Download Chapter 7: Troubleshooting PV Systems

OBJECTIVES
1. Identify the three general steps required for the diagnostics and
troubleshooting of PV systems and demonstrate knowledge of their use.
2. Identify PV system maintenance requirements and demonstrate service
procedures for modules, arrays, batteries, power conditioning equipment,
safety systems, and weather sealing systems.
3. Demonstrate how to measure PV system performance and compare with
specifications.
4. Demonstrate how to perform PV diagnostic procedures and troubleshooting
skills.
5. Demonstrate how to identify PV performance safety issues, and implement
corrective measures.
6. Demonstrate how to test and verify PV system installation functionality and
integrity using proper wire labeling, wire mapping, wire placements,
input/output verifications, and prior documentation.
7. Demonstrate when to communicate with technical support, and what
information is relevant.
(continued)
OBJECTIVES (CONTINUED)
8. Compile, maintain, and deliver appropriate manuals and documentation
(records of system operation, performance, and maintenance activities) to
the client upon the completion of the PV installation.
9. Identify demarcation issues, along with the responsibilities of associated
trades and/or utilities.
If the PV system fails, determine:
Has it been cloudy for several days? Maybe the
battery bank simply needs recharging.
Is the array blocked (shaded) by something, or is
it dirty?
Are any fuses or circuit breakers blown or tripped?
Any loose connections?
Are any connections corroded?
Is the wiring system operating with proper polarity?
(continued)
If the PV system fails, determine: (continued)
Is the system operating under proper voltage
and current?
Are the modules and batteries properly
connected (series and parallel configuration)?
Are any of the components physically
damaged?
The following steps help to round out the general
problem-solving process.
1
Analyze the problem thoroughly enough to be
able to create a clear problem statement. With
a clear problem statement in mind, define the
observed symptoms and their potential causes.
2
Gather enough facts in order to help isolate the
possible causes of the problem.
3
Consider the possible problem causes based on
the facts gathered.
(continued)
The following steps help to round out the general
problem-solving process. (continued)
4
Create an action plan based on those causes.
Begin with the most likely problem, and devise
a plan in which only one variable will be
manipulated.
5
Implement the action plan, performing each
step carefully while testing to see whether the
symptom disappears.
6
Analyze the results to determine whether the
problem is resolved.
(continued)
The following steps help to round out the general
problem-solving process. (continued)
7
Terminate the process if the problem is
resolved.
8
If the problem is not resolved, create an action
plan based on the next most probable cause,
and return to Step 4 to repeat the process until
the problem is solved.
Figure 7-1: Digital Multimeter
Figure 7-2: DC Voltage Check
WARNING
When setting the meter, it is normal
practice to first set the meter to its
highest voltage range, to make certain
that the voltage level being measured
does not damage the meter.
Figure 7-3: Testing an Outlet
WARNING
Remember to keep the power off.
Unlike the voltage check, resistance
checks are always made with power
removed from the system.
Figure 7-4: Measuring Current
The various sections of a photovoltaic system
include components such as:
Photovoltaic cells. These are thin squares, discs,
or films of semiconductor material that generate
voltage and current when exposed to sunlight.
Panels. These are various configurations of
individual PV cells, laminated between a clear
glazing.
(continued)
The various sections of a photovoltaic system
include components such as: (continued)
Arrays. These consist of one or more panels,
wired together to provide a specific voltage.
Figure 7-5 illustrates how cells, modules, panels,
and arrays are related.
Charge controllers. These are equipment
components that regulates battery voltage.
Battery storage. The medium used to store
direct current electrical energy.
(continued)
Figure 7-5: Photovoltaic Cell, Module, Panel, and
Array Example
The various sections of a photovoltaic system
include components such as: (continued)
Inverters. These are electrical devices that
change direct current into alternating current.
DC loads. These are appliances, motors, and
equipment powered by direct current.
AC loads. These are appliances, motors, and
equipment powered by alternating current.
The various arrangements of PV modules and
panels include:
Strings. A string consists of a number
of PV panels connected in series.
Arrays. An array consists of a number of
PV strings connected in parallel.
Figure 7-6: Cleaning the PV Module
Figure 7-7: Partial Shading of a 36-Cell PV Module
Figure 7-8: A Combiner Box
Voltages between strings should match closely
when the sunlight is consistent. Keep the
following key points in mind:
NEC 690.7(A) requires that the open circuit
voltage be multiplied by a correction factor based
on the lowest expected ambient temperature.
Convention dictates that the lowest expected
ambient temperature is the same as the minimum
recorded temperature.
Voltages over 600V are not permitted in one
and two family dwellings, as per NEC690.7(C).
(continued)
Voltages between strings should match closely
when the sunlight is consistent. Keep the
following key points in mind: (continued)
For the majority of New York State, if the nominal
Voc is over 480Vdc then the system will exceed the
600V limit.
Voc over 600Vdc can damage inverters, insulation,
and switchgear.
Open circuit voltage of PV panels is temperature
dependent, generally –0.4%/° C.
(continued)
Voltages between strings should match closely
when the sunlight is consistent. Keep the
following key points in mind: (continued)
Voc is not a strong function of irradiance and it
comes up pretty quickly at dawn before any
direct radiation hits or heats the PV modules.
Night sky radiation actually cools the modules a
few degrees below the ambient temp and that is
why you get frost above 32° F.
The lowest daily temperatures generally occur
just before sunrise.
Table 7-1: Color Coding for AC and DC PV Circuits
Figure 7-9: Multi-contact PV Connectors
Figure 7-10: A Solarlok Junction Box
Figure 7-11: Huber+Suhner Connectors
Table 7-2: IP Ratings
Figure 7-12: A Basic PV Wiring Example
Figure 7-13: PV System Fuses for 600Vdc and
1000Vdc Systems
Figure 7-14: Normal PV Module Operations
Figure 7-15: A Shaded PV Module Hot Spot with No
Bypass Diodes
Figure 7-16: A Shaded PV Module Hot Spot with
Bypass Diodes
Figure 7-17: Module IV Curves With and Without
Bypass Diodes
Figure 7-18: Bypass Diodes Housed In Module
Junction Boxes
Two situations in which blocking diodes can help
prevent the phenomenon include:
1
Blocking reverse current flow from the battery
through the module at night. In battery
charging systems, the module potential drops
to zero at night, and the battery could
discharge all night backwards through the
module. This would not be harmful to the
module, but would result in loss of precious
energy from the battery bank. Diodes placed in
the circuit between the module and the battery
can block any nighttime leakage flow.
(continued)
Two situations in which blocking diodes can help
prevent the phenomenon include: (continued)
2
Blocking reverse current flow through damaged
modules during the day, originating from parallel
modules. In high-voltage systems during daylight
conditions, blocking diodes can be placed at the head
of separate series-wired strings. If one string be
comes severely shaded, or if there is a short circuit in
one of the modules, the blocking diode prevents other
strings from losing current backwards through the
shaded/damaged string. The shaded/damaged string
is “isolated” from the others, and more current
reaches the load. In this configuration, blocking
diodes are called “isolation diodes.”
If the voltage level is too low at the point where
the battery storage system connects to the PV
system, then there are several options to
consider:
The PV system is not supplying enough current to
the battery system to keep it charged up – a PV
panel or string is not functioning, the disconnect(s)
are open, one of the monitoring devices is faulty, or
an overcurrent device has blown or tripped.
(continued)
If the voltage level is too low at the point where
the battery storage system connects to the PV
system, then there are several options to
consider: (continued)
One or more of the batteries in the system is failing
– when a cell within a battery fails, the entire
battery may fail (refusing to take a charge) or it
may simply produce a lower than specified output
voltage. In either case, you will have to isolate the
defective battery and replace it with a working
one. In complex storage systems, this will involve
isolating the terminals of each battery one-by-one
to test its output.
(continued)
If the voltage level is too low at the point where
the battery storage system connects to the PV
system, then there are several options to
consider: (continued)
There has simply not been enough light present to
produce sufficient output to charge the battery
storage system – check for dirty panels or shading
that may be diminishing the output of the PV
array.
Figure 7-19: Battery Storage System Connection Point
If the input voltage is correct, but no (or
improper) output voltages are present, there
are several possibilities to consider:
The battery storage system is configured
improperly (incorrect series-parallel connections)
There are bad connections or devices between the
charge controller and the battery storage system,
causing the charge controller to not sense the
presence of the batteries (charge controllers shut
down when no load is connected to them)
(continued)
If the input voltage is correct, but no (or
improper) output voltages are present, there
are several possibilities to consider: (continued)
One or more of the batteries in the storage system
are defective
The Charge Controller is defective (or it could be
incorrectly sized for the panel array/battery
storage system configurations)
Figure 7-20: A Simple Charge Controller
Figure 7-21: Load Diverter Duties
If the inverter’s input voltage to the inverter is
low (or missing), check the battery storage
system to determine the cause of the low voltage.
Possible causes can include:
The battery storage system is configured
improperly (incorrect series-parallel
connections). Verify the battery system
configuration and rewire as necessary to
achieve the correct configuration.
(continued)
If the inverter’s input voltage to the inverter is
low (or missing), check the battery storage
system to determine the cause of the low voltage.
Possible causes can include: (continued)
There are bad connections or devices between
the inverter and the battery storage system (or
the charging controller), causing excessive
voltage drop between the battery system and the
inverter. Make sure the cabling is large enough
to handle the current flow from the battery
storage system or the PV system. Tighten all the
connections between the batteries and the
inverter.
(continued)
If the inverter’s input voltage to the inverter is
low (or missing), check the battery storage
system to determine the cause of the low voltage.
Possible causes can include: (continued)
One or more of the batteries in the storage
system are defective. Replace the battery
with a working unit.
(continued)
If the inverter’s input voltage to the inverter is
low (or missing), check the battery storage
system to determine the cause of the low voltage.
Possible causes can include: (continued)
The inverter’s load is too large and is pulling
AC current out of the inverter faster than the
battery/PV array systems can produce DC
current to replace it. Disconnect the load and
check the output of the inverter without it.
Manually reset the unit by turning it off and
then back on.
(continued)
If the inverter’s input voltage to the inverter is
low (or missing), check the battery storage
system to determine the cause of the low voltage.
Possible causes can include: (continued)
The Charge Controller or Diverter/Regulator
output voltage is too high, causing the
inverter to shut down for self-protection
purposes.
(continued)
If the inverter’s input voltage to the inverter is
low (or missing), check the battery storage
system to determine the cause of the low voltage.
Possible causes can include: (continued)
The input vents for the inverter’s fan may
be clogged causing it to shut down due to
overheating - clear the vents so that cooling
air can move freely through the inverter.
Allow the inverter to cool off before
restarting it.
CAUTION
Always make sure to disconnect the
AC source before disconnecting any
of the DC connections.
Troubleshooting documentation exists in two
categories:
1
Documentation that was originally organized
or created by the installation team, or previous
repair personnel.
2
Documentation that you, the troubleshooting
technician must generate during any repair
scenario.
Figure 7-22:
A Residential
Solar PV
Wiring
Diagram with
Overlay
Figure 7-23: A Cable Tester