7 Priority Inspection Items for Industrial Equipment with Low Power Output

When you notice a low power generation condition, immediately assuming an equipment failure can make isolating the cause take longer. In industrial-scale solar power installations, multiple factors affect power output, including weather, solar irradiance, the surrounding environment, wiring, equipment, record management, and how monitoring values are interpreted. Therefore, when a drop in generation is detected, it is important to prioritize checks and confirm them while ensuring safety. This article organizes seven items that on-site personnel searching for "low power generation" should check as a priority.

Table of Contents

• When power generation is low, do not assume it is caused by a single factor.

• Confirm solar irradiance and weather conditions first.

• Check for anomalies in monitoring data and measured values

• Check the panel surface for dirt and shading.

• Inspect wiring, connection points, and terminal areas.

• Check the status of the power conditioner and peripheral equipment.

• Check the variation at the string level

• Check for changes in weeds, terrain, and the surrounding environment.

• Keep inspection records to help prevent recurrence.

• Summary: When power generation is low, organize on-site information in a multidimensional way.

When power output is low, don't assume a single cause

When you feel that the power output of industrial power generation equipment is low, the first thing to be aware of is that the cause of the decline is not necessarily a single factor. Power output fluctuates due to a combination of multiple elements such as solar irradiance, ambient temperature, equipment orientation, panel condition, wiring condition, equipment operating status, surrounding obstructions, and grid-side conditions. In particular, with solar power generation systems, sunlight can be reduced by thin clouds or haze even when it appears to be sunny. Also, there may be cases where only part of the site is shaded, or where connection failures occur only in specific circuits.

In practice, inspections often begin with observations like "less than yesterday," "lower than the same month last year," or "lower than neighboring facilities." However, it is premature to judge a fault based on those comparisons alone. If the solar irradiation conditions for the comparison differ, the power generation will also change. Even with the same system capacity, apparent differences can arise from orientation, tilt, installation environment, soiling of the panel surfaces, or differences in the monitoring equipment’s aggregation method. First, it is important to confirm whether the decrease in power generation is occurring across the entire system or is concentrated in certain sections or strings.

In consultations about low power generation, there is often a temptation to judge solely from the data before visiting the site. Of course monitoring data are important, but they do not always reflect the on-site conditions. Sensor malfunctions, communication dropouts, misaligned aggregation periods, or differences in display units can cause the apparent numbers to differ from the actual generation situation. Therefore, in initial responses you should not separate data checks from on-site inspections; it is necessary to examine both sets of information side by side.

In industrial facilities, safety considerations cannot be overlooked. Power generation equipment is located outdoors and includes DC circuits, AC circuits, junction boxes, power conditioners, and power receiving and transforming equipment, so it is dangerous for unqualified or inexperienced persons to touch exposed parts carelessly. Even if the power output is low, on-site personnel should not immediately touch terminals or wiring; instead, it is necessary to separate what can be checked by visual inspection, what can be verified from records, and what should be entrusted to specialist contractors.

As a principle for prioritized inspections, first check external conditions and monitoring data, and then visually confirm the presence of dirt, shading, weeds, or damage. After that, examine in order the condition of wiring and equipment, differences at the string level, and changes in the site environment—this makes it easier to organize possible causes. Rather than immediately proceeding to detailed electrical inspections, starting with items that are low risk, easy to verify, and likely to have a significant impact on power generation leads to faster recovery and safer operation.

Check solar radiation and weather conditions first

When power output is low, the first thing to check is not the equipment itself but the generation conditions for that day. In solar power generation, solar irradiance is strongly related to output, so even with the same equipment the generation will vary depending on the weather. Conditions such as clear skies, thin clouds, cloudy weather, rain, snowfall, yellow dust, fog, and haze cause daily fluctuations in output. Even if the site looks sunny, on days when the whole sky is whitish and hazy or when there were many clouds only in the morning, it may not generate as much as expected.

What operations personnel often overlook is the period used for comparing power generation. For example, even if output is lower than the previous day, if the previous day was clear all day and the current day had thin clouds in the morning, a difference will appear even if there is no equipment problem. The same applies when comparing with the same month of the previous year: if weather patterns differ between the years, differences in generation can occur. Even if monthly generation appears to have declined, there may be no significant problem when viewed in terms of generation efficiency per unit of solar irradiance.

Therefore, when checking power output, it is important to view it together with solar irradiance and weather records. If a pyranometer is installed on site, check whether its readings correlate with the changes in power output. If power output is lower on days when irradiance is reduced, the cause may be external conditions rather than equipment failure. On the other hand, if irradiance is sufficient but only the power output is low, priority should be given to inspecting the equipment.

Temperature effects cannot be ignored. Solar panels generate electricity from sunlight, but in general their output tends to decrease as panel temperature increases. On a clear summer day the solar irradiance is high, but panel temperatures also tend to rise, so the panels won't necessarily achieve the same generation efficiency as they do on clear days in spring or autumn. If comparisons are made without accounting for seasonal temperature differences, normal fluctuations can be misinterpreted as faults.

Be careful even after snowfall or rainfall. If snow remains on the panel surface, power output will be less likely to increase even when it's sunny. After rain, dirt may be washed away, but conversely mud splashes or deposits may remain and affect generation of some panels. In regions with strong winds, dust or fallen leaves can collect on portions of the panel surface. When checking weather conditions, don't just look at the sky for that day; consider rain, wind, snow, yellow dust, and the presence of nearby construction over the past few days to reduce overlooking potential causes.

Verify anomalies in monitoring data and measured values

After checking the weather conditions, next look at the status of the monitoring data and measured values. Many triggers for perceiving low power generation are the figures on the monitoring screen, daily reports, monthly reports, and sold electricity amounts. However, the displayed figures do not necessarily accurately reflect actual on‑site power generation. Communication failures of the monitoring equipment, malfunctions of measuring instruments, missing data, time offsets, and differences in aggregation settings can make the reported generation appear low.

First, what I want to confirm is the scope of the value that is decreasing. Whether it is the facility’s total power generation, the output of a specific power conditioner, the current of a particular string, or the amount of electricity sold will determine where you need to inspect. If the facility’s total power generation is low, suspect solar irradiance conditions, grid-side conditions, or shutdown of main equipment. If only a specific power conditioner is low, focus on that unit and the circuits under it. If only a particular string is low, you need to check the panels, connectors, cables, and the area around the junction box.

Next, check the time periods in the data. The possible causes differ depending on whether power generation is low throughout the day, only in the morning and evening, or only around noon. If it is low only in the morning, shadows on the east side or equipment conditions during startup may be involved. If it is low only in the evening, western obstructions or shadows from nearby trees may be responsible. If output is capped around noon, you should check equipment control, temperature rise, output limits, and grid conditions.

Comparing waveforms with past normal days is also effective when analyzing monitoring data. Rather than looking only at days with low power generation, comparing with days of similar weather, the same period in the previous year, or with normal operation after inspection makes anomalous patterns easier to see. For example, if the entire graph is uniformly lower, the effect of reduced solar irradiance or soiling may be considered. If there is a sudden drop during certain time periods, possibilities include shading, equipment shutdown, communication loss, or protective operation. If only specific equipment shows values close to zero, it is necessary to differentiate between shutdown, disconnection, measurement faults, and communication faults.

Also, it is important to confirm whether the values displayed on the on-site equipment match those on the remote monitoring screen. If the on-site equipment indicates power generation but the remote monitoring shows a lower value, the issue may lie in the communication or measurement pathway rather than the generation equipment itself. Conversely, if both the remote monitoring and the on-site display show low values, it should be treated as an actual drop in generation. When reviewing data, rather than accepting displayed values at face value, it is essential to verify which device, at what time, in what units, and over what period the values are being aggregated.

Check the panel surface for dirt and shading

For industrial installations with low power generation, inspecting the condition of panel surfaces is indispensable. Solar panels generate electricity by receiving light, so any dirt or obstructions on the surface affect power output. Dirt can come from various sources: dust, bird droppings, fallen leaves, pollen, yellow sand, splashed mud, deposits from exhaust, and dust from nearby construction. In large power plants, the entire array may become uniformly dirty, or only certain areas may show noticeable soiling due to wind direction or topography.

Particular attention should be paid to partial soiling and shading. Even if only part of a panel is dirty, that effect can be reflected in the power generation of the entire circuit. When the entire surface is lightly soiled, a decrease in power generation often appears gradual, but when there is localized shading—such as from bird droppings or fallen leaves—output can become uneven, affecting specific panels or strings. In the field, it is important not only to view the whole array from a distance but also to check for uneven soiling by row and by section.

When checking for shading, examine surrounding buildings, trees, utility poles, mounting racks, fences, adjacent equipment, slopes, temporary structures, and the like. Equipment that had no problems at installation may, after several years of operation, be shaded at certain times due to tree growth or the addition of new structures nearby. At the low solar elevation angles of morning and evening, shadows can extend much farther than expected. Rather than judging that there is no shading by looking at a single moment during the daytime, it is necessary to correlate the periods when reductions occur with how shadows fall on the site.

Panel damage or discoloration can also cause reduced power output. If you observe cracks in the surface glass, discoloration resembling scorch marks, internal discoloration, deformation of the frame, or misalignment of the mounting points, a professional inspection is required. Typhoons, flying debris, snowfall, falling branches, contact with animals, and similar events can cause changes in appearance. Even damage that appears minor can lead to water ingress or insulation failure, so it is important to photograph and record the location as soon as you discover it.

Even when considering cleaning, low power output does not necessarily mean you should clean immediately. Water quality, cleaning methods, scaffolding, risk of electric shock, load on the panel surface, and impacts on surrounding equipment must be considered. If on-site personnel perform cleaning work without due care, there is a risk of damage or accidents. First, it is safer to record the extent and type of soiling and its relationship to any drop in power generation, and consult a specialist contractor as needed.

Inspect wiring, connection points, and terminals

When power generation is low, the condition of the wiring, connection points, and terminals should be prioritized for inspection on the equipment side. However, these areas carry risks of electric shock and short circuits, so they are not places for on-site personnel to handle casually. Begin with a visual inspection, and if any abnormalities are suspected, arrange for an inspection by personnel with the appropriate qualifications and authority or by a specialist contractor.

Around wiring, you should look for damage to cable jackets, sagging, excessive tension, loose or detached cable ties, contact with mounting racks, contact with the ground, contact with puddles, chew marks from animals, and damage from mowing operations. In industrial equipment, because wiring is exposed outdoors for long periods, it can be subjected to stress from UV exposure, wind and rain, temperature changes, animals, and contact during work. If a cable’s appearance is abnormal, it can lead not only to reduced power output but also to safety problems.

At connection points, inspectors should check for loose connectors, poorly seated connections, discoloration, scorch marks, damage, moisture ingress, and attached foreign matter. Faults at the connections can lead to reduced power generation and intermittent output fluctuations. Even if a system appears to be generating power on clear days, it can become unstable due to temperature rise, vibration, or humidity. If scorch marks or discoloration are visible, do not attempt to touch them; secure the surrounding area and arrange for an inspection.

Areas around junction boxes and combiner boxes are also important. Check the door closure, waterproofing condition, signs of moisture ingress into the interior, intrusion by insects or small animals, discoloration of terminals, unusual odors, unusual noises, and the status of indicator lights. Outdoor panels may appear normal at first glance, but moisture or condensation can develop inside. Opening panels or inspecting the interior must be done in accordance with equipment management rules and safety procedures. Do not lightly open and work on an energized panel just because power output is low.

Abnormalities in wiring and connections can also show up in monitoring data. If only a particular string has low current, output suddenly drops during specific times, performance tends to decline after rain, or fluctuations are large on windy days, these can be signs of connection- or wiring-related problems. Combining on-site visual inspections with changes in the data makes it easier to narrow down inspection targets.

Check the status of the power conditioner and peripheral devices

When power generation is low, checking the condition of the power conditioner and its peripheral equipment is also essential. The power conditioner is an important device involved in the overall power generation of the system, converting the direct current (DC) electricity generated by the solar panels into alternating current (AC). If this device has stopped, is limiting its output, or some of its inputs are not functioning properly, the power generation will decrease.

First, what you should check is whether the equipment is running or stopped and whether it is issuing any alarms or errors. If the display or monitoring screen shows an alarm, record the alarm details and the time it occurred. Even if an alarm occurred temporarily and then cleared, if the same alarm repeats it may be related to the cause of the drop in power generation. It is important not to look only at the current display but to check the history.

Attention should also be paid to output limiting and protective operations. Depending on the equipment, the device may intentionally curb its output due to grid-side conditions, voltage rise, temperature rise, equipment protection, external control, or similar factors. In such cases, power generation can be low even if the panels and wiring are normal. In particular, if the output plateaus at a fixed value around noon on sunny days, you should check the equipment capacity, control settings, grid conditions, and temperature conditions.

Don't overlook the thermal environment. Power conditioners are often installed outdoors or in equipment rooms, and poor ventilation, clogged filters, direct sunlight, nearby obstructions, or rising internal temperatures can lead to output limiting or shutdown. Check whether objects placed around the equipment are restricting airflow, whether intake or exhaust vents are blocked, and whether weeds or fallen leaves have accumulated nearby. Even visual checks of the exterior can provide information that leads to improvements.

Peripheral equipment to check includes circuit breakers, switches, power receiving and transformer equipment, measuring instruments, and communication equipment. When generation appears low, it may not be the generation itself but a measurement or communication issue causing it to look low. Check the communication equipment’s power supply, antenna, wiring, indicator lights, and communication status, and verify there is no missing data. If the amount of electricity sold is low, it is also important to consider separately whether generation or the sold amount is low.

When checking equipment, it is important not to rush recovery operations. Clearing alarms or restarting may temporarily restore readings, but if the cause is not recorded, it will be difficult to investigate when the issue recurs. Before recovery, record the display contents, time, surrounding conditions, weather, the affected equipment, and take photographs so that the cause can be more easily traced later. If a safety issue is suspected, do not operate based on an on-site judgment; it is appropriate to check with a manager or a specialized contractor.

Check variation at the string level

In industrial solar power installations, it is important to monitor not only the total power output of the facility but also variations at the string level. A string refers to a unit made by connecting multiple panels in series. Even if the total output of the facility appears only slightly low, in reality a particular string may have fallen significantly. In such cases, relying solely on the overall average can delay detection of the anomaly.

For string-level checks, compare circuits that are under the same conditions. If they have the same orientation, the same tilt, the same number of panels, and are measured at the same time of day, their output and current values tend not to differ significantly. Of course they will not be exactly the same, but if only a particular string is markedly lower, you should consider possibilities such as soiling, shading, a broken wire/open circuit, poor connections, defective panels, or a blown fuse.

When examining variability, it is important not to judge based solely on instantaneous values. Cloud movement or temporary shading can cause differences for short periods. Therefore, looking at trends over a certain period or across multiple days makes assessment easier. If the same string is low at the same time every day, fixed shading or a circuit-side issue may be suspected. If a drop occurs only after rain, that is a clue to check for moisture ingress or the condition of connections. If readings fluctuate on windy days, the contact condition of cables or connections may also be involved.

String variations become more valuable when managed by linking them to site locations. If you only see numbers on the monitoring screen but cannot tell which row, which section, or which junction box on site they are connected to, inspections will take longer. Routinely mapping string numbers to panel rows, junction boxes, power conditioners, and positions on the drawings makes on-site verification easier when anomalies occur.

Also, the causes of variability are not just electrical issues. There are environmental factors such as weeds growing in only certain sections, one row experiencing more mud splatter, bird damage being noticeable only in a particular area, or panel angles changing in just one place due to ground subsidence. By combining string-level measurements with on-site photos, location data, and inspection records, you can turn mere numerical anomalies into concrete inspection points.

Check for changes in weeds, terrain, and the surrounding environment

Changes in weeds and the surrounding environment should not be overlooked as causes of reduced power output. Industrial installations are often located on large sites, and the growth of weeds and the surrounding conditions vary with the seasons. Even locations that had no problems immediately after installation can, during continued operation, see vegetation grow and cast shadows on the panel surface. Especially from spring to summer, weeds can grow rapidly in a short period, so areas that showed no issues at the previous inspection may be affecting power generation by the next inspection.

The effects of weeds are more noticeable on the lower panels close to the ground. If grass reaches the lower edge of a panel, it can cause partial shading and may affect the output of the string. Even if it doesn't look like a major issue from a distance, from a low position you may see grass shadows on the panel surface. During inspections, in addition to viewing from the maintenance aisle, checking from the ends of the panel rows and from low positions makes it easier to grasp the shading conditions.

Changes in terrain are also important. After heavy rain, when sediment flows in, slopes collapse, or watercourses change, mounting racks, wiring, and areas around panels can be affected. If foundation settlement or scour alters the tilt of the racks, small differences in panel orientation or height can occur. Even if these do not immediately lead to a large change in power generation, early detection is important from the standpoint of long-term equipment maintenance.

Changes in the surrounding environment include nearby buildings, temporary scaffolding, material storage areas, utility poles, signs, trees, and development of adjacent land. Even changes that occur outside the power plant can cause shading, dust, drainage issues, or sediment inflow. For industrial facilities, regularly checking changes not only within your own premises but also on adjacent land makes it easier to explain the background of decreases in power generation.

When checking site conditions, photographic records are useful. If photos are taken regularly from the same position, direction, and height, it becomes easier to compare weed growth, changes in shadows, sediment buildup, and alterations to surrounding structures. Instead of taking photos for the first time when power generation is low, retaining photos from normal operation makes it easier to identify differences during abnormal conditions. This is especially important on large sites, where inspectors may focus on different areas, so it is important to establish shooting positions and the inspection scope.

Maintain inspection records to help prevent recurrence

When inspecting low power generation, it is important not only to find the cause but also to keep records. If records are inadequate, when a similar decline recurs you will not know what was checked last time, what was repaired, or in what condition it was restored. Industrial facilities involve many stakeholders—managers, on-site staff, inspection contractors, construction companies, and power producers—who need to share information. Poor quality records increase the need to repeat checks and lead to misalignment in understanding.

Inspection records should document the basis for judging that power output is low. Clearly state when, at which equipment, which numerical value was low, and what it was compared against. Simply writing "power output is low" does not allow later verification. Recording solar irradiance, weather, time of inspection, the equipment checked, what the monitoring screen displayed, site photos, alarm history, and whether any recovery operations were performed will create records that can be used to isolate the cause.

Photographic records require both overview photos and detailed photos. Overview photos help identify which section the issue is occurring in. Detailed photos help confirm dirt, damage, wiring condition, display screens, alarm messages, grass shadows, and soil accumulation. Because photos alone can make it difficult to determine the location, organizing them together with the position on drawings, string numbers, equipment numbers, and shooting direction will make them easier to use when reviewed later.

Do not forget to verify after restoration. After performing cleaning, weed removal, repair of connection components, equipment restoration, communication restoration, etc., confirm whether power generation has returned to a normal range. If you stop after carrying out restoration work, you will not be able to determine whether the work actually had an effect. Compare pre- and post-work power generation data, solar irradiance conditions, the values of the target string(s), and equipment alarm status, and record whether improvement was observed.

From the perspective of preventing recurrence, it is also necessary to review inspection frequency and management methods. If weeds are the cause, review the timing and scope of weed control. If dirt is the cause, prioritize management of sections that are prone to soiling. If wiring damage is the cause, review precautions during mowing and methods for protecting wiring. If communication failures are the cause, establish procedures for checking monitoring equipment and the communication environment. Rather than treating a drop in power generation as a one-time incident, turning it into the next operational improvement will lead to long-term generation stability.

Summary: When power output is low, organize on-site information from multiple perspectives

When you suspect low power output from an industrial installation, first check the weather and solar irradiance, then in order review the monitoring data, panel surfaces, wiring, connections, power conditioners, string-level variations, weeds, and the surrounding environment. A drop in power generation can be caused not only by equipment failure but also by external conditions, faulty measurements, communication failures, dirt, shading, environmental changes, and so on. By not assuming a single cause and verifying against both data and the on-site conditions, you can reduce unnecessary work and oversights.

Especially in industrial solar power installations, sites are expansive and involve many devices and circuits, so it is important to organize what is happening and where, together with location information. Even if a decline in power generation is detected early, inspections will take time if you cannot determine which row, which block, which string, or which piece of equipment on site is involved. By routinely linking and managing photos, drawings, inspection records, and monitoring data, it becomes easier to respond when abnormalities occur.

Consideration for safety is also indispensable. Inspections of wiring, terminals, junction boxes, power conditioners, and power receiving and transformer equipment involve hazards, so it is necessary to separate the scope that on-site personnel can check from the scope that requires specialized inspection. By narrowing down potential abnormalities through visual checks and organizing records, and by establishing a workflow to hand cases over to specialist contractors as needed, it becomes easier to ensure both safety and efficiency.

If a low power output is left unaddressed, it can affect not only the amount of electricity sold and equipment utilization rate but also lead to missed anomalies. Conversely, if checks are carried out in the correct order, it becomes easier to determine whether the change is a temporary fluctuation due to weather, a measurement issue, or whether equipment inspection is required. While making use of site photos and location information, it is important to clearly organize inspection targets, verification results, and changes after recovery to enable early detection of declines in power output and to streamline inspection records.