1. “DESIGN OF GRID-CONNECTED PV SYSTEM”
Oleh
TUNKU MUHAMMAD NIZAR BIN TUNKU MANSUR
PPK SISTEM ELEKTRIK

2. METHODOLOGY 1 2 3 4 Undertaking a thorough site audit
Determining the system sizing
Selecting and matching the individual components
Determining location for installation of the components 4
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3. UNDERTAKING SITE SURVEY
To determine the solar access for the site.
To determine whether any shadowing will occur and estimating its effect on the system
Estimating the solar resource for the site.
To determine the available space for the PV array.
To determine whether the roof is suitable for mounting the PV array.
To determine how the modules are mounted on the roof.
To determine where the switchboard is located, where the inverter, and junction boxes will be installed, cabling route and therefore estimate the lengths of the cable runs.
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4. SOLAR ACCESS TO THE SITE
The solar access could be reduced due to:
Natural landscapes such as mountains or hills.
Trees or other vegetation.
Other buildings.
Parts of the actual building where the system will be located such sections of roof, TV aerials.
Needs to consider future development of the site that may block the solar access.
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5. SOLAR RESOURCES AT THE SITE
This irradiation varies as a result of:
Tilt Angle of the array.
Direction the array is facing.
Shading effect of objects.
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6. HOW PV ARRAY ARE MOUNTED ON THE ROOF
Retrofit
Building Intergrated
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7. AVAILABLE SPACE ON THE ROOF
Calculating available space area and number of PV module that could fit on the roof.
Arrangement of PV Module either length-wise up or length-wise across.
Length-wise Up
Length-wise Across
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8. CALCULATING MAXIMUM NUMBER OF PV MODULE THAT COULD BE INSTALLED BASED ON ARRANGEMENT
Length-wise Across
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9. CALCULATING MAXIMUM NUMBER OF PV MODULE THAT COULD BE INSTALLED BASED ON ARRANGEMENT
Length-wise Up
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10. Other factor to consider Gap spacing between PV modules.
CALCULATING MAXIMUM NUMBER OF PV MODULE THAT COULD BE INSTALLED BASED ON ARRANGEMENT
Other factor to consider
Gap spacing between PV modules.
Offset spacing for PV array from all edges of roof.
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11. MATCHING THE INVERTER WITH THE PV ARRAY
The PV array power output to the inverter power rating is calculated as
Where
Pnom_inv = inverter nominal power (W)
Parray_stc = peak power rating of the PV array (W)
k = de-rating factor
The optimal size value of k is depends on the type of PV technology but regardless type of mounting structure.
for crystalline PV array : 0.90 ≤ k ≤ 1.00
for thin film PV array : 1.10 ≤ k ≤ 1.30
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12. MATCHING THE INVERTER WITH THE PV ARRAY
The minimum and maximum number of PV modules could be calculated based on optimal range of de-rating factor.
Where
Pnom_inv = inverter nominal power (W)
Pmod_stc = peak power rating of the PV module (W)
k1 = upper limit of de-rating factor
k2 = lower limit of de-rating factor
for crystalline PV array : k1 = 1.00, k2 = 0.90
for thin film PV array : k1 = 1.30, k2 = 1.10
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13. MATCHING THE INVERTER WITH THE PV ARRAY
It is acceptable to design with a slightly oversized inverter than the recommended range. However, if the inverter is undersized, it will limit the power transferred to the grid and it is a waste of energy.
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14. PV ARRAY SIZING BASED ON INVERTER
INVERTER (AMBO CHART)
Vmax_inv
0.95 × Vmax_inv
Vmin_mpp_inv
Vmax_mpp_inv
1.1 ×Vmin_mpp_inv
Idc_inv
INVERTER MPP VOLTAGE RANGE
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15. MINIMUM NO. PV MODULES PER STRING
The minimum MPP voltage of the module will occurs during the highest cell temperature normally at noon.
Assign a voltage drop of 5% in cables from the array to the inverter DC input. Assume the inverter is located very close to the point of connection to grid. Hence the Minimum Effective Voltage from the module at the inverter DC input is:
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16. MINIMUM NO. PV MODULES PER STRING (continue 1)
Assign a Safety Margin of 10% above minimum window voltage of the inverter DC input to get the lowest allowable voltage input into the inverter.
Hence the minimum no. of modules per string is determined by:
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17. MAXIMUM NO. PV MODULES PER STRING
In the early morning, the cell temperature will be low because the module still not heat up by the sun. The maximum open voltage of the module is given by
Assign a safety margin of 5% below the maximum input voltage of the inverter. Since we are calculating maximum open circuit voltage, then there will be no current, hence no voltage drop between the array and the inverter.
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18. MAXIMUM NO. PV MODULES PER STRING (continue 1)
The minimum no. of modules per string is determined by:
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19. MAXIMUM NO. OF PARALLEL STRING
Normally grid-connected inverter has maximum allowed limit for DC current input. This data normally provided by the manufacturer in the datasheet.
A oversized current factor of 1.25 is used as safety factor in the calculation as below.
Where
Np_max = maximum number of parallel string
Idc_inv_max = maximum DC input current into inverter
Isc_stc = short circuit current of a string at STC.
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20. CHECKING THE DESIGN
Check number of PV modules per string are within the maximum and minimum range calculated.
Check number of parallel string is within the permissible range calculated.
Determine the optimal array configuration.
Check the PV array size is within the optimal range, k.
Check the string voltage not exceeding the maximum system voltage of the PV module.
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21. PREDICTION OF SYSTEM PERFORMANCE
The estimation of the predicted performance of PV system that has been designed is a useful indicator for all parties involved in the PV system project.
Normally system performance indicator used is as follow:
Yield of the system
Specific yield
Performance ratio.
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22. ENERGY YIELD
Energy Yield (Esys) is the amount of energy generated by the PV system.
It can be reported as an annual yield, monthly yield or even daily yield.
Energy Yield is given by:
where
Esys = PV system yield (kWh)
fdirt = dirt de-rating factor
ƞpv_inv = cable efficiency
ƞinv = inverter efficiency
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23. ENERGY YIELD (continue 1)
fmm = module mismatch or power tolerance factor
PSHperiod = PSH value for the specified tilt angle over the
period of interest (h)
ftemp_avg = de-rating factor due to the temperature
Where
γPmp = temperature coefficient for Pmp (% per oC)
Tcell_avg = average daily maximum cell temperature (oC)
Tstc = cell temperature at STC (oC)
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24. ENERGY YIELD (continue 2)
In the context of predicting the energy yield, the calculation of Tcell_avg should be done as below.
In the case of NOCT and irradiance value are available
Where
Tamb_avg_max = average daily maximum ambient temperature (oC)
NOCT = given by the manufacturer (oC)
Gamb_avg_max = average daily maximum solar irradiance (Wm-2)
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25. ENERGY YIELD (continue 3)
In the case of only average maximum ambient temperature Tamb_avg_max available
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26. SPECIFIC YIELD
Specific Yield (Yf) is another system performance indicator that normalizes the different system capabilities.
Specific Yield is given by:
The unit is in kWh per kWp, which represent the number of hours that PV array would need to operate at its rated power to provide energy Esys.
For Malaysian climate, the acceptable value for Yf should be more than 1,000 kWh per kWp.
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27. PERFORMANCE RATIO
Performance ratio (PR) is system performance indicator that takes into account almost all factors involved.
Performance ratio is given by:
It is unitless and sometimes is represented in percentage. It indicates the overall effect of losses on the rated output.
For Malaysian climate, the acceptable value for PR should be more than 70%.
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28. ENERGY COST AND PAYBACK PERIOD
With the implementation of the Feed-in Tariff (FiT), the PV energy producer known as Feed-in Approval Holder (FiAH) could enjoy selling their energy produced from the PV system to the utility (Distribution Licensee) such as TNB.
The tariff rate is available at SEDA website and depends on the size of installation, where it is installed and either made locally or not.
In general the components of the FiT rates are as follow:
Basic rate
Bonus rate
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29. FiT RATES FOR SOLAR PV (INDIVIDUAL)
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30. FiT RATES FOR SOLAR PV (NON-INDIVIDUAL)
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31. EXAMPLE FOR 4kW PV SYSTEM
Estimated current cost per 1kW of the system = RM10,000
Estimated available sun hours per day = 5 (average daily)
For the installation of a 4kW system with installation in a building structure, the FiT rates will be: =  RM  per kWh.
The investment is 4 kW x RM10,000 = RM40,000
The energy produced by the system per month is:
 = 4kW x 5 hours of peak sun per day x 30 days per month  = 600 kWh per month
Payment of FiT per month = 600kWh x RM per kWh   = RM 740
Number of month to payback = RM40,000 / RM740 = 54 months (around 5 years)
In this example, the payback period is around 5 years. In 6th year, profit begins and enjoy until 21st year.
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