Environmental Engineering Reference
In-Depth Information
kWh/(m
2
d)
9
Direct irradiation
Diffuse irradiation
8
7
6
5
4
3
2
1
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Figure 2.7
Daily Direct and Diffuse Irradiation in Berlin
Many meteorological stations measure global irradiance only. However,
most calculations for solar energy systems need a separation into direct and
diffuse irradiance. Empirical functions found by statistical investigations can
split the global irradiation into direct and diffuse irradiation (Reindl et al,
1989). Hourly values of the global irradiance
E
G,hor
, the extraterrestrial
irradiance
E
0
S
(which is calculated in the following
section) define the factor
k
T
as follows:
and the sun height
kWh/(m
2
d)
9
Direct irradiation
Diffuse irradiation
8
7
6
5
4
3
2
1
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Figure 2.8
Daily Direct and Diffuse Irradiation in Cairo
