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four times more electrical power than its counterpart WEH system using a
standard power management circuit. Although the developed WEH system
is validated to deliver more electrical power, a larger energy storage device is
required to store the greater of harvested energy. The stored electrical energy
is used to prolong the operational lifetime of the sensor node in times when
wind is not available. In this chapter, other than relying on the energy storage
device to sustain the sensor node's operations, another EH system to harvest
solar energy in the same environment as the WEH system is explored and
then developed for proof of concept. The role of the additional SEH system
is to augment the reliability and performance of the wind-powered wireless
sensor node.
5.2.2
SEH Subsystem
An overview of the proposed SEH subsystem is illustrated in Figure 5.3 . In
the SEH subsystem, a small solar panel with a physical dimension of 60 mm
×
60 mm is utilized as an energy harvester to harvest solar energy from the sun-
light. The characteristic of the solar panel is first determined experimentally,
followed by the design of a suitable power management circuit to ensure max-
imum power flow from the solar panel to the energy storage device, hence
the electrical load (i.e., wireless sensor node).
5.2.2.1 Characterization of a Solar Panel
The experimental setup for the SEH subsystem is constructed to simulate sun-
light in the laboratory with a controlled environment. It is difficult to conduct
experiments in an outdoor environment where the natural sunlight tends to
fluctuate over time. There is no control over the light intensity of the sunshine.
Hence, the light intensity and spectrum of the sunlight are emulated with a
light source that closely resembles the frequency spectrum of the sunlight.
The light source is an OSRAM 300W Ultra Vitalux lightbulb that has the sun-
like radiation properties and is widely used in industrial applications [141]
for lighting purposes. To vary the solar irradiance of the emulated light, a
variable transformer was used to control the electrical input power to the
lightbulb. The P-R and P-V curves (see Figures 5.4 and 5.5 , respectively) of
the solar panel were obtained experimentally through the variation of the
solar irradiance level and with different load resistances connected across
the solar panel. Throughout the characterization process of the solar panel,
the temperature of the solar panel was kept constant by having a constant
stream of air blowing across the solar panel.
The P-R curve seen in Figure 5.4 illustrates how the source impedance of
the solar panel varies with the changing solar irradiance. As can be seen, the
source impedance of the solar panel decreases from 350 to 50
as the light
irradiance level increases from 80 to 800 W/m 2 . This is due to the higher
output current generated by the solar panel at higher solar irradiance. Com-
paring between the P-R curves of the wind turbine generator and the solar
panel given in Figure 2.4 and Figure 5.4 , respectively, it is clearly seen that
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