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, rooftop solar PV systems are free from many of the mechanical wear, heat and pressureinduced maintenance issues that other types of energy generation equipment 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 could potentially experience include: Pecan Street performed an analysis of the 255 PECAN STREET VISUAL IDENTITY - COLOR STUDY 14197 homes with rooftop solar panels that have participated in its ongoing customer energy research over the past four years. The analysis focused on the following: What maintenance events, if any, did each home s solar PV system encounter? How long did it take the system owner to discover the issue? Significant maintenance issues significant maintenance issues such as panel failures or inverter failures 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 wiring, (4) solar PV breakers being inadvertently turned off and (5) ground fault interruptions triggered by rain- or humidity-induced moisture penetrating the array s electrical system. Two homes (0.8 percent) experienced significant equipment issues. Both were inverter failures. No owner experienced equipment failures or other significant maintenance issues with their solar panels. Minor maintenance issues Another 54 homes experienced one of a variety of minor maintenance issues. Repairing these issues typically required about an hour of electrician labor and less pecanstreet.org
than $25 in parts. In some instances, the issue could be resolved by the homeowner without need for parts or service. Ground fault interruptions were the most common minor maintenance issue, followed by blown AC fuses. Difficulties detecting maintenance issues All of the residential solar PV system owners 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 before the system restarts. As such, these maintenance issues can resemble reduced generation from weather events. Some maintenance events cannot easily be detected by analyzing that home s generation data alone but instead require comparing that home s generation to generation from other residential solar PV systems in the same region. Solar PV systems typically do not provide visual or auditory cues about maintenance events. Even the most engaged customers burn out on checking their data constantly. Implications 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 PV systems weeks to months of lost value from their solar panels. A best-practices maintenance system should include data measurement equipment coupled with software that alerts owners to maintenance issues. Such a system would 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. page!2
Sample and Methodology The sample consisted of 255 homes participating in Pecan Street s residential energy research. Nearly all of the solar PV systems were less than three years old. Six of the homes were located outside of Austin (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 circuits. Residents had access to their home s real-time solar panel generation and energy use through a web portal. The web portal did not proactively alert residents if an outage occurred. A maintenance event was one in which one of the following occurred: the solar PV system suffered a total outage for at least a day, or the solar PV system experienced reduced generation due to a component failure or disconnection that required the services of an electrician or installation firm before normal operations would resume 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 Panel malfunction or failure A maintenance issue was characterized as significant if it required replacement of a major system component, including the inverter or one or more of the solar panels. An issue was characterized as minor if its resolution required de minimis parts such as a new fuse and less than two hours of 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 page!3
completely. For ground fault interruptions, the inverter would typically restart after a few days. Several homes experienced days with no generation due to cloud cover, rain or snow. Outages due to such weather conditions are not included as maintenance events. 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 project manager or master electrician also interviewed the resident. Methodologies for evaluating the performance of rooftop solar PV and of customer interactions with any technology are transferable and broadly applicable. However, if an analyst needs to determine the susceptibility of rooftop solar PV to maintenance issues in a particular locale, homes with solar panels in that locale must be studied. That s because climatic impacts on solar PV systems are highly location specific. Variables include ambient temperature, 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. 13 systems experienced blown AC fuses. 6 systems experienced blown DC fuses. 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 days. Of the remaining 17 homes that experienced outages from ground fault interruptions, homes averaged four outage events. The page!4
average outage lasted 3.5 days, with outages ranging from one to 18 days. Maintenance events were not confined to a 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 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 Street. 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 the system shutting off completely Detecting some maintenance events requires access to generation data from other homes in the same region These two factors are are closely linked. In short, before a system owner could recognize that a system was performing below normal, the owner would need some information on what constituted normal. Reduced generation can occur in two primary variants: 1. Periods of complete outages surrounded 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. 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. A system owner looking at his or her data would continue to see a system that was generating electricity. If the owner detected the reduced generation, he or she might still conclude the reduced levels were due to inclement weather conditions over that 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 multiple site investigations had been performed. Standard diagnostics processes for evaluating the condition of a rooftop solar panel system determined (incorrectly) that the entire systems were operating. page!5
40 20 11/1/13 3/1/14 6/29/14 10/27/14 100% 0% -100% 11/1/13 3/1/14 6/29/14 10/27/14 40% 0% -40% Nov Jan Mar May Jul Sep Three views of solar panel performance for a home with a failing inverter. 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. 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. Source: Pecan Street Failing inverters also show diminished generation over a prolonged period before the system stops producing entirely. For one of the two systems with failing inverters, the rooftop system oscillated between normal generation levels (for that system) and diminished levels for nearly a year. 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). Solar panels, however, operate noiselessly. The absence of operating noise therefore would not alert the system owner that the system had stopped working. The maintenance issues observed here did not lead to smoking or fires, meaning the systems provided no visual cues about their maintenance conditions. And because solar panel systems typically are grid tied, the owner s electricity service typically will not go 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 consumers. However, even solar PV owners lose interest in constantly engaging with their solar PV system s data. page!6
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 circuit. If a lightning strike hits the solar PV system, the excess voltage could cause the AC fuse to blow. However, solar panels are typically installed with surge arrestors. Surge arrestors are one-event devices. Therefore, a lightning strike could cause the AC fuse to blow if it is the second lightning strike to hit the solar PV system and the surge arrestor was not replaced after the first lightning strike. A transient voltage event on the grid could theoretically also cause an AC fuse to blow. This is unlikely, however, because the transient event would most likely impact the inverter before it would impact the fuse. 33 22 11 11/1/13 12/31/13 3/1/14 4/30/14 6/29/14 8/28/14 10/27/14 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. page!8
as long as 10 months had passed. As with blown AC fuses, a blown DC fuse can result from a short circuit that occurs when insulation surrounding wiring at the panels becomes exposed. This can happen if the 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 metallic surface, this can trigger a short circuit. A blown DC fuse can also result if the fuse is undersized or if wiring connections between the panels and the inverter become loose Finally it is rare, but possible, for a fuse or circuit breaker to degrade over time and open circuit with normal operating currents. 40 30 20 10 11/1/13 12/31/13 3/1/14 4/30/14 6/29/14 8/28/14 10/27/14 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. 100% 50% 0% -50% -100% 11/1/13 12/31/13 3/1/14 4/30/14 6/29/14 8/28/14 10/27/14 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. page!9
Maintenance detail: Ground fault A ground fault can occur through a variety of reasons, but moisture getting inside the inverter or wiring system is likely the most common reason. For example, three homes in the studied sample went off-line due to ground faults on September 18, 2014 a day on which Austin 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). When a ground fault occurs, the solar PV system is shut off. Many inverters will automatically re-set and re-start the PV system, though in the studied sample, this could take over a week to occur. Ground faults can also typically be re-set through a menu on inverter screen. This suggests that if a PV system owner received prompt notification of a ground fault, the owner could re-start the system sooner. 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 PV system is at risk of additional interruptions after future rain or high humidity events. 33 22 11 5/15/14 6/14/14 7/14/14 8/13/14 9/12/14 10/12/14 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. page!10