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I'm trying to calculate the daily solar insolation (integrated solar irradiances from sunrise to sunset) for a given location and day of the year. For latitude 43.2° and April 15th, I get:

H0 = (solar constant * scale factor for intra annual variation of sun-earth distance * 86400 seconds/pi) * (cos(latitude) * cos(declination) * sin(hour angle sunset) + (hour angle sunset * pi/180)*(sin(latitude)*(sin(declination))

or with numbers:

H0 = ((1368*0.99226178414418)*(86400/pi))*(cos(43.2°)*cos(9.6423°)*sin(99.1805°)+(99.1805°*pi/180)*sin(43.2°)*(sin(9.6423°)) = 3.39E7 J/day.m2

However, when I try to check the result with online calculators, they say the result should be 2.65E7 J/day.m2 ...

Can anyone please check and help me out if and what I am doing wrong? It would be of very great help!

Thank you!

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# I Calculation of daily solar insolation

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