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
wavelengthis specified this function uses linear interpolation.
If the values in
wavelengthare 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.”