The Impact of System Integration on System Costs of a Neighborhood Energy and Water System

Round 1

Reviewer 1 Report

I commend all authors who contributed in this paper. 
The manuscript addresses an interesting topic, relevant with the journal's objectives. The experimental designs, the theoretical methods and the execution of the study are adequate. The discussion of the results is clear. 

The paper has a good scientific soundness and deserves to be published after some modifications that are required and listed in the following text.
However, to improve the article further it is advisable to review the language and to correct the following points:
- The use of English is quite good; however, I suggest a fast revision of the manuscript, in order to correct some mistakes of syntax: some of them are reported in the following issues.
- The introduction is characterized by a good description of the state of the art; however, I would cite more references, especially regarding the other modelling studies described in the literature to achieve similar results.
- Keywords should be in alphabetical order.

I recommend this manuscript for publication in "Energies" Journal after completing some minor improvements

Author Response

1.The use of English is quite good; however, I suggest a fast revision of the manuscript, in order to correct some mistakes of syntax: some of them are reported in the following issues.

We have the idea that you wanted to list some issues, but they were not visible in the comments that we had access to. If there is anything specific, we could still adjust it. We have done a revision and removed some syntax errors and other small spelling/lay-out mistakes on the following lines: 46,46, 57, 76, 79, 80, 97, 99, 101, 104, 169, 197, 279, 282, 284, 312, 314, 328, 330, 341, 343, 461, 463, 570, 647, 701, 740, 743, 745, 763, 773, 819, 878, 955, 956, 1010, 1105, 1112, 1114, 1125, 1155, 1171, 1224.

In this case, we have chosen to only state the line numbers and not all changes specifically, as the content or meaning of the text has not changed.

2. The introduction is characterized by a good description of the state of the art; however, I would cite more references, especially regarding the other modelling studies described in the literature to achieve similar results.

For the literature review, our focus has been specifically on the modelling of neighbourhood energy systems, and not on modelling studies for countries, cities or just one house or building. Moreover, we have looked for systems based on 100% renewable energy. This limited the selection of available literature, but we are aware that we have not included all available modelling studies. We have included three extra references to recent modelling studies in line 143-145 on the transformation from existing to energy-neutral neighbourhoods [1], line 154-156 on the function of power-to-hydrogen to maximize renewable self-consumption [2] and line 190-196 on seasonal heat storage [3]. If there are other specific suggestions, we could include them if you inform us about which studies you suggest referring to in the manuscript.

 

1. Walker, S.; Labeodan, T.; Boxem, G.; Maassen, W.; Zeiler, W. An Assessment Methodology of Sustainable Energy Transition Scenarios for Realizing Energy Neutral Neighborhoods. Appl. Energy 2018, 228, 2346–2360, doi:10.1016/j.apenergy.2018.06.149.
2. Petkov, I.; Gabrielli, P.; Spokaite, M. The Impact of Urban District Composition on Storage Technology Reliance: Trade-Offs between Thermal Storage, Batteries, and Power-to-Hydrogen. Energy 2021, 224, 120102, doi:10.1016/j.energy.2021.120102.
3. McKenna, R.; Fehrenbach, D.; Merkel, E. The Role of Seasonal Thermal Energy Storage in Increasing Renewable Heating Shares: A Techno-Economic Analysis for a Typical Residential District. Energy Build. 2019, 187, 38–49, doi:10.1016/j.enbuild.2019.01.044.

 

3. Keywords should be in alphabetical order.

Keywords have been placed in alphabetical order in (line 39-40).

Reviewer 2 Report

This work deals with the analysis of returns in the integration of local energy systems. The integration of different energy production and storage technologies as well as water management are taken into account.  

The paper is well written and interesting, however, we must make a series of comments on it.

First, let me congratulate the group of authors for the clarity in explaining the aims of the present work (lines 174-176).

Figure 1. Perhaps "warm aquifer storage" should return first to the heat pump instead of going directly to the heat exchanger to be recovered (it´s too optimistic).

Line 262. Heat storage is prioritized in the use of electricity with respect to the electrolyzer. Taking into account that this storage may require all the energy at hand, the limit of use of this resource is not clear (temperatures reached in the aquifers?).

  Line 372. Maybe hydrogen imports from southern Europe are more likely to happen in a near future.....

Line 492. "Pit thermal energy storage could have been another option, 492 but the space that is needed to create the system is not easily available in existing neighborhoods." Since the storage well field is an underground structure, free space is usually not a problem. Even could be implemented in the same place as the common PV common park.

Line 495. This highly depends on the aquifer/water composition (not specified) and temperature.

line 734, perhaps that sunny day in February is not an ideal example for this work, is it?. Is that usual in The Netherlands?.

Line 772. This may be a problem with the design of the battery dimension?.

Line 934. Therefore a study case with no PV generation so far in the neighbourhood would have been interesting also.

 

 

    

 

 

 

     

  

Author Response

Thanks for your specific and clear feedback!

Hereby we respond to each of your comments. 

• Figure 1. Perhaps "warm aquifer storage" should return first to the heat pump instead of going directly to the heat exchanger to be recovered (it´s too optimistic).

Thanks for your comment, this is indeed true as at a certain period during winter, water from the HT-ATES system is first heated up. In figure 1 (line 270), we have placed an extra (orange) arrow between the heat exchanger and the heat pump to indicate that water from the HT-ATES (or District Heating Network) can be heated further by the heat pump.

 

• Line 262. Heat storage is prioritized in the use of electricity with respect to the electrolyzer. Taking into account that this storage may require all the energy at hand, the limit of use of this resource is not clear (temperatures reached in the aquifers?).

I understand that this is not completely clear, we have explained the heat storage system in detail in the supplementary information. We store enough heat to fulfill the heat demand plus a loss factor according to a certain filling pattern. So when the HT-ATES is full enough, the heat pump will not produce more heat. There is thus a limit on its use. Moreover, the heat pump mainly works from May-September (when the surface water temperature is high enough). Outside that period, the electrolyser is necessary to reduce electricity peaks. To make this more clear in the text, we have added the following sentence:

‘There is a cap on the amount of heat stored based on the yearly heat demand plus a loss factor, explained in S3.3’ (line 318-320).

 

• Line 372. Maybe hydrogen imports from southern Europe are more likely to happen in a near future.....

Thanks for the suggestion, the sentence is now changed to ‘…, but assuming a distance of 3000 km allows for import by pipeline from North Africa, Ukraine [4] or Southern Europe, …’ (line 441).

 

• Line 492. "Pit thermal energy storage could have been another option, 492 but the space that is needed to create the system is not easily available in existing neighborhoods." Since the storage well field is an underground structure, free space is usually not a problem. Even could be implemented in the same place as the common PV common park.

We agree that for underground structures, free space does not always has to be a problem. Yet, in existing neighbourhoods it can still be hard to place such a system because you need a clear space, which is often not readily available in highly urbanized areas. It is a very good suggestion to place the system under the PV park, we have therefore adapted the text as follows:

‘Pit thermal energy storage could have been another option, but free space is needed to install the structure in the subsurface, which is not easily available in existing neighbourhoods. If the PV park is installed close to the neighbourhood (<2 km, to avoid heat losses) on a free space such as a meadow, it could be possible to install a pit thermal energy storage system under the PV park. ‘ (line 561-5685)

 

• Line 495. "With a HT-ATES system, the above-ground impact is small while the system has a sufficient size for function as a seasonal energy storage system and the investment costs are relatively low." This highly depends on the aquifer/water composition (not specified) and temperature.

This is true, the impact does indeed depend on those parameters. In S3.3 we have specified more details about the subsurface characteristics and storage temperatures for the case of Nieuwegein.

However, in this case we focus on the spatial impact, in the sense of how the system fits in the subsurface when installed in an existing neighbourhood. We have adapted the sentence as follows:

‘With a HT-ATES system, the necessary above-ground space to drill, install and operate the wells is relatively small while the system has a sufficient size to function as a seasonal energy storage system and the investment costs are relatively low. ‘ (line 565-568)

 

• line 734, perhaps that sunny day in February is not an ideal example for this work, is it?. Is that usual in The Netherlands?.

We think this is a good example for this work. It happens more often that the coldest days are also sunny because there is no cloud coverage which leads to lower night temperatures. But apart of that, it is interesting to see that even with a sunny day when local PV production lowers the demand from the grid during the day, there is still a peak in electricity demand exceeding the current grid capacity after 5 pm.

 

• Line 772. This may be a problem with the design of the battery dimension?.

We could have dimensioned the battery differently, but a battery of 4MWh is already quite large, and to store all the peaks it should have a capacity of at least 20 MWh. This would have been a very large investment of 6 Meuro, which is not in proportion to the costs of grid extension (about 1 Meuro). Therefore, we have chosen a smaller battery and include grid extension in this scenario. Moreover, a scenario with grid extension is interesting to include in the paper to compare with other conversion and storage technologies.  

 

• Line 934. Therefore a study case with no PV generation so far in the neighbourhood would have been interesting also.

We have also done a reference scenario (see figure 2 at p.14, line 489) without PV generation. In this case, there is a typical energy demand pattern with higher energy demands (for heat) in winter, supplied by gas. The electricity demand is quite stable and slightly higher in summer than in winter.

Reviewer 3 Report

The paper deals with the modern needs of energy system. Authors proposed the integrated energetic system approach. To this purpose they studied different system designs for neighbourhood energy and water systems which is supported by simulation model. The proposals were also evaluated economically.

The paper is long and the topic is presented very well. It consists of six main parts. The first one presents the current policy and situation in aspect of energy production as well the literature review. The various proposed scenarios and combinations were cited what was the background to present the main focus of the study. Second part presents the modelling methodology, consisting of schematic overview of the Power-to-X model, presentation of model parameters, accepted strategy and resulting economic calculations. All  necessary equations were provided with existing limitations. Basing on the accepted methodology reference scenarios were proposed in chapter three. Therefore, different choices and sizing of conversion and storage technologies occurred. All proposed scenarios are described in details with very well presented schemes (all-electric, all-electric H₂, H₂ hybrid, Power-to-X).

Next chapter presents the results. All scenarios were evaluated, considering local energy and water use, import and export of energy, existing peaks in energy demand and supply, as well long time heat storage and economic aspect. All criteria were evaluated properly and presented in a good way. This was the basis of discussion presented in chapter five showing the main benefits and eventual problems for all scenarios. The conclusions made on their basis were listed in the last chapter.

Generally, the paper is very well written. It is very detailed and maybe even too long. Authors did a very good job and I truly recommend the paper to be published in Energies journal.

I noticed that in the front page the word “and” is written in wrong place. It supposes to be before the name of the last Author (Ad van Wijk) and it is written before the penultimate one.

Author Response

Thanks for the kind response and compliments! We agree that the paper is quite long, which is the reason that we have already moved the more specific parts of the model methodology to the supplementary information. We feel that with these type of studies that deal with both the explanation of a model as well as scenarios, this length is necessary to explain everything well enough. From your feedback, we see that it is detailed, clear and well presented, so we think we succeeded in our goal. 

As a response to your specific comment:

• I noticed that in the front page the word “and” is written in wrong place. It supposes to be before the name of the last Author (Ad van Wijk) and it is written before the penultimate one.

Indeed, this was wrong, we have replaced the word “and” to be before the name of the last Author (Ad van Wijk), line 3.