Accessing SAM Defaults

When you create a case in SAM, it loads default values for all of the inputs in the case. These defaults are stored in files that come with the SAM installation, and are updated with each version of SAM to reflect market and industry conditions at the time of the software release. This default data is also accessible from PySAM.

The default() function loads a compute module’s defaults for a given configuration. Use it with the from_existing() function to load defaults for a set of compute modules to build a complete configuration.

For example, to load defaults for the Detailed PV-Battery – Commercial configuration, first, refer to List of SAM Configurations to identify the list of compute modules you need to import for the configuration. Then use default() to initialize the first compute module in the list and load its defaults, and from_existing() to load the defaults for the remaining modules:

import PySAM.Pvsamv1 as pv
import PySAM.Grid as gr
import PySAM.Utilityrate5 as ur
import PySAM.Cashloan as co

system_model = pv.default('PVBatteryCommercial')

grid_model = gr.from_existing(system_model, 'PVBatteryCommercial')
utilityrate_model = ur.from_existing(system_model, 'PVBatteryCommercial')
financial_model = so.from_existing(system_model, 'PVBatteryCommercial')

The from_existing() function ensures that any data that the different modules share is consistent. In this case, for example, gen is both a member of the Outputs group of Pvsamv1 and of the SystemOutput group of Cashloan, and we want to ensure that the two variables have the same value.

To work with defaults in PySAM, you need to know the list of compute modules for the configuration and the configuration name for defaults. You can find this information in List of SAM Configurations.

For SAM versions after SAM 2021.12.02 Revision 2, SAM loads defaults from JSON files that come with the SAM installation. As an alternative to the method described here, you could read the defaults directly from those JSON files, which are in the SAM installation folder on your computer at path/to/sam/version/runtime/defaults. You can also find current development versions of the files are available on the SAM GitHub repository.


Because of the way the weather file path is stored in SAM, when you build a configuration by loading defaults, you have to explicitly set its value to a valid path on your computer. The group name and variable that stores the weather file path is different for different compute modules. Use the List of SSC Compute Modules to find the group and variable name for your compute module’s weather file path.


When you change the value of an input after loading the defaults, you must check that its value is not dependent on other inputs, or that other input values are not dependent on the one you are changing. If the input you are changing is listed in the Interdependent Variables list in the compute module’s documentation, search the documentation page to find interdependent inputs. See Interdependent Variables for more details and examples.

The following code finishes the example above by setting the weather file for the Detailed PV model, running a simulation, and displaying results you can compare to SAM’s results.

import PySAM.Pvsamv1 as pv
import PySAM.Grid as gr
import PySAM.Utilityrate5 as ur
import PySAM.Cashloan as co

print('Loading defaults...')
system_model = pv.default('FlatPlatePVCommercial')
grid_model = gr.from_existing(system_model,'FlatPlatePVCommercial')
utilityrate_model = ur.from_existing(system_model,'FlatPlatePVCommercial')
financial_model = co.from_existing(system_model,'FlatPlatePVCommercial')

# path to small collection of default weather files that come with SAM
# edit and set as needed for Windows, Mac, Linux
wf_paths = ['C:\\SAM\\2021.12.02r1\\solar_resource\\',
wf_name = 'phoenix_az_33.450495_-111.983688_psmv3_60_tmy.csv' # default for PV - Commercial configurations

# for wf_paths 0 = windows, 1=mac, 2=linux as defined above
filename = wf_paths[0] + wf_name
system_model.SolarResource.solar_resource_file = filename