Design and Year-Long Performance Evaluation of a Pump as Turbine (PAT) Pico-Hydropower Energy Recovery Device in a Water Network

Round 1

Reviewer 1 Report

Dear Authors,

The paper deals with an interesting topic, which can help to increase the use of PaT technology in micro and pico-hydropower sector, improving energy consumption and management. As stated in the introduction, the technical literature is characterized by a large number of studies on PaTs regarding different aspects. Starting from the first experimental studies of simple pumps used in reverse mode, the research moved to develop models (both empirical and theoretical) able to predict the performance of these machine in reverse mode. Now, it is necessary to install these machines aiming at a green energy production towards the global decarbonization goal.

In this scenario, the manuscript is interesting and deals with a current issue, regarding the development of a robust tool, which helps the user to select the most suitable machine for a specific site.

However, the number of references is low and need to be increased in order to better expand the state of the art with more recent works. Moreover, the manuscript is well organized but information are somehow confused. Most of the figures are not well referenced, some assumptions are not properly described as well as results.

There are some typos, grammar errors and the English is not always smooth. For this reason, the authors are encouraged to cross-check the paper and proofread it for syntax/grammar errors

The paper is a good base to start. It could be improved; thus, revisions are suggested to enhance the work.

You will find the comments in the attached file.

Best regards

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors present a well elaborated selection tool for PATs. Their approach is considering most of all relevant parameters and the excluded parameters, such as variable speed, are mentioned.

The tool is validated with long time field measurements. The tool is applicable for any possible location of PATs.

The described installation is not typical for probably most PAT installations, since bypass water could be used for long periods. Usually such bypass water is not available and only the water in the system can be used for energy production.

 

equations:

Please clearly distinguish physical quantities and empirical coefficients in all equations and be consistent with dimensions. Physical quantities should have SI-units.

E.g. eq.2 : electrical power = mass flow times pressure difference times unit efficiency

Pel [W]= r [kg/m3]Q [m3/s] g [m/s2] H [m] h [-]

Simplified equations should not be used in a scientific paper

line 319

How can the head be in good agreement with the readings of the flow meter?

How is a "good agreement" defined?

line 327

Where does the electricity price of € 0.139606 /kWh (6 digits provide a wrong impression of the accuracy of this estimation) stem from? Does it make sense to provide so many digits? ((We use generally € 0.06 /kWh for such estimations))

line 341

Why is the rotational speed assumed as 1500 rpm and not 1520 rpm or higher?

line 349

Please eliminate the logos from the figure.

line 393

Is the man power included in the cost? Or is it excluded since in was a research project? What would be the cost of man power if a local company would have done the installation? Please give more detailed information on the estimation of the costs.

line 407

What was the runaway speed?

line 424

Please be more precise with the definition of efficiency. E.g. are mechanical losses included? Which losses are included in which efficiency?

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

The corrections have significantly improved the paper.  In the revised version, the authors have improved the references by focusing on some aspects on empirical and numerical studies on PaTs.

The English has been improved as well as the figures and the equations with their descriptions, which now are appropriate and more consistent.

In conclusion, the paper is improved but requires few simple minor revisions in order to enhance the work.

Best regards

ABSTRACT

1. Page 1, line 19: Please delete “the” in “the scheme has been the monitored over 13 […]”.

SECTION 1

1. Page 3, line 128: CO₂ instead of CO2.

SECTION 2

1. Page 5, line 193: m³/s instead of m3/s.
2. Page 5: line 217: It should be Q_x and H_y as in the previous version. Please proofread it.
3. Page 6, line 240: “Also, the software includes a calculation of the expected installation cost which considers the total cost as the 26% of the cost of the PAT and generator alone”. Please, make it clearer. From Figure 6(c) it is possible to note the cost of the PAT (€ 2744) and the total cost of the installation (€ 10,980). Then, on the contrary the cost of the PAT is the about 26% of the total cost of the installation. Please make it clearer.

SECTION 3

1. Page 8, line: 258: m³/day instead of m3/day.
2. Page 10, line 316-318: I agree with the authors that the maximum recoverable power is with a flow of 17 l/s rather than 18 l/s, and this would not have changed if a different efficiency had been selected other than 60%. At the same time, the shape of the predicted theoretical power in figure 5 cannot be computed by assuming constant the efficiency . For instance, the power cannot be computed with an efficiency of 60% at Q=5 l/s (Q/QBEP = 0.7) or Q=25 l/s (Q/QBEP = 1.47). I understand that this assumption regards the BEP (17 l/s), because those part-load and over-load operating conditions don't happen in your case study. It is correct?
3. Page 11, line 349: Please use the same number of significant digits also for 0.130883 €/kWh

SECTION 4

1. Page 17, line 454: Please fix the error regarding the reference to the equation.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

It is suggested that the authors should have a look concerning efficiency definitions at the standard IEC60193, Annex N.

The efficiency displayed in Figure 9 is hopefully not the hydraulic efficiency, as stated in the text. The reviewer assumes that the displayed efficiency is rather the unit efficiency. The unit efficiency is the product of the mechanical turbine efficiency times the generator efficiency.

Author Response

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Author Response File: Author Response.docx