Sun path calculations including definitions

Sun path calculations including definitions of Examples of zenith angle, latitude. Sun-earth geometry. The sun’s position relative to the earth is first described by the
earth’s rotation about its polar axis. Irradiance
Irradiance is the rate that radiant
energy arrives on a surface of specific
area at a particular time (W/m2)
Direct Normal Irradiance (DNI) is the solar radiation received per unit area on a surface that is perpendicular
(i.e. normal) to incoming solar rays By maintaining a surface such that is always normal to incoming radiation we can maximise the energy captured

1. Examples of zenith angle:
London latitude f=51.5º
Ecliptic
plane
N
S
N
S
Winter solstice Summer solstice
23.5º
23.5º
51.5º
Zenith angle q=51.5º+ 23.5º = 75º
Cos 75º= 0.26, I
b
=351 W/m
2
51.5º
q=28º
q=75º
Zenith angle q=51.5º-23.5º=28º
Cos 29º= 0.88, I
b
=1188 W/m
2
sun
Vernal Equinox
Autumnal Equinox

2. Irradiance
Irradiance is the rate that radiant
energy arrives on a surface of specific
area at a particular time (W/m
2
)
Direct Normal Irradiance (DNI) is the
solar radiation received per unit area
on a surface that is perpendicular
(i.e. normal) to incoming solar rays
By maintaining a surface such that is
always normal to incoming radiation
we can maximise the energy captured
DNI (W/m
2
)
90º

3. Sun-earth geometry
N
δ
Sun rays
(DNI)
Equator
normal
ω
θ
The sun’s position relative to the earth is first described by the
earth’s rotation about its polar axis.
Latitude, ϕ
Hour angle,ω
declination, δ
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