PVWatt Source Code using TMY3 Files

Where would I find the latest source code for the PVWatt calculation? I have some old C source code from NREL but its returning values that are slightly off compared to your code.

Thanks,
Jim

Dear Jim,
NREL does not distribute the PVWatts source code. A technical reference manual will be published when the Beta test period for the next version of PVWatts ends. You can find documentation for the current version as implemented in SAM on the performance models page of this website:
/performance 
Best regards,

Paul.