Page 104 - Design of Solar Thermal Power Plants

92 2. THE SOLAR RESOURCE AND METEOROLOGICAL PARAMETERS

direct radiation, and observation factors of Class B stations only include
global radiation. During this period, various observation sites have been
adjusted many times. Since 1993; observation stations have been adjusted
from Class A and Class B to Level I, II, and III observation stations.
Observation factors of a Level-I station include global, net, scattered,
direct, and reflective radiation; observation factors of a Level-II station
include global and net radiation; and observation factors of a Level-III
station include global radiation.
Before 1993, radiation observation instruments applied in radiation
observation stations nationwide included thermoelectric type (constantan
and manganese steel welding) and inductive surface (regular black paint)
radiation meters with a relative error of 10%; during and after 1993, ra-
diation observation stations nationally started to apply domestically
developed thermoelectric type (wire-wound constantan and plated cop-
per) and inductive surface (specific optical black paint) automatic tele-
metering radiation meters with a relative error of 0.5%.
Except for solar irradiation, China’s regular meteorological data can be
divided into two parts; one is ground observation data including wind
speed, wind direction, atmospheric pressure, temperature, dew-point
temperature, and sunshine duration, which are covered by China’s
main meteorological stations (excluding data from meteorological sta-
tions in Hong Kong, Macao, and Taiwan), involving 740 stations with a
spatial density higher than radiation sites. The other part is sounding
data, the observation factors of which mainly include wind speed, wind
direction, atmospheric pressure, elevation, temperature, and dew-point
temperature.
Actual observation data in China for DNI are far from satisfying the
need for a spatial distribution of the solar resource. Thus calculations in
the book are conducted using annual mean daily DNI data for China with
a “40 km 40 km” spatial resolution provided by the National Renew-
able Energy Laboratory (NREL) in the United States based on a daily
radiation model (Climatological Solar Radiation Model). The respective
data are mainly calculated and deduced based on remote sensing data for
the period from January 1, 1985, to December 31, 1991. The model is used
for analysis and calculation while considering various factors including
clouds, water vapor, trace gases, and aerosol content in the atmosphere.
The calculation model for DNI being transferred from the atmosphere to
the ground is as follows:

DNI ¼ E 0 ðs R s Ozoo s Gas s wv s Ae Þs Cl (2.27)
in which E 0 refers to the solar constant; s R refers to the Rayleigh scattering
transparency; s Ozoo refers to the ozone absorption transparency; s Gas re-
fers to the mixed gas absorption transparency; s wv refers to the water
vapor absorption transparency; s Ae refers to the aerosol absorption or