PVSyst Error Troubleshooting Manual｜6 Common Causes of Errors

When progressing with a PV energy yield simulation in PVSyst, you may get stuck at any of the following: initial settings, meteorological data, equipment selection, wiring configuration, loss settings, or report output. Even if an error or warning appears on the screen, the cause is not necessarily a single one; inconsistencies in input conditions, differences in units, omitted settings, and oversights in earlier steps may overlap.

This article, aimed at practitioners seeking the PVSyst operation manual, summarizes six common causes that tend to cause bottlenecks and how to check them. The goal is not simply to remove error messages, but to preserve the rationale behind the calculation assumptions and to produce analysis results that can be explained later.

Table of Contents

• Causes of errors due to inconsistencies in initial settings

• Causes of problems related to meteorological data and site conditions

• Causes of problems related to module and power conditioner settings

• Causes of problems related to string configuration and voltage range

• Causes of results being compromised by loss settings and shading conditions

• Causes of overlooking warnings before report generation

• Important verification procedures for PVSyst error mitigation

• Summary

Causes of errors due to inconsistencies in initial configuration

The part of PVSyst that most commonly causes initial bottlenecks is the basic conditions set when creating a project. For photovoltaic power estimates, organize in advance the information that will serve as prerequisites for later steps, such as location, azimuth, tilt angle, grid type, installation method, and the analysis period. If the values entered here remain ambiguous, it can become difficult to reconcile settings later when configuring meteorological data and equipment configuration, which may lead to errors or warnings.

A common issue is that the latitude and longitude listed for a site do not match the actual candidate installation location. Even if you simply pick a nearby point as a proxy, solar irradiance, temperature, solar altitude, and the way shadows fall will change. While it can be acceptable to use a nearby location during the rough-estimate stage, if you plan to use the results in internal documents or proposals you must clearly state which location data were used. Even if no errors are reported, explaining the analysis results becomes difficult if the site conditions are ambiguous.

Even when entering azimuth or tilt angles, it's possible to confuse the angle reference. If the orientation on drawings, the azimuth confirmed on site, and the way angles are represented on the input screen do not match, the estimated power output may come out lower than expected, or the direction used for shadow analysis may be off. Especially on rooftops, sloped sites, or systems with multiple orientations, it may not be appropriate to treat them as a single south-facing surface. Before inputting data, it's important to decide whether to treat the mounting surface with a single representative value or to divide it into multiple surfaces.

Unit mix-ups are a common issue during initial setup. For quantities such as area, distance, height, angle, power, and temperature, you need to check the required unit for each input field. When transcribing from drawings or design documents, confusing meters and millimeters, degrees and slope, or DC capacity and AC capacity can lead to implausible values in later calculations. Even if no error message appears, if values on a report are extremely large or small, it's safer to go back and verify the units.

Management of project names and variant names should not be overlooked. When comparing multiple options, initial versions, revised versions, shaded versions, unshaded versions, loss-modified versions, and so on will accumulate. If you save files with ambiguous names, it becomes hard to trace under which conditions an error occurred. For PVSyst error mitigation, it is important not only to preserve the input data itself but also to keep the work history available for later review.

If an error occurs during the initial setup, do not proceed straight to the detailed settings; instead, check the site, installation azimuth, tilt angle, analysis target, system conditions, and assumptions about capacity in order. In particular, when duplicating and using a project created previously, old site conditions or settings from earlier proposals may remain. Duplicating projects is efficient, but because there is a risk that hard-to-see settings will persist, making it a habit to reconfirm the basic conditions can reduce rework.

Causes of Getting Stuck on Meteorological Data and Site Conditions

Weather data has a major impact on PVSyst analysis results. If conditions such as solar irradiance, ambient temperature, and wind speed are not appropriate, the projected power generation may deviate from the actual site conditions. If errors occur when loading or selecting weather data, you should check the data format, location consistency, the target period, missing values, and how time units are handled.

A common reason for getting stuck with meteorological data is a large distance or difference in conditions between the installation site and the weather observation site. For solar power generation, even within the same region, meteorological conditions vary along the coast, in mountainous areas, in urban areas, and in snowy regions. If there is no nearby station, alternative data may be used, but in that case you need to be able to explain the assumptions—for example, "adopted a nearby station" or "used long-term averages." Even if calculations in PVSyst proceed, if the validity of the assumptions is weak, the persuasive power of the documentation for practical use is diminished.

Mismatch in data formats is also a common cause. When using external data, there can be differences in column order, units, time notation, whether values are monthly or hourly, the type of solar radiation, and so on. If formats don't match at import, problems can occur such as errors, blank values, or unnatural monthly aggregates. Before importing data, it's safest to check what each column means and to remove unnecessary columns or reconcile unit differences.

Meteorological data may contain missing or anomalous values. For example, if solar irradiance is recorded during nighttime, if daytime solar irradiance is continuously zero, or if temperatures fall outside a realistic range, calculation results may be compromised. Even if the data appear to be loaded correctly in the PVSyst interface, the quality of the original data is not necessarily sufficient. As an error-prevention measure, after loading the data check that monthly solar irradiance, temperature trends, and annual values are not extreme.

Care must also be taken when handling time. Differences such as standard time, local time, daylight saving time, and whether time intervals are represented by their midpoint or their end time all affect the distribution of solar irradiance and the impact of shadows. In domestic projects there may be less confusion, but when data come from multiple sources the time definitions may not match. If power generation deviates from expectations, it is easier to find the cause by looking not only at the total solar irradiance but also at its hourly distribution.

Also, after changing meteorological data, it is possible to forget to update the project's site conditions. Even if you only replace the meteorological data, if conditions such as the installation site, elevation, azimuth, and tilt angle remain outdated, the calculations may become inconsistent. When comparing multiple meteorological datasets, recording the dataset name, reason for selection, target year, and site differences will make it easier to explain later.

Errors related to meteorological data are not mere operational mistakes; they directly affect the quality of the assumptions underlying an analysis. Simply fixing a format because a file won’t load, or switching to different data just because a warning appears, is insufficient. By checking why you are using that data, how well the measurement site represents the installation location, and whether there are missing or anomalous values, you can make PVSyst analysis results more usable in practical work.

Causes of getting stuck on module and power conditioner settings

Another common sticking point in PVSyst is the configuration of PV modules and power conditioners. This involves conditions such as capacity, voltage, current, temperature characteristics, input circuits, and conversion efficiency. If equipment specifications are entered incompletely or the combinations are inappropriate, errors or warnings may occur.

The first thing to check is the module's ratings. Nominal maximum power, open-circuit voltage, short-circuit current, maximum power operating voltage, maximum power operating current, temperature coefficients, and so on affect string design and annual energy yield calculations. When transcribing values from datasheets, confusing values at standard test conditions with values under other conditions can cause warnings about voltage or current ranges to appear later in the process. Even a small transcription error can affect the number of modules in series or in parallel, so care is required.

On the power conditioner side, check the allowable input voltage range, maximum input voltage, maximum input current, number of input circuits, rated AC output, and how conversion efficiency is handled. In particular, when considering the ratio of DC-side capacity to AC-side capacity, it is necessary to understand the concept of oversizing and how its limitations manifest. Simply increasing module capacity does not necessarily increase power generation, and under some conditions it may be reflected as output limitation or losses.

Even when using an equipment database, the registered specifications do not necessarily match the model or type under consideration. Selecting a device with a similar name, choosing data for the wrong capacity, or using outdated specifications can lead to errors and deviations in calculation conditions. After selection, it is important not to rely on the name alone but to verify the key electrical specifications against design documents and manufacturer specifications. Before negotiations or internal confirmations, it is more practical to check whether the specification values match than to rely on the equipment name.

When creating equipment data yourself, more careful verification is required. Because there are many input fields, you may be tempted to feel reassured just by filling in the required items. However, if information such as temperature coefficients, low-light characteristics, efficiency curves, and current limits is missing, the analysis results may be simplified and end up being more optimistic or conservative than reality. Even if you cannot fully reproduce all values, recording which items were assumed will make it easier to accommodate changes in conditions later.

In combinations of modules and power conditioners, the number of modules in series, the number in parallel, and the assignment to input circuits are important. If an error occurs, evaluate not only the specifications of individual devices but the entire configuration. Check whether the open-circuit voltage rises too much at low temperatures, whether the operating voltage drops too much at high temperatures, whether input current exceeds its limit, and whether there is any imbalance among input circuits. Because noncompliance can occur only under specific seasonal or temperature conditions, it is necessary to assess conditions throughout the year.

When installing on multiple surfaces, connecting strings with different orientations or tilts to the same power conditioner can cause operating conditions to be mismatched. Even if you can configure them on-screen, differences in generation characteristics during actual operation can lead to losses. The absence of errors and what is desirable in the design are not the same thing. In PVSyst, it is important to review equipment specifications, wiring configurations, and the conditions of the installation surfaces together while checking warnings.

Causes of Getting Stuck with String Configuration and Voltage Range

When troubleshooting errors in PVSyst, a common point where practitioners get stuck is the string configuration. How many PV modules are connected in series, how many strings are connected in parallel, and to which input they are assigned affect the voltage, current, output limits, and losses. Mismatches here tend to appear as on-screen errors or warnings and can take time to isolate the root cause.

When determining the number of modules in series, check the open-circuit voltage at low temperatures and the operating voltage at high temperatures. At low temperatures the module voltage rises and can exceed the maximum input voltage. Conversely, at high temperatures the operating voltage falls and can drop below the lower limit of the operating range. If you set the series count based only on standard conditions without accounting for annual temperature variations, PVSyst may display a voltage-range warning.

In parallel configurations, the upper limit of the input current becomes the issue. Depending on the combination of the module current rating and the number of parallel circuits, the input-side allowable current can be exceeded. Especially when increasing the number of circuits to aim for higher capacity, you may see warnings on the current side even if the voltage is within range. It is important to check whether the error indication refers to voltage or current, and to determine whether you should change the number of series modules or the number of parallel circuits.

Handling leftover panel counts is also a tricky issue in string configuration. Due to the roof shape or site layout, it may not be possible to make all strings the same number of modules. However, if strings with different module counts are connected to the same input, their operating conditions will not match, which can cause losses and warnings. Just because you can set it in PVSyst doesn’t mean you should force them together; it’s more stable to base the design on arranging circuits under the same conditions.

For installations with multiple orientations or multiple tilts, how strings are divided becomes even more important. If east- and west-facing surfaces, north- and south-facing surfaces, different tilts, or surfaces with different shading patterns are grouped into the same input, the power generation characteristics by time of day will be misaligned. As a result, this can lead to increased losses in simulations, warnings, and generation amounts that do not match expectations. The assignment of input circuits should be considered not only to shorten wiring distances but also from the perspective of aligning power generation characteristics.

To resolve string configuration errors, first verify whether the setup works with a simple single-face configuration, then expand to multiple faces and multiple inputs—this makes it easier to trace the cause. If you include all conditions from the start, it becomes difficult to determine which face, which input, or which temperature condition is causing the inconsistency. The more complex the case, the more effective it is to confirm with the minimal configuration and then add elements.

Also, always confirm that the design drawings and the inputs in PVSyst match. If the number of modules in series shown on the drawings, the number of circuits in the combiner box, the allocation to the power conditioners, and the total number of modules do not match the values in PVSyst, the capacity and energy yield will be incorrect. Before exporting the report, cross-check the total number of modules, DC capacity, AC capacity, and number of strings against the design documents to prevent simple input errors.

Causes of Results Breaking Down Due to Loss Settings and Shadow Conditions

In PVSyst, various loss conditions affect the calculation of energy yield. Temperature loss, wiring loss, mismatch loss, soiling loss, shading loss, conversion loss, and output limitations accumulate to determine the final energy yield. Even if no errors or warnings are reported, inappropriate loss settings can cause the results to deviate from actual conditions.

A common problem with loss settings is continuing to use the initial values unchanged. Initial values are useful as a guideline to start an analysis, but they do not necessarily reflect site or design conditions. For example, for installations with long cables, environments where ambient temperatures tend to be high, locations prone to soiling, or sites susceptible to shading, loss conditions need to be checked individually. Being able to calculate with the initial values is not the same as those values matching actual field conditions.

Wiring losses involve cable length, cross-sectional area, current, and circuit configuration. At the estimation stage, calculations may be performed using representative values, but as you approach detailed design, confirmation that takes wiring routes and the positions of junction boxes into account becomes necessary. If wiring losses are extremely small, some inputs may be missing. Conversely, if they are extremely large, the distance or units may be incorrect. Rather than looking only at the loss rate, verify the basis for the input conditions.

Soiling losses should be assessed according to the region and installation environment. In conditions such as abundant airborne dust nearby, anticipated bird fouling, low tilt angles that make natural cleaning unlikely, or the effects of snow and falling leaves, simple standard values may not adequately explain the situation. When entering values into PVSyst, it is important not to use overly optimistic figures. If the basis is unclear, adopt values that can be justified together with the maintenance plan and local site conditions.

Shading conditions are an important cause of differences in power generation. If there are shadows from surrounding buildings, trees, utility poles, shadows between rows of racking, or shadows caused by terrain, omitting shading inputs can lead to an overestimation of power generation. Conversely, entering shading shapes or heights too conservatively can result in an unnecessarily low estimate of power generation. In shading analysis, site inspection, drawings, survey data, and mounting heights are aligned to verify that the input conditions are close to reality.

If you get stuck when setting shadows, the cause can sometimes be the input of the 3D geometry itself. If an obstacle’s height, distance, azimuth, or reference plane is misaligned, the shadow direction and time of day will appear unnatural. When adding multiple obstacles, rather than creating a complex model all at once, add them sequentially from the main shading factors and check how the results change to more easily identify the cause. If the power output drops significantly after applying shading, recheck the units for the obstacles’ dimensions and positions.

Temperature losses are another item that are easy to overlook. Module temperature is affected not only by ambient air temperature but also by the installation method and ventilation conditions. The tendency for temperature rise varies depending on whether the modules are installed close to a roof, ground-mounted with good ventilation, or have different racking heights. If the temperature conditions do not match the site, annual energy production will differ. Even if PVSyst is not showing an error, it is necessary to check the loss breakdown to ensure that the temperature losses are not anomalous.

Loss settings are not a knob for adjusting power generation. They are parameters for reflecting design conditions, site conditions, and maintenance conditions in the calculations. Rather than changing them to convenient values to avoid errors, it is important to use values that can be explained. When submitting a report, being able to explain which losses were set and the rationale behind them will make it easier to respond to reviews and requests for revisions.

Causes of Overlooking Warnings Before Report Output

In PVSyst, even after calculations are complete and a report can be generated, warnings and notes may still remain. In practice, it's common to assume the job is finished simply because a report can be produced, but depending on their content, warnings can include important issues that affect the assumptions behind the analysis results. When addressing errors, you need to pay attention not only to problems that stop calculations but also to issues where calculations proceed but require verification.

Before generating the report, what you should check is a summary of the input conditions. Verify that the site, meteorological data, installation azimuth, tilt angle, module capacity, inverter capacity, string configuration, and loss conditions match the design documents and internal review parameters. Even if you think you set each item individually on the screen, settings from the original template may remain or conditions you tested midway may still be left in place.

Next, check whether the power generation results are intuitively reasonable. Look at the annual energy output, indicators equivalent to capacity factor, the monthly generation trend, and the breakdown of losses to see if there are any extreme values. If a specific month’s generation is unusually low, the cause might be the weather data or shading conditions. If a single item is large in the loss breakdown, go back and check the input conditions for that item. It is important not only to compare magnitudes but also to be able to trace why those values occurred.

Warning messages are not necessarily fatal problems. Some warnings may be acceptable in preliminary assessments, while others cannot be overlooked in submission documents. The important thing is not to eliminate warnings, but to understand their content and then decide whether to proceed. For example, warnings about equipment configuration margins, voltage ranges, overloading, shading losses, and insufficient data can affect design decisions and accountability.

When interpreting a report, focusing only on total energy generation will cause you to overlook the root cause. PVSyst reports contain multiple checkpoints such as input conditions, energy yield, loss diagram, equipment configuration, and monthly values. Even if total energy generation is close to expectations, if the breakdown of losses looks unnatural, it may be being offset by another input error. Conversely, even if total energy generation is low, if that results from properly entered shading or temperature conditions, the assessment may still be realistic.

When using this for internal review or for explaining to clients, we recommend keeping notes of the input conditions in addition to the report file. Recording the reasons for adopting the meteorological data, the basis for loss values, how shading conditions were created, the date equipment specifications were verified, drawing revision numbers, and so on will make it easier to compare results if conditions change later. Measures to address PVSyst errors should not be limited to on-screen operations alone; they need to be considered together with the management of design information.

Important verification procedures for PVSyst error countermeasures

When an error occurs in PVSyst, trying to fix only the item shown can be a roundabout approach. Because solar power generation simulation links site conditions, meteorological data, equipment specifications, electrical design, and loss settings, the cause is often in an upstream step. To deal with errors efficiently, it is useful to establish a procedure to check items in order from upstream.

The first thing to check is the project's basic conditions. If the assumptions about the installation site, meteorological data, azimuth, tilt angle, and capacity are not correct, adjusting later settings will not address the root cause. In particular, when duplicating past projects, the location, meteorological data, and loss conditions may remain outdated. When an error occurs, making it a habit to first return to the basic conditions will reduce the likelihood of overlooking the cause.

Next, check the equipment specifications and string configuration. Verify that the specifications of the modules and power conditioners match, that the number of modules connected in series and in parallel falls within the voltage and current ranges, and that there is no imbalance in the assignment of input circuits. At this stage, it is important not to judge solely by total capacity. Even if the total capacity matches, if the conditions for each circuit are not met, it can lead to errors or warnings.

After that, check the loss settings and shading conditions. If the power generation differs significantly from expectations, examine the loss breakdown to identify whether the discrepancy arises from the weather data, shading, temperature, wiring, soiling, or output limits. If you change multiple values at once, you won't be able to tell which adjustment was effective. Change one value, check the results, and work in a way that allows you to revert the change if necessary.

When comparing multiple proposals, clearly identify the changes. For example, managing separately a proposal where only the meteorological data is changed, a proposal where only the tilt angle is changed, and a proposal where only the shading conditions are changed makes it easier to explain the reasons for differences in power generation. If all conditions are changed at the same time, it becomes difficult to determine which factor caused the differences in the results. In practice, as the number of options under consideration increases, the precision in managing the conditions becomes increasingly important.

It is also useful to record errors and warnings. When similar projects are repeated, sharing the causes of past problems within the company can shorten the time required for the next job. If you record which screen, which setting, what warning appeared, and how it was resolved, it will be easier to maintain quality even if the person in charge changes. People who are familiar with PVSyst are more likely to rely on tacit knowledge, so it is worthwhile to formalize and document the verification procedures.

Finally, before outputting the report, always perform an overall check. Verify the input conditions, equipment configuration, breakdown of losses, monthly power generation, and warnings, and confirm that no values remain that cannot be explained to the intended recipient. A state in which errors have disappeared only means that calculations can be performed. To use the report as public materials, proposal documents, or internal approval documents, you must confirm the validity of the calculation conditions and their explainability.

Summary

Common causes of problems in PVSyst can be grouped into initial setup, meteorological data, equipment settings, string configuration, loss settings, and reviewing warnings before generating reports. When an error appears, it is important not to look only at the specific spot on the screen but to check upstream conditions in order. Because photovoltaic simulations have interdependent settings, a single input mistake can appear as multiple warnings or as differences in energy production.

In practice, what matters is not only eliminating errors. It is ensuring you can explain why you used that meteorological data, why you chose that equipment configuration, and why you adopted those loss values. PVSyst's calculation results serve as material for design decisions, profitability assessments, internal reviews, and customer explanations. For that reason, condition management and verification records are as important as operating procedures.

Especially in projects that involve comparing multiple options or frequent design changes, organizing the project name, variant name, drawing revision numbers, meteorological data, and loss conditions makes it easier to reduce rework. If you keep the project in a state where you can trace what caused a change when power generation changes, the speed and reliability of the analysis will improve.

To translate analyses conducted with PVSyst into practical work, you need a perspective that links and verifies not only the simulation results but also site conditions, design conditions, construction conditions, and operation and maintenance conditions. By checking each error and warning and documenting the rationale for the input conditions, it becomes easier to explain the energy yield assessment later.