Dual MPPT

How can I model a PV system that has three orientations using a Dual MPPT inverter? Specifically, I wanted to do an East/West Split on MPPT one, with 1 string on each (2 strings total). Followed by 2 strings on MPPT 2 at an azimuth of 180. How can I ensure that when I set up the sub-arrays SAM will distribute the system the way I intended it to be distributed?

When you model a PV system with more than one subarray, SAM assumes that each subarray in the system operates at its maximum power point.

When subarrays have different maximum power voltages (Vmp) because of their different orientations, SAM estimates the inverter input voltage by either averaging the subarray Vmp values, or using a more sophisticated algorithm if you check the box under "PV Subarray Voltage Mismatch" on the System Design input page.

We do hope to add support for both multiple MPPT inputs to an inverter, and for multiple inverter types in one system in a future version of SAM.

Best regards,
Paul.

Paul,

If an inverter does have multiple MPPTs, but all modules were in the same orientation, do you see any reason why the results assuming one MPPT per inverter wouldn't be valid? SAM doesn't actually model say, partial shading on a subarray correct? Shading is modeled using averaged percentage values right? It seems more likely that SAM would actually overestimate an installation that did not have multiple MPPTs per inverter.

-Jen

Dear Jen,

If all of the modules are in the same orientation, and the module string length for each MPPT input on the inverter is the same, then SAM's single MPPT input model will work fine to represent an inverter with multiple MPPT inputs.

When you model the array using multiple subarrays, you can assign different tilt and azimuth angles to each subarray (or combine subarrays with fixed arrays and trackers). The only limitation is that SAM requires all subarrays to have the same number of modules per string (and type of module), and models the inverter as if all subarrays were connected to a single inverter. In that case, SAM estimates the effect of voltage mismatch between the subarrays.

You are correct that SAM models shading of the array by nearby objects as a reduction of the beam irradiance incident on the array.

Best regards,
Paul.