Page 97 - Design of Solar Thermal Power Plants

2.6 SOLAR IRRADIANCE PREDICTION METHODS 85

Astronomic radiation on the horizontal surface is calculated as follows:
24 3600 p
H 0 ¼ I 0 f cos l cos d sin u s þ u s sin l sin d (2.17)
p 180
2
in which I 0 ¼ 1367 W/m (solar constant); l refers to the local geographic
latitude; and d refers to the declination angle.
n

f ¼ 1 þ 0:033 cos 360 (2.18)
365
in which n is the chronological order (for example, the chronological order
for January 1 is 1).
Declination angle is calculated as follows:

248 þ n
d ¼ 23:45 sin 360 (2.19)
365
u s refers to the sunset hour angle, which is calculated as follows:
u s ¼ cos 1 ð tan l tan dÞ (2.20)
The longest sunshine duration is calculated as follows:
2
S 0 ¼ u s (2.21)
15
in which values of H 0 ; S 0 can be obtained through Eqs. (2.17) and (2.21).
Coefficients a and b can be obtained from H and S samples through linear
H 0 S 0
regression, in which the values of H and S can be obtained from the
meteorological database of eight selected typical cities during the period
of 1994e2003.
Coefficients a and b are calculated as follows:
! !
n
n
n
P H S P H P S
n
S
i¼1 H 0 S 0 i¼1 H 0 i¼1 0
b ¼ (2.22)
! 2 2
n S P S
n
n P
S
i¼1 S 0 1¼1 0
n
n
1 X H b X S
a ¼ (2.23)
n H 0 n S 0
1¼1 1¼1
in which n is the quantity of measuring points.
Global solar radiation and sunshine data of selected sites during the
period of 1994e2003 correspond to the typical climatic cities provided by
the China Meteorological Administration (CMA), which serves as the
main data analysis source in the book. The positions of various sites are
shown in Table 2.13.