Add an inverter by clicking Add Inverter and selecting an inverter from the list view.  The inverter can be changed by clicking Change Selection and selecting a different inverter.  Note that the DC:AC Ratio may change when the inverter is changed.

Add a module by clicking Add Module and selecting a module from the list view.  The module can be changed by clicking Change Selection and selecting a different module.  Note that differences in module dimension may cause the GCR to change when the module is changed.