Causes of Low Power Output and How to Increase It｜7 Checks Needed for Improvement

Table of Contents

• Do not assume a single cause for low power output

• Check 1: Review power output data by time of day

• Check 2: Narrow down the extent of the decline by comparing with systems under the same conditions

• Check 3: Isolate the effects of weather, solar irradiance conditions, and seasonal variations

• Check 4: Inspect panel surfaces for dirt and deposits

• Check 5: Inspect for shading caused by weeds, trees, or structures

• Check 6: Inspect connections, cables, and power conversion equipment for faults

• Check 7: Identify potential causes of recurrence from drainage, topography, and inspection records

• Approach to sustaining measures to increase power output

• Summary

Don't assume there is a single cause for low power generation.

When you feel that the power generation of a solar power system is low, the most important thing initially is not to assume a single cause. Even if the result—reduced generation—is the same, the actual causes can vary greatly from site to site. Various factors can lead to reduced generation, such as dirt on the panel surface, bird droppings and fallen leaves, shading from weeds or trees, faults in connection points, cable damage, stoppage of conversion equipment, output curtailment, temperature rise, poor drainage, and lack of inspection records. Moreover, these factors may not occur in isolation; multiple issues can happen at the same time.

For a practitioner searching for "how to increase power generation," it is important to interpret the phrase "increase power generation" as reducing generation losses. In solar power generation, you cannot increase the amount of solar irradiance at the site. You cannot increase the number of sunny days or change the sun’s seasonal altitude. However, you can move the system closer to a state that converts the received sunlight into electricity with as little waste as possible. In other words, to increase power generation you need to find where the electricity that should be generated is being lost and implement measures appropriate to those causes.

When power output is low, immediately proceeding with cleaning or repairs can sometimes fail. For example, even if panels look dirty, the main cause may actually be shading in the morning and evening. Even if the grass appears overgrown, the primary cause of reduced output may be short interruptions of the conversion equipment. Conversely, even when nothing looks visually wrong, only a particular string may be producing less power. Relying solely on on-site impressions can lead to misidentifying the causes that significantly affect power generation.

The basics of identifying the cause are to link power generation data with on-site conditions. Check when output is low, which equipment is underperforming, whether there is a difference compared with 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, equipment, drainage, and records. The mere result that power generation is low does not tell you what to address first. Having a process to isolate causes clarifies the priority of cleaning, weeding, repairs, equipment checks, and drainage measures.

Furthermore, efforts to increase power output are not something that can be completed in a single action. Solar power plants are outdoor facilities, and their condition changes with the seasons, weather, surrounding environment, and equipment aging. Even if cleaned, dirt will return; even if weeds are removed, grass will regrow; trees will grow; and drainage routes will change due to sediment and fallen leaves. To reliably increase power output, operational practices are necessary that identify causes, implement countermeasures, verify their effectiveness, and use the records to inform the next inspection.

Check 1: Verify power generation data by time of day

When investigating the cause of low power generation, the first thing to check is the generation data. If you only look at monthly or annual generation figures, you can't tell when generation losses occur. Even with similarly low overall output, the suspected cause changes depending on whether it's low only in the morning, the midday peak doesn't rise, it drops only in the evening, or there's a sudden dip during the day. To increase generation, the starting point is to look at the generation curve by time of day rather than the totals.

If generation is low in the morning, shadows from trees on the east side, embankments, 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 rise, candidates include dirt on the panel surface, temperature increases, limitations of power conversion equipment, output curtailment, or equipment shutdowns. If the generation curve suddenly drops during a clear day, you should cross-check shutdown and alarm histories with the timestamps.

When checking by time of day, it is important to use data from clear days whenever possible. On cloudy or rainy days, power generation fluctuates greatly due to cloud movement. As a result, it becomes difficult to determine whether an issue is due to equipment malfunction or weather. By looking at the generation curve for clear days, it is easier to find patterns such as the effect of shadows that fall at the same time every day, equipment shutdowns that occur only at specific times, and output curtailment that flattens the top of the curve.

When reviewing power generation data, we distinguish between sudden drops and gradual declines. A sudden drop may indicate equipment shutdown, a broken cable, poor connections, or the emergence of an obstruction. A gradual decline may be related to accumulation of dirt, the growth of weeds or trees, worsening site conditions due to poor drainage, or equipment degradation. By interpreting the shape of the decline, you can narrow down the locations that should be prioritized for on-site inspection.

If you go to the site without reviewing the data, inspections tend to be wide-ranging but shallow. Even if you walk around the entire power plant, if the period of reduced output doesn’t coincide with the time of the on-site check, you may miss causes such as shading or shutdowns. If output is low in the morning, check the on-site conditions in the morning; if it’s low in the evening, look for evening shadows. Inspections to increase power generation start with reviewing the data before going to the site.

Check 2: Narrow down the range of degradation by comparing with equipment under the same conditions

Identifying the cause of low power output cannot rely on the plant-wide total alone. Even if there is no obvious anomaly at the overall level, generation can be low only in certain rows, certain strings, or in areas connected to specific power conversion equipment. Such partial generation losses may be inconspicuous in the monthly totals, yet if they persist over a long period they can cause significant losses. To increase power generation, it is important to narrow down the reduced range by comparing with equipment under the same conditions.

When making comparisons, choose installations whose orientation, tilt, number of panels, shading conditions, and connection configuration are similar. If you simply compare installations with different conditions, you may mistake normal differences for abnormalities. Even within a single power plant, power generation will vary if the orientation or tilt differs. The purpose of the comparison is to identify locations that are consistently underperforming among installations that should have similar power generation.

If only part of an installation is performing lower compared with equipment under the same conditions, local soiling, partial shading, poor connections, cable damage, or issues on the converter side can be suspected. For example, if a particular column is lower than adjacent columns even on sunny days, it could be due to grass growing in front of that column, concentrated soiling on the lower edge, or a fault in the wiring route. Narrowing the abnormal range in the data before inspecting the site will improve the accuracy of your verification.

When narrowing down the affected area, it is also important to be able to accurately pinpoint the location on site. At sites where equipment numbers or row numbers are unclear, even if an anomaly is found in the data, it can take time to locate the corresponding spot in the field. A photo alone may not convey the location. For improving power generation output, being able to share the exact location among stakeholders is as important as finding the anomaly.

Even small differences in power generation can become a large loss if they persist day after day. Rather than concluding there’s no problem just because the overall output hasn’t dropped significantly, continuously compare performance with equipment under the same conditions. This comparison makes it easier to narrow down the areas that should be cleaned, the spots that need weeding, the connection points that should be inspected, and the equipment that should be checked.

Check 3: Separate weather, solar radiation conditions, and seasonal variations

When you feel that power generation is low, before suspecting an equipment fault check the weather, solar irradiance conditions, and seasonal differences. Solar power generation is heavily influenced by the amount of sunlight, so during periods with frequent clouds or rain generation can fall even if the equipment is fine. If you compare only the monthly generation with the same month of the previous year or with the previous month and immediately conclude there is an anomaly, it may turn out that weather differences were the main cause.

On the other hand, you must also avoid missing real anomalies by attributing them to the weather. If the entire plant is declining uniformly in line with regional weather, the influence of solar irradiance conditions is likely significant. However, if only part of the plant is underperforming while other equipment in the same plant is operating normally, or if there is a clear difference compared with equipment under the same conditions, the weather alone cannot explain it. In such cases, 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-related ones, it is effective to compare sunny days with other sunny days or days with similar weather. Cloudy or rainy days have large fluctuations in power generation, making it difficult to see the characteristics of anomalies. If you select and inspect the generation curves for sunny days, it becomes easier to find effects such as shadows that cause drops at the same time every day, string anomalies that are low only on specific equipment, and equipment shutdowns that cause drops only for certain periods.

Seasonal differences are also an important factor to consider. In winter, the sun’s altitude is lower, and shadows from surrounding trees and terrain tend to lengthen. In summer, while solar radiation is stronger, panel and nearby equipment temperatures rise, which can make it harder for output to increase. During periods of heavy rain, monthly power generation tends to be lower, and after strong winds or heavy rain attention should be paid to fallen leaves, sediment, deposits, poor drainage, and the condition around cables.

To increase power output, you need to distinguish between natural variability and generation losses that can be improved on-site. If weather is the cause, cleaning or repairs will not significantly improve power output. Conversely, if low output persists even on sunny days, there is a high likelihood that there is room for improvement at the site. To improve the accuracy of identifying causes, it is important to carefully separate equipment-side issues from solar irradiance conditions, without ignoring the irradiance conditions.

Check 4: Inspect the panel surface for dirt and deposits

A common cause of low power output that should be checked at many sites is dirt and deposits on the panel surface. Because solar panels generate electricity by receiving solar radiation at the surface, when dirt adheres the amount of light reaching the cells is reduced. The type of soiling varies with the site environment and includes soil dust, pollen, yellow sand (yellow dust), bird droppings, fallen leaves, sap, dust from nearby construction, road-derived dust, and contaminants containing salt that tend to adhere near the coast. Even light soiling spread over a wide area can affect power generation, and localized deposits can act as strong shading even over a small area.

Particular attention should be paid to band-like dirt that remains along the bottom edge of the panels and around the frame. It is often assumed that rain will wash it away naturally, but in reality the flow of rainwater can collect dirt at the lower edge and leave it there. Panels with a gentle slope do not drain water easily, making dirt more likely to accumulate. Even dirt that is not noticeable from a distance can affect power generation if it covers part of a cell. During on-site inspections, it is necessary to carefully look not only at the overall color of the panel but also at the bottom edge, the corners, and around the frame.

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 densely and therefore inhibit power generation as partial shading. If only some installations show reduced power output, prioritize checking the panel surfaces around those installations. Rows near trees, around structures where birds tend to perch, rows that are often downwind, and areas near unpaved access ways are more prone to dirt and deposits.

When carrying out cleaning, it is practical to prioritize locations that have the greatest impact on power generation. Rather than cleaning all panels at the same frequency, focus on installations where drops in power generation have been confirmed, rows with concentrated soiling, areas where lower-edge soiling is conspicuous, and locations with heavy bird damage or fallen leaves. Comparing photos and power generation before and after cleaning makes it easier to determine how much the soiling at that site was affecting generation.

However, cleaning must be performed in a way that does not damage the equipment. Avoid vigorously scrubbing with hard tools, carrying out sudden work during periods when panels are at high temperatures, or working without confirming the electrical safety of the equipment. Cleaning aimed at improving insufficient power generation is not a cosmetic task but a maintenance operation to restore the panels' light-receiving condition and to keep the equipment in stable long-term use. Recording the locations and extent of dirt and the likely causes of its occurrence will also be useful for future inspections.

Check 5: Manage shading from weeds, trees, and structures

Shading effects are an item that must always be checked as a cause of low power generation. Because solar panels generate electricity by receiving sunlight, even a shadow covering part of a panel can reduce power output. Causes of shading vary and include weeds, trees, fences, utility poles, surrounding buildings, mounting racks, adjacent panel rows, and monitoring equipment. Because shadows move with the time of day and season, the absence of visible shading at the time of inspection does not necessarily mean there is no problem.

Weeds are a common cause of power generation losses at sites. Even if there are no issues in winter or immediately after installation, they can grow rapidly from spring through summer and cast shadows on the lower edges of panels and the front rows of panels. Even if the vegetation does not touch the panels, the low sun angle in the morning and evening causes long shadows. Furthermore, when weeds become overgrown, airflow is reduced, inspection walkways become blocked, and it becomes harder to inspect around equipment. Because it affects not only power output but also maintainability and safety, weed management is fundamental to improving power generation.

Shading from trees is a factor that tends to become problematic during long-term operation. 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 located near forests or slopes, the combined height of the terrain and the trees can create long shadows in winter. If output 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.

When checking shadows, it is important to match the times when power generation data shows a decline. If output is low in the morning, check the on‑site conditions in the morning; if it is low in the evening, inspect for evening shadows. Even if there are no problems at noon, large shadows can appear in the morning and evening. When you find a shadow, record the time of occurrence, the source, the equipment affected, and take photos. For weeding and pruning, prioritize areas that have the greatest impact on power generation.

Attention must also be paid to shadows cast by surrounding structures and added equipment. Adding new equipment within the power plant, or installing fences, signs, or monitoring poles, can create shadows at certain times of day. To increase power output, it is important not only to reduce existing shading but also to operate in ways that do not create new shading. Shadow management is not something that can be finished with a single weeding; it requires ongoing action while monitoring seasonal changes.

Check 6: Inspect connectors, cables, and conversion devices for abnormalities

The causes of low power generation are not limited to the panel surface or shading. Even if solar panels are receiving sunlight normally, faults in connections, cables, or power conversion equipment can prevent the generated electricity from being fully extracted. String-level differences in generation, loose terminals, poor contacts, damage to cable insulation, moisture ingress, animal damage, shutdowns of power conversion equipment, and output curtailment are all significant causes of reduced generation.

When checking for anomalies at the string level, compare strings under the same conditions. If you simply compare ones with different numbers of panels, orientations, tilts, shading conditions, or connection configurations, you may mistakenly judge a normal difference as an anomaly. Check whether any string is consistently lower compared with adjacent rows or equipment with the same orientation. If only a particular string is low, candidates include soiling, partial shading, poor connections, cable damage, or device-side problems.

Suspected problems with connections or cables include when only specific equipment has low power output, when abnormalities tend to appear after rain, when power output suddenly drops, or when the output fluctuates unstably. In areas with heavy weed growth it becomes difficult to inspect the condition of cables. In locations with poor drainage, moisture and standing water can affect the connections. At sites that are easily accessible to animals, cable damage may also occur.

For power conversion equipment, check the operating status, shutdown history, alarm history, and whether output curtailment has occurred. Even brief outages can cause significant losses if they occur during the daytime when generation is high. If the generation curve levels off on sunny days, check for output curtailment, the equipment’s capacity limit, temperature rise, and measurement anomalies. Do not judge based solely on the generation curve; it is important to review equipment records together with on-site conditions.

When checking electrical equipment, safety must be the top priority. Even if you want to increase power output, on-site personnel should avoid forcibly touching connection points or the inside of equipment to make a judgment. Organize which equipment is showing abnormalities, the time of occurrence, changes in power output, on-site photographs, and the surrounding environment, and, as necessary, arrange for professional inspection. At the stage of identifying the cause, it is important to clearly specify where and what kind of abnormality is suspected.

Check 7: Identify Recurrence Factors from Drainage, Topography, and Inspection Records

When investigating the causes of low power generation, you need to check not only the panels and equipment but also the plant's overall drainage, topography, and inspection access routes. Places where water tends to accumulate, locations where sediment can flow in, sections prone to becoming muddy, slope failures, scour around the racking, and areas where cables are likely to be exposed can directly or indirectly cause a reduction in power output. These are important factors that lead to soiling, weeds, connection faults, and deterioration of inspectability.

In locations where puddles remain after rain, weeds are more likely to grow. When weeds grow, they create shade, reduce ventilation, and make inspections more difficult. Muddy walkways slow down work and can reduce the frequency of cleaning and weeding. Where sediment flows in, it can accumulate beneath panels and around cables, causing soiling and damage. If cleaning or weeding repeatedly results in the same problems in the same place, drainage or terrain issues should be suspected.

When checking topography and drainage, on-site inspections after rain are effective as well as checks in sunny conditions. Identify where water flows in from, where it pools, and where it drains away. Recording puddles, sediment accumulation, vegetation overgrowth, pathway subsidence, and slope changes will reveal locations prone to recurrence. If poor drainage is left unaddressed, dirt and weeds will recur, resulting in the same power generation losses happening repeatedly.

Inspection records are also important for identifying factors behind recurrence. If you can confirm whether the same location previously showed dirt, whether grass has grown in the same row, or whether the same equipment has experienced stoppages, you can narrow down the cause more quickly. If records are insufficient, start recording from this inspection: photos, date and time, equipment number, location, details of the abnormality, and the response status, so they can be used for the next inspection.

By identifying the causes of recurrence, countermeasures change from temporary tasks to continuous improvement. Rather than simply cleaning dirt, check why that location tends to get dirty. Rather than just cutting grass, look into why grass grows easily in that spot. Rather than merely repairing connections, verify background factors such as moisture, drainage, and cable exposure. With this perspective, it becomes easier to sustain the effects of power generation improvements for a longer time.

Approach to Sustaining Measures to Increase Power Generation

Measures to increase power output cannot be completed with a single cleaning or repair. A solar power plant is an outdoor installation, and its condition changes with the seasons, weather, surrounding environment, and the aging of equipment. Even if you clean it, dirt will return; even if you remove weeds, grass will grow; trees will grow; and equipment and wiring will change condition over long-term operation. To stably improve power output, a system for continuous inspections and countermeasures is necessary.

First and foremost, compare the power output before and after the measures. After carrying out cleaning, weeding, repairs, equipment inspections, and drainage checks, check how the power output has changed. It is difficult to completely remove 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 had a large effect going forward, and if an effect is not apparent, consider other causes.

Next, keep places that are prone to recurrence as items under management. If you record rows where dirt tends to accumulate, time periods when shadows are likely to occur, places where water pools, walkways that are prone to damage, and equipment that tends to show abnormalities, you can check them before power generation drops significantly. To steadily increase power generation, it is important not only to respond after output falls but also to identify conditions that are likely to cause declines in advance and take countermeasures.

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

Summary

To identify the causes of low power generation and raise output, it is important to sequentially isolate where generation losses occur and why. In solar power generation you cannot increase the solar irradiance itself at the site. However, you can improve generation by bringing the system closer to a state that converts the received irradiance into electricity without waste. To do this, you need to check, in order, the generation data; comparisons with installations under the same conditions; weather and irradiance conditions; dirt on the panel surfaces; shading from weeds or trees; connection points and conversion equipment; drainage and terrain; and inspection records.

When you feel that power generation is low, don't immediately carry out cleaning or repairs; first, separate and analyze 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. With that information, an on-site inspection will clarify where cleaning is required, the areas that need weed removal, the connection points that should be checked, the equipment to verify, and the drainage or access routes that need reconsideration. For improving power generation, it is important to make decisions by linking data with on-site conditions rather than relying on intuition.

Also, efforts to increase power generation are not completed with a single task. Even if you clean, dirt will return; even if you remove weeds, grass will grow; trees will grow; and equipment and wiring will change condition over time. By comparing power generation before and after measures, keeping site photos and records of work performed, and using them for the next inspection, the accuracy of improvements will increase. To raise power generation stably, it is essential not only to remove 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 dirt-prone rows, shadowed areas, places where water accumulates, abnormal strings, repair locations, cleaning coverage, and inspection photos are recorded together with location information, stakeholders can more easily confirm the same spot. By combining generation data with on-site location information, it becomes easier to explain priorities for cleaning, weeding, and repairs, and it also streamlines recurrence checks on subsequent visits.

If you want to continuously identify the causes of low power generation and ways to increase it 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 within a solar power plant, areas prone to dirt, locations where shading occurs, areas with poor drainage, abnormal equipment, repair locations, cleaning ranges, and on-site photos together with high-precision positional information. By retaining the results of cause identification with positional information, it becomes easier to pursue power generation improvements based on on-site data rather than intuition.