Page 72 - Advances in Renewable Energies and Power Technologies

6. Circuit and Device Simulation of Solar Cells and Modules 45

fraction. Ideally r ¼ 0, and a ¼ 0for l ¼ 0.3e1 mm. There is no ideal optical
cover. Acrylic absorbs much less than glass. The content of iron in glass affects
its transmittance. Especially the overall reflected part of the incident solar radiation
on solar cells can be reduced by the cover if the optical matching condition is satis-
fied. This can be achieved by choosing the encapsulate refractive index
p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
n e ¼ n cover n sc ,where n cover is the refractive index of the cover and n sc is
the refractive index of the antireflective coating of the solar cell. The glassing fac-
tor F g is defined by the ratio of the output power with encapsulation to the output
power without encapsulation, i.e., F g ¼ (P o with cover)/(P o without cover) [36].
This factor may be less or slightly greater than 1. It describes the optical perfor-
mance of the encapsulation.

6. CIRCUIT AND DEVICE SIMULATION OF SOLAR CELLS
AND MODULES
6.1 CIRCUIT-LEVEL SIMULATION
The equivalent circuit models are widely used to simulate PV cells and modules. The
main advantage of using circuit models is the availability of the standard electrical
Ò
software such as Matlab (or Simulink) and PSpice, where the PV model can be
easily integrated into a larger system. The choice of any simulation program stands
behind the desire of giving the reader the ability of modifying system parameters
freely and examining the corresponding effects.
PSpice has become the standard industrial electrical circuit simulator. Most
semiconductor devices are modeled such that they can be included in the Pspice li-
brary. The models of the PV cell could be implemented by using subcircuit capa-
bility found in most PSpice programs [37].
Ò
In addition, Matlab has become an important mathematical tool for simulation
in all areas of engineering. Implementation of equations needed for modeling the PV
Ò
cell is an easy task and can be done either by using Matlab functions or Simulink
models [38]. The purpose of this section is to demonstrate a simple, yet effective way
Ò
to model solar cells using Matlab and PSpic.
6.1.1 Summary of Mathematical Modeling
The first step in circuit simulation of solar cells is to build a mathematical model
representing the governing equations. Table 1.1 summarizes the basic mathematical
equations based on the single-diode model of the solar cell explained in Section 1.4,
where the temperature dependence of parameters is also included.
6.1.2 Parameter Extraction
The precise modeling of a solar cell model is based on the accuracy of the
extracted parameters in that model. It is necessary to identify the model param-
eters before the use of the selected model to simulate the cell behavior. According
to the model presented above, there are five parameters to be extracted; I ph , I s , R s ,