Page 20 - Applied Photovoltaics
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sunlight
h
s
Figure 1.5. Calculation of Air Mass using the shadow of an object of known
height.
The spectral distribution of sunlight outside the atmosphere (Air Mass Zero or AM0),
and at AM1.5 are shown in Fig. 1.6. Air Mass Zero is essentially unvarying and its
total power density, integrated over the spectrum, is referred to as the solar constant,
with a generally accepted value (ASTM, 2000, 2003; Gueymard, 2004) of
Ȗ . 1 3661 kW/m 2 (1.5)
Figure 1.6. The spectral power density of sunlight, outside the atmosphere (AM0)
and at the earth’s surface (AM1.5), showing absorption from various atmospheric
components.
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