The inverter size includes two parts: voltage and current size. When adjusting the size of the inverter, different configuration restrictions need to be considered
Solar panel type: TSM-PD14 320 W solar inverter type: SMA Sunny Boy 6000-US
Open circuit voltage VOC = 45.8 V maximum. Input voltage Vmax = 600 V
Maximum power supply voltage VMPP (STC) = 37.1 MPPT voltage range: 250 V-480 V
The temperature coefficient of VOC = -0.32%/°C maximum. Input current = 25 A
ISC temperature coefficient = 0.05%/°C
Short circuit current ISC = 9.10 A
Minimum temperature: -10°C
Maximum temperature: 70°C
Voltage adjustment
At the lowest temperature (depending on the location, here is -10°C), the open circuit voltage U oc of the modules in each string must not exceed the maximum input voltage of the inverter (600 V):
1) Calculation of open circuit voltage at -10°C:
U OC (-10°C) = ((1-(35 * (TC OC / 100))) * U OC STC) = ((1-(35 * (-0.32 / 100))) * 45.8)
= 50.93 volts
2) Calculate the maximum number of N modules in each string:
N = maximum input voltage (600 V) / 50.93 volts = 11.78 (always rounded down)
The number of solar photovoltaic panels per string must not exceed 11 modules
In addition, at the highest temperature (depending on the location, here is 70°C), the MPP voltage V MPP of each string must be within the MPP range of the solar inverter (250 V – 480 V):
3) Calculate the maximum power supply voltage VMPP at 70°C:
V MPP (70°C) = ((1+(45 * (TC OC / 100))) * V MPP (STC)) = ((1+ (45 * (-0.32 / 100))) * 37.1)
= 31.76 volts
4) Calculate the minimum number of modules M in each string:
M = lowest MPP voltage (250 V) / 31.76 volts = 7.87 (always rounded up)
The number of solar photovoltaic panels in each string must be at least eight modules.
B) Current size
The short-circuit current I SC PV array must not exceed the maximum allowable input current of the solar energy converter:
1) Calculate the maximum current at 70°C:
U SC (70°C) = ((1 + (45 * (TC SC / 100))) * I SC) = ((1 + (45 * (0.05 / 100))) * 9.1)
= 8.89A
2) Calculate the maximum number of strings of P:
P = maximum input current (25A)/8.89 A = 2.84 string (always rounded down)
PV array must not exceed two strings
