Environmental Engineering Reference
In-Depth Information
of these challenges related to the weak and uncertain energy sources, EH in
an indoor environment from a single energy source might not be adequate to
sustain the operation or even to enhance the performance of the miniaturized
wireless sensor nodes over the lifetime.
Hybrid energy harvesting has been recently discussed in the literature
[35, 126-129] as a potential micropower supply solution to minimize the size of
the energy supply as well as to extend the operational lifetime of the wireless
sensor node. Researchers have considered a number of methods to combine
different small-scale EH sources, and these methods can be classified into four
main categories as described in Section 5.2. For the first three HEH methods
discussed in the literature, each EH source is required to have its own unique
power management unit (i.e., DC-DC converter) and associated circuitry to
condition the power flow from the energy source to its output load. As more
energy sources are combined, the number of power management units for
each individual energy source increases, hence more components are needed
and larger volumetric size, higher power losses, and costs are incurred. This
is not the case for the fourth HEH method proposed in this chapter. The pro-
posed HEH system requires only one power management unit to condition
the combined output power harvested from the solar and thermal energy
sources.
Emphasis of this section is placed on enhancing the performance of the
wireless sensor node deployed in the challenging indoor context using HEH
from solar and thermal energy sources. A near MPPT technique is explored for
the HEH system to maximize power transfer from the hybrid energy sources
to the sensor node. The rest of the section is organized as follows: Section 5.3.1
provides an overview of the indoor energy sources. Section 5.3.2 illustrates
the details of the indoor SEH subsystem, while Section 5.3.3 explains the TEH
subsystem. Section 5.3.4 discusses how the SEH and TEH subsystems are
combined directly in parallel configuration. Following that, the optimized
HEH system using a single power management unit for an indoor wireless
sensor node prototype is illustrated in Section 5.3.5; the section ends with a
summary and discussion in Section 5.3.6.
5.3.1
Overview of Indoor Energy Sources
The characteristics and performances of the renewable energy sources avail-
able in outdoor environmental conditions are very different from those found
in indoor industrial, commercial, and biomedical environments. Within an
enclosed environment like offices, hospitals, factories, and so on, the energy
sources are generally generated by some artificial means. Table 5.2 shows a
summary of the indoor energy sources and their characteristics.
As seen in Table 5.2 , the artificial energy sources found in an indoor envi-
ronment are generated from electrical appliances such as artificial lighting,
air conditioners, machines, and so on, and human movement. Each of these
appliances and human bodies has its own primary purpose. Artificial light-
ing and an air conditioner, for example, are primarily used to generate light
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