
291Fundamentals of Solar Radiation
© 2008 Taylor & Francis Group, LLC
of the diffuse solar radiation within the view angle. Figure 5.22 shows the geometry of a
pyrheliometer sky occulting tube.
In this gure, the opening half angle
θ
o
=
−
tan
1
(5.81)
The slope angle
θ
p
Rr
=
−
−
tan
1
(5.82)
The limit half angle
θ
−
=
+
tan
1
Rr
(5.83)
FIGURE 5.21
A pyranometer with a shade ring to measure sky diffuse radiation.
TABLE 5.10
Shading Band Correction Factors due to Anisotropy
Solar Altitude Angle
k
T
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
<20° 0.0 0.0 0.0 0.0 0.015 0.06 0.14 0.23 0.24 0.24
20°–40° 0.0 0.0 0.0 0.0 0.006 0.05 0.125 0.205 0.225 0.225
40°–60° ...