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IV. Atmospheric Effects on Solar Intensity

After reaching our atmosphere, light responds in several ways. The light is partially absorbed and partially scattered, and therefore the intensity is decreased somewhat. Sunlight is attenuated by at least 30% during its passage through the atmosphere1

 
Causes of attenuation in the earth’s atmosphere include:
  • Absorption by the earth’s constituent atmospheric gases. Water and carbon dioxide tend to deplete light intensity in the infrared section of the electromagnetic spectrum, whereas oxygen and ozone weaken light mainly in the visible and ultraviolet ranges respectively2.
  • Scattering of light by aerosols and dust particles in the atmosphere.
  • Rayleigh scattering, or the scattering of light by particles in the atmosphere that are smaller than the wavelength of incoming light. This is the reason that sunsets have a red shift; the light reflects off of more particles as the angle of the sun decreases relative to the atmosphere. This type of scattering occurs especially with light of short wavelengths (or high-energy photons).
  • Mie scattering occurs in clouds, which appear white because light is scattered equally at all wavelengths. This is due to the size of the cloud’s water droplets.
sct1.gif
Source: ww2010.atmos.uiuc.edu. 25 Feb. 2012. <http://ww2010.atmos.uiuc.edu/%28Gh%2...t/mch/sct.rxml>
 

References

1. Goetzberger, Adolf et.al. Crystalline Silicon Solar Cells. Chichester: John Wiley & Sons Ltd., 1998.
2. Green, Martin A. Solar Cells: Operating Principles, Technology, and System Applications. Englewood Cliffs: Prentice-Hall, Inc., 1982. Full book ordering information at www.pv.unsw.edu.au.