Environmental Engineering Reference
In-Depth Information
Figure 2.13 Definition of the Solar Angle of Incidence on a Tilted Surface
θ tilt = arccos( s n ) =
= arccos(-cos
α S
cos
γ S
cos
α t
sin
γ t -
sin
α S
cos
γ S
sin
α t
sin
γ t + sin
γ S
cos
γ t )
= arccos) - cos
γ S
sin
γ t
cos(
α S -
α t ) + sin
γ S
cos
γ t )
(2.24)
I RRADIANCE ON T ILTED S URFACES
The global irradiance E G,tilt on a tilted surface is composed of the direct
irradiance E dir,tilt , the diffuse sky irradiance E diff,tilt and the ground reflection
E refl,tilt (a factor that does not exist for horizontal surfaces):
E G,tilt = E dir,tilt + E diff,tilt + E refl,tilt
(2.25)
Direct irradiance on tilted surfaces
The horizontal surface in Figure 2.14 with the area A hor
receives the same
radiant power
as a smaller area A s which is normal (perpendicular) to the
incoming sunlight.
Φ
With
Φ dir,hor = E dir,hor
A hor =
Φ dir,s = E dir,s
A s
and
A s = A hor
cos
θ hor = A hor
sin
γ S
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