Function computing the Sun's declination depending on (t0 + t) given in seconds

Hypothesis and equations

The function return the Sun's declination in radians given by the following equation:

delta:=(0.302 - 22.93*cos(wd) - 0.229*cos(2*wd) - 0.243*cos(3*wd) + 3.851*sin(wd) + 0.002*sin(2*wd) - 0.055*sin(3*wd))*pi/180

Where wd=2*pi/365<.25 * d (d day of the year according to t0+t)

The year is supposed to be not bisextile.


H. BOUIA, "Amélioration du temps de calcul dans BuildSysPro par traitements numériques optimisés de la conduction et des calculs solaires", Note H-E14-2013-00715-FR, 03/2013.

Instructions for use


Known limits / Use precautions



Validated function - Hassan BOUIA 03/2013.

Licensed by EDF under a 3-clause BSD-license
Copyright © EDF 2009 - 2023
BuildSysPro version 3.6.0
Author : Hassan BOUIA, EDF (2013)


function SunDeclination
  input Real t0 = 0 "Time in seconds at t=0";
  input Modelica.Units.SI.Time t "Time in seconds";
  output Modelica.Units.SI.Angle delta "Sun's declination (angle in radians)";
end SunDeclination;


Hassan Bouia 03/2013 : Simplification de l'écriture et adaptation au nouveau modèle MeteoFile

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