Page 109 - Design of Solar Thermal Power Plants

2.7 DISTRIBUTION OF SOLAR DIRECT NORMAL RADIATION 97

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have annual total direct solar irradiation above 1400 kWh/m ,
showing zonal distribution characteristics of the south being higher
than the north; areas to the east of the boundary have annual total
2
direct solar irradiation of less than 1400 kWh/m ; North China has
the largest amount.
The national annual mean solar direct normal irradiation is
2
1472 kWh/m . The area southwest of Tibet is an extremely high-value
zone, while the extremely low-value zone is located in the Shannan
Prefecture of Tibet, Sichuan Basin, and ChongqingeGuizhoueHunan
region.
2. Based on the geographic statistics of solar radiation resources in
various provinces (cities, districts), annual total direct solar
irradiation on an average climate condition in various provinces
(cities, regions) can be obtained. Tibet, Qinghai, Xinjiang, Gansu,
Ningxia, and Inner Mongolia are the provinces (regions) in China
with the most abundant solar radiation resources, while various
provinces (cities, regions) in North China and Yunnan have
intermediate radiation resources, and Chongqing, Guizhou, and
Hunan have the poorest radiation resources.
3. During a clear day, the global irradiance on the horizontal surface is
less than the DNI; during a cloudy day, the global irradiance on the
horizontal surface is more than the DNI. Therefore, in northwestern
areas of China with fewer cloudy days, DNI values are higher than
the global irradiance on the horizontal surface.

Solar meteorological stations that are currently the most commonly
used include APL in the United States, Kipp & Zonen in the Netherlands,
and the RSP-3G irradiation meter in Germany, which are all available for
measuring solar direct normal, global, scattered, direct, and other radia-
tion (refer to Figs. 2.11 and 2.12 and Table 2.16). Data collection frequency

FIGURE 2.11 Kipp & Zonen irradiance meters at an operational station.