5 Preparations Before Consulting a Contractor When Power Generation Is Low

When you feel that the power output of your solar power system is low, it’s natural to want to contact a service provider right away. If your monthly generation figures are lower than expected, the numbers on the monitoring screen aren’t increasing as they used to, or the amount of electricity sold or self-consumed appears to have decreased, you may worry that there is a problem with the equipment. However, declines in generation can be caused by various factors such as weather, season, solar irradiance conditions, shading, dirt, equipment shutdowns, communication or metering status, and differences in comparison methods. If you consult without sufficient preparation, your explanation of the situation can become vague, making it more likely that confirmations will need to be redone or on-site inspections rescheduled.

Before consulting a service provider, what’s important is not to determine the cause on your own. Instead, organize the necessary information and clearly state the basis for judging that the power output is low. Summarize when the change in power output occurred, over what range, and what you are comparing it to when you consider it low; doing so makes it easier for the party you consult to narrow down the cause. This article explains the preparations to make before consulting a service provider when power output is low, presented as a workflow that field staff can use immediately.

Table of Contents

• Initial considerations to organize when you feel power generation is low

• Preparation 1 Check the decline in power generation on a daily and monthly basis

• Preparation 2 Organize the relationship with weather, seasons, and sunlight/solar radiation conditions

• Preparation 3 Collect abnormal information from monitoring screens and equipment displays

• Preparation 4 Check for shadows, dirt, and nearby changes within the visible area on site

• Preparation 5 Summarize the consultation points and items you want the service provider to confirm

• Points to note for smoothly proceeding with consultations about decreased power generation

• Summary When power generation is low, organize your records before consulting

First things to consider when you feel power generation is low

The power output of solar photovoltaic systems is not constant from day to day. Even with the same system capacity, it can vary greatly between periods of prolonged clear weather and periods with frequent rain or clouds. Also, while summer tends to bring higher solar irradiance, output can decrease due to temperature rises in the photovoltaic modules. In winter, ambient temperatures may be advantageous in some respects, but shorter daylight hours and lower solar elevation make systems more susceptible to shading. In this way, generation is strongly affected not only by equipment faults but also by natural conditions.

Therefore, when you feel that power generation is low, it is important to first clarify "what criteria you are using to judge it as low." Whether it is lower than the previous day, lower than the same month of the previous year, lower than the simulated value, or lower than other nearby facilities will change what needs to be checked. Simply saying "I feel it's been low recently" makes it difficult for the person you consult to form an assessment of the cause.

In practice, it is necessary to distinguish whether a decline in power generation should be viewed as a temporary fluctuation or treated as a persistent anomaly. The factors to suspect differ between a drop in monthly generation after several days of rain and an obvious failure to increase generation even on sunny days. Furthermore, inspection priorities change depending on whether overall generation has decreased, only some systems are underperforming, or output is dropping only during specific time periods.

Preparing before consulting a contractor is not meant for performing a professional diagnosis yourself. Rather, it is a preliminary step to assemble materials that make it easier for a specialist contractor to assess the situation. By organizing records of power generation, weather trends, monitoring screen readouts, on-site changes, and past inspection records, the subject of your consultation becomes more concrete. As a result, the range that needs to be checked can be narrowed, and unnecessary back-and-forth reduced.

The lower the power generation, the more important it is not to rush to conclusions about the cause. You may have arranged cleaning assuming dirt was the problem, only to find that part of the equipment had actually stopped. Conversely, you may suspect equipment failure when the real cause was temporary bad weather or local environmental influences. By organizing information before consulting, you can avoid misguided countermeasures and more easily get closer to the true cause of the decline in power generation.

Preparation 1 Check the decrease in power generation by day and by month

The first step is to check decreases in power generation on both a daily and a monthly basis. Even if you feel the power generation is low, looking only at daily data can be strongly affected by the weather, making it difficult to determine whether it is an equipment malfunction. Conversely, looking only at monthly data can make it hard to see when the decline began and which time periods are showing anomalies. By checking both daily and monthly data together, you can more easily clarify the trend of the decline.

When examining data by day, check whether days with extremely low power generation occur as isolated incidents or persist for several days. If they are low only on rainy or cloudy days, it may be a natural fluctuation. Conversely, if days that are clearly lower than other days with similar conditions continue despite clear skies, inspection of the equipment may be necessary. In particular, changes such as the power output curve on a sunny day suddenly dropping partway through, not generating for certain periods, or failing to increase overall from morning through evening are important clues to bring up during consultations.

When viewing data by month, compare it with the same month of the previous year and the trends of the past few months. However, even when comparing with the same month of the previous year, large differences in weather can lead to differences in power generation. Therefore, do not judge an anomaly solely on the fact that output is lower than the previous year; it is important to also check the number of sunny days and the frequency of rainy days. If possible, review not only the monthly power generation but also the daily generation side by side to determine whether the decline is concentrated on specific days or is generally low across the entire month.

When checking generation figures, you need to pay attention to the units. Generated energy, electricity sold, self-consumption, electricity purchased, and the instantaneous output displayed each have different meanings. What you thought was a drop in generation may actually be a reduction in the amount sold. If self-consumption increases, the amount sold may fall even though the generation itself has not changed significantly. Before a consultation, check what the numbers you are looking at actually represent to avoid misunderstandings in explanations.

Also, looking at declines in generation on a per-capacity basis can be useful. If you manage multiple generation facilities, comparing only total generation while capacities differ can prevent you from accurately understanding the degree of decline. Even within the same facility, if you can view generation by system, by power conditioner, or by string, it’s a good idea to confirm whether the drop is overall or only partial. If only part is low, the cause is more likely to lie within that range, making it easier to isolate the issue when consulting.

When reporting to a contractor, it's ideal to be able to explain in writing "since when," "to what extent," and "compared to what" it is lower. For example, organize it as: since the beginning of this month it appears lower even on clear days compared with days of similar conditions in the same month last year; generation suddenly dropped from a specific date; or the generation curve drops unnaturally only during afternoon hours. You don't need to fully analyze the numbers, but leaving the basis for why you feel it is low will improve the accuracy of the consultation.

Preparation 2: Organize the relationships among weather, seasons, and solar radiation conditions

Next, what we want to check is whether the decline in power generation can be explained by weather or seasonal influences. Solar power generation depends on solar irradiance and is affected by cloud cover, rain, snowfall, yellow sand, fog, heavy haze, and similar conditions. Even when generation is low, if the weather is poor it may be a natural outcome. Conversely, if sunny weather continues but generation remains low, you need to check for other causes such as equipment shutdowns, shading, soiling, grid-side output control, and communication or measurement problems.

Seasonal variations are also important. Spring and autumn can often see relatively higher power generation, but trends vary depending on the region and installation conditions. In summer, daylight hours are longer and solar radiation is stronger, but high module temperatures can suppress output. In winter, while lower temperatures can be advantageous in some respects, daylight hours are shorter and the sun’s elevation is lower, so shadows from surrounding buildings and trees tend to extend further. Therefore, it is necessary not to judge monthly power generation simply as high or low, but to view it in conjunction with the characteristics of that period.

If the month in which you feel the power generation is low coincides with a period of frequent rain or clouds, it becomes easier to assess by extracting and checking only the sunny days within that month. Even if the monthly generation is low, if the generation curve on sunny days is normal, there may be no major fault with the equipment itself. On the other hand, if even on sunny days the peak output is lower than before, generation starts later, generation ends earlier, or there is an unnatural dip around midday, it is worth proceeding with on-site and equipment checks.

Before consulting, it is helpful to leave a brief weather memo for the period when power generation was low. A detailed meteorological analysis isn’t necessary, but note whether it was mostly sunny, whether rain or cloudy conditions persisted, whether there was snow or strong winds, or whether the period might have been affected by yellow sand, pollen, volcanic ash, or dust. If the on-site person in charge keeps track of daily weather, their firsthand observations are also useful. Local circumstances that aren’t visible from monitoring data alone can sometimes help explain reductions in power generation.

However, you should avoid dismissing everything as being due to the weather. Weather has a large impact on power generation, but partial equipment shutdowns, connection failures, or the emergence of obstructions may also occur at the same time. In particular, if a specific installation performs worse than other installations in the same area or another system on the same site, it can be difficult to explain this by weather alone. The purpose of accounting for the effects of weather is not to assume there is no anomaly, but to align the assumptions when consulting a contractor.

Changes in solar irradiation conditions also include changes in the surrounding environment. New obstructions that did not exist before—such as nearby buildings being constructed, trees growing, temporary structures or material storage yards being installed, or fences and signs casting longer shadows—can affect power generation. Especially in winter or at dawn and dusk, shadows become longer, so things that normally would not be a concern can fall on the generation surface. Before consulting a contractor, it is a good idea to recall not only the weather and season but also any changes in the installation environment.

Preparation 3 Collect abnormal information from monitoring screens and equipment displays

When power generation is low, the monitoring screen or equipment display may retain clues to abnormalities. Power generation equipment may be equipped with systems that allow you to check generated power, output, operating state, stopped state, alarms, communication status, and so on. Before consulting a contractor, collecting the screen displays and records you can check will make it easier to narrow down the cause. In particular, it is important to determine whether the period of low generation coincides with the timing of alarms or shutdowns.

On the monitoring screen, what you want to check is not just the total power generation. If possible, check the operating status of each device, any output imbalances, the presence of communication errors, and the history of stoppages and recoveries. In facilities with multiple converters, even if the total power generation appears slightly low, in reality only some devices may have stopped. In that case, looking only at the total power generation makes it difficult to identify where the anomaly is. If you can view output on a per-device basis, understanding the extent of the decline will make consultations more specific.

If there are alarms or error displays, record the displayed content exactly as shown. Even if you do not understand the technical meaning, it is important to note the displayed text, any codes, the time of occurrence, the time of recovery, and whether the condition is ongoing. Clearing alarms or repeatedly restarting equipment on your own can make it harder to trace the history needed to investigate the cause. Except for actions required for safety, if you are unsure about operating the equipment, do not touch it unnecessarily; it is safer to record the display and seek advice.

Be aware of communication faults. Even if the values on the monitoring screen are low or not being updated, the actual power generation equipment may not have stopped. Power output can appear low for reasons such as interrupted communication, measurement data not being transmitted, or display updates having stopped. When you suspect a drop in power generation, also check the monitoring data’s last update time and the communication status. It is important to distinguish whether the issue is an actual fault in the power generation equipment or a problem with monitoring or measurement.

If there are on-site display devices, it is useful to be able to check whether the displayed information matches the monitoring screen. If remote monitoring shows a low reading but the local display indicates operation, communication or data integration problems may be suspected. Conversely, if the local display also shows a stop or an alarm, an inspection of the equipment is likely required. However, tasks that involve entering the interior of electrical equipment or opening panels are dangerous, so do not perform them without the required qualifications or authority.

Before consulting, it is useful to keep the information you collected as screenshots or photos of the screen and as notes with dates and times. Rather than saying verbally that “I think an error occurred,” showing the actual display is more accurate. If you compile the periods of low power generation, the dates and times when alarms occurred, the status of equipment shutdowns, and the communication status together, the service provider will find it easier to determine the necessary scope of checks and to prioritize on-site inspections. The accumulation of small records leads to earlier detection of drops in power generation.

Preparation 4 Check for shadows, dirt, and surrounding changes within the visible range on site

When power output is low, it is also important to check for shadows, dirt, and changes in the surrounding environment within the visible area on site. Because solar panels are installed outdoors, they can be affected by bird droppings, fallen leaves, dust, pollen, yellow sand (Asian dust), snow accumulation, or the overgrowth of vegetation. In addition, if new buildings or temporary structures are erected nearby or trees grow taller, shadows that did not exist before may fall on the power-generating surface. These kinds of changes can be difficult to detect from monitoring data alone, so on-site inspections are helpful.

However, any checks should be conducted only within ranges that appear safe. You should avoid actions such as climbing onto the roof, getting too close to electrical equipment, opening electrical panels, or attempting to take photographs from heights or in muddy or unstable conditions. It would be counterproductive if investigating the cause of low power generation led to hazards such as falls or electric shocks. What operational staff should do before consulting a professional is not specialist work, but to assess the situation from a safe position and gather information and materials that can be passed on to the contractor.

When checking shadows, it is important to see which areas are shaded at which times of day. Whether shadows occur only in the morning, remain around midday, or spread widely in the evening affects power generation differently. In particular, in winter the sun’s altitude is low and shadows stretch longer, so shadows that weren’t a problem in summer can cause a drop in output. Before a consultation, if possible visit the site at different times of day so it’s easier to explain whether shadows are present.

Regarding soiling, sometimes the entire power-generating surface is lightly dirty, while other times dirt is concentrated only in certain areas. Even localized soiling such as bird droppings or fallen leaves can affect power output depending on installation conditions and circuit configuration. Also, equipment installed at a low tilt angle or in environments where dust is easily airborne may be more prone to soiling. If soiling is visible to the naked eye, record the location where it occurs, the extent, and when it began to become noticeable.

Overgrowth of vegetation is another factor that is easy to overlook. For ground-mounted installations, surrounding weeds and trees can grow and cast shadows on the panels. Trees along fences or site boundaries, and plantings on neighboring land, may be affecting the system and are not easily managed by your company. Because the impact of vegetation changes with the seasons, check whether the period of reduced power generation coincides with the vegetation growth period. Keeping photos makes it easier to share the situation with contractors and management personnel.

Examples of surrounding changes to check include temporary construction scaffolding, materials, vehicles, signs, antennas, air-conditioning equipment, and additional rooftop installations. Even if the power generation equipment itself shows no abnormalities, changes in the surrounding environment can alter sunlight conditions. In particular, on building rooftops and within factory premises, equipment upgrades or layout changes can change how shadows fall. If the period when power generation decreased is close to the time when something changed in the surroundings, be sure to report this during consultation.

Preparation 5 Summarize the consultation topics to convey to the contractor and the items to confirm

After you have organized records of power generation, the weather, monitoring screens, and on-site conditions, finally summarize the points to communicate to the contractor. What’s important here is not to stop at “The power generation is low, so please check,” but to specify what you want them to check. The contractor is a specialist, but they will not necessarily know all the on-site conditions and day-to-day changes. By clearly conveying the information held by the person responsible for operations, it becomes easier to align the direction of the inspection.

In your inquiry, first specify the period during which you felt the power output was low. Clarify when it became low, whether it is still ongoing, or whether it was temporary. Next, indicate what you compared it to: whether you compared it with the same month last year, with the most recent sunny day, with the expected generation, or with other installations. If the comparison baseline is unclear, the contractor will find it difficult to assess the extent of the power drop.

Next, describe how the decline appears. Organize whether the output is low overall, only certain pieces of equipment are low, it dips only at specific times of day, it dropped suddenly, or it is gradually declining. If you can view the power generation curve, changes in its shape are also important. On clear days it usually follows a smooth, mountain-like shape, but if it suddenly falls midway, levels off at a certain ceiling, or is unusually weak only in the morning or evening, report these characteristics when consulting.

If there is an alarm on the monitoring screen or equipment display, share the displayed content as is. You do not need to over-interpret its meaning yourself. Rather, it is important to convey exactly what was displayed. Also record the occurrence date and time, duration, whether recovery occurred, and whether the same alarm is repeating. If a communication failure is suspected, also report the monitoring screen’s update time and whether there is missing data, as this makes it easier to distinguish between a problem on the power generation equipment side and a problem on the monitoring side.

For site conditions, briefly summarize changes that could affect power generation, such as shadows, dirt, snow cover, vegetation, nearby construction, and equipment modifications. If you have photos, it's helpful to indicate the date/time they were taken and the shooting location. If the same location is photographed at different times of day, changes in shading will be easier to see. Rather than sending photos alone, include brief explanatory notes—for example, "in the morning a portion on the south side is shaded" or "recently the neighboring trees have grown"—to make the situation clearer.

When consulting, organize the items you want to confirm with the service provider. For example: whether they can check the equipment shutdown history; whether an on-site inspection is necessary; the extent of what can be checked remotely; whether there are any checks that should be done before cleaning or weeding; and how many days of data are needed to determine whether a decline in power generation is temporary or ongoing. If you prepare your questions in advance, subsequent communications are less likely to become disorganized.

Considerations for Smoothly Handling Consultations on Reduced Power Generation

When consulting about low power generation, the desire to know the cause quickly comes first. However, the cause of reduced power generation is not necessarily singular. In addition to reductions caused by weather, there may be cases where dirt and shadows overlap. There may also be situations where part of the equipment has stopped while monitoring data communication failures are occurring simultaneously. Therefore, in consultations it is important to avoid definitive statements such as "the equipment must be broken" or "cleaning will restore it," and to communicate separately the facts that have been confirmed and the points that are suspected.

Also, it is important not to operate equipment excessively based on your own judgment. Power generation equipment involves electrical hazards, and incorrect operation can lead to safety problems or adversely affect the equipment. Even if power output is low, you should avoid needlessly operating switches or circuit breakers, repeatedly stopping and restarting equipment, or checking inside panels. Whether an operation is necessary should be determined in accordance with management rules and the instructions of specialist contractors.

Be careful about how you record data. Rather than keeping only the data from the moment you notice a drop in power output, also retain the data from before and after that moment, because it makes assessment easier. This allows you to check whether things were normal up until just before the anomaly, whether output declined gradually, or whether it returned to its original level after recovery. If you isolate only the day of the output drop, you may overestimate the impact of weather or temporary control actions. Looking at the flow before and after adds depth to your consultation.

When multiple people manage equipment, consolidating information is also important. If the on-site person, the manager, the person handling accounting or monitoring power sales performance, and the maintenance contact each hold different information, consultation matters can easily become fragmented. Before contacting a contractor, organize who has checked which information and which data will serve as the official basis for consultation to prevent duplicate contacts and inconsistent explanations.

Even when a decline in power generation affects project cash flow or operational plans, it is important not to rush to judgment based on a single data point. Daily generation can vary greatly with the weather, and monthly generation is also influenced by meteorological conditions. While it is necessary to be vigilant for potential abnormalities, without a perspective that separates natural variation from equipment faults you may end up with unnecessary investigations or incorrect countermeasures. Preparing before seeking consultation provides the foundation for making calm, well-reasoned decisions.

When consulting a service provider, convey the level of urgency as well. The priority of the response will vary depending on whether power generation has completely stopped, only part of it is low, alarms are continuing, or there are safety-related abnormalities such as smoke, unusual odors, strange noises, or burn marks. If a safety-related abnormality is suspected, prioritize ensuring safety over analyzing power output, and avoid forcing continued on-site inspections. Even when the consultation is about low power output, always organize and provide safety-related information.

Summary: When power generation is low, organize your records before consulting

Before consulting a contractor when power generation is low, it is important to organize the power generation trends, the effects of weather and season, monitoring screens and device displays, on-site shading and soiling, and the items you want to check during the consultation. A drop in power generation can be caused not only by equipment failure but also by multiple factors such as solar irradiation conditions, temperature, shading, soiling, communication errors, and changes in the surrounding environment. If you consult without preparing, it can take longer to isolate the cause and necessary checks may be postponed.

As an initial preparation, check daily and monthly power generation to clarify when the decline started, how large it is, and what it is being compared against. Next, organize the effects of weather and seasons and consider whether the decrease can be explained by natural conditions. Furthermore, check alarms on monitoring screens and device displays, communication status, and output differences among devices to gather clues of abnormalities. On site, within a safe range, look for changes such as shading, dirt, vegetation, and nearby construction, and record photos and notes. Finally, if you summarize what to tell the contractor and the questions you want them to check, the consultation will be more concrete and the response is more likely to be accurate.

The important thing is not to conclude the cause of low power output before consultation. The preparations that operations personnel should make are not a substitute for a professional diagnosis, but rather gathering information that makes it easier for specialists to assess. When records are in order, it becomes easier to distinguish between issues that can be resolved by remote verification, those that require on-site inspection, those that warrant consideration of cleaning or weeding, and those where equipment checks should be prioritized. As a result, unnecessary back-and-forth is reduced and it becomes easier to proceed with measures to address reduced power output.

To operate a solar power generation system reliably, it is important not only to respond when output is low but also to routinely keep records in an easy-to-read format. If generation data, on-site conditions, inspection history, and consultation history are consolidated, it becomes easier to detect signs of abnormalities early. When you notice a decline in output, instead of hastily assigning a cause, start by organizing the information needed for consultation. Recording daily generation and establishing a system to review it alongside weather and on-site changes is the first step to making consultations with service providers proceed smoothly.