Page 84 - Design of Solar Thermal Power Plants

2.5 DISTRIBUTION OF THE SOLAR RESOURCE IN SEVERAL 73

2.5.3.3 Golmud Sunshine Duration
During the 1971e2007 period, the maximum sunshine duration in
Golmud occurred in 1985, at about 3323 h; whereas the minimum value
occurred in 2007, at about 2918 h. Yearly sunshine duration has main-
tained a range of 2900 to 3320 h. Especially after 1999, however, solar
radiation has remained stable but with a decreasing trend. In Golmud,
May has the longest monthly sunshine duration at about 296 h. It is
basically consistent with changes in global solar radiation. Based on
national solar energy resource distribution, Golmud has a comparatively
longer sunshine duration.

2.5.4 The Solar Resource in Dunhuang

Dunhuang city is in the westernmost part of the Hexi Corridor, Gansu
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province, the coordinates of which fall in the range 92 13 e95 30 E and
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39 40 e41 35 N. The city area is 31,200 km ; its elevation falls in the range

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of 800e1800 m; the elevation of the urban area is 1138 m. The area has
higher terrain in the south and north than in the middle and has a
basineplain topography that inclines from southwest to northeast; it is also
known as the “Andun Basin” together with Guangzhou County. Dun-
huang city is inland and is surrounded by the Gobi Deserts and subject to a
typical continental climate; the area has strong solar radiation, sufficient
sunshine, abundant thermal, a short frost-free period, limited precipita-
tion, large variability, intensive evaporation, and frequent disasters [9].
2.5.4.1 Weather Conditions of Dunhuang
Climatic features of Dunhuang obviously include its arid climate, low
precipitation, large evaporation, great temperature difference between
day and night, and long sunshine duration. The area has four distinctive
seasons: a warm and windy spring, hot summer, cool autumn, and

freezing winter. The annual mean temperature is 9.4 C with a maximum

monthly mean temperature of 24.9 C (July), whereas the minimum

monthly mean temperature is 9.3 C (January); the maximum extreme
temperature is 43.6 C, whereas the minimum temperature is 28.5 C; the

annual mean frost-free period is 142 days; the area has a typical warm
temperate zone and arid climate (one minor type of temperate zone in a
continental climate). Being inland, Dunhuang is separated by high
mountains and far from the humid ocean climate; it has an extremely arid
continental climate with arid weather all year and limited precipitation. It
has three major features: (1) sufficient sunshine; (2) aridity, low precipi-
tation, and a downward air flow to the north over Dunhuang that create
an arid region with an annual mean precipitation of only 39.9 mm,