Basics of Renewable Energy Supply - Renewable Energy: Technology, Economics and Environment - page 40

< 800
800 - 1,200
1,200 - 1,600
1,600 - 2,000
> 2,000
Values in kWh/m 2
Fig. 2.11 Distribution of annual mean values of total global radiation world wide (data
according to /2-11/)
Maps as shown in Fig. 2.11 can only give a rough estimate of the global radia-
tion to be expected within a larger region. Locally the solar radiation can thus
vary within the boundaries indicated in Fig. 2.11. Therefore Fig. 2.12 shows ex-
emplarily the distribution of the mean solar global radiation over many years
within Germany and Austria.
It becomes apparent that South Germany is characterised by the highest supply
of solar radiation. In North Germany - with the exception of the North and Baltic
Sea islands - the radiation totals are sometimes significantly lower. The reason for
the higher radiation supply in South Germany is the more southern location, and
the proximity to the equator. Additionally, the area is less cloudy on average. Both
taken together lead to an increased global radiation and a longer average sunshine
duration. The mean global radiation total over many years varies between around
290 and 470 kJ/(cm 2 a) or approximately 800 and 1,300 kWh/m 2 due to regional
differences.
The situation is also basically similar for Austria. But as this country is located
further south the average global radiation is slightly higher. This is also true for
the maximum solar radiation which is measured on some mountain tops. This is
attributable to the fact that the atmosphere on high mountains is thinner compared
to lowlands, and thus the solar radiation is less weakened.
Time variations. The solar radiation supply in one location is subject to signifi-
cant time fluctuations. Some of these fluctuations are of deterministic, some of
them of stochastic nature.
Fig. 2.13 shows the timely differences of the global solar radiation supply ex-
emplarily with radiation data measured in one location in North Germany. The
annual course of the mean daily radiated power is thus characterised by a lower
radiation supply during the winter months and a higher supply during the summer.