an unnecessary terminal dot.

Within the text, the terms “Hydrogen”, “H2” and “H2 (subscript)” are found. It is suggested using only one of the forms for a more coherent presentation.

- About the content of the manuscript, as aforementioned, it covers an interesting topic. The comments after a careful revision are the following:

In the subsection 3.4, smart grids are described together with their objectives and main features. The concept of micro-grid should also be mentioned given the fact that they share such objectives and features, being the main difference the scale. Indeed, recent literature dealing with micro-grids that use surplus of energy for hydrogen generation would enhance the contextualization in this sense. Some recent publications are now suggested for consideration by the authors in this regard:

-        Stand-Alone Microgrid with 100% Renewable Energy: A Case Study with Hybrid Solar PV-Battery-Hydrogen. Sustainability 2020, 12, 2047. https://doi.org/10.3390/su12052047

-        Optimal Energy Management in a Standalone Microgrid, with Photovoltaic Generation, Short-Term Storage, and Hydrogen Production. Energies 2020, 13, 1454. https://doi.org/10.3390/en13061454

-        Innovative Multi-Layered Architecture for Heterogeneous Automation and Monitoring Systems: Application Case of a Photovoltaic Smart Microgrid. Sustainability 2021, 13, 2234. https://doi.org/10.3390/su13042234

-        Two-Stage Energy Management Strategies of Sustainable Wind-PV-Hydrogen-Storage Microgrid Based on Receding Horizon Optimization. Energies 2022, 15, 2861. https://doi.org/10.3390/en15082861

 

The authors use the term “mega-batteries”, but there is no a quantitative description of the difference between common battery and mega-battery. This information must be provided for a clearest description.

The captions of figures 3 and 10 are the same, one of them must be modified.

The quality of certain figures should be improved, for example, 7, 11 and 12.

What is the specific version of HOMER that has been used?

How is the degradation of the mega-batteries taken into account?

What is the technology considered for such mega-batteries? Lithium-ion? Lead-acid? Vanadium Redox? This information should be given for a higher degree of description.

Author Response

Reviewer #2:

 

First, we would like to thank you for your valuable comments, and we appreciate the time you spent reviewing our work. We have addressed your comments as follows:

The manuscript covers an interesting R&D topic and fits the scope of the Journal. Hydrogen production from renewable energies is a prolific research field. Nonetheless, the paper requires extra efforts to improve its quality and presentation. A set of comments are expounded hereaft er.

  1. The manuscript is, in general, well organized. However, there are some mistakes or improvements to introduce regarding the format of the document, as commented below. The type of paper should be indicated, chosen from the offered by the Journal. For instance, in this case, it probably corresponds to article. In line 154, there is an unnecessary terminal dot. Within the text, the terms "Hydrogen", "H2" and "H2 (subscript)" are found. It is suggested using only one of the forms for a more coherent presentation.

Response: The option of article has been chosen. The duplicated terminal dot has been eliminated. The term "H2" has been used for coherent presentation in all the manuscripts.

  1. About the content of the manuscript, as aforementioned, it covers an interesting topic. The comments after a careful revision are the following:

 

In the subsection 3.4, smart grids are described together with their objectives and main features. The concept of micro-grid should also be mentioned given the fact that they share such objectives and features, being the main difference the scale. Indeed, recent literature dealing with micro-grids that use surplus of energy for hydrogen generation would enhance the contextualization in this sense. Some recent publications are now suggested for consideration by the authors in this regard:

 

-Stand-Alone Microgrid with 100% Renewable Energy: A Case Study with Hybrid Solar PV-Battery-Hydrogen. Sustainability 2020, 12, 2047. https://doi.org/10.3390/su12052047

-Optimal Energy Management in a Standalone Microgrid, with Photovoltaic Generation, Short-Term Storage, and Hydrogen Production. Energies 2020, 13, 1454. https://doi.org/10.3390/en13061454

-Innovative Multi-Layered Architecture for Heterogeneous Automation and Monitoring Systems: Application Case of a Photovoltaic Smart Microgrid. Sustainability 2021, 13, 2234. https://doi.org/10.3390/su13042234

-Two-Stage Energy Management Strategies of Sustainable Wind-PV-Hydrogen-Storage Microgrid Based on Receding Horizon Optimization. Energies 2022, 15, 2861. https://doi.org/10.3390/en15082861

 

Response: We agree with the reviewer’s suggestion since microgrids offer vast possibilities that should be explored in off-grid systems. Consequently, we have revised the reviewer's proposed documents and rewritten part of the document, mainly section 3.4, which focuses on smart grids and demand management aspects.

 

  1. The authors use the term "mega-batteries", but there is no a quantitative description of the difference between common battery and mega-battery. This information must be provided for a clearest description.

Response: Thank you for your comment; we agree with you. The term mega batteries is used for batteries able to store a large quantity of energy, probably bigger than 1 MWh. Nevertheless, there is no a rule about the amount of energy. Tesla uses the term megapack for its 2.5-3 MWh capacity batteries. To avoid a miss understanding, the term mega has been eliminated.

  1. The captions of figures 3 and 10 are the same, one of them must be modified.

Response: The reviewer is entirely right, it was a mistake, and the caption of figure 10 has been modified.

  1. The quality of certain figures should be improved, for example 7, 11 and 12.

Response: The quality of the figures has been improved; nevertheless, since the figure has enough quality, we think the quality of some figures is reduced when the word uploaded to MDPI platform is converted into PDF.

 

  1. What is the specific version of HOMER that has been used?.

Response: It has been used version 2.68. This information has been added to section 4. Methodology

  1. How is the degradation of the mega-batteries taken into account?

 

Response: For Hydrogen production, this work is based on the Gran Canaria surpluses energy obtained in the paper "Optimization of All-Renewable Generation Mix According to Different Demand Response Scenarios to Cover All the Electricity Demand Forecast by 2040: The Case of the Grand Canary Island" https://doi.org/10.3390/su14031738. Information used from this paper is explained in the current article in sections 3.2 and 3.3. Section 5, presents the analyzed scenarios for estimating Hydrogen production. In this sense, all the information about the battery systems is not directly used for our work, and it is available at https://doi.org/10.3390/su14031738. The editor has asked the author to reduce the similarity percentage to under 20%; for this reason, and because the information is available in another publication, the author has decided not to include it in the present manuscript.

 

  1. What is the technology considered for such mega-batteries? Lithium-ion? Lead-acid? Vanadium Redox? This information should be given for a higher degree of description.

Response: The technology used by the batteries is Lithium-ion; information about the batteries can be found in https://impulsoragdl.com/wp-content/uploads/2020/09/Ficha-Tecnica-Mega-Pack.pdf. Nevertheless, as explained in the previous point, the storage system is not part of the system under study, and information about the excess of energy in a 100% renewable system in Gran Canaria island was taken from https://doi.org/10.3390/su14031738. The study gives information about the battery system. To take advantage of the energy typically wasted in the renewable system,  the excess has the purpose of producing Hydrogen, which is the core of the carried-out work. It is explained in the current article in section 3.2 and 3.3. In point 5, it is explained the analyzed scenarios for estimating Hydrogen production.

Round 2

Reviewer 1 Report

I believe that the manuscript can be accepted for publication.

Reviewer 2 Report

The new version of the manuscript has addressed the reviewers concerns in a proper manner.