2 Solar Angles
2.1 Solar Altitude
is the angle ROQ (Figure 3) on a vertical plane between the sun's rays and the horizontal
plane on the earth's surface.
Solar altitude (
2.2 Solar Azimuth
Solar azimuth (f ) is the angle SOQ
(Figure 3) on a horizontal plane between the due-south direction line and the horizontal
projection of the sun's rays.
2.3 Solar Declination
Solar declination (d) is the angle
between the earth-sun line and the equatorial plane (Figure 2). Solar declination varies
throughout the year.
2.4 Surface-solar Azimuth
Surface-solar azimuth (g) is the angle
POQ (Figure 3) on a horizontal plane between the normal to a vertical surface and the
horizontal projection of the sun's rays.
Figure 3 Solar Angle with Respect to the
4 Solar Intensity and
Horizontal and Vertical
2.5 Surface Azimuth
Surface azimuth (y) is the angle
POS (Figure 3) on a horizontal plane between the normal to a vertical surface and the
north-south direction line.
2.6 Hour Angle
Hour angle (H) is the angle SPD (Figure 3)
on a horizontal plane between the local solar noon (meridian which contains the
south-north line) PS and the horizontal projection of the sun's rays PD. The hour angle is
where T = solar time
In the morning, the hour angle is positive.
At noon the hour angle is zero. In the afternoon, the hour angle is negative.
2.7 Latitude Angle
Latitude angle (L) is the angle S'OP
(Figure 2) on the longitudinal plane between the equatorial plane and the line PO which
joins the point P on the earth surface and the centre of the earth O.
2.8 Angle of Incidence
The angle of incidence (q) is the angle
between the sun's rays irradiated on a surface and the line normal to this surface. In
Figure 3, the angle of incidence q H for a horizontal surface is ROV; for vertical
surface, the angle of incidence q V is ROP. In Figure 4, the angle of incidence between
the sun's rays and a tilted surface is q S , where q S is given by:
2.9 Solar Intensity
The solar intensity at a direction normal
to the title surface (IS ) is the vector sum of the components along the line normal of the
where IDN = the solar intensity
irradiated on a surface normal to the sun's rays
For a horizontal surface S = 0o,
the solar intensity normal to the horizontal surface is:
For a vertical surface S = 90o,
the solar intensity normal to the vertical surface is:
Figure 5 Solar Spectra Compared
with The 600K Black Body Emission Spectrum