Wow, there is a lot that goes into SAM. I muddled my way through entering two strings, one at 0° tilt and the second at 8° tilt, using a Trina Solar panel (TSM-300DD05a.05II) since it was in their database and it seemed to match up with a panel that is currently available. The database of modules in SAM is from Dec 2019. This is not the same panel I used in my prior post. The application also requires the selection of an inverter. I picked one pretty much at random since I'm not concerned about the inverter.
With both string at 0° tilt the output is 1,222 kWh/year.
With one string at 0° tilt and the other at 8° tilt the output is 1,259 kWh/year.
There isn't a way to setup a string with panels at different tilts. The model assumes that all panels on a string are at the same tilt. Consequently, I don't see a way to calculate the output if a string is made up of panels A1, B1 and B2.
I used a south facing orientation (180°). That was the default. Just for giggles, I chose an east facing orientation (90°) and the output numbers didn't change.
It looks like the "loss" for an array with some panels tilted and some not tilted is 3%. I'm backing into that number simply based on the simulated kWh output. 3% gives me a good indicator of the scope of the "loss" due to different angles. At 3% I'm not going to worry about it.
I think the only way to get a better handle on this is to get the system installed and switch the wiring around, using different panel arrangements on a string. Or, I'll just over panel and call it a day.
The SAM help manual has this to say about mismatches:
Subarray Mismatch Losses For a system with more than one subarray, SAM can estimate losses due to maximum power point mismatches between subarrays, but only with the CEC module submodel (either with database parameters or user-defined inputs, see Section 9.5). For the Sandia module model and simple efficiency module model, SAM does not estimate subarray mismatch losses as explained in Section 10.1.
The subarray mismatch loss algorithm (Dobos 2012b) is intended to model situations that may occur in residential rooftop systems when the array is installed on different parts of the roof with different orientations and connected to a single inverter. The group of modules on each roof surface is a subarray, and may have its own set of parameters defining its tilt and azimuth angles, tracking, shading factors, and DC losses.
In larger systems, modules are typically oriented uniformly across the entire array. SAM’s subarray mismatch algorithm is not suitable for such systems. SAM does not calculate mismatch losses due to maximum power point losses between individual modules in the array or in each subarray.
The algorithm determines the system’s maximum power point in a given hourly time step by running the CEC module model over a range of maximum power point voltage values to find the voltage that results in the complete array’s highest maximum power given each of its subarray’s effective incident irradiance, module performance and temperature parameters.