Environmental Engineering Reference
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almost cloudless; only the fall of the global radiation around mid-day indicates
that clouds are passing over.
Furthermore, the course of the average radiated power per minute at mid-day
confirms that the analysed day in January was characterised by an evenly overcast
sky with a small amount of solar radiation that only varied a little. In contrast, on
the exemplarily investigated day in October, the solar radiation incident was gen-
erally higher and thus subject to larger variations due to changes in the level of
cloudiness.
Similar curves will also be found at other sites on earth. But significant varia-
tions may occur. For example the order of magnitude of the measured global solar
radiation might vary depending among other things on the latitude of the measur-
ing spot. The daily cycle is also influenced by the latitude and by the time of the
year. And the radiated power is very much controlled by the micro-meteorological
conditions (i.e. blue sky or cloudy weather).
300
300
250
250
Hourly cycle
200
200
150
150
100
100
Hourly cycle
50
50
0
0
0
5
10
15
20
25
30
35
40
45
50
55
60
0
5
10
15
20
25
30
35
40
45
50
55
60
Time in minutes
Time in minutes
300
300
250
250
Daily cycle
200
200
Daily cycle
150
150
100
100
50
50
0
0
0
3
6
9
12
15
18
21
24
0
3
6
9
12
15
18
21
24
Time in hours
Time in hours
300
Annual cycle
250
200
150
100
50
0
0
30
60
90
120
150
180
210
240
270
300
330
360
Fig. 2.13
Annual, daily and hourly curves of measured global radiated power based on an
exemplary site in North Germany (see /2-7/)
Time in days
The fact that for example the annual cycle of the solar radiation can vary sig-
nificantly is also shown in Fig. 2.14. This graphic displays the global radiation at
Stockholm/Sweden, Kuala Lumpur/Malaysia, Victoria/Argentina, Béchar/Algeria
and Manaus/Brazil. The relatively far north located city of Stockholm shows a
well developed annual cycle. The same characteristic also shows the city of Victo-
ria but mirror-inverted. This is due the fact that Victoria is located in the southern
hemisphere and Stockholm on the northern side of the earth. Compared to these
cities, Kuala Lumpur and Manaus show a much less pronounced annual cycle
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