Page 107 - Design of Solar Thermal Power Plants

2.7 DISTRIBUTION OF SOLAR DIRECT NORMAL RADIATION 95

shorter; on the plateau, the atmospheric density is lower (thin air),
the contents of water vapor and solid impurities in the atmosphere
are smaller; there are fewer clouds; and the atmospheric
transparency is satisfactory. Based on the above, the refraction,
scattering, and absorbing effects of solar radiation are greatly
weakened, which intensifies solar radiation; summer has more clear
days with longer sunshine duration than other areas. Thus the
QinghaieTibet Plateau is the region in China with the largest annual
global solar radiation, and also the region in China with intensive
solar radiation during summer. However, due to the high elevation
of the QinghaieTibet Plateau, the air is thin and thus there are fewer
clouds in the sky and less atmospheric counter-radiation. On the
other hand, the thermal insulation function of the atmosphere is
quite poor and cannot preserve thermal from ground radiation well;
in addition, the wind speed is higher on the plateau, making it even
less conductive to thermal storage and preservation. Even in
summer, mean temperatures in most areas of the QinghaieTibet
Plateau are quite low; it is the region in China with the lowest mean
summer temperature.
Due to isolated topographic conditions in the Sichuan Basin, a low-
value center for global radiation is created. The QinghaieTibet
Plateau and Sichuan Basin are typical in terms of the reflecting
influences of topography on radiation distribution. Topographic
influences of other areas are comparatively less significant due to
low mountain heights or the small scale of horizontal extension of
mountains, etc.
3. Features of atmospheric circulation influences. The influences of
atmospheric circulation on global radiation distribution are mainly
reflected through cloud status development. The actual global
radiation distribution is the result of the integrated influences of
latitude, topography, and atmospheric circulation conditions. The
influences of the first two are comparatively stable, whereas the
influences of atmospheric circulation conditions feature the greatest
variability. Summer global radiation is most significantly reflected
by subtropical anticyclone in the middle and lower reaches of the
Yangtze River and its southern areas as well as the rainband in
North China. The influence of rainy weather on the global radiation
of QinghaieTibet Plateau is also quite strong.
The influences of atmospheric circulation conditions on the annual
variation of global radiation in various areas are also considerable,
mainly resulting in displacement months in certain areas when
maximum and minimum values of global radiation occur.