Hi Joel,
That configuration requires modeling each building as a separate case.
You could model the combined system using the Generic System model, which allows you to provide a generation profile (hourly or subhourly) as input. To do that, start with a .sam file with the two Detailed PV cases and set up the system design for each building (don't worry about the financial model inputs yet. Next, add a third case using the Generic System performance model with a financial model appropriate for your project. Then, on the Power Plant page, choose Calculate generation profiles and nameplate capacity from open cases, and click Select Cases and follow the prompts. This will create a generation profile by adding the profiles of the two PV cases that you can use to model the two buildings as a single system. After SAM creates the combined generation profile, you can set up the inputs for the financial model (load, electricity rates, financial parameters, etc.) for the project.
Let me know if you need help getting that to work.
Best regards,
Paul.