String Configuration of HT1100V
(SA-E-20220315-002)
Background
Many project designers have some doubts about the string configuration. How many PV modules
should be connected to each PV string? Normally, we should ensure that the temperature-adjusted
string voltage is within the input voltage window of the inverter. Actually, there are more points we
need to consider.
This article will focus on the GW100K-HT models to facilitate the project design.
In this design, LONGi's latest product LR5-72HBD 520M is used as an example. The specifications
are as follows, and assume the ambient temperature is - 20 ~ 40°C
Electrical characteristics
LR5-72HBD 520M (STC)
Open Circuit Voltage(Voc/V)
Short Circuit Current(Isc/A)
48.9
13.57
Voltage at maximum power(Vmp/V)
Current at maximum power(Imp/A)
41.05
12.67
Temperature coefficient (�� ) of Voc
Temperature coefficient (���)of Isc
-0.284%/°C
+0.050%/°C
Electrical characteristics
GW100K-HT
No. of independent MPPT inputs
Max. number of input connector per MPPT
Max. PV input current/string(A)
10
2
15
Max. PV input current/MPPT(A)
Max. input DC voltage(V)
MPPT voltage range for nominal power(V)
30
1100
500~850
The inverters’ spec is as below:
1. String current
It is required that the current of each string (���)should be less than the Max. input current (����)
of the inverter: ��� ≤ ����. Considering the low effect of the temperature on the current and the
8% back generation of the modules, the maximum current Imp (max) is about 12.67 * (1 + 8%) =
13.69A, which is also lower than the maximal input current 15 A of one string of GW100K-HT. So it
meets the first condition.
2. Input voltage
Usually, the Voc of the string should be less than the maximum DC voltage of the inverter. In addition,
it is required that the Vmp voltage of the string should be within the MPPT voltage range for full load.
1
String Configuration of HT1100V
(SA-E-20220315-002)
That means that the voltage should meet the following two conditions:
��� ��� = � ∗ � + � − ��°� ∗ �� ∗ ��� ≤ ����
�������� ≤ ��� ∗ � ≤ ��������
The Voc of the LR5-72HBD-520M module is as below
Voc(max)= [1+(-20-25)*-0.284%]*48.9=55.15V
The Max. input DC voltage of GW100K-HT is 1100V, MPPT voltage range for full load is 500V~850V.
And the number of modules of each string should meet:
n < {Max input DC voltage / Voc(max)} → n< 1100/55.15=20
(500/Vmp) < n < (850/Vmp) → (500/41.05) < n < (850/41.05) → 13≤n≤20
Then the number of modules for one string should be 13 to 20.
In addition,DC bus voltage must be higher than the grid peak voltage (�� ) to ensure the the inverter
circuit can work normally. Furthermore, the ripple on the sampling and capacitance will also be
considered. After detailed investigation and laboratory verification tests,
the best Input voltage of the HT100K, HT110K and HT120K should be 650V.
the best input voltage for HT136K should be 750V due to the higher gird voltage.
Then we can calculate the number of the modules per string for the HT100K is:
� = ����/��. ��� = ��
Advantages of 16 modules per string
High Efficiency
When we connect 16 modules per string to the inverter, the input voltage of the inverter is 650V, and
when we connect 20 modules, the input voltage is 850V. With the input voltage of 650V, the efficiency
can reach the maximum value, which is higher than the efficiency at 850V. Higher efficiency can also
bring higher power production.
higher utilization of MPPT
2
String Configuration of HT1100V
(SA-E-20220315-002)
The following table shows the max. DC/AC ratio that the system with 16 modules and 20 modules
per string can reach.
Max. DC capacity (520W module)
Max. DC/AC ratio
16 modules per string
166.4kW
1.664
20 modules per string
208.0kW
2.08
That means either 16 modules or 20 modules per string can meet the requirement of the DC/AC ratio.
When we set the DC/AC ratio of about 1.2, then we can calculate the number of the strings under the
same system capacity.
Number of strings
Real DC capacity
16 modules per string
20 modules per string
15
12
124.8kW
124.8kW
Here we can see that if we connect 16 modules per string, we can connect 15 strings for the inverter.
That means we can connect more MPPTs compare to 20 modules per string. Therefore, the system
is less affected by the failure of one string, such as shadow. And more MPPT can be applied to a
wider range scene, including different toward and inconsistent modules.
More Economic
Then trough the simulation of PVsyst and the calculation we can see the extra wiring cost of the 16
modules solution can be offset by the 2 years more power generation.
16 modules
20 modules
Price difference
Produced Energy
226MWh/year
223MWh/year
Electric price
0.45rmb/kWh
0.45rmb/kWh
Profit per year
101700rmb/year
100350rmb/year
1350rmb/year
DC wiring
2104.81m
1401.72m
Wiring price per meter
3.5rmb/m
3.5rmb/m
Wiring price
7366.8rmb
4906.0rmb
2460.8rmb
That means 16 modules per string can make more profit.
In summary, 16 modules per string, i.e, the input voltage of the inverter of 650V is the best string
configuration solution for HT100K.
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