Environmental Engineering Reference
In-Depth Information
Reflection
scattering
Absorption
Diffuse solar
irradiance
Direct solar
irradiance
Figure 2.6
Sunlight Passing Through the Atmosphere
Days with low global irradiation have a high percentage of diffuse
irradiation, sometimes approaching 100 per cent; however, the contribution
of diffuse irradiation decreases to less than 20 per cent on days with very high
global irradiation values. Figure 2.7 shows the variation of direct and diffuse
irradiation throughout one year in Berlin as an example of a location with
relatively low annual irradiation. Figure 2.8 shows irradiation values for
Cairo as an example for a location with relatively high annual irradiation.
There are significant differences between these locations. In Berlin, variation
of both diffuse and direct irradiation is much higher throughout the year than
in Cairo.
Table 2.6
Monthly Average Daily Direct and Diffuse Irradiation
in kWh/(m
2
day) in Berlin and Cairo
Jan
Feb
Mar
Apr
May June July
Aug
Sep Oct
Nov
Dec
Average
Berlin
Direct
0.17 0.40 1.03 1.42 2.13 2.58 2.29 2.05 1.38 0.54 0.22 0.10
1.20
Diffuse 0.44 0.74 1.41 2.07 2.64 2.86 2.97 2.53 1.67 1.05 0.54 0.35
1.61
Cairo Direct
1.74 2.37 3.07 3.78 4.56 5.16 4.93 4.57 3.86 3.07 1.96 1.58
3.39
Diffuse 1.35 1.63 2.08 2.49 2.47 2.40 2.41 2.19 2.01 1.62 1.49 1.28
1.95
Table 2.7
Annual Average Daily Direct and Diffuse Irradiation in
kWh/
(
m
2
day)
Bergen
Berlin
London
Rome
LA
Cairo
Bombay
Upington Sydney
Direct
0.86
1.20
0.99
2.41
3.03
3.39
2.75
4.70
2.42
Diffuse
1.29
1.61
1.47
1.78
2.07
1.95
2.39
1.47
2.13
