How can I simulate a PV design with not the same number of modules in each string?

SAM assumes that all modules in the PV array are connected either to a single inverter or to a bank of identical inverters with a single input. For that reason, all subarrays must have the same number of modules per string to maintain a single voltage level.

You could use the "Combine Cases" macro to model your system, or you could model Subarray 3 with 11 modules. To use the macro, you would create a separate case for each subarray, and a fourth case using the generic system model for the financial inputs. See the instructions provided with the macro for details.

UPDATE: As of SAM 2021.12.02, the Combine Cases macro is replaced by the Calculate generation profiles and nameplate capacity from open cases option on the Power Plant page for the Generic System model and Generic Battery model. See the SAM YouTube channel for a short tutorial .

Best regards,
Paul.

As of SAM 2018.11.11, the Detailed Photovoltaic model supports inverters with up to four MPPT inputs, which means that you can model a system with up to four subarrays with different string lengths without using the Combine Cases macro. Each string operates at its own voltage, so voltage clipping losses are modeled in a more realistic way than in previous versions of SAM.

Best regards,
Paul.