Environmental Engineering Reference
In-Depth Information
10.1.6.1 Pyroelectric Energy Harvesting: Concepts and a Theoretical
Evaluation of the Performance
Pyroelectric energy harvesting devices can be divided into two groups. The prop-
erty of the devices in the
rst group is that they do not need any external control and
any external electrical power source. They simply take advantage of the change of
the spontaneous polarization of the pyroelectric material due to its temperature
fl
uctuation. We will name this group of devices the self-driven pyroelectric energy
converters. On the other hand, the devices in the second group work on the basis of
the so-called Ericsson or Olson thermodynamic cycle [
67
]. In order to execute such
a cycle, an external voltage source and therefore a power supply is needed.
Self-Driven Pyroelectric Energy Converters
The most straightforward technique to convert the temperature
uctuations of a
pyroelectric material into electrical energy is based on the concept already descri-
bed in Sect.
10.1.4
. In this case, the pyroelectric material is cyclically subjected to
the temperature
fl
uctuations and, as a consequence, if the pyroelectric material is
short-circuited, an electrical current is generated, as stated in Eq. (
10.16
). A tem-
perature
fl
uctuation in a pyroelectric material can be induced in many different
ways, for example, by the changing weather conditions (such as solar radiation [
63
,
68
]) or by the alternating movement of a pyroelectric material from a heat source to
a heat sink [
69
,
70
]. The electrical energy can then be harvested using different
electrical circuits, thereby subjecting the pyroelectric material to different thermo-
dynamic cycles. Some of them were presented and discussed in detail by Sebald
et al. [
71
]. An important characteristic of such devices is that they do not need any
external power supply and could therefore be used instead of batteries for powering
sensors, monitoring hot pipes and microcontrollers. Some of the
fl
rst such prototype
devices are presented later in this chapter.
Pyroelectric Energy Harvesters Based on the Ericsson Cycle
In contrast to the self-driven pyroelectric energy converters, a pyroelectric material
used in a device working under the pyroelectric Ericsson cycle must be connected
to a voltage source. The material is subject to the thermodynamic cycle presented in
Fig.
10.17
. Let us start with our explanation in the lower left corner of the cycle,
where in its initial state the pyroelectric material is subjected to a small electric
eld
(E
low
) and has the temperature T
high
.
In the
rst step (1
-
2), the temperature of the material is decreased to T
low
at a
constant electric
eld and thereby the polarization of the material increases. In the
next step (2
eld is isothermally increased to the value E
high
and the
polarization of the material increases even further. Then the material`s temperature
is decreased at a constant electric
-
3), the electric
eld (3
4) and in the last step the electrical
eld is
-
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