9 Ways to Respond When Power Generation Drops｜How to Improve by Cause

Table of Contents

• When power generation drops, isolate the causes sequentially

• Countermeasure 1: Check power generation data by time of day and by equipment unit

• Countermeasure 2: Check weather, solar irradiance conditions, and seasonal differences

• Countermeasure 3: Remove dirt and deposits from panel surfaces

• Countermeasure 4: Eliminate shading from weeds, trees, and structures

• Countermeasure 5: Check generation differences at the string level

• Countermeasure 6: Inspect connections and cables for faults

• Countermeasure 7: Check the shutdown history of power conversion equipment and output curtailment

• Countermeasure 8: Review elevated temperatures and inadequate ventilation

• Countermeasure 9: Organize drainage, terrain, and inspection records to prevent recurrence

• Management methods to prevent recurring declines in power generation

• Summary

When power output drops, isolate the causes one by one.

When solar power generation drops, the first important thing is not to assume a single cause. When output declines, it's tempting to immediately suspect dirty panels or equipment failure. However, at real sites multiple factors can overlap: weather, solar irradiance conditions, dirt on panel surfaces, shadows from weeds or trees, faults in connections, inverter shutdowns, output curtailment, poor drainage, lack of inspection records, and so on. Even if nothing appears wrong at a glance, when viewed by time of day or by individual equipment you can find cases where only part of the system shows reduced output.

For a practitioner searching for "how to increase power generation," the important thing is to regard increasing generation as an effort to reduce generation losses. In solar power generation, you cannot increase the solar irradiance itself at the site. On the other hand, you can move closer to a state in which the incident solar radiation is converted into electricity with as little waste as possible. In other words, the countermeasure when generation falls is to find where the power that should have been generated is being lost and to implement improvements according to each cause.

When checking for a decline in power output, don't jump straight into cleaning or repairs; first understand how the decline appears. Is it low only in the morning, only in the evening, is the midday peak suppressed, does it become unstable after rain, is only specific equipment underperforming, or is the entire plant underperforming? The suspected causes vary accordingly. From the result of low power output alone, you cannot determine whether you should clean, perform weed control, check equipment history, or reassess drainage and topography.

Follow-up verification after countermeasures is also important. Even if you carry out cleaning, weed removal, repairs, and equipment inspections, if you have not recorded the power generation before and after the work or taken on-site photographs, you cannot tell whether those measures were truly effective. When power generation drops, handling the entire process—from identifying the cause, implementing countermeasures, verifying their effectiveness, to updating records—as a single workflow will speed up responses next time. Below, I explain nine practical countermeasures you should check in the field when power generation declines, organized by cause.

Countermeasure 1: Check power generation data by time of day and by facility

The first step when power generation drops is to closely examine the generation data. If you only look at monthly or annual generation totals, you can’t tell when, where, or how generation losses are occurring. Even if nothing looks abnormal on a monthly basis, there may be times when generation falls during certain hours on sunny days, or when only specific equipment continues to underperform. To increase generation, it is important to first identify declines by time of day and by individual equipment, rather than by the overall total.

Viewing data by time of day makes the direction of the cause easier to understand. If generation is low in the morning, shadows from east-side trees, slopes, nearby structures, or adjacent equipment may be involved. If it is low in the evening, check for shadows on the west side and the influence of surrounding terrain. If the midday peak does not develop, candidates include dirt on the panel surface, temperature rise, limitations of power conversion equipment, output curtailment, or equipment shutdowns. If on sunny days the generation curve suddenly drops partway through, you need to cross-reference shutdown and alarm logs with the timestamps.

When comparing at the equipment level, 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 localized soiling, partial shading, connection failures, cable damage, or equipment-side faults.

Pay attention to how the power output declines. If it drops suddenly, possible causes include equipment shutdowns, broken wiring, poor connections, or the emergence of obstructions. If it is decreasing gradually, possible causes include accumulation of dirt, growth of weeds or trees, deterioration of site conditions due to poor drainage, and aging of equipment. By interpreting the pattern of the decline, you can narrow down the locations that should be checked on site.

Countermeasure 2: Check weather, solar radiation conditions, and seasonal variations

When power generation drops, before suspecting an equipment malfunction, check the weather, solar irradiance conditions, and seasonal differences. Solar power generation is strongly affected by the amount of sunlight, so during periods with many cloudy or rainy days generation will decrease even if there is no problem with the equipment. If you compare only monthly generation with the same month of the previous year or with the previous month and immediately conclude an equipment fault, it may turn out that differences in weather were the main cause.

On the other hand, you must avoid overlooking real anomalies by attributing them to weather. If the entire power plant is declining uniformly in line with regional weather, the effect of solar irradiance conditions is likely significant. However, if only part of the plant is underperforming while other equipment at the same plant is operating normally, or if output is clearly lower compared with other sites in the same region, weather alone cannot explain it. In such cases, it is necessary to check for soiling, shading, poor connections, inverter shutdowns, output curtailment, and similar issues.

To separate weather-related differences, it is effective to compare sunny days with other sunny days or days with similar weather. On cloudy or rainy days, power generation can fluctuate greatly due to cloud movement, making it difficult to distinguish from equipment anomalies. If you select and compare power generation curves from sunny days, features such as shading, shutdowns, curtailment, and string anomalies become easier to identify. Rather than looking only at days when generation dropped, it is important to compare them with days under similar conditions.

Seasonal variations are also considered. In winter the sun altitude is lower, and shadows from surrounding trees and terrain tend to stretch longer. In summer, although solar irradiance is stronger, panel and surrounding equipment temperatures rise, which can hinder increases in output. During periods of heavy rainfall, monthly power generation tends to be lower, and after strong winds or heavy rain it is necessary to pay attention to deposits, sediment, poor drainage, and the condition around cables. By separating weather-related causes from equipment-side causes, priorities for countermeasures become clear.

Remedy 3: Remove dirt and deposits from the panel surface

Contamination and deposits on the panel surface are common causes of reduced power output. Because solar panels generate electricity by receiving sunlight on their surface, adhered dirt reduces the light reaching the cells. The type of soiling varies with site conditions, such as soil dust, pollen, yellow sand (Asian dust), bird droppings, fallen leaves, sap, dust from nearby construction, road-borne dust, and dirt containing salts that readily adhere in coastal areas. Even a thin layer of dirt can affect power generation if it spreads over a wide area, and localized deposits can act as strong shading even over a small area.

Particular attention should be paid to the band-like dirt that remains along the lower edge of the panels and near the frame. It is often assumed that rain will wash this away naturally, but in reality rainwater flow can collect the 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 output 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 cover specific spots more heavily and act as partial shadows that hinder power generation. If only certain installations show low power output, focus inspections on the panel surfaces around those installations. Rows near trees, areas around structures where birds tend to perch, downwind rows, and locations close to unpaved walkways are more prone to dirt and deposits.

When carrying out cleaning, it is practical to prioritize areas 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 soiling at the lower edge is conspicuous, and locations with heavy bird fouling or leaf accumulation. Comparing photos and power output before and after cleaning makes it easier to judge how much the soiling at that site was affecting power generation. When performing work, choose methods that will not damage the equipment and do not omit safety checks.

Solution 4: Eliminate shadows from weeds, trees, and structures

When power output drops, the impact of shading is something you should always check. Because solar panels generate electricity from sunlight, even a shadow covering part of a panel can reduce output. Causes of shading include weeds, trees, fences, utility poles, nearby buildings, mounting racks, adjacent rows of panels, monitoring equipment, and more. Since shadows move with the time of day and the seasons, just because you did not see any shading during an inspection does not necessarily mean there is no problem.

Weeds are a common cause of on-site power generation loss. 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 lower edges of panels and on the front rows. Even if the vegetation does not touch the panels, shadows become long when the sun is at a low altitude in the morning and evening. Furthermore, when weeds become overgrown, airflow is reduced, inspection walkways are blocked, and it becomes difficult to check around equipment. Because this affects not only power output but also maintenance and safety, weed management is fundamental to improving power generation.

Shadows from trees are a factor that tend to become problematic during long-term operation. Trees that had little effect at the time of installation can grow over several years and reduce power generation. Trees located to the south, east, and west in particular cast shadows on the panels depending on the time of day. At power plants near forests or slopes, the terrain height and tree height can combine to create long shadows in winter. If power generation is low only in winter, or there are large drops in the morning and evening, it is necessary to check both the trees and the terrain together.

When checking for shadows, aligning the power generation data with the timing of the on-site inspection makes it easier to identify the cause. If power output is low in the morning, check the on-site conditions in the morning; if it is low in the evening, inspect the evening shadows. Even if a noon inspection shows no issues, large shadows can appear in the morning or evening. When you find a shadow, record the time it occurs, its source, the equipment affected, and take photos. For weeding and pruning, prioritize areas that have the greatest impact on power generation.

Countermeasure 5: Check power-generation differences at the string level

When power generation declines, it is important to check output differences not only at the plant-wide level but also at the string level. Even if the total output does not look like a major problem, output may be reduced in only some strings. Such partial declines, if left unaddressed, will continue to cause generation losses over a long period. To increase power generation, do not be reassured by the overall average; you need to find discrepancies at the equipment level and the string level.

When checking for abnormalities at the string level, it is fundamental to compare strings that are under the same conditions. If you simply compare ones that differ in number of panels, 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, candidates include panel soiling, partial shading, poor connections, cable damage, or problems on the equipment side.

Pay attention to how the anomaly appears. If output is consistently lower than the surroundings even on sunny days, dirt or connection problems may be suspected. If it is lower only in the morning and evening, check for shadowing effects. If anomalies tend to occur after rain, moisture ingress or the condition of connection points may be involved. If it becomes unstable during periods of high temperature, poor contact or the temperature environment around the equipment are also possible causes. Combining the power generation waveform with on-site conditions makes it easier to narrow down the cause.

Even a small difference in power output can lead to significant losses if it persists over a long period. Furthermore, if poor connections or cable damage are involved, it can lead not only to reduced generation but also to safety risks. For locations suspected of abnormalities, recording the equipment number, position, photos, and time of occurrence makes it easier to hand the case over for subsequent inspections or expert checks. When power generation drops, it is precisely the time to look at the details rather than the whole.

Solution 6: Inspect connection points and cables for faults

In solar power generation, even if panels are receiving sunlight normally, faults in connections or cables can reduce power output. There are many causes that impede the flow of electricity, such as loose terminals, poor contacts, damage to cable sheathing, moisture ingress, animal damage, damage during mowing, and deterioration due to aging. Because these issues can be difficult to detect by visual inspection, it is necessary to narrow down the abnormal range using power output data and verify it against on-site conditions before making a determination.

Connection or cable faults should be suspected when only certain equipment shows low power generation, when anomalies occur more often after rain, when power generation suddenly drops, or when the output fluctuates unstably. If some parts show lower output despite no visible dirt or shading, electrical faults should also be considered. If there is a persistent difference compared with another string under the same conditions, prioritize inspecting the connections and cables.

Cables are parts that are easily affected by on-site environmental conditions. In areas with heavy weed growth, it becomes difficult to inspect the condition of cables. During grass-cutting operations, there is a risk of equipment contacting the cables. In areas with poor drainage, moisture or standing water can affect the connections. At power plants where animals can easily enter, cable damage may also occur. It is important not to view connection faults in isolation, but to inspect them together with the surrounding environment.

Inspections of electrical equipment must be carried out with safety as the top priority. Rather than having on-site personnel forcibly handle equipment to make a judgment, organize information about the equipment showing abnormalities, the time of occurrence, changes in power generation, on-site photographs, and the surrounding environment, and, if necessary, arrange for a professional inspection. You should avoid performing work that skips safety checks just to increase power generation. After repairs, check background factors such as moisture, vegetation, exposed cables, and animal intrusion to ensure the same issue does not recur in the same location.

Countermeasure 7: Check the shutdown history and output curtailment of the conversion equipment

The cause of a drop in power generation is not limited to the panels or wiring. If the equipment that converts the generated electricity has stopped or its output is being restricted, generation will not increase even when solar irradiance is sufficient. When power generation drops, it is essential to check the operating status of the conversion equipment, its shutdown history, alarm history, and whether output curtailment is in place.

When reviewing downtime history, confirm which equipment stopped, when it stopped, and for how long. Even a short stoppage can cause significant losses if it occurs during daytime when power generation is high. If stops and restarts are repeated during the day, they may not be noticeable in the monthly totals, but in reality you could be missing generated power. Whether only a specific device stops or multiple devices stop simultaneously will change the suspected causes.

If output curtailment is occurring, power generation can plateau even on sunny days. If the top of the generation curve appears flat, check operational data and history. However, a flat curve does not necessarily indicate output curtailment. Similar patterns can be caused by equipment capacity limits, temperature increases, soiling, shading, or measurement anomalies. Do not judge based solely on the generation curve; it is important to verify by cross-checking equipment records and on-site conditions.

What’s important when checking the equipment side is to correlate the time when power output dropped with the time of shutdown. If the time the output dropped matches the time of alarms or shutdowns, it becomes easier to narrow down the range of possible causes. If there are no anomalies in the equipment records, check other causes such as the panels, wiring, shading, soiling, and solar irradiation conditions. Addressing issues based on data and history rather than on speculation is the key to preventing failed remediation.

Countermeasure 8: Reassess temperature rise and poor ventilation

Temperature rise and poor ventilation are causes that are often overlooked when power generation falls. While solar power generation tends to increase with stronger solar irradiance, output can become harder to raise if panel temperature or the temperature around equipment rises. If, on a sunny summer day, generation does not reach the expected level, you need to check not only the solar irradiance but also the thermal environment.

Panels are exposed to strong sunlight outdoors, so their surface temperature can become high. If surrounding ventilation is poor, or if weeds are proliferating under the panels, heat is likely to become trapped. Temperature-related output declines may appear not as a sudden shutdown but as a slower increase in power output. Especially at sites where power output tends to plateau around midday in summer, it is worth checking the ventilation conditions.

Power conversion equipment is also affected by temperature. If grass or other objects around the equipment obstruct heat dissipation, it can lead to reduced efficiency or the activation of protection functions. The area around the equipment should be kept easy to inspect, allow airflow, and be in a condition where any abnormalities can be checked immediately. Vegetation or accumulated debris that makes it difficult to see around the equipment is undesirable not only for power generation but also for ease of inspection and safety.

You cannot completely eliminate the loss of power generation caused by temperature increases. However, you can reduce unnecessary heat buildup. Managing weeds under the panels, ensuring ventilation around equipment, maintaining inspection walkways, and checking for dust and deposits are measures that can be taken on site. From the perspective of increasing power output, it is necessary to review not only direct causes such as dirt and shading but also indirect factors like the thermal environment.

Countermeasure 9: Improve drainage and topography, and organize inspection records to prevent recurrence

When power output drops, you need to check not only the panels and equipment but also the plant's overall drainage, topography, and inspection access routes. Areas where water tends to accumulate, locations where sediment can flow in, paths that easily become muddy, slope failures, scour around mounting structures, and places where cables are likely to be exposed can all cause a reduction in power output, either directly or indirectly. Poor drainage and changes in topography may at first seem unrelated to power output, but they are important factors that lead to soiling, weeds, faults at connection points, and a reduced ease of inspection.

In locations where puddles remain after rain, weeds are more likely to grow. When weeds grow, they create shade, worsen ventilation, and make inspections more difficult. Muddy pathways slow work and can lead to reduced frequency of cleaning and weeding. In areas where sediment flows in, it can accumulate beneath panels and around cables, causing soiling and damage. If the same problems recur in the same locations despite cleaning and weeding, drainage or terrain issues should be suspected.

When checking topography and drainage, it is useful to inspect the site not only in fine weather but also after rain. Identify where water flows in, where it accumulates, and where it drains. Recording puddles, sediment deposition, vegetation overgrowth, pathway subsidence, and changes to slopes will reveal locations prone to recurrence. To stably restore power generation output, it is important to review not only the immediate causes but also the site conditions that allow the same causes to repeat.

Inspection records are also indispensable for preventing recurrence. If you record the locations of equipment with low power output, rows prone to soiling, spots where shading occurs, areas where water accumulates, locations of connection failures, places that have been repaired, and the areas where cleaning or weeding has been carried out, it will be clear which places should be checked at the next inspection. If records are insufficient, you cannot learn the causes even if the same problems recur, and responses tend to be ad hoc.

Management Methods to Prevent Repeated Declines in Power Generation

Addressing a drop in power generation cannot be completed with a single action. Solar power plants are outdoor installations, and their condition changes with the seasons, the weather, the surrounding environment, and equipment aging. Even after cleaning, dirt will return; after weeding, grass will regrow; trees will continue to grow; and drainage routes will change. To prevent repeated declines in power generation, it is necessary to record the measures taken and apply them to the next inspection and management.

First, compare power generation before and after the measures. After performing cleaning, weed removal, repairs, equipment checks, and drainage checks, verify how the power output changed. It is difficult to completely eliminate the influence of weather, but by comparing sunny days with each other or comparing systems under the same conditions, you can identify consistent trends. Prioritize measures that produced large effects for future work, and if an effect is hard to see, consider other possible causes.

Next, record on-site photos, equipment numbers, location information, and work details. Because photos alone can make it difficult to identify a location, it is important at large power plants to manage them together with location data. If you record shadowed areas, rows prone to soiling, places where water accumulates, abnormal strings, and repair locations using the same approach, stakeholders will find it easier to confirm the same location.

If you manage multiple power plants, it is also important to standardize the formats for inspections and records. If each site uses different recording methods, sharing information takes longer. With a consistent approach to managing power output data, on-site photos, location information, and work histories, it becomes easier to compare trends in power output decline. Ideally, you should not only respond quickly when output falls, but also identify locations prone to declines in advance and inspect them proactively.

Summary

When dealing with a drop in power generation, it is important not to assume a single cause but to isolate causes one by one in sequence. In photovoltaic power generation, it is not possible on-site to increase the amount of solar irradiance itself. However, by bringing conditions closer to a state that converts the received solar irradiance into electricity without waste, you can reduce generation losses. To do this, you need to check, in order, the power generation data, weather and solar irradiance conditions, dirt on the panel surface, shadows from weeds or trees, generation differences at the string level, connection points and cables, conversion equipment, the temperature environment, drainage, and topography.

When you feel that power generation has dropped, rather than immediately performing cleaning or repairs, it is important to first break down and examine the data. Determine when the output is low, which equipment is underperforming, and whether there is a difference compared with equipment under the same conditions. By then inspecting the site, the places that need cleaning, the areas where vegetation should be removed, the connections that should be checked, the equipment to be inspected, and the drainage or access routes that should be reviewed will become clear. By addressing issues according to their causes, you can reduce unnecessary work and more easily choose measures that lead to recovery of power generation.

Keeping records after measures is also indispensable. Dirt will return after cleaning, grass will regrow after weeding, and equipment and wiring change condition with age. Comparing power generation before and after measures, retaining on-site photos and work histories, and using them in the next inspection will improve the accuracy of the improvements. To prevent repeated declines in power generation, it is necessary not only to eliminate the causes but also to create 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 dirt-prone rows, areas where shadows occur, places where water accumulates, abnormal strings, repair locations, cleaning areas, and inspection photos together with location information, stakeholders can more easily confirm the same spots. 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 subsequent checks for recurrence.

If you want to improve responses to drops in power generation while accurately recording countermeasures by cause, using 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, areas with poor drainage, abnormal equipment, repair sites, cleaning coverage, and on-site photos together with high-precision location information. By accurately identifying the causes of reduced power generation and managing so that the same locations can be continuously checked, it becomes easier to take practical steps toward power recovery and preventing recurrence.