Solar Radiation - Understanding Renewable Energy Systems - page 76

Table 2.14 Average Relative Shading Losses _ and Overall Correction Factor
c for Points P 0 , P 1 and P 2 at Different Ground Utilizations and Tilt Angles
Calculated for Berlin (52.5°N)

γ t = 30° γ t = 10°

_ _ u g c g c

1:1.5 0.098 1.193 1.076 0.018 1.088 1.068

1:2.0 0.048 1.193 1.136 0.006 1.088 1.081

1:2.5 0.032 1.193 1.155 0.004 1.088 1.084

1:3.0 0.021 1.193 1.168 0.003 1.088 1.085

1:3.5 0.016 1.193 1.174 0.002 1.088 1.086

1:4.0 0.013 1.193 1.177 0.002 1.088 1.086

The reduction of the ground utilization u below 0.33 (that is a ratio of the
length of the solar energy system rows to the distance of the rows of 1:3) does
not result in a significant reduction of the shading factor. Ground utilization
higher than 0.4 (1:2.5) may be favoured by lower tilt angles. Considering the
5 per cent higher losses that result from soiling at a tilt angle of 10° instead of
30°, lower tilt angles are recommended for ground utilization values above 0.5
(1:2).
Solar thermal systems are less sensitive to shading than photovoltaic
systems. Here, the average irradiance can be used for the estimation of the
output of solar thermal systems. This is done by calculating the average
shading losses at the points P 0 , P 1 and P 2 shown in Figure 2.24. The losses at
point P 0 have already been estimated. Point P 1 will never be shaded. For point
P 2 , the shading angle

(2.49)

in the centre of the tilted surface is relevant. Table 2.14 shows the average
relative shading losses _ as well as the overall correction factor c for the three
points P 0 , P 1 and P 2 . Compared to point P 0 , the shading losses are much lower.
No significant improvements are possible for ground utilization u <0.4
(1:2.5). Lower tilt angles are generally not recommended.