5 Measures to Prevent Increased Losses During Months with Low Power Generation

At solar power plants, there can be months with low power generation due to seasonal and weather variations. A drop in generation during periods of low solar irradiance or prolonged rain is a natural phenomenon, but the problem is when those declines include losses that could have been prevented. The lower the generation in a month, the more susceptible revenues and accountability become to minor stoppages, dirt, shading, delayed inspections, and inadequate recordkeeping. This article summarizes practical measures for operations personnel who are investigating causes under the query "low power generation" to avoid increasing losses during low-generation months.

Table of Contents

• For months with low power generation, distinguish normal decreases from abnormal decreases.

• Visualize losses based on solar irradiance and expected power generation

• Check early for site-derived degradation factors, such as dirt and shadows.

• Establish a system to ensure equipment stoppages and output declines are not left unaddressed until the end of the month.

• Organize records and reports to improve the ability to explain months with low power generation

• Summary

For months with low power generation, distinguish normal declines from abnormal declines

The first thing to do in a month with low power generation is not to judge it solely by the low result. Solar power generation output is influenced by many factors such as solar irradiance, temperature, snowfall, rain, cloudy weather, installation angle, orientation, the surrounding environment, and equipment condition. Therefore, if you look only at a single month's output and conclude "this month is bad" or "the solar plant's condition is poor," you may waste time on unnecessary measures or risk overlooking abnormalities that truly need to be checked.

Especially in winter, during the rainy season, after a typhoon passes, or in months with prolonged rain, solar irradiance conditions themselves worsen. In such cases, even if power generation is lower than the same month of the previous year or the previous month, it does not necessarily indicate an equipment fault. On the other hand, if, even after considering solar irradiance conditions, output is lower compared with nearby power plants or other sections within the same site, or if only specific equipment shows reduced output on days with the same weather, there may be causes at the site or with the equipment. The lower the monthly generation, the more important it is to distinguish between this normal decline and an abnormal one.

In practice, you do not look at monthly generation in isolation; instead you check the ratio of generation to solar irradiance, the difference from the same month of the previous year, the difference from neighboring or similarly conditioned sections, and output differences between pieces of equipment. For example, if the entire plant is similarly low, weather or seasonal factors are likely to have a large influence. Conversely, if only a specific power conditioner, a specific string, or a specific section is low, you need to check for faults, poor connections, shading, dirt, vegetation, remaining snow, breaker operation, and other possible causes.

One reason losses tend to increase in months with low power generation is that, because there are fewer opportunities to generate power to begin with, coincident abnormalities or outages leave little room for recovery. In months with many sunny days, a short stoppage may not noticeably affect the month's total generation. However, in months with many cloudy or rainy days, equipment being down during even one of the limited sunny periods can have a large impact on the monthly output. It is precisely in low-generation months that careful management is required to make the most of the few generation opportunities.

Moreover, months with low power generation make it more difficult to explain the situation to stakeholders. The more people involved with a power plant—power producers, management companies, maintenance personnel, landowners, financial institutions, insurers, and so on—the more often you will need to explain “why it was low,” “whether it was due to natural causes,” “whether it was an equipment anomaly,” and “whether the response was appropriate.” Because explanations based on intuition are hard to accept, separating the factors behind the decline and leaving the basis for judgments helps prevent losses.

What’s important here is to treat low power generation not merely as an outcome but as a management signal. In months with low generation, it is necessary to carry out, in an integrated manner, checks of solar irradiance conditions, equipment operating status, on-site conditions, comparisons with historical data, and the organization of reporting materials. By doing this, declines due to natural factors will not be overemphasized, and losses caused by anomalies can be detected and addressed early.

Visualize losses based on solar irradiance and expected power generation

To prevent losses in months with low power generation, it is essential to compare not only the actual generation but also the expected generation. Expected generation is a benchmark indicating how much power can be anticipated given that month’s solar irradiance conditions, system capacity, and installation conditions. If actual generation is low but the expected generation is similarly low, the primary cause is likely the weather or seasonal factors. Conversely, if actual generation falls well short of expected generation, some kind of loss factor may be occurring.

What operational staff should be careful about is not judging power generation solely by month‑on‑month comparisons. For example, from spring to the rainy season, from summer to autumn, and from autumn to winter, solar irradiance conditions, temperature, and hours of sunlight change. Even if generation is lower than the previous month, if that decline is a natural seasonal change, it cannot be deemed a problem. Year‑over‑year comparisons for the same month are also useful, but because the weather can differ between last year and this year, that alone may not be sufficient. To correctly identify the causes of low generation, it is necessary to use solar irradiance and expected generation as benchmarks.

Using expected power generation clarifies the attribution of losses. Rather than simply stating "generation is low," it becomes easier to judge whether it is "lower than expected even after accounting for solar irradiance," "close to generation appropriate for the solar irradiance," or "only specific equipment deviates from the expected value." This makes it possible to decide whether to rush an on-site inspection, prioritize equipment checks, or focus on organizing records as a weather-related factor.

In power plant operations, small losses become harder to detect in low-generation months. Because overall generation is low, underperformance of part of the equipment can be overlooked with “it was due to bad weather.” However, checking generation efficiency against solar irradiance and output by equipment can reveal anomalies. For example, items to check include: only certain systems showing lower output under the same irradiance conditions; delayed ramp-up of output during sunny periods; or unnatural drops in output around midday.

When using expected power generation as a reference, you don't need to aim only for overly precise calculations. What matters is having a comparison metric that can be used consistently in the field. Checking daily, weekly, and monthly generation alongside solar irradiance conditions, and simply continuously monitoring output differences between installations, can lead to the detection of anomalies. If you manage multiple power plants, comparing plants in the same area or under similar conditions is also effective. However, because installation angle, orientation, shading patterns, vegetation condition, and equipment specifications differ, you should seek to verify the reasons for any differences rather than simply judging which is better or worse.

Also, comparing actual generation with expected generation is useful for explanatory materials both inside and outside the company. If you explain a low-generation month simply as "because the weather was bad," recipients may not accept that as sufficient justification. Therefore, by combining solar irradiation conditions, expected generation, actual generation, equipment downtime, and on-site inspection results in your explanation, the reasons for the decline can be clarified. To prevent losses in low-generation months, it is important not just to look at generation figures but to visualize the decline from both numerical and on-site condition perspectives.

In analyzing months with low power generation, it is important not only to search for anomalies but also to document improvement measures to prevent the same losses from recurring in subsequent months. By accumulating information on which conditions tend to cause generation to drop, which equipment is prone to shutdowns, and which locations are more likely to experience increased shading or soiling, the weaknesses specific to each power plant become apparent. This makes it easier to carry out inspections, cleaning, mowing, and reviews of monitoring settings before a low-generation month arrives.

Confirm on-site degradation factors, such as dirt and shadows, early

One factor that tends to increase losses in months with low power generation is changes in site conditions. Solar power plants are outdoor facilities and are affected by dirt on panel surfaces, fallen leaves, bird damage, dust, pollen, yellow sand (Asian dust), snowfall, vegetation growth, shadows from surrounding structures, and mud or sediment accumulation caused by poor drainage. Each of these may seem minor on its own, but in months with low generation they are more likely to show up as losses.

Shadows in particular change with the seasons. When the sun’s elevation is low, features that are usually not problematic—trees, fences, utility poles, slope faces, adjacent buildings, or steps in mounting structures—can cast shadows. Shadows that were not a concern in summer can affect morning or afternoon power generation in winter. If checks for shadows are neglected during months of low generation, there is a risk of overlooking ongoing losses masked by weather-related factors.

Soiling is not necessarily washed away by rain. Dirt tends to remain on panels with a shallow tilt, and mud or pollen can accumulate near the frames. If bird droppings, fallen leaves, or dust adhere locally, they can cause output reductions in some cells or strings. The impact of soiling is not necessarily uniform across the entire power plant; it can vary by location depending on wind direction, nearby roads, construction sites, agricultural land, forests, drainage paths, and so on.

To prevent site-originated causes of performance decline, it is effective to perform inspections before periods when declines are likely to occur, rather than scrambling to check after months of low generation. For example: before the season when vegetation grows, before the season when fallen leaves increase, before winter in regions where snowfall is expected, and after typhoons or heavy rain. Deciding the timing when risks increase for each plant reduces the chance of missed inspections. During on-site checks, it is important to inspect not only the panel surfaces but also under the racks, drainage channels, slopes, along fences, around junction boxes, around collection equipment, and cable routes.

Also, when power generation is low in a given month, the decision to visit the site tends to be delayed. While assuming the low output is due to bad weather, shadows from vegetation, dirt, and minor equipment abnormalities can persist, causing missed generation opportunities even on sunny days. Remote monitoring data alone may not be sufficient to reveal shadows, dirt, changes to the ground surface, poor drainage, or the distribution of remaining snow. Therefore, it is important to make a judgment by combining the trend of declining generation with on-site photos, aerial records, and patrol inspection records.

An important point during on-site inspections is not to draw definitive conclusions about the cause from a single check. Causes of reduced power output can be multiple and overlapping. In months with low solar irradiance, shading from vegetation, soiling of panels, and partial equipment outages can occur simultaneously. In such cases, fixing only one of these issues may not be sufficient to achieve meaningful improvement. Faced with the outcome of low power generation, it is necessary to take an approach that reduces losses comprehensively by cross-checking site conditions, equipment status, and operational data.

Reducing site-originated losses also requires proper recordkeeping. Instead of just taking photos during inspections, record the photo location, direction, date and time, the equipment inspected, and the inspection items, as this makes it easier to later correlate with power generation. When checking shadows, because their appearance changes with the time of day, you need to compare the times when generation drops with how shadows appear on site. For dirt and vegetation, recording the extent of occurrence and which equipment they are likely to affect makes it easier to prioritize responses.

Build a system to ensure equipment stoppages and output drops are not left unattended until the end of the month

In months with low power generation, a system for quickly detecting equipment downtime and output declines is indispensable for preventing losses. Outages cause losses even in high-generation months, but in low-generation months the impact of missing limited sunny hours is greater. In particular, operational practices that only identify stoppages that occurred at the start or middle of the month when compiling end-of-month totals delay responses and increase unrecoverable losses.

Stops or reductions in output can occur in ways that are clearly recognizable as complete failures, or in forms that are easy to overlook. For example: only some equipment has low output; the peak on sunny days does not appear; morning and evening ramp-up is slow; output drops only during specific time periods; communications are functioning but generation values are unnaturally low; or alarms are present but mistakenly considered resolved. These cases can be masked by poor weather if you only look at monthly generation figures.

Therefore, in managing low-generation months, it is important to carry out not only monthly checks but also daily or weekly checks. You do not need to analyze everything in detail every day, but you need a system to regularly verify the plant’s total generation, equipment-level output, alarms, communication status, downtime, and differences compared with equipment under the same conditions. In particular, if output differences appear on sunny days, they should be prioritized for inspection, as they are difficult to explain by weather.

In a system designed to prevent equipment shutdowns, it is important to clarify who monitors what, when, and under what conditions they should proceed to on-site response or arrange maintenance. Even if alarms appear on the monitoring screen, response will be delayed if the person in charge does not have clear decision criteria. Conversely, if on-site responses are made every time for minor fluctuations, the operational burden becomes large. In practice, it is advisable to set confirmation criteria for each power plant and use them as guidelines for response decisions—such as output differences above a certain threshold, stoppages longer than a certain time, repeatedly occurring alarms, communication outages, or unnatural drops during sunny conditions.

Also, during months of low power generation, it is important not to misprioritize maintenance. Rather than treating every anomaly with the same level of urgency, prioritize those that cause large generation losses, are persistent, affect safety, or impact other equipment. For example, a shutdown that affects the entire plant and a small output discrepancy affecting only part of the system require different priority levels. However, even small output discrepancies can accumulate losses if they persist for long periods, so they should be recorded and tracked.

Communication issues also require attention. When monitoring data are not being collected, you cannot determine whether the system is generating power, has stopped, or the communication has simply been lost. If communication issues are left unaddressed during a low-generation month, you may be slow to notice an actual stoppage. Restore communications, carry out on-site inspections, record missing measurements, and verify the data after restoration so that no gaps remain in the monthly report.

Furthermore, when responding to equipment outages, the confirmation of recovery should be treated as part of the same task. Merely checking the alarm and making a notification is not sufficient for preventing losses. It is important to verify after restoration work whether power generation has returned to normal, whether the same equipment has experienced a recurrence, and whether related equipment has been affected. Without records after recovery, it will be difficult to demonstrate the appropriateness of the response when explaining low power generation at the end of the month.

The lower the monthly power generation, the more important it is that responses to shutdowns or declines follow the sequence: "notice quickly," "set priorities," "follow through until recovery," and "keep records." At power plants with this system in place, even if weather-related declines are unavoidable, it becomes easier to reduce losses caused by inadequate management.

Organize Records and Reports to Improve Explanations of Low-Generation Months

In preventing losses during months of low power generation, not only on-site responses but also the organization of records and reports is important. Months with low generation often lead to requests for explanations of the causes afterward. If generation data, solar irradiance conditions, equipment status, on-site inspections, and response histories are not organized, explanations will become vague even if the situation was managed appropriately. Insufficient explanations leave stakeholders uneasy and may necessitate additional checks or reinvestigations.

The items to record are not limited to monthly power generation. It is important to organize daily generation trends, solar irradiance conditions, output by equipment, downtime, alarm history, the presence or absence of communication abnormalities, on-site inspection date, inspector, inspection locations, photos, actions taken, recovery date and time, and whether recurrence occurred. You don’t need to compile everything in a complicated way, but you should keep the records in a state that allows you to trace the reasons for low power generation.

In reporting materials, it is also important not to attribute low power generation to a single cause. For example, phrasing such as "Poor weather is considered the primary factor, but some equipment experienced a short-term shutdown and has been restored" and "Although the decrease in solar irradiance had a large impact, shadowing was confirmed in a specific section and countermeasures are planned" — explaining natural factors and management factors separately makes the situation easier to understand. Conversely, if you only write "because the weather was bad," it is unclear whether equipment checks were performed.

In reporting low-generation months, the important thing is to connect numerical data with on-site information. Graphs and tables of generation alone do not reveal what was happening at the site. Conversely, photos alone can make it difficult to understand the impact on generation. If you record and link the days when generation dropped, the times alarms were triggered, the locations where shading or soiling was observed, and the timing of recovery, it becomes easier to explain the causes and the responses taken.

Reports can also be used for comparisons with the past. Even if power output is low at the same time every year, countermeasures differ depending on whether the cause is solar irradiance conditions, seasonal shading, vegetation growth, or snowfall. If records of past low-generation months are kept, you can plan measures in advance. For example, if shading affected the same period last year, you can carry out tree removal, branch trimming, and shading checks before that time this year. If communication outages persisted last year, you can review monitoring arrangements and communication routes.

Organizing records and reports also contributes to improving maintenance quality. If issues that occurred during months with low power generation can be reflected in improvements in subsequent months, the documents become not just monthly reports but materials for operational improvement. Because on-site staff, managers, and power producers can discuss while looking at the same records, it becomes easier to reassess response priorities, allocate budgets, and review inspection frequencies.

Moreover, keeping records of low-generation months is useful in the event of any trouble. If disasters, equipment failures, damage caused by external factors, insurance claims, or contractual verifications occur, how easy it is to explain the situation depends on whether past generation data and on-site records are organized. If routine records are kept, it becomes easier to track when the anomaly began, what area was affected, and what response was taken.

Low-generation months are also times when a plant’s management condition becomes easier to see. Rather than stopping at the mere result of low output, organizing the sequence of cause analysis, responses, recording, and reporting makes it possible to prevent losses while improving management quality.

Summary

To prevent losses that increase in months with low power generation, it is important first not to treat declines in generation uniformly as abnormal, but to distinguish between normal declines and abnormal ones. Decreases due to weather or season are unavoidable, but it is necessary to check whether preventable losses—such as equipment shutdowns, soiling, shading, vegetation, communication faults, or delayed inspections—are mixed in among them.

For that purpose, it is useful to look not only at actual power generation but also at solar irradiance and expected generation as references. The lower the monthly generation, the more weather effects can conceal anomalies. By combining expected generation, equipment-specific output, historical data, and on-site records, it becomes easier to identify the reasons for the decline.

Also, it is essential to confirm site-related factors as early as possible. Panel soiling, fallen leaves, bird damage, shadows from vegetation, remaining snow, poor drainage, and sediment buildup, if left unaddressed, reduce opportunities for power generation. In particular, because the appearance of shadows and soiling changes with the seasons, it is important to plan and conduct on-site inspections before and after months of low power generation.

For equipment outages and output reductions, rather than checking them collectively at the end of the month, a system for early detection on a daily or weekly basis is necessary. Creating a workflow of noticing an outage, setting priorities, restoring service, confirming power generation after restoration, and keeping records makes it less likely to lose limited power generation opportunities.

Finally, by organizing records and reports, the ability to explain months with low power generation improves. If you can explain the reasons for low generation together with solar irradiance conditions, equipment condition, site conditions, and response history, it will be easier to gain stakeholders’ understanding. Months with low generation may be unavoidable, but losses caused by poor management can be reduced. By continuously recording the condition of each power plant and linking on-site inspections with data management, it becomes easier to prevent losses from low-generation months and to promote operational improvements.