Microturbines at Drinking Water Tanks Fed by Gravity Pipelines: A Method and Excel Tool for Maximizing Annual Energy Generation Based on Historical Tank Outflow Data

Round 1

Reviewer 1 Report

The reviewer wants to thank the authors for their resubmitted paper about the specification of microturbines in a drinking water system. He/she also reviewed the first version of the paper but decided to deal with this submission independently. Nevertheless, it has to be stated that the quality of the paper definitely increased but he/she would like to suggest the following points:

1.    Supplementary file: Please don’t use special characters like umlauts. 

2.    Figure 1: Please include the potential passion of the turbine. The second Flow rate over Hour diagram could be deleted and the one from class one used. This allows to reduce the needed space. Is this really a typical consumption with a second peak around midnight? 

3.    Table 1 can be deleted. The paper is comparable long and so repetitions should be avoided. Please also shorten the paper significantly. 

4.    Line (L) 94: The reviewer is not very happy with this comment. First Excel as well as Matlab both are commercial programs. But for both software solutions free clones are available. Plus, the provided Excel-file requires obviously macros, which for example don’t run on (the reviewers) Mac-Version of Excel. Which version of Excel is supported? The reviewer has to admit that she/he is a Matlab-user, who record the last macro years ago, and consequently it would take ages to check the code, but yes, it is provided. The authors argue that some authors don’t provide the code but show the algorithms. This is due to the fact, that the algorithm includes the novelty. Based on this comment, the authors see the novelty in the implementation of known equations in an Excel interface. Is this correct? 

5.    Section 2.2: The authors should start with the Bernoulli equation and define the two cross sections. Please clearly define the used values in relation to a reference plane. The reviewer assumes that $h_{max}$ is the water level (WL) of the upper reservoir, which should be monitored as well as the WL of the lower reservoir. It seems that the authors assume that those are constant? How accurate is this? Did the reviewer understand it correctly, that the authors argue that the measurement of only two operations modes is enough? Hence it takes only 30 minutes (L180) it would be highly recommendable to test more conditions because the losses are critical for the complete calculations and can change under specific conditions. How is the measurement accuracy included in the calculation?

6.    Did the reviewer understand this correctly: Only the data of two different turbine manufactures are included and the result is the recommendation of one of those? Is there the possibility to implement a different supplier? The fitting of the AXENT turbine with two points seems to be discussable. 

7.    Table 2 is very interesting but the reviewer missed the source of the values and the installation year (period).

8.    Figure 4 please clarify where the potential turbine should be installed. 

9.    Figure 4 II: the L1, L2, L3 should be km not m? Otherwise the height difference is bigger than the length. 

10.  Figure 8/input data: The reviewer assumes that the 15-minute intervals are mean values over the period. Did the author try to further reduce this to a bigger interval? How big are the gaps in the previous time? The reviewer would argue that it is better to use a longer period with an interpolation of missing data in comparison to such a comparable short period. Are the approximate 9 months representative for the full year? It could be argued that the spring/ summer months are missing as well as a change of a wet to a dry year. 

The mentioned limitations (Sec. 4.3) are significant and the model only include simple calculations (as mentioned by the authors in L460), which are done for nearly every hydro power project. The authors correctly state this is a low-hanging fruit (L108), which leads to the main questions of the novelty. The provided Excel Tool targets very early feasibility studies and users, which don’t have the time/knowledge to themselves implement the equations. The reviewer would argue that those readers are better targeted with another journal or part of an additional document, which is provided with the Excel file as a manual. Nevertheless, the gained knowledge of the authors due to their installation of 9 projects should be the main part of the paper. The reviewer is confident that discussion of the measurement, data acquisition/analysis as well as the final comparison of the installed turbines with the predicted result is definitely interesting for a wide scientific community. He/she would like to motive the authors to modify the paper. 

Author Response

See attached Word document!

Author Response File: Author Response.docx

Reviewer 2 Report

The plants to which the proposed method is applicable, to your knowledge are not few and you have already shown in this work more examples of plants in Germany. My impression (I don't have statistical data on this matter) was different, above all because I didn't think that the aqueducts were built in the past with pressure losses so low as to allow a convenient energy exploitation. I feel I agree with you when the construction of a new aqueduct or the reconstruction of an obsolete one occurs. Attention to renewable energy and knowledge of appropriate design methods can lead to systems that have good performance from multiple points of view, all of which are important.

The "green" purpose of the work and the free availability for the community of the developed method are very appreciable things.

I report a printing error in formula (3) (a * sign instead of /). Also lines 232-236 didn't seem clear to me until I read the rest.

I also had difficulty reading the equation (9), but I think this will be solved with the final print.

Author Response

See attached Word document!

Author Response File: Author Response.docx

Reviewer 3 Report

The authors present a method for optimizing hydropower systems in drinking water installations. The manuscript is well-written and covers a relevant topic. The methods are clearly and correctly presented.

The method is verified by its application to 9 different emplacements. The results are very conclusive and well explained.

I consider that the manuscript demonstrate a good quality and can be accepted as is. 

Author Response

See attached Word document!

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The reviewer wants to thank the authors for their corrections as well as answers to the previous questions. Some small points:

-      Ok, brewery is a good reason for this, but please add this comment in the paper or choose a more typical case. 

-      Open source is binary. Please delete this expression. It is enough to say, that it is free to use and base on the common tool Excel. For further work the reviewer can only recommend to switch to Matlab or Python. 

-      The comment about the missing scientific literature about turbines in combination with hydro power is misleading. Fact is that in nearly every textbook about hydraulic comparable examples are given and based on the reviewers experience those basic facts are part of the first hydraulic courses at Bachelor level. Consequently, the research papers focusing on those problems are rare hence the methods are well-known and part of the everyday work. Furthermore, the highly project depending boundary conditions for hydro power makes it hard to present the results of the detailed optimisations of those hydraulic systems. The reviewer sees the benefit for the owners of water supply systems to use the presented tool as a first approach but this cannot replace a detailed study including all project specific boundaries. The reviewer highly appreciates the critical discussion and presentation of the limitation.

-      Answer concerning h_downstream: The answer is not really clear but the Figure A1 shows the correct relation. Please clarify in the text that the downstream value has to considered as well as in general the difference in the heights in the two tanks.  

-      The authors may be right that a short measurement campaign allows to get the basic values for the losses. Nevertheless, under specific circumstances and after the first basic evaluation a more detailed measurement campaign should be conducted. With the sentence in L190 and ”the 30-minute visit” the authors make it not easier to argue for a longer campaign, which allows to reduce the uncertainty. The reviewer hopes that the authors agree that such an economical far reaching decision should be based on sound evaluations. 

-      The limitation to only two specific turbine manufactures should be mentioned in section 4.3 as well as all possible funding links with one of the companies. 

All in all, the quality of the paper is further increased. The obvious limitations are presented and the other reviewer accepted the paper. The reviewer hopes that the authors can be part of a realisation and present the gained further knowledge.

Author Response

See attached Word document!

Author Response File: Author Response.docx

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Review

The authors present the operation and application of an excel tool to design a hydropower turbine for a specific setting within water supply networks. The authors write very well and the paper is very readable and easy to follow. However I have some reservations as follows:

1.       The introduction is written in an unusual manner for a scientific paper. It seems more methodological than introductory/literature review. It has been written as a mix of both but with an emphasis on method. The inclusion of a figure in an introduction is unusual for example. Particularly one as detailed as Fig 1. I would suggest restructuring the paper a little.

2.       The gap in knowledge addressed here is claimed to be an advance on the technical guidance given at national level in Germany. It seems a low-level form of novelty. Does this tool advance knowledge beyond anything that has been conducted in the scientific literature ? This is not mentioned but is an important point.

3.       In the methodology section the authors do not give sufficient levels of detail in how their tool works. For example the rough estimate calculates the energy generation and costs/benefits but it is not mention how these calculations are performed, on what basis costs are estimated etc. The method section in this regard appears more like a user guide than a scientific description of the method. This applies to all steps.

4.       Continuing from the previous point in Section 3 the results of the case study are very difficult to interpret when we have no idea on what they are based. Basic information such as what type of turbine has been chosen, how its efficiency and characteristic curves were obtained, etc, is not provided. Again this section reads like a users guide to the excel tool. An example of this is 368/369 ‘the user clicks the button …..’. It is not important to a scientific audience which buttons the user must push, only on what basis there underlying calculations are conducted.

5.       Figure 5 is not useful at all. Remove it.

6.       Figure 6 – the efficiency of this turbine seems very high and unvaried considering such a wide flow range and low power output ?

Reviewer 2 Report

The reviewer wants to thank the authors for their paper about the application of the Excel tool, which allows to design the optimisation of a turbine in a water supply system. He/she has some small points and also a big concern about the paper:

-      Abstract: the gravity pipelines should be included, so that the reader knows that an existing potential is used.

-      Literature review: there are a lot of German literature mentioned but it should be further expanded. 

-      Fig.1 case (b) … it is an extreme case of (c), in which the friction in the pipes consumes the full available height. Nevertheless, the reviewer would argue that the turbine would always cause a slightly small step in the energy line hence all losses at the point. Or did the reviewer misunderstand the graphic? 

-      Line (L) 91: nearly freely and not fully freely. There are always some restrictions to have a minimum water level in the tank. 

-      L144: The references to the Figures 6,8,11 is confusing. 

-      Section 2.1 the bypass is mentioned far to often. It can be reduced to one explanation.

-      L191: The authors promote their tool but it is not clear where to get it. … only later the authors offer to provide it. 

-      Section 2.5 Starting L: why does the tool not allow to interpolate the missing data? The reviewer is more a Matlab-User and would just run a quality check and interpolate the missing points. … but yes, that can be done by the user. 

-      L314: SCADA is not explained. 

-      Starting L394: interesting aspect, this would be worth to see in detail including the chosen integration in the model. 

-      L425: other 3 methods … they are not clearly explained.

-      L606: where to download? 

-      Acknowledgments are mixed with Funding details. 

-      The figures in the Appendix seem to be a little bit unrelated or should be included in the text. … bypass. 

In addition to those small points the reviewer would assume that the authors address the wrong kind of audience. The paper is more a manual to use the tool and gives some good argument, why. This is very useful for somebody planning such a tool and need a quick optimisation in the frame of the German boundary conditions. For this use, the paper is very good. But in contrast to this, the view of a researcher is different and the reviewer was constantly asking him/herself what approach, model, assumptions … are used in the calculations in the background. In additions, the details of the other three methods should be presented (only German speakers can look it up) as well as the mathematic model which was used to calculate this. There is some interesting potential included but the manual part has to separate in the appendix and the comparison of the methods should be part of the main paper. 

The reviewer hopes that the authors understands the mentioned big concern and is looking forward to a corrected version of the paper. Thank you. 

Reviewer 3 Report

The manuscript describes  a new method to determine optimal parameters for the design of hydropower schemes in gravity pipes. It is well described, presented and well introduced.

However, in my opinion, the topic is not suitable to be published as scientific paper. It could be published as conference paper or as engineering guideline, because it can be effectively used as engineering tool, and the Reviewer appreciated this. The manuscript is not suitable as scientific paper, since it lacks of scientificity. Furthermore, if the scope is to show an excel sheet, the excel sheet should be attached to the paper.

See also some minor comments on the attached manuscript.

Comments for author File: Comments.pdf