Irradiation Data

We are confirming the annual operation of a CSP plant and have noticed that the data measured on site is 1-2 hours later (time stamp measured data 9 AM time stam TMY 8 AM for example) than the time stamp in the TMY file that is being used for the simulation. Is this related to the creation of the TMY file, or something to do with SAM and could it have a material impact on the simulation?
This seems like it might be caused by the data in the weather file. SAM determines local time by counting rows in the weather file (where, for hourly data, the first data row is the hour ending at 1 a.m. on January 1), and converts from local time to solar time using the latitude, longitude, and time zone in the weather file. If any of those values are inconsistent, it could cause the time offset you see in the data. Is the time zone in your weather file correct?
Best regards,

Paul.