Dear Pia,
When you model a PV-battery system with either the Residential or Commercial financial model, you can model a building electric load. SAM assumes that the grid is available to either absorb excess power from the system or deliver power as needed to meet the building load or charge the battery, depeding on the dispatch options you specify.
For the PPA financial models, SAM assumes that the grid is available to absorb power from the system, and to deliver power as needed to charge the battery, depending on the dispatch options you specify. You can use the "Input Battery Dispatch" option to manually specify when the battery charges and discharges, but it is not possible to define a load profile for the grid.
Best regards,
Paul.