Six Checks to Detect PCS Failures Early at Solar Power Plants

In solar power plant maintenance, attention often falls on panel soiling, weeds, racking, and cables, while one piece of equipment that is likely to be related to reduced or stopped power generation is the PCS. PCS stands for power conditioner, and it converts the direct current power generated by solar panels into alternating current power that is suitable for grid connection and self-consumption. If a PCS stoppage or output reduction is overlooked, it can lead to lost generation opportunities and delays in recovery response.

Not all PCS abnormalities become apparent only after a complete shutdown. By continuously checking power generation data, alarm history, on-site sounds and odors, temperature increases, ventilation conditions, and deterioration of connections, you may be able to detect signs of failure or abnormalities in surrounding equipment earlier. In this article, we explain the key points for early detection of PCS failures that you should be aware of in practical maintenance of solar power plants, divided into six checks.

Table of Contents

• The importance of early detection of PCS failures

• Check 1 Verify the difference between generated power and PCS unit output

• Check 2 Regularly review error history and shutdown history

• Check 3 Verify temperature rise around the PCS and ventilation issues

• Check 4 Look for signs that can only be detected on site, such as unusual noises, odors, and vibrations

• Check 5 Inspect for degradation of cables, terminals, and connection points

• Check 6 Continue cleaning, environmental management, and record keeping

• How to build a maintenance system that will not overlook PCS failures

• Summary Place PCS inspections at the center of power plant management

Importance of Early Detection of PCS Failures

In a solar power plant, the PCS is the core equipment that converts generated electricity into a usable form. The electricity produced by solar panels is direct current, and for typical grid interconnection or on-site use, conversion to alternating current by the PCS is required. Because the PCS operates properly, the plant can use the generated power for selling to the grid or for self-consumption. Conversely, even if the panels are generating power, if the PCS or peripheral equipment malfunctions, the power may not be fully utilized.

What you should be aware of with PCS failures is that losses can occur even if the entire power plant does not stop completely. In power plants made up of multiple PCS units, even if only one unit stops, the others may still be operating, so the plant as a whole can appear to be generating. However, generation opportunities are lost in the area connected to the stopped PCS, so the longer it takes to discover the problem, the more generation loss accumulates. Also, if degradation of internal components, poor cooling, or faults in peripheral equipment are progressing, what may at first be only temporary output reductions or automatic recoveries can, over time, lead to an increase in shutdown frequency.

What operational staff should emphasize is treating the PCS not only as equipment to be dealt with after it breaks, but as equipment whose condition is monitored on a routine basis. By continuously checking the PCS’s condition during daily, monthly, and annual inspections, it becomes easier to detect signs of abnormalities. Extra caution is required especially during hot seasons, after typhoons, after weather likely to have involved lightning strikes, after heavy rain, in seasons when weeds and dust increase, and after nearby construction, because the PCS and peripheral equipment are more likely to be affected.

In inspections of the PCS, it is important to make a comprehensive judgment that includes not only the numerical values from remote monitoring but also on-site visual checks, sounds, odors, ventilation conditions, signs of rainwater ingress, and the surrounding environment. Even if remote monitoring does not show any abnormalities, on-site inspections may find clogged intake and exhaust vents, weeds around the enclosure, discoloration or corrosion of terminal parts, or signs of insects or small animals entering. Not overlooking these small anomalies leads to early detection of PCS failures and abnormalities in surrounding equipment.

Check 1 Confirm the difference between the generated power and output per PCS unit

To detect PCS failures early, the fundamental step is to check generation and output differentials. If you only look at the power generation for the whole plant, you may overlook abnormalities at the PCS-unit level. At plants with multiple PCS units installed, a particular PCS may show lower output despite receiving similar irradiance conditions within the same site. It is important to distinguish whether this difference is due to temporary shading, a problem on the PV array side, an anomaly on the PCS side, or grid-side conditions.

During routine management, you check not only the plant’s total generation but also the generation and output trends of each PCS. By comparing each PCS’s output at the same time of day on sunny days with its usual performance, it becomes easier to detect clues to abnormalities. However, differences in connected panel capacity, azimuth, tilt, shading effects, string configuration, and output control settings can cause output discrepancies. Therefore, it is important not to simply compare numbers side by side, but to understand the plant’s normal tendencies.

Of particular concern are cases in which equipment that previously generated power with a trend similar to other PCS units has remained consistently lower since a certain point. When a decline in output persists and cannot be explained by solar irradiance or weather alone, factors such as output suppression caused by rising internal PCS temperature, malfunction of the cooling system, increased resistance at connection points, abnormalities on the solar array side, or grid-side conditions may be involved. Do not assume a failure based solely on short-term differences; check daily, weekly, and monthly trends to confirm whether the anomaly is continuing.

Also, when checking generation output, merely confirming whether it is generating is insufficient. You should also check the time the PCS starts up, the period during which output ramps up, the stability of output during the daytime, and the timing of shutdown in the evening. Behaviors such as starting up later than PCS units under the same conditions, a sluggish ramp-up even on clear days, repeated drops in output during the day, or shutting down before evening may indicate a fault or the influence of protection controls.

In practice, having past normal data as a baseline makes decision-making easier. If you retain data from periods when conditions were stable—such as immediately after completion, after inspections, or after cleaning—you can compare it later if a decline in output occurs. Rather than looking only at the days when you notice anomalies, checking the differences from normal conditions improves the accuracy of early detection.

Check 2: Regularly check error and stop histories

PCS abnormalities may be recorded in error displays or stoppage history. Even if the PCS appears to be operating on site, it may have experienced repeated temporary pauses or restarts in the past. Therefore, during inspections it is important to check not only the current display state but also the historical log information. If errors have been auto-recovering, the system may appear normal by the time the technician arrives on site.

When checking error history, examine the occurrence date and time, occurrence frequency, duration, and recovery method. If the same type of error repeats within a short period, it may not be incidental but could be caused by equipment or the surrounding environment. Overvoltage, undervoltage, temperature anomalies, insulation-related alarms, communication abnormalities, and cooling-system abnormalities require isolating the cause. Do not judge based only on the error name; verify it together with the time of occurrence, weather, power generation status, grid-side condition, and the local environment.

Shutdown history is also an important inspection item. By checking when the PCS stopped and when it resumed, it becomes easier to estimate the extent and cause of generation loss. If it stopped during the power generation peak hours on a sunny day, internal temperature rise, cooling failure, load conditions, or grid-side conditions may be involved. If insulation-related abnormalities occur after rainy days or on high-humidity days, the effects of moisture on cables, junction boxes, terminals, and the inside of enclosures should also be checked.

Be aware of communication failures. If data is interrupted on remote monitoring, you must determine whether it is a fault in the communication equipment or line, or a shutdown of the PCS itself. If a communication device fault only prevents acquisition of generation data, the system may actually be generating power. Conversely, inability to communicate can delay detection of a PCS shutdown. Do not rely solely on the remote monitoring screen; when necessary, perform on-site checks and cross-check with the energy meter readings.

Error history should not only be checked at each inspection but also retained as a record. If the details of alarms, the conditions observed, the measures taken, and the post-recovery status are recorded, it becomes easier to track trends in subsequent inspections. Although PCS failures may appear to occur suddenly, tracing past records can reveal that minor alarms or communication losses had been recurring. Proactively using these histories helps enable earlier detection of faults.

Check 3: Confirm temperature rise around the PCS and inadequate ventilation

A PCS unit generates heat during operation. Because internal power conversion components and control components are affected by heat, whether cooling and ventilation are functioning properly is crucial for stable operation. Conditions such as high temperatures around the PCS, blocked ventilation paths, or unstable cooling fan operation can be precursors to reduced output or shutdown.

During the on-site inspection, check the environment where the PCS is installed. Locations exposed to direct sunlight, poorly ventilated areas, or places where weeds and materials are densely clustered can trap heat. If there is grass, fallen leaves, dust, insect nests, bird nests, or airborne debris around the PCS unit’s intake and exhaust vents, cooling performance may be reduced. Even if there are no major visible abnormalities, if ventilation paths become clogged, the internal temperature can rise more easily.

When temperature rises, the PCS may suppress its output or shut down as a protective action. In such cases, generation data may show behaviors like output not increasing during daytime peak hours despite sufficient solar irradiance, output plateauing above a certain level, or shutting down during the hottest periods and recovering in the evening. Because these behaviors can be caused not only by a fault in the PCS unit itself but also by deterioration of the cooling environment, checking the on-site environment is essential.

For PCS models with cooling fans, also check the fan’s operating noise and rotation condition. Conditions such as unusually loud noise, unstable rotation, large vibration, or weak airflow during operation can lead to reduced cooling performance. If a filter is present, check for dirt and clogging according to the manufacturer’s procedures. In locations with a lot of dust, where earthworks are being carried out nearby, or close to farmland or unpaved areas, dirt may accumulate more easily than usual.

When checking temperatures, avoid methods that involve inadvertently touching energized parts or the inside of the enclosure. Use PCS display readings, remote monitoring data, alarm history, temperature measuring instruments, thermal imaging, etc., as needed, and perform checks in a way that ensures compliance with work procedures and safety. Recording whether output decreases occur only during high-temperature periods, whether temperature anomalies are limited to specific PCS units, and whether cleaning has led to improvements will make it easier to identify the cause.

Check 4: Look for signs that can only be detected on-site, such as abnormal noises, unusual odors, and vibrations

Remote monitoring is useful for PCS management, but there are abnormalities that can only be detected on site. Typical examples include abnormal noises, unusual odors, vibrations, discoloration, burn marks, and traces of rainwater intrusion. These may not immediately show up in numerical data, but if left unaddressed they can lead to serious failures or safety issues. During on-site inspections, observation at the location as well as checking the numbers on the screen are indispensable.

For abnormal noises, pay attention to rumbling sounds that differ from the normal operation, sounds like metal scraping, intermittent high-pitched noises, and irregular sounds around the fans. PCS emits a steady operating noise while running, but if you are not familiar with its usual sound you may not notice abnormal noises. Therefore, it is effective for inspection personnel to record the sounds during normal operation. If multiple PCS units are present, comparing machines operating under the same conditions by listening to them makes it easier to detect abnormalities.

Unusual odors are also an important sign. If you notice a burning smell, a resinous, heated smell, or a damp or moldy smell, overheating of internal components, abnormalities at connection points, or the effects of rainwater or condensation may be suspected. You cannot determine the cause from smell alone, but if you detect an odor different from normal, you should check the operating status, alarm history, the condition around the enclosure, and inspect the connection points.

Do not dismiss vibration as mere operating noise. If the enclosure is vibrating unnaturally, fasteners are loose, doors or covers are resonating, or shaking occurs synchronized with the cooling fan’s rotation, components may be deteriorating or fastening failures may be progressing. After exposure to strong winds, earthquakes, heavy snowfall, or nearby construction, also check the condition of fastenings and for distortion of the enclosure.

During visual inspection, check the PCS unit itself for discoloration, peeling or bubbling of paint, corrosion, improper door sealing, deterioration of gaskets, rain drip marks, and signs of insect or small-animal intrusion. For outdoor installations, continuous exposure to wind, rain, and sunlight can cause minor deterioration around the enclosure to affect the internal environment. In particular, ingress of rainwater can lead to insulation failure or corrosion of terminal parts, so attention is required.

If an anomaly is found on site, do not attempt internal inspections or recovery work there; instead, record photos, the date and time, the weather, the PCS number, the power generation status, and whether any alarms are present. Internal inspections of electrical equipment and work involving energized parts are hazardous, so they must be carried out by personnel with the necessary qualifications and knowledge, following manufacturer procedures and safety procedures. For early detection of PCS failures, it is important to combine remote data with on-site observations.

Check 5: Inspect cables, terminals, and connection points for deterioration

PCS abnormalities can be caused not only by the PCS unit itself but also by deterioration of surrounding cables, terminals, and connection points. The PCS has many connection points, such as the DC side, AC side, grounding conductors, and communication lines. If the condition of these connections deteriorates, it can lead to overheating, voltage abnormalities, communication errors, insulation faults, and reduced output.

During the on-site inspection, we check the appearance of cables. We look for cracks in the sheath, abrasion, discoloration, swelling, damage caused by birds and animals, sagging wiring, supports coming loose, damage to protective conduits, and the like. In solar power plants, many cables are exposed outdoors for long periods and can be affected by UV radiation, wind and rain, temperature changes, mowing operations, and animals. Around the PCS in particular, wiring tends to be concentrated, so we inspect carefully to ensure nothing is overlooked.

At the terminal sections, check for looseness, discoloration, scorch marks, corrosion, and signs of overheating. If resistance increases at connection points, heat can be generated and cause deterioration of surrounding components. If there is visible discoloration or odors, or deformation of resin components, they may have been subjected to high temperatures in the past. However, retightening terminals or performing work inside panels involves the risk of electric shock and arcing, so the scope and procedures of the work must be clearly defined and carried out by personnel with the necessary knowledge and qualifications.

Junction boxes, combiner boxes, circuit breakers, disconnect switches, and other equipment around the PCS should also be inspected. Even if a PCS alarm is triggered, the root cause may lie in the surrounding equipment rather than inside the PCS. DC-side string faults, insulation degradation, circuit breaker malfunctions, grounding issues, and AC-side connection conditions can all have an impact. Rather than examining the PCS in isolation, it's important to inspect the peripheral equipment along the flow of electricity.

Connections to communication lines and monitoring devices should not be overlooked. When power generation data is missing, the cause is sometimes not a shutdown of the PCS itself but a poor connection in the communication line or a fault on the monitoring device side. Conversely, communication faults can delay detection of abnormalities in the PCS. Communication stability affects the quality of power plant maintenance. During inspections, also check the communication status, data update timestamps, and whether any measurements are missing.

Deterioration of cables and connectors can take longer to recover from if discovery is delayed. If detected at the stage of minor insulation damage or discoloration of terminals, it becomes easier to proceed with planned repairs and detailed inspections. Early detection of PCS failures is not just about looking at the PCS unit’s display; it is important to check the surrounding electrical pathways that carry power safely.

Check 6 Continue cleaning, environmental management, and record keeping

To detect PCS failures early and reduce failure risk, it is essential to maintain regular cleaning, environmental management, and record keeping. Rather than simply searching for abnormalities at each inspection, it is important to keep an environment where abnormalities are unlikely to occur and to create conditions that allow changes to be tracked. Power plant maintenance is not completed by a single inspection; its accuracy improves through the accumulation of daily management.

During cleaning, check for dust, fallen leaves, dead insects, grass, and mud splashes around the PCS. If dirt accumulates around the air intake or exhaust vents, cooling performance can easily deteriorate. Placing objects around the PCS unit or letting grass grow unchecked reduces airflow and makes inspections harder. Especially in summer and during periods when vegetation grows rapidly, it is important to keep the area around the PCS clear.

In environmental management, inspection items are determined according to the conditions of each power plant, such as weeds, drainage, animals, salt damage, dust, snowfall, and debris blown in after strong winds. Factors affecting the PCS differ depending on the installation environment—mountainous areas, coastal areas, areas near farmland, areas near factories, and alongside unpaved roads, among others. In practice, it is important not just to mechanically carry out the same inspection items, but to conduct inspections while anticipating the kinds of trouble that are likely to occur at that particular power plant.

In record management, record the inspection date, weather, power generation status, output for each PCS, alarm history, abnormalities found on site, cleaning performed, repairs carried out, and photographs. Without records, you cannot determine whether a condition has worsened since the previous inspection or has been the same for some time. Discoloration of terminals, corrosion of enclosures, dirt in ventilation openings, and the state of surrounding weeds are easier to track if photographed.

How records are kept is also important. Simply writing "no abnormalities" makes the record less useful when you want to review it later. Recording which PCS were checked, which items were inspected, whether numerical values changed, and whether conditions improved after cleaning will improve the quality of the next inspection. When multiple people manage the records, it is also important to standardize the record format. If the level of detail checked varies by person, abnormalities can be overlooked.

To detect PCS failures early, you need to view the plant’s condition not as a single snapshot but over time. By overlaying trends in power output, error histories, site photos, cleaning records, and repair histories, it becomes easier to spot signs of abnormality. Cleaning and record-keeping are unglamorous tasks, but they are important maintenance that supports the stable operation of the plant.

How to Build a Maintenance System That Doesn't Miss PCS Failures

To detect PCS failures early, merely knowing the inspection items is not enough. You need to decide who will check what, when, and according to which criteria, and how to respond if an anomaly is found. As the scale of the power plant increases, the number of equipment items grows and the risk of missed checks rises. It is important to establish a reproducible inspection system rather than relying solely on individual experience.

First, it is necessary to clarify the management unit for each PCS. If there are multiple PCS units within a power plant, organize their numbers, locations, connected circuits, and the related panels and cables. Keeping this information so you can immediately tell which PCS and which area to check when an anomaly occurs will shorten response time. On-site drawings, equipment layout diagrams, and management materials with photos make it easier for staff to understand the situation even if the person in charge changes.

Next, determine the inspection frequency and the items to be checked. On a daily basis, confirm abnormalities using remote monitoring and power generation data; during routine on-site inspections, check the exterior, ventilation, abnormal noises, terminal connections, cables, and the surrounding environment. In addition, when conditions differ from normal—such as typhoons, weather that suggests lightning, heavy rain, snowfall, extreme heat, or after grass-cutting operations—carrying out ad hoc inspections makes it easier to detect abnormalities. Because the PCS is affected by environmental changes, inspections should be performed not only at fixed intervals but also as circumstances require.

You should also share the criteria for judging abnormalities. Decide how large and for how long an output deviation warrants verification, which alarms require on-site inspection, how long a communication outage must continue before action is taken, and how to report if unusual noises or odors are found—doing so reduces variability in judgment. If the criteria remain vague, some staff may choose to wait and monitor while others check immediately, which can delay the response.

Also, a mechanism to translate inspection results into follow-up actions is important. Even if abnormalities are found, if they end with just being recorded they will not lead to improvement. Separate items that require detailed investigation, those that can be improved by cleaning, those that need parts replacement or expert verification, and those to be monitored, and clarify response deadlines and persons in charge. In power plant maintenance, it is important not to interrupt the cycle of detection, recording, judgment, response, and verification.

Furthermore, abnormalities in the PCS may affect not only power generation but also safety. If there are scorch marks, unusual odors, overheating, insulation-related abnormalities, or suspected rainwater ingress, do not make a hasty decision to continue operation; prioritize safety in your response. Because checking electrical equipment involves hazards, it is assumed that personnel with the necessary knowledge and qualifications will carry out the work in accordance with procedures. Rather than having on-site personnel forcibly perform internal inspections, there must be a system to accurately record signs of abnormalities and hand them over to the appropriate personnel.

Summary: Make PCS inspections central to power plant management

To detect PCS failures at a solar power plant early, it is important to comprehensively monitor power output, error history, temperature, ventilation, abnormal noises, unusual odors, cables, terminals, cleanliness, and record management. The PCS is a core piece of equipment in the plant, and even small abnormalities can lead to generation losses or operational shutdowns. Rather than responding only after a complete shutdown, management should capture daily changes and avoid missing early warning signs of abnormalities.

In practical work, it is important not to be reassured by only the plant’s total power output. Compare outputs on a per-PCS basis, cross-check them with past normal data, and verify that the same alarms are not recurring. In addition, by checking site-specific cues—sounds, odors, vibrations, soiling, corrosion, and the effects of vegetation—you can more easily detect abnormalities that data alone will not reveal.

To improve the quality of PCS inspections, continuous record-keeping is essential. If you record when, which PCS, and what condition was checked, you can assess changes at the next inspection. Managing photos, power generation data, and alarm histories together makes it easier to share the status even when personnel change. Early detection of failures is not achieved only by special procedures; accuracy improves by continuously performing basic checks.

In maintenance of a solar power plant, it is important to create an inspection plan centered on the PCS, just as you would for panels and weed control. By detecting reductions in power generation early, accurately grasping on-site conditions, and connecting those findings to necessary responses, you move closer to stable plant operation. Continuing inspections and record-keeping not only of the PCS itself but also of junction boxes, cables, communications, and the surrounding environment is the basic practice of plant management.