Five differences between remote monitoring and on-site displays to check when power output is low

When you feel the power generation is low, the first things commonly checked are the generation shown on the remote monitoring screen, the on-site displays such as those of the power conditioners and measurement panels, and the records on the feed-in meter and the receiving equipment side. However, these figures do not necessarily represent the same thing even when looking at the same power plant. Remote monitoring often shows values aggregated as daily or monthly reports, while on-site displays may show instantaneous output or device-level status. If update times, aggregation ranges, measurement locations, communication conditions, or rounding differ, the generation may appear low even though in reality the only issue is that the display assumptions are misaligned.

In this article, we organize five differences between remote monitoring and on-site displays that operations personnel should check when power generation is low. Rather than simply assuming "the numbers in remote monitoring are correct" or "the on-site display numbers are correct," we aim to calmly narrow down the causes of reduced power generation by sequentially verifying which numbers are produced where, when, and based on what criteria.

Table of Contents

• Do not treat remote monitoring and on-site display as the same value when power generation is low

• Difference 1: Check the difference in aggregation periods and update timing

• Difference 2: Check the difference in measurement location and the target equipment

• Difference 3: Check the difference between instantaneous values and cumulative values

• Difference 4: Check the difference between communication loss and on-site abnormality indications

• Difference 5: Check the difference between correction conditions and display rounding

• Procedure for isolating the cause after confirming the differences

• Summary

When power output is low, do not treat the remote monitoring and the on-site display as the same value.

When you receive a complaint about low power generation, a common on-site mistake is to compare the numbers on the remote monitoring screen and the local display side by side as if they were equivalent. For example, the remote monitoring may make today's generation look lower than expected, while the local power conditioner display appears to be producing output. Conversely, the remote monitoring may not show a major anomaly, yet on site some equipment may be stopped, alarms may be active, or a displayed value may be lower than other devices. What matters in this situation is not to immediately assume one is falsely displaying data, but to consider that the numbers may be generated differently.

Remote monitoring is a mechanism for understanding the overall condition of a power plant from a remote location. Data are often aggregated by day, by month, by equipment, or by system and can be viewed as graphs or reports, making it suitable for comparison with past data. However, because it collects and displays information acquired from on-site equipment and measurement devices via communications, communication delays, data loss, differences in aggregation timing, and screen refresh intervals can affect the numbers. The values shown on the screen do not necessarily reflect the current on-site state simultaneously.

On the other hand, on-site displays provide information that can be checked near the equipment or control panels. They may allow detailed viewing of each device’s status, such as power conditioner output, input voltage, input current, operating status, alarm history, and cumulative power generation. Because they are checked directly on-site, they have the advantage of being less affected by communications, but if you mistake whether the displayed scope is the individual device, multiple strings, or the entire system, it will not agree with the overall values from remote monitoring. Also, on-site displays often show instantaneous values, which differ in nature from remote monitoring’s daily or hourly totals.

When investigating low power generation, you should first confirm whether the figures are "for the same time", "for the same period", "for the same equipment scope", and "for the same measurement point". If these are not aligned, judging that there is a discrepancy may lead you in the wrong direction for the root-cause investigation. The phenomenon of low power generation can include various factors such as actual equipment faults, solar irradiance conditions, shading, soiling, output curtailment, equipment shutdowns, communication failures, and aggregation delays. Organizing the differences between remote monitoring and on-site displays is an entry point for isolating these factors one by one.

In practice, when low power output is detected, there are often situations where you want to immediately proceed to on-site measures or equipment replacement. However, if you act without first checking for display discrepancies, you may later discover that the problem was actually missing communication data, that the daily report's cutoff time differed, that the irradiance conditions used for comparison were different, or that only certain equipment had been checked on-site. To find the cause quickly, it is important to align the assumptions between remote monitoring and on-site displays from the outset.

Difference 1: Examine differences in aggregation period and update timing

The first differences to check are the aggregation period and the update timing. The power generation reported by remote monitoring is often displayed by aggregating data collected at fixed intervals, so the values shown on the screen are not necessarily final up to the current moment. For example, the "Today's generation" shown on a remote monitoring screen may be based on data from a few minutes ago, about ten minutes ago, or as far back as the last communication. By contrast, the on-site display shows the instantaneous output or values accumulated within the equipment, so if the two timestamps are out of sync, discrepancies will occur.

Before determining that power output is low, check the last update time on the remote monitoring screen. If the screen shows an update time, see whether that time is close to the current time. If the last update time is old, it may be that communications have stopped or data updates are delayed, rather than that generation is low. Especially during morning or daytime periods when generation is increasing, even a delay of tens of minutes can greatly change how the output appears. If there is output on site but the remote monitoring does not show an increase in generation, you should suspect delays on the communications side as well as equipment shutdown.

Also, the cutoff time of the daily report is important. A "day" in remote monitoring does not necessarily run from midnight 0:00 to 24:00; the aggregation boundaries can differ depending on the settings and the report specifications. If you check daily power generation by subtracting the cumulative values shown on-site, the numbers will not match unless the start and end times of that subtraction align with the remote monitoring daily report. At boundaries between yesterday and today, during month-end/month-beginning aggregations, or when re-aggregating after power outages are restored, shifts in the reporting period can appear as a decrease in generated power.

The same applies to hourly graphs. The hourly generation shown by remote monitoring may be displayed as the accumulated value for a given time period, while the on-site display may show the instantaneous output at that time. For example, if the remote monitoring graph labeled 11:00 actually indicates generation during the 10:00 hour, whereas the on-site display is showing the output at 11:00, the meaning of the numbers is very different. When trying to identify periods of low generation, you need to confirm whether the horizontal axis of the graph represents the time itself, the end of the time interval, or the aggregation interval.

Differences in update timing are more likely to be overlooked on days with large weather changes. On days when clouds move and solar radiation changes suddenly, after rain when irradiance recovers, or during morning and evening periods with large output fluctuations, a difference of just a few minutes can cause a big change in output. Even if the output you see on site at a given moment is high, the immediately preceding period may have been cloudy and generation may not have been rising. Conversely, a remote monitoring graph may look like it shows high output, but by the time you arrive on site clouds may have moved in and the output may have fallen.

In practice, it is useful to record together the display time from remote monitoring, the on-site verification time, and the time when the equipment display was recorded. If you only note “low generation in remote monitoring” and “no abnormalities on-site,” you will not know the comparison conditions when reviewing later. By clearly stating which remote monitoring value and which on-site display were compared, it becomes easier to determine whether it was an update delay or an actual drop in generation. In the initial response to low generation, it is more important to first check the consistency of the timestamps than the numbers themselves.

Difference 2: Comparing measurement locations and target equipment

The next thing to check is the difference in measurement location and the equipment being monitored. Whether the generation output shown on the remote monitoring screen is the total for the entire plant, per power conditioner, per combiner box, or per system will change how you compare it with on-site displays. Even if you look at a single device’s on-site display and judge that it is generating, if the remote monitoring covers the entire plant there may still be other devices that are stopped or operating at reduced output. Conversely, if you judge the generation to be low based only on values from some devices in the remote monitoring, you may be looking at different equipment on-site.

Solar power generation systems have multiple measurement points. The DC input on the PV side, the AC output of the power conditioner, meters near the point of interconnection, measurements on the substation side, and measurement devices for remote monitoring each observe power and energy at different locations. If the DC side shows a steady input but the AC-side output is low, you need to check the conversion equipment’s operating condition, control, and protection actions. On the AC side, if there is output but the remotely monitored generation readings are not increasing, it may be necessary to check the metering devices, communications, and aggregation settings.

When investigating the causes of low power generation, identify which measurement point the figures on the remote monitoring screen are coming from. For example, whether the system is collecting the accumulated value inside the power conditioner, obtaining it from an external energy meter, or the monitoring device is calculating it independently will affect how closely it matches the on-site display. If the on-site display shows the power conditioner’s output while the remote monitoring is looking at the energy on the point-of-interconnection side, they may not be exactly the same due to losses within the equipment, auxiliary consumption, and differences in measurement location.

You also need to pay attention to the scope of the equipment in question. In remote monitoring, multiple power conditioners may be grouped and displayed together. When a group’s power generation is low, you must check all devices included in that group on-site without omission. If you check only some devices and conclude there is no abnormality, you may overlook another device that has stopped. Conversely, even if a specific device shows low output on-site, that anomaly may be masked in the remote monitoring overall value by other devices and not stand out.

Also, even within the same power plant, natural differences in generation per unit can occur when orientation, tilt, shading conditions, or installation area differ. If remote monitoring shows low generation in a particular section, it is important when comparing with on-site readings to compare equipment under the same conditions. Simply comparing east-facing and west-facing units, shaded and open locations, or lower, dirt-prone positions and well-ventilated positions can lead to mistaking differences that are not equipment faults for abnormalities.

During on-site checks, recording the panel name, equipment number, circuit name, and type of display screen makes it easier to reconcile with remote monitoring. On site, similarly named equipment and panels are sometimes lined up, and misreading a number can cause an investigation to go off track. To correctly assess an instance of low power generation, it is essential to match which numbers represent which pieces of equipment. By accounting for the differences between the measurement location and the target equipment, you can turn discrepancies between remote monitoring and on-site displays into information useful for root-cause investigation.

Difference 3: Comparing Instantaneous and Cumulative Values

The third difference is between instantaneous values and cumulative values. When generation is low it is easy to confuse "how much power is being produced now" with "how much energy has been generated over a certain period." On-site displays often show output in kW, which indicates the strength of generation at that moment. On the other hand, daily and monthly generation figures, which are often the focus of remote monitoring, are accumulated values measured in kWh. Even if there are periods of high instantaneous output, if those periods are brief the daily generation will not increase much. Conversely, even if there are moments when instantaneous output appears low, if generation remains stable throughout the day the total production may not fall significantly.

When you feel the generated power is low, it is premature to conclude there is no problem just because output is present on site. For example, if the equipment was stopped in the morning and recovered in the afternoon, output may look normal at the time of the on-site check, but the day's cumulative generation will be low. The reason the daily generation shown in remote monitoring is low may be due not to the on-site status at the time of inspection but to a stoppage or reduced output during the past few hours. You need to check the remote monitoring hourly graph and the alarm history to determine from which time period the discrepancy arises.

Conversely, even if the on-site display shows low output, you cannot determine a decrease in daily power generation from that alone. Instantaneous output can fluctuate greatly due to cloud cover, morning and evening periods, rain, or brief passages of shadow. To judge whether generation is low, you need to look at past data for the same time of day, nearby systems or systems under similar conditions, and changes in solar irradiance and weather. Local instantaneous values are important information for understanding equipment condition, but when evaluating generation it is essential to use them with an understanding of their relationship to cumulative (integrated) values.

There are different types of cumulative totals. These include the cumulative generation recorded within the equipment, the daily, monthly, and annual totals in the remote monitoring system, and the totals on the sales meter; each has different starting points and aggregation criteria. Because cumulative generation is a long-term total, it does not directly indicate short-term drops. Daily totals are useful for checking the condition during a single day, but they are affected by solar irradiance conditions and by the time at which the total is aggregated. Monthly totals are convenient for observing trends, but declines over a few days can be buried in the overall figure. When investigating the cause of low generation, be clear about which period’s cumulative total you are looking at.

When using the cumulative value displayed on-site, the time at which you take the difference from the previous value is important. Simply looking at the cumulative value shown during an inspection will not tell you the energy generated on that day or during that time period. Only when you have a reference point you can subtract—such as the previous record, the start of the inspection, or the end of the inspection—can you evaluate the generation for the period. When comparing with remote monitoring values, you must also subtract using the same start and end times. If these do not align, on-site and remote monitoring generation may appear to disagree.

When you clarify the difference between instantaneous values and cumulative values, the way the causes of low power generation appear changes. If the instantaneous value is low, check the current operating state, solar irradiance, shading, input voltage, input current, output control, device alarms, and so on. If the cumulative value is low, check when the decline began, during which time periods the output is not accumulating, and whether there are stoppage times or communication losses. In this way, by treating instantaneous values as a snapshot of the present and cumulative values as the result over the entire period, you can correctly interpret differences between remote monitoring and on-site displays.

Difference 4: Distinguishing Between Communication Loss and On-site Abnormality Indications

The fourth difference is between communication loss and an on-site abnormality indication. If the remote monitoring shows low power generation or the graph is interrupted, that does not necessarily mean the equipment has actually stopped. If data is interrupted anywhere — between the monitoring device and equipment, on the communication line, during data transmission, or in the server-side reflection — remote monitoring can show a low power output. Even if the system is generating power normally on-site, the displayed generation will not increase if data is not reaching the remote monitoring.

A characteristic of communication loss is that not only the power generation data but other data often stop during the same time period. If updates to output, voltage, current, status signals, solar irradiance, ambient temperature, etc. stop simultaneously, suspect a communication-side problem as well as an equipment shutdown. If the remote monitoring graph remains flat at a constant value, data are blank, the last update time is outdated, or multiple devices become unavailable at the same time, you should verify this against the on-site display.

On the other hand, on-site abnormality indications may show operation stoppages, alarms, protective actions, input abnormalities, output abnormalities, and so on detected by the equipment itself. If an alarm or stop indication is displayed on-site, it becomes more likely that a drop in power generation observed by remote monitoring is actually caused by the equipment’s condition. However, on-site indications also have a distinction between history and current status. You must confirm whether an alarm that occurred in the past remains only as a historical record or whether the abnormality is still ongoing. If you judge from history alone that the system is still stopped, you may incorrectly attribute the cause to an event that has already been resolved.

When comparing remote monitoring with on-site indications, it is important to distinguish between communication faults and equipment faults. If a deterioration is observed in remote monitoring, first check the communication status at the same time, then check the on-site operating status. If the equipment is operating normally on-site while the remote monitoring data has stopped, investigate the communication system, the monitoring device, and the data collection settings. If a shutdown or alarm is confirmed on-site, investigate the equipment's protective actions, input conditions, system conditions, and installation and maintenance history.

What makes communication data loss troublesome is that sometimes the missing data are later filled in and sometimes they are not. Depending on the remote monitoring setup, unsent data may be reflected after communications are restored. In that case, even if power generation temporarily appears low, the daily report may later be revised. Conversely, if the data for the missing period are not recovered, the remote monitoring system may continue to show low generation even though generation actually occurred. When judging that power generation is low, checking whether data are missing and how those missing data are handled in reports will make later explanations easier.

During on-site inspections, you may check the power status of communication devices, indicator lamps, connection status, the time on monitoring equipment, and communication with devices. However, internal inspections of electrical equipment and restoration work must be performed based on safety management and authorization. If the situation exceeds the scope that operational staff can verify, it is important to hand it over to specialists or maintenance personnel according to the area of responsibility. When power generation is low, there is a greater temptation to act hastily, but simply distinguishing between communication loss and on-site anomaly indications can reduce unnecessary on-site work and incorrect device handling.

Difference 5: Viewing differences between correction conditions and display rounding

The fifth discrepancy is correction conditions and display rounding. Numbers shown on remote monitoring and on-site displays may, at first glance, appear to indicate the same power generation or output, but internally unit conversions, digit handling, averaging, corrections, and aggregation methods can differ. If the difference is small, it may be due to display specification differences rather than equipment malfunction. When you feel that power generation is low, if you start an investigation without evaluating the magnitude of the numerical difference, you may treat a display discrepancy as an actual anomaly.

Display rounding is a common, everyday source of differences. Values that appear with decimal places on local displays may be shown as integers or with fewer digits in remote monitoring. When summing values from multiple devices, slight discrepancies arise depending on whether you add individually rounded values or round after summing. In daily or monthly reports, the method of stacking hourly values and the method of using the difference between a meter’s start and end readings may not match exactly. It is necessary to determine whether a difference used to judge that power generation is low falls within the range of display rounding or represents a clear decline.

There are also differences in averaging. On remote monitoring graphs, one of the average, maximum, minimum, or cumulative values over a given time period may be displayed. Comparing the instantaneous output shown on site with the averaged output in remote monitoring reveals differences caused by passing clouds or temporary fluctuations. Especially on days when output fluctuates rapidly over short periods, it is natural for the instantaneous value seen on site to be higher or lower than the average. When checking periods of low power generation, confirm whether the graph shows an n‑minute average, a cumulative value, or sampled point values.

Attention must also be paid to correction conditions. Depending on the monitoring screen, it may display indicators other than generated energy, such as solar irradiance, equipment capacity, generation efficiency, and equipment utilization metrics. These differ from simple generation figures and may involve processing such as dividing by equipment capacity, comparing with solar irradiance, or comparing with a set reference value. When the search intent is that generation is low, users will often want to know the actual decrease in generated energy first, but you must confirm whether the indicator shown on the screen is the generation itself or an evaluated value derived from processed generation data.

Also, if the registered value of the system capacity is incorrect, evaluations in remote monitoring can be skewed. Even if the actual power generation is the same, if the reference capacity or comparison target is wrong, the result may appear lower or higher. If the on-site display is showing the rating or output of individual equipment while remote monitoring is looking at indicators based on the registered system capacity, it is necessary to check the registered information. In particular, after expansions, equipment replacement, setting changes, or updates to the monitoring device, it is reassuring to verify that the display conditions match the on-site equipment.

How far you take into account temperature and solar irradiance conditions also affects how differences appear. Photovoltaic power generation tends to increase when irradiance is strong, and high panel temperatures can affect output. However, the generation values shown by remote monitoring are not necessarily temperature‑corrected. Even when viewing irradiance and air temperature data together, interpretation changes depending on the sensor’s installation location, update timing, and distance from the asset. When attributing low generation to irradiance or temperature, it is important not to confuse the display conditions for generation with the data acquisition conditions for the meteorological measurements.

While you should not overreact to small numerical differences, you need to carefully follow up on discrepancies that cannot be explained by rounding or corrections. For example, if a particular device is clearly lower than others in a group of devices under the same conditions, if the difference between remote monitoring and on-site displays continues to widen, if cumulative readings do not increase during periods of sufficient solar irradiance, or if the timing of on-site alarms coincides with drops seen in remote monitoring, you should move beyond display specifications and proceed to verify the actual equipment condition. The purpose of checking correction conditions and display rounding is not to stop the investigation but to distinguish differences that require investigation from those that can be ignored.

How to proceed with isolating the cause after checking differences

After checking the five differences between remote monitoring and on-site displays, the next step is to pragmatically isolate the causes of low power generation. The first thing to do is to align the comparison conditions and determine whether a real drop in generation has occurred. If the remote monitoring update timestamp is outdated, the aggregation period is misaligned, the target equipment is different, instantaneous and cumulative values are being confused, or the discrepancy falls within display rounding, first correct the display and data assumptions and recheck. If the decrease still remains, examine causes on the equipment side, the environmental side, and the operational side.

When evaluating a low power output event from the equipment side, check the extent of the decline. Whether the entire plant is low, only some power conditioners are low, or only specific strings or sections are low will change the suspected causes. If the whole system is similarly low, consider weather, solar irradiance, output curtailment, grid-side conditions, total shutdown, or the influence of common/shared equipment. If only part is low, check localized factors such as equipment shutdowns, input-side abnormalities, fuses, connections, shading, soiling, or equipment settings.

Environmental factors are also important. Whether the low power generation occurs for just one day, continues for several days, or only during specific time periods changes how you interpret the effects of weather and shading. It is natural for generation to be low on cloudy or rainy days, but if it is clearly lower compared with other installations under the same solar irradiance conditions, inspection of the equipment side is necessary. If there is a tendency for low output only in the morning, only in the afternoon, seasonally low output, or step changes during specific time periods, consider shading, orientation, output control, delayed start-up, temperature conditions, and so on.

Operational causes include failure to restore systems after inspections, changes to device settings, power interruptions to communications equipment, breaker status after on-site work, changes to monitoring settings, and mismatches in registration information following equipment replacement. When power generation is low, comparing past work history with the time the decline began makes it easier to pinpoint the cause. If the start time of the decline in remote monitoring coincides with on-site work, power outages, lightning, typhoons, cleaning, equipment updates, or similar events, check how the local display and settings changed immediately before and after.

How you record information also affects fault isolation. If you record the time you viewed the remote monitoring screen, the period that was displayed, the name of the facility concerned, the device name shown on site, the time of on-site confirmation, the weather, whether any alarms were present, and whether any on-site operations were performed, it will be easier to explain the cause later. Reports that power generation is low tend to result in scattered information the more people are involved. Rather than relying only on a remote monitoring screenshot, only on-site photos, or only verbal reports, it is important to record data in a way that makes the assumptions behind the numbers clear.

Ultimately, instead of treating remote monitoring and on-site displays as opposing sources of information, combine them as information with different roles. Remote monitoring is suited to tracking changes over time, comparing multiple pieces of equipment, and reviewing past trends. On-site displays are suited to checking current equipment status, alarms, inputs and outputs, and verifying against the actual equipment. When power output is low, use remote monitoring to grasp the extent and timing of the decline, and then use on-site displays to confirm the equipment status and the device(s) involved at that time; this workflow reduces the risk of omissions in the investigation.

Summary

When power generation is low and the remote monitoring and on-site displays do not match, it can be difficult to know which figure to trust. However, in many cases it is not that one is simply wrong; rather, the assumptions may differ—such as the aggregation period, update timing, measurement location, monitored equipment, instantaneous versus cumulative values, communication status, correction conditions, and display rounding. First align the meanings of the figures, and then determine whether a real decrease has actually occurred.

With remote monitoring, you can determine the scope and timing of a drop in power generation from the last update time, hourly graphs, daily reports, and equipment-by-equipment comparisons. On-site displays allow you to check each device’s operating status, alarms, inputs and outputs, and cumulative totals. Combining both makes it easier to distinguish whether it is a communication loss, a difference in display conditions, an actual equipment shutdown, or environmental factors such as solar irradiance or shading. The more pronounced the low generation situation, the more important it is not to rush to conclusions; aligning the comparison conditions one by one is the quickest way to identify the cause.

In daily operations, recording the differences between remote monitoring and on-site displays and understanding how large a discrepancy is within the normal range helps detect anomalies early. During times when conditions are likely to change—such as inspections, cleaning, equipment replacement, communication recovery, or after typhoons and lightning strikes—the habit of checking remote monitoring readings and on-site displays at the same time, for the same target, and in the same units is useful. If you want to avoid missing declines in power generation and organize the causes clearly, it is important to establish a system that links and manages on-site records and remote monitoring data.