Page 101 - Design of Solar Thermal Power Plants

2.7 DISTRIBUTION OF SOLAR DIRECT NORMAL RADIATION 89

daily at 2:00 p.m. Beijing time that corresponded with the same period,
they discovered that visibility in most areas of China showed a decreased
tendency; they also believed that increases in atmospheric turbidity and
the concentration of atmospheric suspended particles served as possible
reasons for decreased direct radiation in some domestic areas. The in-
fluences of atmospheric suspended particles and other aerosols on solar
radiation are a complex problem. HU Liqin et al. [16] studied the in-
fluences of clouds and aerosols on solar radiation absorbed by the at-
mosphere. During the same period, some scientists pointed out that solar
radiation actually absorbed by clouds was much more than the amounts
estimated using current theory. Robert D. Cess et al. from the State Uni-
versity of New York at Stony Brook measured solar radiation in five
different locations by satellite and concluded that global mean radiation
2
absorbed by clouds was around 25 W/m , which is much more than the
2
estimated range of 0e10 W/m given by the theoretical model. Generally
speaking, current studies on the influences of clouds and aerosols on solar
radiation are still not complete.
In terms of radiation observation, LIU Guangren et al. [17] measured
solar radiation gradients by utilizing the 325-m meteorological tower in
Beijing and preliminarily achieved certain observation results that indi-
cated that under pollution conditions, radiation attenuation was signifi-
cant between the ground and a height of 320 m; under perfectly clear
weather conditions, solar direct radiation during midday hours varied
2
around 10 W/m . Otherwise, under severe pollution conditions on the
2
surface, the relative difference was as high as 140 W/m , indicating that
under severe pollution conditions on the surface, solar direct radiation
consumption was great. With clear weather, total ultraviolet radiation in
the sky and on the ground varied insignificantly; in cases of poor atmo-
spheric visibility, total ultraviolet radiation decreased, but the difference
between that in the sky and on the ground comparatively increased.

2.7 DISTRIBUTION OF SOLAR DIRECT NORMAL
RADIATION RESOURCES IN CHINA

Presently, research methods on solar direct normal radiation mainly
include ground station observation, satellite remote sensing, and nu-
merical simulation. Ground station observation has the advantage of time
continuousness, but stations are located separately. Normally, it is sug-
gested to adopt the method of geographic space interpolation for
compensation, which is accompanied by great interpolation errors,
especially for areas where stations are sparsely located. H. Broesamle et al.