Variation in power output on a PV system

I have downloaded SAM and work on design in India.
When i make a selection for PV commercial model, what i want is :
1 I use TMY files. I am not able to do 1:1 AC to DC ratio. if i do, it obviously tells the inverter power is under utilized. what to do if i want 1:1 ratio ??
2 What is the general ball park variation in output between SAM, PVSyst and Actual for a specific location ??

Hello,

You can ignore the message about the inverter being undersized. That message does not prevent the simulation from running, or SAM from displaying results.

Please see the reports and documents on the SAM Validation page for comparisons between SAM and other models:

sam.nrel.gov/case-studies

Best regards,
Paul.