Page 119 - Design of Solar Thermal Power Plants

2.8 VARIOUS SPECIAL CLIMATE CONDITIONS 105

3. Sand blow. Monthly mean sand-blowing days, the minimum sand-
blowing month, and the no-sand-blowing month by season and
year. These data can be used for references in mirror surface cleaning.
4. Rainfall. Annual mean precipitation is the mean value obtained by
dividing the sum of multiyear precipitations at a certain location
with the number of years or the mean value of annual precipitation
measured in various observation sites at a certain location, which
also serves as a major measurement index for a specific local climate.
5. Snowfall. Annual mean snowfall is the mean value obtained by
dividing the sum of multiyear snowfall at a certain location with
the number of years or the mean value of annual snowfall measured
in various observation sites at a certain location, which also serves as
a major measurement index for a specific local climate.
6. Thunderstorms. Thunderstorms can be used as a reference for the
lightning protection design of the concentrator. The mean number
of thunderstorm days in a year obtained through multiple years of
observation is referred to as the mean number of thunderstorm days
in a year, in which a day with at least one instance of audible
thunder is recorded as one thunderstorm day.
7. Overcast conditions. The number of longest continuous overcast
days and dates of occurrence have significant reference values for
thermal storage system design. In Changsha of Hunan, during
1440 h from January to February 2012, sunshine duration was only
38.6 h. The city encountered its most severe continuous overcast
condition in 60 years, with more than 50 overcast days. Such a
location is obviously not suitable for establishing an CSP plant.
8. Freeze. Moist soil freezes when the temperature drops to 0 C. This is

called frozen ground in meteorology. The maximum frozen ground
depth refers to the maximum value of frozen ground depth over a
year, which can be used as a reference for foundation and thermal
pipeline design. In the urban area of Beijing, the maximum frozen
ground depth approximates 85 cm and exceeds 100 cm in Badaling,
is about 103 cm in Lanzhou, and is 200 cm in Harbin. An alternate
concept is standard frozen ground depth, which refers to the mean
value of frozen ground depth over years.
9. Snow accumulation. On flat and broad ground, snow accumulation
depth refers to the vertical depth of the snow layer; maximum snow
accumulation depth refers to the maximum depth of snow
accumulation at a certain location over years, which can be used as a
reference in concentrator load design. If the concentrator is
equipped with snow-avoidance control, it is not necessary to
consider the respective load during heliostat and parabolic trough
concentrator design. Figs. 2.16 and 2.17 indicate the condition of the
concentrator after a heavy snow on November 5, 2012.