PVSyst Simulation Procedure | 5 Points for Verifying Results

When checking the energy output of a photovoltaic system in PVSyst, simply running a simulation and generating a report may not provide usable input for practical decision-making. It becomes a document that is easy to use for design review, internal approval, and client briefings only after you verify that the input conditions match the on-site conditions, that loss settings are neither over- nor under-applied, and that the resulting figures show no unnatural bias.

PVSyst is simulation software for photovoltaic power generation systems, sometimes written as PVsyst. While convenient, its results are influenced by the entered location, meteorological data, equipment conditions, shading, and loss conditions. Therefore, personnel seeking a PVSyst manual should not only learn the sequence of on-screen operations but also understand how to verify each condition and how to interpret the results.

This article, intended for practitioners looking for the PVSyst manual, outlines basic simulation procedures and five points that are particularly easy to overlook when checking results. Because specific screen names may vary by version or settings, this piece focuses on an approach to verification that can be readily applied on any site.

Table of Contents

• Overall picture to check first in a PVSyst simulation

• Step 1: Prepare site, meteorological data, and orientation conditions

• Step 2: Enter system capacity and equipment parameters

• Step 3: Check layout and shading effects

• Step 4: Set various losses realistically

• Step 5: Review simulation results from five perspectives

• Points to watch to avoid looking only at numbers when reviewing reports

• Summary to connect to practical energy-yield assessments for use in practice

The overall picture to check first in a PVSyst simulation

PVSyst simulation is an important task for evaluating the power generation of a photovoltaic system in a desk-based study. However, the simulation results do not automatically indicate the correct answer. Because they are calculated based on the input conditions, if the assumptions are insufficient, the reported energy output and loss rates will also diverge from the actual situation.

What matters in practice is not to treat data entry and result verification as separate tasks. After entering the site, meteorological data, system capacity, azimuth, tilt, shading, losses, balance of equipment capacities, and so on, you need to check whether the results are reasonable. Rather than judging “higher than expected” or “lower than expected” by looking only at the power generation figures, it is important to be able to trace why those results occurred.

In particular, personnel searching for the PVSyst manual often get confused not only about the order of screen operations but also about which items to check and to what extent. For example, checks such as whether you have reviewed the monthly trends after selecting the meteorological data, whether the irradiance on the module surface is not unnaturally low, and whether loss settings have not been left at their default values without justification all affect the reliability of the results.

Furthermore, even with the same installed capacity, the annual energy yield varies depending on the installation angle, orientation, presence or absence of shading, the capacity design of the power conditioner, wiring losses, and temperature conditions. In other words, the PVSyst simulation procedure should be regarded not simply as filling in input fields, but as a series of verification tasks: how to reflect site conditions in the model and how to interpret the results.

In this article, following the workflow commonly used in practice, we first organize the input procedures and then explain five key points for checking the results. The content is centered on ideas that can be easily applied in any workplace, without relying too heavily on specific screen names or differences between versions.

Step 1: Prepare the site, meteorological data, and orientation conditions

The first step in the simulation is to establish the site conditions for the power plant. Solar power generation is affected by the installation site's solar irradiance, temperature, surrounding terrain, orientation, and tilt. Therefore, if the initial site settings remain ambiguous, the overall reliability of the results will decline even if subsequent inputs are entered carefully.

First, confirm the basic information for the planned site, such as latitude, longitude, and elevation. If the location is significantly displaced, solar irradiance and solar altitude conditions will change, affecting the forecast for annual power generation. Even when using meteorological data from nearby sites, be aware that actual weather tendencies can differ—for example, coastal, mountainous, basin, or urban environments. Rather than assuming identical conditions just because the distance is short, it is important to select data in light of the site's local characteristics.

Next, review the meteorological data. In PVSyst, power generation is calculated based on meteorological conditions such as solar irradiation and temperature. What is important here is not only which data were used, but also whether those data can be considered representative of the project site. Check monthly solar irradiation and temperature trends and seasonal variability, and look for months that are unusually high or low. If you judge based only on annual values, you may overlook monthly anomalies or seasonal biases.

Orientation and tilt settings also directly affect power generation. The way angles should be set differs for ground-mounted, roof-mounted, and sloped-site installations. Even when entering the azimuth and tilt angles shown on design drawings, you must confirm whether they are referenced to true north, to the drawing’s orientation, or whether they match the reference used in the site survey. If you mix up the units or the signs of the input values, you may see not only differences in generated energy but also inconsistencies in the monthly generation patterns.

Decide whether, when multiple array surfaces exist, it is acceptable to consolidate them into a representative value or whether they should be separated by surface. Treating everything as a single surface simplifies input, but in practice it may not adequately reflect the effects of areas with different orientations or tilts. In particular, for ground-mounted installations that include roofs with east- and west-facing sections or areas with differing grading slopes, organizing conditions by surface makes it easier to explain the results.

Insufficient checks at this stage are difficult to correct in later processes. Before attempting to adjust equipment capacity or loss settings to match energy production, the basic principle of PVSyst simulation is to first verify that the site, meteorology, azimuth, and tilt match the design documents and the on-site conditions.

For Step 2, enter the equipment capacity and device conditions

Once the site conditions are set, the next step is to enter the system capacity and equipment specifications. Here you organize the PV module capacity, the number of modules, string configuration, the power conditioner's rated capacity, input voltage range, connection conditions, and so on. In power generation simulations, errors in entering the system capacity will directly lead to differences in annual generation, so confirming consistency with drawings, single-line wiring diagrams, and equipment lists is indispensable.

The first thing to check is the total capacity on the DC side. Verify whether the capacity calculated from the modules' nominal output and the number of modules matches the capacity listed in the project plan and design documents. Differences in the handling of decimal places, unit discrepancies, and omissions when summing by section can cause unexpected variances. In particular, projects that have undergone multiple design changes may still retain capacities from older documents, so caution is required.

Next, check the string configuration. Verify that the number of modules in series, the number in parallel, and the number of circuits fall within the power conditioner’s input specifications. What needs to be checked here is not only standard operating conditions. The relationship with open-circuit voltage at low temperatures, operating voltage at high temperatures, the maximum input voltage, and the MPPT range is also important. Even if the simulation accepts the configuration, when there is little margin under actual design conditions, cross-checking with the design engineer and the electrical design documents is required.

The capacity setting on the inverter side is also important. Depending on how the AC-side capacity compares to the DC-side capacity, losses can occur when the output is capped during periods of strong solar irradiation. This is not necessarily a bad thing; depending on the design approach the DC side may be intentionally oversized. However, when reviewing the results it is necessary to check how large those losses are and determine whether they are within the expected range.

Also, when entering equipment conditions, it is important not to focus too much on model types or detailed specifications but to understand what the simulation is intended to represent. In practice, approximate evaluations are sometimes conducted at a stage when detailed specifications have not yet been finalized. In such cases, clearly stating in reports and internal documents that the values are provisional conditions rather than final specifications will make it easier to explain the meaning of the numbers later.

The input of system capacity and equipment parameters is a part that tends to be carried out mechanically once you become familiar with PVSyst operations. However, inconsistencies here affect annual energy production, loss rates, perceived equipment utilization, and monthly generation data. After input, always review the consistency of capacity, number of modules, number of circuits, and converter/inverter capacities, and confirm they match the design documentation.

Step 3: Check the impact of layout and shadows

Shading is an important factor when assessing the energy yield of solar PV. When running simulations in PVSyst, it is necessary to verify not only the installed system capacity entered, but also the extent to which shading from surrounding obstacles, array spacing, terrain, buildings, fences, trees, and so on is taken into account.

First, clarify the layout conditions. For ground-mounted installations, the spacing between array rows, the mounting-frame height, the tilt angle, and the relative positions of front and rear rows affect shading. For roof-mounted installations, changes in roof surface level, roof penthouses, equipment foundations, railings, and adjacent buildings are factors that cause shading. Because shading effects can be difficult to interpret from design drawings alone, on-site photographs, survey data, and checks of the surrounding conditions are helpful.

When checking shading, it is important not only to consider the annual reduction in power generation but also to see when, at what times of day, and to what extent shadows occur. With the low solar altitude in winter, shadows from front rows and nearby objects become long. Conversely, in summer the solar altitude is higher, so the same obstacles may have a smaller shadow impact. Focusing only on the annual loss rate can cause you to miss shadows that are concentrated in particular seasons or times of day.

Also, shading from distant terrain and shadows from nearby objects need to be considered separately. The reduction in solar irradiance in the morning and evening caused by mountains and hills affects a wide area. In contrast, shadows from nearby buildings or equipment can have a localized effect on specific arrays or strings. When local shading occurs, it can appear not only as simple irradiance loss but also as electrical mismatch losses.

The more closely the layout is reproduced, the easier it is to reflect on-site conditions, but in practice there are constraints of time and available documentation. Therefore, rather than modeling everything precisely, it is realistic to prioritize reflecting elements that are likely to affect power generation. Confirm items with large impacts—large buildings, long fences, shading from front and rear rows, terrain shielding—and simplify minor ones as long as they can be reasonably explained.

After configuring shadows, verify how shadow losses are reflected in the results. Even if you believe you have set shadows, they will not appear as losses in the report unless they are incorporated into the calculation conditions and case settings. Conversely, applying overly conservative conditions can cause the estimated power generation to be lower than necessary. Although entering shadow data is a single operational step, as a design decision it is a critical process that affects the reliability of the power output.

Step 4: Set various losses realistically

In PVSyst simulations, you set various losses in addition to solar irradiance conditions and system capacity. Representative examples include losses due to temperature, wiring, equipment conversion, mismatch, soiling, aging/degradation, downtime, and output limits. If these settings do not match reality, the expected energy production will change.

What should be avoided when setting losses is reusing initial values or settings from past projects without justification. Even with similar equipment, differences in installation environment, wiring distance, maintenance conditions, surrounding dust, snowfall, salt damage, temperature conditions, and so on will change the appropriate way to think about losses. In practice it is difficult to predict every loss with complete accuracy, but it is necessary at least to understand what each item means and to be able to explain them as assumptions appropriate to the project.

Temperature loss is the reduction in output caused by an increase in the temperature of photovoltaic (PV) modules. In regions with high ambient temperatures or under installation conditions that impede heat dissipation, temperature losses tend to be larger. Installations close to the roof surface or in poorly ventilated conditions may require a different approach than ground-mounted installations. When reviewing results, check whether the temperature loss is unnaturally small or large compared with the site conditions.

Wiring losses are electrical losses that occur in cables on the DC and AC sides. In large-scale projects with long cable runs or projects with complex collection routes, they can have a non-negligible impact. During the estimation stage they may be set to standard values, but as the design approaches the detailed design stage they need to be reviewed based on the actual wiring routes and cable specifications.

Soiling losses are also an item that can vary considerably depending on site conditions. In locations with a lot of dust in the surroundings, near farmland or development sites, where bird damage is expected, or where the cleaning effect of rainfall is limited, the impact of soiling needs to be considered carefully. However, including excessively large losses will result in underestimating power generation more than necessary. It is important to use realistic values in conjunction with maintenance plans and cleaning policies.

Conditions related to shutdowns and output limits are also easy to overlook. Inspections, equipment failures, communication faults, grid-side constraints, and equipment capacity limits can all reduce the final amount of electricity generated even when there is available solar irradiance. Although it is difficult to predict everything precisely in advance, when using estimates for business feasibility assessments or long-term planning, it is necessary to present results not as simple ideal generation but as figures that take operational losses into account.

Loss settings are an area where the judgment of the simulation engineer tends to appear. That is precisely why it is important to document the rationale for the values entered. If you ensure you can explain which basis—internal standards, past projects, on-site conditions, design documents, maintenance conditions, etc.—you used to set them, it will increase credibility in result reviews and when explaining to the client.

Step 5: Review the simulation results from five perspectives

After running the simulation, review the results. The points to look at here are not limited to the annual power generation figure. In practice, it is easier to judge the validity of the results if you check from five perspectives: annual values, monthly trends, breakdown of losses, balance with equipment capacity, and consistency with the input conditions.

The first point is whether the annual energy production is at a reasonable level for the system size. If the production is unusually high or low relative to the installed capacity, there may be errors in the input parameters. Possible causes include selecting the wrong site, mistakes in the azimuth or tilt inputs, using the wrong units for capacity, or insufficient loss settings. Don’t be satisfied with annual energy production alone—check whether the generation per unit of capacity feels consistent.

The second point is the shape of the monthly power generation. In solar power generation, seasonal changes in solar irradiance and temperature cause consistent patterns in monthly generation. Although these vary with region and installation tilt, if a single month is unusually high or unusually low, the cause may be meteorological data, shading, snow accumulation, output limits, or input conditions. Check the monthly graphs and monthly figures to judge whether the breakdown of the annual total looks natural.

The third point is the breakdown of losses. In PVSyst's results, you can check at which stages and how much loss occurs from solar irradiation to the final electricity generation. What is important here is not only to identify items with large losses, but also to verify that those losses correspond to the input conditions. If you set shading to be severe but shading losses are almost nonexistent, or if you assumed long cabling but cabling losses are small, you need to review whether the settings have been applied correctly.

The fourth point is the capacity balance with the power conditioner. If the DC-side capacity is larger than the AC-side, output may be capped during periods of strong solar irradiance. Confirm to what extent this effect occurs and determine whether it is acceptable from a design standpoint. The evaluation approach varies depending on whether you want to maximize generation, balance equipment cost and generation, or match grid conditions.

The fifth point is the consistency between the report’s assumptions and the input materials. Even if the resulting numbers appear reasonable, the submission is inadequate if the location names, equipment capacities, orientation, tilt, meteorological conditions, and loss conditions do not match the materials. In internal reviews or client presentations, reviewers may pay more attention to whether the assumptions are correctly organized than to the numerical results. When you produce the report, be sure to check not only the numerical tables but also the sections describing the conditions.

By checking from these five perspectives, you move closer to "analysis results" that can be explained in practice rather than mere "simulation results." The purpose of using PVSyst is not simply to calculate energy production once, but to verify the validity of the planning conditions and to organize information that can be used for design and business decisions.

Points to Note to Avoid Looking Only at Numbers When Reviewing Reports

When reviewing PVSyst reports, many reviewers focus on annual energy production and loss rates. Of course, those are important figures. However, in practice, resubmissions and rechecks are more likely to be caused not by the numbers themselves but by insufficient explanation of assumptions and inconsistencies in the inputs.

For example, even if the annual energy production falls within the expected range, the credibility of the documentation is reduced if the weather data point is far from the planned site or if calculations were performed using an outdated design capacity. Also, if the drawings show multiple mounting surfaces but the simulation treats them as a single representative surface, reviewers will have lingering doubts unless you can explain whether that simplification is justified.

When checking a report, first verify the basic information listed on the cover and the conditions summary. Check that the project name, location, equipment capacity, azimuth, tilt, meteorological conditions, and calculation conditions match the information to be presented to the intended recipient. If managed only by internal working file names, the names on the report may remain provisional. This is not a technical error, but it is a shortcoming you want to avoid in submitted documents.

Next, check the flow of results. Examine whether the progression—from solar irradiance incident on the module surface, through various losses, to the final AC generation—is realistic. If any stage shows a sudden large loss, verify the cause. Conversely, be cautious if losses that should occur given the site conditions are not apparent. While low losses may at first seem favorable, they can appear small due to omitted settings.

Also, when comparing multiple cases for the same project, it is important to align the comparison conditions. If system capacity, weather data, and loss settings differ while you think you are only comparing orientation and tilt, you will not be able to make a correct judgment. When comparing cases, you need to clearly identify which conditions were changed and which were kept fixed, and be able to explain the reasons for any differences in energy production.

When issuing a report to external parties, the reader may not be familiar with operating PVSyst. Therefore, rather than simply listing technical figures, it is important to supplement them with what assumptions were made, what results were obtained, and which items require attention. If the power generation is high, explain the reasons; if it is low, organize the contributing factors such as shading, orientation, losses, and capacity balance.

Simulation results are used in design, sales, construction, maintenance, and business decision-making. Therefore, when reviewing reports, you need to be mindful not only of whether the operation screen shows completion but also of whether a third party reading the report can understand the relationship between the assumptions and the results. Rather than checking only the numbers, examining the input conditions, calculation results, and their consistency as explanatory documentation together improves practical quality.

Summary to Guide Practical Power Generation Assessments

The procedure for a PVSyst simulation proceeds by preparing the site and meteorological data, entering the system capacity and equipment parameters, checking the layout and shading effects, setting various losses, and finally reviewing the results. While this sequence itself is simple, the reliability of the results can vary greatly depending on which conditions are checked and to what extent at each step.

What is especially important is not to look only at the annual generation during the result-checking stage. If you check from five perspectives—annual generation, monthly trends, breakdown of losses, capacity balance, and consistency of the assumptions—you will be more likely to notice input errors or omitted settings. Also, when using the report as a submission or an internal review document, it is important not only that the numbers are reasonable but also that the reader can understand the assumptions.

PVSyst is a convenient tool for evaluating energy yield, but simply accepting its calculated results is insufficient for practical decision-making. It is important to be able to explain why the energy yield is what it is by taking into account site conditions, design conditions, construction conditions, and maintenance conditions. By retaining the basis for inputs, understanding what the losses represent, and organizing the analysis so multiple cases can be compared, the accuracy and persuasiveness of the energy yield assessment are improved.

Also, when planning a solar power plant, not only desk-based simulations but on-site topography, pile locations, array layouts, as-built conditions after construction, and verification information for maintenance are important. To bring power generation forecasts closer to practical reality, it is essential to incorporate field-collected positional and construction information into design and management and to continuously check the differences between simulation conditions and actual site conditions.

Rather than just learning PVSyst's manual-style operating procedures, treating input conditions, loss settings, result verification, and report explanations as a single workflow makes energy yield simulations more practical and usable in real-world work. The foundation for using PVSyst simulations professionally is not just to 'produce' calculated values but to be able to 'explain' them.