5 Ways to Identify Voltage Rise Suppression That Causes Reduced Power Generation

When field staff notice low power generation, many first suspect insufficient sunlight, dirty panels, or equipment failure. However, if generation fails to increase only on clear days, output plateaus around midday, or the amount of electricity sold does not rise despite no obvious major abnormalities in the generation equipment, voltage-rise suppression may be involved. Voltage-rise suppression is a control measure used to maintain grid interconnection conditions and differs from a simple fault. Therefore, proceeding only with cleaning or parts replacement without determining whether voltage-rise suppression is occurring can fail to address the root cause of the reduced generation. This article organizes five on-site checkpoints for practitioners to distinguish voltage-rise suppression that leads to decreased power output.

Table of Contents

• How suppression of voltage rise leads to reduced power generation

• How to tell 1: The power generation curve becomes flat only on sunny days

• How to tell 2: The power conditioner’s history contains suppression-related records

• Identification method 3: Periods when high grid voltage and drops in power generation overlap

• Identification method 4: Imbalances in voltage and wiring conditions within the equipment

• Distinguishing method 5: Linked to the operating status of the surrounding environment and nearby facilities

• Records to be compiled after suspecting voltage rise suppression

• Summary: Isolate the causes of low power generation and connect them to subsequent countermeasures

How Suppressing Voltage Rise Leads to Reduced Power Generation

In photovoltaic power generation systems, generated electricity is not only used within the installation but surplus can be fed into the power grid. In order to send electricity from the generation equipment to the grid, the voltage on the equipment side may need to become somewhat higher. However, if the grid-side voltage is already high and generation increases, the voltage may approach or exceed the range that is desirable for management. Therefore, the power conditioner may, as a control required for grid interconnection, reduce output or limit the amount of electricity sold. This phenomenon is commonly called voltage rise suppression.

The important point is that voltage-rise suppression does not necessarily indicate equipment failure. Rather, equipment may be adjusting its output to avoid excessively high voltage and to maintain grid interconnection conditions. Therefore, it is premature to immediately conclude that low power output is due to panel faults or power conditioner failure. If voltage-rise suppression is the cause, even cleaning the panel surface or having good weather may not restore generation to the expected level.

What is troublesome in practice is that the reduction in power generation caused by voltage-rise suppression is hard to recognize from appearance alone. The equipment is not stopped, and generation is not zero. It appears as scenarios such as not increasing as much as expected on sunny days, lower generation peaks, or drops only during specific time periods, making it easy to confuse with solar irradiance conditions, temperature effects, shading, soiling, wiring losses, and so on.

Also, suppression of voltage rise may not be achieved by the equipment alone. Grid-side voltage, nearby generation facilities, the condition of loads connected to the same distribution line, wiring distances and conductor sizes within the installation, and conditions up to the connection point all interact in a complex way. Therefore, to narrow down the cause on site, it is important to check not only the power output but also the generation curve, equipment history, voltage records, time of day, and the surrounding environment in combination.

In consultations about low power generation, people tend to look first at annual or monthly generation records. However, to identify voltage rise curtailment, it is necessary to observe changes in generation on a daily or hourly basis, or, if possible, at even finer intervals. In particular, how the output behaves around midday on sunny days provides useful clues. To narrow down the causes of reduced generation quickly, it is essential to check not only how much lower it is but also when and in what pattern it is lower.

How to tell 1: The power generation curve becomes flat only on sunny days

The first clue that suggests voltage-rise suppression is the shape of the power generation curve. Normally, on a clear day with stable weather, solar power output gradually rises from the morning, forms a peak around midday, and falls toward the evening. Of course, the shape changes with the season, installation orientation, tilt, surrounding shading, and temperature, but on days with stable sunlight it tends to form a relatively smooth, mountain-shaped curve.

On the other hand, when voltage rise suppression is involved, the generation curve around midday can become unnaturally flat. During a period when output would normally rise somewhat in line with increasing solar irradiance, it stays at a certain level and forms a plateau. This indicates that, even if the power conditioner attempts to raise output, it may be limiting output to avoid an increase in grid voltage.

However, a flat power generation curve does not immediately mean voltage-rise suppression. It may simply be that the power conditioner has reached its rated output, and similar patterns can result from output reduction due to high temperatures, the design relationship between panel capacity and equipment capacity, the effects of clouds, or the way shadows fall. To distinguish between these, you need to compare the season, temperature, solar irradiance conditions, and past generation performance on days with the same conditions.

In practice, it is easier to make a judgment if you select several clear-sky days and line up the power generation curves for the same time periods for comparison. In particular, if output plateaus around midday even in seasons such as spring or autumn when temperatures are not extremely high, this cannot be explained by high-temperature losses alone. Also, when there are few clouds and solar irradiance is stable, yet the output fluctuates slightly or is suppressed around a certain value, this should also be checked as a potential voltage-rise suppression.

If you look only at monthly totals when dealing with low power output, differences in generation curves like this can be overlooked. Even if monthly generation is lower than the previous year, you cannot tell whether the cause is bad weather, equipment degradation, or curtailment. Therefore, after checking daily generation, it is important to dig down into hourly data for clear days. Voltage-rise curtailment does not always show up in the same pattern, but because it is more likely to appear during the hours when output grows under clear skies, checking the curves on clear days is a high‑priority task.

Furthermore, when multiple power conditioners are installed within the same facility, compare the generation curve of each unit. If all units level off in the same way, conditions on the grid side or at the point of supply may be involved. If the issue occurs only on some units, you need to check the circuit connected to those units, wiring distance, connection location, settings, and the condition of the equipment. Finding imbalances that cannot be seen from the facility’s total generation will help narrow down the cause.

Identification method 2: The power conditioner’s history contains records related to curtailment

Verifying the power conditioner’s history is essential for identifying voltage rise suppression. In many facilities, the power conditioner or monitoring device retains operation logs, alarm logs, shutdown logs, suppression logs, and similar records. The displayed names and recorded items vary by device, but if records exist with meanings such as voltage rise, output suppression, interconnection voltage, system voltage, overvoltage, suppression operation, or voltage control, it is worth checking their relationship to any reduction in power generation.

One thing to be aware of is that the absence of an alarm does not necessarily mean that suppression of a voltage rise is not occurring. Such suppression, unlike an abnormal shutdown, may be handled within the control system. Therefore, it may not be apparent if you only look at the list of major-fault alarms. It is important to check not only daily and monthly generation reports but also the operation history, duration of suppression, number of suppression events, maximum grid voltage, and output trends for each piece of equipment.

When checking the logs, match days with low power generation against days with curtailment-related records. For example, select days when it was sunny but generation did not increase, days when the generation curve flattened around midday, or days that dropped significantly compared with the same month of the previous year, and check whether curtailment-related records exist for those time periods. If the times of the records overlap with the times of the generation drop, overvoltage curtailment becomes one possible cause.

On the other hand, care is needed when interpreting the history. Even if there is only one recorded curtailment in the past, that does not necessarily mean it is the primary cause of the current drop in power generation. If it was a short, temporary curtailment, its impact on monthly generation may be limited. Conversely, even if it does not stand out as an alarm, if it occurs every day for gradually long periods, it may affect annual electricity sales. Therefore, rather than the mere presence or absence of a single occurrence, it is necessary to examine the frequency, duration, time of occurrence, and overlap with generation.

Also, at sites there are cases where "the history is too old and no longer available," "the monitoring device does not show details," or "you can’t tell unless you check the equipment screen directly." In such cases, for future verification it is important to set up how you will record data starting from the day you notice low power generation. In addition to daily generation, keep records of hourly output on sunny days, output by each device, voltage-related display values, and whether any curtailment is indicated; this will make it easier to explain the situation later when consulting the installer or maintenance personnel.

The power conditioner’s history is not intended for on-site personnel to definitively determine the cause; it should be used as material for isolating issues. If the history shows any suppression-related indications, that provides a basis for suspecting voltage-rise suppression. Even if no history is found, judging in conjunction with the power generation curve and voltage records will reveal the direction to investigate next.

Identification Method 3: Periods of High Grid Voltage Coincide with Decreased Power Generation

To determine whether voltage-rise curtailment is occurring, recordings of voltage as well as generation output are important. If, during periods when the power facility's output is reduced, the system voltage or the voltage near the point of interconnection is high, voltage-rise curtailment may be involved. In particular, a key check point is whether times when generation output does not increase around midday on sunny days coincide with periods of high voltage.

In solar photovoltaic systems, the amount of power exported to the grid increases during periods of higher generation. If nearby generation facilities are also operating similarly, the voltage across the distribution network can tend to rise. Also, in areas where local power consumption is low during daytime, the load relative to generation becomes small and the voltage may run higher. When these conditions coincide, control systems that curtail output on the generation side are more likely to be engaged.

In practice, where possible, obtain hourly voltage data and review it alongside the generation data. If voltage is high during periods of low output and the generation curve naturally recovers in the evening or under cloudy conditions, this is difficult to explain by insufficient solar radiation or panel soiling alone. Conversely, if generation is low even when voltage is not high, you need to check for other causes such as shading, soiling, panel faults, poor connections, equipment malfunctions, settings, or temperature effects.

However, caution is required when measuring voltage. Looking only at instantaneous values can make it difficult to determine the relationship with generation declines. Even if conditions appear normal at the time you visit the site, suppression may have occurred in the periods immediately before or after. In particular, voltage rise suppression tends to occur during periods of high solar irradiance or when nearby loads are low, so a site inspection that is not timed correctly can miss it. Therefore, it is desirable to check continuous records whenever possible, or multiple days of records for the same time period.

When checking voltages, it is also important to note where the measurements are taken — for example, near the point of supply, on the power conditioner side, or near distribution boards or combiner boxes. Because the wiring within the facility can change how voltage drops or rises appear, confusing measurement points can lead to incorrect judgments. When organizing values collected on site, record the measurement date and time, weather, power generation output, measurement location, the phase or circuit measured, and the load conditions together; doing so makes later review easier.

Also, even if a voltage-rise suppression function is suspected, you should avoid changing equipment settings on your own. Settings related to grid interconnection affect safety and system operation, so confirmation with a specialist contractor or the power utility may be necessary. The first action on-site personnel should take is not to force adjustments, but to record the relationship between the drop in generation and the voltage rise and be able to explain it.

Identification Method 4: Uneven voltage differences or wiring conditions within the equipment

Voltage rise suppression can vary not only on the grid side but also depending on the wiring conditions within the facility. Even within the same power plant, differences in how the voltage rises can occur depending on the power conditioner’s installation location, the distance to the connection point, the wiring route, conductor size, and the configuration of junction boxes and collector panels. As a result, only some equipment may be more likely to be suppressed, which can lead to a reduction in overall power generation.

For example, in a facility with multiple power conditioners of the same capacity, if only a particular unit has low power generation, you need to check not only that unit for a fault but also the wiring and circuit conditions to which it is connected. Factors such as being far from the connection point, long wiring, biased routing, increased contact resistance at terminals, or changes in wiring conditions after facility modifications can affect how likely voltage rise suppression is to occur.

In this method for distinguishing causes, comparing the power generation of individual units is effective. Compare outputs on sunny days between units that have the same orientation, the same tilt, and similar panel capacities. If only a specific unit’s output drops or plateaus around midday, check the AC-side voltage connected to that unit, the condition of the terminals, the cable routing, and the conditions up to the connection point. Conversely, if all units experience similar curtailment at the same time of day, prioritize checking the overall facility or grid-side conditions.

Imbalances within a facility cannot be seen from monthly total generation alone. Even if the overall output appears only slightly low, some circuits or pieces of equipment may actually be repeatedly curtailed. When a particular piece of equipment is consistently low, it is easy to mistake this for a performance decline of the generation system, but viewing data by time of day can reveal characteristics of voltage-rise suppression. In practice, it is important to break down and check by equipment, by circuit, and by time of day.

When checking wiring conditions, it is also important that the drawings match the actual site. If the as‑built drawings differ from current conditions, if connection configurations have changed due to renovation or expansion, or if the panel labels do not correspond to the actual circuits, fault investigation can take a roundabout path. Before investigating the cause of low power generation, organize which power conditioner is connected to which circuit and the route it takes to the point of interconnection; doing so makes it easier to identify locations that are likely to experience curtailment.

However, tasks that involve checking voltage differences or wiring conditions inside equipment require electrical safety management. It is dangerous for on-site personnel to open panels or approach live parts without proper qualifications. The scope of work for on-site staff should be limited to comparing monitoring data, organizing drawings, recording the time periods when incidents occurred, and checking for visible abnormalities; measurements and detailed inspections should be entrusted to qualified specialists.

Identification Method 5: Linked to the operating status of the surrounding environment and nearby facilities

Voltage rise suppression may not be confined to your own equipment. If many solar power generation systems are connected in the same area or on the same distribution line, the total generation in the surrounding area can increase during sunny daytime hours, making voltages more likely to rise. Even if there is no fault in your equipment, changes in nearby generation or local electricity demand can make voltage rise suppression more likely to occur.

As clues for distinguishing the cause, check whether drops in power generation are noticeable in specific seasons, days of the week, or times of day. For example, if there is a tendency such as generation failing to increase only during sunny daytime hours, curtailment occurring more often on holidays than on weekdays, or incidents being more frequent during hours when nearby factories or facilities are not operating, you should consider the relationship with local loads and grid conditions. Of course, this alone cannot provide a definitive conclusion, but it can prompt you to take a perspective different from a fault in the equipment itself.

Also, if a noticeable decline in power output begins after new generation facilities have been added around the power plant, this should be checked. An increase in nearby facilities does not necessarily cause curtailment, but when generation becomes concentrated on the same grid, voltage conditions may change. When comparing with past generation performance, recording changes in the surrounding environment as well as deterioration of the equipment itself makes it easier to assess.

Long-term records are useful for examining interactions with the surrounding environment. Lining up daily power generation, weather, temperature, generation curves, voltage records, and curtailment history makes it easier to see whether an issue is a one-off anomaly, a seasonal phenomenon, or a problem that recurs under specific conditions. In particular, judging solely by year-on-year comparisons for the same month can be skewed by weather and seasonal differences. Multiple perspectives are necessary, such as comparing similar sunny days with each other, comparing sunny days within the same month, and comparing individual pieces of equipment within the facility.

The important point in this inspection is not to assume the surrounding environment is the cause. Causes of low power generation can include dirt, weeds or shading, panel damage, faulty connectors, cable degradation, equipment failures, incorrect settings, communication failures, temperature effects, and others. Even if it appears to be linked to the surrounding environment, the problem inside the system may simply be manifesting at the same time. Therefore, it is necessary to check a combination of the power generation curve, equipment history, voltage records, and imbalances within the system.

When surrounding factors are suspected, the practical course of action is to organize the records and consult through the maintenance personnel or the installation contractor. Matters involving the power system are limited in what can be assessed and addressed solely on site. That is why it is important to be prepared to show "when it occurred," "at what time of day," "which equipment," "how the voltage evolved," and "how the generation curve changed" when consulting.

Records to compile after suspecting voltage rise suppression

When voltage rise suppression is suspected, it is important to first organize the records before immediately moving on to countermeasures. If you consult with insufficient records, the mere impression that generation is low makes it difficult to narrow down the cause. What is needed on site are materials that can explain under what conditions the decrease in power generation is occurring.

The first thing to organize is the actual power generation data. Check daily, monthly, and, if possible, hourly generation to determine when the decline began, whether it occurs every day, only on sunny days, or is particularly noticeable in certain seasons. In addition to year‑on‑year comparisons for the same month, comparing days with similar weather makes it easier to distinguish declines caused by insufficient solar irradiance from those caused by curtailment.

Next, save the power generation curve. If voltage-rise suppression is suspected, it is important to see how the output behaves around midday on sunny days. Check whether it is plateauing, fluctuating slightly, suddenly dropping, or whether there are differences between devices. Showing the shape of the generation curve makes it easier to share the situation than simply stating that the power generation is low.

Also check the histories of the power conditioners and monitoring devices. Compile displays related to curtailment, records related to voltage, stop and restart histories, and output differences for each piece of equipment. If records are only displayed on-screen, make a note that shows the date and time so they can be reviewed later. Because some systems automatically overwrite their histories, it is advisable to save them promptly if you notice a drop in power generation.

Voltage recording is also important. Organize records by location—such as near the interconnection point, on the power conditioner side, and display values visible inside the panel—so it is clear which location each voltage refers to. If measurement or inspection is required, always request a qualified specialist. On-site personnel should record not only the measurement results but also the measurement date and time, weather, generation conditions, and load conditions, as keeping these together makes it easier to investigate the cause.

Additionally, recording the on-site environmental conditions is useful. Check for factors that may affect power generation, such as weeds, shading, dirt on the panel surfaces, snow or fallen leaves, bird damage, changes around fences, nearby construction, and the presence or absence of equipment modifications. Even if voltage rise suppression is suspected, other factors may be overlapping. When multiple causes exist simultaneously, the way a drop in power generation appears can become complex, so it is important to keep both electrical records and records of the site conditions.

When organizing records, it is important not to rush to conclusions. Even if there are signs suggestive of voltage rise suppression, a formal determination may require professional verification. The role of on-site personnel is to clarify the conditions under which the event occurred and to prepare information that makes it easy for consultants to form a judgment. By assembling power output, generation curves, voltage, historical records, and on-site conditions, it becomes easier to reduce unnecessary inspections and misguided countermeasures.

Summary: Isolate the causes of low power generation and use them to guide subsequent countermeasures

Voltage-rise suppression that leads to reduced power generation is a phenomenon that is difficult to detect by appearance alone. The equipment does not completely stop; it can manifest as generation failing to increase on sunny days, output plateauing around midday, or differences in output between devices. Therefore, when you feel generation is low, you need to check not only the total monthly generation but also combine the generation curve by time of day, output per device, voltage records, and operation history.

The basic way to distinguish is to look, in order, at the shape of the power generation curve, the history of the power conditioner, overlap with the grid voltage, wiring conditions within the installation, and interaction with the surrounding environment. By assembling this information, it becomes easier to determine whether voltage-rise suppression is suspected or whether other factors—such as panel soiling or shading, equipment malfunction, wiring troubles, or temperature effects—should be prioritized.

On the other hand, because suppressing voltage rise involves safety and grid operations, you should avoid changing settings or forcing adjustments based solely on on-site judgment. The first thing operational staff should do is record the conditions under which the generation drop occurred and be able to explain them to technical specialists. If you organize when, on which equipment, during which time period, what the generation curve looked like, and what changes occurred in voltage and in the logs, further investigation and consultation will proceed more smoothly.

Low power output often has more than one cause. In addition to voltage rise suppression, dirt, weeds, shading, poor wiring connections, equipment degradation, and missing communication logs can occur together. That is why it is essential to continuously record daily generation data and on-site conditions and to have a system that detects early signs of abnormalities.

To identify the cause of reduced power generation on site, it is important not to judge by total generated power alone, but to check changes by time of day, differences by equipment, voltage trends, history displays, on-site photos, and inspection notes together. If the same records can be shared among stakeholders, it becomes easier to explain the situation even in cases where voltage-rise suppression is suspected. To quickly isolate the cause of low power generation, establish record-keeping and verification procedures and ensure you can consult maintenance personnel or electrical specialists as needed.