What to pay attention to in PVSyst? Checklist to reduce input errors

Table of Contents

• What PVSyst is used to verify

• Impact of input errors on energy production forecasts

• Project condition inputs to verify first

• Verification of meteorological data and irradiance conditions

• Verification of site location, orientation, and tilt angle

• Common input mistakes in module conditions

• Verification of inverter parameters and capacity ratio

• Verification of array configuration and string settings

• Verification of shading settings and surrounding conditions

• Tips to avoid entering excessive loss conditions

• How to detect input errors from the results screen

• Internal review procedures to reduce mistakes

• Approach to supporting PVSyst input accuracy with on-site measurements

• Summary

What is PVSyst used to verify?

PVSyst is a specialized design-support software that simulates the power output of photovoltaic installations and is used to verify the expected annual generation based on design parameters and loss conditions. In practice, it is used in a variety of situations, including basic plant planning, design comparisons, energy yield forecasting, preparation of explanatory materials for financial institutions and stakeholders, and pre-construction validity checks.

Many practitioners who search for "What is PVSyst" are not simply seeking an overview of the software; they want to know what to watch out for when they actually start entering data. On the screen you enter many items in sequence, and each one affects the energy production calculation in some way. Site location, meteorological conditions, module parameters, inverter parameters, string configuration, shading, and loss rates all add up gradually and are reflected in the final annual energy production and performance indicators.

Therefore, when using PVSyst, what matters is not just memorizing the operational procedures. Rather, in practice you need the ability to verify that the values entered match the site conditions and the design intent. Even for the same power plant, results will differ if the orientation input, the selection of meteorological data, the approach to loss rates, or the method of representing shading differ. Being able to enter numbers and being able to produce a reliable simulation are separate matters.

This article organizes the items you should check in PVSyst to reduce input errors, aimed at practitioners. It is intended not only for first-time users but also for those with prior operational experience, and can be used as a review checklist before submitting results.

Impact of Input Errors on Power Generation Forecasts

What makes input errors in PVSyst scary is that the calculation can still complete even when the inputs are incorrect. The software may issue a warning if a value is clearly abnormal, but mistakes that are only slightly different from actual site conditions, unit mix-ups, or misunderstandings of the azimuth reference can be hard to notice on the screen. If you adopt the results as-is, the generation forecast will deviate from reality and affect design and business decisions.

For example, if the installation site coordinates or meteorological data are offset from the actual site, the calculations will be based on assumptions about solar irradiance and temperature conditions that differ from reality. If the azimuth or tilt angle is incorrect, the way the array receives sunlight changes, which affects the monthly power generation trends. If the number of modules or the rated capacity is entered incorrectly, the calculation will reflect a different system size altogether. Errors in inverter specifications or string configuration can affect the assessment of conversion losses, clipping, and operating voltage range.

Another point to watch out for is overlapping loss assumptions. Because of a desire to be conservative, people sometimes input higher loss rates, but if you re-enter losses that have already been considered under another item, it can lead to an underestimated energy yield prediction. Conversely, being too optimistic about unavoidable on-site issues such as soiling, shading, wiring losses, or temperature rise will produce an overestimated projection. Since PVSyst’s results are built up from the input conditions, you need to be careful not only about a single major mistake but also about the accumulation of small discrepancies.

To reduce input errors, simply filling the screens in sequence is not sufficient. You need a process that organizes the design conditions before input, cross-checks the results after input, and has a third party verify before submission. In particular, in practice you work while referring to multiple documents—design drawings, layout plans, single-line wiring diagrams, equipment specifications, on-site survey data, meteorological data, and shading study materials—so you must also be careful about inconsistencies between documents.

Input the project conditions to be confirmed first

What you should first confirm in PVSyst are the project's basic conditions. If you start entering data while the location, project name, equipment involved, grid-connection assumptions, or scope of the design are still unclear, you'll end up with more revisions later in the process. This is especially important when comparing multiple options: if you don't clearly specify which case corresponds to which design proposal, it can lead to misinterpretation of the results.

When entering the site location, confirm that the latitude, longitude, and elevation match the actual site. In power generation simulations, location information affects calculations of solar radiation conditions and solar altitude. If conditions from a location distant from the actual site are used, solar irradiance, temperature, shadowing patterns, and other factors may differ from reality. This is especially true in mountainous areas, coastal areas, snowy regions, basins, and areas with large elevation differences, where weather conditions can vary even between nearby locations.

Project names and variant names should not be overlooked. In practice, you may create multiple cases such as initial drafts, revised drafts, final drafts, different capacities, different orientations, different tilt angles, and different loss conditions. If names are ambiguous, you may not be able to tell later which result is the latest. Even if it isn’t an input error per se, poor file management or case management can lead to the risk of submitting incorrect results.

Also, it is important to clearly define the scope of the design target. Whether you are calculating the entire power plant, only a specific section, or only the added/expanded portion will change the capacities and equipment configuration you need to input. Cross-check the drawings and equipment lists, and first confirm that the system size in PVSyst matches the actual subject under review; this basic step prevents mistakes later.

Confirmation of Meteorological Data and Solar Radiation Conditions

Meteorological data are a very important input for PVSyst's power generation forecasts. Because power generation is greatly influenced by solar irradiance, the results change depending on which meteorological data are used. To reduce input errors, you should not only import the data but also verify that the data are reasonable as representative values for the site.

First, you should check the distance between the target site and the weather-data location. Even if the data come from a nearby point, it may not be appropriate as an assumption for power generation if topography, elevation, sea breezes, snowfall, fog, or the propensity for cloud cover differ. In particular, be careful in mountain slopes, valley terrain, coastal areas, industrial zones, and heavy-snow regions, where local differences tend to be large.

Next, check the period covered and the representativeness of the meteorological data. The nature of the data differs depending on whether it is measured values for a single year, long-term averages, satellite-derived estimates, or values from a nearby observation station. Because PVSyst performs calculations based on the input weather conditions, using data without understanding its origin makes it difficult to explain the results. When explaining the power generation forecast in submission materials, it is also important to understand the characteristics of the meteorological data adopted.

Be careful about the units and types of solar irradiance. Solar radiation can be represented in multiple ways—horizontal-plane irradiance, tilted-plane irradiance, direct components, diffuse components, etc. Misunderstanding the format of the input data can change the assumptions used in calculations. Also, when handling monthly values, the ordering of months or mix-ups in units can occur. Because even small transcription errors can affect annual power generation, it is important to check the monthly graphs and annual values after loading to make sure there are no unnatural seasonal variations.

Air temperature and wind speed should also be checked. In solar photovoltaic systems, module output decreases as module temperature rises, so ambient temperature conditions are related to temperature-related losses. Wind speed can be relevant when evaluating heat dissipation conditions. Don’t focus solely on irradiance; also verify that the monthly temperature trends match local expectations and that there are no extremely anomalous values.

Confirm installation location, orientation, and tilt angle

When specifying the installation site conditions, errors in entering the azimuth and tilt angle are often a problem. PVSyst calculates how much sunlight an array receives based on which direction it faces and at what angle it is installed. Therefore, if the azimuth or tilt angle is entered incorrectly, it will cause differences not only in the energy output but also in the month-by-month generation trends and the effects of shading.

When checking orientation, it is important to correctly understand the reference direction. The orientation shown on the drawings, the orientation on site, the coordinate axes of the survey results, and the input direction in PVSyst do not necessarily align. You must verify whether to use true north or magnetic north as the reference, or whether it is acceptable to treat the top of the drawing as north. In particular, misreading the orientation is likely when the site plan has been rotated for drafting or when the layout’s display direction does not have north at the top.

With slope angles, take care when reading roof pitch and mounting/rack angles. Mistakes can occur depending on whether the angle is entered in degrees or converted from pitch notation. For roof-mounted installations, you need to confirm that the roof surface slope and the module surface slope match. For ground-mounted installations, also verify the racking angle shown on the design drawings, the actual construction conditions, and whether any angle changes have been made to account for snow or wind.

Extra care is required for installations that feature multiple orientations and tilts. For roofs split into east and west orientations, roofs with multiple planes, distributed layouts following the terrain, or designs where each section has a different tilt angle, entering a single representative value can deviate from the actual conditions. It is important to decide—based on the design intent—whether to model them as multiple arrays in PVSyst or to approximate them with a representative value, and to record that decision.

After entering the azimuth and tilt angle, check not only the annual energy production but also the monthly trends. For installations that are nearly south-facing, verify that production is not overly skewed toward a particular season; for east- or west-facing installations, confirm that the morning and evening generation patterns are as expected; and for low-tilt installations, check that the difference between summer and winter is not unnatural. It is important to have the mindset of working backwards from the shape of the results to identify input errors.

Common input mistakes in module conditions

Module parameters are among the PVSyst input items where mistakes are most likely to directly affect energy production. Because rated output, number of modules, temperature characteristics, electrical characteristics, and degradation conditions are involved in the calculations, cross-checking against specification sheets and design documents is essential. In particular, exercise caution when similar model numbers have different outputs or when the selected module changes due to design modifications.

First, what I want to confirm is the module rated power and the number of modules. The system capacity is determined by the combination of module rated power and the number of modules. If you misinterpret the output per module here or enter the number of modules based on an old drawing, you will end up with a simulation that represents a different system size. This will not only cause a large discrepancy in the absolute amount of generated energy, but also affect how capacity ratios and losses are evaluated.

Next, check the electrical characteristics of the module. Open-circuit voltage, short-circuit current, maximum output operating voltage, maximum output operating current, temperature coefficients, and so on are related to the string configuration and the combination with the inverter. Even when using pre-entered data, you must verify that the specifications adopted match the design documents. Selecting a model with a similar model name can lead to a mistake that is difficult to detect at a glance.

Temperature characteristics are also important. Since a module's output decreases as temperature rises, the temperature coefficient and assumptions about the installation method affect power generation. Modules heat up differently depending on whether they are installed close to the roof surface, on ground-mounted racks, in well-ventilated installations, or in poorly ventilated ones. Verify that the actual installation conditions match the assumptions about temperature losses.

Also, in designs that account for rear-side reflected light, such as bifacial configurations, assumptions about reflectivity, installation height, ground-surface conditions, and row spacing become important. If these are overestimated, projected power generation may be overly optimistic. Conversely, if a design that could actually benefit from rear-side effects is treated under standard single‑sided conditions, it may be underestimated. For module conditions, it is necessary to consider not only the rated capacity but also the compatibility between the installation environment and the module characteristics.

Verification of inverter conditions and capacity ratio

In the inverter settings, check that the equipment specifications you entered and the designed number of units, capacities, and connection configuration match. Inverters convert DC power to AC power, and parameters such as conversion efficiency, rated capacity, input voltage range, maximum input current, and number of circuits affect energy yield calculations. In PVSyst results, they also relate to inverter losses and the presence or absence of clipping, so leaving input errors uncorrected can lead to incorrect design assessments.

First, check the inverter's rated capacity and the number of units. The capacity ratio, which indicates how the inverter capacity compares to the module capacity, affects how you view energy production and losses. In designs where the AC capacity is small relative to the DC capacity, output clipping may occur during periods of strong irradiance. Conversely, if there is excessive headroom, you need to consider the system's economics and efficiency at low loads. Always verify that the capacity ratio in PVSyst matches the design intent.

Next, check the input voltage range. If the number of modules in series per string is too high, the voltage at low temperatures may exceed the upper limit, and if it is too low, the system may fall outside the proper operating range at high temperatures. Even if PVSyst shows no errors or warnings, it is important to verify that the configuration is reasonable by considering the conditions in the datasheet and the safety margins.

Pay attention to how conversion efficiency is handled. If the input data includes an efficiency curve, efficiencies at low and high loads will be reflected in the calculations. When using provisional equipment data or approximate data, it is necessary to understand that the reliability of the results is limited. In particular, while provisional assumptions may be used during the initial study phase, it is important to reconfirm the results for submission to match the actual equipment to be adopted.

Also, when using multiple inverters, check whether the array capacity connected to each inverter is uniform. In some designs, only certain inverters may have a different number of modules connected. Entering an averaged value can fail to correctly reflect individual losses or limitations. In practice, you should verify that the input configuration in PVSyst matches the actual wiring plan by cross-checking with the single-line wiring diagram and the circuit schedule.

Verification of Array Configuration and String Settings

Array configuration and string settings are common sources of input errors in PVSyst. The settings for how many modules to put in series and how many strings to put in parallel affect system capacity, voltage range, inverter input, mismatch losses, and other factors. Even if entering the number of modules looks like a simple task, in practice cross-checking with the design documentation is indispensable.

The first thing to check is whether the total number of modules matches the design drawings. After entering the number of modules in series and the number in parallel, verify that the total count matches the drawings. For example, even a single-module mistake in the series count will not only change the total capacity but also alter the voltage conditions. If the total capacity is displayed on the PVSyst screen, cross-check it against the capacity shown on the drawings and the equipment list.

Next, verify whether the number of modules in series per string falls within the inverter's input voltage range. Voltage rises at low ambient temperatures and falls at high ambient temperatures. Therefore, you must consider operation not only under standard conditions but also at low and high temperatures. Compare the range calculated in PVSyst with the allowable range in the equipment specifications to confirm that the design is feasible.

Verifying the number of parallel connections and the number of input circuits is also important. Each inverter input has limits on the number of strings that can be connected and on the maximum current, so incorrect entry of the parallel count can lead to overcurrent or mismatches in connection conditions. Because this also relates to the actual configuration of junction boxes and combiner boxes and to the conditions of protective devices, it is necessary to confirm consistency with the electrical design documentation.

When a system spans multiple roof surfaces or zones, it's also important not to over-consolidate strings with different orientations or shading conditions into the same input. Treating strings whose conditions differ substantially as a single group makes it harder to accurately capture mismatches and shading effects. How you handle this depends on whether the simulation is for a rough estimate or for detailed design, but keeping a record of how extensively you modeled the system will make later explanations easier.

Confirmation of shadow settings and surrounding conditions

Shadow settings are a factor that greatly influence PVSyst results. The times of day and seasons when shadows fall on module surfaces vary depending on surrounding buildings, trees, utility poles, terrain, the spacing between equipment rows, mounting height, and so on. Underestimating shadows leads to an overestimation of power generation, while overestimating shadows leads to an underestimation of power generation. Because both affect design decisions, careful verification is required.

First, check for the presence of nearby obstructions. Based on site photos, layout drawings, survey maps, and information on the heights of surrounding buildings, verify that you have not overlooked any objects that could cast shadows. In particular, when the solar altitude is low in winter, shadows from distant buildings and slopes can extend farther than expected. Because on-site checks conducted only in summer can make it easy to miss winter shadows, it is important to be mindful of seasonal differences.

Next, check the mutual shading between arrays. For ground-mounted and flat-roof installations, if the inter-row spacing is narrow, shadows from the front row will fall on the rear row. Because the appearance of shading changes with tilt angle, installation height, inter-row distance, and orientation, it is important to accurately reflect the dimensions shown on the design drawings. If you input the inter-row spacing wider than on the drawings, you will underestimate shading losses; if you input it narrower, you will overestimate them.

When configuring shadow settings, you must also pay attention to the height reference. If you confuse whether the height is measured from the ground surface, the roof surface, the underside of the racking, or the module surface, the shadow calculations will change. When reading height information on drawings, confirm the reference plane and make it consistent with the inputs in PVSyst.

Also, for items whose conditions change due to growth or removal—such as trees—consider how to treat future conditions. Even if there is little shading at the time of the on-site inspection, branches and foliage may grow over the next few years. Conversely, if an obstacle scheduled for removal prior to construction is left in the calculation as shading, it will lead to an underestimation of power generation. It is important to base shadowing assumptions not only on the current situation but also on the state at the time of operation.

Precautions to Avoid Including Too Many Loss Conditions

In PVSyst, you can set various loss conditions. Many factors affect energy production, such as soiling, wiring, temperature, mismatch, degradation, shading, inverter conversion, shutdowns, and output limitation. When trying to reduce input errors, it is important not only to avoid overlooking losses but also to avoid entering the same loss more than once.

For example, if you have modeled shading effects in detail but then add a shading-equivalent loss as a separate line item, you may be double-counting the same shading. Similarly, for temperature losses, confusing elements already accounted for in the module temperature model with additional correction values can lead to an unintended underestimation. It is acceptable to include loss rates on the conservative side, but you must distinguish between a safety margin and double-counting.

For soiling loss, verify the reasonableness according to the region and the installation environment. In areas with little rainfall, high amounts of dust, proximity to farmland or construction sites, or bird damage, the impact of soiling may be greater. Conversely, setting excessive losses without considering cleaning schedules or rainfall conditions will underestimate power generation. It is important to consider the local environment together with the maintenance and management policy.

For wiring loss, verify the distinction between the DC and AC sides, the cable length, current, voltage, conductor cross-sectional area, and connection configuration. Even when entering approximate values, as the design progresses you should bring them closer to the actual wiring plan. If the wiring loss is extremely small or large, check whether you have mistaken the units or the input fields.

Handling of degradation and aging is also a point to watch. Whether you look at first‑year energy production, the long‑term average, or the total generation over the project period will change how you treat degradation. If you use PVSyst's single‑year simulation results directly for long‑term evaluation, you need to separately account for degradation rates. Conversely, if degradation is already accounted for in other documentation and you enter the same conditions within PVSyst, there is a risk of double counting.

How to spot input errors on the results screen

In PVSyst, you can sometimes detect input errors by checking the results screen after entering data. The important thing is not to look only at the annual energy production number, but to combine multiple indicators to spot anomalies. Input mistakes can appear as something off somewhere in the results.

First, what I want to check is the relationship between installed capacity and annual generation. If the generation is extremely large or small, reconfirm the location, meteorological data, number of modules, loss conditions, shading conditions, and so on. If the installed capacity has been mistaken, the absolute amount of generation will change significantly. Checking the generation per unit of capacity makes it easier to avoid overlooking issues caused by differences in scale.

Next, check the trends in monthly power generation. In typical solar power systems, monthly generation shows certain trends due to solar irradiance conditions, temperature, snowfall, the rainy season, and shading. If the monthly values differ greatly from the region’s climatic expectations, you should review the selection of meteorological data, azimuth, tilt angle, and shading conditions. If only a particular month is abnormally low, check for shading or data-entry errors.

Checking the loss diagram is also useful. Look at which losses are large, whether the order of losses seems odd, and whether any unexpected losses are unusually large. If inverter losses are too large, check the capacity ratio and equipment selection; if shading losses are large, check for obstacles and the entered row spacing. If wiring losses or soiling losses are extreme, check the units of the input values and for duplicate entries.

Performance indicators should not be overlooked. If a performance indicator deviates significantly from common expectations, the cause may lie in the input conditions. However, because performance indicators vary by region, design, and loss conditions, it is important not to judge them solely as high or low but to be able to explain why the value occurred. If there are values you cannot explain, you should return to the input items and verify them.

Operational methods to reduce mistakes in internal checks

To reduce input errors in PVSyst, operational procedures must not rely solely on individual attention. In practice, situations such as tight deadlines, handling multiple projects simultaneously, and repeated design changes are common. To prevent mistakes in those circumstances, it is important to standardize the items to be checked so that anyone can review them from the same perspective.

First, make it a habit to gather the necessary documents before entering data. Check the layout drawings, equipment specifications, single-line wiring diagrams, string tables, on-site survey data, meteorological conditions, shading study materials, design change histories, and so on, and decide which documents to treat as authoritative. Mixing old and new drawings can cause discrepancies in input values. Confirm the document revision numbers and creation dates, and enter data based on the latest conditions.

Next, prepare a checklist to use after entering the data. If you format it so you verify, in order, location, weather data, capacity, number of modules, orientation, tilt, number of inverters, string configuration, shading, loss rate, and result indicators, you can reduce oversights. The checklist should not be filled out merely as a formality; it is important to use it as a tool to cross-check drawings and specifications.

Third-party verification is also effective. The person who entered the data is often unaware of their own assumptions. Having a different staff member check the results screen and the input conditions makes it easier to detect mistakes such as swapped orientations, capacity mismatches, duplicated losses, or confusion between case names. In particular, for power generation forecasts intended for external submission, it is desirable to separate the data entrant and the verifier.

Also, when design changes occur, record which input items were updated. Errors such as the number of modules changing while the inverter conditions remain old, or the tilt angle changing without updating the shading conditions, commonly happen. Keeping a change history and grouping the input items related to the modified elements for rechecking helps prevent inconsistencies caused by partial revisions.

Approach to Supporting PVSyst Input Accuracy with On-site Measurements

To improve PVSyst input accuracy, it is important to accurately capture on-site conditions, not just rely on desk-based materials. Power generation simulations are predicated on the site's terrain, orientation, obstructions, installation area, elevation differences, and surrounding environment. Judging only from drawings and publicly available information can cause you to overlook conditions that are unique to the site.

For example, if the on-site orientation or site boundaries are misaligned with the drawings, it will affect the layout plan and shadow assessment. If there are elevation differences in the ground, the mounting structure height and the way shadows form between rows will also change. If buildings or trees are present nearby, the impact of shadows will vary by season and time of day. To enter these conditions correctly, on-site position measurements, photographic records, and checks for obstacles are indispensable.

In recent years, situations in which high-precision positional information is handled even during on-site surveys have become more common. In power plant design and maintenance, it is important to link survey results, drawings, photos, point clouds, construction records, and other data using positional information. Inputs to PVSyst are made within the software itself, but if the accuracy of the underlying on-site data is low, there will be limits to the reliability of the simulation results.

An effective approach is to use devices that streamline on-site position verification. LRTK, as an iPhone-mounted GNSS high-precision positioning device, acquires on-site location information with high accuracy and helps improve the precision of design conditions and survey records. When considering photovoltaic power generation systems, many tasks involving location information arise, such as confirming candidate installation sites, recording survey points, identifying obstacle locations, and checking site conditions after construction. To reduce input errors in PVSyst, it is important not only to perform checks within the software but also to improve the accuracy of the baseline data collected on site. By combining PVSyst’s generation forecasts with LRTK’s high-precision on-site awareness, you can reduce discrepancies between desk studies and field conditions and produce design evaluations that are easier to explain.

Summary

PVSyst is a powerful design support software for simulating the energy production and losses of photovoltaic power systems, but the reliability of the results depends heavily on the accuracy of the input conditions. There are many items to check: location, weather data, azimuth, tilt angle, module parameters, inverter parameters, string configuration, shading, loss rates, and so on. If any single input is significantly incorrect, the results will of course be off, and even multiple small mistakes will reduce the accuracy of the production forecast.

To reduce input errors, it is necessary not only to memorize the operating procedures but also to cross-check against design documents, ensure consistency with on-site conditions, verify for any anomalies on result screens, have a third party review, and re-check when design changes are made. In particular, common practical pitfalls include duplicated loss conditions, inconsistent orientation references, mixing up capacity and number of units, and overlooking shading conditions.

When using PVSyst results in submission documents or business decisions, the mere fact that a calculation was performed is not sufficient. It is important to be able to explain which conditions were entered, why those values were adopted, and whether the results are consistent with on-site conditions. To that end, in addition to verifying inputs within the software, efforts to improve the accuracy of on-site data are indispensable.

In the assessment of photovoltaic power generation systems, only when design drawings, on-site surveys, shadow checks, and post-construction records are linked together does reliable simulation and operation management become possible. Practitioners who want to reduce input errors in PVSyst will feel more secure if, in addition to checking numbers on the screen, they establish a system to accurately acquire on-site location information. By using an iPhone-mounted GNSS high-precision positioning device such as LRTK, location information obtained during field surveys becomes easier to handle and also helps verify the prerequisites before entering data into PVSyst. The accuracy of simulations is not determined solely within the software; it also depends greatly on how accurately information can be collected on site.