Can I Accurately Model PV System Performance for Dual MPPT Inverters with SAM?

Hello,

Many residential solar energy systems use dual-MPPT inverters with dissimilar strings landed on each DC input. Can this be modeled using SAM (either through the UI or SamUL)? Through the UI it seems I'm only able to model systems with even stringing (e.g. two strings of 10 modules). For example how would one model a Power-One 4200 inverter with a string of 11 modules facing west on MPPT1 and a string of 9 modules facing south on MPPT2, each MPPT having a unique shade profile?

If this functionality is not available then I would kindly like to submit this as a feature request.

Thanks so much,
Noah Ginsburg

Hi Noah,

If you model a PV system with the Flat Plate PV model that has two subarrays, SAM assumes that each subarray operates at its maximum power point, and that both subarrays are connected to the same inverter or bank of inverters. That should accurately represent the scenario you describe. If you provide a separate shading scene for each subarray, SAM will adjust each subarray's incident radiation to account for losses due to shading.

Best regards,
Paul.

Hi Paul,

Thanks for your response. I attempted this technique and I'm able to allocate strings to subarrays with unique tilt/azimuth/shading, but it seems the strings must all have the same number of modules (Modules per String and Strings in Parallel are defined on the Array).

Is it possible to model performance for a system with a dual MPPT inverter powered by one string of 11 modules and another string of 9 modules?

Best regards,
Noah Ginsburg

Hi Noah,

That is a limitation of SAM -- the flat plate PV model assumes that all PV subarrays have the same number of modules per string because it only models a single inverter or bank of inverters, and it assumes that the system has a single MPPT component.

Sorry about my misleading earlier reply.

Best regards,
Paul.