Hybrid Energy Harvesting System - Energy Harvesting Autonomous Sensor Systems - page 140

of the output power of the solar panel P pv ( V pv ), which is expressed as follows:

V pv I o exp V pv
n s V t

1

P pv ( V pv ) = V pv I pv = V pv I L − −

V pv I o exp

V pv
n s kT c

≈ V pv I sc − (5.3)

/ q

I sc
[130]. The harvested PV power P pv ( V pv ), as expressed in Equation 5.3 , is for-
mulated as a function of the PV voltage V pv , and it can be estimated based on
the technical characteristics of the PV module and the environmental variables
such as light irradiance and ambient temperature. Based on Equations 5.1
and 5.3 , the current voltage (I-V) and power voltage (P-V) curves of a solar
panel at a particular solar irradiance and operating temperature are plotted
in Figure 5.2 .
Referring to Figure 5.2 , there exists a particular operating voltage and cur-
rent of a PV module under a certain irradiance and temperature that yields
the maximum power throughput P ma x . The maximum power point (MPP) of
the PV module seen in Figure 5.2 corresponds to a specific operating volt-
age V mppt and current I mppt .Various maximum power point tracking (MPPT)
techniques have been discussed in the literature [133, 134] to operate the PV
module at its MPPs. These MPPT techniques include perturbation and ob-
servation (P&O), incremental conductance (IncCond), constant voltage (CV),
fractional open-circuit voltage (FOCV), and others.
Among the MPPT techniques, the P&O method is most commonly used by
the majority of researchers in large-scale PV systems [74-87]. It is an iterative

Note the term exp ( V pv / n s V t ) 1 and the light-generating current, I L ≈

P max

I sc

I mpp

MPP

V mpp

V oc

PV Voltage (V)

FIGURE 5.2
Maximum power points on I-V and P-V curves of a photovoltaic module.