Page 92 - Design of Solar Thermal Power Plants

2.5 DISTRIBUTION OF THE SOLAR RESOURCE IN SEVERAL 81

of 19.1 C and extreme minimum temperature of 38.1 C. Precipitation

is scarce for the entire year; 5 months have precipitation totaling only
35.1 mm and accounting for only 6.6% of total annual precipitation. The
second characteristic is a warm humid summer with concentrated pre-
cipitation: summer (JuneeAugust) in Harbin has plenty of rainy days and
concentrated precipitation influenced by a subtropical marine air mass. It
has a high temperature season that demonstrates obvious characteristics
of simultaneous thermal and moisture. The mean precipitation of Harbin
in summer is 350.9 mm, accounting for 66.1% of the annual total; inter-
mittent precipitation is most commonly seen, with about 11.1 rainy days.
The third characteristic is a dry spring with changing temperatures and
strong winds. During spring (AprileMay), dominant cold air in the North
is less severe, while warm air in the south starts to increase along with a
rapid temperature increase. Due to frequent cyclones during this period,
the temperature changes constantly; a one-time temperature increase or
drop can be as large as 20 C. The fourth characteristic is an autumn with a

fast temperature drop and an early first frost. Due to plunging tempera-
tures in autumn, frost may occur; the mean first-frost day is September 21
(refer to Table 2.12).
2.5.8.2 Solar Radiation in Harbin
Harbin is located between the Tropic of Cancer and the Arctic Circle.
Solar altitude variation and various corresponding seasonal solar radia-
tion variations are significant. In Harbin, the sun rises at 7:37 a.m. and sets
at 4:20 p.m. on the winter solstice; the respective day length is a mere 8 h
43 min with a solar altitude during midday of 20 15 . The sun rises at 4:19

0
a.m. and sets at 7:53 p.m. on the summer solstice; the respective day
length is as long as 15 h 34 min with a solar altitude during midday of

0
67 45 . During winter and summer, length of day varies significantly and
the midday solar elevation on the winter solstice is less than one-third that
on the summer solstice.
According to data from the solar radiation observation station of
Harbin during 1961e86, the mean annual global solar radiation of Harbin
2
2
is 4634 MJ/m with a maximum value of 5009 MJ/m (1976) and mini-
2
mum value of 4173 MJ/m (1978). The maximum value for monthly
2
global radiation occurred in June at 703 MJ/m ; the minimum value
2
occurred in December at 105 MJ/m ; the amplitude of variation within
2
the year is 598 MJ/m . The daily variation of global radiation increased
2
from February to March with an amplitude as high as 1549 MJ/m ;it
decreased from July to September with a monthly decrease amplitude of
2
109e113 MJ/m .
Among the global solar radiation types in Harbin, direct and scattered
radiation components change significantly by season. Due to differences