7 Cause-Specific Measures for Reduced Power Generation | How to Reduce Unnecessary Losses

Table of Contents

• Power output declines are easier to address when analyzed by cause

• Cause-specific measure 1: Eliminate oversights in power generation data

• Cause-specific measure 2: Distinguish weather, solar radiation conditions, and seasonal variations

• Cause-specific measure 3: Remove dirt and deposits from panel surfaces

• Cause-specific measure 4: Mitigate shading from weeds, trees, and structures

• Cause-specific measure 5: Check for abnormalities in strings, connection points, and cables

• Cause-specific measure 6: Review inverter shutdowns, curtailment, and thermal environment

• Cause-specific measure 7: Organize drainage, site topography, and inspection records to prevent recurrence

• Operational approach to prevent recurring power output declines

• Summary

Declines in power generation are easier to address when examined by cause

When the power output of a solar power system decreases, the most important thing at first is not to assume a single cause. If you feel that output has dropped, is not increasing as expected, or is lower than the same month last year, you may immediately suspect dirty panels or equipment failure. However, in actual field situations, multiple factors can combine to reduce output, such as weather, solar irradiation conditions, dirt on the panel surface, shadows from weeds or trees, faults in connections, shutdown of conversion equipment, temperature rises, poor drainage, and a lack of inspection records.

For practitioners searching "how to increase power generation," the important thing is to regard the idea of increasing generation as bringing the system closer to a state in which the power that should be generated is not lost. In solar power generation, you cannot increase the amount of solar irradiance at the site. You also cannot increase the number of sunny days or change the sun's altitude by season. However, you can move closer to a state in which the received solar irradiance is converted into electricity with as little waste as possible. In other words, measures to counteract declines in power generation are efforts to identify on-site generation losses by cause and reduce unnecessary losses.

A common mistake when trying to improve a decline in power output is deciding on countermeasures based only on impressions at the site. Cleaning because the panels look dirty, trimming because the grass is overgrown, or suspecting the equipment side because the devices look old—such judgments are sometimes necessary. However, if the actual main cause lies elsewhere, the work will not fully restore power output. Even if you clean the panels, if shading remains in the morning and evening the power output is likely to stay low, and even if you remove vegetation, if the inverters continue to experience brief stoppages, daytime power output will not increase.

To analyze by cause, first check the power generation data to determine during which time periods, at which equipment, and to what extent output has declined. Then inspect the site and, in order, check the condition of soiling, shadows, connections, equipment, drainage, inspection access routes, and records. By isolating the causes, you can clarify which areas need cleaning, which areas require weed removal, which equipment needs inspection, and which operational practices should be reviewed. Organizing generation declines by cause is fundamental to reducing unnecessary work and concentrating on measures that lead to improved power generation.

Cause-specific countermeasure 1: Eliminate oversights in power generation data

When investigating the cause of a decline in power generation, the first thing to check is the power generation data. If you only look at monthly or annual generation figures, you cannot tell when, where, or how generation losses are occurring. Even if nothing appears abnormal on a monthly basis, there may be cases where generation drops only during certain hours of sunny days, or where only specific rows, specific strings, or the areas connected to specific inverters remain at a low level.

Viewing generation by time of day makes it easier to identify the likely cause. If generation is low in the morning, shadows from trees on the east side, slopes, nearby structures, or adjacent equipment may be involved. If generation is low in the evening, check for shadows on the west side or the influence of surrounding terrain. If the midday peak fails to develop, possible causes include dirt on the panel surface, temperature rise, limitations of conversion equipment, output curtailment, or equipment shutdown. If the generation curve drops suddenly during a sunny day, it is necessary to cross-check shutdown histories and alarm histories with the timestamps.

When comparing equipment on a unit basis, it is important to compare equipment under the same conditions. If you simply compare equipment that differ in orientation, tilt, number of panels, shading conditions, or connection configuration, you may mistake normal differences for abnormalities. If a specific area is consistently lower compared with adjacent rows or equipment with the same orientation, suspect local soiling, partial shading, connection faults, cable damage, or abnormalities on the power conversion equipment side.

As a countermeasure, it is effective to establish criteria for reviewing power generation data. Deciding how often to check, how large a deviation should trigger an on-site inspection, and down to which equipment unit comparisons should be made makes it easier to detect signs of declining power generation early. Relying solely on the intuition of staff can lead to oversights and inconsistent judgments. Standardizing the way power generation data is reviewed improves the accuracy of on-site inspections and speeds up the detection of losses.

Pay attention to how the power output is declining. If it drops suddenly, possible causes include equipment shutdown, wire breakage, poor connections, or the emergence of obstructions. If it is falling gradually, accumulation of dirt, growth of weeds or trees, deterioration of the site environment due to poor drainage, or aging of equipment and components may be involved. For sudden declines versus gradual declines, the places to check on site and the priority of countermeasures differ. Examining the data in detail is the first measure to improve a decline in power output.

Cause-specific Countermeasure 2: Separate Weather, Solar Radiation Conditions, and Seasonal Differences

When you feel the power output is low, before suspecting an equipment fault check the weather, solar irradiance conditions, and seasonal variations. Solar power generation is strongly affected by the amount of sunlight, so output will decrease during periods with many cloudy or rainy days even if there is no problem with the equipment. If you compare only the monthly output with the same month of the previous year or with the previous month and immediately conclude there is an equipment failure, the main cause may actually have been differences in the weather.

On the other hand, we must avoid overlooking true anomalies by attributing them to the weather. If the entire power plant is declining in the same way in line with regional weather, the influence of solar irradiance conditions is likely large. However, if only part of the plant is performing lower while other equipment within the same plant is operating normally, or if there is a clear difference compared with equipment under similar conditions nearby, the weather alone cannot explain it. In that case, it is necessary to check for on-site causes such as soiling, shading, poor connections, equipment shutdowns, or output curtailment.

To separate weather-related causes from equipment-side causes, it is effective to compare sunny days with each other or days with similar weather. Cloudy or rainy days exhibit large fluctuations in power output, making the characteristics of anomalies hard to see. By selecting and inspecting generation curves from sunny days, it becomes easier to find effects such as shadows that fall at the same time every day, string-level anomalies where only specific equipment shows low output, and equipment shutdowns that cause drops for only a certain period.

Seasonal differences are also an important factor in decision-making. In winter, the sun's elevation is lower, and shadows from surrounding trees and terrain tend to extend further. In summer, although solar radiation is stronger, panel temperatures and temperatures around equipment rise, which can reduce output. During periods of heavy rain, monthly power generation tends to be lower, and after strong winds or heavy downpours attention should be paid to fallen leaves, sediment, surface deposits, poor drainage, and the condition around cables.

As a countermeasure, rather than judging based only on days with low power generation, you should check them together with weather, solar irradiance conditions, season, and differences from equipment under the same conditions. By distinguishing whether the decrease is a natural drop caused by weather or a generation loss that can be mitigated on-site, you are less likely to misprioritize cleaning or repairs. When addressing causes of reduced power generation, it is important, after understanding natural variability, to focus on unnecessary losses that can be reduced at the site.

Cause-specific Countermeasure 3: Remove Dirt and Deposits from the Panel Surface

Dirt and deposits on the panel surface are a common cause of reduced power output. Because solar panels generate electricity by receiving sunlight at the surface, when dirt accumulates the light reaching the cells is reduced. The type of soiling varies by site environment, such as soil dust, pollen, yellow sand, bird droppings, fallen leaves, sap, dust from nearby construction, road-derived dust, and salt-containing deposits that readily adhere in coastal areas. Even light soiling can affect power generation if it spreads over a wide area, and localized deposits can act as strong shadows even over a small area.

What deserves particular attention is the band-like dirt that remains along the lower edge of panels and near the frames. It is often assumed that rain will naturally wash it away, 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 well and dirt tends to accumulate. Even dirt that is not noticeable from a distance can potentially affect power generation if it covers part of a cell.

Localized deposits such as bird droppings and fallen leaves should not be overlooked. Unlike dirt that spreads thinly across the entire surface, these heavily cover specific spots and reduce power generation by casting partial shadows. If only some equipment shows reduced power output, focus on inspecting the panel surfaces around those installations. Rows near trees, areas around structures where birds tend to perch, rows that are often downwind, and areas near unpaved walkways are prone to dirt and deposits.

As a mitigation measure, determine cleaning targets starting with locations that have the greatest impact on power generation. Rather than cleaning all panels at the same frequency, focus on installations where a drop in power output has been confirmed, rows with concentrated soiling, areas where lower-edge soiling is conspicuous, and places with heavy bird damage or fallen leaves. Comparing photos and power output before and after cleaning makes it easier to judge how much the soiling was affecting power generation at that site.

However, cleaning must be carried out 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 working without verifying electrical safety as electrical equipment. Cleaning to improve reduced power generation is not a cosmetic task but a maintenance operation to restore the light-receiving condition and ensure the long-term stable use of the equipment. Recording the locations cleaned, the types of soiling, and the conditions that tend to cause recurrence will be useful for future inspections.

Cause-specific Countermeasure 4: Reduce shading caused by weeds, trees, and structures

Shading is always a factor that must be checked when investigating reduced power generation. Because solar panels generate electricity from sunlight, even a shadow over part of a panel can reduce its output. Causes of shading include weeds, trees, fences, utility poles, nearby buildings, mounting structures, adjacent rows of panels, and monitoring equipment. Shadows move with the time of day and the seasons, so the fact that no shadow was visible at the time of inspection does not necessarily mean there is no problem.

Weeds are a common cause of power generation loss at sites. Even if there is no problem in winter or immediately after installation, they can grow rapidly from spring to summer and cast shadows on the lower edge of panels or the front row of panels. Even when vegetation does not touch the panels, the low sun angle in the morning and evening causes shadows to extend far. Furthermore, when weeds become overgrown they reduce ventilation, block inspection walkways, and make it difficult to check around equipment. Because they affect not only power output but also maintainability and safety, weed management is fundamental to improving power generation.

Shadows from trees are a factor that can become problematic during long-term operation. 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 in particular cast shadows on the panels depending on the time of day. At power plants near forests or slopes, the heights of the terrain and the trees can overlap and create long shadows in winter. If power generation is low only in winter, or if there are large drops in the morning and evening, it is necessary to check both the trees and the terrain together.

As a countermeasure, check the site at the times when the power generation data shows a decrease. If output is low in the morning, inspect site conditions in the morning; if it is low in the evening, check for evening shadows. Even if there is no problem at noon, large shadows can appear in the morning and evening. Also, even if there is no problem in summer, shadows can lengthen in seasons when the solar altitude is low. When you find shadows, record the time of occurrence, the source of the shadow, the equipment affected by the shadow, and take photographs.

Care must also be taken regarding shadows from surrounding structures and additional equipment. Adding new equipment within the power plant, or installing fences, signs, or surveillance poles, can create shadows at certain times of day. To prevent a drop in power generation, it is important not only to reduce existing shading but also to operate in ways that do not create new shading. Shade management is not finished with a single weeding; it must be ongoing while monitoring seasonal changes.

Cause-specific Countermeasure 5: Check for abnormalities in strings, connection points, and cables

Declines in power output do not necessarily manifest uniformly across the entire plant. Even if the plant's total output does not appear to show a major anomaly, only some strings may be experiencing reduced output. Such partial generation losses can be inconspicuous in monthly totals, but if they persist over a long period they can lead to significant losses. When implementing countermeasures for causes of power output decline, it is important not to be reassured by the overall average but to check differences at the string level.

When checking for anomalies at the string level, compare strings that are under the same conditions. If you simply compare ones with different numbers of panels, azimuth, tilt, shading conditions, or connection configurations, you may mistakenly judge normal differences as anomalies. Check whether any are persistently lower compared with adjacent rows or equipment with the same orientation. If only a specific string is lower, possible causes include soiling, partial shading, poor connections, cable damage, or equipment-side problems.

Faults in connection points and cables are also significant causes of reduced power output. Loosened terminals, poor contact, damage to cable sheathing, ingress of moisture, damage by animals, damage during grass-cutting operations, and deterioration due to aging can all impede the flow of electricity. These issues can be difficult to detect from appearance alone, so it is necessary to assess them by combining power generation data with on-site conditions.

You should suspect faults in connection points or cables when only certain installations have low power output, when abnormalities tend to appear after rain, when power generation suddenly drops, or when output fluctuates unstably. If only some units are low despite no visible dirt or shading, electrical faults should also be considered. When there is a persistent difference compared with a string under the same conditions, prioritize checking the connection points and cables.

When inspecting electrical equipment, safety must be the top priority. Even if the goal is to increase power generation, on-site personnel should avoid forcibly touching connections or the interior of equipment to make a judgment. Organize the equipment showing abnormalities, the time of occurrence, changes in power generation, on-site photographs, and the surrounding environment, and, when necessary, arrange for professional inspections. To reduce unnecessary losses, it is important to detect abnormalities while they are still small and narrow down the cause before generation losses become prolonged.

Cause-specific Countermeasure 6: Review Shutdown, Suppression, and Thermal Environment of Conversion Equipment

The causes of low power generation are not limited to the panels and wiring. If the equipment that converts the generated electricity has stopped or its output is being limited, generation will not increase even when solar irradiance is sufficient. For cause-specific countermeasures against reduced power generation, it is essential to check the conversion equipment’s operating status, shutdown history, alarm history, and whether output curtailment is occurring.

When reviewing downtime history, check which equipment stopped, when, and for how long. Even short stops can cause large losses if they occur during daytime when power generation is high. If stops and restarts repeat during the daytime, the monthly total may not stand out, but in reality you may be missing out on generated power. Whether only a specific piece of equipment stops or multiple pieces stop simultaneously will change the suspected causes.

If output curtailment is occurring, power generation can plateau even on clear days. When the top of the generation curve appears flat, check operational data and history. However, a flat curve does not necessarily mean output curtailment. Similar shapes can result from equipment capacity limits, temperature rise, soiling, shading, or measurement anomalies. Do not judge based on the generation curve alone; it is important to confirm by comparing equipment records with on-site conditions.

Temperature conditions are another point to review. For solar power generation, while stronger solar irradiance generally makes generation easier, higher panel temperatures or elevated temperatures around equipment can limit output. If power generation does not increase as expected on a sunny summer day, you should check the temperature environment as well as the irradiance. If weeds are overgrowing under the panels, there is grass or other obstructions around the equipment, or dust and deposits are making heat dissipation difficult, these can affect the increase in power generation.

As a countermeasure, compare the time when power output dropped with the equipment history. If the time the power output fell coincides with alarm or shutdown times, it will be easier to narrow down the possible causes. If there are no anomalies in the equipment records, check other causes such as the panels, wiring, shading, dirt, and solar irradiance conditions. Around the equipment, reducing grass and debris and ensuring ventilation and access for inspection helps enable early detection of abnormalities and more stable operation.

Cause-specific Countermeasure 7: Organize Drainage, Topography, and Inspection Records to Prevent Recurrence

To prevent repeated declines in power output, it is necessary to check not only the panels and equipment but also the entire plant’s drainage, terrain, and inspection routes. Areas where water tends to pool, where sediment can flow in, pathways prone to becoming muddy, slope failures, scouring around mounting structures, and spots where cables are likely to be exposed can directly or indirectly cause reductions in power generation. These are important factors that lead to soiling, weed growth, connection faults, and reduced ease of inspection.

In areas where puddles remain after rain, weeds tend to grow more easily. When weeds grow, they cast shade, reducing ventilation and making inspections more difficult. Muddy pathways can delay work and may lower the frequency of cleaning and weeding. Where sediment flows in, it can accumulate under panels and around cables, causing soiling and damage. If the same problems recur in the same place even after cleaning and weeding, drainage or topography issues should be suspected.

When checking topography and drainage, on-site inspections after rain as well as during fair weather are effective. Identify where water flows in, where it accumulates, and where it drains out. Recording puddles, sediment accumulation, vegetation overgrowth, pathway subsidence, and slope changes will help pinpoint locations prone to recurrence. If poor drainage is left unaddressed, dirt and weeds will recur, resulting in the same power generation losses occurring repeatedly.

Inspection records are also essential for preventing recurrence. If you record the locations of equipment with low power generation, rows that are prone to soiling, places where shadows occur, areas where water accumulates, spots where connection faults occurred, locations that were repaired, and the areas where cleaning or weeding was performed, the places to check at the next inspection will be clear. If records are insufficient, even if the same problem repeats you will not be able to identify the cause and will have to check from scratch every time.

As an improvement measure, use inspection records as a basis for decisions to improve power generation. Do not just clean soiling; check why that location is prone to becoming dirty. Do not just mow grass; look into why grass tends to grow easily in that spot. Do not just repair connections; verify underlying factors such as moisture, drainage, and cable exposure. Record causes of recurrence and prioritize checking them at the next inspection to more effectively reduce unnecessary losses.

Operational Approach to Prevent Recurring Declines in Power Generation

Measures to address causes of reduced power output cannot be completed by a single cleaning or repair. Solar power plants are outdoor installations, and their condition changes with the seasons, weather, surrounding environment, and equipment aging. Even if you clean, dirt will reaccumulate; even if you remove weeds, grass will regrow; trees will continue to grow; and equipment and wiring will change condition during long-term operation. To achieve a stable improvement in power generation, a system for ongoing inspections and countermeasures is necessary.

First and foremost, compare power generation before and after the measures. After performing cleaning, weeding, repairs, equipment checks, and drainage checks, confirm how the power generation has changed. It is difficult to completely eliminate the influence of weather, but by comparing sunny days with each other or comparing installations under the same conditions, you can identify consistent trends. Prioritize measures that showed a large effect for future efforts, and if an effect is hard to see, suspect another cause.

Next, keep locations that are likely to experience recurrence as management targets. If you record rows where dirt easily accumulates, time periods when shadows are likely to occur, places where water pools, aisles that are prone to damage, and equipment that is prone to faults, you can inspect them before power generation drops significantly. To prevent a decline in power generation, it is important not only to respond after output has fallen but also to identify in advance the conditions that tend to cause drops and implement countermeasures.

When multiple people are responsible for management, it is also important to be able to share exact locations. At a large power plant, rows or pieces of equipment that look similar may be lined up, making it difficult to identify a location from photos alone. If equipment numbers, location information, photos, and work histories are recorded together, field personnel, managers, inspectors, and repair teams can more easily confirm the same location. Improving power output is also about creating systems that put on-site observations to use in the next improvements.

It is also important to clarify the priority order for improving power generation. If you try to address all issues at once, the workload becomes large and measures that would have the greatest impact on power generation can be postponed. Prioritize checking equipment that shows a clear decline in power generation in the data, shadows that have a long impact duration, recurring soiling or drainage problems, and equipment that experiences frequent stoppages even for short periods. Practical countermeasures for power generation declines are to classify the causes and proceed in order from the locations with the largest generation losses.

Summary

In addressing causes of reduced power generation, it is important to sequentially isolate where and why generation losses occur, and to make improvements starting with the locations that have the greatest impact on power output. In solar power generation, it is not possible on-site to increase the amount of solar radiation itself. However, by bringing the system closer to a state that converts the received solar radiation into electricity without waste, power output can be improved. To that end, it is necessary to check, in order, power generation data, weather and irradiance conditions, dirt on panel surfaces, shadows from weeds and trees, strings and connection points, conversion equipment, and drainage and inspection records.

When you feel that power output is low, rather than immediately carrying out cleaning or repairs, it is important to first separate and examine the data. Determine when the output is low, which equipment is underperforming, and whether there is a difference compared to equipment under the same conditions. By then inspecting the site, you can identify where cleaning is needed, the areas that require weeding, connections that should be inspected, equipment to check, and drainage or traffic routes that should be reconsidered. To improve reduced power output, it is important to make decisions by linking data with on-site conditions, not by intuition.

Also, measures to address reduced power generation cannot be completed in a single operation. Even if you clean, dirt will reaccumulate; even if you remove weeds, grass will grow back; trees will continue to grow; and equipment and wiring will change condition over time. Comparing power generation before and after the measures, keeping on-site photos and work records, and using them for the next inspection will improve the accuracy of the improvements. To consistently increase 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.

Especially at large power plants, a system for accurately sharing problem locations is important. If you record rows that are prone to soiling, spots where shadows occur, areas where water accumulates, abnormal strings, repair locations, cleaning areas, and inspection photos along with location information, stakeholders can more easily confirm the same location. By combining power generation data with on-site location information, it becomes easier to explain the prioritization of cleaning, weeding, and repairs, and it also streamlines checks for recurrence in subsequent inspections.

If you want to continuously implement cause-specific countermeasures for decreases in power generation based on on-site data, using LRTK is also effective. As an iPhone-mounted GNSS high-precision positioning device, LRTK is useful for recording inspection locations, easily soiled areas, shadowed spots, poor drainage points, abnormal equipment, repair locations, cleaning areas, and on-site photographs within a solar power plant together with high-precision location information. By recording the details of cause-specific countermeasures with location information, it becomes easier to pursue power generation improvements based on on-site data rather than intuition, and to continuously reduce unnecessary losses.