Six records to organize before inspection of equipment with low power generation

When faced with a system with low power output, you naturally want to go to the site first to investigate the cause. However, if pre-inspection record keeping is insufficient, the areas that need to be checked on site can become too broad, and isolating the cause can take time. A decrease in power output may not only be due to a malfunction of the equipment itself, but can appear as the result of multiple overlapping factors such as solar irradiance conditions, seasonal variations, shading, soiling, weeds, missing measurement values, communication failures, post-construction terrain changes, and past repair history. That is why it is important to organize the records before inspection to determine "what is low, since when, to what extent, and over what range."

In this article, aimed at operations personnel searching for information under "low power generation," we explain six records you should organize before inspections. To streamline on-site checks and make it easier to explain to stakeholders, we review not only power generation data but also weather, equipment, on-site photos, inspection histories, the surrounding environment, and records organized for reporting.

Table of Contents

• Basic records for determining a decrease in power generation

• Meteorological records correlating solar radiation with weather conditions

• System-specific records for identifying differences between equipment

• On-site photographic records to check for dirt, shadows, and weeds

• Maintenance records that can track past inspections and repairs

• How to Create Organized Records That Are Easy to Share Before Inspections

• For equipment with low power output, narrow down the cause by organizing the records.

Basic Records for Determining a Decrease in Power Generation

When you feel that power generation is low, the first thing to examine is the trend in power generation itself. What’s important here is not simply to say “this month’s generation is low,” but to clarify which period you are comparing it to. Looking only at month-over-month figures can be heavily affected by seasonal influences, and looking only at year-over-year for the same month can be influenced by last year’s weather or temporary stoppages. For that reason, it is effective to check from multiple angles, such as daily, monthly, and by time of day.

In recording power generation, we first examine the overall generation of the entire facility as a time series. By arranging daily generation, it becomes apparent whether output dropped suddenly on a particular day or declined gradually over several weeks or months. If the drop is sudden, it is easier to check for events tied to a specific date such as equipment shutdowns, communication failures, disconnections or tripping, protection actions, grid-side restrictions, or changes after construction or weed clearing. Conversely, when the decline is gradual, it prompts suspicion of factors that progress over time, such as accumulation of dirt, weed growth, changes in shading, deterioration of components, or environmental changes due to poor drainage.

Next, check whether the drop in power generation continues throughout the day or is concentrated in specific time periods. If generation is low only in the morning, only in the evening, or dips around noon, such time-of-day characteristics make it easier to distinguish the effects of shading, orientation, tilt, obstructions, and surrounding terrain. For example, low generation only in the morning can point to an influence from the east side, while low generation only in the afternoon can point to an influence from the west side. However, in reality terrain, racking orientation, panel layout, and relationships with adjacent equipment also play a role, so it is important not to determine the cause based solely on time of day but to review it together with on-site records.

Also, organize the power generation records to include downtime and missing-data periods. Even if generation appears low, it may simply be that data are missing due to faults in the measurement instruments or communication equipment. Periods when data are interrupted, periods when the same value persists for a long time, or instances of unnatural values appearing at night should be treated as measurement or recording issues rather than generation equipment problems. Checking this before an inspection makes it easier to avoid spending time on unnecessary equipment checks in the field.

When organizing basic records of power generation, you also look at how much is being generated relative to the installed capacity. This is because raw generation figures alone make it difficult to compare facilities with different capacities. By organizing generation as output per unit of installed capacity, it becomes easier to compare with another plot or installation. If you manage multiple facilities, comparing with ones in the same region and under similar installation conditions helps determine whether only the target facility is underperforming or whether there is a broader regional tendency toward lower output.

At the pre-inspection stage, there is no need to assume the cause. Rather, it is important to organize the records to answer "when did the output start to be low," "during which times of day is it low," "how large is the decrease," "are there any missing data," and "are there differences compared with other facilities." If these basic records are not in order, it becomes difficult to judge whether the items confirmed during the on-site inspection are related to the drop in power generation. The initial organization of records is an unglamorous task, but it provides the foundation for determining the direction of the inspection.

Meteorological Records Correlating Solar Radiation with Weather Conditions

When considering the causes of low power generation, you should avoid judging based only on the generation figures. Solar power systems are affected by solar irradiance and weather. During periods of cloudy skies or frequent rain, output will drop even if the equipment is functioning normally. Conversely, if weather conditions have not changed significantly but only the output has fallen, it is more likely that the cause lies with the equipment or the site environment. Therefore, it is important to compare generation data with meteorological records before carrying out inspections.

The first meteorological parameter to check is solar radiation. If days with low power generation coincide with days of low solar radiation, the decrease can be more easily attributed to weather factors. On the other hand, if solar radiation is sufficient yet generation output is not increasing, that leads to prioritizing checks on the equipment and at the site. If solar radiation records are available from on-site equipment, use those values; otherwise, check nearby observation data or the meteorological data saved for management. However, if the observation point is far away, local clouds or rainfall may not be well reflected, so be careful about the accuracy of the records.

In weather records, we check not only clear, cloudy, rainy, and snowy conditions but also events that affect equipment and the surrounding environment, such as typhoons, heavy rain, snowfall, yellow sand, strong winds, and lightning. For example, if power generation remains low after heavy rain, you can decide to add inspection items such as poor drainage, inflow of sediment, scouring around the racking, and moisture impact around electrical equipment. After snowfall, it becomes necessary to check for remaining snow on panel surfaces, accumulation of snow under the racking, meltwater flow, and muddy conditions of the surrounding ground. After strong winds, it provides an opportunity to check for flying debris, soiling on panel surfaces, sagging cables, and changes to fixings.

Temperature records should not be overlooked. Photovoltaic modules tend to see their output decrease as temperature rises. Therefore, even in summer when solar irradiance is high, power generation does not necessarily reach its maximum. If periods of high temperature coincide with a decline in power output, before concluding the equipment is faulty, confirm whether the decrease can be explained as a seasonal factor. However, if the subject installation’s output is lower than that of similar installations in the same region, temperature alone may not explain it. In this way, meteorological records are used to separate the decline in power generation into the portion that can be explained by natural conditions and the portion that requires on-site inspection.

Also, before an inspection, it is useful to align the weather records and the time series of power generation for the same period. Rather than extracting only the days with low generation, include the periods before the decline, during the decline, and after recovery, as this makes it easier to identify the cause. For example, if generation only recovers on the day after rain, consider the possibility that dirt on the panel surface was washed away. Conversely, if generation does not recover even after rain, it is necessary to check for factors other than dirt or for equipment-side problems.

Weather records are also useful when explaining things to stakeholders. If you only share that power generation is low, it’s hard to tell whether that’s due to equipment failure or poor weather. However, if you organize them together with solar irradiance, weather conditions, temperature, rainfall, snowfall, and disaster history, it becomes easier to explain why inspections are necessary and how to prioritize them. Before inspecting equipment with low output, it is important to treat weather records not as mere reference information but as primary records for narrowing down the cause.

System-specific records to find differences between facilities

In installations with low power output, looking only at the total generation widens the range of possible causes. What you should organize before inspection are records that show which system, which section, which piece of equipment, and which circuit are producing low output. Whether the entire installation is uniformly low or only part of it is low greatly affects how the inspection is carried out. If the entire installation is low, check the weather, grid-side conditions, complete shutdowns, common equipment, and measurement settings. If only part is low, focus on the panels, wiring, junction boxes, power converters, shading/obstructions, dirt, weeds, and terrain changes in that area.

In system-specific records, you check the power generation, current, voltage, and operating status for each section. If only a particular system is lower than its surroundings, you can prioritize inspection of equipment and on-site environmental factors related to that system. For example, if under the same solar irradiance conditions one section alone has lower power output, the items to check are narrowed to shading, dirt, poor connections, equipment shutdowns, open circuits, protective tripping, abnormalities on the panel surface, and so on. Conversely, if multiple sections are similarly low, you need to look for common causes rather than individual components.

When organizing records by system, matching them to equipment drawings and layout plans is also important. If you only look at system names in the data and cannot tell where they refer to on site, inspection efficiency will not improve. Make sure you can determine whether a system with low power output is on the north or south side of the site, at the lower or upper part of a slope, close to trees or buildings, or in a location where water tends to accumulate. When the data is linked to on-site locations, it becomes easier to decide the order of checks during inspections.

Also, when comparing by system, look not only at the absolute power generation but also at the difference from systems under the same conditions. An installation can include zones with different orientations, tilts, numbers of panels, installation angles, wiring lengths, and surrounding environments. Simply because a zone generates less power does not necessarily indicate an anomaly. If the original equipment conditions differ, comparisons must take those conditions into account. When organizing records before an inspection, it is practically useful to select systems that can be compared under the same conditions and identify locations with large deviations from the average.

Also, check historical system-specific data. Whether a system that is currently low has been low for a long time or has recently declined will change the assessment. If it has been lower than its surroundings from the start, installation conditions or design differences may be involved. If the decline is recent, you need to check for changes in the site environment, component defects, wiring damage, or changes after construction or maintenance work. By comparing with past data, you can separate the "original difference" from the "newly arisen difference" before inspection.

System-specific records directly inform post-inspection reports. Even if an anomaly is found on site, if you cannot tie it to a reduction in power output at that location, it becomes difficult to prioritize corrective actions. Organizing the power generation status by system before inspection makes it easier to link on-site photos, drawings, measurements, and power generation data. For equipment with low power output, confirming not only the overall figures but also where within the equipment the discrepancies occur is essential for narrowing down the cause.

On-site photo documentation for checking dirt, shadows, and weeds

At facilities with low power output, changes in the site environment that cannot be detected from data alone may be the cause. What you should organize before inspection are records of past site photos and recently taken photographs. Soiling on the panel surface, bird droppings, fallen leaves, dust, soil accumulation, vegetation growth, shadows from surrounding structures, conditions under the mounting structure, and drainage flow are factors that are difficult to judge from generation data alone. If site photos are organized, it becomes easier to narrow down the locations to check before inspection.

On-site photos should first be used to check the condition of the panel surface. If soiling is widespread on the panel surface, it can affect power generation. However, you should avoid determining the extent of the loss based solely on the appearance of soiling. Confirm the type of soiling, its extent, location, time of deposition, whether it has been washed away by rain, and its relationship with surrounding power generation data. For example, if soiling is noticeable only on a particular row, comparing it with that row's system data makes it easier to prioritize inspections.

When checking shadows, the time a photo was taken is extremely important. Because shadows change with the time of day and the season, judging based on photos alone can lead to misunderstandings. Photos taken in the morning, at noon, and in the evening will show different shadow positions and lengths. Before inspection, confirm that the time of low power generation corresponds to the time the photo was taken. If generation is low in the morning, you need to check morning shadows; if it is low in the afternoon, you need to check afternoon shadows. Because the sun’s altitude changes with the seasons, pay attention to the time of year when comparing past photos with current ones.

The growth of weeds and trees can also contribute to reduced power generation. This is especially true for ground-mounted installations, where vegetation in front of panels, beneath racking, along fences, around drainage channels, and near boundaries with adjacent properties tends to change easily. Checking past photos before inspections makes it easier to spot changes such as grass that used to be low now encroaching on panels, trees outside fences having grown taller, or cut grass remaining after weeding. Having such records allows you to specify the scope of checks needed during on-site inspections.

Site photographs should be organized together with records of the capture locations. Even if you think you photographed the same spot, a slight difference in angle can make comparison difficult. When using photos before inspections, organizing the capture date, capture time, capture location, capture direction, and the subject area makes it easier to explain changes between past and present. Because photo file names alone often become unclear later, it is preferable to manage them linked to a logbook or positional information on drawings.

Also, site photos can contain information that does not appear to be directly related to power generation. Examples include clogged drainage channels, sediment accumulation, muddy areas, subsidence around mounting structures, deformed fences, exposed cables, and signs of animal intrusion. These may not immediately manifest as reduced power output, but they are relevant to future malfunctions and to safety checks during inspections. Before inspecting equipment with low power output, it is practically useful to broadly check the condition of the area around the equipment, not just photos that seem related to power generation.

The purpose of organizing photo records is not just to produce polished reports. It’s to determine, before going on site, what to inspect, which time of day to inspect it, and which system to cross-check against. For installations with low power generation, it is important to connect drops seen in the data with what is visible on site. Organizing site photos serves as the record that bridges those two.

Maintenance records that enable tracking of past inspections and repairs

Before inspecting equipment with low power output, it is necessary to review past inspection and repair records. Even if the current drop in power output appears to have occurred suddenly, similar symptoms may have occurred previously in the same system. In addition, if the power output has changed since past work was performed, it is important to check the relationship between the work performed and the power output. Conducting an on-site inspection without reviewing maintenance records risks repeating the same checks and overlooking signs that had been found previously.

Maintenance records confirm periodic inspection results, abnormal findings, measured values, cleaning, weeding, component replacements, wiring checks, restoration work, power outage responses, communication restorations, and post-disaster inspections. It is particularly important to know what work was carried out immediately before periods of low power generation. For example, if power generation drops after weeding, it prompts checking for leftover cut grass, contact near cables, equipment shutdowns during the work, and changes in the site environment. If a decrease occurs after component replacement, it is necessary to review the records of the replacement scope, connection status, setting values, and restoration confirmation.

Recording measurement data is also important. If past inspections have recorded voltage, current, insulation resistance, the condition of connections, whether there has been a temperature rise, etc., you can compare them with the current condition. If values have been gradually changing over time, they provide material for considering possible degradation or environmental changes. Conversely, if past values showed no problems but power output has recently dropped suddenly, prioritize checking for events that occurred recently. Measurement records are important not only for making standalone judgments about abnormalities but also for tracking changes.

Maintenance records also include technicians' observations. These observations may not be as neatly organized as numerical data, but they provide clues about on-site conditions. Descriptions such as "noticeable dirt in some areas," "sediment in the drainage channels," "grass overgrowing on the north side," or "looseness in some cable supports" make it easier to decide which locations to prioritize for inspection this time. Even small observations can become important information if they coincide with periods of reduced power generation.

Also review past incident responses. If repeated interventions have occurred on the same equipment or the same system, temporary recoveries may have been applied while the root cause remains. For example, with equipment where communications are repeatedly restored, the problem may be missing records or inconsistencies in monitored values rather than the power generation itself. If alarms recur at specific connection points or devices, understanding that history before inspection will improve the accuracy of on-site verification.

When organizing maintenance records, it is effective to view them alongside periods of decreased power generation data. Placing inspection dates, repair dates, shutdown dates, cleaning dates, weeding dates, disaster occurrence dates, communication anomaly dates, and so on in chronological order makes it easier to identify events that may be related to changes in power generation. When inspecting equipment with low power generation, it is important to understand not only the current condition but also the sequence of events that led to it. Maintenance records are important documentation for explaining that sequence.

How to Create Organized Records That Are Easy to Share Before Inspections

Before inspecting equipment with low power output, it is necessary to organize the collected records in a format that stakeholders can easily review. If power generation data, weather records, grid-specific data, site photos, and maintenance history are each stored separately, it becomes difficult to share the inspection strategy. Pre-inspection organized records should not be a mere compilation of materials; they should be presented in a way that makes the process of narrowing down the cause clear.

First, organize the basic information about the facility in question. Compile the facility name, location, installed capacity, start date of operation, scope of management, the period during which power generation was judged to be low, the period used for comparison, and the types of data reviewed. This ensures stakeholders can discuss the issue on the same assumptions. The phrase "low power generation" alone can be interpreted differently by different people. By specifying the exact period and the comparison criteria, the purpose of the inspection becomes clear.

Next, organize an overview of the decline in power generation in chronological order. Describe in prose when the generation became lower, how much lower it is, which times of day it is most noticeable, whether there were days when it recovered, and whether the decline is ongoing. Here, rather than determining the cause, focus on facts that can be read from the records. Organizing it in forms such as "the decline is seen from this date," "differences tend to appear in the morning," "irradiance was also low during the same period," and "only a particular system is lower than its surroundings" will make clear what should be checked during inspections.

When organizing by system, make the correspondence with the equipment layout clear. If the system name in the data is separate from its on-site location, inspectors can become confused in the field. In the pre-inspection organization record, link and record the location of the relevant system, the surrounding environment, photo numbers, past findings, and related maintenance history. This enables concrete on-site checks such as "the panel surface in this section," "the shadow on this row," "around this connection point," and "near this drainage channel."

Photographic records are among the clearest information in pre-inspection materials. However, simply lining up many photos can make it difficult to know what to look for. It is important to include with each photo the date taken, the location, the shooting direction, the target section, and the items you want to check. When comparing past photos with current ones, also note whether they were taken at the same location and whether the time of day or season is similar. When photo descriptions are well organized, they can be used directly in reports after on-site inspections.

In pre-inspection preparatory records, unconfirmed items should also be clarified. By separating what can already be confirmed from the records and what needs to be checked on site, you can reduce omissions in the inspection. For example, power generation data may show a drop in a particular system, but because on-site photos are outdated, current shading or soiling is unconfirmed; there may be a record of past weed control, but no photos after the work; and weather records may suggest changes after heavy rain, but drainage conditions are unconfirmed. Clarifying unconfirmed items in advance makes the purpose of the on-site inspection more concrete.

Also, to make it easier to judge after the inspection, we organize pre-inspection hypotheses. However, these hypotheses are not definitive. They indicate directions to be checked, such as "shadow effects may be a factor," "check for possible soiling," "check for communication dropouts," and "check the relationship with past repair locations." Having hypotheses makes it easier to decide which photos to take on site, which points to measure, and which times of day to check.

It is important that organized records be presented in a form that allows stakeholders with different roles—such as power plant operators, maintenance personnel, on-site workers, and internal managers—to confirm the same information. Simply listing technical data as-is delays decision-making. At the pre-inspection stage, compiling materials so that facts, comparisons, locations, photographs, history, unconfirmed items, and inspection policies can be understood in a single flow makes it easier to proceed through to post-inspection decision-making.

Narrow down the causes of low power generation in installations by organizing records

For installations with low power generation, on-site inspections themselves are important, but how well records have been organized beforehand affects the outcome. Reductions in power generation can result from various factors such as temporary fluctuations due to weather, faults in specific systems, dirt on panel surfaces, shading, weeds, changes in the surrounding environment, communication or measurement issues, and changes following past work. If you go to the site without organizing records, the scope of checks will expand and explanations after the inspection are likely to become vague.

Before inspection, the first thing to organize is the basic record of power generation. Confirm when the output began to be low, how low it is, at what times of day it is low, and whether there are missing data or shutdowns; doing so clarifies the starting point for the inspection. Next, by cross-referencing meteorological records such as solar irradiance, weather, temperature, rainfall, snowfall, and disaster history, you can distinguish declines that can be explained by natural conditions from those that require on-site verification.

Furthermore, reviewing records by system makes it easier to determine whether the problem affects the entire facility or only certain sections. By linking the locations of decline in the data to their on-site positions, you can narrow down the areas to be inspected. Records of site photographs are useful for checking dirt, shadows, weeds, sediment, drainage, and changes in the surrounding environment. By reviewing past inspection and repair records together, you can also confirm whether the current decline is related to previous findings or work history.

And finally, it is important to compile this information into an organized record that stakeholders can easily share. The pre-inspection record should include the basic information of the equipment in question, an overview of the power generation decline, its relationship with the weather, differences by grid/system, photographic records, maintenance history, unresolved items, and the inspection policy. This clarifies what needs to be checked during the on-site inspection and makes post-inspection reporting and decision-making on countermeasures easier.

When dealing with equipment that has low power generation, it is more important to methodically isolate causes from the records than to rush to a conclusion. Rather than judging based solely on generation data, reviewing weather, equipment configuration, site conditions, and maintenance history together reduces unnecessary inspections and makes it easier to focus on the checks that are needed. Especially when managing multiple pieces of equipment, standardizing how records are organized makes it easier to compare units and to verify issues if they recur.

To accurately preserve site conditions and make it easier to explain causes of reduced power generation, a method for recording and a system for organizing records are indispensable. If photos, location information, power generation data, and on-site conditions can be linked and managed before inspection, this reduces misunderstandings among stakeholders and makes it easier to proceed to the next steps. When preparing inspections for equipment with low power generation, establishing a system that allows centralized review of site photos, location information, power generation data, and inspection history is also one practical measure that is easy to consider in actual operations.