Environmental Engineering Reference
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Harvested Electrical Power (µW) vs. Load Resistance (kΩ)
250
∆
T
= 5 K
∆
Maximum Power
Points (MPPs)
T
= 7 K
∆
T
= 10 K
200
150
100
50
0
0
50
82 kΩ
100
150
200
Load Resistance (kΩ)
FIGURE 5.21
P-R curves of a thermoelectric generator at different thermal gradients.
5.3.4
HEH from Solar and Thermal Energy Sources
5.3.4.1 Characteristics of a Solar Panel and Thermal Energy Harvester
Connected in Parallel
For the HEH approach proposed in this section, the terminal output voltages
of the solar panel and the thermal energy harvester
V
pv
and
V
TEG
,respectively,
are directly connected to the load, each via a Schottky diode to block reverse-
biased current flow. An overview of the equivalent electrical circuit of the
hybrid energy harvester is shown in
Figure 5.22
.
According to
Figures 5.17
and
5.20
, the output voltages of the two energy
sources are not that low, typically a few volts, hence the series energy sources
configuration is not used to step up the voltage across the load
V
R
L
. Instead,
a parallel energy source configuration,
V
R
L
=
V
pv
=
V
TEG
,isemployed to
produce more current flows, that is,
I
R
L
I
TEG
. The power harvested
from the solar panel
P
pv
(
V
pv
) and the thermal energy harvester
P
TEG
(
V
TEG
),
expressed by
Equations 5.3
and
5.10
, respectively, are summed together to
=
I
pv
+
I
pv
I
TEG
+
+
+
I
D
R
S
D
pv
D
TEG
I
RL
R
s,TEG
V
oc
I
L
+
-
V
pv
V
RL
R
L
V
TEG
-
-
-
FIGURE 5.22
Equivalent electrical circuit of the proposed hybrid energy harvester.
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