Several strings of series-connected solar cells can be connected in parallel, which is
sometimes done in PV modules for rural applications. In principle, several groups of
parallel-connected cells can also be connected in series. However, this is not usually done
in reality because when cells are connected in parallel, the currents become higher which
increases resistivity losses in the cables.
The reader may have noticed that we used I-V curves, i.e. the current-voltage
characteristics, in the previous paragraphs. This is different to Chapters 4–14, where we
used J-V curves instead, i.e. the current density–voltage characteristics. The reason for this
switch from J to I is that PV modules usually are characterized by short circuit and
maximum power point currents instead of current densities. As the area of a module is a
constant, the shapes of the I-V and J-V curves of a module are similar.
For a total module, therefore, the voltage and current output can be partially tuned via
the arrangements of the solar cell connections. Figure 15.3 (a) shows a typical PV module
that contains 36 solar cells connected in series. If a single junction solar cell has a short
circuit current of 5 A, and an open circuit voltage of 0.6 V, the total module would have an
output of V oc = 36 × 0.6 V = 21.6 V and I sc = 5 A.
However, if two strings of 18 series-connected cells are connected in parallel, as
illustrated in Figure 15.3 (b), the output of the module will be V oc = 18 × 0.6 V = 10.8 V
and I sc = 2 × 5 A = 10 A. In general, for the I-V characteristics of a module consisting of m
identical cells in series and n identical strings in parallel, the voltage multiplies by a factor
m while the current multiplies by a factor n. Modern PV modules often contain 60, 72 or
even 96 solar cells that are usually all connected in series in order to minimize resistive
losses and to enable high voltages that are required for an efficient operation of the
inverter, which we will discuss in Section 19.2.
sometimes done in PV modules for rural applications. In principle, several groups of
parallel-connected cells can also be connected in series. However, this is not usually done
in reality because when cells are connected in parallel, the currents become higher which
increases resistivity losses in the cables.
The reader may have noticed that we used I-V curves, i.e. the current-voltage
characteristics, in the previous paragraphs. This is different to Chapters 4–14, where we
used J-V curves instead, i.e. the current density–voltage characteristics. The reason for this
switch from J to I is that PV modules usually are characterized by short circuit and
maximum power point currents instead of current densities. As the area of a module is a
constant, the shapes of the I-V and J-V curves of a module are similar.
For a total module, therefore, the voltage and current output can be partially tuned via
the arrangements of the solar cell connections. Figure 15.3 (a) shows a typical PV module
that contains 36 solar cells connected in series. If a single junction solar cell has a short
circuit current of 5 A, and an open circuit voltage of 0.6 V, the total module would have an
output of V oc = 36 × 0.6 V = 21.6 V and I sc = 5 A.
However, if two strings of 18 series-connected cells are connected in parallel, as
illustrated in Figure 15.3 (b), the output of the module will be V oc = 18 × 0.6 V = 10.8 V
and I sc = 2 × 5 A = 10 A. In general, for the I-V characteristics of a module consisting of m
identical cells in series and n identical strings in parallel, the voltage multiplies by a factor
m while the current multiplies by a factor n. Modern PV modules often contain 60, 72 or
even 96 solar cells that are usually all connected in series in order to minimize resistive
losses and to enable high voltages that are required for an efficient operation of the
inverter, which we will discuss in Section 19.2.