Using polystring interconnection, completely different PV modules or strings can be connected in parallel or in series to an MPP tracker. This opens up new possibilities of configuration:
A polystring circuit can only be defined manually, it is not available in the circuit proposals.
If the Polystring interconnection is selected, new strings can be defined for an MPP tracker using the button. The strings are connected in parallel as standard. Various strings can be connected in series by clicking on the Connect strings in series button. The series connection can also be combined with a parallel connection, as the following example (Figure: Polystring connection: Example series connection) illustrates.
Here 2 strings are connected in parallel on an MPP tracker. String 1 consists of two strings connected in series with 10 modules each and string 2 also consists of 10 PV modules. Accordingly, 20 and 10 modules are connected in parallel.
This wiring serves as an example and should not be implemented in practice.
Since a wide variety of modules or strings are interconnected in a polystring circuit, the configuration check changes.
For system checks, the strings with the lowest MPP voltage and the highest MPP voltage are checked for parallel strings. If different PV modules are connected in a string, the module with the highest MPP current serves as a guideline for system testing.
If the MPP voltages between the strings differ by more than 4%, the wiring is within the tolerance range . However, if the MPP voltages between the strings differ by more than 10%, the wiring is in the blocking range. . The same limits apply to different currents in one string.
Using the polystring circuit also changes the circuit diagram. Parallel strings are connected together in front of the inverter (connection point circle). Series connections with different sub-strings are connected together to form a string, this is indicated by arrows and letters.