Hello,
When you use the Flat Plate PV model's "Specify Array Size" option to size the system, SAM does its best to find the number of modules per string, strings in parallel and inverters that results in the system size in DC kW and DC-to-AC ratio that you specify. How close it can get depends on the characteristics of the module and inverter that you choose. Because the module and inverter capacities and ratings are discrete, the sizing algorithm does not always result in a system capacity as close to the desired capacity as you might like.
For a detailed description of the sizing algorithm, see the "Sizing the Flat Plate PV System" topic in Help -- scroll down to the "PV Array Sizing Calculator Algorithm" section. Here is a link to that topic in the copy of Help on the SAM website:
Sizing the Flat Plate PV System
.
We recommend only using the "Specify Array Size" option to get a preliminary sense of the number of modules and inverters. To design the system to meet your requirements, you should use the "Specify Modules and Inverters" option.
Best regards,
Paul.