Read the ASTM G173-03 AM1.5 global spectrum on a 37-degree tilted surface, optionally interpolated to the specified wavelength(s).

Global (tilted) irradiance includes direct and diffuse irradiance from sky and ground reflections, and is more formally called hemispherical irradiance (on a tilted surface). In the context of photovoltaic systems the irradiance on a flat receiver is frequently called plane-of-array (POA) irradiance.


wavelength (1-D sequence of numeric, optional) – Wavelengths at which the spectrum is interpolated. By default the 2002 wavelengths of the standard are returned. [nm]


am15g (pandas.Series) – The AM1.5g standard spectrum indexed by wavelength. [(W/m^2)/nm]


If wavelength is specified this function uses linear interpolation.

If the values in wavelength are too widely spaced, the integral of the spectrum may deviate from the standard value of 1000.37 W/m^2.

The values in the data file provided with pvlib-python are copied from an Excel file distributed by NREL, which is found here: https://www.nrel.gov/grid/solar-resource/assets/data/astmg173.xls

More information about reference spectra is found here: https://www.nrel.gov/grid/solar-resource/spectra-am1.5.html



ASTM “G173-03 Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface.”