Assessment Method to Identify the Potential of Rooftop PV Systems in the Residential Districts

Round 1

Reviewer 1 Report

Review notes for Assessment of rooftop PV systems toward zero energy suburbs in Sydney

The manuscript presents an analysis of the rooftop solar potential for four suburban areas surrounding Sydney, Australia. The authors use an online tool for mapping rooftop solar potential and apply it to a large sample of houses to get average suitability characteristics and solar potential for the different suburbs, further extending that analysis to the full electricity generation potential for these suburbs relative to their electricity consumption.  The analysis is both a nice demonstration of the approach and provides a useful planning output.

I have the following suggestions on how to improve the manuscript to make the results clearer and more useful to the reader.

 

Figure 4 – it appears that the line connecting the data points in this plot has a spline fit to smooth the transition.  This implies a much finer granularity to the input data than is actually present.  Please remove the spline fit. If you choose to keep the connecting line segments between the data points, I suggest you increase the size of the data points and perhaps make the lines dashed to make it clearer that they simply guide the eye.

Figure 5 – I would suggest you change the form of these plots to histograms or some other frequency distribution. This plot form is based on the assigned sample number of the houses in the study and this is a rather arbitrary designation, or at least there is no information on the significance of the number designation in the text.  A histogram or a re-ordering into a rank by area would be more helpful for illustrating the differences in distribution between the suburbs. This comment also applies to Figures 6 and 7.

Regarding Figures 5-7, if the authors wish for readers to be able to compare the performance of a particular house across the three metrics, and that is what leads them to use the house sample designation as the x-axis, this reader finds these plots impractical.  With so many data points and so much variation between them over narrow length scales, it’s not possible to pick out individual houses and compare across multiple plots. Consequently, I can’t identify or rule out any correlation between the various factors based on the way the data are presented.  For this reason, I suggest using histograms to present the frequency of values for the four suburbs, preferably in a more compact form that allows easier comparison between suburbs, with a discussion in the text of the correlations or lack thereof between the suitability characteristics. One way to present this graphically would be to plot the suitability factor for the four suburbs.

In the results and discussion section the manuscript lists the average roof area suitable for solar in the four suburbs, but there is no listing of the average suitability factor.  Please include at least a sentence or two on the average suitability factors so that the reader can compare the rooftop solar potential for these towns to the baseline system. 

Author Response

Thank you for your valuable comments, changes were made accordingly as explained below in red.

Figure 4 – it appears that the line connecting the data points in this plot has a spline fit to smooth the transition.  This implies a much finer granularity to the input data than is actually present.  Please remove the spline fit. If you choose to keep the connecting line segments between the data points, I suggest you increase the size of the data points and perhaps make the lines dashed to make it clearer that they simply guide the eye.

• We have increased the data points and made the line dashed

Figure 5 – I would suggest you change the form of these plots to histograms or some other frequency distribution. This plot form is based on the assigned sample number of the houses in the study and this is a rather arbitrary designation, or at least there is no information on the significance of the number designation in the text.  A histogram or a re-ordering into a rank by area would be more helpful for illustrating the differences in distribution between the suburbs. This comment also applies to Figures 6 and 7.

• Thank you for this great idea, we have changed Fig. 5 to show the histogram of the usable area. Fig 6 and 7 are kept in the same shape to show average of roof slop and orientation which they are used to estimate suitability factor in equation 2. To clarify this dotted line showing the average value of all suburbs is now added to Fig 6 and 7. Also, all figures are rearranged now in matrix form.

Regarding Figures 5-7, if the authors wish for readers to be able to compare the performance of a particular house across the three metrics, and that is what leads them to use the house sample designation as the x-axis, this reader finds these plots impractical.  With so many data points and so much variation between them over narrow length scales, it’s not possible to pick out individual houses and compare across multiple plots. Consequently, I can’t identify or rule out any correlation between the various factors based on the way the data are presented.  For this reason, I suggest using histograms to present the frequency of values for the four suburbs, preferably in a more compact form that allows easier comparison between suburbs, with a discussion in the text of the correlations or lack thereof between the suitability characteristics. One way to present this graphically would be to plot the suitability factor for the four suburbs.

• As mentioned above the aim of figure 6-7 is to identify the average of roof slop and roof orientation of each suburb by using the data of house samples. These average values (which are now added to figures 6 and 7) are used to find average suitability factor in Sydney from figure 1. The idea here is to estimate the average production of rooftop PV system of a certain suburb by referring to the average suitability factor rather than measuring the production of every single house in each suburb. This was highlighted by adding a paragraph after equation 2 (line 286– 288)

In the results and discussion section the manuscript lists the average roof area suitable for solar in the four suburbs, but there is no listing of the average suitability factor.  Please include at least a sentence or two on the average suitability factors so that the reader can compare the rooftop solar potential for these towns to the baseline system. 

• Statement is added now in line 311 – 312

Reviewer 2 Report

In this paper, the authors proposed a new method of assessing the potential of the rooftop PV system to meet energy demand in residential districts

In particular, the study is based on using the online tool “SunSpot” and solar performance software “PVSYST” to develop a formula that can estimate the suburban annual energy production from the residential rooftop PV systems.

In general, this topic falls within the aim and scope of the Energies journal.

The scientific context is interesting, but in my opinion some aspects need to be clarified:

 

• Abstract: Should have one sentence for each: context and background, motivation and novelty, hypothesis, methods, results with values, conclusions.

 

• Introduction: The Introduction section should be thoroughly improved. A robust comparison with other tools or approaches published in this field in high impact journals should be presented

 

• Introduction: Why this paper is presented? The authors should define the motivations, the innovative aspects respect to the other studies already published.

 

• Line 135: who determines that the error in 4-year estimated annual energy production is reliable and within the accepted range? Please explain and insert a reference if necessary.

 

• The methodology is not well defined. Why were the suburbs close to the central area of Sydney chosen? How were the houses sampled? How was the "SunSpoT" online tool used to estimate the sample output of the rooftop PV system?

 

 

• Line 191: “It is worth to notice here that although the usable area of the suburb in Figure 5 (d) is half of the other suburbs its floor area is almost doubled the floor area of the other three suburbs which allows more space for PV panels’ installation”. This sentence is not clear. The usable area is not a function of the floor area? Please explain.

 

• In my opinion, the results need to be better presented and expanded.

 

 

In conclusion, the work could have potential if revised, but obviously as it appears, I do not recommend publication. Rather the authors should carry out a major revision process in order to make the work interesting, innovative, original and with an clarified methodology and an expanded result analysis.

Author Response

Thank you for your valuable comments, changes were made accordingly as explained below in red.

 Abstract: Should have one sentence for each: context and background, motivation and novelty, hypothesis, methods, results with values, conclusions.

• The abstract is rearranged to meet the requested format.

 Introduction: The Introduction section should be thoroughly improved. A robust comparison with other tools or approaches published in this field in high impact journals should be presented

 Introduction: Why this paper is presented? The authors should define the motivations, the innovative aspects respect to the other studies already published.

The introduction is improved by addressing the points above and adding information about Sydney 2030 strategy plan (see line 26 -32 and lines 73 - 90 ), also adding two references (2 and 11) which are related to motivation and innovative aspects.

 Line 135: who determines that the error in 4-year estimated annual energy production is reliable and within the accepted range? Please explain and insert a reference if necessary.

New data generated by PVSYST software is added to figure 2 to justify the error in the results by SunSpot. A paragraph was also added to explain this ( see line 159 – 163).

 The methodology is not well defined. Why were the suburbs close to the central area of Sydney chosen? How were the houses sampled? How was the "SunSpoT" online tool used to estimate the sample output of the rooftop PV system?

Extra information is added now to this section highlighted in yellow, north direction is added in Fig. 3, and more points are added to figure 4 for clarification.

 Line 191: “It is worth to notice here that although the usable area of the suburb in Figure 5 (d) is half of the other suburbs its floor area is almost doubled the floor area of the other three suburbs which allows more space for PV panels’ installation”. This sentence is not clear. The usable area is not a function of the floor area? Please explain.

This has been clarified now by adding extra information in line 237 – 240.

 In my opinion, the results need to be better presented and expanded.

Figures 2, 4,5,6,and 7 are all modified with some extra information added to them.

Author Response File: Author Response.docx

Reviewer 3 Report

The paper presents shortly a case assessment analysis of PV-systems in Sydney suburbs. The manuscript is of average quality and does not promote a novel theory/application. The authors can improve the article in many points the case study.

• Type and Title need changing. It is not a pure research article. What does zero-energy suburbs mean?
• Abstract: The abstract needs rewriting. Please use adverbs and connecting words/phrases.
• Introduction: The paper structure is missing at the last paragraph.
• Section 2 can be deployed/improved.
• Section 3 presents the results of the four suburbs.
  • Figure 5, 6 and 7. Please arrange the graphs in a table 2x2 and the sub-caption (a,b,c,d) under them. Note that the x-axis can be labeled as "Number of Houses samples". Correct also Fig.7 (numebr).
  • Table 1. It is not a pure Table.  Please insert a new column in the right and add the values.
• Conclusions: The case study can be improved by taking into account the distribution network topology/architecture. Of course there are limitations due to network constraints (e.g. lines thermal rating) in order to transform the suburbs in Sydney to zero-energy.

Author Response

Thank you for your valuable comments, changes were made accordingly as explained below in red.

• Type and Title need changing. It is not a pure research article. What does zero-energy suburbs mean?

Title has been changed now to “Assessment method to identify the potential of rooftop PV systems in the residential districts”

• Abstract: The abstract needs rewriting. Please use adverbs and connecting words/phrases.

The abstract is now rewritten considering the above comments

• Introduction: The paper structure is missing at the last paragraph.

New information added to introduction (see line 26 -32 and lines 73 - 90 ), structure is added in line 84-94

• Section 2 can be deployed/improved.

Many information were added in this section: Fig.2, 3 and 4 have now new data to clarify these figures with some comments in line 159 – 163.

• Section 3 presents the results of the four suburbs.
• Figure 5, 6 and 7. Please arrange the graphs in a table 2x2 and the sub-caption (a,b,c,d) under them. Note that the x-axis can be labeled as "Number of Houses samples". Correct also Fig.7 (numebr).

All figures in this section are now arranged in matrix format to show the four suburb results. Spelling correction was made as well.

• Table 1. It is not a pure Table.  Please insert a new column in the right and add the values.

This has been added now

• Conclusions: The case study can be improved by taking into account the distribution network topology/architecture. Of course there are limitations due to network constraints (e.g. lines thermal rating) in order to transform the suburbs in Sydney to zero-energy.

Thank you this valuable point we have added this statement as one the recommendations for local councils in the abstract “The package should consider the option of a battery storage system in dwellings to enhance power system flexibility, enable high level of PV energy integration and reduce grid energy congestion.” , See line 358 – 360.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I thank the authors for the review process, but in my opinion, the paper has not been improved, and also the authors have not answered my questions posed about some doubts. Therefore, I invite the authors to respond to my comments and improve the paper.

Introduction: The Introduction section should be thoroughly improved. A robust comparison with other tools or approaches published in this field in high impact journals should be presented

The methodology is not well defined. Why were the suburbs close to the central area of Sydney chosen? How were the houses sampled? How was the "SunSpoT" online tool used to estimate the sample output of the rooftop PV system?

Line 191: “It is worth to notice here that although the usable area of the suburb in Figure 5 (d) is half of the other suburbs its floor area is almost doubled the floor area of the other three suburbs which allows more space for PV panels’ installation”. This sentence is not clear. The usable area is not a function of the floor area? Please explain.

Author Response

Please find below my answer to your comments

comment 1: Introduction: The Introduction section should be thoroughly improved. A robust comparison with other tools or approaches published in this field in high impact journals should be presented

In this work we did not develop the online tool to investigate rooftop PV system performance, yet we used a tool of other researcher to develop a method to estimate the potential of a suburban rooftop PV system. However, we made the following changes to the introduction based on your comment:

The introduction is divided into 3 parts:  the first part showed the work done worldwide on assessing the viability of the rooftop PV system. Two recent papers from energies [ 2, and 3] were added to the list of reference. Details are shown in this paragrapb Line 26 - 36. “The grid connect roof top PV system was considered in energy strategy planning of many countries and many related research works which consider technical, economic, and environmental criteria showed that this technology is a feasible solution for electricity generation and would play a significant role in the future electricity supply [2, 3, 4, 5, 6, 7, 8, 9, 10 ]. In the Australian context the residential rooftop PV systems started to feed energy into the local grid at the end of the first decade of 21st century following the generous local and federal governments rebate schemes which opened the door for local councils to consider these systems in their building sustainability plans such as the sustainable Sydney 2030 strategy plan that comprises ten targets some them are linked to environment sustainability such as the reduction of 1990 greenhouse gas emissions by 50% and the capacity to meet local electricity demand [4].”

The second part presents the tool used by different researcher to investigate the potential of the technology. In this part we found that there is similarity in the methodology used by these researchers. This paragraph is added “Different types of case studies were conducted to estimate the energy potential of rooftop PV systems, however most of them adopted the same methodology by considering solar irradiation map layers on roof surfaces and geographical information for the respective site.” Also, we ended this part by this paragraph to compare between the adopted tool SunSPot and other tools in the literature “The work presented in the above literature do not provide an online tool that is available to researcher to investigate the potential of rooftop PV electricity in residential districts. This research gap was tackled recently by Roberts M. et al. [12, 13] who developed an online tool called “SunSpot” that estimates the total potential of PV rooftop systems by using roof space mapping tool that evaluates available roof spaces and estimates shading and roof orientation. The work was conducted for different zones, residential and commercial, in states and local government area in Australia. The study showed that annual solar electricity output from the available roof spaces in Australia is greater than current consumption in the national electricity market.”

The last part of the introduction show the research gap we worked on by adding this paragraph “ The methods described in the above literature review estimate the overall energy production by rooftop PV system referring to geographic scan and solar irradiation mapping to building roofs, however this kind of mapping do not identify the actual usable area of different types of roofs and the obstacles to the solar PV array layout such as solar windows, satellite dishes, chimneys, air conditioning units.. etc..  The method developed in this work is focused basically on identifying the usable area of dwellings roof for PV arrays layout by introducing the roof suitability factor.  “. Also in this section we described that the reason why we have chosen the four suburbs to assess the viability of the sustainability Sydney 2030 strategy plan by adding these paragraphs “The aim here is to draw more accurate picture about the rooftop PV potential of Sydney City suburbs that are contributed in the sustainable Sydney 2030 strategy plan, and to estimate the actual annual PV energy production using adequate number of roof samples to justify the proposed average roof suitability factor for each suburb.”

Other changes in the introduction are highlighted in yellow in the manuscript for your reference.

 

comment 2: The methodology is not well defined. Why were the suburbs close to the central area of Sydney chosen? How were the houses sampled? How was the "SunSpoT" online tool used to estimate the sample output of the rooftop PV system?

This paragraph is added to the methodology to show why the four suburbs was chosen “The aim of conducting this study on these four suburbs is to assess the viability of the sustainable Sydney 2030 strategy plan and find out whether the suburbs of Sydney City Council can meet the two environment sustainability targets; the reduction of 1990 greenhouse gas emissions by 50% and the capacity to meet local electricity demand [4]”

The paragraph in line 199 – 207 in the methodology shows how were the houses sampled “ Due to the variety of roof design in the selected suburbs, relative standard deviation of average energy production was calculated versus number of house samples to find the number of samples that can be selected in each suburb. It is clearly shown in Figure 4 that relative standard deviation of average energy production changes with number of house samples until it reaches to almost steady values between 80 - 120 house samples. Based on this finding the 100 house samples in each suburb were selected in the PV system analysis. Each suburb was divided into 10 zones each one consists of 10 random samples of houses that eligible to the rooftop PV system installation to estimate the average production of solar electricity of the suburb.”

To show how the Sunspot online tool used we have replaced the given information in methodology section by the following 5 major steps:

The “SunSPoT” online tool [16] was used to estimate the output of the rooftop PV system samples by using the following steps:

1-            Locate a house in a respective suburb by zoom in the SunSpot online map.

2-            Identify the usable roof area from the total area of the roof samples by removing the area of objects obstruct the PV panels layout such as the area of chimneys, satellite dishes, antenna, air-conditioning unit,...etc. More than one side of the roof between (North, east, and west) can be considered if their area is suitable for PV panel installation ( > 4 m²).

3-            Draw the location of the PV array on the selected house roof by using the SunSpot roof space mapping tool as described in Figure 3. This figure shows an example of the selected area of a north east roof that would be suitable for PV panels’ installation and the eliminated roof area in the east and west side as it is less than 4 m². The southern roof of all house samples was not considered in the analysis as it is not feasible from the economic perspective.

4-            Perform the analysis by using the calculate function in SunSpot to estimate the rooftop PV system information such as: the PV panel array area, roof orientation, roof tilt angle, the capacity of the system, the annual yield, CO₂ emissions avoided and annual savings.

5-            The data collected in step 4 are copied into excel sheet to perform the statistical analysis.

Comment 3: Line 191: “It is worth to notice here that although the usable area of the suburb in Figure 5 (d) is half of the other suburbs its floor area is almost doubled the floor area of the other three suburbs which allows more space for PV panels’ installation”. This sentence is not clear. The usable area is not a function of the floor area? Please explain.

The floor area is replaced by roof area as expressed in line 231 – 233 by the paragraph “ It is worth to notice here that although the percentage of roof usable area of the suburb in Figure 5 (d) is half of the other suburbs, its total roof area is almost double the total roof area of the other three suburbs and consequently the PV array area can be doubled.”   

Author Response File: Author Response.docx

Reviewer 3 Report

The authors have performed the suggested changes to the manuscript and the output has been improved. 

While the quality is average, the article can be very interesting to the readers.

The references list can be enhanced more in order to highlight the research survey of the work. Note that only one article [Ref. 9] from Energies journal has been cited.

Author Response

Thank you for your comment we have now added another 2 papers from energies published in 2021 and improved the introduction accordingly as you can see in the followings:

The introduction is divided into 3 parts:  the first part showed the work done worldwide on assessing the viability of the rooftop PV system. Two recent papers from energies [ 2, and 3] were added to the list of reference. Details are shown in this paragrah Line 26 - 36. “The grid connect roof top PV system was considered in energy strategy planning of many countries and many related research works which consider technical, economic, and environmental criteria showed that this technology is a feasible solution for electricity generation and would play a significant role in the future electricity supply [2, 3, 4, 5, 6, 7, 8, 9, 10 ]. In the Australian context the residential rooftop PV systems started to feed energy into the local grid at the end of the first decade of 21st century following the generous local and federal governments rebate schemes which opened the door for local councils to consider these systems in their building sustainability plans such as the sustainable Sydney 2030 strategy plan that comprises ten targets some them are linked to environment sustainability such as the reduction of 1990 greenhouse gas emissions by 50% and the capacity to meet local electricity demand [4].”

The second part presents the tool used by different researcher to investigate the potential of the technology. In this part we found that there is similarity in the methodology used by these researchers. This paragraph is added “Different types of case studies were conducted to estimate the energy potential of rooftop PV systems, however most of them adopted the same methodology by considering solar irradiation map layers on roof surfaces and geographical information for the respective site.” Also, we ended this part by this paragraph to compare between the adopted tool SunSPot and other tools in the literature “The work presented in the above literature do not provide an online tool that is available to researcher to investigate the potential of rooftop PV electricity in residential districts. This research gap was tackled recently by Roberts M. et al. [12, 13] who developed an online tool called “SunSpot” that estimates the total potential of PV rooftop systems by using roof space mapping tool that evaluates available roof spaces and estimates shading and roof orientation. The work was conducted for different zones, residential and commercial, in states and local government area in Australia. The study showed that annual solar electricity output from the available roof spaces in Australia is greater than current consumption in the national electricity market.”

The last part of the introduction show the research gap we worked on by adding this paragraph “ The methods described in the above literature review estimate the overall energy production by rooftop PV system referring to geographic scan and solar irradiation mapping to building roofs, however this kind of mapping do not identify the actual usable area of different types of roofs and the obstacles to the solar PV array layout such as solar windows, satellite dishes, chimneys, air conditioning units.. etc..  The method developed in this work is focused basically on identifying the usable area of dwellings roof for PV arrays layout by introducing the roof suitability factor.  “. Also in this section we described that the reason why we have chosen the four suburbs to assess the viability of the sustainability Sydney 2030 strategy plan by adding these paragraphs “The aim here is to draw more accurate picture about the rooftop PV potential of Sydney City suburbs that are contributed in the sustainable Sydney 2030 strategy plan, and to estimate the actual annual PV energy production using adequate number of roof samples to justify the proposed average roof suitability factor for each suburb.”

Other changes in the introduction are highlighted in yellow in the manuscript for your reference.

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

In my opinion the paper continues to have the shortcomings highlighted in my comments, and the authors have not improved the paper.