Fluke 381 Service Guide

Troubleshooting

photovoltaic systems:

three typical problems

Application Note

By Ron Auvil

With the push to energy independence and renewable
energy sources, HVAC technicians need to know how
to troubleshoot photovoltaic systems

With the energy situa­tion and problems in the
last few years has come
a major effort to increase
the amount of energy from
renewable resources. State
and federal government
policies in many areas
mandate increased use
of solar power. An HVAC
technician who is servic­ing other equipment in the
building might encoun­ter solar power systems.
Because the concepts and
arrangements of these
systems are new to HVAC
technicians, a short over­view of the systems and
components is in order.

Photovoltaic systems convert
sunlight (photo) into electrical
power (voltaic). The sunlight that
strikes the semiconductor mate­rial in the individual cells causes
electrons to move through a
wire. The electricity gener­ated by photovoltaic systems
can be used to run a range of
equipment, from domestic appli­ances to commercial production
equipment.

There are a number of vari­ables in a PV system, but
ordinarily the PV array is
mounted on a roof that faces
the south as much as possible.
Obstructions are avoided. Note

This electrical conduit connects a series of sola r cell arrays.

that less power will be gener­ated in the winter than the
summer due to the shorter days.
Also, maximum power will be
generated at midday rather than
in the morning or evening.

As part of the PV installa­tion, some facilities provide a
real-time computer display that
shows the amount of energy
produced by the PV display, the
dollars saved, and the amount
of fossil fuel usage avoided. It is
great to know that facilities are
increasingly leading the way to
energy independence and low­ering the amount of pollutants
released into the atmosphere!

The electricity generated by a
PV system may be used imme­diately by that facility, stored, or

in some cases sold back to the
local electric utility.

It is only natural for facilities
that have PV systems installed
to expect HVAC technicians to at
least know the basics. As these
systems become more com­monplace we may be expected
to perform some basic trouble­shooting of them.

Components of a PV
system

PV systems consist of the follow­ing general components:

Individual cells. An indi­vidual cell is a small part of a
PV system. A cell consists of
the semiconductor material, a
support structure, and a trans­parent material that allows the

From the Fluke Digital Library @ www.fluke.com/library

sunlight to strike the semicon­ductor 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 combin­ers. 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 pres­ent. 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 pro­duced by a PV system is dc. The
vast majority of loads in a build­ing 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, concen­trator/combiner and inverter.
The PV system in the build­ing may be providing power to
HVAC equipment or affecting the
power quality of the building.
This means that HVAC techni­cians 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 troubleshoot­ing 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 capabili­ties 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
vital for troubleshooting these
photovoltaic problems. Since
large numbers of wires connect
each module and array to the

attaches the i Flex™

Clamp Meter as he
prepares to trouble­shoot a photovoltaic

™ probe is absolutely

A technician

flexible current

probe of a 381

system.

concentrator box, the junction
boxes are stuffed with individual
wires. The iFlex

™ probe makes

the measurement of the individ­ual 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 infor­mation 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 mod­ules. You will have to trace out
the individual branch wiring
backward from the concentra­tor. Again, the iFlex

™ makes this

an easier job than it would be
otherwise.

2 Fluke Corporation Troubleshooting photovoltaic systems: three typical problems