What is PVSyst? 10 Common Questions Answered

Many practitioners investigating what PVSyst is want to confirm how far the software can be used in their work—not just know an overview—but also for energy production forecasting, loss analysis, comparison of design conditions, report preparation, internal explanations, and business feasibility studies. In designing and evaluating photovoltaic systems, looking only at panel capacity is not sufficient. Solar irradiance, orientation, tilt, shading, temperature, wiring, conversion efficiency, degradation over time, operating conditions, and other multiple factors overlap to determine the final energy production. PVSyst is specialized software used to organize these conditions and to simulate energy production and the breakdown of losses.

On the other hand, for first‑time users the many input fields and the technical terms displayed on result screens can make it hard to know "where to start," "how much to trust the calculation results," and "how to use them for design decisions." This article assumes a practitioner searching for "PVSyst とは" and organizes common questions into ten items. Rather than merely introducing features, it explains even the lines of thinking that tend to cause confusion in practical use.

Table of Contents

• What kind of software is PVSyst

• Question 1: Is PVSyst software that can accurately predict power generation

• Question 2: Can beginners use PVSyst

• Question 3: What are the main parameters to input into PVSyst

• Question 4: Which items should be checked first in the PVSyst results

• Question 5: How should the loss analysis be interpreted

• Question 6: To what extent can shading and terrain conditions be reflected

• Question 7: Can the report be used as-is for internal briefings and review materials

• Question 8: What should be checked when PVSyst results differ from expectations

• Question 9: Is it acceptable to complete design decisions using only PVSyst

• Question 10: What are practical tips for using PVSyst in day-to-day work

• Summary: PVSyst is a decision-support tool for visualizing design conditions

What kind of software is PVSyst?

PVSyst is a specialized software used for forecasting the energy production of photovoltaic systems, performing loss analysis, comparing design conditions, and creating simulation reports. In typical energy production calculations, it is sometimes common to estimate annual generation by multiplying system capacity by solar irradiance and simple coefficients. However, actual energy production is not that simple. Many factors influence it: the amount of solar radiation reaching the panels, the angle at which sunlight is incident, surrounding shading, module temperature, losses during conversion, losses in wiring, and the operating conditions of the equipment.

PVSyst is software for setting these conditions individually and checking how they affect the final energy production. In practical work, it is especially important not only to look at “how much will be generated annually” but also to analyze “which losses are large,” “how much improvement can be achieved by changing design conditions,” and “where the causes are when generation is lower than expected.” For this reason, it is easier to understand PVSyst not as calculation software but as an evaluation tool for organizing the rationale behind design decisions.

Also, PVSyst is used in a wide range of situations, such as preliminary studies for photovoltaic power plants, detailed design, feasibility assessment, preparation of technical documents, and explanations to stakeholders. Because power generation forecasts relate to revenue planning and the review of equipment specifications, it is essential to verify the validity of the assumptions as well as the calculated figures. If the input conditions deviate from the actual on-site conditions, no matter how precise the calculations are, the results will diverge from reality. The purpose of using PVSyst is that it allows you to organize complex conditions one by one and visualize the factors that affect power generation.

Question 1 Is PVSyst software that accurately predicts energy production?

One of the most frequently asked questions about PVSyst is, "If I use this software, can it accurately predict actual energy production?" The short answer is that PVSyst is not a tool for perfectly forecasting future generation. It is intended to predict generation based on the input conditions and to provide information to support design and decision-making. Actual energy production is influenced by year-to-year weather variability, the quality of equipment installation, the state of operation and maintenance, soiling, failures, changes in the surrounding environment, and other factors.

For example, even at the same site, one year may have high solar irradiance while another year may have more rain and clouds. The meteorological conditions used in PVSyst are often based on past statistics and representative weather data, so they do not reproduce the actual performance of any particular year exactly. In other words, PVSyst’s results show “what level of power generation can be expected on average under these conditions,” and do not guarantee that “these figures will definitely occur next year.”

In practice, it is important to use PVSyst results not as absolute values but for comparing conditions and understanding the loss structure. For example, you can compare how energy output changes when you alter the azimuth, change the tilt, revise wiring conditions, or take shading effects into account. By checking the differences among multiple scenarios in this way, you can identify which factors are important in the design.

Also, because there is uncertainty in power generation forecasts, it is important to make the basis for input values clear. If you record choices of solar irradiance data, settings for loss coefficients, assumptions about equipment performance, shading modeling, and assumptions about operating rate, it will be easier to explain the results later. Thinking of PVSyst not as a “box that automatically produces the correct answer” but as “a tool that makes the relationship between assumptions and results explainable” will help avoid excessive expectations and misunderstandings.

Question 2: Can beginners use PVSyst?

PVSyst is specialized software, but that doesn't mean beginners are completely unable to use it. However, when using it for the first time, simply filling in the fields on the screen in order is not sufficient. This is because, unless you understand how each input parameter affects the energy production, you cannot judge the validity of the results. To use PVSyst you need at least basic knowledge such as the basic configuration of a photovoltaic system, the concept of solar irradiance, panel orientation and tilt, conversion losses, the effects of shading, wiring conditions, and how to think about system capacity.

A common stumbling block for beginners is the large number of input fields. There are many settings—site information, meteorological data, system configuration, module plane orientation, combinations of equipment, loss coefficients, shading conditions, and so on. You don’t need to understand all of these perfectly before you start using the tool, but trying to tackle every detail from the outset can easily lead to confusion. It’s helpful to run one simulation under standard conditions first, and then check the annual energy production, monthly generation, and the flow of losses on the results screen.

Next, your understanding will deepen if you change one condition at a time and observe how the results vary. For example, check how changing the tilt angle affects annual energy production and seasonal generation trends, how much impact shifting the azimuth (orientation) has, and to what extent changes in temperature losses or wiring losses are reflected in the overall results. In this way, when learning PVSyst it is important not to change many settings at once, but to carefully examine the relationship between a single condition and its resulting outcome.

What matters for beginners is not aiming for advanced analysis from the start, but being in a position to explain the results. If you can explain why the generation is at that level, which losses are large, and which sources the input conditions are based on, practical reliability will be greatly improved. PVSyst takes time to get used to, but once you grasp the basic workflow, it becomes an easy-to-use tool for design and comparative studies.

Question 3: What are the main inputs to enter in PVSyst?

The conditions to be entered into PVSyst cover a wide range, but broadly fall into those related to location, equipment, mounting surface, losses, and the surrounding environment. For location-related conditions, the plant’s position and the meteorological conditions are important. Because solar power generation depends heavily on solar irradiance, the predicted energy production will vary depending on which location’s meteorological data is used. It is fundamental to use data close to the site and to take elevation and climatic characteristics into account.

Under equipment-related conditions, you set the solar panels' capacity, the number of panels, the connection configuration, the capacity of the conversion equipment, and the overall system configuration. What is important here is not just matching the total capacity, but confirming that the combination of devices is appropriate. If the panel-side output conditions and the conversion-equipment allowable ranges do not align, losses may increase and the intended operation may become difficult.

For conditions related to the installation surface, set the azimuth, tilt, type of installation surface, and the layout approach. Because the power generated by solar panels changes depending on the angle at which they receive sunlight, azimuth and tilt directly affect power generation forecasts. For roof installations, the roof’s orientation and pitch are relevant; for ground-mounted installations, the mounting structure’s angle and the spacing between rows are relevant. In particular, for projects divided into multiple surfaces, it is necessary to consider each surface separately.

In the conditions related to losses, set assumptions such as temperature loss, wiring loss, equipment conversion loss, losses due to soiling, aging-related degradation, and assumptions about stoppages or restrictions. Even though each of these may appear to be a small percentage individually, in aggregate they have a large impact on power generation. For conditions related to the surrounding environment, consider shading from buildings, trees, terrain, and adjacent equipment. Because the impact of shading changes by time of day and season, an evaluation over the entire year is necessary.

When preparing input conditions, it is important to provide justification rather than entering default values casually. Organizing referenceable information—such as on-site survey documents, design drawings, equipment specifications, survey results, maintenance plans, and past similar projects—will also be useful when reviewing later. The accuracy of PVSyst is greatly influenced not only by the software itself but also by the quality of the input conditions.

Question 4 What should be checked first in the PVSyst results?

PVSyst's result screen displays a lot of information, so for first-time users it can be difficult to know where to start. The first things you should check are annual energy production, energy production per unit of installed capacity, performance indicators, monthly generation trends, and the breakdown of losses. Annual energy production is the easiest figure to understand, but it's risky to judge based on that alone, because systems with the same annual energy production can have different loss profiles and seasonal biases.

Looking at power generation per unit of installed capacity makes it easier to compare proposals of different scales. If you only consider total generation, options with larger capacity will appear more advantageous, but by examining generation per capacity you can more easily compare the quality of the design. Also, examining performance indicators allows you to understand how efficiently the entire system is generating power. However, this indicator alone does not determine whether a proposal is good or bad; it must be interpreted together with installation conditions and regional characteristics.

Monthly generation trends are also important. Even if the annual power generation looks reasonable, if a particular month is extremely low it may indicate the effects of shading, snow accumulation, equipment constraints, weather conditions, or the system’s orientation and tilt. Viewing generation by season can reveal issues that are hard to detect from the annual total. In particular, shading can have a large impact during winter when the sun’s altitude is low, so checking by month and by time of day is effective.

The breakdown of losses is very important for understanding PVSyst results. If power generation is lower than expected, you can check where energy is being lost. By examining, in sequence, losses due to incident irradiance conditions, shading, temperature, wiring, and conversion, you can identify areas with potential for improvement. When reviewing the results, it is important to follow the intermediate loss processes as well as the final value.

Question 5 How should loss analysis be read?

PVSyst's loss analysis is among the most practically valuable parts of energy yield prediction. By examining the loss analysis, you can see where and by how much the energy received as sunlight is reduced before it becomes the final usable electrical energy. A result showing low generation alone does not reveal whether the cause is design conditions, shading, temperature, or equipment configuration. Loss analysis provides clues to break down and investigate those causes.

When reading a loss analysis, check it by tracing the flow of energy from top to bottom. First, there is the solar irradiance incident on horizontal and tilted surfaces, and from there the effects of angle of incidence and shading, soiling, temperature, electrical losses, and conversion losses are reflected in order. By examining the losses at each stage individually, you can identify which factors have the greatest impact on the overall result. Items with large values are of course important, but even small losses can combine to produce a non-negligible effect.

What you should pay particular attention to is not only the magnitude of losses but also whether those losses are improvable. For example, the effects of local solar radiation conditions and climate may not be greatly changeable through design. On the other hand, wiring conditions, layout, avoiding shading, combinations of equipment capacity, and installation angle may be improved by design measures. The purpose of reviewing a loss analysis is not simply to find bad items, but to identify the parts that can realistically be improved.

Also, the loss items change depending on the assumptions. Results will vary depending on how much soiling loss is expected, how temperature conditions are set, and how the operational range of the equipment is considered. In practice, it is important not to take the loss-analysis figures at face value, but to verify “which assumptions gave rise to these losses.” When explaining to stakeholders, showing the flow of losses as well as the final energy output makes the explanation more persuasive.

Question 6: To what extent can shadows and terrain conditions be reflected?

In solar power generation, shading has a major effect on power output. Buildings, trees, mountains, the spacing between rows of equipment, and surrounding structures can cast shadows during certain times of day or seasons. PVSyst can model these shading conditions and assess their impact on energy production. However, the accuracy of shading representation depends on the precision of the shapes and location information entered. If site conditions are known only roughly, the shading assessment will also be rough.

Shadows can be caused by distant terrain or by nearby structures. Distant mountains and topography can affect power generation around sunrise and sunset. Shadows from nearby buildings, trees, and from between rows of racking can strongly affect generation at specific times of day or during certain seasons. In particular, during periods of low solar altitude, even short obstacles cast long shadows, making winter power generation especially susceptible to being affected.

When reflecting terrain conditions, it is important to understand local elevation information and the surrounding environment. If treated simply as flat ground, slopes, steps, and nearby obstructions that actually exist may not be reflected. Conversely, even if an unnecessarily complex model is created, reliability will not increase if the source data accuracy is low. What matters is determining the required level of accuracy according to the stage of study. A rough outline may be sufficient in initial assessments, but detailed design and power generation evaluations require site conditions to be reflected more carefully.

In shading assessments, what you should pay attention to is not just whether shading occurs, but when, over what area, and to what extent it has an effect. Even brief shading can have a significant impact if it coincides with periods of high power generation. In addition, shading on a portion of the panels can cause electrical losses to spread more widely than expected. When analyzing shading with PVSyst, don’t be satisfied with shape input alone; you need to verify how much the shading is actually reflected in the results.

Question 7 Can the report be used as-is for internal presentations or review materials?

Reports generated by PVSyst are useful for organizing energy production forecasts and design conditions. Because they consolidate annual generation, monthly generation, key input parameters, loss analyses, and other information, they are presented in a format that is easy to use as a basis for internal briefings and review materials. However, simply submitting the report as-is is not sufficient. What matters in practice is being able to explain the background and assumptions behind the figures shown in the report.

In internal briefings, not all stakeholders are necessarily familiar with solar power generation or simulations. For that reason, simply showing a PVSyst report may not make it clear which figures are important or what should be judged. Emphasizing only the annual energy yield can also lead to the assumptions about losses and uncertainties being overlooked. When using it as explanatory material, it is advisable to supplement the report with the main conclusions, the rationale for input conditions, the options compared, the items with large losses, and any points to note.

Also, the numerical values in the report must be understood together with the input conditions. If meteorological data, system capacity, azimuth, tilt, loss coefficients, shading conditions, etc. change, the results will change as well. Therefore, when sharing the report it is important to make clear under which assumptions the calculations were performed. When comparing multiple proposals, organizing and explaining which conditions were held fixed and which were changed makes the rationale for the conclusions easier to understand.

PVSyst reports are useful as technical supporting documents, but supplementary information tailored to the reader is necessary. For technical staff, explain in detail the breakdown of losses and the validity of the input conditions; for those responsible for management decisions or business feasibility assessments, organize the information around power generation, risks, uncertainties, and potential for improvement. Rather than using PVSyst outputs as-is, adding interpretation according to the purpose increases their value as practical documents.

Question 8: What should be checked when PVSyst results differ from expectations?

When using PVSyst, you may find that the energy production appears to be lower or higher than expected. In such cases, the first thing to check is the input conditions. Because the simulation results are calculated based on the input values, if there are setting errors or differences in assumptions, the results can change significantly. When the energy production differs from expectations, rather than worrying only about the results screen, it is important to review, in order, the location information, meteorological conditions, system capacity, azimuth, tilt, loss factors, and shading conditions.

First, check that the system capacity and connection configuration are set correctly. Mistakes in capacity units, the number of panels, or the number of connections can cause large deviations in the power output. Next, check the orientation and tilt. If the azimuth reference is mistaken or the tilt angle differs from the actual one, it will affect seasonal variations in generation and the annual total. Furthermore, it is important to ensure that the location of the meteorological data is appropriate for the site. If data from a location far from the site is used, the trends in solar irradiance and temperature may differ.

The settings for loss coefficients also need to be checked. If assumptions such as dirt, wiring, temperature, conversion, shutdowns, aging, etc. are over- or underestimated, the overall impression of the results can change significantly. In particular, if any items are still using their initial/default values, you should review whether those values are appropriate for the project. Standard values do not always match the site. You must verify their validity according to the surrounding environment, maintenance conditions, and design specifications.

Shadow settings are also a point that is easy to overlook. If shadows are not taken into account, the power output may be overestimated, while conversely, assuming excessive shading can lead to an underestimated power output. Check that the shadow shape, height, position, and row spacing are correct, and review how they are reflected in the monthly energy yield and loss analysis. When PVSyst results differ from expectations, it is important not to adjust values based on intuition but to isolate, one by one, which assumptions are producing the discrepancy.

Question 9 Is it acceptable to rely solely on PVSyst for design decisions?

PVSyst is a powerful simulation software, but it is not appropriate to complete all design decisions using only PVSyst. PVSyst is an excellent tool for forecasting energy production and analyzing losses, but it does not automatically assess on-site constructability, regulatory requirements, structural conditions, maintainability, detailed electrical design, land-use constraints, or future changes in the surrounding environment. In practical photovoltaic projects, decisions must be made by integrating simulation results with on-site conditions, design drawings, construction plans, and maintenance plans.

For example, a layout that appears to yield high generation in PVSyst may in practice be difficult to construct. There are site conditions that cannot be judged by generation alone, such as land shape, delivery and access routes, ground conditions, drainage, maintenance access routes, and clearance from surrounding facilities. Also, tilt angles and layouts that maximize generation are not necessarily optimal for the overall project; equipment costs, constructability, maintainability, and the potential for future retrofits must also be considered.

Furthermore, PVSyst simulation results are outcomes within the range of the input assumptions. If on-site surveying is insufficient and the understanding of terrain and obstacles is lacking, evaluations of shading and layout conditions will also be uncertain. For design decisions, the quality of information obtained on-site and of drawing data is extremely important. In particular, for ground-mounted installations, complex terrain, or projects with many surrounding obstacles, the accuracy of location and elevation information affects the results.

PVSyst is an important tool for supporting design decisions. However, final decisions require verification by engineers, on-site surveys, alignment of design conditions, and consensus building among stakeholders. Rather than relying solely on PVSyst, comparing simulation results with on-site information enables evaluations that are stronger in practical terms. While placing power generation forecasts at the center of the design, it is important to make comprehensive judgments that also include constructability and maintainability.

Question 10: What are the tips for using PVSyst in practical work?

The key to using PVSyst effectively in practice is less about producing calculation results and more about organizing the relationship between assumptions and outcomes. The purpose of using PVSyst is not simply to generate a number for energy production. Its real value is being able to explain which conditions are affecting energy output, which losses are significant, and which design proposals are reasonable. To do that, you need the habit of recording input conditions, clarifying comparison conditions, and interpreting the differences in results.

First, it is important to organize the rationale for the input conditions for each project. For meteorological data, equipment capacity, orientation, tilt, shading conditions, loss coefficients, and so on, keeping a record of which documents were used to set them will make later review and explanation easier. Especially when multiple people are working together, if the intent behind the settings is not shared, the same project can produce different results. Managing the assumptions is indispensable for improving the reproducibility of simulations.

Next, when conducting comparative evaluations, it is important not to change many conditions at once. If you change azimuth, tilt, capacity, loss coefficients, and shading conditions simultaneously, it becomes difficult to understand why the results changed. In practice, you first create a baseline case and then change one condition at a time to check the differences. This makes it possible to grasp which changes are affecting power generation. To explore opportunities for design improvement as well, it is important to clarify the relationship between condition changes and results.

When reviewing results, we check not only annual energy production but also monthly generation, loss analysis, performance indicators, and shading effects. Even if two proposals have the same annual yield, one that drops sharply in winter and one that remains stable year-round can have different operational implications. Examining the breakdown of losses reveals where there is room for improvement. How effectively PVSyst is used depends on how multidimensionally the results can be interpreted.

Furthermore, it is important to improve the accuracy of on-site information. Terrain, surrounding structures, trees, existing equipment, site boundaries, maintenance access routes, and other elements that cannot be determined from drawings alone need to be confirmed on site. If location and height information remain ambiguous, uncertainties will persist in shadow and layout assessments. To make PVSyst simulations practical, it is essential to consider site inspection, surveying, and the organization of design conditions together.

Summary: PVSyst is a decision-support tool for visualizing design conditions

PVSyst is specialized simulation software used for predicting the energy production of photovoltaic power generation systems, performing loss analysis, comparing design conditions, and creating reports. It does not automatically guarantee energy production; rather, it is a decision-support tool that, based on the input conditions, helps determine what level of energy production can be expected, where losses are occurring, and how the results change when design conditions are modified.

Common questions include whether the predicted energy production is accurate, whether beginners can use it, which conditions to input, what to look at on the results screen, how to read the loss analysis, how much shading and terrain can be reflected, whether the report can be used as-is, what to check when the results differ from expectations, whether it is acceptable to judge based only on PVSyst, and how to use it in practice. The common answer to these is that you should not treat PVSyst's results as mere numbers but understand them together with the underlying assumptions.

In practice, you should not draw conclusions based solely on annual energy production; you need to check monthly generation, the breakdown of losses, the impact of shading, system configuration, and consistency with site conditions. By organizing the rationale for input conditions and being able to explain the differences between alternative scenarios, PVSyst results become easier to use for internal review and stakeholder explanations. Conversely, merely adjusting numbers while site information remains vague does not increase the reliability of design decisions.

Particularly, understanding shading, terrain conditions, site boundaries, equipment layout, and surrounding obstructions is important as a premise for power generation forecasts. To improve the accuracy of solar power generation simulations, it is essential not only to configure settings in the software but also to accurately acquire on-site location information and reflect it in the design conditions. Therefore, using LRTK (iPhone-mounted GNSS high-precision positioning device) is also effective as a means to streamline on-site inspections and surveying and to make the location information needed for design studies easier to handle. By evaluating energy yield and losses with PVSyst and acquiring high-precision on-site location information with LRTK, it becomes easier to link desk-based simulations with actual site conditions. If you want to improve the design accuracy of solar power generation, considering PVSyst analysis together with improved accuracy of on-site data acquisition will lead to more reliable studies.