6 Signs to Spot a Drop in Power Generation｜Improvement Measures Explained

Table of Contents

• Detecting small signs of power output decline early is important

• Sign 1: On sunny days, the peak of the power generation curve is low

• Sign 2: Power output drops only in the morning or evening

• Sign 3: Only part shows lower output compared to equipment under the same conditions

• Sign 4: There are sudden drops or stoppages during the daytime

• Sign 5: Power output becomes unstable after rain or during seasonal transitions

• Sign 6: Dirt, weeds, and poor drainage repeatedly occur on site

• Improvement procedures after detecting a decline in power output

• Summary

Early detection of small signs is important for declines in power generation

Declines in solar power generation can sometimes manifest suddenly as a major failure, but in practice they often appear gradually as small signs. Even if monthly generation figures don't seem to show a serious anomaly, changes such as slightly lower generation curves on sunny days, some sections being lower compared with equipment under the same conditions, generation not increasing in the morning and evening, or instability after rain can be the beginning of power loss.

For practitioners searching "how to increase power generation," what matters is to regard increasing output not simply as adding equipment but as moving toward a state in which you do not lose the electricity that should be generated. In solar power generation, you cannot increase the solar irradiance itself at the site. You cannot increase the number of clear days, nor change the sun’s altitude by season. However, you can arrange conditions so that the received solar irradiance is converted into electricity with as little waste as possible.

There is not a single cause for reduced power generation. Dirt on panel surfaces, bird droppings and fallen leaves, shading from weeds or trees, anomalies at the string level, faults in connections, cable damage, PCS stoppages, output curtailment, temperature increases, poor drainage, and insufficient inspection records are among multiple factors that can overlap. Even when there appear to be no major visual abnormalities, signs of generation loss can show up if you examine generation data by time of day or by equipment unit.

To avoid overlooking a drop in power generation, it is important to isolate the cause as soon as a sign is detected. There are situations in which decisions such as cleaning because the panels are dirty, removing weeds because the grass has grown, or suspecting the equipment side because the devices look old are necessary. However, if the main cause of the generation drop lies elsewhere, performing those tasks will not lead to sufficient improvement.

If morning and evening shadows are the cause, simply cleaning will hardly restore generation, and if short-term PCS stoppages are the cause, merely removing weeds will not increase daytime generation.

To detect a decline in power generation early, it is necessary to manage and link power generation data, site photographs, inspection records, and work history. Check when the output is low, which equipment is underperforming, whether there is a difference compared to equipment under the same conditions, whether it is low even on sunny days, and whether it becomes unstable after rain. Based on that, review in order: soiling, shading, connections, PCS, drainage, and inspection routes. Below, we explain six signs you should check to avoid overlooking a decline in power generation, and the corresponding remedial measures for each.

Sign 1: The peak of the power generation curve is low even on sunny days

A clear sign of reduced power generation is when, on a sunny day, the peak of the generation curve is low. On days with few clouds and stable solar radiation, generation gradually increases from the morning, rises sharply around midday, and declines toward the evening. However, if despite good weather the entire generation curve is lower, the midday peak does not rise, or the peak is smaller compared with sunny days in the same season, there may be on-site generation losses.

When this sign appears, first check the weather and solar irradiation conditions. Because thin clouds or atmospheric conditions can suppress generation on some days, it is important not to draw conclusions from a single day. Compare with sunny days that have as similar weather as possible, and compare with the generation curve for the same period. If the entire plant shows similarly low output, the impact of solar irradiation conditions may be large; if only specific equipment shows low output, suspect soiling, shading, poor connections, or restrictions on the PCS side.

A common cause of a lack of increase in the midday peak is soiling on the panel surface. When soil dust, pollen, yellow sand, bird droppings, fallen leaves, tree sap, or surrounding dust adheres to the panel surface, the light reaching the cells is reduced. In particular, band-like soiling that remains along the lower edge of the panel or near the frame can affect power generation even if it is not noticeable from a distance. If overall power output remains sluggish even on sunny days, check the condition of the panel surfaces.

In summer, a rise in temperature and poor ventilation are also possible causes. While stronger sunlight makes power generation easier, if the panel temperature or the temperature around the PCS becomes high, the power output may not increase as much. If weeds are overgrown under the panels, there is grass or debris around the equipment, or airflow is restricted, the thermal environment may be affecting power generation.

As countermeasures, first compare power generation curves on multiple sunny days to determine whether the decline is temporary or persistent. Then check panel surface soiling, ventilation around the equipment, the output history of the PCS, and differences compared to installations under the same conditions. If you perform cleaning or weeding, record the power generation and photos before and after the work and verify whether the peak of the generation curve actually improved. The power generation curve on sunny days is the first important sign for detecting a drop in power output.

Sign 2: Power output drops only in the morning or evening

If power generation drops only in the morning or evening, suspect shading. When the sun is low, shadows from weeds, trees, embankments, fences, support poles, nearby buildings, and adjacent equipment tend to stretch long. Even if you inspect the site at noon and see no shadows, panels can be shaded in the morning or evening. To avoid overlooking a drop in generation, it is important to pay attention to the rise of the generation curve and how it falls in the evening.

If the power output in the morning is low, check for shadows on the east or southeast side. Trees, slopes, weeds, nearby structures, and grass along fences can reduce morning power output. If it is low in the evening, check shadows on the west or southwest side. If the output drops early only in the evening, shadows from western trees, terrain, or nearby equipment may be involved.

Weeds require particular attention as a cause of power generation loss due to shading. Even if they are not a problem in winter or immediately after installation, they can grow rapidly from spring to summer and cast shadows on the front and lower edge of the panels. Even if the weeds do not touch the panels, shadows can extend when the sun is low in the sky in the morning and evening. Furthermore, when weeds become dense, ventilation worsens, inspection access paths are blocked, and it becomes difficult to inspect around equipment.

Shadows from trees are a factor that can become problematic in long-term operation. Trees that had little impact at the time of installation can grow over several years and cast long shadows in the morning and evening or during winter. At power plants near forests or on slopes, terrain and tree height can combine so that shadows lengthen only in specific seasons. If generation is low only in the mornings and evenings during winter, you should suspect seasonal shading.

As a countermeasure, inspect the site during the times when power generation is low. If output is low in the morning, take photos in the morning; if it’s low in the evening, record the evening shadows. If you record the time the shadow occurs, its source, the equipment affected by the shadow, and the power generation before and after maintenance, it becomes easier to judge the effectiveness of weeding or pruning. Reductions that occur only in the morning and evening can be easily missed in monthly figures, yet over the long term they lead to significant generation losses. Detecting signs of shading early is the quickest way to improve power generation.

Sign 3: Some parts are lower compared to equipment under the same conditions

To avoid overlooking reductions in power generation, it is important to compare equipment under the same conditions, not just the total for the entire plant. Even if there does not appear to be a major anomaly overall, power output may be low in only certain rows, certain strings, or areas connected to particular PCS units. Such localized declines are easy to miss in monthly totals and, if left unaddressed, can lead to long-term losses.

When making comparisons, select installations with similar orientation, tilt, number of panels, shading conditions, and connection configuration. Simply comparing installations with different conditions can cause a normal difference to be misidentified as an anomaly. The purpose of comparison is to find locations that are consistently underperforming among installations that should naturally have similar generation. If only a part is lower compared with installations under the same conditions, suspect localized soiling, partial shading, string faults, poor connections, cable damage, or an issue on the PCS side.

When only certain pieces of equipment are performing poorly, first check that area on site. Inspect the panel surfaces for dirt on the lower edge, bird droppings or fallen leaves, and for shading from weeds or trees. If no dirt or shading is found, check for differences in power generation at the string level and inspect connections, cables, and the input side for faults. If instability occurs only after rain, consider water ingress, moisture around connections, or poor drainage as possible causes.

When only part of the system remains at a low level, the impact on power generation may look small but should not be underestimated. If you lose a little generation each day, it becomes a large loss over the long term. In particular, if a specific PCS or string remains continuously low, you need to narrow down the cause promptly. If you judge there is no problem because the plant’s total output hasn’t fallen significantly, you may miss localized generation losses.

As a countermeasure, regularly perform equipment-level comparisons and link any units that show deviations to field records. By managing equipment IDs, location information, photos, and power generation data together, stakeholders can more easily confirm the same location. Accurately identifying the scope of anomalies makes it easier to prioritize cleaning, weeding, connection checks, and PCS checks. A decline in some units is an important early sign of reduced power generation.

Sign 4: Sudden dips or stops during the day

If there is a sudden drop in the middle of the power generation curve, suspect equipment shutdown, alarms, poor connections, output curtailment, or measurement anomalies. If a sudden decline occurs during midday when solar irradiance is strong, even a short period can have a large impact on generation. Even if it does not stand out in the monthly generation totals, it can appear as a valley-like shape when looking at the time-of-day generation curve.

If this sign appears, first check the PCS shutdown history and alarm history. If the time of the drop in the power generation curve coincides with the time of a shutdown or an alarm, prioritize inspection on the equipment side. Whether only a specific PCS has stopped or multiple PCS have stopped simultaneously changes the suspected causes. If multiple PCS stop at the same time, you need to check for common external conditions and any output restrictions.

If the top of the power generation curve is flattened out, candidates include output curtailment, equipment capacity limits, temperature rise, or insufficient input. However, a flat curve does not necessarily indicate a PCS problem. Dirt on the panel surface, reduced input-side string output, shading, ambient temperature conditions, or measurement issues can produce a similar shape. Do not conclude the cause from the generation curve alone; verify it by checking the history, differences with equipment under the same conditions, and the on-site situation.

If there is a sudden drop but no alarm or shutdown history, check for faults in connection points or cables, abnormalities on the input side, or measurement errors. If it tends to occur after rain, suspect moisture around the connection points or poor drainage. If it tends to occur during periods of high ambient temperature, check for poor ventilation or temperature rise around the PCS. If grass or accumulated debris makes the area around the equipment hard to see, detection of anomalies may be delayed.

As a countermeasure, record the time of the drop, the affected equipment, the history, and on-site photos together. If you keep records of the time the generation fell, the PCS status, the surrounding environment, and the weather, you will be able to make faster judgments if it recurs. When checking electrical equipment, prioritize safety: the local staff should not forcefully touch the interior, and, as needed, arrange for a professional inspection. Sudden drops during daytime have a large impact on power generation, so early detection and isolating the cause are important.

Sign 5: Power output becomes unstable after rainfall and during seasonal transitions

If power generation becomes unstable after rain or during seasonal transitions, changes in the on-site environment may be involved. Because solar power generation is affected by the weather, lower output on rainy days is to be expected. However, if only certain equipment shows low output on sunny days after the rain has stopped, if generation becomes unstable, or if the same abnormality recurs at the same location, it is necessary to check for residual moisture after rain, sediment, dirt, the condition around connection points, and poor drainage.

What to watch for after rain is dirt at the lower edge of the panels. Rain sometimes washes dirt away, but in practice the flow of rainwater can collect dirt at the lower edge and leave it there. On panels with a shallow tilt, water drains poorly and band-like dirt tends to accumulate. If power generation is lower than expected on sunny days after rain, check the condition of the panel surface and the lower edge.

After heavy rain or a typhoon, attention is also needed for fallen leaves, branches, airborne debris, sediment inflow, and clogging of drainage paths. If leaves adhere to panel surfaces or sediment accumulates around cables, it can lead to reduced power generation and decreased ease of inspection. In areas where puddles remain, weeds can grow more readily, which may later cause shading or poor ventilation. Abnormalities after rain can affect not only that day's power generation but also become factors that lead to recurrence later.

Signs of reduced power output are also more likely to appear around seasonal transitions. In spring, pollen and yellow dust; before summer, the rapid growth of weeds; in summer, high temperatures; in autumn, fallen leaves; and in winter, shadows and frost caused by the lower solar altitude all have an impact. If power output decreases at the same time every year for the same equipment, seasonal on-site factors may be involved. Confirm season-specific declines by looking not only at monthly values but also at generation curves per installation and by time of day.

As a countermeasure, conduct targeted inspections after rain and during seasonal transitions, and record locations that are prone to abnormalities. By noting places where water accumulates, where sediment flows in, rows where fallen leaves tend to collect, slopes where grass grows easily, and equipment where frost tends to linger, you can get ahead of future inspections. Instability caused by post-rain conditions or seasonal changes is a sign of power generation losses that are likely to recur.

Sign 6: Dirt, weeds, and poor drainage repeatedly occur on site

To avoid overlooking declines in power generation, it is necessary to pay attention to small, recurring anomalies on site. Conditions such as dirt accumulating in the same row, weeds growing in the same spot, the same pathway becoming muddy after rain, vegetation flourishing around the same PCS, or the same drainage route becoming clogged are signs of a recurring decline in power generation. Even if appearance improves after a single cleaning or weeding, if the factors causing recurrence remain, generation losses will repeat.

In locations where soiling repeatedly occurs, inspect the surrounding environment. There may be conditions such as unpaved walkways that easily raise dust, trees that readily shed leaves or sap, structures that tend to attract birds, or rainwater that tends to concentrate dirt at the lower edge of panels. It is important not only to clean the soiling but also to determine why that location is prone to becoming dirty.

In locations where weeds recur, check drainage, sunlight exposure, slope faces, soil condition, and inspection access paths. Areas where water tends to pool promote weed growth. At the base of slopes and along fences, work is often postponed, and by the time it’s noticed shadows may appear in front of the panels. Even if weeds do not directly touch the panels, when the sun is low in the morning and evening shadows stretch long. Recurring weeds not only cause power generation losses due to shading but also lead to poor ventilation and reduced ease of inspection.

At locations where poor drainage recurs, inspect for sediment, mud, standing water, and the condition around cables. Where sediment flows in, dirt tends to accumulate under the panels and around cables. In areas where water remains, it can lead to moisture around connection points and the recurrence of weeds. Even if it does not appear to be a direct cause of reduced power generation, poor drainage can lead to long-term losses through dirt, weeds, and delayed inspections.

As a countermeasure, record locations where incidents recur and make them priority inspection points. If you keep the equipment number, location information, photos, time of occurrence, actions taken, and the impact on power generation, future decisions can be made more quickly. In operations designed not to overlook declines in power generation, it is important not only to respond after an anomaly occurs but also to proactively check locations that are prone to recurrence.

Improvement Procedures After Detecting a Decline in Power Generation

When you detect a sign of reduced power generation, don’t immediately decide on countermeasures; instead, verify by isolating the cause. First, use power generation data to identify the time periods and the equipment range where output is declining. Next, determine whether the variation is a natural change due to weather or solar irradiance conditions, or a generation loss that can be improved on-site. Then, in order, inspect soiling, shading, string mismatches, connection points, PCS history, temperature environment, drainage, and inspection records.

The priority for improvements is decided starting with those that have the greatest impact on power generation. If dirt is concentrated on equipment with low power output, prioritize cleaning. If the morning and evening declines coincide with shadows, consider weeding or pruning. If only a specific string is low, suspect the connection points or cables. If the timing of the power drop matches the PCS shutdown history, prioritize checking the PCS. If the same locations show problems after rain, review drainage and terrain.

After the countermeasures, check how power generation has changed. After cleaning, weeding, repairs, PCS checks, and drainage checks, record the power generation before and after the work, on-site photos, the scope of work, and the weather conditions. It is difficult to completely eliminate the influence of weather, but by comparing sunny days with each other and by comparing equipment under the same conditions, certain trends can be identified. Prioritize measures that showed large effects in future work, and if an effect is hard to see, suspect other causes.

Improving power output is not something that can be completed in a single operation. A solar power plant is an outdoor facility, and its condition changes with the seasons, the weather, the surrounding environment, and the aging of the equipment. Even if you clean it, dirt will return; even if you remove weeds, grass will grow; trees will grow; and the condition of equipment and wiring will change as well. To consistently increase power output, a system is needed that repeatedly carries out inspections, countermeasures, performance verification, and record updates.

When multiple people are managing a site, it is also important that they can accurately share the exact location. In a large power plant, similar rows and equipment can make it difficult to identify a location from photos alone. If you record the equipment number, location information, photos, and work history together, field personnel, managers, inspectors, and repair staff will find it easier to confirm the same location. When you find signs of decreased power generation, it is important not to leave them as a one-off but to keep records that can be used for future improvements.

Summary

To avoid overlooking declines in power generation, it is important to check six signs on a daily basis. Changes such as the peak of the power generation curve being low on sunny days, generation dropping only in the morning or evening, part of the system producing less than comparable systems under the same conditions, sudden dips or stoppages during the daytime, instability after rain or during seasonal transitions, and repeated soiling, weed growth, or poor drainage in the same location are signs of power loss.

When you feel that power generation is low, rather than immediately performing cleaning or repairs, it is important to first break down and review the data. Identify when the output is low, which equipment is underperforming, and whether there is a difference compared with equipment under the same conditions. Then, by inspecting the site based on that information, the places that need cleaning, the areas that need weeding, the connection points that need inspection, the PCS to be checked, and the drainage and access routes that should be reconsidered will become clear. When improving power generation, it is important to make decisions by linking data with on-site conditions, not by intuition.

Also, improving a decline in power generation cannot be completed with a single operation. Even if you clean, dirt will return; even if you remove weeds, grass will regrow; trees will grow; and equipment and wiring will change condition with age. By comparing power generation before and after countermeasures, keeping on-site photos and work records, and using them for the next inspection, the accuracy of improvements increases. To consistently raise power generation, it is essential not only to eliminate the causes but also to establish a site environment and management system that make the same causes less likely to recur.

In particular, at large power plants, a system for accurately sharing the locations where signs of generation decline appear is important. If you record, along with location information, the equipment showing abnormalities in the generation curve, rows that are prone to soiling, spots where shadows occur, places where water accumulates, abnormal strings, PCS shutdown locations, cleaning areas, repair positions, and inspection photos, stakeholders can more easily confirm the same location. By combining generation data with on-site location information, it becomes easier to explain the prioritization of cleaning, weeding, repairs, and specialized inspections, and it also streamlines follow-up checks for recurrence.

If you want to avoid overlooking a decline in power generation and continue implementing countermeasures based on on-site data, leveraging LRTK is also effective. 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, locations where shading occurs, spots with poor drainage, abnormal equipment, areas around PCS, cleaning areas, repair locations, and on-site photographs together with high-precision positional information. By keeping signs of power generation decline and the results of improvements with location information, it becomes easier to carry out power generation improvements based on field data rather than on intuition.