Application Note

2 Fluke Corporation Troubleshooting photovoltaic systems: three typical problems
sunlight to strike the semicon-
ductor material. The cell must be
physically tough as it is exposed
to the weather. The transparent
material that covers the cell also
must be stain and dirt resistant.
Each individual cell produces
only a few watts of electricity.
Modules and arrays. A
module consists of a number
of cells connected together
side by side. Modules may be
in either series or parallel, as
needed to obtain the desired
voltage and current. Since each
individual cell only produces
a small amount of electricity
large numbers of them must be
joined together to get significant
amounts of electricity. As may
be imagined, these modules can
become quite large and limited
by the size of the roof dedicated
to their use. Modules joined
together are then called arrays.
Wiring connects the individual
cells together to form these
arrays. The arrays are then
wired together to a central point.
Concentrators and combin-
ers. A concentrator or combiner
is a central wiring point for the
cells and modules. It represents
the aggregate power output
of the entire solar array. Even
though the output of each solar
cell is small, at the point where
multiple modules are connected
many amps of current are pres-
ent. Metering and conditioning
of the power may also take
place at the concentrator. The
concentrator is then connected
to either electrical storage or an
inverter. Storage may consist of
a large number of batteries.
Inverters. The power pro-
duced by a PV system is dc. The
vast majority of loads in a build-
ing are ac. An inverter is used
to convert the dc power created
by the modules into usable ac
power. The output of the inverter
may also be connected to the
local utility so that any excess
unused power is put back into
the grid and purchased by the
local utility to be used by other
customers. Metering and power
monitoring equipment are
installed here as well.
Since there are really few
components in a PV system
there are not many things to go
wrong. As mentioned previously
the major components are the
cells, modules, arrays, concen-
trator/combiner and inverter.
The PV system in the build-
ing may be providing power to
HVAC equipment or affecting the
power quality of the building.
This means that HVAC techni-
cians may need some basic
troubleshooting skills. (After all,
we are expected to know how to
work on everything on the roof
anyway, right?)
Three typical PV
troubleshooting
situations
In the examples below, the
person doing the troubleshoot-
ing is taking advantage of the
features of the new Fluke 381
Remote Display True-rms Clamp
Meter with iFlex™. While you
can use a true-rms ac/dc clamp
meter with voltage capabili-
ties for most of the work, we
used the Fluke 381 because
of its wireless feature (remote
readout and display), and the
iFlex
™ flexible current probe.
The iFlex
™ probe is absolutely
vital for troubleshooting these
photovoltaic problems. Since
large numbers of wires connect
each module and array to the
concentrator box, the junction
boxes are stuffed with individual
wires. The iFlex
™ probe makes
the measurement of the individ-
ual module wires MUCH easier,
thus saving time and increased
accuracy.
Troubleshooting Problem #1:
Cell/Module/Array Problem
As with any troubleshooting
call, try to get as much infor-
mation from the customer as
possible. Try to find out when
the problem occurred and when
the last time the PV system
operated normally. Get as much
information, such as prints,
outputs, and wiring diagrams, as
possible.
A good place to start is to
check the output of the entire
system at the metering system
or at the inverter. Prior to getting
on the roof, check and record
the inverter’s input voltage and
current level from the array. If
the entire PV system is down
and not producing power it may
be an inverter problem. If the PV
system is operating at a reduced
power output the problem may
be one of the arrays or mod-
ules. You will have to trace out
the individual branch wiring
backward from the concentra-
tor. Again, the iFlex
™ makes this
an easier job than it would be
otherwise.
A technician
attaches the iFlex™
flexible current
probe of a 381
Clamp Meter as he
prepares to trouble-
shoot a photovoltaic
system.