Selection of weather station

I had a quick question regarding location based weather files. We are currently evaluating a building for solar in La Joya, TX 78560. We have a couple of choices for weather file for the analysis: (1) TMY3 data from McAllen Miller International Airport and (2) csv file for 26.25, -98.5 location. The first is closest available TMY3 to the site and the second is even closer as it is the same longitude/latitude of site location.

Our questions relates to which one we should use. The first (TMY3 data) is yielding a production of 1442 kWh/kW/year and the second is giving 1543 kWh/kW/year – a significant variation when considering its financial implications.

Hello,

We recommend using the latest weather data from the NREL National Solar Radiation Database (NSRDB), called PSM for "Physical Solar Model" for your analysis. If you used the latitude and longitude above to download data from the current version of SAM, then that CSV file is PSM data.

For a description of the different NSRDB data see:

nsrdb.nrel.gov/current-version

Best regards,
Paul.