Environmental Engineering Reference
In-Depth Information
Figure 2.25
Shading Angle
as a Function of the Degree of Ground
Utilization
u
and the Surface Tilt Angle
α
γ
t
The
shading angle
(2.45)
is a function of the ground utilization
u
and the surface tilt angle
γ
t
(see Figure
2.25). If the sun is directly in front of the solar energy system and the sun
height is below the shading angle
, self-shading will occur.
With rising shading angles the irradiance losses increase. However, shading
losses must be calculated individually for every location. The following
calculations are made for Berlin but can easily be transferred to other locations
with latitudes around 50° and with a central European climate. Locations at
lower latitudes will have significantly reduced shading losses that often can be
neglected.
Figure 2.26 shows the relative shading losses
s
at the point
P
0
as a function
of the shading angle
α
γ
t
. The annual irradiation
H
G,tilt
on
tilted but unshaded solar energy systems and the same annual irradiation
H
G,tilt,red
, reduced as a result of self-shading, define the
relative shading losses
:
α
and the tilt angle
(2.46)
It is apparent that solar energy systems are more sensitive to shading losses
with higher surface tilt angles.
Since photovoltaic systems are very sensitive to shading, the irradiance at
point
P
0
could be used as a reference for the whole photovoltaic system. Table
2.13 shows the shading angle
and the resulting shading losses
s
for different
degrees of surface utilization for tilt angles between 10° and 30°.
α
