Page 67 - Design of Solar Thermal Power Plants

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2.4 CALCULATING METHODS FOR SOLAR POSITION 59

For a vertical surface with b ¼ 90 , Eq. (2.10) turns into:

cos q ¼ sin d cos f cos g þ cos d sin f cos g cos u þ cos d sin g sin u
(2.11)
For a surface that revolves by surrounding a horizontal eastewest axis,
only adjusting the slope during the midday so that the incident solar
radiation can be perpendicular to the surface, the corresponding solar
incidence angle calculation during daytime is as follows:
2
2
cos q ¼ sin d þ cos d cos u (2.12a)
The corresponding daily ﬁxed surface slope angle is:
b ¼ jf dj (2.12b)
The azimuth angle of surface normal is 0 or 180 degrees, which is
determined by local latitude and solar declination angle; namely:
g ¼ 0 ; ifðf dÞ 0

(2.12c)

g ¼ 180 ; ifðf dÞ < 0
For a surface that continuously revolves by surrounding a horizontal
eastewest axis and is required to revolve to the point where the solar
incidence angle is of minimum value at a speciﬁed time, the corre-
sponding incidence angle equation is:

q ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
p ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
2 2 2 2
cos q ¼ 1 sin q z sin g ¼ 1 cos d sin u (2.13a)
s
The corresponding equation for the surface slope angle is:
tan b ¼ tan q z jcos g j (2.13b)
s
The azimuth angle of surface normal is 0 or 180 degrees, namely:
g ¼ 0 ; if jg j 90

s
(2.13c)
g ¼ 180 ; if jg j > 90

s
For a surface that continuously revolves by surrounding a horizontal
northesouth axis and is required to revolve to the point where the solar
incidence angle is of minimum value at a speciﬁed time, the corre-
sponding incidence angle equation is:
q ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
3
2
2
cos q ¼ cos q z þ cos d sin u (2.14a)
The corresponding equation for the surface slope angle is:
tan b ¼ tan q z jcosðg g Þj (2.14b)
s

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