Page 331 - A Comprehensive Guide to Solar Energy Systems

336 A CoMPreheNSIVe GuIDe To SolAr eNerGy SySTeMS

grid operation. In addition, the issues and failure types of PV systems, cells and modules
are discussed to highlight the limitations on energy harvesting, and provide an insight
into future improvements.

16.2 Electrical Characteristics of PV Cells/Modules

A solar PV cell is simply a diode that is optimized to absorb photons from the sun and
convert them into electrical energy. The amount of solar power available per unit area is
called the irradiance and is usually expressed in watts per square meter. The efficiency of
a PV cell basically defines how effectively the irradiance (available power at the surface)
is converted to a useful power at the output terminals of a PV cell that is connected to an
electrical load. however, due to the unique electrical characteristics of PV cells (nonlinear
current–voltage relationship), a matching circuit (converter) is commonly required to ob-
tain the maximum power. Therefore, it is important to consider the electrical characteris-
tics of PV cells as they have a direct impact on converter design, which may be connected
to an electrical load directly or injecting power to a local AC grid.
Typical PV cells exhibit the current–voltage characteristic curve as seen in Fig. 16.3A.
Note that in a converter design, five critical values of such curves are utilized namely the

FIGURE 16.3 Typical characteristics of PV cells and modules (A) current–voltage and power curves of a healthy PV cell,
(B) current–voltage curves of a cracked cell, (C) current–voltage curves of a failed cell, and (D) current–voltage curves of
a module which accommodates power electronics.