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Direction of Beam Radiation: The geometric relationships between a plane of
any particular orientation relative to the earth at any time and the incoming
beam solar radiation can be described in terms of several angles (Latitude(
φ
),
Declination(
δ
), Slope(
β
), Surface azimuth angle(
γ
), Hour angle(
ω
), Angle of
incidence(
θ
), Zenith angle(
θ
z
), Solar altitude angle (
α
s
) and solar azimuth
angle (
γ
s
)).
Observer-Sun Angles
θ
z
=
90
o
−
α
s

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ψ
ψ
ψ
α
sin
Sun’s Position
α
=
sin
δ
sin
φ
+
cos
δ
cos
ω
cos
ψ
=
sin
α
sin
φ
−
sin
δ
cos
α
cos
ω
Zenith

S
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Source: Photovoltaic systems Engineering by Messenger & Ventre, CRC 2000.
Observer-Sun Angles

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