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Typical Year Files

Typical year data is commonly used for solar resource availability assessment at potential project sites or for running energy simulations to obtain P50 solar production estimates. SolarAnywhere® typical year files can be downloaded with access to a Typical Year license.

SolarAnywhere typical year data can be downloaded or requested as either a typical GHI year (TGY) or typical DNI year (TDY) file. These files contain a years’ worth of hourly observations (8760 hourly observations) selected with 100% weighting on either GHI or DNI. The files are generated for a specified location using the following two-step process:

    1. The long-term average monthly total irradiance is calculated for each month. The years considered in calculating the long-term averages is dependent upon the geographic data region:
    2. The actual months in the historic record with the monthly total irradiance values closest to the long-term averages calculated in step 1 are included in the TGY or TDY files.

The final TGY or TDY file will include 12 months of actual data from various years in the historical time series. For example, if January of 2010 has the monthly total irradiance closest to the long-term average monthly total irradiance for all Januarys as calculated in step 1, it will be included in the file. This is illustrated below.

Typical Year (TMY) SolarAnywhere data is derived from 25 years of historical data

Users can demo typical year files with SolarAnywhere Public.


Typical GHI Year (TGY) files are commonly used for running energy simulations to obtain P50 solar production estimates. When modeling tracking systems, however, it can be useful to compare simulation outputs based on Typical DNI Year (TDY) data to outputs based on TGY data.

It is more important to have an accurate representation of typical DNI conditions in modeling tracking systems than in modeling fixed tilt systems, and in some cases, the TDY data has been found to produce more representative results than the TGY data. TDY files are also useful in modeling concentrated PV plants.

TMY Data

SolarAnywhere TGY and TDY data are SolarAnywhere’s version of TMY data. TMY stands for typical meteorological year. This term was originally used by NREL to describe the dataset they first released in 1977 that used ground measurement data collected from 1952-1975 to generate weather data files containing a year of hourly meteorological data. These files were originally generated for use in facilitating solar heating and cooling simulations for buildings.1

Since the first NREL TMY dataset was released in 1977, NREL has released two additional versions: TMY2 in 1994, and TMY3 in 2007. The data and methodologies used to generate TMY files has been refined throughout the years to provide datasets more specific to solar PV modeling use cases. TMY file construction methodology can vary by data provider, but in general, the months of data selected to represent typical conditions are now more heavily weighted on the solar irradiance fields than the additional weather fields (ambient temperature, wind speed, etc.).

The white paper, “How Misuse of Solar Resource Datasets Is Reducing Solar Industry Profits” provides a helpful comparison of SolarAnywhere typical year and NREL TMY3 datasets.



  1. T. Freeman. 1979. “Evaluation of the “Typical Meteorological Years” for Solar Heating and Cooling System Studies Final Report.” Altas Corporation.