5 Checks for Export Meter Abnormalities When Power Generation Is Low

When you feel the power output is low, many sites first suspect the weather, dirty panels, shading, a stopped power conditioner, string faults, and so on. These are typical causes of reduced generation, but if no major abnormalities are found on the generation equipment side and only the amount of electricity sold is unusually low, it is also necessary to check around the sales meter.

The feed-in meter is an important metering point for determining the amount of electricity generated that has been sent into the grid. If the generation equipment's monitoring screen appears to show sufficient generation but the feed-in statements or meter readings show less, the discrepancy may lie not in the generation itself but somewhere in the metering, communication, recording, contracting, or reading.

However, export meters should not be disassembled or have their seals tampered with without authorization. Even when you suspect an anomaly, it's important to organize what can be checked on site and accurately communicate the situation to the relevant parties. This article explains five items to check before suspecting an export meter malfunction, presented in a form that's easy to use for on-site troubleshooting, aimed at operational staff who are searching for the cause with queries like "low power output".

Table of Contents

• Clarify the assumptions under which the export meter should be suspected when power generation is low.

• Check 1: Are you confusing generated electricity with sold electricity?

• Check 2: Do the meter readings and monitoring data cover the same period?

• Check 3: Are there any unusual changes in meter displays or recorded values?

• Check 4: Confirm delays in communication, remote meter reading, and data updates

• Check 5: Review surrounding conditions such as wiring, power outages, and replacement history

• Safe steps to take when you suspect an abnormality in your electricity export (sell-back) meter

• Summary When power generation is low, check the equipment side and the metering side separately

Clarifying the assumptions for suspecting the export meter when power generation is low

When judging that power generation is low, the first thing to clarify is what you are looking at to judge it as "low." In solar power generation systems, there are multiple similar figures such as the monitoring data of the generation equipment, the cumulative generation reported by the power conditioner, the meter readings of the feed-in meter, the energy amounts on the feed-in statements, and the monthly generation in the management ledger. These may sometimes be used interchangeably, but in practice they may not simply match because the measurement locations and aggregation periods differ.

For example, the display on the generation equipment side may indicate the amount of generated electrical energy acquired by the power conditioner or monitoring device. On the other hand, the sales meter is installed at the point where the amount of electricity sent to the grid is measured. In systems with self-consumption, systems where auxiliary equipment or monitoring devices consume power, or systems where the relationship between received and sold electricity is complex, the amount of electricity generated within the facility may not match the amount actually measured as sold.

Also, there are various criteria behind perceiving that power generation is low, such as comparisons with the same month in the previous year, with the previous month, with nearby installations, with the expected simulation, and a sense of discrepancy from the amount on the power sales statement. Before suspecting a problem with the power sales meter, you must first align the comparison targets. If you compare a month with low solar irradiance to one with high irradiance, or a month that includes the start-up date to a normal month, the output can appear low even when the meter is functioning correctly.

The export meter is not the cause of reduced power generation; it is the point where the result is measured. Therefore, you should suspect a meter malfunction when there is an inexplicable discrepancy between the condition of the generation equipment and the export figures. A common on-site case is when monitoring data shows sufficient daytime output, yet the exported energy on the sales statement appears extremely low. Also, be cautious when multiple sections within the same plant experience similar irradiance conditions but only a particular metering point shows an anomalous trend.

However, you should avoid assuming that the export meter is faulty. In addition to a failure of the meter itself, there are many factors that can produce similar symptoms, such as misalignment of the meter-reading period, delays in data being updated, communication failures, meter replacements, power outages, contract changes, output control, equipment shutdowns, breaker operations, and transcription errors in records. The important thing is to work through them in order and distinguish whether the issue is an actual generation problem on the equipment side, a reading error on the metering side, or a problem with administrative processing or period settings.

The lower the power output, the stronger the urge to find the cause quickly. However, if you rush to suspect only the meter, on-site inspections and contacting related parties can become a detour. First, separating and considering "the amount of electricity generated by the power generation equipment," "the amount of electricity consumed on-site," "the amount of electricity exported to the grid (sold)," and "the amount of electricity reflected in bills and statements" is the first step to identifying an abnormality in the sales meter.

Check 1: Are you mistaking the difference between generated electricity and electricity sold?

When you suspect an anomaly with the feed-in meter, the first thing to check is whether generation and sold electricity are being treated as the same figure. Generation often refers to the amount of electricity produced by the solar panels and output to the AC side through the power conditioner. On the other hand, sold electricity refers to the amount of electricity sent to the grid and measured by the feed-in meter. In systems that sell all generated power, the values may be close, but differences can occur depending on the equipment configuration and the measurement location.

When you feel the generated output is low, there are cases where the generation shown by the monitoring device is compared directly with the energy on the sales statement. However, if the monitoring device displays a cumulative value on the generation side while the sales statement shows the energy at the metering point, factors such as receiving and transformer equipment, on-site loads, auxiliary power supplies, measurement errors, communication losses, and differences in aggregation periods can come between them. If you conclude that "the meter is measuring less" without understanding this difference, you may overlook other actual causes.

In systems with on-site consumption, some of the electricity generated is used within the facility, so the amount of electricity sold is less than the amount generated. Even if generation is sufficient, if daytime on-site consumption has increased, the energy shown on the export meter can look low. When combined with factories, warehouses, offices, agricultural facilities, charging equipment, etc., you need to check not only generation but also changes on the consumption side. If changes such as new equipment being added, operating hours changing, or increased use of air conditioning or pumps occur, it may appear that only the exported electricity has decreased.

Even when operating close to selling all generated electricity, the generation recorded by the monitoring device and the value on the export meter do not necessarily match exactly. If the measurement locations differ, losses in transformers and wiring, consumption by auxiliary equipment, and rounding of measurement units can affect the readings. A small discrepancy on a daily basis can appear as a noticeable difference when viewed on a monthly or yearly basis. What matters is not the existence of a difference itself but whether that difference deviates significantly from historical trends.

As a procedure for verification, first place the cumulative value from the power generation equipment and the meter reading from the feed-in (sales) meter for the same period side by side. Next, examine how the difference has developed over the past several months or in the same month of the previous year. If there is a consistent difference each month and the proportion has not changed significantly, the discrepancy is likely a normal one due to the system configuration rather than a meter fault. On the other hand, if the difference suddenly becomes large from a certain month, or if the amount sold drops unnaturally relative to solar irradiation conditions, it is worth proceeding to check the metering side and the surrounding conditions.

One point to note here is not to limit the causes of low generation to the export meter alone. If the generation itself is low, you need to check for panel soiling, shading, power conditioner shutdown, string disconnection, abnormalities in the junction box, output control, and weather conditions. You should suspect an export meter malfunction when there is no significant drop visible in the data from the generation equipment but only the export-side figures are low. Simply distinguishing between generated output and exported energy can greatly clarify the direction of the investigation into the cause.

Check 2: Are the meter readings and monitoring data periods aligned?

One reason that can easily lead to mistaking a feed-in meter for being faulty is a mismatch in the reporting period. The generation system’s monitoring screen may allow you to check generation by day, by month, or for custom periods. On the other hand, feed-in meter readings and feed-in statements do not necessarily represent generation from the first to the last day of a calendar month. If the meter reading date falls mid-month, the period covered by the feed-in statement will differ from a calendar month.

For example, monitoring data may show power generation from April 1 to April 30, while the sales statement may cover electricity from mid‑March to mid‑April. If you compare the two as they are, differences in weather, days when generation was stopped, and whether output control was applied will be reflected out of sync. In periods when solar irradiance conditions change easily—such as spring and autumn—during the rainy season or typhoon season, or when there is snow or yellow sand, merely the difference in the covered period can greatly change the perceived amount of generation.

What you need to check is whether the usage period or meter-reading period shown on the feed-in statement, the previous and current meter readings, and the period extracted from the monitoring device all match. If the periods do not match, you need to re-extract the generation data from the monitoring device for the same date range as the feed-in statement. If you can retrieve daily data, summing it from the feed-in statement’s start date through its end date will improve the accuracy of the comparison.

Also, attention is needed regarding the date boundaries of monitoring data. Depending on whether the monitoring device aggregates with a midnight cutoff or depends on the time of data retrieval, and on how days with missing data are handled, daily and monthly totals can differ. If remote monitoring communications were temporarily interrupted, data may later be supplemented, or may remain missing. A low reading on the monitoring screen does not necessarily mean that actual power generation was low.

On the meter side, meter replacement or changes to the meter-reading method can alter how you interpret the readings before and after. In the month a meter replacement is carried out, you need to treat the final reading of the old meter and the initial reading of the new meter separately. If you simply join the values before and after the replacement, the amount of electricity sold may appear to have suddenly decreased or, conversely, increased. It is important to check the sales statements and management documents to see whether the meter replacement date, readings, and any changes to the measurement point are recorded.

For period verification, daily reconciliation is effective. Looking only at monthly totals makes it hard to see the cause, but lining up daily generation with daily or similarly granular sold electricity reveals the day from which the discrepancy widened. If sold electricity alone falls from a specific day, you can correlate it with events such as power outages, meter replacements, communication failures, breaker operations, output control, or equipment shutdowns. Conversely, if the entire month is slightly lower, consider influences such as weather, dirt, shading, self-consumption, and seasonal variation.

Before suspecting an export meter malfunction, simply confirming that you are comparing the same time periods can reduce unnecessary site inspections and inquiries to relevant parties. A sense that generation is low is an important starting point, but to assess that concern correctly it is essential to align the time periods of the figures you are comparing.

Check 3: Are there any unusual changes in meter displays or recorded values?

If a large discrepancy remains after aligning the time periods of the generation equipment data and the amount of power sold, check the export meter’s displayed and recorded values. What you should look at here is not opening the meter itself but the display values that can be safely checked from the outside, meter-reading records, past indicated readings, and trends in the power-sales statements. Do not touch sealed parts or sections managed under contract; compile any signs of abnormalities within the range you can verify.

First, focus on how the meter readings increase. If there are consecutive sunny days and the generation equipment is producing output during the day but the export meter’s reading hardly increases, you need to check around the metering point. However, in systems with high self-consumption, there can be periods when the amount exported is small even though generation is occurring. Also check at the same time whether on-site load has increased during the day or whether the generated electricity is being used within the facility.

Next, check whether the export meter reading shows a sudden discontinuity. Normally, cumulative readings tend to increase over time. If the current reading appears smaller than the previous one in the records, possible causes include meter replacement, misreading of digits, recording errors, or confusion between display items. It does not necessarily mean the meter itself has failed. If the meter has multiple display items, you need to verify that you have not mistaken the export-side value for the import-side value, time-of-use values, or other display selection items.

Taking photos on site can also be useful. Recording the meter display, the date and time the photo was taken, the condition of the surrounding panel, the presence or absence of warning indicators, the condition of any seals, and the meter number or management number as far as they can be confirmed will make it easier to explain things to relevant parties later. However, follow the facility’s rules when photographing and recording, and handle any captured personal or contract information with care. If multiple on-site personnel are present, it is also important to standardize the reading procedure so that everyone looks at the same display and records the same values.

Pay attention to the meter readings on the feed-in statement. Often the difference between the previous reading and the current reading on the statement is treated as the amount of exported electricity, but that difference may include corrections or adjustments related to meter replacement. Rather than judging based only on the readings, check the statement’s billing period, the metering point, contract details, any notes, and the continuity from the previous month. By looking not only at the month with a sudden drop but also at the months before and after, it becomes easier to determine whether it was a single-month recording error or a continuing anomaly.

Also, when a plant has multiple feed-in meters or multiple power conditioners, comparisons can be helpful. If equipment on the same site receiving similar solar irradiance shows that only one metering point has an extremely low amount of electricity sold, it becomes easier to suspect a problem specific to that metering point. Conversely, if the output is uniformly low by the same proportion across the board, factors other than the meters—such as weather, output curtailment, grid-side constraints, or the shutdown of common equipment—must be considered.

When checking meter displays and recorded values, the important thing is not to immediately conclude a fault when you find an apparently abnormal number. On site, misreading the display items, overlooking the number of digits, differences in units, misunderstanding the meter-reading date, and replacement history that has not been reflected can occur. To suspect an export-meter anomaly, it is necessary—by comparing with past trends—to clarify when it started, to what extent, at which metering point, and which specific data are abnormal.

Check 4: Verify delays in communication, remote meter reading, and data updates

Causes for an apparently low amount of electricity sold include not only metering faults in the meter itself but also communication or data reflection issues. When using remote meter reading or monitoring systems, even if the on-site meter is correctly registering the totals, the data reflected on the management dashboard or in reports can be delayed or missing. In such cases, the generation may not actually be low; rather, the displayed data may simply not yet be reflected or may be incomplete.

Communication problems can occur in mountainous areas, suburban areas, newly developed sites, and other places where the communication environment is unstable. Various factors such as the antenna position, power supply to communication devices, temperature inside the panel, recovery after power outages, the status of the communication contract, and configuration changes after equipment upgrades can prevent data from being transmitted. Sometimes monitoring data from the power generation equipment side is missing, while in other cases only the meter reading data from the feed-in meter is delayed. It is important to identify which data are missing and check them separately.

What you need to check is whether the local meter’s displayed value matches the value you are seeing remotely. If the on-site display shows the meter advancing but the management dashboard hasn’t changed since the previous day or several days earlier, a communication or update delay is suspected. Conversely, if the dashboard shows low generation but the on-site meter reading and the power conditioner’s cumulative value are increasing normally, that can likewise be identified as a problem on the data acquisition side.

In cases of communication errors, the figures in monthly reports and electricity sales statements may be revised later. Confusing preliminary figures, provisional aggregates, and finalized figures can lead to prematurely concluding that generation is low. In particular, at the beginning of the month or immediately after a meter reading, the data may not yet be finalized. If preliminary figures are transcribed into internal management sheets and not updated with the later finalized figures, the low numbers can persist.

When checking for delayed data updates, focus on daily gaps and sequences of identical values. If a day that should have been sunny shows values close to zero, if exactly the same value persists for several days, or if unusually large values appear all at once on the day communications are restored, these patterns may indicate a data acquisition problem rather than an actual drop in generation. What looks like a malfunction of the export meter may actually be an issue with the communication device or the aggregation system.

Also, remote monitoring data and the official electricity sales statement serve different purposes. Remote monitoring is convenient for understanding daily conditions, but it can be affected by communication outages and configuration settings. The sales statement is treated as a metered document, but you need to understand the meter‑reading period and the timing of when amounts are reflected. Rather than making a judgment based on just one source, cross‑checking the on‑site display, monitoring data, statements, and inspection records is the quickest way to prevent incorrect conclusions.

Problems with communication, remote meter reading, and data reflection can present symptoms similar to an export (feed-in) meter malfunction. That is why it is important to check the flow of data before suspecting a failure of the meter itself. By tracing where the numbers change—from being measured on site, transmitted via communication, displayed on the management screen, to being reflected in statements and reports—you can more accurately isolate the cause of low power generation.

Check 5: Review wiring, power outages, replacement history, and other surrounding conditions

When you suspect an anomaly with the export meter, you need to check not only the meter itself but also the surrounding conditions. The meter is installed at the metering point, but between the generator and that point there are wiring, switches, transformer/substation equipment, protective devices, communication equipment, power supply, terminal connections, the environment inside the panel, and so on. Even if the generation equipment appears normal, changes in the conditions around the metering point can affect how the exported electricity is measured.

What I want to check first are the histories of power outages, grid-side shutdowns, and equipment-side stoppages. If there were days with power outages, days when the grid interconnection was temporarily stopped, days when switches were operated for maintenance inspections, or days when power conditioners were shut down, the amount of electricity sold during those periods will be lower. Cross-check site daily work reports, inspection reports, monitoring alerts, power-related notifications, work permit records, and so on, and verify whether they coincide with the periods of reduced electricity sales.

Next is the history of meter replacements and metering-point changes. Meters may be replaced during long-term operation. When a replacement occurs, you need to confirm the old and new meter readings, the date and time of the replacement, and how the carried-over reading is handled. If the amount of electricity sold is extremely low only in the month of replacement, or if the continuity of the readings looks unnatural, checking the replacement history is essential. Having records in the management ledger or the statement, or being able to confirm them with relevant parties, will speed up the response.

The condition of wiring and the inside of panels should also be organized as items for inspection by specialist contractors. It is dangerous for on-site personnel to force open panels or approach energized parts. Record any visible abnormalities, burnt odors, unusual noises, warning indicators, traces of rainwater ingress, flooding around the panel, effects from animals or plants, abnormalities after lightning strikes, etc., to the extent that it can be done safely. If there are signs of abnormality, it is important to request an inspection by personnel with the appropriate qualifications and authority.

Also check whether construction or renovation at the power plant has affected the amount of electricity sold. If there have been panel additions, power conditioner replacements, substation equipment upgrades, communications equipment replacements, changes to monitoring device settings, or changes to grid interconnection conditions, the way generation and sold electricity appear can change. After equipment upgrades, if the data measurement points have changed or values from the old equipment and the new equipment are treated in the same management sheet, it may look as if output has decreased.

Output curtailment and grid-side constraints must not be overlooked. If output curtailment is applied, even under solar irradiance conditions capable of generating power, the amount of electricity actually sent to the grid may be limited. In this case, a low amount of electricity sold does not indicate a meter malfunction. Check monitoring data, control histories, the status of the power conditioner, and notification records to administrators to see whether any curtailment or shutdown occurred during the period of reduced output.

When you suspect an abnormality in the export meter, recording the surrounding conditions is particularly helpful. If you cannot determine the cause from the meter readings alone, comparing them with a history of what happened on site will reveal reasons for the decrease. In investigations into low power generation, it is important to take an approach that checks equipment, metering, communications, contracts, and work history together.

Safe steps to take when you suspect an abnormality in the feed-in meter

Even when the likelihood of an abnormality in the power export meter increases, on-site personnel should not, on their own, disassemble it, alter wiring, remove seals, or inspect its interior. The power export meter is a critical device related to contracts and metering, and must be checked in accordance with the roles of the relevant parties—such as the administrator, the electric utility, safety authorities, the construction contractor, and the inspection company. Following proper procedures is essential not only for safety but also to protect the reliability of the metering values.

The first thing to do is to organize the facts. Summarize which figures you have judged to be low, what the period in question is, what the comparison reference is, what the value on the generation equipment side is, what the value at the feed-in meter side is, and how large the difference is compared with past values. If you rely only on subjective impressions here, it will be difficult to isolate the cause even when consulting related parties. It is important to make clear "since when," "at which metering point," "which data in particular," and "to what extent" the values are low.

Next, record what can be safely confirmed on site. Gather photographs of meter displays, the date and time the photos were taken, screenshots of monitoring data, power sales statements, inspection records, alert history, and records of outages and work. When taking photos, it is important that the displayed values are readable, the shooting date is identifiable, and the same meter is being recorded continuously. At sites with multiple meters, take care not to confuse meter numbers or installation locations.

When contacting relevant parties, it is better to say things like "there is a discrepancy between the cumulative reading on the generation equipment side and the indicated value on the sales meter that differs from past trends," "there is a difference between the on-site display and the remote data," or "even when aligning the meter-reading periods, only the amount of power sold is low," rather than definitively stating "the meter is broken." Definitive expressions can cause confusion if another cause is found later. In practice, it is appropriate to request a check while presenting the basis for your suspicion.

Also, the longer a period of low electricity sales continues, the more difficult it becomes to investigate the cause. If daily records are not kept, it becomes impossible to cross-check weather, stoppages, control actions, communication losses, and work history. When you sense something amiss, it is important to save daily data and compile related documents. Sometimes you only notice after the monthly statement arrives, but even then, check the solar irradiance conditions, monitoring data, and inspection records for the relevant period as soon as possible.

In investigations of anomalies in power export meters, both equipment-side expertise and meter-side verification may be required. Inspection of the generation equipment alone may not be enough to determine metering issues, and checking only the meter side can miss abnormalities in the generation equipment. To quickly identify the cause of low generation output, it is effective to have a structure in which the site manager, chief electrical engineer, maintenance and inspection personnel, installation contractor, and power company personnel work through the diagnosis together while viewing the same documentation.

One thing to be especially careful about is stopping your response because you assume a drop in sold electricity is due to a meter malfunction. In reality, it can also be caused by partial shutdowns of the power conditioner, faults in the junction box, increased shading, growth of vegetation, dirt, deterioration of insulation, output control, loss of communications, and so on. It is necessary to consider a meter malfunction, but it should be treated as one possible cause, and it is realistic to proceed in parallel with inspections of the equipment.

A safe way to proceed is to gather information that can be determined without touching, align the conditions for comparison, and convey the findings accurately to the relevant parties. This enables you to efficiently narrow down the causes of low power generation while avoiding unnecessary hazardous work.

Summary: When power generation is low, inspect the equipment side and the metering side separately

When power generation is low, suspecting an export-meter malfunction is one important perspective for investigating causes. However, relying only on the export meter can cause you to overlook generation-side faults, period mismatches, communication failures, delays in data updates, increased self-consumption, output curtailment, power outages, or maintenance/work history. First, it is important to distinguish between generated power and exported power, compare them over the same period, and check for changes in meter displays and recorded values.

You should suspect an anomaly in the export meter when there is no significant drop on the generation-equipment side but only the export-side figures are unnaturally low. In that case, check in order the meter-reading period, the indicated values, the on-site display, remote data, communication status, replacement history, and records of outages or maintenance work. If you can determine when the discrepancy in the numbers began and in which data it appears, consulting with the relevant parties will proceed more smoothly.

On the other hand, the export meter is not a device that may be handled arbitrarily. Rather than interfering with sealed components or internal wiring, it is important to leave displays and records that can be safely checked and, when necessary, request confirmation from the administrator or a qualified professional. When investigating the cause of low generation output, you should adopt an approach that separates the equipment side from the metering side while protecting on-site safety and the reliability of the measured values.

Continuously collecting daily monitoring data, power sales statements, on-site photos, and inspection records makes it faster to isolate the cause when an anomaly is detected. A decline in power generation is easier to limit in terms of losses and rework the earlier the cause is found. If you want to centrally confirm the condition of generation equipment, including suspected abnormalities in the power sales meter, visualizing field data, storing daily data, organizing inspection records, and establishing rules for sharing among stakeholders will make it easier to determine causes and decide on responses.