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Cells, Modules, and Arrays
Photovoltaic Cells
Current-Voltage (I-V) Curve
Device Response
Modules and Arrays
Basic Building Blocks
The basic building
blocks for PV
systems include
cells, modules,
and arrays.
Semiconductors
Semiconductor
materials with
special electrical
properties can be
made by adding
small amount of
other elements to
silicon crystals.
Photovoltaic Effect
The photovoltaic effect produces free electrons that
must travel through conductors in order to recombine
with electron voids, or “holes”.
PV Material Efficiencies
Various PV materials and technologies
produce different efficiencies.
Monocrystalline Ingots
Monocrystalline silicon wafers are
sawn from grown cylindrical ingots.
Electromagnetic Spectrum
Polycrystalline
silicon wafers are
sawn from cast
rectangular ingots.
Cell Fabrication
Several steps are involved
in turning silicon wafers into
PV cells.
Different PV Cells
The different materials,
processes, and
manufacturing steps
produce a range of PV
cell types.
I-V Curve
An I-V curve
illustrates the
electrical output
profile of a PV
cell, module, or
array.
Open-Circuit Voltage
Open-circuit voltage
is easily measured
with a digital
multimeter (DMM).
Short-Circuit Current
Using in-line and
clamp-on ammeters
are two methods of
measuring shortcircuit current.
I-V Curve with Power
A power against
voltage curve
clearly shows the
maximum power
point.
Fill Factor
Fill factor
represents the
shape of an I-V
curve.
Efficiency
Efficiency is a
measure of how
effectively a PV
device converts
solar power to
electrical power.
Equivalent Circuit
A PV cell can be
modeled by a
current source in
parallel with a
diode, with
resistance in series
and in parallel.
Series Resistance
Increasing series
resistance in a
PV system
flattens the knee
in the I-V curve,
reducing
maximum power,
fill factor, and
efficiency.
Shunt (Parallel) Resistance
Decreasing shunt
resistance reduces
fill factor and
efficiency and
lowers maximum
voltage, current,
and power, but it
does not affect
short-circuit current.
Solar Irradiance Response
Voltages increases
rapidly up to about
200 W/m2, and then
is almost constant.
Current increases
with irradiance.
Temperature Response
Increasing cell
temperature
decreases voltage,
slightly increases
current, results in a
net loss of power.
Module Construction
Modules are
constructed from PV
cells surrounded by
several layers of
protective materials.
Arrays of PV Modules
An array is a group
of PV modules
integrated as a
single powergenerating unit.
Panel from Modules
Several modules
may be connected
together to form a
panel, which is
installed as a
preassembled unit.
Junction Box
A junction box on the
back of a module
provides a protected
location for electrical
connections and diodes.
Series Connections of Cells and Modules
PV cells or
modules are
typically
connected in
series strings to
build voltage.
I-V Curves of Series Strings
The overall I-V characteristics of a series strings
are dependent on the similarity of the current
outputs of the individual devices.
Parallel Connections
Strings of PV cells or modules may be connected
in parallel to build current.
Building an Array
Modules are added in series
to form strings or panels,
which are then combined in
parallel to form arrays.
I-V Curve for PV Devices in Parallel
The overall I-V characteristics
of a system of PV devices in
parallel are dependent on the
similarity of the current
outputs of the individual
devices.
Bypass Diode
Bypass diodes allow current to flow around devices that
develop an open circuit or high-resistance condition.
Breakdown Voltage
A bypass diode prevents
a large breakdown
voltage from allowing a
PV device to dissipate a
large amount of power.
Module Nameplates
Module nameplates must
include performance
ratings for the module and
may include other
information used to design
a PV system.
Test Conditions
Various test conditions
can be used to evaluate
module performance
and may produce
different results.