Environmental Engineering Reference
In-Depth Information
represents a penalty factor due to the presence of solar cell material, glass and EVA for
a glass-to-glass PV/T system, and
α
c
represents absorptance of the solar cell.
The solar exergy rate is calculated by
1
I
T
0
T
sun
A
1000
×
Ex
so
=
−
(3.3.14)
where
Ex
so
represents solar exergy rate, and
T
sun
represents temperature of the Sun.
The thermal energy and exergy efficiencies of the solar thermal system are defined
as
Q
so
I
×
A
η
th,en
=
1000
(3.3.15)
Ex
PV
/
T
Ex
so
η
th,ex
=
(3.3.16)
where
1
T
0
T
c
Ex
PV
/
T
=
×
Q
so
−
τ
g
×
β
c
×
I
×
(α
c
−
η
c
)
+
U
t
×
T
0
+
h
t
×
T
bs
T
c
=
U
t
+
h
t
z
×
I
+
(
U
t
+
U
tb
)
×
T
0
+
h
ba
×
T
air
T
bs
=
U
b
+
h
ba
+
U
tb
exp
−
b
×
U
L
×
L
˙
exp
−
b
×
U
L
×
L
˙
⎡
⎤
⎡
⎤
T
0
1
−
1
−
×
×
h
p2G
z
I
m
a
×
cp
a
m
a
×
cp
a
⎣
1
⎦
+
⎣
⎦
T
air
=
+
×
−
T
ai
×
U
L
b
×
U
L
×
L
b
×
U
L
×
L
m
a
×
˙
cp
a
m
a
×
˙
cp
a
where
Ex
PV
/
T
represents exergy rate of PV/T,
T
c
represents cell temperature,
U
t
repre-
sents the overall heat transfer coefficient from solar cell to ambient through the glass
cover,
h
t
represents the heat transfer coefficient from a black surface to air through
glass,
T
bs
represents back surface temperature,
U
tb
represents the overall heat trans-
fer coefficient from glass to black surface through solar cell,
h
ba
represents the heat
transfer coefficient from black surface to air,
T
air
represents temperature of air flowing
through the duct, and
U
b
represents the overall heat transfer coefficient from bottom
to ambient.
The electrical energy and exergy efficiencies of solar PV system are defined as
W
so
I
×
A
η
el,en
=
1000
(3.3.17)
η
el,ex
=
η
c
×
(1
−
0
.
0045
×
(
T
c
−
25))
(3.3.18)
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