angle at or near the location’s latitude will give the most energy on an annual
basis. Tilt angles of latitude plus or minus 15 degrees will increase energy produc-
tion in winter and summer, respectively Figure 4-1.
Central Inverter Concept
PV cells, modules, strings, and arrays produce electricity in the form of direct
current (DC). The array captures energy in times of high insolation. A charge
controller stores the energy in a battery bank or on the grid. Storing energy makes
it available during periods of no insolation.
When voltages match, you can run DC-powered devices directly from the
PV system. Most electrical devices are manufactured to use AC, however. For this
reason, PV systems need an inverter to convert DC to AC. If the PV system is
grid-tied, the inverter will automatically mirror the AC waveform produced by
the grid. Most PV systems use a single inverter, although some systems do use
more than one (although the number of inverters used is limited).
Module Inverter Concept
Instead of using a single or a limited number of inverters, PV designers some-
times use micro inverters. When a system uses micro inverters, it means that each
module has its own micro inverter. There are advantages and disadvantages to
using micro inverters in a PV system.
PV modules mounted by PerfectPower in Phoenix, Ariz., showing module orientation.
Courtesy of PerfectPower, Inc.
One advantage of using micro
inverters is that you mount them
on the back of each module, which
reduces energy loss. Matching
modules and their inverters
together is critical to ensure max-
imum efficiency of the module
and the PV system. The micro
inverter is specific to the module,
which may give the PV designer
greater flexibility.
Because there is one inverter
per module, strings size is limited
to one. This can help address
shading issues on complex roof
structures or where it is difficult to
assemble coherent strings. In addi-
tion, you can monitor micro
inverters on each individual
module. Because you can individ-
ually monitor each module, it is
easy for the client or the moni-
toring company to identify a trou-
blesome panel.
There are some disadvantages
to micro inverters. Because each
panel has its own micro inverter,
there are more inverters that can
fail. More micro inverters also
mean more parts and more con-
nections. This makes the PV
system complicated. Complicated
systems are more likely to fail than
simple systems.
Micro inverters solve shading issues, but reduce the panel’s efficiency by 25 to
50 percent. It can be difficult to fit all the micro inverters in the system. You should
locate micro inverters where they will be easy to replace if necessary. Another dis-
advantage of the micro inverter is that it requires more monitoring than other
parts of a PV system. If the PV system owner chooses, a monitoring company can
be hired to take care of this, although this would create additional expense.
90° angle to the sun
Less sun on a
vertical surface
Less sunlight comes through
on a horizontal surface
FIGURE 4–1 Module tilt.
Photovoltaic Array Configuration and Sizing 75

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