7 Panel Inspections to Boost Power Output｜How to Distinguish Degradation from Dirt

Table of Contents

• Panel inspections to increase power output should start by distinguishing soiling from degradation

• Inspection 1: Check power output data to determine how the decline appears

• Inspection 2: Inspect the panel surface for soiling and deposits

• Inspection 3: Distinguish between shading and soiling and inspect accordingly

• Inspection 4: Check the panel appearance for degradation and damage

• Inspection 5: Check for abnormalities in strings, connection points, and cables

• Inspection 6: Determine whether the cause is soiling or degradation by comparing changes before and after cleaning

• Inspection 7: Prevent recurrence through drainage, surrounding environment management, and inspection records

• Operational practices to translate panel inspections into power output improvements

• Summary

To increase power generation, panel inspections should begin by distinguishing between dirt and degradation

When you want to increase the power output of a solar power system, the first thing to check is the condition of the panels. Solar panels generate electricity by receiving sunlight, and surface dirt, shadows, deposits, visible damage, abnormalities at connection points, and deterioration of the surrounding environment can affect power output. If you feel the generation is low, you need to determine whether you should clean them immediately, suspect degradation or damage, or check for shading or problems on the equipment side.

For practitioners searching "how to increase power generation", the important thing is not to judge solely by whether the panels are dirty. If the panel surface has soil dust, bird droppings, fallen leaves, pollen, yellow sand, or a band-like stain at the lower edge, cleaning may improve the light-receiving condition. On the other hand, if there is surface discoloration, cracks, delamination, frame distortion, defects around connection points, or declines at the string level, simple cleaning may not restore power output. Distinguishing between dirt and degradation is the first step to reducing unnecessary work and achieving improved power generation.

You cannot increase solar irradiance at the site. However, you can bring the system closer to a state where the received solar irradiance is converted into electricity with as little waste as possible. The purpose of panel inspection is not to make the panels look clean, but to find where the power that should be generated is being lost. It is necessary to check, in order, whether the cause is reduced irradiance due to soiling, time-dependent losses caused by shading, output decline due to degradation or damage, or electrical losses at connections and cables.

Moreover, panel inspections are not a one-time task. Solar power plants, as outdoor facilities, change condition with the seasons, weather, surrounding environment, and equipment aging. Even if cleaned, dirt will accumulate again; even if weeds are removed, grass will grow back; trees will grow; and drainage routes will change due to sediment and fallen leaves. In addition, panels and wiring gradually change condition during long-term operation. To steadily increase power generation, it is important to continue operations of inspection, countermeasures, effect verification, and record updating.

Inspection 1: Confirm how the decline manifests in the power generation data

Before starting a panel inspection, first check the power generation data. If you only look at monthly or annual generation, you won't know when, where, or how the generation is declining. Even with the same overall drop in generation, the suspected causes differ depending on whether output is low only in the morning, the midday peak fails to develop, it falls only in the evening, or only a particular string is low. Before judging panel soiling or degradation, it is important to examine the shape of the generation curve.

If morning generation is low, shadows from east-side trees, slopes, surrounding structures, or adjacent equipment may be involved. If generation is low in the evening, check for shadows on the west side and the effects of surrounding terrain. If the midday peak does not materialize, possible causes include dirt on the panel surface, temperature rises, limitations of conversion equipment, output curtailment, equipment shutdowns, or abnormalities in panels or connections. If the generation curve suddenly drops during a sunny day, it is necessary to cross-check shutdown history and alarm history with the timestamps.

Comparing on an equipment-by-equipment basis is also indispensable. If you only look at the total power generation of the plant, some anomalies can be masked by the average. Compare systems with the same orientation, the same tilt, similar numbers of panels, and the same shading conditions, and check whether only specific rows or strings are performing lower. If only a specific area is underperforming, focus inspections on the panel surfaces in that area, shading, connections, cables, and the surrounding environment.

When distinguishing soiling from degradation, it is also important whether the drop in power output is temporary or persistent. If output recovers after rain or cleaning, soiling or surface deposits may have been affecting performance. If the same area remains underperforming even after cleaning, you should suspect degradation, damage, poor connections, or string faults. A sudden drop could indicate a cable break, connection failure, equipment shutdown, or new shading. If the decline is gradual, accumulation of dirt, growth of nearby trees, poor drainage, or aging-related changes may be involved.

If you go on site without looking at the power generation data, inspections tend to be broad and superficial. Knowing which time periods show low output and which specific equipment is underperforming makes it clear where to focus on site. Panel inspections should not begin with visually scanning surfaces on site; it is important to start by narrowing down possible causes from the power generation data.

Inspection 2: Check the panel surface for dirt and deposits

Dirt and deposits on the panel surface are a common cause of reduced power generation. Because solar panels generate electricity by receiving sunlight on their surface, when dirt accumulates the light reaching the cells is reduced. The type of soiling varies depending on the site environment: soil dust, pollen, yellow sand, bird droppings, fallen leaves, sap, dust from nearby construction, road-derived dust, and salt-containing deposits that tend to adhere in coastal areas. These are not degradation but power losses that may be improved by cleaning.

Particular attention should be paid to the band-like dirt that remains along the panel bottom edge and around the frame. It is often assumed that rain will wash it away naturally, but in reality the flow of rainwater can gather dirt at the lower edge and leave it there. On panels with a shallow tilt, water does not drain easily and dirt tends to accumulate. Even dirt that is not noticeable from a distance can affect power generation if it covers part of a cell. During panel inspections, it is necessary to carefully check not only the overall coloration but also the bottom edge, the corners, and the areas around the frame.

Localized deposits such as bird droppings and fallen leaves are also important. Unlike dirt that spreads thinly across the entire surface, these heavily cover specific spots and act as partial shading that reduces power generation. Rows near trees, around structures where birds like to perch, rows that tend to be downwind, and areas near unpaved walkways are more prone to soiling and deposits. If only some installations show low power output, focus inspection on the panel surfaces around those installations.

To distinguish between dirt and deterioration, it is important to check whether the contamination is merely adhering to the surface or whether the panel’s color or structure itself has changed. Soil dust, bird droppings, and fallen leaves often sit on the surface and are easy to see changes in by comparing photos taken before and after cleaning. By contrast, discoloration that does not change after cleaning, linear anomalies visible inside, delamination of surface materials, cracks or chips in the glass, and distortion of the frame may indicate deterioration or damage rather than simple dirt.

When cleaning, prioritize areas that have the greatest impact on power generation. Rather than cleaning all panels at the same frequency, focus on equipment where a drop in power output has been confirmed, rows with concentrated dirt, areas where dirt along the lower edge is conspicuous, and places with high levels of bird damage or fallen leaves. Cleaning must be performed in a way that does not damage the equipment. Avoid vigorously scrubbing with hard tools, performing sudden work during times when panels are hot, and skipping electrical safety checks.

Inspection 3: Distinguish Shadows from Dirt During Inspection

When power output is low, you need to check not only dirt on the panel surface but also the effects of shadows. Both dirt and shadows reduce the amount of sunlight received, but the countermeasures differ. If it’s dirt, cleaning may be effective, but if it’s shadows from weeds or trees, weed removal, pruning, or a review of the surrounding environment will be necessary. Confusing dirt with shadows can lead to cleaning without restoring power output.

Causes of shading include weeds, trees, fences, utility poles, surrounding buildings, mounting racks, adjacent panel rows, monitoring equipment, and others. Because shadows move with the time of day and season, the absence of shadows at the time of inspection does not necessarily mean there is no problem. Even if an on-site inspection at noon shows no issues, long shadows may fall on the panels in the morning and evening. If power generation data shows patterns such as lower output only in the morning or only in the evening, prioritize checking for shading.

Weeds are a common cause of shading at sites. Even if there is no problem in winter or immediately after installation, they can grow rapidly from spring through summer and cast shadows on the lower edges of panels and on the front rows. Even when the plants are not touching the panels, the low sun angle in the morning and evening causes shadows to stretch long. Furthermore, dense weed growth reduces ventilation, blocks inspection walkways, and makes it harder to check around equipment. A drop in power generation that looks like soiling can actually be caused by weed shading.

Don't overlook the shadows cast by trees. Even trees that had little impact at the time of installation can grow over several years and reduce power generation. Trees located on the south, east, and west sides can cast shadows on the panels at different times of day. At solar power plants near forests or slopes, the heights of the terrain and trees can overlap and create long shadows in winter. If generation is low only in winter, or if there are significant drops in the morning and evening, you should suspect shadows from trees or terrain rather than soiling.

To separate shadows from soiling, combine power generation data with on-site photographs. If output drops only during specific times of day, it is likely due to shading, and if it improves after cleaning, soiling may have had a significant impact. However, because many sites experience both soiling and shading simultaneously, it is important not to assume it is just one or the other. To increase power generation, assess the panel surface, surrounding vegetation, structures, and the generation curve together.

Inspection 4: Check panel appearance for deterioration or damage

During panel inspections, we check not only for dirt but also for visible deterioration and damage. Dirt is something that adheres to the surface and may be improved by cleaning. On the other hand, deterioration and damage are changes in the condition of the panel itself and may not be remedied by cleaning alone. To increase power generation, it is important to distinguish whether an issue is dirt, deterioration, or damage.

Visual changes to check for include cracks or chips in the surface glass, peeling of surface materials, internal discoloration, burn-like changes in color, deformation of the frame, deterioration of the sealing areas, and abnormalities on the back or edges. These are not things that will disappear simply by wiping the surface like dirt. In particular, if the power output continues to decline at the same spot and cleaning does not improve it, you should suspect panel degradation or damage.

When distinguishing between degradation and dirt, it is helpful to compare changes before and after cleaning. Items that disappear with cleaning are likely dirt or deposits, while discoloration, cracks, delamination, or shape abnormalities that remain after cleaning may indicate degradation or damage. Also, if only a particular panel in the same row looks different, check the power generation data and the connection status around that panel. If you cannot determine the cause from appearance alone, it is important to follow up with power generation data or a professional inspection.

Even if deterioration or damage is suspected, on-site personnel should avoid forcibly disassembling panels or touching electrical components. First, record the location where the anomaly is suspected, the equipment number, photographs, the date discovered, changes in power output, and the weather and surrounding environment. If there are cracks or fractures, the effects of rainwater and moisture must also be considered. Accurate records and appropriate inspections are necessary not only for decreases in power output but also from the perspectives of safety and preventing recurrence.

Also, deterioration of appearance may be related to the surrounding environment. Windborne debris, fallen branches, accumulated snow, strong winds, contact during grass cutting, poor drainage, and splashback of soil and sediment can affect panels and frames. If deterioration or damage is found, confirm not only the condition at the site but also why an anomaly occurred at that location. Recording the causes can lead to measures to prevent similar damage.

Inspection 5: Check for abnormalities in strings, connection points, and cables

When inspecting panels to increase power output, it is necessary to check not only the panel surface but also the electrical pathways that extract the power. Even if solar panels are receiving sunlight normally, if there are faults in the strings, connection points, or cables, the generated power cannot be fully extracted. If a panel appears clean but its power output is low, you should suspect not only surface dirt or degradation but also abnormalities in the electrical pathways.

When checking for abnormalities at the string level, compare units under the same conditions. If you simply compare systems that differ in panel count, orientation, tilt, shading conditions, or connection configuration, you may mistakenly judge normal differences as abnormalities. Check whether any string is consistently lower compared with adjacent rows or equipment with the same orientation. If only a specific string is low, possible causes include soiling, partial shading, panel defects, poor connections, cable damage, or equipment-side problems.

Problems with connection points and cables include loose terminals, poor contact, damage to cable sheathing, moisture ingress, damage by animals, damage during grass-cutting operations, and age-related deterioration. These issues can be difficult to detect from appearance alone. If only certain equipment has low power generation, becomes unstable after rain, suddenly experiences a drop in generation, or the output fluctuates irregularly, prioritize checking the connection points and cables.

However, when inspecting electrical equipment, safety must be the top priority. Even if the goal is to increase power generation, on-site personnel should avoid forcing connections or touching the inside of equipment to make judgments. Organize the equipment showing anomalies, the time of occurrence, changes in power generation, on-site photos, and the surrounding environment, and, if necessary, escalate to a specialized inspection. In panel inspections, it is important not only to look at the surface but also to clarify which areas are suspected of having electrical abnormalities.

Malfunctions of connection points and cables are also related to the surrounding environment. In areas overgrown with weeds, it becomes difficult to inspect the condition of cables. In locations with poor drainage, moisture and standing water can affect the connections. On sites where animals can easily enter, cable damage may occur. Rather than stopping at repairs alone, confirming site conditions that can lead to recurrence makes it easier to maintain the effects of power generation improvements for a longer time.

Inspection 6: Determine whether contamination or degradation is the cause by observing changes before and after cleaning

An effective way to distinguish between soiling and degradation is to check the changes before and after cleaning. If a decrease in power generation is caused by soiling, appropriate cleaning can improve the light-receiving condition and may show a trend of power recovery. On the other hand, if the same range of reduced power generation continues even after cleaning, it is necessary to check for other causes such as degradation, damage, poor connections, equipment-side limitations, or shading.

Before cleaning, record the target equipment, the type of soiling, the extent of soiling, on-site photographs, power generation data, and weather conditions. After cleaning, verify photographs taken from the same angle and power generation under solar irradiance conditions as close as possible. If the weather differs greatly before and after cleaning, it becomes difficult to compare power generation. Comparing sunny days with other sunny days and equipment under the same conditions makes it easier to assess the effect of cleaning.

If power output improved after cleaning, it is possible that dirt or deposits at the site were contributing to generation losses. In particular, if output improved in areas affected by lower-edge soiling or bird droppings, you can decide to prioritize cleaning of those areas in future. Recording locations where soiling tends to recur allows you to inspect them before power output falls significantly.

On the other hand, if power generation does not improve after cleaning, suspect causes other than dirt. If it remains low only in the mornings and evenings, suspect shading; if only a specific string remains low, suspect connections or cables; if the midday peak does not increase, suspect equipment limitations or the temperature environment; if visual abnormalities remain even after cleaning, degradation or damage are candidates. The cleaning results not only serve to determine whether power generation has improved, but also provide information to narrow down the causes that should be checked next.

When performing cleaning, it is also important not to damage the equipment. You should avoid scrubbing vigorously with hard tools, rubbing the surface while sand or small stones remain, carrying out sudden work during periods when the panels are at high temperature, and omitting safety checks for electrical equipment. Cleaning to increase power generation should be treated not as a cosmetic task to make things look clean, but as part of an inspection to isolate the causes of generation loss.

Inspection 7: Prevent Recurrence Through Drainage, Surrounding Environment, and Inspection Records

To distinguish panel soiling from degradation, you need to inspect not only the panels themselves but also the surrounding environment. Locations where soiling repeatedly occurs may have underlying factors such as poor drainage, sediment inflow, nearby trees, structures that attract birds, unpaved access paths, and prevailing wind direction. Areas prone to degradation or damage may also hide causes such as flying debris, falling branches, contact during grass cutting, moisture, and difficulty of inspection.

In locations where puddles remain after rain, weeds are more likely to grow, and mud splashing and sediment accumulation are more likely to occur. Where sediment flows in, dirt accumulates under panels and around cables, leading to reduced power generation and poorer inspection accessibility. If the same places get dirty again soon after cleaning, it is necessary to check not only the panel surface but also the flow of rainwater and the surrounding terrain.

The condition of inspection access routes is also important. If grass has overgrown so you cannot pass, if it is too muddy to approach, if equipment numbers are hard to read, or if photos alone do not clearly convey the location, discovery and sharing of abnormalities will be delayed. Even if you identify equipment with low power output from the data, if it is difficult to reach the corresponding site location, corrective actions will be delayed. To link panel inspections to improvements in power output, it is necessary to maintain a site environment that makes inspections easy.

Inspection records are also essential for preventing recurrence. By recording the locations of equipment with low power output, rows that are prone to soiling, areas suspected of degradation, locations where shading occurs, places where water pools, spots where poor connections have occurred, and the areas cleaned or repaired, you will know exactly what to check at the next inspection. If records are insufficient, you cannot learn the causes even if the same problems recur, and you will have to start the investigation from scratch each time.

To prevent recurrence, it is important to apply inspection results to subsequent work. Not only should you clean away dirt, but you should check why that location is prone to getting dirty. Not only should you find deterioration and damage, but you should look into why they occurred at that location. Panel inspections aimed at increasing power generation are not only about detecting abnormalities but also serve as on-site management to prevent the same generation losses from recurring.

Operational Practices to Turn Panel Inspections into Power Generation Improvements

To connect panel inspections to improvements in power generation, it is necessary to operate inspection, countermeasures, effect verification, and record-keeping as a single process. Use data to find locations with low power output, check on-site for dirt, shading, deterioration, connection points, and the surrounding environment, and implement the necessary countermeasures. After that, confirm how the power output has changed and keep records that can be used for decisions next time. Without this flow, inspections and cleaning become one-off tasks, and it becomes difficult for improvement effects to accumulate.

The first and most important step is to determine inspection priorities. Instead of inspecting all panels with the same density, give priority to equipment where a drop in power output has been confirmed, areas that are lower compared with equipment under the same conditions, rows that are prone to dirt or shading, and locations suspected of degradation. By checking locations that have a large impact on power generation first, it becomes easier to find causes that can lead to improvements even within limited inspection time.

Next, confirm the effects of cleaning and repairs. If dirt has been cleaned, compare the power generation and photographs before and after cleaning. If shadows have been removed, check whether the morning and evening generation curves have improved. If degradation or damage is suspected, continue to monitor the power generation trends of the equipment in question and the differences compared with surrounding equipment. If the effects of countermeasures are understood, you can determine the priorities for future inspections and work more accurately.

When multiple people are responsible for management, it is also important to be able to share the exact same location. In a large power plant, rows or equipment that look similar can make it difficult to identify locations from photos alone. By recording the equipment number, location information, photos, and work history together, field staff, managers, inspectors, and repair personnel can more easily confirm the same location. Improving power output is also about creating a system that uses on-site observations for the next set of improvements.

To reliably increase power output, it is important not only to respond after output drops but also to identify conditions that tend to cause drops in advance. If you record rows that easily accumulate dirt, time periods when shadows are likely to occur, equipment suspected of degradation, places where water pools, walkways prone to damage, and strings that are prone to abnormalities, you can inspect them before output falls significantly. Panel inspections should ideally be carried out as an operation to prevent declines in power output, rather than as a check after output has already decreased.

Summary

In panel inspections aimed at increasing power generation, it is important to check, in order, dirt, shading, degradation, connection points, and the surrounding environment to isolate the causes of generation losses.

In photovoltaic power generation, you cannot increase the amount of solar irradiance itself on site. However, you can improve power output by bringing the system closer to a state in which the received solar irradiance is converted into electricity without waste. To do this, it is necessary to check power generation data, reassess dirt and deposits on the panel surface, distinguish between shading and degradation, and check for abnormalities in the strings and connection points.

When distinguishing between dirt and degradation, one criterion is whether the condition changes with cleaning. Soil dust, bird droppings, fallen leaves, and soiling at the lower edge may improve with cleaning. In contrast, discoloration, cracks, delamination, frame distortion, and persistent declines in specific strings that remain after cleaning should raise suspicion of degradation, damage, or electrical faults. It is important not to judge by appearance alone, but to combine power generation data, before-and-after cleaning photos, and equipment-level comparisons.

Also, panel inspections are not something that can be completed in a single operation. Even if cleaned, dirt will accumulate again; even if weeds are removed, they will grow back; trees grow; drainage paths change. Deterioration and abnormalities in connections also evolve during long-term operation. By comparing power generation before and after countermeasures, keeping on-site photos and work histories, and applying them to the next inspection, the accuracy of improvements increases. To consistently increase power generation, it is essential not only to eliminate causes but also to create a site environment and management system that make the same causes less likely to occur.

In particularly large power plants, a system for accurately sharing problem locations is important. If you record dirt-prone rows, locations suspected of degradation, areas where shadows occur, places where water pools, abnormal strings, cleaning extents, repair locations, and inspection photos together with location information, it becomes easier for stakeholders to confirm the same spots. By combining power generation data with on-site location information, it becomes easier to explain the priority of cleaning, weeding, repairs, and specialist inspections, and it also makes follow-up checks in subsequent visits more efficient.

Using LRTK is also effective when you want to carry out panel inspections to increase power generation based on field data, starting with distinguishing soiling from degradation. As an iPhone-mounted GNSS high-precision positioning device, LRTK is useful for recording inspection locations within a solar power plant, areas prone to soiling, equipment suspected of degradation, shadow occurrence points, poor drainage spots, cleaning areas, repair locations, and on-site photos together with high-precision positional information. By keeping panel inspection results with location information, it becomes easier to proceed with power generation improvements based on field data rather than intuition.