7 Things to Check in the First Month for Newly Installed Solar Power Systems with Low Power Output

When the power output in the first month from a newly installed solar power system seems low, it's natural to immediately suspect installation defects or equipment failures. However, the first month's generation is affected not only by the system's performance itself but also by various factors such as the grid connection start date, the metering period, weather, output control, measurement settings, delays in reflecting monitoring data, and remaining work after construction. Therefore, judging solely on impressions like "less than expected" or "lower than neighboring systems" risks misidentifying the cause.

Especially for newly installed solar systems, the first month may not be a full month of operation, and the monitoring equipment settings may not yet be stable. Even if the generation output appears low, it can actually fall within a reasonable range once adjustments for the number of days of operation and for solar irradiance conditions are taken into account. On the other hand, there are faults you especially want to detect early in the first month, such as unconnected strings, breakers left off, imbalanced current values, incorrect communication settings, and mismatches with the feed-in meter.

In this article, we organize seven items to check during the first month for newly installed solar PV systems showing low power generation, arranged in a flow that makes it easy for operational staff to assess both on-site conditions and data. Use these checkpoints to correctly interpret first-month figures and to separate issues that can be monitored from those that require early intervention.

Table of Contents

• Do not treat the first month's power generation as a full month's output.

• Item 1 Confirm the number of operating days and the grid connection start date

• Item 2 View solar irradiance and weather conditions for the same period

• Item 3 Check for discrepancies between monitoring data and on-site meters

• Item 4: Examine the output differences of each power conditioner

• Item 5 Check the current and connection status of each string

• Item 6: Verify whether output control or stop history exists

• Item 7 Check for the effects of shadows, dirt, and temporary structures after construction

• Use the first month's verification results as the standard for subsequent months.

• Summary

Do not treat the first month's power generation as a full month's worth

When you feel that power generation from a newly installed solar system is low, the first thing to be careful about is not to evaluate the first month's generation under the same conditions as a normal month. In the first month, the construction completion date, the grid-connection date with the utility, the date when the monitoring device begins communication, and the meter-reading period for the export/sales meter may not coincide. For example, even if the system actually began generating partway through the month, the monitoring screen may only show data from after communications started. Also, sales statements and meter-reading values may be aggregated for the period from one meter reading date to the next rather than by calendar month, so a simple comparison as a monthly generation can be misleading.

What you should look at in the first month is not only what percentage of the annual expected value has been achieved. First, you need to align the number of days that actually generated power, the hours during the day when it was offline, any weather bias, and the timing when measurement data started. A judgment that generation is low only makes sense when comparisons are made over the same period, the same conditions, and the same units. Right after installation these assumptions are prone to break down, so instead of immediately concluding that the equipment is underperforming, it is important to adjust the data's time period and scope.

Also, with newly installed solar power systems, commissioning runs and temporary shutdowns may occur before and after handover. There may be records showing only some circuits were operated during trial runs, that the system was run for a short time to check communications, or that it was stopped to verify protective devices. If these are included in the first month's totals, the average generation can appear lower. Therefore, you should consider that the first month's generation figures do not necessarily reflect only the stable operating state after completion.

In practice, rather than looking only at the total generation for the first month, you compare daily generation and operational status side by side. Are the days that generate close to expectations, but there are simply fewer operating days? Is the output clearly not reaching expected levels even on sunny days? Is there a large drop only on specific days? Is it consistently low every day? Depending on this perspective, the items to be checked change. For low generation in the first month, you need to start by distinguishing whether it is a period issue, an environmental issue, or an equipment issue.

Item 1 Confirm operating days and the start date of grid connection

For newly installed solar systems with low generation, the first things to check are the number of operating days and the grid connection start date. A common reason for low generation in the first month is that the system did not actually operate for a full month. If you compare the output to the monthly expected value assuming generation from the beginning of the month, a system that was connected partway through the month will look low. For example, if a system began exporting power in the latter half of the month and you compare it to that month's expected generation, the result will show low output. However, this is not necessarily an anomaly; it may simply be a mismatch in comparison conditions.

The grid connection start date is not necessarily the same as the date the installation became capable of generating power. Even if construction is complete, procedures for grid interconnection, verification of protection devices, checks by the utility, and configuration of monitoring equipment may not be finished, so stable generation may not be able to start. Also, even if the power conditioner is running on site, the period during which generation is recorded as sold electricity and the period reflected in monitoring data may not align. Therefore, when looking at the first month’s generation, you should check the date when the system was actually connected and able to continue generating power, not the construction completion date.

The basic check is to divide the first month's power generation by the number of days in operation and view it as the daily average. However, a simple daily average alone is not sufficient. Because sunny, cloudy, and rainy days are mixed, you need to examine it together with the weather for each day. Even so, adjusting for the number of operating days is closer to the actual situation than comparing it with the assumed value for a full month. In particular, when the system is connected near the end of the month, the monthly generation can appear significantly low, but a day-by-day view may show that there is no problem.

After the grid connection has begun, check whether there were any days when operations were stopped due to on-site circumstances. If there were temporary stoppages for touch-ups before handover, adjustments to communication settings, inspections around the cubicle or distribution board, or work connecting remote monitoring, those periods will not be reflected in the power generation. In the first month after a new installation, such stoppages tend to be scattered, so if you do not record the days and times of stoppage, you will not be able to trace the cause of low generation later.

Before evaluating the first month's power generation, the person responsible should at minimum confirm the grid-connection start date, the start date for power sales, the start date for acquiring monitoring data, the meter-reading period, and whether any manual shutdowns occurred. If you judge the generation to be low when these items are not all in place, you may needlessly suspect that functioning equipment is defective. On the other hand, if generation on sunny days remains low even after adjusting for the number of operating days, you should proceed to the next item to investigate the cause in more depth.

Item 2 Examine solar radiation and weather conditions over the same period

To determine whether generation is low, it is essential to check solar irradiance and weather conditions for the same period. Because solar power generation is strongly affected by sunlight, months with persistent cloudy or rainy weather will have lower output even if there are no issues with the equipment. If the first month after installation happens to coincide with a period of poor weather, the difference from the expected generation can appear large. Therefore, it is not appropriate to conclude construction defects or equipment failure based solely on the first month's generation.

What’s important here is to align the solar irradiance conditions with the same period as the power generation. If you look at monthly generation but use irradiance from a different period or from long-term averages, the accuracy of the comparison will decline. If the grid-connection start date falls mid-month, you need to check against the irradiance conditions from that date onward. Even if the first month’s generation is low, if much of the period in operation was covered by rain or thick clouds, the primary cause of the decrease may be weather.

However, it is dangerous to simply dismiss the issue because the weather was bad. Even under the same cloudy sky, power generation can change depending on the system’s orientation, tilt, surrounding shadows, dirt on the panel surface, and circuit configuration. On days with weak solar irradiance, abnormalities are hard to detect, and output differences may only become apparent when conditions approach a clear, sunny day. Therefore, it is important to choose a day within the first month when solar irradiance was relatively stable and check the power generation curve for that day.

When looking at a power generation curve, check whether it rises gradually from morning, reaches a peak around midday, and then declines in the evening. On days with many passing clouds the waveform becomes irregular, so it is difficult to judge an anomaly based on the shape of a single day alone. Even so, if there are tendencies such as output being extremely low on days close to clear weather, a sudden drop during the daytime, not rising beyond a certain level, or remaining low not only in the morning and evening but also during the day, you should suspect factors other than the weather.

Also, if there are nearby facilities of similar size, comparing the daily power generation and generation curves for the same day can be helpful. However, if the comparison facilities differ in orientation, tilt, capacity, shading conditions, or commissioning date, they will not produce exactly the same amount of power. Use such comparisons only as a guideline for detecting abnormalities, and it is important not to attribute low generation to a single cause.

In the initial month after commissioning, it is necessary to distinguish between natural declines due to solar irradiance and weather and declines caused by equipment-related problems. If you judge solely on total energy generation during periods of poor weather, this can lead to an increase in unnecessary on-site inspections. Conversely, if low generation persists even on sunny days, you should proceed to check the monitoring data, meters, power conditioners, and strings.

Item 3 Verify discrepancies between monitoring data and on-site meters

If you feel that power generation from a newly installed solar system is low, do not judge based only on the output shown on the monitoring screen; check whether there is any discrepancy with the on-site meter or the readings on the equipment. During the first month, settings of the monitoring device, communication start date, measurement channels, current transformer (CT) ratio, and data collection intervals may not yet be stable. Therefore, the monitoring screen may show a lower generation value even though the system is actually producing power.

Low monitoring data can be caused not by insufficient power generation of the equipment but by measurement or communication problems. For example, if a monitoring device’s communication starts partway through, generation prior to that will not be reflected on the display. If there has been a communication outage, data during the outage may be missing or may appear low until it is later supplemented. In addition, if measurement units or scaling settings are misaligned, the displayed values may appear smaller than the actual values.

The basic check is to compare, for the same period, the monitoring data, the power conditioner’s cumulative generation, the measurements on the power-receiving equipment side, and the feed-in meter values. These may not match exactly because measurement locations and aggregation methods differ, but if they diverge significantly you need to verify the measurement system rather than the generation itself. Especially in the first month, if you don’t decide which value will be used as the official management figure, stakeholders may end up making decisions based on different numbers.

When checking consistency with on-site meters, you need to pay attention to the meter-reading period. While the monitoring screen can aggregate by calendar days or arbitrary periods, the sales meter may be handled based on meter-reading dates. If these periods are misaligned, generation figures for the same installation can appear inconsistent. Before reporting low generation, you need to align which period the numbers refer to, which device the numbers come from, and which units are being used.

Also, in monitoring data we check not only power generation but also communication status and whether there is data loss. Conditions such as blank entries in daily data, no values recorded after a certain time, specific power conditioners not being displayed, or power readings appearing while cumulative totals do not increase may indicate a problem on the monitoring side. The first month after a new installation is also a period for confirming that the monitoring system is functioning correctly as well as checking the generation equipment.

When power generation is low, judging solely from the monitoring screen can cause you to confuse an actual generation shortfall with a data-display issue. Cross-check the on-site cumulative meter readings with the remote monitoring figures, and if there is a discrepancy, confirm which value more closely reflects actual conditions before proceeding with further decisions. Performing this reconciliation in the first month increases the reliability of generation assessments and maintenance reports in subsequent months.

Item 4: Examine output differences for each power conditioner

If the power generation of a newly installed solar system is low, check not only the total output for the entire facility but also the output differences among individual power conditioners. A low total generation result alone cannot determine whether the irradiance was generally weak or whether only some equipment was not producing. Especially in installations composed of multiple power conditioners, the output reduction or shutdown of a single unit can reduce the overall power generation.

When checking, compare the outputs of each power conditioner for the same time period. If capacity and the number of connected modules are the same and installation conditions are similar, but one unit’s output is clearly lower, there may be a problem with that device or its connected circuit. Conversely, if capacities or string counts differ, you need to look at generation per capacity or output ratio rather than simple generated power. Deciding a unit is underperforming without normalizing the comparison conditions can lead to incorrect judgments.

Output differences between power conditioners are easier to detect during periods close to clear-sky conditions. On cloudy or rainy days, solar irradiance is unstable, making it difficult to determine whether short-term output differences are caused by environmental factors or by the equipment. Choose a day with relatively stable irradiance within the first month and compare outputs in the morning, around midday, and in the afternoon to more readily grasp the trends. If output is low only at a specific time, it is likely due to shading; if it is low all day, it is likely due to connections or settings; and if it suddenly stops, you should check for protective operations or abnormal event logs.

At initial installation, also verify that the power conditioner’s settings and operating mode match the equipment specifications. If the grid voltage condition, protection settings, power factor settings, start/stop conditions, communication settings, etc. are not as intended, the output may not be as expected. However, because these settings require specialized verification, operational staff should not change them themselves; proceed while confirming with the installation contractor or maintenance personnel.

Also, the power conditioner's shutdown history and alarm history are important. In the first month, protection trips can occur due to insufficient post-construction checks or temporary grid conditions. Even if alarms are issued, they may auto-reset, making them hard to notice from daily generation figures alone. If you find a day with low generation, check that day's shutdown history, the alarm time(s), and the recovery time(s), and see whether they coincide with the drop in the generation curve.

When the overall plant generation is low, the appropriate response depends greatly on whether all equipment is equally low or only some units are underperforming. If everything is uniformly low, suspect weather, solar irradiance, output control, overall settings, or the measurement period. If only some units are low, prioritize checking strings, connections, shading, equipment settings, and shutdown history. Establishing a baseline per power conditioner in the first month makes it easier to detect abnormalities from the following month onward.

Item 5 Check string-level current and connection status

If energy production is low from the first month after a new solar installation, checking string-level currents and connection status is important. A string is a circuit unit made by connecting multiple photovoltaic modules in series. Even if the overall system is generating power, if some strings are not connected, have reversed polarity, poor contacts, broken wiring, or are in a disconnected/tripped state, the corresponding generation is lost. When production is low at commissioning, it is important to detect these initial faults early.

String faults can be overlooked if you only look at total power generation. For example, if only one circuit out of multiple circuits is not producing, the facility as a whole is still generating, so it won’t show up as a conspicuous anomaly like a complete shutdown. However, it will contribute to a drop in monthly power generation. If this state is missed in the first month, generation losses can continue afterward and identification of the cause may be delayed.

In inspections, current values are compared between strings under the same conditions. If they have the same orientation, the same tilt, the same number of modules, and the same irradiance conditions, current values are generally unlikely to deviate greatly. If only a particular string is not producing current, or its current is extremely low compared to others, check the connection condition and the effects of shading. However, simply comparing strings with different orientations, tilts, or different numbers of connected modules can lead to misjudgment, so it is necessary to review them while cross-checking with the drawings and the connection table.

At initial installation, also verify that the string configuration on the drawings matches the actual connections. If the wiring route was changed on site, the junction box numbers do not match the monitoring identifiers, labels are hard to read, or system names remain provisional, it will be difficult to trace faults when an anomaly occurs. In the first-month inspection, it is important not only to assess power generation performance but also to organize the correspondence between circuit numbers and the actual wiring so it can be used for future maintenance.

When checking string current, sufficient attention to safety is required. Photovoltaic systems generate DC-side voltage as long as sunlight is present, so unqualified or inexperienced personnel should not casually open circuits or change connections. Operational personnel should establish a process to identify potential abnormalities from monitoring data and inspection reports and, when necessary, request confirmation from specialized staff.

The purpose of performing string-level checks in the first month of low power generation is to isolate early defects. There can be low generation that cannot be explained by weather or adjustments for the number of days, and if only certain power conditioners or circuits are underperforming, it is worth proceeding to string-level verification. If unconnected strings or imbalances can be detected at an early stage, it becomes easier to reduce generation losses in subsequent months.

Item 6 Confirm the presence of output control and stop history

When a newly installed solar power system shows low generation, also check whether there are any records of output control or shutdown. Even if the equipment is not faulty, output can be curtailed by grid-side conditions or control commands. In addition, depending on the operation of protective devices and the state of the grid voltage, the power conditioner may temporarily stop or reduce output. If you determine the cause of low generation in the first month without reviewing these histories, you may confuse equipment faults with operational control measures.

When output curtailment occurs, it can manifest as the generation curve capping out above a certain level despite sunny conditions, the output dropping only during certain parts of the daytime, or multiple power conditioners being suppressed at similar times. However, you should avoid concluding that output curtailment is occurring based solely on the generation curve. Similar patterns can be caused by cloud effects, voltage rise, equipment settings, or missing measurements. Always cross-check with historical data and control information before making a determination.

In the downtime history, check when a shutdown occurred, how long it lasted, and which equipment was affected. The first month is a period when commissioning, configuration checks, protective operations, communication adjustments, and manual shutdowns due to on-site work are likely to occur. If these stoppages overlap during daytime, the monthly power generation will be low. Especially if the system was stopped during daytime on sunny days, even short outages have a large impact on generation. When you find a day with low daily power generation, it is important to cross-check it against that day’s downtime history.

Also, even when there are no stoppage or alarm histories, the reported power generation may appear low due to missing data or communication outages. If the generation curve is interrupted midway, nighttime-like values continue into daytime, or data are blank for specific devices only, consider a monitoring-side problem rather than a generation stoppage. In this respect, cross-checking with on-site meters and the cumulative totals on the equipment is useful.

For newly installed equipment, it is also necessary to confirm that settings and operating conditions related to output control are correctly reflected. Organizing the target equipment’s control method, communication method, how to check control history, and the items displayed in remote monitoring will make it easier to judge when power generation is low. If stakeholders do not know whether output control is in effect, they may mistake normal control for an abnormality or, conversely, blame control for a real fault.

When investigating the causes of low power generation, the stoppage history is a valuable clue. Daytime stoppages or curtailments that aren’t visible from total generation can become clear by reviewing the history. If you decide during the first month how to check the history and how to keep records, you’ll be able to get to the cause more quickly if similar low generation occurs in subsequent months.

Item 7 Check the effects of shadows, dirt, and temporary structures after construction

For newly installed solar PV systems, shading, soiling, and the effects of temporary structures after construction are also important items to check during the first month. Obstacles that were not anticipated during the design phase, materials left over from construction, temporary enclosures, scaffolding, signage, heavy machinery, and surrounding vegetation may cast shadows after power generation begins. Immediately after installation, the sense of relief that the system is complete can make it easy to overlook subtle changes in the site environment, so when power output is low, on-site visual inspections are indispensable.

The effect of shadows varies greatly depending on the time of day. There may be cases where shadows occur only in the morning, only in the evening, or where the length of shadows changes with the seasons. If, in the first month's power generation curve, there are tendencies such as a slow rise in the morning, an early drop in the evening, or unnaturally low output only during specific time periods, suspect the influence of shadows. However, since clouds or orientation can produce similar patterns, confirm by comparing with on-site photos and time-of-day conditions.

Dirt can also be an issue even with a newly installed system. Construction dust during installation, bird droppings, fallen leaves, mud splashes, and dust from nearby work can adhere to the module surfaces. Usually, minor soiling alone does not necessarily cause a significant drop in power generation, but if dirt is concentrated in specific areas or has accumulated along the lower edge, it can affect power output. If generation is particularly low in the first month, it is reassuring to check the cleaning condition at completion of construction and the surrounding environment.

The effects of temporary structures and leftover items should not be overlooked. If construction materials are temporarily stored, the positions of fences or equipment cabinets differ from what was assumed in the design, or nearby structures cast shadows, these are things you may only discover by visiting the site. In monitoring data, only some strings or power conditioners may appear to have lower output, which can be misinterpreted as a circuit malfunction. During on-site verification, it is important to determine which areas are shaded and link those shaded areas to the corresponding circuits.

It's also advisable to check weed control and drainage conditions from the first month. For ground-mounted solar, the way weeds grow varies by season and can cast shadows on lower modules. Even if there are no problems immediately after installation, grass can grow within a few weeks and cause shading. In areas with poor drainage, dirt is more likely to remain due to splashback or standing water. If power generation is low in the first month, you need to check not only the equipment's performance but also whether the surrounding environment is hindering generation.

When checking for shadows and soiling, it is important to record their relationship to power generation. Simply writing "there was a shadow" or "there was soiling" makes it difficult to use for determining the cause. By recording the date and time of day the shadow appeared, its extent, the affected circuit(s), and any drop on the power generation curve together, future inspections become easier. Keeping these records during the first month after a new installation allows you to identify differences between the design assumptions and the actual environmental conditions at an early stage.

Use the first month's confirmation results as the standard for subsequent months

When a newly installed solar installation produces low generation in its first month, it is important not only to investigate the causes but also to record the findings as a baseline for subsequent months. The first month is the initial opportunity to understand the system’s quirks, responses to solar irradiance conditions, output differences among devices, how to interpret monitoring data, and the impact of the on-site environment. If you organize records at this stage, it will be easier in later months to determine whether a perceived drop in generation is within the normal range or indicates an anomaly.

What you should retain as a baseline is not just the monthly generation figures. Keeping the grid connection start date, number of operating days, daily generation, the generation curve on clear days, output by each power conditioner, string current trends, stoppage history, whether output control was applied, discrepancies between monitoring data and on-site meters, and the condition of shading and soiling will make later comparisons easier. If these are not kept, then even if you feel the generation is low the following month, it will be unclear what you are comparing it against.

The record for the first month also plays a role in creating a shared understanding among the construction company, maintenance personnel, equipment owner, and operations staff. A report that generation is low is a phrase that can be easily interpreted differently depending on the recipient. By clarifying which period’s generation is being referred to, which data are being used as the reference, whether solar irradiance conditions are being taken into account, and whether shutdown history has been checked, you can reduce unnecessary back-and-forth and misunderstandings.

Also, even if no abnormalities are found in the first month, the records are meaningful. The normal power-generation curve on sunny days and the output balance of each device become baseline references for future comparisons. If a low-generation condition occurs later, comparing it with the first month’s normal data makes it possible to identify which device or circuit has changed. In particular, when only part of the same installation shows reduced output, having past baselines speeds up narrowing down the cause.

If a minor anomaly appears in the first month, do not immediately conclude it is a serious problem; instead, manage it as an item to be monitored continuously from the following months. For example, conditions such as output being slightly lower only during certain time periods, output being marginally low only for specific equipment, or partial gaps in monitoring data should be judged by continued observation. However, unconnected strings, equipment shutdowns, obvious configuration errors, or large discrepancies with on-site meters require prompt verification rather than a wait-and-see approach.

The purpose of the first month after commissioning is not to draw a definitive conclusion about whether generation performance is good or bad. It is to confirm whether the equipment has started operating normally, whether data are being collected correctly, and whether a baseline that can be used for future operations has been established. When you feel the first month's generation is low, it is important not to rush to attribute the cause to a single factor, but to organize the investigation in the following order: period, solar irradiance, measurement, equipment, circuits, history, and environment.

Summary

The point to check in the first month for newly installed solar power systems with low generation is not simply whether the monthly generation is higher or lower than expected. In the first month, the grid-connection start date and the number of operating days often do not align, and the start of monitoring data acquisition and the meter-reading period may also not coincide. Therefore, the starting point should be to first confirm whether it operated for a full month and which period's generation you are looking at.

Next, compare solar irradiance and weather conditions over the same period to distinguish between a natural decline and an equipment-side problem. If the weather is poor, generation will be lower, but if output does not rise even on sunny days, you need to proceed to check monitoring data, on-site meters, power conditioners, strings, shutdown history, and for shading or soiling. Especially in the first month after installation, there may be factors you want to detect early, such as incorrect measurement settings, some circuits left unconnected, or the effects of temporary structures remaining after construction.

To correctly determine whether power output is low, it is important to look not only at the total but also broken down by day, by time of day, by equipment, and by circuit. Is the whole system uniformly low, or is only part of it low? Is it not generating at all, or is the generation simply not being reflected in the monitoring? Is it due to weather, or due to shutdowns or control actions? Performing this breakdown makes it easier to identify the necessary actions.

Also, the inspection results from the first month should serve as the baseline for power generation management in subsequent months. If you record the normal generation curve immediately after grid connection, the output balance for each power conditioner, trends in string current, differences between on-site meters and monitoring data, and the presence or absence of shading and soiling, it will make future comparisons easier when generation is low. Establishing these baselines at the time of installation is highly meaningful for improving the long-term accuracy of generation management.

The first month of a newly installed solar power system is not only the time to determine whether generation is low, but also a period for getting the equipment and data into order. Do not ignore any anomalies in that first month, nor jump to conclusions; by checking seven items in sequence, you can reduce the chance of overlooking the cause. To make generation checks efficient as part of routine operations, prepare on-site records, monitoring data, inspection logs, photographs, and methods for sharing information among stakeholders in advance, and build a system that can consistently track from first-month verification through subsequent operational management.