Hukseflux SR05 series - Appendix On Meteorological Radiation Quantities

SR05-D1A3-PV manual v1801 71/83
9.6 Appendix on meteorological radiation quantities
A pyranometer measures irradiance. The time integrated total is called radiant exposure.
In solar energy radiant exposure is often given in W∙h/m
2
.
Table 9.6.1 Meteorological radiation quantities as recommended by WMO (additional
symbols by Hukseflux Thermal Sensor). POA stands for Plane of Array irradiance. The
term originates from ASTM and IEC standards.
SYMBOL DESCRIPTION CALCULATION UNITS ALTERNATIVE
EXPRESSION
E↓
downward irradiance
E↓ = E
g
↓ + E
l
↓
W/m
2
H↓
downward radiant exposure
for a specified time interval
H↓ = H
g
↓ + H
l
↓
J/m
2
E
↑
upward irradiance
E
↑
= E
g
↑
+ E
l
↑
W/m
2
H↑
upward radiant exposure
for a specified time interval
H↑ = H
g
↑ + H
l
↑
J/m
2
W∙h/m
2
Change of
units
E direct solar irradiance
normal to the apparent
solar zenith angle
W/m
2
DNI Direct
Normal
Irradiance
E
0
solar constant W/m
2
E
g
↓
h
global irradiance;
hemispherical irradiance on
a specified, in this case
horizontal surface.*
E
g
↓
= E cos θ
h
+ E
d
↓
W/m
2
GHI
Global
Horizontal
Irradiance
E
g
↓
t
global irradiance;
hemispherical irradiance on
a specified, in this case
tilted surface.*
E
g
↓ = E∙cos θ
t
+
E
d
↓
t
+ E
r
↑
t
***
W/m
2
POA Plane of
Array
E
d
↓
downward diffuse solar
radiation
W/m
2
DHI Diffuse
Horizontal
Irradiance
E
l
↑
, E
l
↓
upward / downward long-
wave irradiance
W/m
2
E
r
↑
reflected solar irradiance
W/m
2
E* net irradiance
E* = E↓ – E↑
W/m
2
T
↓
apparent surface
temperature**
ºC or K
T↑
apparent sky
temperature**
ºC or K
SD
sunshine duration
h
θ is the apparent solar zenith angle θ
h
relative to horizontal, θ
t
relative to a tilted surface
g = global, l = long wave, t = tilted *, h = horizontal*
* distinction horizontal and tilted from Hukseflux,
** T symbols introduced by Hukseflux,
*** contributions of E
d
↓
t
and E
r
↑
t
are E
d
↓ and E
r
↑ both corrected for the tilt angle of the
surface