Minor maintenance issues proving difficult to detect
for many solar PV system owners
Challenges occurring even when system owners have access to their realtime and historical generation data
Lack of detection leads to extended system outages from minor issues such as ground
fault interruptions and blown fuses
Vol. 2 • No. 5
Executive Summary
With no moving parts or internal combustion,
Pecan Street performed an analysis of the 255
rooftop solar PV systems are free from many
homes with rooftop solar panels that have
of the mechanical wear, heat and pressure-
participated in its ongoing customer energy
induced maintenance issues that other types
research over the past four years. The analysis
P E C A N S T R E E T V I S UA L I D E N T I T Y - C O LO R S T U DY
of energy generation equipment encounter.
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focused on the following:
• What maintenance events, if any, did each
home’s solar PV system encounter?
Because solar PV systems are located
outdoors and contain sophisticated
electronics, however, they can be expected to
encounter other maintenance issues.
Maintenance issues that any solar PV system
• How long did it take the system owner to
discover the issue?
could potentially experience include:
Significant maintenance issues
• significant maintenance issues — such as
panel failures or inverter failures
Two homes (0.8 percent) experienced
• minor maintenance issues (in terms of cost
and difficulty of repair) — such as (1)
blown AC fuses, (2) blown DC fuses, (3)
intermittent generation due to loose
“significant” equipment issues. Both were
inverter failures. No owner experienced
equipment failures or other significant
maintenance issues with their solar panels.
Minor maintenance issues
wiring, (4) solar PV breakers being
inadvertently turned off and (5) ground
Another 54 homes experienced one of a
fault interruptions triggered by rain- or
variety of “minor” maintenance issues.
humidity-induced moisture penetrating the
Repairing these issues typically required
array’s electrical system.
about an hour of electrician labor and less
pecanstreet.org
than $25 in parts. In some instances, the issue
generation from other residential solar PV
could be resolved by the homeowner without
systems in the same region.
need for parts or service.
Ground fault interruptions were the most
common minor maintenance issue, followed
by blown AC fuses.
• Solar PV systems typically do not provide
visual or auditory cues about maintenance
events.
Difficulties detecting maintenance issues
• Even the most engaged customers burn out
on checking their data constantly.
All of the residential solar PV system owners
Implications
had access to their system’s real-time and
historic generation. Even so, many system
owners did not discover the maintenance
issue until they were contacted by Pecan
Street. In many instances, their systems were
down for weeks to months before the owner
discovered the maintenance issue.
Several factors contribute to making it
difficult for solar PV system owners to detect
maintenance issues even when they have
access to their generation data. They include:
• Some maintenance issues result in reduced
generation rather than than the system
shutting off.
• Some maintenance issues cause the solar
PV system to shut off for a only a few days
To the extent the observations reported here
are replicated in other research, they
primarily raise the following implications:
• Having real-time and historic generation
data was critical to identifying many
maintenance issues. In several instances,
analysis of a system’s generation data
identified a maintenance issue when other
typical methods for identifying
maintenance issues as part of an on-site
inspection did not detect the issue.
• Providing solar PV system owners with their
data was frequently insufficient for owners
to detect maintenance issues in a timely
manner. As a result, even minor, easily
fixed maintenance issues cost these solar
before the system restarts. As such, these
PV systems weeks to months of lost value
maintenance issues can resemble reduced
from their solar panels.
generation from weather events.
• Some maintenance events cannot easily be
detected by analyzing that home’s
• A best-practices maintenance system should
include data measurement equipment
coupled with software that alerts owners to
generation data alone but instead require
maintenance issues. Such a system would
comparing that home’s generation to
function in a manner similar to a check
engine light on a car.
Confidential to Pecan Street licensees. Do not distribute without permission of Pecan Street.
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Sample and Methodology
The sample consisted of 255 homes
participating in Pecan Street’s residential
• the solar PV system experienced reduced
generation due to a component failure or
energy research. Nearly all of the solar PV
disconnection that required the services of
systems were less than three years old. Six of
an electrician or installation firm before
the homes were located outside of Austin
normal operations would resume
(Boulder, Dallas, Houston, Pflugerville and
Plano); the balance were located in Austin.
In all 255 homes, the rooftop systems were
installed by solar PV installation firms
selected and managed by the homeowner. At
least nine companies installed solar PV
systems for homes in the sample. Pecan Street
did not perform or manage any of the rooftop
solar PV installations.
All homes were instrumented with current
transformer (CT) systems installed at the
resident’s breaker panel box. These CT
systems reported one-minute interval
electricity use and solar panel generation to
Pecan Street’s datacenter. In most homes, the
CT systems also measured up to 23 additional
Potential maintenance issues included:
• Fuse for AC circuit blows
• One of the DC circuit fuses blows
• Ground fault interruptions
• Wiring becomes disconnected
• Some panels are inadvertently not
connected during installation
• Panels are turned off at solar breaker box
by a non-solar contractor working on
electrical service unrelated to the solar PV
system and are not turned back on
• Inverter failure
circuits.
• Panel malfunction or failure
Residents had access to their home’s real-time
A maintenance issue was characterized as
solar panel generation and energy use
through a web portal. The web portal did not
proactively alert residents if an outage
“significant” if it required replacement of a
major system component, including the
inverter or one or more of the solar panels.
occurred.
An issue was characterized as “minor” if its
A “maintenance event” was one in which one
new fuse and less than two hours of
of the following occurred:
• the solar PV system suffered a total outage
for at least a day, or
resolution required de minimis parts such as a
anticipated labor by an electrician or installer.
Blown DC circuit fuses and failing inverters
resulted in diminished solar PV system
generation. The other maintenance issues
resulted in the system shutting down
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completely. For ground fault interruptions, the
Methodologies for evaluating the
inverter would typically restart after a few
performance of rooftop solar PV – and of
days.
customer interactions with any technology –
Several homes experienced days with no
are transferable and broadly applicable.
generation due to cloud cover, rain or snow.
However, if an analyst needs to determine
Outages due to such weather conditions are
the susceptibility of rooftop solar PV to
not included as maintenance events.
maintenance issues in a particular locale,
All maintenance issues were confirmed as
such by Pecan Street’s master electrician, lab
director, or both. For most of the identified
maintenance issues, Pecan Street’s research
homes with solar panels in that locale
must be studied. That’s because climatic
impacts on solar PV systems are highly
location specific.
project manager or master electrician also
Variables include ambient temperature,
interviewed the resident.
humidity and precipitation for that location.
Observations
Pecan Street field researchers recorded the
following maintenance events from the
studied sample:
Significant maintenance issues
• None of the maintenance events occurred
due to a malfunction or failure of the solar
panels.
• Two systems experienced inverter failures.
Minor maintenance issues
• 29 systems experienced outages to their
rooftop solar panels from ground fault
interruptions.
• In one home, an electrician working on
non-solar panel electrical work turned off
the solar panel breakers and failed to turn
them back on after completing work. This
was not discovered for three weeks.
• For two systems, a portion of the home’s
solar panels were never connected at the
time of installation.
• 4 systems’ outages were characterized as
unknown. In each, the solar panels were
off for a single day
Of the homes that experienced ground fault
outages, 11 experienced one such event. The
average duration of this single outage was 7.3
• 13 systems experienced blown AC fuses.
days.
• 6 systems experienced blown DC fuses.
Of the remaining 17 homes that experienced
outages from ground fault interruptions,
homes averaged four outage events. The
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average outage lasted 3.5 days, with outages
Reduced generation can occur in two primary
ranging from one to 18 days.
variants:
Maintenance events were not confined to a
1. Periods of complete outages surrounded
particular solar panel installer. Observed
incidents occurred in homes installed by at
least five installers.
Of the six non-Austin homes, two in Texas
experienced maintenance events (blown AC
fuse and inverter failure). Two homes in
Boulder experienced multi-day outages due to
snow accumulation; these are not included
among the listed maintenance events.
Difficulties detecting maintenance issues
by periods of normal generation
2. Periods of reduced generation with no
outages
Ground fault interruptions are an example of
complete outages surrounded by periods of
normal generation. These outages – which
represent the most frequently observed
maintenance issue – are particularly difficult
to identify for customers whose only
generation data comes from a monthly utility
bill.
All of the residential solar PV system owners
had access to their system’s real-time and
historic generation. Even so, system owners
frequently did not discover maintenance
issues until they were contacted by Pecan
Blown DC fuses are an example of
maintenance conditions that will frequently
shut down a portion of the overall system
while the other portions continue to generate.
Street.
A system owner looking at his or her data
Several factors contribute to making it
generating electricity. If the owner detected
difficult for solar PV system owners to detect
the reduced generation, he or she might still
maintenance issues even when they have
conclude the reduced levels were due to
access to their generation data. They include:
inclement weather conditions over that
• Some maintenance issues result in
reduced generation rather than the
system shutting off completely
• Detecting some maintenance events
requires access to generation data from
other homes in the same region
would continue to see a system that was
period.
Pecan Street researchers found two homes
where portions of the rooftop solar PV system
were inadvertently never connected at the
time the system was installed. In both cases,
the cause of the PV system’s
underperformance was not determined until
These two factors are are closely linked. In
multiple site investigations had been
short, before a system owner could recognize
performed. Standard diagnostics processes for
that a system was performing below normal,
evaluating the condition of a rooftop solar
the owner would need some information on
panel system determined (incorrectly) that
what constituted “normal”.
the entire systems were operating.
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Three views of solar panel performance for a
home with a failing inverter.
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The middle graphic shows by what percentage
the system’s daily generation exceeded or fell
short of average generation compared to a larger
sample. As this view shows, even as the system’s
overall performance declined, it still generated at
high levels on many days.
The bottom graphic looks at the system’s
percentage deviation compared to other systems
on a monthly basis. At that view, the existence of
the maintenance issue becomes clearer.
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The top graphic shows the system’s daily
generation (kWh) over one year. It demonstrates
the difficulty of determining the existence of a
maintenance issue from viewing raw generation
data alone.
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Jul
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Source: Pecan Street
Failing inverters also show diminished
system had stopped working. The
generation over a prolonged period before the
maintenance issues observed here did not
system stops producing entirely. For one of
lead to smoking or fires, meaning the systems
the two systems with failing inverters, the
provided no visual cues about their
rooftop system oscillated between normal
maintenance conditions. And because solar
generation levels (for that system) and
panel systems typically are grid tied, the
diminished levels for nearly a year.
owner’s electricity service typically will not go
• Solar PV systems typically do not
provide visual or auditory cues about
maintenance events.
When consumer products such as cars, air
conditioners or light bulbs fail completely or
even partially, they provide visible clues. They
can smoke, make loud noises, or cease
functions with which the end user is directly
interacting (such as when a car stalls).
down if the solar panels cease operating.
In fact, information delivered through data
represents one of the few ways that a
customer can learn of a maintenance issue
with his or her solar panel system.
• Even the most engaged customers burn
out on checking their data constantly.
Solar PV system owners arguably are among
the most engaged and interested electricity
Solar panels, however, operate noiselessly.
consumers. However, even solar PV owners
The absence of operating noise therefore
lose interest in constantly engaging with their
would not alert the system owner that the
solar PV system’s data.
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Maintenance detail : AC Circuit Fuse blows
Photo of two inverters for solar PV system with
two arrays. The panel for the inverter on the right
has been removed. The system disconnect box is
located to the right of the inverters; this houses
the AC fuses for the solar PV system.
Close-up view of system disconnect box with
door closed on left and door open on right. The
two AC circuit fuses are visible. The PV system’s
surge arrestor is the metallic cylinder extending
from the underside of the box.
A solar PV system’s AC circuit fuse is typically
outage had not been fixed when the fuse was
located between the inverter and the home
replaced the first time.
electric service.
A blown AC fuse most commonly will result
When an AC fuse bows, the entire solar PV
from an inverter fault, a short circuit event or
system immediately stops supplying electricity
a lightning strike.
from the rooftop solar PV system.
An inverter fault can occur because of a
Of the six homes in the studied sample that
component failure inside the inverter, such as
experienced blown AC fuses, outages lasted
with a capacitor. If this is the cause of the
one to three months. According to affected
blown fuse, replacing the fuse will not solve
residents who were subsequently interviewed,
the problem, and the system will be prone to
these long outages occurred because the first
later experiencing another blown AC fuse.
electric bill after the AC fuse failure showed
some generation for the month. It was not
until the second electric bill arrived, showing
no generation for the month, that they
realized their systems were not operating.
A short circuit can occur for a variety of
reasons. One possible cause occurs when
insulation surrounding wiring at the panels
becomes exposed. This can happen if the
insulation is rubbed off or it degrades from
Two homes that experienced AC fuse events
exposure to elements (possibly because
later experienced a second blown AC fuse,
conduit comes dislodged). If exposed wiring
suggesting that the underlying cause for the
hits the solar panels’ racking, conduit or other
page !7
metallic surface, this can trigger a short
the second lightning strike to hit the solar PV
circuit.
system and the surge arrestor was not
If a lightning strike hits the solar PV system,
replaced after the first lightning strike.
the excess voltage could cause the AC fuse to
A transient voltage event on the grid could
blow. However, solar panels are typically
theoretically also cause an AC fuse to blow.
installed with surge arrestors. Surge arrestors
This is unlikely, however, because the
are one-event devices. Therefore, a lightning
transient event would most likely impact the
strike could cause the AC fuse to blow if it is
inverter before it would impact the fuse.
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Electricity generation per day (kWh) for one residential solar PV system. The AC circuit fuse for this home’s
rooftop solar PV system blew on Jan. 6, 2014. The homeowner did not realize the system was off-line
until the end of the first full billing cycle without generation; the system was down for 60 days. The
system experienced a second blown AC fuse on Nov. 26, 2014.
Maintenance detail : DC Circuit Fuse blows
While a blown AC fuse will cause the entire
solar PV system to stop generating, a blown
DC fuse will frequently only cause a portion
of the system to stop generating (this is the
portion protected by the fuse).
As a result, the PV system owner may not
realize from looking at generation data that
the system is operating at a degraded level. In
fact, of the six PV system owners who had
experienced blown DC fuses, four did not
discover they had a maintenance issue until
Solar PV system DC fuse. This fuse is only visible
when the front panel of the inverter is taken off.
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as long as 10 months had passed.
As with blown AC fuses, a blown DC fuse can
metallic surface, this can trigger a short
circuit.
result from a short circuit that occurs when
A blown DC fuse can also result if the fuse is
insulation surrounding wiring at the panels
undersized or if wiring connections between
becomes exposed. This can happen if the
the panels and the inverter become loose
insulation is rubbed off or it degrades from
exposure to elements (possibly because
conduit comes dislodged). If exposed wiring
hits the solar panels’ racking, conduit or other
Finally it is rare, but possible, for a fuse or
circuit breaker to degrade over time and open
circuit with normal operating currents.
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The DC circuit fuse for this home’s rooftop solar PV system blew on May 13, 2014. The fuse was
replaced 39 days later on June 20, 2014. During this period, the home’s solar panels did not stop
producing altogether, but rather produced at a lower level. This makes it challenging for a homeowner
to detect a blown DC fuse just by reviewing the system’s generation data.
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This view of the same home’s solar PV system shows by what percentage the solar PV system was
producing more or less than the average of all solar PV systems in the same area. Viewed this way, the
event that resulted in the blown DC fuse becomes obvious.
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Maintenance detail : Ground fault
A ground fault can occur through a variety of
system, though in the studied sample, this
reasons, but moisture getting inside the
could take over a week to occur.
inverter or wiring system is likely the most
common reason.
Ground faults can also typically be re-set
through a menu on inverter screen. This
For example, three homes in the studied
suggests that if a PV system owner received
sample went off-line due to ground faults on
prompt notification of a ground fault, the
September 18, 2014 — a day on which Austin
owner could re-start the system sooner.
received 3.66 inches of rain (nearly all of
which occurred between midnight and 3 am).
Another three homes went off-line due to
ground faults on May 27, 2014 — a day on
which Austin received 1.75 inches of rain
(nearly all of which occurred between 3:30
and 6 am).
Simply re-starting the system will be
insufficient if the underlying reason for the
ground fault interruption remains
uncorrected. For instance, if moisture is
penetrating the wiring because insulation
surrounding the wiring has rubbed off or
degraded from exposure to elements, then the
When a ground fault occurs, the solar PV
PV system is at risk of additional interruptions
system is shut off. Many inverters will
after future rain or high humidity events.
automatically re-set and re-start the PV
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This home experienced four ground fault-causes outages of its solar PV system over five months. The
average duration of each outage was three days. All four outages occurred within 24 hours of rain
totals exceeding one inch.
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