Environmental Engineering Reference
In-Depth Information
Chapter 2
Solar Radiation
I
NTRODUCTION
The sun is by far the most significant source of renewable energy. The previous
chapter showed that energy from geothermal sources and planetary gravitation
are relatively insignificant compared with solar energy. This abundant source
of energy can be utilized directly by solar thermal or photovoltaic systems. In
principle, wind power and hydro-electricity are transformed solar energy and
are sometimes called indirect solar energy.
This chapter is dedicated to solar irradiation, since knowledge of solar
irradiation is important for many renewable energy systems. Later sections
contain calculations in the field of photometry. Table 2.1 summarizes the most
important photometric quantities; for the use of solar energy, mainly radiation
physics-based quantities are used. Daylight quantities refer only to the visible
part of light, whereas solar energy also includes invisible ultraviolet and
infrared light.
Many of the following calculations use physical constants, a summary of
which is given in the Appendix.
T
HE
S
UN AS A
F
USION
R
EACTOR
The sun is the central point of our solar system; it has probably been in
existence for 5 billion years and is expected to survive for a further 5 billion
Table 2.1
Important Radiant Physical Quantities and Daylight Quantities
Radiant physical quantities
Daylight quantities
Name
Symbol
Unit
Name
Symbol Unit
Radiant energy
Q
e
Ws = J
Quantity of light
Q
v
lm s
Radiant flux/radiant
power
Φ
e
W
Luminous flux
Φ
v
lm
Specific emission
M
e
W/m
2
Luminous exitance
M
v
lm/m
2
Radiant intensity
I
e
W/sr
Luminous intensity
I
v
cd = lm/sr
Radiance
L
e
W/(m
2
sr)
Luminance
L
v
cd/m
2
Irradiance
E
e
G
W/m
2
Illuminance
E
v
lx = lm/m
2
Irradiation
H
e
Ws/m
2
Light exposure
H
v
lx s
Note:
W = watt; m = metre; s = second; sr = steradian; lm = lumen; lx = lux; cd = candela
Source:
DIN, 1982; ISO, 1993
