Page 65 - Design of Solar Thermal Power Plants

2.4 CALCULATING METHODS FOR SOLAR POSITION 57

FIGURE 2.4 Schematic diagram of solar zenith, altitude, and azimuth angles.

8. Solar azimuth angle, g s , is the included angle between the projection
line of solar vector on the horizontal ground from one specific spot
on the ground to the center of the sun and the south direction, the
basic calculation equation of which is as follows:

sin d cos f cos d cos u sin f
g ¼ arccos 180 (2.8)
s
cos a s
g ¼ g ; if sin u > 0 (2.9)
s
s
To be intuitive, Fig. 2.4 indicates the geometrical relationship of the
solar zenith, altitude, and azimuth angles mentioned above.
9. Solar flare angle is the flare angle of the profile of the sun
corresponding to one specific spot on the ground, which is also
known as the solar radiation divergence angle. As shown in Fig. 2.5,
due to the eccentricity of Earth’s orbit, the SuneEarth distance
changes within a range of 1.7%.
11
For a SuneEarth mean distance of 1.495 10 m, the cone angle of the
sun is 32 . The cone angle of the sun is used to indicate that the incident
0
solar direct normal radiation light onto one specific spot on the ground is
not a parallel beam. Thus, when designing the specular surface shape of

FIGURE 2.5 Basic geometrical relationship of the Sun and Earth.