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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