pvlib.irradiance.get_extra_radiation(datetime_or_doy, solar_constant=1366.1, method='spencer', epoch_year=2014, **kwargs)[source]

Determine extraterrestrial radiation from day of year.

  • datetime_or_doy (numeric, array, date, datetime, Timestamp, DatetimeIndex) – Day of year, array of days of year, or datetime-like object

  • solar_constant (float, default 1366.1) – The solar constant.

  • method (string, default 'spencer') – The method by which the ET radiation should be calculated. Options include 'pyephem', 'spencer', 'asce', 'nrel'.

  • epoch_year (int, default 2014) – The year in which a day of year input will be calculated. Only applies to day of year input used with the pyephem or nrel methods.

  • kwargs – Passed to solarposition.nrel_earthsun_distance


dni_extra (float, array, or Series) – The extraterrestrial radiation present in watts per square meter on a surface which is normal to the sun. Pandas Timestamp and DatetimeIndex inputs will yield a Pandas TimeSeries. All other inputs will yield a float or an array of floats.



M. Reno, C. Hansen, and J. Stein, “Global Horizontal Irradiance Clear Sky Models: Implementation and Analysis”, Sandia National Laboratories, SAND2012-2389, 2012.


<http://solardat.uoregon.edu/SolarRadiationBasics.html>, Eqs. SR1 and SR2


Partridge, G. W. and Platt, C. M. R. 1976. Radiative Processes in Meteorology and Climatology.


Duffie, J. A. and Beckman, W. A. 1991. Solar Engineering of Thermal Processes, 2nd edn. J. Wiley and Sons, New York.


ASCE, 2005. The ASCE Standardized Reference Evapotranspiration Equation, Environmental and Water Resources Institute of the American Civil Engineers, Ed. R. G. Allen et al.