How to Handle PVSyst Warning Messages｜6 Common Practical Examples Explained

Table of Contents

• PVSyst warning messages are not errors but signs to verify the design

• Warning 1: How to handle when string voltage is out of range

• Warning 2: Mismatch between power conditioner capacity and array capacity

• Warning 3: Handling warnings related to meteorological data and site conditions

• Warning 4: Inconsistencies in shading settings or 3D scenes

• Warning 5: Loss settings are missing or set too high/too low

• Warning 6: Minor warnings that often persist before report output

• How to proceed when checking warning messages in practice

• To reduce PVSyst warnings, the accuracy of site conditions is important

• Summary

PVSyst warning messages are not errors but signs to confirm the design

When using PVSyst to simulate the energy production of a solar power generation system, warning messages may appear on the settings screen, during calculation runs, or before report output. For personnel operating it for the first time, simply seeing a warning can easily cause concern—“Can I proceed with the calculation as is?”, “Is the design incorrect?”, or “Is this unsuitable as submission material?”. However, PVSyst’s warning messages do not necessarily mean that the calculation is impossible. In many cases they are confirmation signs indicating a possible inconsistency in the input conditions, remaining assumptions that should be checked, or settings that require attention in practical work.

When using PVSyst, the important thing is not simply to clear warnings, but to read what the warnings mean and judge whether they are reasonable in light of the design intent and the actual site conditions. If you change numbers just to eliminate warnings, you may achieve superficially neat results yet produce simulations that stray from the real design conditions. Conversely, even if warnings remain, if you can explain the reasons for them, the results can still be fully usable as material for internal review or design comparisons.

Common warnings in practical work tend to concentrate on string voltage, inverter capacity, meteorological data, shading, loss settings, and unchecked items before report output. These are areas in photovoltaic (PV) system design where conditions have a particularly large impact. For example, warnings about string voltage are related to open-circuit voltage at low temperatures and operating voltage at high temperatures. Warnings regarding capacity ratios affect not only the amount of energy generated but also how peak shaving is evaluated. Shading warnings are important because the shape of the 3D model and the arrangement of arrays greatly affect the results; overlooking them can lead to differences in energy production.

In this article, aimed at practitioners searching for "how to use PVSyst", I explain the rationale behind and countermeasures for warning messages commonly seen in PVSyst, divided into six examples. Without relying on specific equipment names or other companies' service names, I organize which items should be checked and how to make judgments, following the general workflow of photovoltaic system design. The goal is not to be afraid of warnings, but to be able to treat them as checkpoints for reviewing design conditions.

Warning 1: How to handle cases where the string voltage is out of range

One of the warnings that frequently appears in PVSyst in practical work concerns string voltage. When you set how many photovoltaic modules to connect in series, a warning may be displayed if the open-circuit voltage at low temperatures could exceed the power conditioner's maximum input voltage, or if the operating voltage at high temperatures could fall below the allowable operating range. This is not merely a data-entry mistake but an important check related to electrical design safety and operating range.

When a string voltage warning appears, first check the number of modules connected in series. If the number of modules in series is too high, the open-circuit voltage can rise under low module temperature conditions, such as on cold mornings, and may exceed the equipment's allowable voltage. Conversely, if the number of modules in series is too low, the voltage can drop during high temperatures in summer, and you may not be able to secure sufficient operating voltage. PVSyst evaluates voltage ranges by taking temperature conditions into account, so if you only look at the nominal values at standard temperature, the reason for the warning can be hard to understand.

The basic approach is to adjust the number of modules in series so that both the maximum voltage at low temperature and the operating voltage at high temperature fall within acceptable limits. However, changing the number of modules in series also affects the number of parallel circuits, the total capacity of the array, and the capacity ratio with the power conditioner. Therefore, when correcting a string voltage warning, you need to check not only the voltage but also the overall system configuration.

Next to check are the design temperature conditions. In PVSyst, the setting of minimum and maximum temperatures or temperature conditions based on meteorological data affects the voltage assessment. For projects in cold climates, the open-circuit voltage at low temperatures tends to become more problematic, and using the same number of modules in series as for warm-climate projects may trigger warnings. Conversely, for installation conditions that tend to become very hot—such as rooftop locations or sites close to the ground surface—the voltage drop at high temperatures cannot be ignored. If you ignore the site’s climate conditions and racking/mounting conditions and judge only by standard temperatures, the actual operating conditions may differ.

Also, it is necessary to verify the input values of the module specifications being used. If the open-circuit voltage, maximum power operating voltage, temperature coefficients, etc. are not entered correctly, the assessments in PVSyst will not match reality. Special attention is required when module data have been entered manually or when duplicating similar specifications. Check that the module model, rated output, voltage values, and temperature coefficients match the design documentation.

In practice, when a string voltage warning appears, it is important for the electrical design engineer and the simulation engineer to align their understanding. Changing the number of modules in series to clear a warning in PVSyst can result in a mismatch with the on-site wiring plan or panel configuration. Conversely, it may simply be that the string configuration decided by the design side has not been reflected in PVSyst. When a warning appears, first check whether "the PVSyst inputs match the design drawings," and then determine whether "the design itself needs to be revised" — that sequence is the safe approach.

Warning 2: Mismatch between Power Conditioner Capacity and Array Capacity

The next most common warnings relate to the relationship between the power conditioner's capacity and the solar array capacity. In photovoltaic systems, the total capacity of the modules does not necessarily equal the AC-side capacity of the power conditioner. Systems are sometimes designed assuming a certain amount of oversizing, but if that ratio is too large or too small, PVSyst may issue a warning.

To understand this warning, you first need to look at the relationship between DC-side capacity and AC-side capacity. The larger the DC-side capacity, the more likely inputs will exceed the rated output of the power conditioner during periods of high solar irradiance. In such cases, the portion the power conditioner cannot handle is treated as peak clipping, and part of the generated energy is lost. In PVSyst results, this can appear as losses due to oversizing and the effects of output limiting.

On the other hand, if the DC-side capacity is too small, the amount of time during which the power conditioner cannot be fully utilized increases. From an equipment-utilization perspective it may appear to have spare margin, but from the standpoint of investment efficiency and design intent it may be inappropriate. PVSyst’s warning indicates that such a capacity balance may fall outside the typical range.

As a countermeasure, first check whether the capacity ratio matches the design policy. The appropriate capacity ratio depends on whether you want to maximize power generation, are willing to accept some peak shaving to secure annual generation, or are limiting the AC-side capacity to meet grid-connection constraints. A warning does not necessarily mean you must reduce the array capacity. What matters is whether you can explain the reason for that capacity ratio.

Next, verify the number of power conditioners, the number of input circuits, and the number of strings assigned to each circuit. Even if the overall capacity appears acceptable, if strings are concentrated on specific inputs or if input currents approach their upper limits, other warnings may occur. In PVSyst, equipment configuration and string configuration are evaluated in relation to each other, so it is important to check consistency at the input-unit level rather than relying solely on a simple total-capacity sum.

Also, when peak clipping is large, check not only the annual energy generation but also the monthly and hourly output trends. Whether peak clipping is concentrated on a few clear-sky days or occurs frequently over long durations changes its design implications. Check the breakdown of losses in the generation report to understand how large the losses from oversizing are compared with other losses.

In practice, when sharing a capacity-ratio warning internally, simply conveying “there’s a warning, so it’s NG” can lead to incorrect decisions. Rather, it is important to present the capacity ratio, peak-cut loss, annual energy production, and equipment constraints together, and explain whether they are reasonable with respect to the design intent. PVSyst does not substitute for the design decision itself; it is a tool to visualize the materials for decision-making. In practice, warnings should be used as an opportunity to review those decision-making materials.

Warning 3: Handling warnings regarding meteorological data and site conditions

Meteorological data and site conditions have a major impact on the accuracy of PVSyst simulations. If conditions such as solar irradiance, air temperature, wind speed, elevation, latitude and longitude, or time zone are inappropriate, the results for energy production can differ significantly. Therefore, PVSyst may display warnings about insufficient meteorological data, inconsistencies in site information, or problems during data conversion.

When a warning about meteorological data appears, the first thing to check is whether you are using data appropriate for the site in question. In solar power generation simulations, solar irradiance and temperature conditions can vary within the same prefecture depending on whether the location is coastal, mountainous, in a basin, or urban. If you are using data from an observation site that is far away, or reusing data from a site with a large elevation difference, be cautious about the reliability of the results.

Next, check the data period and time resolution. For annual simulations, a representative one-year set of weather data is normally used, but if there are missing data or hourly values have been generated from monthly values, a warning may appear. Using data with many gaps as-is can make generation for certain seasons or times of day appear unrealistic. Check the data overview in PVSyst and look for any extreme values in monthly irradiance or temperature.

Discrepancies in time zones and latitude/longitude are also easy-to-overlook points. Because calculations of solar altitude and azimuth depend on location information, if the position data are off it can particularly affect shadow analysis and calculations of solar irradiance on inclined surfaces. When handling overseas projects or projects across multiple regions, don’t judge based only on the site name; check that the latitude and longitude, elevation, and time zone are consistent with the target location. Even for domestic projects, when duplicating an existing project to create a case for a different site, the location settings can sometimes remain as they were in the previous project.

Warnings about meteorological data cannot always be fully resolved. There may be constraints on the available data, or approximate values may be used during early-stage evaluations. In such cases, it is important to clearly define the status of the simulation results. The required data accuracy will vary depending on whether the analysis is a preliminary study, an assumption for detailed design, for internal comparison, or intended to be close to submission materials.

As a practical response, when a warning about meteorological data appears, first check four points: site conditions, data type, the presence of missing data, and monthly trends. Then, as necessary, perform sensitivity checks using alternative meteorological data. For example, by creating cases that keep the same design conditions but change only the meteorological data, and comparing differences in annual and monthly power generation, it becomes easier to understand the impact of data selection.

Weather data is the entry point for simulations. If there are inconsistencies here, no amount of detailed adjustment to loss settings or equipment configuration later will increase the reliability of the results. In practice, it is very important to first verify via PVSyst warning messages that the foundation of the input conditions is correct.

Warning 4: Inconsistencies between shading settings and 3D scenes

When performing shadow analysis in PVSyst, warnings about the 3D scene or shading settings may appear. These indicate that there may be inconsistencies in the relative positions of the PV array and obstructions, object dimensions, the orientation of the array surface, or the definitions within the scene. Because the impact of shading directly affects energy production, shading-related warnings should be checked carefully.

A common issue is that the array surfaces are not correctly defined within the 3D scene. For example, the array azimuth or tilt does not match the system settings, the area on the 3D scene does not correspond to the array capacity in the electrical design, or the assignment of multiple array surfaces is unclear. In PVSyst, because parts of the 3D scene and the system configuration are linked, a model can look correct visually yet not be properly associated for calculation purposes.

The first step in addressing the issue is to confirm that the array surfaces in the 3D scene match the array configuration in the system settings. Check that the number of modules, area, azimuth, tilt, and installation coverage are not significantly different. In particular, for projects with installations across multiple surfaces or split roof planes, it is easy for it to become unclear which surface corresponds to which sub-array. If you duplicated settings while working, leftover information from old surfaces can remain and cause warnings.

Next to check are the positions and dimensions of obstructions. When entering buildings, trees, equipment, fences, and surrounding structures into a 3D scene, dimensions and heights are sometimes entered approximately. That may be acceptable for preliminary studies, but for analyses close to detailed design it can significantly affect shadow length and the timing of their occurrence. If warnings appear, verify that obstructions are not overlapping the array, are not placed extremely close, and that the ground height reference is not misaligned.

Also, care should be taken if near-field shading and far-field shading are being confused. Shadows from nearby buildings or rows of racking are often handled in the 3D scene, while distant obstructions such as mountains or the horizon may be handled by different methods. Setting both redundantly can lead to an overestimation of shading losses. Conversely, if neither is set, shadows that actually exist may be treated as absent in the simulation.

For shading warnings, it is important not to judge solely by the numerical value of shading losses. Even if the annual shading loss appears small, it may be concentrated in the mornings and evenings during winter or in specific time periods. In self-consumption projects, the generation profile by time of day is critical, so relying only on annual values can cause you to overlook impacts. When reviewing PVSyst results, check annual losses, monthly losses, and time-of-day trends together.

In practice, when the site topography and surrounding structures have not been accurately determined, making shading settings too detailed can actually increase errors. For a simple shading study, it is preferable to treat it as an approximate model while clearly stating the assumptions, and to verify dimensions and positions during the detailed design stage using site surveys or point cloud data. Warnings from PVSyst are an important signal to re-examine whether the 3D scene inputs can be trusted as calculation conditions.

Warning 5: The loss setting is left blank or set too high or too low

In PVSyst, various loss items are configured to realistically estimate power generation. Soiling loss, wiring loss, mismatch loss, temperature loss, equipment loss, degradation, downtime rate, and other items that should be considered in practice span a wide range. If these settings are left blank or deviate significantly from typical ranges, warnings may be displayed.

One thing to be careful of with loss-setting warnings is that not getting a warning does not necessarily mean the settings are correct. For example, calculations using the default values may produce no warning, but those defaults may not be appropriate for the project. Conversely, if you enter special values to match site conditions, PVSyst may issue a warning. In that case, it can be acceptable as long as you can explain the rationale behind the values.

The first thing to check is whether any loss items have been unintentionally left unset. If wiring losses are not specified, soiling losses are left at their default values, or downtime rates are not accounted for, the estimated energy production may be overly optimistic. In particular, when comparing multiple cases, if only one case has different loss settings, the results will change because of input differences rather than design differences.

Next, check whether the loss values are excessively large or small. If the wiring loss is extremely large, there may be errors in the inputs for cable length, cross-sectional area, current conditions, or voltage classification. If the soiling loss is large, verify that the settings reflect the installation area's dust levels, rainfall, cleaning schedule, and tilt angle. For mismatch loss, the way you set it will vary depending on how you view module variability, string configuration, shading effects, and aging.

If warnings about temperature losses or abnormal results appear, check the mounting structure conditions and ventilation conditions. Installations close to the roof, ground-mounted racking, rooftop installations, and installations near walls change how module temperature rises. Poor ventilation conditions tend to increase temperature losses and can also affect power generation. Because PVSyst reflects temperature-model settings in the results, review whether the mounting structure conditions and temperature settings match the actual installation configuration.

Settings related to degradation and long-term projections can also cause warnings or caution notices. How you treat the degradation rate depends on whether you are looking at single-year energy production or long-term financial performance. Confusing single-year comparisons that do not account for degradation with energy production values based on long-term averages can lead to misunderstandings when shared internally. When using PVSyst results in submission or explanatory materials, it is important to clearly state which year’s energy production is being shown—whether it is the first-year assumption or a long-term average.

When addressing warnings about loss settings, base your decision on whether they match site conditions and operational conditions rather than reducing values to make projected energy production look higher. In practice, loss settings tend to be an adjustment item that influences energy production, so approaches can vary between persons in charge. Maintain a standard internal policy for settings, and if you change them for a specific project, record the reasons so that it is easier to review the results later.

Warning 6: Minor warnings that tend to persist before report output

In PVSyst, even when the calculation itself has been completed, minor warnings can remain before report output or on the results confirmation screen. For example, project information left unentered, inconsistencies in case names, insufficient entries in the description field, or specific sub-settings left unconfirmed. These may not have a major impact on the power generation calculation itself, but caution is necessary when using them for submission documents or internal sharing materials.

Before generating the report, the first things to check are whether the project name, site name, variant name, creation date, and description of the design conditions are appropriate. In PVSyst, multiple cases are often created and compared, so if the naming is ambiguous you may not know which conditions the results correspond to. Even if there are no warnings, case names that are abstract, such as "Plan 1" and "Plan 2", make it difficult to trace their contents later.

Next, verify that the main conditions shown in the report match the actual design intent. The number of modules, inverter capacity, tilt angle, azimuth, site conditions, loss settings, and whether shading is present are the items a report reader will check first. Even if warnings are minor, errors in these conditions can affect the reliability of the overall results.

Also, when reusing multiple simulation cases, old descriptions or notes from previous projects may remain. These may not be shown as warnings, but in practice this is a very common error. For example, if you duplicated a case from a different site yet the previous site name remains in the description field, the person receiving the report will be confused. Before outputting the report, check not only the input values but also the text information that will be displayed.

Minor warnings often concern the consistency of the documentation more than the validity of the calculation results. Even if they are not a major issue during internal review stages, they can cause misunderstandings when the materials are used for client explanations, stakeholder sharing, design reviews, or approval documents. A PVSyst report is not simply an output of calculation results but also a document that explains the design conditions. Therefore, even minor warnings should be resolved so that readers can correctly understand the conditions.

As a countermeasure, create a habitual checklist to use before outputting reports. Rather than converting to PDF immediately after calculations are complete, first confirm the main conditions on the screen, then check the displayed content in the report preview. In particular, for materials to be shared externally, review whether the consistency of conditions, units, names, notes, and differences between cases is clear. Do not rely only on warning messages; it is important for a person to visually confirm the material’s clarity.

How to Proceed When Verifying Warning Messages in Practice

When addressing PVSyst warning messages, it's more efficient to review them by classifying the causes than to make ad hoc corrections in the order they appear. The warnings are diverse, but in practice it's easiest to organize them by treating each as one of: "input errors", "inconsistencies in design conditions", "insufficient data", "intended special conditions", or "unorganized documentation".

First, check for obvious input errors. Mistakes such as a wrong number of digits, unit mix-ups, incorrect site selection, omitted module counts, or an incorrect sign for the azimuth are common causes of warnings. In particular, when creating a new project by copying a past one, previous settings tend to remain. Not limited to PVSyst, leftover inputs from duplication work in simulation software can lead to major mistakes.

Next, verify whether there are truly any inconsistencies in the design conditions. Parameters such as string voltage, capacity ratio, input current, and equipment configuration can produce warnings in PVSyst that prompt a design review. At this stage, it is advisable not to decide based solely on the simulation engineer’s judgment but to confirm with the personnel responsible for electrical design and construction planning. This is to avoid discrepancies between what was corrected in PVSyst and the actual design drawings.

Next, classify warnings caused by data insufficiency and approximate settings. Meteorological data, terrain conditions, shading conditions, and loss settings may not be available in detail during the initial study phase. In such cases, rather than trying to eliminate warnings completely, it is important to explicitly state the assumptions and to distinguish what is being treated approximately from what requires detailed study. Because the accuracy of a simulation depends on the accuracy of its input data, it is more practical to address data insufficiencies openly rather than conceal them.

Warnings may also appear because of intentionally applied special conditions. For example, cases such as adopting a higher capacity ratio than normal, assuming special mounting conditions, or using conservative loss values. Such warnings should not be simply corrected; they should be documented so they can be explained as part of the design intent. It is important that a third party reviewing them later can understand why those settings were chosen.

Finally, check for any disorganization in the documentation. If the report name, case name, notes, descriptive text, or display settings are not organized, the reader may be misled even if the calculation results themselves are correct. When reviewing PVSyst warnings, check not only calculation-related warnings but also how the output appears as a deliverable.

What's recommended in practice is that when you find a warning, you shouldn't delete it immediately; instead, jot down its contents and record the cause and the planned response. Briefly documenting why the warning occurred, which items you corrected, why you didn't correct others, and the impact on the results will be useful for internal reviews and later recalculations. The more familiar you become with PVSyst, the more likely you are to treat warnings mechanically, but explainability is extremely important in real-world work.

Accurate on-site conditions are essential to reduce PVSyst warnings

To reduce PVSyst warning messages and increase the reliability of simulation results, it is essential not only to operate the software but also to accurately understand the on-site conditions. The power output of a solar PV system is affected by many factors beyond irradiance and temperature, including terrain, orientation, tilt, surrounding obstructions, rack height, module spacing, and ground undulations. If these conditions are entered into PVSyst ambiguously, warnings may be generated, or even if no warnings appear the results may deviate from reality.

Especially for shading analysis and layout planning, on-site dimensional information is important. Even land that appears flat on drawings can actually have undulations that affect mounting structure height and inter-row shading. Surrounding buildings, trees, equipment, slopes, and retaining walls also cast shadows depending on the time of day. If these are entered only approximately, the estimated shading loss may differ.

Also, if the on-site orientation or coordinates are inaccurate, the array orientation and the positional relationships with obstructions will be misaligned. In solar photovoltaic simulations, azimuth angle differences of a few degrees can affect annual energy production and the generation profile by time of day. In particular, for self-consumption systems, the balance between morning and afternoon generation is important, so azimuth errors cannot be ignored. To enter data accurately in PVSyst, it is effective to utilize position information and surveying data obtained on site.

In understanding site conditions like these, using an iPhone-mounted GNSS high-precision positioning device such as LRTK makes it easier to use location data collected on-site when organizing the assumptions for design and simulation. For example, by recording with high accuracy the site boundaries, planned racking locations, positions of obstructions, and inspection target points, you can more clearly justify the input conditions for PVSyst. Furthermore, if you attach location information to site photos and keep them, it becomes easier for colleagues to identify which location the information refers to when confirming conditions later.

PVSyst's warning messages may appear to be issues that can be resolved solely by settings within the software. However, in reality many of them are related to site conditions, design conditions, and the accuracy of input data. If you can obtain accurate location and terrain information at the site and reflect them in the simulation conditions, it becomes easier to identify the causes of warnings and the explanatory power of the results improves. When mastering PVSyst, collecting accurate on-site information is as important as the on-screen configuration operations.

Summary

PVSyst warning messages are not shown to stop calculations but are important signs to review design conditions and input data. Common warnings encountered in practice concentrate on string voltage, the relationship between inverter (power conditioner) capacity and array capacity, meteorological data, shading settings, loss settings, and unresolved items before report output. Because each warning is linked to elements that affect energy production and design decisions, it is important to understand the cause and address it rather than simply dismissing it.

For string voltage warnings, check the open-circuit voltage at low temperatures and the operating voltage at high temperatures, and review the number of modules in series, the temperature conditions, and the module specifications. For capacity ratio warnings, verify the relationship between DC-side capacity and AC-side capacity, peak shaving, and the design intent. For meteorological data warnings, check the location, the period, any gaps, and monthly trends, and, if necessary, assess the validity of the data. For shading warnings, organize the 3D scene, the array surface, obstructions, and the handling of near-field and far-field elements. For loss setting warnings, check for missing inputs or extreme values, and set justified values that match local conditions. For minor warnings before report output, it is important to prepare the materials so they do not give readers a misleading impression.

The difference in how PVSyst is used lies in the judgment made when a warning appears. Instead of immediately changing numbers when you see a warning, classify and consider whether it is an input error, a design inconsistency, insufficient data, or an intended condition—this will make the simulation usable in practice. Furthermore, if you record how you dealt with it, it will be easier to explain during internal reviews, recalculations, or design changes.

To fundamentally reduce PVSyst warnings and increase the reliability of the results, it is essential to accurately understand the on-site conditions. In photovoltaic installations, slight differences in orientation, tilt, terrain, obstructions, and installation location affect power generation and shading losses. If conditions can be organized based on accurate positional information acquired on site, inputs to PVSyst become clearer and it becomes easier to assess warning messages. LRTK, as a device that can be attached to an iPhone to perform high-precision GNSS positioning, can be used for on-site verification of solar power plants, layout planning, recording obstructions, and position management before and after construction. As a preliminary step before evaluating power generation with PVSyst, accurately acquiring on-site positional information and establishing the basis for simulation conditions can lead to design studies that are stronger in practical application.