Page 103 - Design of Solar Thermal Power Plants

2.7 DISTRIBUTION OF SOLAR DIRECT NORMAL RADIATION 91

The two low-value zones exist separately around Tian Shan Mountain
and the Shannan Prefecture of Tibet.
In the east, North China has the largest global annual radiation,
whereas the southeast and northeast have lower solar radiation; in the

area of 20 e40 N, solar radiation decreases with increases in latitude. The

main factor influencing solar radiation distribution in East China is cloud
cover distribution caused by atmospheric circulation. The area is influ-
enced by moist airflow from the ocean with large amounts of intermediate
and low-level clouds, which may weaken the solar radiation reaching the
ground, especially in the southeast with sufficient precipitation, even for
multiple preliminarily selected low-value minor centers (which are esti-
mated to be related to the complex terrain of the locality; the southeastern
area has a mountainous hilly topography that may easily create topo-
graphic precipitation); in the northeast, global annual radiation shows
significant zonal distribution characteristics. Solar elevation has a domi-
nant role toward the solar radiation distribution of the area. The area
features high latitude and low solar altitude; when radiation passes
through the atmosphere, the optical path is long and radiation is greatly
weakened. Thus the global annual radiation is low.
The southern QinghaieTibet Plateau (except for the Shannan Prefec-
ture) is a major high-value center for annual global solar radiation due to
its high elevation and the atmosphere’s short optical path. Solar radiation
loss in the atmosphere is insignificant, and solar short-wavelength radi-
ation reaching the ground is strong; there is also a comparatively high-
value zone along the Qaidam Basin, Altun Mountains, and Kunlun
Mountains north of the QinghaieTibet Plateau; on a national scale, there
are two comparative deep low-value centers for annual global solar ra-
diation: the leeward slope in the eastern QinghaieTibet PlateaueSichuan
Basin and the Shannan Prefecture of Tibet, in which the Sichuan Basin
low-value center is mainly influenced by cloud cover at the junction of the
southenorth flows of the QinghaieTibet Plateau, with frequent weather
system activities and rainfall that have greatly weakened the global
radiation reaching the ground. The Shannan Prefecture is south of the
Himalayas with great elevation variation. When the moist Indian
monsoon branch passes through the area, the air mass climbs over the
mountains and creates an intensive precipitation. The area is the conti-
nental rain pole of the world. The large number of intermediate and low-
level clouds brought by rainy weather has weakened the global solar
radiation reaching the ground, leading to low values.
The operational observation system of the CMA has 98 radiation
observation stations, including 17 first-level stations capable of con-
ducting direct radiation observation. China’s meteorological radiation
observation stations were categorized as Class A and Class B before 1993;
observation factors of Class A stations include global, scattered, and