The string inverter is a key device used in solar power generation systems. It is responsible for converting the DC power generated by the solar panels into AC power, which can be used in the power grid or stored in batteries. Compared with traditional single-channel inverters, string inverters allow multiple solar panels to be connected in series to the same inverter, which can improve the efficiency, flexibility and reliability of the system.

the following key factors in calculating the number of PV panels in the string inverter

  1. Rated power of the inverter: First, you need to determine the rated power of the string inverter you are using, usually in kilowatts (kW). This determines the maximum power the inverter can handle.
  2. Solar panel power and voltage ratings:Next, review the solar panel specifications to find the power and voltage ratings of each panel. Power ratings are usually measured in watts (W) and voltage ratings are usually measured in volts (V).
  3. Total voltage of the string:When multiple solar panels are connected in series to the same inverter, the total voltage of the formed string must be within the range that the inverter can handle. The total voltage is equal to the rated voltage of each panel multiplied by the number of panels in series.
  4. Total power of the string:Similarly, the total power of the string also needs to be within the rated power range of the inverter. The total power is equal to the power rating of each panel multiplied by the number of panels in series.
  5. Maximum input voltage and maximum input current of the inverter: Ensure that the total voltage and total current of the string do not exceed the maximum input voltage and maximum input current specified by the inverter, otherwise it will affect the performance of the inverter or even damage the inverter device.

The following steps to calculate the number of solar modules in a string:

  1. Determine the power rating of the string inverter used.Determine the installation capacity of the solar photovoltaic panels.
  2. Check the technical specifications of the solar panel, including power rating and voltage rating.

3. Calculate the total voltage and total power of each string to ensure they are within the specified range of the inverter.

4. Check whether the total voltage and current of the string are within the maximum input voltage and maximum input current range of the inverter.

5. Adjust the number of solar panels in a string until the requirements of the inverter are met.

Through the above steps, you can determine the appropriate number of components to be connected in series in a string to ensure stable operation and efficient performance of the solar power generation system.

For 110kW inverter as an example

For 110kW inverter as an example to explain how to confirm the number of solar modules in the string .

Suppose we have an inverter with a rated power of 110kW, and each solar panel has a rated power of 400W and a rated voltage of 40V.

First, we need to determine the maximum input voltage and maximum input current of each inverter. This information can usually be found in the inverter's technical specifications or data sheet.

110kW inverter datasheet

The maximum input voltage of the inverter is 1000V and the maximum input current is 234A . The number of MPPTs is 2, and each MPPT can connect to 9  strings. So there are 18 strings of inverter.

Calculate the number of series solar modules of string.

Next, we calculate how many series solar panels there are for each string of the inverter.

  1. Calculate the total power for each string:The rated power of the inverter is 110KW, and the installed capacity of the photovoltaic panels is usually 1.3 times the rated capacity of the inverter. Total pv installed capacity =1.3 * 110kW=143kW.

Therefore, the inverter has a total of 18 strings, and the total power of each string is 143 KW / 18 = 7.9 KW.

  1. Calculate the total voltage of each string: Suppose the number of solar panels we want to connect in series is N. The total voltage is equal to the voltage rating of each board multiplied by the number of boards in series. Assuming each board is rated at 40V, the total voltage is 40V * N.
  1. Check whether the total voltage and total current of each string are within the maximum input voltage and maximum input current range of the inverter.
  • Total voltage: According to the inverter parameter requirements, the total string voltage must be greater than the starting voltage, greater than the normal operating voltage of the inverter.

Total current: Calculate the total current, that is, the rating of each board Power divided by rated voltage multiplied by the number of boards in series.

The caculate of PV modules
  1. Adjust the number of series-connected panels: Determine the number of series-connected solar panels in each string according to the specifications and requirements of the inverterand the maximum number of roofs installed in a photovoltaic power station.

Through the data summary analysis of the inverter, it is possible to determine how to group the strings so that the solar power generation system can maximize the use of the inverter's capacity while ensuring the stability and safety of the system.

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