Environmental Engineering Reference
In-Depth Information
%
50
110
105
100
95
90
85
80
75
70
65
60
55
90°
vertical
80°
70°
60°
50°
40°
30°
20°
10°
horizontal
0°
-180° -150° -120° -90°
-60°
-30°
0°
30°
60°
90°
120°
150°
180°
north
east
SE
south
SW
west
north
orientation
Figure 5.16
Change in annual solar radiation in Berlin depending on orientation and tilt
angle of photovoltaic systems.
The proportion of solar radiation that photovoltaic modules convert into electric
energy depends on the quality of the system. Solar modules rarely achieve the rated
power indicated. Dust, bird droppings, increases in air temperature, line losses,
refl ection, inverter losses and other factors reduce performance. The relationship
between real effi ciency and rated effi ciency is called performance ratio (
PR
). Table
5.3 lists the criteria for performance-ratio values for grid-connected photovoltaic
systems.
Table 5.3
Performance ratio for grid-connected photovoltaic systems.
Performance
ratio
PR
Description
0.85
Top-quality system, very good ventilation, no shade, minimal pollution
0.8
Very good system, good ventilation, no shade
0.75
Average system
0.7
Average system with minimal losses due to shade or poor ventilation
0.6
Poor system with major losses due to shade, pollution or system failures
0.5
Very poor system with large areas of shade or defects
