How Often Should Solar Power Plants Be Maintained? A Guideline for Annual Inspections

Maintenance of solar power plants is essential not only for sustaining power output but also for safety management, equipment preservation, consideration for the surrounding environment, and ensuring reliability over long-term operation. What operational staff often find unclear are: "how often and what should be checked," "how extensive should annual inspections be," and "whether remote monitoring and daily checks alone are sufficient."

Solar power plants are said to have relatively few moving parts. However, as they operate outdoors for long periods, the items that need to be checked increase over time, such as soiling of photovoltaic modules, deformation of mounting structures and foundations, cable degradation, faults at connection points, poor drainage, weeds, fence damage, and abnormalities in monitoring devices and power conversion equipment. Rather than responding only after a drop in power output becomes apparent, it is important to separate the roles of daily checks, regular patrols, annual inspections, and ad-hoc inspections, and to continuously record the condition.

It should be noted that maintenance frequency is not “once a year for all solar power plants.” The required checks vary depending on the facility’s power output classification, interconnection conditions, safety regulations, the manufacturer’s inspection procedures, the O&M contract, and the installation environment. This article organizes a way of thinking for determining frequency in practice while using the annual inspection as an inventory of equipment condition.

Table of Contents

• Basic approach to solar power plant maintenance

• Conditions to check before determining maintenance frequency

• Power generation and signs of abnormalities to look for in daily checks

• Site items to check during monthly and regular patrols

• Equipment conditions to focus on during annual inspections

• Inspection points around panels, mounting racks, and foundations

• Inspection points for electrical equipment and wiring

• Checking surrounding environment such as weeds, drainage, and fences

• Characteristics of power plants that warrant increased inspection frequency

• Importance of keeping maintenance records

• Practical approaches to streamline annual inspections

• Summary: Solar power plant maintenance should be managed continuously with annual inspections as the core

Basic Approach to Solar Power Plant Maintenance

Maintenance of a solar power plant is not simply the task of repairing failed equipment. It is continuous management to operate the plant safely, keep it close to the planned power generation, detect abnormalities early, and reduce the risk of accidents and shutdowns. Many practitioners who search for "太陽光発電所 メンテナンス" understand the need for inspections, yet often struggle with how frequently they should check the site and which items they should prioritize.

The basic approach is to combine daily checks of power generation status, regular on-site patrols, annual inspections, and ad hoc inspections after abnormalities or disasters. Generation output and monitoring metrics can sometimes be checked remotely, but there are issues that can only be identified by visiting the site. For example, tilting of the mounting racks, loose bolts, shading from vegetation, clogged drains, damaged fences, signs of animal intrusion, sagging cables, or damage to cable sheathing are items that are easy to overlook if you rely solely on on-screen figures.

On the other hand, if you try to check every item with the same level of detail each time, inspection work becomes burdensome and difficult to sustain. Therefore, it is effective to divide responsibilities: during daily checks, monitor power generation and error indications; during regular patrols, inspect the site appearance and surrounding environment; and during annual inspections, organize the overall condition of the equipment to guide repairs and improvements in the following fiscal year and beyond.

A solar power plant is not finished once installed; its long-term stability depends on how well its condition can be understood after operation begins. In particular, the annual inspection is an opportunity to take stock of the equipment's condition for that year. Rather than treating it as a mere formality, reviewing together generation trends, on-site degradation status, repair history, and changes in the surrounding environment makes it easier to predict faults that are likely to occur next.

Conditions to Check Before Determining Maintenance Frequency

The maintenance frequency for solar power plants should not be the same for all plants. The required inspection frequency varies depending on the plant’s scale, its classification under the Electricity Business Act, installation site, topography, equipment configuration, operational framework, presence or absence of remote monitoring, and history of past faults. In practice, a practical approach is to combine on-site patrols, annual inspections, and ad hoc inspections as needed while routinely checking generation performance.

The first thing to confirm is the power plant’s output classification and interconnection conditions. Low-voltage, high-voltage, and special high-voltage installations differ in equipment configuration and safety management systems. For plants that include receiving and transforming equipment, safety management is required for the entire electrical installation, not just the photovoltaic modules and mounting structures. In particular, for equipment at high voltage and above or for installations above a certain scale, it is necessary to develop an inspection plan after confirming conditions related to laws and notifications, such as safety regulations, the chief electrical engineer, and the scope of outsourcing.

Next, check the installation environment. In mountainous areas, sloped sites, converted farmland, reclaimed land, locations near the sea, snowy regions, areas prone to strong winds, and places with heavy leaf fall, the inspection points for maintenance differ. In mountainous and sloped sites, slope failures, poor drainage, and influx of sediment are likely to be problems, while locations near the sea require attention to corrosion of metal components. In snowy regions, it is necessary to check the effects of snow load, deformation of the mounting structures after snowmelt, and changes in drainage routes. At power plants surrounded by many trees, shading and accumulation of fallen leaves can also cause reduced power generation.

Whether or not remote monitoring is available is also an important factor in determining the inspection frequency. If power output and equipment abnormalities can be checked remotely, daily anomaly detection becomes easier. However, having remote monitoring does not mean on-site inspections are unnecessary. Remote monitoring is a means of capturing abnormalities in numbers and signals, and it cannot fully grasp physical degradation at the site or changes in the surrounding environment. Rather, a realistic division of roles is to detect signs of abnormalities through remote monitoring and confirm the causes with on-site inspections.

Past trouble histories should not be overlooked. Power plants that have experienced equipment shutdowns, connection failures, reduced power output, flooding, wind damage, overgrowth of weeds, fence damage, or similar issues may be prone to the same faults recurring. In annual inspections, it is important to review past records and check whether the same locations have shown any changes. Inspection frequency should be adjusted not only to the type of equipment but also to the site's tendencies.

Daily Checks: Power Output and Signs of Abnormalities

When considering the maintenance frequency of a solar power plant, the most fundamental element is the daily check. "Daily check" does not mean visiting the site every day. It is the task of checking power generation, power output, abnormal indicators, and communication status to identify any changes that differ from normal. If remote monitoring is available, the generation status is checked on-screen to look for sudden drops in generation or equipment stoppages.

In daily checks, it is important not to judge an anomaly based solely on a single day’s power generation. Solar power generation is affected by weather, season, temperature, and solar irradiance. It is natural for generation to drop on cloudy or rainy days. Conversely, if generation falls significantly despite clear skies, if only certain sections within the same plant show low output, if a declining trend continues compared with the same period in past years, or if only specific equipment experiences frequent stoppages, these are signs that should lead to an on-site inspection.

When checking power output, it is helpful to compare not only with the previous day but also under the same weather conditions, the same month, and the same time of day. If the entire plant's power output has decreased, weather or grid-side impacts may be considered; however, if only some circuits or pieces of equipment show low output, possibilities include equipment malfunction, wiring faults, shading, soiling, or module damage. In routine checks, the goal is to narrow down the areas to inspect on site rather than to conclusively determine an abnormality.

Be aware of communication failures. If power is being generated but monitoring data cannot be obtained, the issue may lie with the communication or measuring devices rather than the power generation equipment itself. If communication failures continue, you may be slow to notice when the actual power output drops. Therefore, as part of maintenance you should check not only the power output but also whether monitoring data is being continuously acquired.

The frequency of routine checks varies depending on the power plant’s management structure. In practice, it is important to establish a system that enables remote monitoring and verification of generation data at the shortest possible intervals, and to define contact points, decision criteria, and procedures for on-site inspection in case of anomalies. Don’t stop at merely looking at the numbers; specify who will check, when they will visit the site, and where the findings will be recorded so that operations remain stable even when the person in charge is absent.

On-site items to be checked during monthly and periodic inspections

If daily checks are a numerically focused form of management, monthly or periodic inspections are management practices for observing the on-site condition. At solar power plants, even at stages where power generation has not yet been affected, signs of abnormalities may already be developing on site. To detect small anomalies early, it is important to conduct on-site patrols at regular intervals according to the plant’s condition and to visually inspect the equipment and the surrounding environment.

During routine inspections, the first thing to check is the appearance of the photovoltaic (PV) modules. Check for cracks, chips, discoloration, dirt, bird droppings, fallen leaves, dust, and shadows from vegetation. Dirt on the module surface may be washed away naturally by rain, but it tends to remain in areas with a gentle tilt or where soil is easily stirred up nearby. Localized soiling or shading can cause not only partial power loss but also an increased risk of long-term degradation, so care should be taken.

Checking the mounting structures and foundations is also essential. Look for loose bolts, deformation of members, corrosion, settlement, tilting, and scour around the foundations. On sloping sites or where drainage is poor, rain can wash away soil and change the support conditions around the foundations. If small changes are recorded during patrols, they will be easier to compare during annual inspections.

When inspecting wiring, check for cable sagging, damage to outer sheathing, loose fasteners, abnormalities around junction boxes, and chew marks from animals. During the season when grass grows tall, cables can become hidden by vegetation and hard to see. If walking routes are not secured during inspections, this can lead to missed checks or stepping on cables during work, so it is advisable to check the condition of walkways along with regular patrols.

The condition of fences, gates, warning signs, and management notice boards should also be included in regular patrols. Torn fences or inadequately locked gates increase the risk of unauthorized entry or animal intrusion. Even if the power generation equipment itself shows no abnormalities, inadequate site management can lead to safety issues. In solar power plant maintenance, it is important to treat the entire site—not just the electrical equipment—as part of the management scope.

Equipment conditions to prioritize during annual inspections

An annual inspection is an important opportunity to comprehensively check the condition of a solar power plant. However, an annual inspection does not mean “it is sufficient to check only once a year.” When positioned as a once-a-year inventory to organize equipment condition and records—combined with daily checks, regular patrols, inspections based on safety regulations, and manufacturer-specified inspections—the purpose of the inspection becomes clear.

The first thing to do for an annual inspection is to organize pre-inspection information. By checking in advance the power generation trends, history of anomalies, equipment downtime history, past repairs, and records of regular patrols, you can identify where to focus on site. For example, if a particular section tends to have lower generation, you should closely inspect that section’s modules, wiring, junction boxes, and shading conditions. Simply doing a general on-site walkthrough without prior information may cause you to miss important abnormalities.

On-site, inspect the modules, mounting structures, foundations, wiring, junction boxes, power conversion equipment, substation equipment, monitoring systems, fences, drainage, slopes, and access routes. In the annual inspection, it is important not only to check for the presence of abnormalities but to classify locations where deterioration is progressing, locations that should be monitored until the next inspection, and locations that should be repaired promptly. The role of the annual inspection is not just to detect abnormalities that immediately lead to shutdowns, but to identify potential future failure candidates.

When measurements or detailed inspections are required, specialized judgment may be necessary. Electrical measurements, verification of insulation condition, inspection of connection points, and examination of equipment interiors must be performed in accordance with safety procedures. Because equipment that is generating power poses the risk of electric shock and short circuits, it is important to clearly define the scope of work and shutdown procedures and to avoid attempting checks that cannot be safely carried out.

The results of the annual inspection will be reflected in the maintenance plan for the next year. By translating inspection findings into concrete actions—such as advancing the timing of mowing, improving drainage channels, repairing fences, prioritizing monitoring of areas with reduced power generation, and considering the timing of equipment replacement—the annual inspection becomes more than a mere record-keeping exercise.

Inspection Points for Panels, Mounting Structures, and Foundations

The most visually obvious components of a solar power plant are the solar modules and their mounting structures. However, the larger the plant, the harder it is to inspect everything with the same level of detail. For annual inspections, in addition to visual checks from a distance, you need to compare conditions by section and adopt a perspective that identifies areas where abnormalities are concentrated.

On the modules, inspect the glass surface for cracks, chips, discoloration, clouding, and dirt accumulation, and check the frame for deformation and the condition of the mountings. Cracks and chips are anomalies that are easy to detect, but minor discoloration and localized soiling are items that are easy to overlook. In particular, when bird droppings or fallen leaves remain in certain areas, they can not only reduce power output but also lead to localized loading. It is important to assess visible findings together with trends in power output.

On the mounting structures, check for loose bolts and nuts, corrosion of components, deformation, tilting, and the condition of fasteners. In power plants affected by strong winds, snow accumulation, or heavy rain, loads on the mounting structures can cause slight deformation or looseness. Even if there are no obvious visual problems, if any section in the same row shows an unnatural difference in height or angle, the foundation or mounting structure may have experienced changes.

Around the foundation, check for settlement, uplift, cracking, scouring/undermining, soil washout, and changes in the surrounding ground. Especially on reclaimed or filled land and on sloping sites, drainage flow can alter ground conditions. Even if the foundation itself shows no abnormalities, surrounding soil may have been washed away, changing the bearing conditions. In annual inspections, it is important to assess not just the foundation alone but also the flow of rainwater and the surrounding topography together.

Modules, racking, and foundations may appear to be separate components, but in reality they function as a single system supporting the stability of the power plant. If a module’s tilt has changed, deformation of the racking or settlement of the foundation may be the cause. Areas where racking corrosion progresses can also be related to poor drainage or vegetation overgrowth. In annual inspections, it is important not only to check the components showing abnormalities but also to consider causes that include the surrounding conditions.

Inspection Points for Electrical Equipment and Wiring

In solar power plant maintenance, electrical equipment and wiring require particular care.

Even if there appear to be no visible problems, issues such as poor connections, insulation degradation, overheating, equipment failures, and communication faults can lead to reduced power generation and safety risks. During annual inspections, it is important to combine visual checks with reviews of operational data to ensure signs of abnormalities are not overlooked.

In wiring inspections, check the cable's fastening, damage to the outer jacket, sagging, contact with the ground or support structures, and the condition of connectors. If cables are hanging down, they become more susceptible to wind-induced swaying, contact during mowing operations, animal damage, and exposure to UV rays and moisture. Areas around connections are prone to causing overheating and poor contact, so carefully inspect them for any visible abnormalities.

In junction boxes and collector equipment, check for proper door closure, signs of moisture ingress, corrosion, the condition of terminals, abnormal noises, unusual odors, and display abnormalities. Equipment installed outdoors is affected by rain, wind, and temperature changes. Moisture can enter through small gaps or degraded components and lead to internal deterioration. During the annual inspection, check not only the condition of the enclosure but also whether the surrounding environment tends to allow water to accumulate.

For power conversion equipment, such as power conditioners, check the operating status, fault history, condition of the cooling components, clogging of filters and ventilation paths, and the installation environment. Equipment that tends to generate heat can experience performance degradation or shutdown if ventilation becomes poor. Also check whether vegetation or objects are too close and whether the equipment is in a position where it is exposed to direct sunlight or susceptible to high temperatures.

Safety management is the top priority when inspecting electrical equipment. Solar photovoltaic systems that are generating power may retain voltage in some parts even after shutdown operations, so it is dangerous to touch them casually. If there is submersion, fire, damage, scorch marks, or unusual odors, do not approach or touch them; make sure you have a system in place to contact appropriate specialists such as the chief electrical engineer, maintenance and inspection contractors, or the installation company.

Checking the surrounding environment: weeds, drainage, fences, etc.

In maintaining solar power plants, managing the surrounding environment is just as important as maintaining the equipment itself. On actual sites, causes of reduced power generation and equipment malfunctions are often not the equipment itself but weeds, poor drainage, soil and sediment, damaged fencing, animal intrusion, and the like. Especially for ground-mounted power plants, it is necessary to have the awareness of managing the entire site as a single piece of equipment.

Weeds are the most conspicuous maintenance item at solar power plants. When vegetation grows, it casts shadows on the modules and can reduce power generation. It also makes it harder to inspect cables and racking, hindering maintenance work. In addition, there is a risk of damaging cables during mowing and safety risks during periods when a lot of dry grass is present. In annual inspections, it is effective to record not only the height of the vegetation but also when and where it tends to grow, and to reflect that information in the weed control plan for the following year.

Drainage is also an important inspection item. Because solar power plants cover large areas, changes in rainwater flow can create puddles on site, erode slopes, or wash away soil around foundations. Check for clogged drains, sediment accumulation, the condition of drainage outlets, and locations where rainwater is concentrating. Since these issues can be difficult to detect during inspections conducted only in fine weather, carrying out an ad hoc inspection after heavy rain makes it easier to identify problems that are not visible during routine inspections.

Fences and gates are important for safety management and security. Conditions such as holes in a fence, leaning posts, insufficient gate locking, or unreadable signage can lead to unauthorized entry by third parties or intrusion by animals. Even if the power generation equipment is operating normally, inadequate management of site boundaries can cause the entire power plant to be regarded as having poor overall management quality.

The surrounding environment changes with the seasons. From spring to summer there are weeds; during the rainy season and typhoons drainage and sediment are concerns; in autumn falling leaves; and in winter snow accumulation and freezing — the points to check vary by season. Therefore, in practical maintenance of solar power plants it is important not only to carry out annual inspections but also to combine them with inspection schedules tailored to seasonal changes.

Characteristics of power plants that require more frequent inspections

Even when inspections are performed at standard frequency, plant conditions may mean it’s better to shorten the inspection intervals. Understanding the characteristics of power plants that should have increased inspection frequency lets you prioritize high-risk areas even with limited personnel and time.

First, power plants installed on slopes or on developed/reclaimed land require caution. This is because changes related to the ground and drainage—such as rainwater flow, slope conditions, soil movement, and foundation settlement—are likely to occur. In particular, after heavy rain or typhoons, it is necessary to decide to carry out an ad hoc inspection rather than wait for the regular patrol schedule. If drainage channels are left clogged with sediment, the next rainfall could cause much greater damage.

Areas near the sea and environments prone to corrosion are conditions that call for more frequent inspections. If corrosion advances on metal components, mounting racks, fastening hardware, enclosures, terminals, or the like, it can affect not only appearance but also structural strength and electrical safety. Because corrosion is irreversible once it progresses, it is important to assess the condition at an early stage and consider repair or replacement as necessary.

Areas where weeds grow easily, locations with many surrounding trees, and sites with frequent animal intrusions should also be targeted for increased inspection frequency. The presence and extent of shadows cast by grass and branches vary with the season and time of day. Even if no problems are visible during annual inspections, shadows can become larger in the summer. At power plants where animals cause cable damage or enter beneath fences, frequent visual inspections are necessary.

Power plants that have repeatedly experienced declines in power generation or equipment shutdowns in the past should also review their inspection frequency. If similar anomalies recur, it is possible that the root causes have not been fully addressed. Even if equipment is replaced, the problem can recur if causes remain in the surrounding environment or in wiring routes. In annual inspections, it is effective to designate priority monitoring areas based on past records of anomalies.

The Importance of Keeping Maintenance Records

One thing that tends to be overlooked in solar power plant maintenance is the quality of recordkeeping. Even if inspections are carried out, vague records prevent comparisons at the next inspection and make it difficult to judge the progression of abnormalities. Especially during annual inspections, it is important to check what has changed compared to the previous year. Therefore, inspection results need to be recorded as clearly as possible, including photos, locations, details, and the status of any actions taken.

In records, it is useful to preserve not only the presence or absence of abnormalities but also the normal condition. For example, photographing the condition of mounting racks and foundations, the condition of drainage channels, and the condition of fences from the same position every year makes it easier to compare changes. Rather than taking photos only when an abnormality occurs, retaining a baseline condition makes it easier to assess the progression of deterioration and deformation.

Also, it is important to link power generation data with on-site photos. If there are sections where generation has declined, recording module soiling, shading, wiring, and equipment condition for that section will make cause analysis easier. If numerical data and on-site conditions are managed separately, it becomes difficult to identify the cause when reviewing later.

Records are important when personnel change. Solar power plants are operated over long periods, so the same person will not necessarily manage them indefinitely. If past inspection results, repair histories, points of concern, and seasonal issues are organized, a new person in charge can more easily grasp the characteristics of the site. Accumulating management histories for each plant, rather than relying on individual memory, leads to stable operation.

Annual inspection reports are more useful in practice when they record not only the facts of the inspection but also the planned course of action. Separating items that require immediate repair, items to be monitored over time, and items to be prioritized at the next inspection makes it easier to plan the following year’s inspection. Maintenance records are not only for preserving the past but also serve as documentation for deciding the next actions.

Practical Steps to Streamline Annual Inspections

To carry out annual inspections efficiently, preparation before going on-site is important. Review the power plant drawings, equipment register, safety regulations and inspection procedures, past inspection records, history of abnormalities, and power generation data, and determine the inspection route and priority checkpoints. If you tour the site without preparation, checks are likely to be missed and post-inspection organization will take more time.

Inspection routes should be determined according to the configuration of the power plant. Rather than simply walking from the entrance in sequence, organizing the inspection so that checks can be made by sections, circuits, and individual pieces of equipment makes it easier to match records to equipment. When taking photographs, it is important to make clear from which position, in which direction, and for what purpose the picture was taken. If later the location cannot be determined from a photo alone, its value as a record is diminished.

On site, when an anomaly is found, record its location and details on the spot. If you try to compile them from memory after an inspection, you may confuse the locations or the conditions. Especially at large-scale power plants, where rows of similar modules and equipment are lined up, it is important to record location information together with photographs.

After the annual inspection, list the inspection results and assign priorities. Even if it is difficult to address everything at once, organize them so that items with the greatest impact on power generation and safety are dealt with first. By separating highly urgent anomalies, anomalies that should be repaired promptly, and items that can be monitored over time, it becomes easier to share the information with stakeholders.

In recent years, the importance of digitally recording on-site conditions and centrally managing photos, location information, and inspection results has grown. Relying on paper inspection forms or photos managed individually by each inspector makes comparing past records and sharing with stakeholders cumbersome. In solar power plant maintenance, not only the quality of on-site inspections but also how well records are preserved in a usable form determines inspection efficiency.

Summary: Solar power plant maintenance should be managed continuously with annual inspections at its core

The frequency of maintenance for solar power plants varies depending on the plant’s scale, installation environment, equipment configuration, whether remote monitoring is available, safety regulations, and past failure history. In practice, it is important to combine daily checks of generation status, monthly or periodic patrols, annual inspections, and ad hoc inspections after abnormalities or disasters. Daily checks look at generation output and abnormal indications; periodic patrols inspect the site’s appearance and surrounding environment; annual inspections organize the overall condition of the equipment and link that information to management for the following year.

During the annual inspection, we comprehensively check solar photovoltaic modules, mounting structures, foundations, wiring, junction boxes, power conversion equipment, substation equipment, monitoring systems, fences, drainage, weeds, slopes, and other components. The important thing is not to treat the inspection as a one-time task. By linking and recording trends in power generation, past anomalies, on-site photos, and repair histories, it becomes easier to identify each plant's weaknesses and changes.

Also, inspection frequency is not fixed and should be reviewed according to site conditions. On sloping terrain, in areas prone to poor drainage, where weeds easily proliferate, in corrosion-prone locations, or at power plants with a history of frequent abnormalities, standard patrols alone may be insufficient. After heavy rain, typhoons, snowfall, strong winds, lightning strikes, and similar events, it is important to decide whether to carry out ad hoc inspections in addition to the regular annual inspections.

The longer a solar power plant is in operation, the more differences in record-keeping become differences in management quality. If it is clear and well organized where inspections were carried out, what kinds of abnormalities occurred, how far they have progressed, and what should be checked next, stable management can be maintained even when personnel change. Conversely, if records remain ambiguous, the same abnormalities can be overlooked repeatedly, and it can take a long time to determine the causes of declines in power generation.

Going forward, solar power plant maintenance should center on annual inspections while integrating on-site checks, generation data, photographs, location information, and inspection histories into a single management system. By determining inspection frequency according to each plant’s conditions and using records to inform subsequent improvements, it becomes easier to enhance long-term operational stability and safety.