to create a visual impact is to post photos. Photos of the PV system, diagrams of
the PV system, and informational data make a great impact. No one can truly see
a PV array in action when it is mounted to a roof.
Long-Term Behavior of PV Modules
PV systems function very well if planned and installed properly. The modules are
the most crucial component in a PV system. The modules are also the most
durable components. Studies have concluded that well-built 50-year-old silicon
PV modules can operate at 70 to 75 percent of their original output power. This
takes into account weathering and aging. All PV modules experience initial degra-
dation for a time after production. The degradation tapers off.
Damage or abuse to the PV modules accelerates aging.
The type of plastic used to encase the module also accelerates aging. Thin-
film PV modules degrade more quickly than other PV module types. Thin-film
PV modules have inconsistent deterioration characteristics. Unfortunately, the
degradation characteristics are not well understood. As a result, thin-film PV
module performance decreases. It decreases anywhere from 0.25 percent to
0.5 percent per year, or worse.
Quality and Reliability of Inverters
Inverters are the weakest component link in a PV system. They usually operate
without worry for five to eight years. But after 10 years, many inverters have to
be replaced. There are several causes of inverter faults and failures including
The NREL’s newest PV array at the National Wind Technology Center near Boulder, Colo.
Courtesy of DOE/NREL
CHAPTER 10 Quality Control, Testing, Troubleshooting, Monitoring 251
over- and under-voltage conditions from loading, temperature, power surges,
short circuits, yield losses, fuse failures, and faulty surge protectors.
In high-performing PV systems, inverters can last 18 to 20 years. Check with
the PV manufacturer about inverter warranties and manufacturer’s guarantees.
There are service agreements that last up to 20 years. These service agreements
include replacement as well as routine service.
Inverters are usually very reliable. They become less reliable if they are over-
loaded or placed in the sun. The best way to ensure that your inverter does not
overload is to apply the 80 percent inverter loading rule, and continuously mon-
itor it. Remember to perform scheduled maintenance—on schedule.
At present, many if not most PV systems have oversized arrays on undersized
inverters. The data indicates that matching the inverter and modules to the
inverter MPPT window and not the NEC window will work better, provide better
output, and last longer.
Stacking a number of inverters in a cabinet provides redundancy and increases system uptime
in the event of a unit failure. This Fronius product allows the master inverter to change,
thereby leveling usage on each unit, and can bypass a nonperforming inverter until it can be
repaired or replaced.
Courtesy of Kopie
252 ADVANCED PHOTOVOLTAIC INSTALLATIONS
Chapter 10 Summary
This chapter looks at quality control issues, system and component testing, system
monitoring, and troubleshooting. It also explains troubleshooting principles and
procedures for PV power systems. The chapter aids in evaluating a PV system’s
common issues and devising resolutions for those issues. It concludes with
describing maintenance requirements for various PV system components such as
arrays, batteries, inverters, and charge controllers.
Ampere (A)
Archimedes hydrometer
Extensible markup language (XML)
Irradiance meter
Refractive index hydrometer
Relational database system
Chapter 10 aSSeSSment
Quality Control, Testing, Troubleshooting, Monitoring,
and PV System Operations and Maintenance
1. Inverters may be heavy, weighing as much as 150 pounds.
A. True
B. False
2. Inverters can last between _______ years in high-performance PV systems.
A. 3 to 5
B. 10 to 12
C. 18 to 20
D. 20 to 30
3. When mounting a heavy inverter or other piece of equipment to a “drywall”
type of wall, to provide a solid attachment to the wall it may be necessary
to use:
A. thumb tacks.
B. plastic anchors.
C. plywood.
D. bolts.
Key ConCeptS and termS
CHAPTER 10 Quality Control, Testing, Troubleshooting, Monitoring 253
4. Which of the following is the first step in system checkout after completing the
installation?
A. Test open-circuit voltage.
B. Visually check the entire system.
C. Install the source-circuit fuses.
D. Close all disconnects.
5. What is the first thing to do before applying PV power to an inverter, a charge
controller, batteries, and load?
A. Check the polarity of the PV output.
B. Install the source-circuit fuses.
C. Call the electrical inspector.
D. Close all disconnects.
6. If the current in one source circuit is significantly lower than the currents in
the remaining source circuits of a PV array, and all modules are in full sun, then
without disconnecting any conductors, an appropriate follow-up test is to:
A. measure the individual module currents in this source circuit.
B. measure the voltage at the inverter input.
C. calculate the short-circuit current of this source circuit.
D. determine the individual module voltage and current in this source
circuit.
7. Which of the following are causes of PV system faults?
A. An internal fault at the inverter
B. Connection faults due to loose wiring
C. Flawed string fuses
D. Defective bypass diodes
E. Imperfect surge voltage protectors
F. Faults with insulation
G. All of the above
8. Studies have concluded that a well-built, 50-year-old PV module can operate
at _______ percent of its original output power.
A. 50
B. 90
C. 35
D. 75
254
ADVANCED PHOTOVOLTAIC INSTALLATIONS
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