School of Engineering and Energy ENG460€¦ · School of Engineering and Energy ENG460 Engineering...
Transcript of School of Engineering and Energy ENG460€¦ · School of Engineering and Energy ENG460 Engineering...
School of Engineering and Energy
ENG460
Engineering Thesis
2011
Performance Evaluation, Simulation and Design
Assessment of the 56 kWp Murdoch University
Library Photovoltaic System
Digital Appendices for software and data handling purposes
Stephen Rose
30658774
“A report submitted to the School of Engineering and Energy, Murdoch University in partial
fulfilment of the requirements for the degree of Bachelor of Engineering”
Unit Coordinator: Professor Parisa Bahri
Supervisor: Dr. Martina Calais
Associate Supervisor: Dr. Trevor Pryor
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Contents
1 Appendix B ..........................................................................................................................4
1.1 Establishment of Data Logging System ......................................................................4
1.2 Data Downloading Steps .............................................................................................4
18 Appendix F....................................................................................................................12
18.1 PVsyst Component Electrical Parameters .................................................................12
18.1.1 SMA SMC 6000A.............................................................................................. 12
18.1.2 Kyocera KD135GH-2P ...................................................................................... 14
18.1.3 Sungrid SG-175M5 – Default Model ................................................................ 16
18.1.4 Sungrid SG-175M5 -V – Voltage Temperature Coefficient Adjusted Model ... 19
18.1.5 PVsyst Model Parameters .................................................................................. 21
19 Appendix G ...................................................................................................................24
19.1 PVsyst Shading Study ...............................................................................................24
20 Appendix I ....................................................................................................................25
20.1 AS 5033 Compliance Notes ......................................................................................25
21 Appendix J ....................................................................................................................28
21.1 Solar Unlimited Cable Calculations ..........................................................................28
21.2 Solar PV Cable Calculations .....................................................................................31
22 Appendix K ...................................................................................................................37
22.1 Shading Study Photos for May 22 2011 ....................................................................37
11 am .....................................................................................................................................39
12 noon..................................................................................................................................40
1 pm ......................................................................................................................................41
2 pm ......................................................................................................................................42
3 pm ......................................................................................................................................44
4 pm ......................................................................................................................................45
23 Appendix L ...................................................................................................................46
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23.1 Afternoon Shading Study for December 2011 ..........................................................46
Figures
Figure 59 Existing Sunny Porta display..................................................................................... 9
Figure 60 SMA FlashView screenshots ................................................................................... 10
Figure 64 SMA SMC 6000A main parameters ........................................................................ 12
Figure 65 SMA SMC 6000A secondary parameters ............................................................... 12
Figure 66 SMA SMC 6000A efficiency curve parameters ...................................................... 13
Figure 67 SMA SMC 6000A physical parameters .................................................................. 13
Figure 68 Kyocera KD135GH-2P basic data ........................................................................... 14
Figure 69 Kyocera KD135GH-2P model parameters – Shunt and series resistances ............. 14
Figure 70 Kyocera KD135GH-2P model parameters – shunt resistance characteristics ......... 15
Figure 71 Kyocera KD135GH-2P model parameters – Power temperature coefficient
characteristics ........................................................................................................................... 15
Figure 72 Kyocera KD135GH-2P Physical characteristics, diode and system voltage
parameters ................................................................................................................................ 16
Figure 73 Sungrid SG-175M5 basic data ................................................................................. 16
Figure 74 Sungrid SG-175M5 model parameters – Shunt and series resistances ................... 17
Figure 75 Sungrid SG-175M5 model parameters – shunt resistance characteristics ............... 17
Figure 76 Sungrid SG-175M5 model parameters – Power temperature coefficient
characteristics ........................................................................................................................... 18
Figure 77 Sungrid SG-175M5 Physical characteristics, diode and system voltage parameters
.................................................................................................................................................. 18
Figure 78 Sungrid SG-175M5-V basic data ............................................................................ 19
Figure 79 Sungrid SG-175M5-V model parameters – Shunt and series resistances ............... 19
Figure 80 Sungrid SG-175M5-V model parameters – shunt resistance characteristics .......... 20
Figure 81 Sungrid SG-175M5-V model parameters – Power temperature coefficient
characteristics ........................................................................................................................... 20
Figure 82 Sungrid SG-175M5-V Physical characteristics, diode and system voltage
parameters ................................................................................................................................ 21
Figure 83 Inverter and module inputs for installation one ....................................................... 21
Figure 84 Inverter and module inputs for installation two, with stings of 11 panels .............. 22
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Figure 85 Inverter and module inputs for installation two, with stings of 12 panels .............. 22
Figure 86 Thermal losses and NOCT factor used in simulations ............................................ 23
Figure 87 PVSyst hourly shading study for 28th
June 2011 from 8am to 4pm ........................ 24
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1 Appendix B
1.1 Establishment of Data Logging System
One of the objectives for this project was to establish a reliable data logging system where
information from the inverters and meteorological sensors can be stored and accessed for
analysis and educational purposes. The SMA WebBox provides a FTP Push protocol where
daily data collected from the SMA equipment is stored. Through the help of Will Stirling of the
School of Engineering and Energy, this has been established and is currently operational.
The data stored is in the form of individual 5 minute averages of measured parameters in a XML
file format which is embedded within multiple layers of compressed folders. This has posed
problems with data accessibility which, through the work of Caleb Duggan of IT Services, a
script has been created to extract these files.
Further issues have been encountered with the importation and handling of the files due the
inability of Microsoft Excel to be able to import the files without error. For these reasons,
weekly manual downloading of data from the WebBox has been undertaken throughout the
project, and is recommended to continue. The manually downloaded data is in the form of a
single Comma Separated Variable (CSV) file each day which is easily handled by MS Excel or
other spreadsheet programs or mathematical analysis software such as Matlab. It is not possible
for this to be done automatically and a reminder should be set to ensure this is done.
It is possible through access to the WebBox via the internet and the WebBox’s IP address, to
access the data from anywhere with an internet connection, with additional accessibility on
campus through direct file access over the network. Access details for both these methods are
provided on the supplied CD rom.
1.2 Data Downloading Steps
On Campus Access
Manual downloading of data while on campus can be achieved by direct FTP access to the
WebBox by double clicking on the My Network Places icon on the desktop, or My Computer. In
the address bar, enter the following address:
ftp://user:[email protected]/
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This will bring up the internal Data folder. Double click on this and the enclosed sub-folder
which contains the data files which can then be simply copied to your computer or external
drive.
Internet Access
After opening a web browser, enter the following URL to the address bar:
http://134.115.91.42/
This will take you to the web interface of the WebBox. Entre the password: sma
This password is case sensitive.
NB: For security reasons, it may be advisable to have the password changed once access is
gained. If this is done, advise the Office of Commercial Services and anyone else who has access
of the new password. This will also affect the ftp access noted above and the sma in the address
will need to be substituted with the new password.
Within the home page, click on WebBox
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Then click on Recording
Then click on Download to download all the available files for the month.
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If files of the past month are required, click on the drop menu to the left of the download button
to select the previous month and then click Download.
Data Handling
It is recommended that due to the process involved, data should be imported in batches to avoid
repetitive work when not needed. A months data is easily handled and takes little more time to
process.
Once the data is downloaded and ready to be analysed, double click on My Computer, then C
drive.
Create a new folder named CSVs (if one hasn’t already been created) and place the downloaded
CSV files within it. If previously edited files are in an old folder, remove these and archive them
or rename the old file.
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Open the MS Excel file names MACROS, this file contains all the scripts used to get the data
into a more useable format.
Then open a second blank workbook which the files will be stored in.
If macros functionality has not been enabled on this computer, this will need to be done
When enabled, click on the View tab, then Macros.
This will bring up the Macros for the data processing.
The Macros are in order of execution beginning with AMultiCSVImport. When this macro has
completed successfully, delete the final sheets not named with dates. If not, the following
macros will hit errors.
When macro D (D1dataCullEU and D2dataCullEZ), inspect the worksheets to ascertain the
final column the data is stored in. It will either be column EU or EZ. Then use the corresponding
macro.
Once macro ECombinedData has been executed, STOP. The remaining macros should only be
run for specific reasons which are explained by highlighting the macro and clicking Edit.
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Once data is downloaded and processed, the original CSV files should be archived for possible
future use or data recovery.
Data Displaying
Finding an alternative method for displaying information regarding the array was another task of
the project. The existing Sunny Portal data display is simple, static and provides little
information for people entering the library foyer
Figure 1 Existing Sunny Porta display
(lImage: SMA Sunny Portal, URL:
http://www.sunnyportal.com/Templates/PublicPageOverview.aspx?page=3c53adf2-dae5-4080-a51b-
e0a02819c968&plant=a26c7f29-3188-4db7-9a9a-a2c1392b286b&splang=en-US, Accessed 17/06/11)
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SMA has produced an alternative free software package specifically for this purpose called
FlashView.
Flashview is a dedicated display application which provides live information direct from the
WebBox, with finer information resolution and animations.
Figure 2 SMA FlashView screenshots
(Images: SMA, FlashView, URL: http://www.sma-australia.com.au/en_AU/products/software/flashview.html,
Accessed 17/06/11)
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It was hoped to have this software up and running by the completion of the project, however
approval was still being sought for it to be loaded on the dedicated display computer.
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18 Appendix F
18.1 PVsyst Component Electrical Parameters
18.1.1 SMA SMC 6000A
Figure 3 SMA SMC 6000A main parameters
Figure 4 SMA SMC 6000A secondary parameters
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Figure 5 SMA SMC 6000A efficiency curve parameters
Figure 6 SMA SMC 6000A physical parameters
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18.1.2 Kyocera KD135GH-2P
Figure 7 Kyocera KD135GH-2P basic data
Figure 8 Kyocera KD135GH-2P model parameters – Shunt and series resistances
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Figure 9 Kyocera KD135GH-2P model parameters – shunt resistance characteristics
Figure 10 Kyocera KD135GH-2P model parameters – Power temperature coefficient characteristics
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Figure 11 Kyocera KD135GH-2P Physical characteristics, diode and system voltage parameters
18.1.3 Sungrid SG-175M5 – Default Model
Figure 12 Sungrid SG-175M5 basic data
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Figure 13 Sungrid SG-175M5 model parameters – Shunt and series resistances
Figure 14 Sungrid SG-175M5 model parameters – shunt resistance characteristics
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Figure 15 Sungrid SG-175M5 model parameters – Power temperature coefficient characteristics
Figure 16 Sungrid SG-175M5 Physical characteristics, diode and system voltage parameters
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18.1.4 Sungrid SG-175M5 -V – Voltage Temperature Coefficient Adjusted Model
Figure 17 Sungrid SG-175M5-V basic data
Figure 18 Sungrid SG-175M5-V model parameters – Shunt and series resistances
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Figure 19 Sungrid SG-175M5-V model parameters – shunt resistance characteristics
Figure 20 Sungrid SG-175M5-V model parameters – Power temperature coefficient characteristics
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Figure 21 Sungrid SG-175M5-V Physical characteristics, diode and system voltage parameters
18.1.5 PVsyst Model Parameters
Figure 22 Inverter and module inputs for installation one
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Figure 23 Inverter and module inputs for installation two, with stings of 11 panels
Figure 24 Inverter and module inputs for installation two, with stings of 12 panels
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Figure 25 Thermal losses and NOCT factor used in simulations
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19 Appendix G
19.1 PVsyst Shading Study
Figure 26 PVSyst hourly shading study for 28th
June 2011 from 8am to 4pm
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20 Appendix I
Appendix I can be found on the attached CD Rom as the digital Appendices.
Headings have been kept as reference and for the table of contents.
20.1 AS 5033 Compliance Notes
§ 1.1 Scope
The MULPVS falls in under the 600 V scope and is therefore not affected.
Table 2.1 Number of parallel strings without OC protection
Current standards use IMOD REVERSE , with recommendations for the use of the maximum fuse
rating.
Installation 1:
Limiting reverse current is stated as 15 A and has been assumed to refer to the max fuse rating,
with the short circuit current being 8.37 A. Using table 2.1 and 2 parallel strings per inverter, we
obtain:
Therefore, OC protection is NOT required.
Installation 2:
Short circuit current rating is 5.48 A, with a Series fuse rating of 10 A (assuming this is fuse max
rating), with 3 parallel strings per inverter, we obtain:
Therefore, OC protection is required as two times the short circuit current is greater than the
reverse current carrying capacity of the modules.
OC protection, as well as DC isolation and fuse protection, is installed as one component, being
an ABB DC isolation switch (ABB S802PV, S20, 800 Vdc) installed on each string and
therefore complies.
1 ISC IFUSEMAX 2 ISC
8. 37A 15A 16. 74A
2 ISC IFUSEMAX 3 ISC
10. 96A 10A 16. 44A
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§ 2.5.4 ELV Segmentation
Installation 1 has been installed with M/C connections every 5 panels, limiting voltage at STC to
110.5 V.
Installation 2 is not clear on whether or not ELV sectionalisation has been incorporated into the
system. However, module cables with removable connectors may be considered acceptable.
§ 3.3.3 Temperature Rise
As recommended by AS4502, PV arrays are assumed to operate at 25°C above ambient.
However, data obtained from the array Sensorbox shows temperatures regularly reaching well in
excess of 70°C (with a maximum of 77°C), more than 30°C above ambient, with occasions
greater than 40°C above ambient.
When factoring this into module performance,
Kyocera (using -0.42%/°C)
Sungrid (using -0.47%/°C)
So the reduction in cell performance is regularly between 19% and 22%.
Two factors play a key part to this. The first being that the array is fixed on top of the metal roof
sheeting, which provides minimal air ventilation to the rear of the panels. The second being the
arrays sheltered position from cooling breezes. As the array faces north, with many buildings
surrounding the Bush Court area, wind is substantially lower than experienced at the Murdoch
Meteorological (MET) station, with differences up to 5.3 m/s (19 km/h) seen, at an average of
1.4 m/s (5.2 km/h). It should be noted that the Sensorbox, with the wind anemometer, ambient
and module temperature sensors, is located on the eastern end of the library roof where it has
more exposure from southerly to south easterly winds.
Temperature Derating Tmod TSTC PDeratingFactor
Temperature Derating 70 25 0. 42%
Temperature Derating 18. 9% max 21. 84% at 77°C
Temperature Derating 70 25 0. 47%
Temperature Derating 21. 15%max 22. 44% at 77°C
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This may result in lower ambient and also cell operating temperatures than the majority of the
modules installed. Modules mounted centrally on the library roof would experience less breeze
and reduced ventilation, as well as higher temperatures from radiation and convection from
surrounding modules. This has the potential to result in temperatures above 80°C on a regular
basis through summer months, giving losses in the order of:
Kyocera (using -0.42%/°C)
Sungrid (using -0.47%/°C)
So as can be seen, temperature regulation plays a key role in maximising the performance of
roof mounted PV arrays.
§ 4.5 Fuses
Both installations uses a combination DC isolator, OC protection and fuse in one unit per string.
Temperature Derating 80 25 0. 42% 23. 1%
Temperature Derating 80 25 0. 47% 25. 85%
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21 Appendix J
21.1 Solar Unlimited Cable Calculations
Data is not available for connector cables on SunGrid panels. Information has been requested
from the manufacturer and calculations will be done when received.
Cable Technical Data
DC Circuit breakers = 20 A/sub-array No. of strings = 2 Strings/sub-array No. of string cables/sub-array = 4 No. of cables Total = 30 DC String Cable Used = 6mm2 Cu Single Core at 90°C DC Sub-Array Cable Used = 10mm2 Cu Single Core at 90°C AC Circuit Breaker = 32 A AC Cable Used = 4mm2 Cu Twin Core at 90°C
String Cables
Assumptions:
All cables are spaced from surface
Cable type according to AS3008.1.1:2009 = X90
All cables bunched. Worst case, 4 cables when close to junction boxes, giving derating of
0.65
Thermal derating for X90 (90°C) cable operating at 60°C, giving a derating of 0.73
Longest cable run = 43.28 m (Solar Unlimited)
Calculations based on short circuit current
Current Carrying Capacity
Current carrying capacity of 4m m2 (nearest to 3.3mm
2) X90 spaced from surface = 48 A
Derating for 4 cables at 60°C:
(Assuming: ‘Bunched on a surface or enclosed’ according to AS3008.1.1, Table 22)
Therefore, cables are adequately sized for current capacity.
Icable,derated Tderating ncable,derating Icable,rating 0. 73 0. 63 48 22. 0752A
Istring,max 1. 25 Isc 1. 25 8. 37 10. 4625A
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Maximum operating temperature for cables:
Using Table 27 of AS3008.1.1 gives Tmax = 80 °C
With module operating temperature approaches 80°C, this still should be considered acceptable
as cables are shaded from direct sun and should operate below module operating temperature.
Sub-Array Cables
Assumptions:
All cables are enclosed in conduit/ducting
Cable type according to AS3008.1.1:2009 = X90
All cables bunched. Worst case, 8 cables when close to inverters, giving derating of 0.52
Thermal derating for X90 (90°C) cable operating at 60°C, giving a derating of 0.73
Longest cable run = 11.75 m (Solar Unlimited)
Calculations based on circuit breaker rating, short circuit current and max power point
current
Current Carrying Capacity
Current carrying capacity of 10mm2 X90 enclosed in air = 65 A
Derating for 8 cables at 60°C:
(Assuming: ‘Bunched on a surface or enclosed’ according to AS3008.1.1, Table 22)
Therefore, cables are adequately sized for current capacity.
Maximum operating temperature for cables:
Dtemp,max Istring,max
nderatingIrated 1.258.37
0.6348 0. 346
Icable,derated Tderating ncable,derating Icable,rating 0. 73 0. 52 65 24. 674A
Isubarray,max 1. 25 2 Isc 1. 25 2 8. 37 20. 825A
Dtemp,max Istring,max
nderatingIrated 28.37
0.5265 0. 495
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Using Table 27 of AS3008.1.1 gives: 70 < Tmax < 75 °C
With module operating temperature approaches 80°C, this still should be considered acceptable
as cables are shaded from direct sun and should operate below module operating temperature.
Voltage Drops and Power Losses
Calculations carried out by Solar Unlimited were conducted using higher resistance cables than
X 90 from AS 3008. Therefore, are a worse case and are adequate.
Losses were calculated at 0.992 % and therefore conform to Australian Standards and Clean
Energy Council Guidelines.
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21.2 Solar PV Cable Calculations
Data is not available for connector cables on SunGrid panels. Information has been requested
from the manufacturer and calculations will be done when received.
Cable Technical Data
DC Circuit breakers = 10 A/string No. of strings = 3 Strings/sub-array No. of cables/sub-array = 6 No. of cables Total = 30 DC String Cable Used = 4mm2 Cu Single Core at 90°C AC Circuit Breaker = 32 A AC Cable Used = 6mm2 Cu Twin Core at 90°C
Assumptions:
All cables are enclosed in conduit/ducting
Cable type according to AS3008.1.1:2009 = X90
All cables bunched. Worst case, 30 cables when close to inverters, giving derating of
0.38
Thermal derating for X90 (90°C) cable operating at 60°C, giving a derating of 0.73
Longest cable run = 70 m (based on longest run from Solar Unlimited being 43.28 m)
Calculations based on circuit breaker rating, short circuit current and max power point
current
Current Carrying Capacity
Current carrying capacity of 4mm2 X90 enclosed in air = 38 A
Derating for 30 cables at 60°C:
(Assuming: ‘Bunched on a surface or enclosed’ according to AS3008.1.1, Table 22)
Therefore, cables are adequately sized for current capacity.
Icable,derated Tderating ncable,derating Icable,rating 0. 38 0. 73 38 10. 54A
Istring,max 1. 25 I_sc 1. 25 5. 48 6. 85A
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Maximum operating temperature for cables:
Using Table 27 of AS3008.1.1 gives Tmax = 75°C
With module operating temperature approaches 80°C, this still should be considered acceptable
as cables are shaded from direct sun and should operate below module operating temperature.
Voltage Drops
Resistance of 4mm2 X90 at 90°C = 5.88 Ω/km
Reactance of 4mm2 X90 at 90°C = 0.131 Ω/km
R>>X, therefore X ignored
Resistance for longest run:
Circuit breaker current voltage drop:
Short circuit current voltage drop:
Max power point current voltage drop:
Voltage at max power point: = 11 x Vmpp = 11 x 35.2 = 387.2 V
%voltage drop for 11 panels (worst case):
Percentage voltage drop at circuit breaker rated current:
Dtemp,max Istring,max
nderatingIrated 6.85
0.3838 0. 474
Rmax 5.888
100070 0. 4116Ω
Vdrop,cb Icb R 10 0. 4116 4. 116V
Vdrop,sc Isc R 5. 48 0. 4116 2. 256V
Vdrop,mpp Impp R 4. 97 0. 4116 2. 046V
Vmpp,array Vmpp npanels 35. 2 11 387. 2V
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Percentage voltage drop at short circuit current:
Percentage voltage drop at maximum power point:
Power Loss
Circuit breaker current power loss:
Short circuit current power loss:
Max power point current loss
% power loss for 11 panels per string (worst case):
Power losses at circuit breaker rated current:
Power losses at short circuit current:
Power losses at maximum power point:
%Vdrop,cb Vdrop,cb
Vmpp,array 100% 4.116
387.2 100% 1. 063%
%Vdrop,sc Vdrop,sc
Vmpp,array 100% 2.256
387.2 100% 0. 538%
%Vdrop,mpp Vdrop,mpp
Vmpp,array 100% 2.046
387.2 100% 0. 528%
Ploss,cb Icb2 R 102 0. 4116 41. 16W
Ploss,sc Isc2 R 5. 482 0. 4116 12. 36W
Ploss,mpp Impp2 R 4. 972 0. 4116 10. 17W
%Ploss,cb Ploss,cb
nPrated 100% 41.16
11175 100% 2. 138%
%Ploss,sc Ploss,sc
nPrated 100% 12.36
11175 100% 0. 642%
%Ploss,sc Ploss,sc
nPrated 100% 10.17
11175 100% 0. 528%
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Using both short circuit current and maximum power point losses, the cable selection is
considered acceptable.
Inverter to Switchboard
Cable installed is 6mm2 Cu Twin Core at 90°C
Assumptions:
Cable length assumed as 12 m as must run overhead to switchboard
All inverter cables run in same conduit, therefore 10 cables with derating of 0.54
As cable is indoor, maximum operating temperature should not exceed 35°C, giving a
derating factor of 1.05
Current Carrying Capacity
Current carrying capacity of 6mm2 X90 enclosed in air = 47 A
Derating for 10 cables at 35°C:
(Assuming: ‘Bunched on a surface or enclosed’ according to AS3008.1.1, Table 22)
As inverter output is 6.0 kW, current output is:
Therefore cable selection is only just adequate. However, normal temperature is expected to be
less than 35°C, which would increase current carrying capacity.
Voltage Drops
Resistance of twin core 6mm2 X90 at 45°C = 3.38 Ω/km
Reactance of twin core 6mm2 X90 = 0.114 Ω/km
R>>X, therefore X ignored
Icable,derated Tderating ncable,derating Icable,rating 1. 05 0. 54 47 10. 54A
Imax Pinverter,max
Vgrid 6000
240 25A
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Resistance of cable (12m)
Voltage Drops:
Circuit Breaker (32A):
Inverter max (25A):
Percentage voltage drop for CB:
%Voltage drop for Inverter:
Power Loss
Circuit Breaker (32A):
Inverter max (25A):
%Power loss for CB:
%Power loss for Inverter max:
Rmax 3.38
1000 12 0. 04056Ω
Vdrop,cb Icb R 32 0. 04056 1. 298V
Vdrop,Inv,max IInv,max R 25 0. 04056 1. 014V
%Vdrop,cb Vdrop,cb
Vgrid 100% 1.298
240 100% 0. 541%
%Vdrop,Inv,max Vdrop,Inv,max
Vgrid 100% 1.014
240 100% 0. 423%
Ploss,cb Icb2 R 322 0. 04056 41. 53W
Ploss,Inv,max IInv,max2 R 252 0. 04056 25. 35W
%Ploss,cb P loss,cb
PInv,rated 100% 41.53
6000 100% 0. 692%
%Ploss,cb Ploss,Inv,max
PInv,rated 100% 25.35
6000 100% 0. 423%
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Totals
Total %voltage drop at mpp:
Total %power loss at mpp:
Therefore, the cable selections are adequate and conform to Australian Standards and Clean
Energy Council Guidelines.
%Vdrop,mpp,total %Vdrop,mpp,array %Vdrop,mpp,invsb 0. 528 0. 423 0. 951%
%Pdrop,mpp,total %Pdrop,mpp,array %Pdrop,mpp,invsb 0. 528 0. 423 0. 951%
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22 Appendix K
22.1 Shading Study Photos for May 22 2011
9am (photos from 23 May 2010 due to cloud cover at 9am may 22 2010)
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10 am
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11 am
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12 noon
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1 pm
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2 pm
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44
3 pm
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4 pm
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23 Appendix L
23.1 Afternoon Shading Study for December 2011