7 Ways to Prevent Reduced Power Output | Check Panel Soiling, Shading, and Wiring

When operating a solar power generation system, you may encounter issues such as output not increasing as much as expected from a certain point, generation being lower than the previous year, or output not rising despite sunny conditions. When considering ways to increase generation, rather than immediately thinking about adding equipment or making major renovations, it is important to first separate and check the factors causing the decline in output.

The methods referred to here for increasing power generation do not mean raising output beyond the equipment’s design specifications or the prevailing weather conditions. Rather, it is an approach that identifies factors—such as soiling, shading, poor connections, or insufficient record-keeping—that are reducing the generation that should otherwise be achieved, and improves them within reasonable limits.

Power output is not determined solely by panel performance. It varies due to multiple overlapping factors such as dirt on the panel surface, nearby shading, the condition of wiring and connections, installation angle, weather conditions, variability across installations, and how inspection records are kept. Therefore, if you want to increase power output, you should not assume a single cause but verify conditions both on-site and in the data.

This article organizes seven items to review to prevent declines in power generation, aimed at operations personnel. By checking them during daily inspections, regular inspections, pre-renovation surveys, and before considering measures to improve power output, you can reduce unnecessary work and more easily determine which areas need improvement.

Table of Contents

• It is important to identify and check the causes separately when power output declines

• Check panel soiling and surface condition

• Review the locations and times when shading occurs

• Check differences in wiring, connection points, and systems

• Inspect panels for damage, degradation, and temperature conditions

• Check for deviations in installation angle and installation conditions

• Compare power generation data and weather conditions separately

• Keep inspection records and use them to guide improvement decisions

• Summary

It is important to check the causes of reduced power output separately

When you feel that power generation is low, the first thing to do is not to assume a single cause. Solar power generation is affected by solar irradiance, ambient temperature, the condition of the panels, the condition of equipment, wiring, the surrounding environment, and operational management. For example, even on equally sunny days the solar elevation angle differs by season, and panel temperature changes. Even if generation is lower than the previous month, that alone does not indicate an abnormality. On the other hand, if you compare days with similar conditions and output is clearly lower, there may be a malfunction or a change in the surrounding environment.

In operational work aimed at finding ways to increase power generation, it is important to first set the criteria for comparison. Rather than comparing only yesterday and today, compare the same month in the previous year, the same season, the same time of day, and days with similar solar irradiance conditions. Also, instead of judging solely by the power generation of the entire plant, examining by section, by circuit, and by equipment makes it easier to determine whether the decline is overall or localized.

If overall power output has decreased, weather conditions, soiling, snowfall, widespread shading, or changes in settings/configuration may be involved. If only some strings are low, suspect wiring, connection points, equipment, shading of specific panel rows, localized soiling, or damage. If you proceed with cleaning or parts replacement without this troubleshooting, you may increase the amount of work without addressing the actual cause.

Also, when confirming a decline in power generation, both visual inspection and numerical data are necessary. Relying on data alone can easily cause you to overlook things like bird droppings, fallen leaves, shadows from weeds, sagging cables, or abnormalities around mounting hardware. Conversely, visual inspection alone cannot fully capture output differences between circuits or downward trends by time of day. By cross-checking what is visible on site with what the data reveals, it becomes easier to prioritize improvements.

Measures to increase power output range from cleaning, weed control, and shading countermeasures to wiring inspections, equipment inspections, reviewing installation conditions, and improving operational records. However, which measures are effective depends on the site. The important thing is to decide the order in which to check the causes of reduced power output and to carry out inspections using reproducible methods. Establishing a system in which the same criteria can be applied even when personnel change makes it easier to detect declines in power output early.

Check panel soiling and surface condition

To prevent a decline in power generation, the first thing to check is dirt on the panel surface. Because solar panels generate electricity by receiving light, dirt on the surface can reduce the amount of light received and affect power output. There are many types of dirt, such as dust, yellow sand, pollen, bird droppings, fallen leaves, rain streaks, mud splashes, tree-derived deposits, and dust from nearby construction. Because the way panels become dirty varies depending on the installation site, it is important to check the on-site conditions rather than simply assuming rain will wash them away.

What you should pay particular attention to is localized soiling. While a thin layer of dust over the entire panel can also affect power generation, soiling that covers part of the panel—such as bird droppings or fallen leaves—can have a greater impact than it appears. Because solar panels are made up of multiple cells, shading of a portion can reduce the power generation efficiency of that panel or of the area connected to the same circuit. Do not judge solely by the area of the soiling; you need to check where it is located.

When checking for soiling, inspect the panel surface not only from a distance but also from different angles to assess the condition of the surface. Because reflections can make dirt difficult to see in sunny conditions, inspections are often easier in the morning or evening or on cloudy days. For installations where dirt tends to accumulate at the lower edge of a row, also check for rainwater runoff traces and mud deposits near the frames. In low‑slope installations, water tends to remain, and after drying dirt can remain as streaks. On rooftop installations, nearby exhausts, surrounding trees, areas where birds congregate, and dust from roofing materials also have an impact.

When considering cleaning, it is important to record its relationship to declines in power generation. Rather than deciding to clean immediately just because something is dirty, record the generation before and after cleaning, irradiance conditions, time of day, and the scope of the work. This makes it possible to verify whether cleaning actually led to improved generation. If there is no significant change after cleaning, other causes should be suspected. Conversely, if improvement is observed in a particular string after cleaning, it becomes easier to conclude that soiling in that section was a contributing factor to the generation decline.

However, safety must also be considered when inspecting or cleaning panel surfaces. At heights, on slopes, on wet roofs, or around energized equipment, there is a risk of falls or electric shock. Rather than forcing yourself to get close to check, rely on observation from a safe position, record photographs for inspection, and, when necessary, have qualified professionals carry out the work. In addition, tools that scratch the surface or improper cleaning methods can affect long-term power generation performance. Trying to increase output by performing work that damages the panels will be counterproductive.

Inspections for soiling should be carried out not only when power output drops, but regularly. Recording how soiling accumulates seasonally, how it persists after rain, locations prone to bird damage, and the effects of nearby construction makes it easier to determine the need for cleaning. To stabilize power output, it is important not to clean soiling just once, but to identify the conditions that lead to soiling and establish a management system that can respond early.

Review the locations and times when shadows occur

Shading is an often-overlooked cause of reduced power generation. In solar power generation, when the light hitting the panels decreases, the power output also falls. Shadows can be caused by buildings, trees, utility poles, mounting racks, fences, nearby equipment, hills or slopes, adjacent rows of panels, and more. Even locations that had few problems at the time of installation can later experience greater shadow impacts due to tree growth, newly constructed nearby buildings, or seasonal changes in the sun’s altitude.

When checking for shadows, the important thing is not to look at a single moment but to observe how they move over time. In the morning, east-side structures cast shadows; in the evening, west-side structures do; and in winter, the low sun angle produces long shadows that are more likely to have an effect. If you only look around noon it may appear that there are no shadows, but shadows can be present in the morning and evening. Verifying whether the times when power generation drops coincide with the times when shadows appear on site makes it easier to isolate the cause.

Particularly important to watch for are thin shadows and partial shading. Shadows from power lines, handrails, lightning protection equipment, racking members, the tips of weeds, the edges of adjacent panels, and so on may look small from a distance. However, when a shadow crosses part of a panel, it can affect power generation. It is important to check not only the area of the shadow but also which position on the panel, in what direction, and at what times of day it falls.

In ground-mounted power plants, shadows from weeds can also cause a reduction in power generation. Grass growing under the panels and between rows can cast shadows on the panel surface in the morning and evening. Even if there appears to be no problem when viewed from the front, from an angle you may see grass casting shadows on the lower edge of the panels. Even when weeding is performed, inconsistencies in work between sections can cause only some systems to have lower power output. After weeding, it is important not only to record that the work was carried out but also to confirm that the shadows have been eliminated.

For rooftop installations, check for shadows cast by nearby protrusions and equipment. Antennas, ventilation equipment, railings, adjacent buildings, rooftop equipment, and the like can cast shadows on the panels depending on the time of day. Even if shading effects were considered during design, additions of equipment later or changes in the surrounding environment during operation can affect power generation. Since roofs are difficult to inspect, do not rely solely on visual observations from the ground; record findings using safe methods as needed.

When considering shading countermeasures, classify causes into those that can be removed and those that cannot. Weeds and some branches can sometimes be remedied through maintenance, but shadows cast by buildings or terrain are not easily changed. In such cases, it is important to determine the times and extent of shading and incorporate them into the assumptions for energy yield assessments. In practice, both addressing removable shading and correctly accounting for non‑removable shading are necessary to prevent declines in power generation.

Shadows change with the seasons, so the timing of inspections is also important. Even if there are no problems in summer, shadows can lengthen in winter and reduce power generation. Conversely, judging year-round power generation solely on the impression of shadows observed in winter can lead to overestimating their impact. By keeping seasonal records and comparing them with generation data, you can assess the impact of shadows more realistically.

Check for differences across wiring, connection points, and systems

To prevent a drop in power generation, inspecting wiring and connection points is also essential. In solar power systems, the electricity generated by the panels flows through wiring and is used or transmitted after passing through junction boxes, power conditioners, and other components. If anywhere along this path there is a poor connection, a broken wire, loose connections, deterioration, damage, overheating, water ingress, or similar issues, it can cause a reduction in power generation. Even if the panels themselves have no problems, a fault in the electrical pathway can reduce the output of the entire system.

Wiring-related issues can be difficult to detect from appearance alone. Scratches to cable jackets, looseness at connector joints, undone or loosened cable ties, damage caused by animals, deterioration from ultraviolet light or exposure to wind and rain, contact with the ground, and water ingress due to poor drainage can all progress over time. Even if there are no problems immediately after installation, conditions can gradually worsen during long-term operation, so regular inspections are necessary.

In practical operations, it is important to look not only at the total power output of the plant but also at differences between systems. If, despite being sections with the same orientation, the same tilt, and the same size, only certain circuits or pieces of equipment show lower output, there may be a problem with the wiring or connections in that area. While the effects of weather conditions or soiling often appear over a wide area, abnormalities in wiring or connections can be localized. Finding such a bias is the first step in identifying the cause.

In inspections of connection points, we check not only visible abnormalities but also the surrounding conditions. We look for signs of moisture or water ingress inside the junction box, discoloration or burn-like marks around the terminals, whether undue stress is being placed on cable entry points, and whether covers and seals are intact. For outdoor equipment, factors such as rain, wind, temperature changes, and intrusion by insects or small animals must also be considered.

Even if the routing of wiring is not a direct cause of reduced power output, it can be a precursor to future faults. Conditions such as cables sagging and touching puddles, rubbing against sharp components, being easily swayed by the wind, or having loose fastenings are points that should be corrected promptly. Rather than responding after power output has dropped significantly, it is important to perform preventive inspections before they lead to a decline in power generation.

When inspecting wiring and connection points, specialized measurements may be required. Even if a visual inspection does not reveal obvious damage, signs of a fault can be detected by measuring voltage and current, checking the insulation condition, and checking for abnormal temperatures. However, work on energized equipment carries risks. Rather than having unqualified or inexperienced personnel attempt such work, it is important to address it based on the necessary safety procedures and professional expertise.

When reviewing wiring as a way to increase power output, it is necessary not only to decide whether to replace cables but also to verify where abnormalities exist and which data they correspond to. Organizing power output by system, inspection photos, the condition of connection points, and measurement results allows you to narrow down the areas that need improvement. Wiring and connection points are usually inconspicuous, but they are important checkpoints for preventing a decline in power output.

Inspect the panels for damage, deterioration, and temperature conditions

When considering a decline in power generation, it is also necessary to check the condition of the panels themselves. Because solar panels are used outdoors for long periods, they are exposed to wind and rain, ultraviolet radiation, temperature fluctuations, airborne debris, snow accumulation, salt, and sand and dust. Even if there appears to be no major problem externally, fine cracks, surface scratches, warped frames, degradation of sealing parts, discoloration, or localized heating can affect power generation.

Visible abnormalities that are easy to detect by visual inspection include cracks in the glass surface, clouding, discoloration, scorch-like marks, deformation of the frame, lifting of the panel surface, and damage to the rear side or cable connection points. After typhoons or strong winds, in locations with frequent flying debris, or in places affected by snow accumulation or falling snow, it is recommended to carry out a condition check separately from regular inspections. Leaving damaged panels unattended can lead not only to reduced power output but also to safety hazards.

However, panel degradation does not always appear suddenly or dramatically. Over long-term operation, output can decline gradually. Therefore, when looking at changes in power generation, it is important to examine long-term trends as well as a single day's output. Compare the same season and similar levels of solar irradiance to check how much it changes year by year. Whether the decline is sudden or gradual will change which causes you should suspect.

Temperature conditions also affect power generation. Solar panels tend to generate more as solar irradiance increases, but in general their output decreases as panel temperature rises. Therefore, if generation on a clear midsummer day is lower than expected, it does not necessarily indicate a fault. High ambient temperatures, weak winds, and conditions that trap heat on the panel’s rear make temperature-related output reductions more likely.

For roof-mounted installations, the ventilation conditions on the back side of the panels should also be checked. If there is not enough airflow between the panels and the roof, heat can become trapped. Even for ground-mounted installations, temperature conditions vary depending on the surrounding ground surface, weeds, the height of the mounting structure, and how the wind flows through the site. It is difficult to eliminate temperature effects completely, but if temperature conditions are ignored when evaluating power output, you may mistakenly judge normal behavior as an anomaly.

Cross-referencing with power generation data is effective for identifying panel damage or degradation. If only certain rows or sections show low output, there may be a localized anomaly in the panels within that area. Even if no abnormalities are found on visual inspection, check for variations in power output, variations in temperature, past inspection history, and the post-disaster situation together. Keeping inspection results together with photos and location information makes it easier to recheck the same spot later.

When you want to increase power generation, rather than immediately considering panel replacement or large-scale measures, it is important to first confirm the extent and cause of any abnormalities. If dirt or shading is the cause, replacing the panels themselves will not provide a fundamental solution. Conversely, if the panels have obvious damage or abnormalities, cleaning or weeding alone will not improve the situation. By combining panel condition, surrounding environment, and generation data when making a judgment, it becomes easier to arrive at appropriate measures.

Verify deviations in installation angle and construction conditions

To prevent a decline in power generation, it is also important to verify the installation angle and construction conditions. Solar panels receive different amounts of solar radiation depending on their orientation and tilt. If there is a discrepancy between the azimuth and tilt assumed during the design stage and the actual installation, the expected power output may not be achieved. In addition, over long-term operation the mounting structure can settle, fastenings can loosen, ground conditions can change, and snow accumulation or strong winds can alter the original installation state.

At ground-mounted solar power plants, the tilt of the racking and the alignment of the rows are checked. Situations such as only some racks having different angles, heights not being consistent from row to row, or ground subsidence causing twisting of the panel surface can lead not only to reduced power generation but also to structural concerns. Even if there is no obvious visual anomaly, surveying and comparison with record photographs can reveal gradual changes.

For roof-mounted installations, panels are often installed to follow the slope and orientation of the roof surface, so generation conditions differ for each building. Even systems with the same capacity will produce different amounts of power depending on whether they face south, face east-west, have a low pitch, or on the presence or absence of surrounding upstands. When comparing generation, you should not judge solely by system capacity; you must take the conditions of the mounting surface into account. If panels are installed on multiple buildings, check each building’s orientation, pitch, and the effects of shading separately.

As construction-condition deviations, panel spacing and row spacing are also points that should be checked. If row spacing is insufficient, shadows from the front row can fall on the rear row depending on the season and time of day. Even if no problem was identified during design, actual variations in ground elevation and racking height across the site can change how shadows fall. If only certain rows show reduced power output, it is necessary to check for row-to-row shading and height differences.

Drainage conditions are also related to reductions in power generation. In areas with poor ground drainage, mud splatter and moisture can more easily cause equipment deterioration. On roofs, if rainwater does not drain well, dirt tends to remain at the lower edges of the panels. When the installation angle is shallow, dirt is less likely to wash off and tends to accumulate on the surface. To increase power generation, it is important not only to consider solar irradiance conditions but also to check installation conditions, including how rainwater and dirt flow.

When verifying installation conditions, compare the design drawings and the records at completion with the current state. Because drawings alone may not reveal the actual as‑built condition, verify the situation using current photos, measurement data, and inspection records. In particular, when a decrease in power generation has persisted for a long period or when you want to clarify causes before refurbishment, it is important to accurately assess the current condition. Misalignments in the installation angle or in the racking condition are difficult to detect through routine power monitoring alone, so on‑site verification is especially valuable.

When considering improvements to power output, distinguish whether problems with installation conditions can be remedied. Some issues are easy to address in the short term, such as cleaning or weeding, while others require planned action, like racking adjustments or revisiting the surrounding environment. Deciding on countermeasures without understanding the current situation may lead to spending time on measures with little effect. Verifying the installation angle and construction conditions is an important step to fundamentally sort out the causes of reduced power output.

Compare power generation data and meteorological conditions separately

When you suspect low power output, comparing data is as important as on-site inspections. However, drawing conclusions based only on power output can easily lead to misunderstandings. Solar power generation output varies with solar irradiance, temperature, cloud cover, rainfall, snowfall, wind, and season. Even if output appears to have dropped, it may simply be due to poor weather. Conversely, if sunny conditions continue but output remains low, there may be problems with equipment or the surrounding environment.

When looking at data, first align the periods you are comparing. Don’t just view by day, month, or year—also check generation by time of day. Whether output is low only in the morning, only at noon, only in the evening, or low throughout the day changes the causes you should suspect. If it’s low only in the mornings and evenings, suspect shading; if there’s a tendency to plateau at midday, suspect temperature or equipment limitations; if it’s suddenly low on specific days, suspect weather or temporary anomalies.

Comparing with the same month of the previous year can also be useful, but it is risky to judge based solely on a simple year-on-year comparison. If the previous year had many consecutive sunny days while this year has many consecutive cloudy days, generation will fall even if the equipment is functioning normally. Therefore, if possible, check solar irradiance and weather conditions as well. At minimum, it is desirable to compare under matched conditions, such as sunny days with sunny days, cloudy days with cloudy days, or the same time of day in the same season.

Also, it is important to view the facility’s total power generation separately from the generation by each system. If only the overall generation is slightly low, it can be difficult to identify the cause, but when you look by section or by circuit you may find that only a specific area is underperforming. If only a part is low, prioritize checking localized causes such as soiling, shading, wiring, connections, or panel abnormalities. If the entire facility is similarly low, check weather conditions, widespread soiling, overall facility settings, and the condition of common equipment.

When considering ways to increase power generation, it is also important to keep data from before and after improvements. For example, if you perform cleaning, weeding, wiring repairs, or removal of shading sources, check how generation changed before and after. However, if the solar irradiance conditions differ before and after the improvements, a simple comparison cannot be made. Choose days with as similar conditions as possible and examine trends by time of day. This makes it easier to assess the effectiveness of the measures.

In data comparisons, establishing criteria to detect anomalies early is also useful. For example, compare sections under similar conditions within the same facility to determine how much difference normally occurs. If a difference exceeds that range, it should be targeted for inspection. Judging by intuition without criteria can lead to missing anomalies or misidentifying normal fluctuations as problems.

Power generation data alone does not lead to improvements simply by being accumulated. Only when it is linked with on-site inspection results, weather conditions, work history, and equipment modification history does it become information usable for analyzing the causes of declines in power generation. For operations staff aiming to increase power output, what matters is not just examining data in detail but verifying it against facts on site when making decisions. Handling data and on-site information together rather than separately leads to more reliable decisions about improvements.

Keep inspection records to inform improvement decisions

To prevent a decline in power generation, it is essential not only to carry out inspections but also to keep records. If you rely solely on the memory of the person who inspected the site, you will not be able to make comparisons at the next inspection and will end up checking the same problem repeatedly. To determine the cause of low power generation, you need to record when, where, what you checked, and what condition it was in.

In inspection records, it is important to link photos, location, date and time, weather, findings, power generation data, and work history. For example, if panel soiling is confirmed, record not only photos of the soiling but also which block and which row it is in, whether it corresponds to the system showing reduced output, and how it changed after cleaning. When shadows are observed, record the cause of the shadow, the time of day, the season, and the area affected by the shadow. This makes future decision-making easier.

If records are insufficient, you'll have to search for the cause of a drop in power generation from scratch each time. You can't determine whether the same spot was previously affected by soiling, whether it improved after weeding, whether a wiring fault has recurred, or whether it's due to seasonal shading. Conversely, if records are organized, when generation falls you can compare with past trends and narrow down the inspection scope.

Inspection records are also useful for determining the priority of improvements. It is not realistic to address all issues at once. You need to assess and separate areas that have a large impact on power generation, areas that pose safety risks, areas prone to recurrence, and areas that can be improved within a short period. To do that, it is important to make sure site conditions can be compared using records rather than by subjective impression.

Records are also helpful when explaining improvements to power generation. When making improvement proposals internally, you need to explain to managers and stakeholders why the work is necessary. If you have photos, generation data, and inspection results, it becomes easier to explain how dirt, shading, and the condition of wiring are related to reduced power output. Rather than simply saying you want to take action because power output is low, presenting concrete evidence makes it easier to reach a decision.

When keeping records, it is also important that they be easy to review later. If you have a large number of photos with no information about location or date and time, they become difficult to use in practical work. Managing and standardizing the section name, equipment name, inspection date, inspection items, and action status makes re-inspection and handovers easier. Ensuring that the same information can be checked even when staff change reduces the likelihood that responses to declines in power output will rely on specific individuals.

Efforts to increase power generation cannot be completed with a single inspection. Dirt, shading, wiring, installation conditions, and weather conditions change over time. That is why it is important to accumulate inspection results and evaluate them together with generation data. Inspection records are not merely reports; they are the foundational material for making the next improvement decisions quickly and accurately.

Summary

To prevent a decline in power output, it is important not only to look at the fact that output is low but to identify and check the causes separately. There are multiple factors that affect power output, such as panel soiling, shading, wiring, connections, panel condition, temperature conditions, installation angle, construction conditions, weather conditions, and insufficient inspection records. If you assess only one of these, you may overlook the true cause.

In practical work aimed at increasing power generation, we first link the site with the data and verify. If there is soiling, we check whether that soiling corresponds to the areas showing reduced generation. If there is shading, we check whether the periods of shading match the periods of reduced generation. If there are concerns about wiring or connections, we cross-check differences between systems with inspection results. If installation conditions deviate, we compare drawings and past records with the current state.

When addressing a decline in power generation, it is important not to immediately consider major renovations, but to organize actions in order from items that are easiest to check. In some cases cleaning or weeding can lead to improvement, while in others wiring inspections or equipment checks are necessary. If long-term degradation or installation condition issues are involved, planned improvements are required. What is important is to record the cause, confirm changes after countermeasures, and apply the findings to the next round of maintenance.

A decline in power generation can often be remedied with minor measures if detected early. However, without records and with no defined inspection scope, detection of abnormalities tends to be delayed. By combining daily inspections, periodic inspections, review of generation data, and organization of on-site photographs, it becomes easier to identify early warning signs of declining power generation.

In operating solar power generation systems, it is important not only to increase generation output but also to identify and prevent factors that cause declines as early as possible. By continuously checking on-site conditions and generation data—focusing on panel soiling, shading, and wiring—it becomes easier to determine priorities for improvement. Accurately assessing site conditions and selecting measures based on recorded data is the basic approach to preventing declines in generation output.