What is PVSyst? 5 Things to Know Before Using It for Design Studies

PVSyst is a specialized analysis software used for simulating the power generation of photovoltaic systems and for comparing design conditions. The official notation is generally "PVsyst", but in Japanese searches and in practical conversation it is sometimes written as "PVSyst". It combines solar irradiance, installation tilt, azimuth, shading, equipment conditions, loss conditions, and other factors to confirm the expected power generation and system performance at the planning stage.

However, using PVSyst does not automatically lead to correct design decisions. If the approach to input conditions or the interpretation of results is mistaken, a report that looks well-formed on the surface can become difficult to use for actual design evaluation.

Table of Contents

• What is PVSyst a tool for verifying

• Note 1: If you do not align the assumptions of the input conditions, you cannot compare results

• Note 2: Power generation varies depending on the handling of meteorological data and solar irradiation conditions

• Note 3: Shading analysis is not only about creating shapes; interpreting the results is important

• Note 4: Using standard loss conditions as-is can deviate from actual site conditions

• Note 5: Read the result report as material for design decision-making

• Procedure for using PVSyst in design studies

• Summary: Connecting PVSyst results to on-site decision-making

What is PVSyst used to check?

PVSyst is a simulation tool used for design studies and generation forecasting of photovoltaic power systems. It allows you to set the layout of solar panels, tilt angle, azimuth, installed capacity, meteorological conditions, shading effects, electrical losses, and so on, and to check annual energy production, monthly generation trends, and the breakdown of losses. In practice, it is used for basic plant design, comparison of layout plans, checking shading impacts, establishing assumptions for profitability analysis, and understanding the effects of design changes.

Practitioners who search for "What is PVSyst" are often not just looking for an overview of the software; they want to confirm how much it can be relied on for design studies, what inputs they should provide, and how to interpret the results. Simulations of photovoltaic systems may seem simple at first glance because entering numbers on a screen produces results. However, in reality each input has design implications, and using the tool without understanding its assumptions can lead to comparing options that should not be compared or to adopting overly optimistic generation estimates.

The results shown by PVSyst are estimates based on the conditions you set. Actual energy yield is affected by weather variability, the surrounding environment, construction accuracy, operation and maintenance, soiling, equipment aging, downtime, and other factors. Therefore, it is more practical to regard PVSyst’s role not as “perfectly predicting future energy yield” but as “clarifying design conditions, comparing multiple proposals under the same assumptions, and visualizing risks and loss factors.”

In design studies, what matters is not just looking at the numerical results, but checking the assumptions from which those numbers were derived. Even with the same installed capacity, annual energy yield and performance ratio will change if the tilt angle or azimuth, the way shading is handled, loss assumptions, or the selection of weather data differ. Rather than judging superiority solely by the magnitude of the numbers, it is important to be able to explain why those differences occurred.

PVSyst is a useful analysis tool for designers and those responsible for power generation projects, but the act of entering data itself is not the objective. Its proper purpose is to organize design conditions, share them with stakeholders, and make it possible to verify assumptions later. Below, I will explain five points to be aware of, in order, before using PVSyst for design studies.

Note 1: You cannot compare results unless the assumptions behind the input conditions are aligned.

When using PVSyst for design studies, the first thing to pay attention to is making the assumptions for the input conditions consistent. In solar PV studies, it is common to compare multiple design options such as layout, tilt angle, azimuth, system capacity, number of panels, racking conditions, and how surrounding obstacles are treated. If factors other than the conditions you want to compare are changed at the same time, it becomes difficult to determine what caused the differences in the results.

For example, if you want to compare different tilt angles but simultaneously change system capacity and loss conditions, you cannot determine whether the difference in energy production is due to the tilt angle, the capacity difference, or the loss conditions. In design studies, it is important to clearly define what is being compared and to keep other conditions fixed as much as possible. This may seem like a simple task, but in practice it is surprisingly easy for it to go wrong.

Especially in the process of moving from initial studies to detailed design, drawings, equipment specifications, layout conditions, grid conditions, and site conditions are updated step by step. When reusing simulation data created in the past, old conditions can remain and end up being treated as a new proposal. If you judge only by file names or case names, the meteorological data, installation angle, loss settings, and shading conditions may actually still be the ones from the previous study.

Therefore, before using PVSyst, it is advisable to first decide how you will manage the input conditions. Make clear which conditions you will fix and which you will use as comparison variables. Record the items changed for each design proposal so that they remain understandable later; this will improve the accuracy of any explanations of the results. In practice, it is very important not only to produce figures for energy generation but also to retain the history of the analysis.

Also, the assumptions underlying the input conditions need to be aligned not only within the company but also among stakeholders. If the design team, the business planning team, the construction team, and the maintenance team each view the results under different assumptions, interpretations will diverge even when looking at the same report. If one person treats the results as a preliminary estimate while another treats them as values suitable for detailed design, misunderstandings will occur in later stages.

Results from PVSyst are output as well-formatted reports, so the numbers can appear highly persuasive. However, those figures depend heavily on the conditions entered. At the design review stage, when sharing results it is essential to explain together "what assumptions the calculations were based on," "which cases are being compared," and "which conditions remain undecided."

Aligning input conditions is not a trivial clerical task but a fundamental practice that supports the reliability of simulations. Adopting this mindset before you start using PVSyst will make it less confusing when you review results later. In particular, when comparing multiple options, create a baseline case first and then change one condition at a time; this approach makes it easier to explain changes in power generation and losses.

Note 2: Electricity generation varies depending on how meteorological data and solar irradiance conditions are handled

When evaluating energy production in PVSyst, the handling of meteorological data and solar irradiance conditions is crucial. Because photovoltaic output is influenced by the amount of solar irradiance, the estimated annual energy yield will vary depending on which region’s and what kind of meteorological data you use. Using data close to the installation site is the basic approach, but proximity alone is not necessarily sufficient.

Solar radiation, temperature, and wind conditions vary depending on topography and the surrounding environment. Even within the same municipality, actual power generation conditions can differ in coastal areas, mountainous regions, basins, snowy regions, and places prone to fog. The meteorological data used in PVSyst are an important assumption for simulations. If they are used without checking whether they significantly differ from local meteorological characteristics, the assessment results will also be disconnected from on-site conditions.

Also, meteorological data differ in terms of the periods covered and the methods used to produce them. Some show long-term average trends, while others are based on observations from specific periods. In design studies, the appropriate approach depends on whether you want values that approximate single-year actuals or to examine long-term average trends. In planning power generation projects, it is important to use assumptions that are explainable and reproducible, rather than simply selecting data that yield higher generation.

What you need to be careful about when selecting meteorological data is that the resulting numbers can take on a life of their own. If the projected annual power generation figure comes out high, the plan will look attractive. However, if the solar irradiance assumptions underpinning that figure are more optimistic than the actual local conditions, it will affect later business decisions. Conversely, if overly conservative assumptions are used, the true differences between design proposals can become difficult to discern.

Practitioners using PVSyst should, when selecting meteorological data, check the distance to the installation site, terrain conditions, elevation, climatic characteristics, the effects of snow and fog, and nearby obstructions. Even if it is difficult to reflect everything perfectly, being aware of what limitations exist makes it easier to explain the results.

Moreover, solar irradiance conditions are also related to shading effects and the incidence conditions on the panel surface. Even if the solar irradiance on a horizontal plane is the same, the irradiance received changes depending on the panel’s tilt angle and azimuth. How much morning and evening sunlight can be received, how far the orientation deviates from due south, and whether shadows are likely during periods of low solar elevation all affect power generation. It is important to consider installation conditions in combination with meteorological data, not just the weather data alone.

Because meteorological data and solar irradiance conditions can appear technical, someone using PVSyst for the first time may be tempted to rely on the default settings. However, if you are using it for design studies, you should at minimum verify "why that data was used," "whether it does not significantly conflict with site conditions," and "whether the results can be adequately explained." When asked for the basis of the estimated energy production, simply replying with numbers produced by the software is insufficient.

When reviewing PVSyst's energy production results, focus not only on the final annual value but also on monthly trends. Check whether output is significantly higher in summer, whether the winter drop is large, and when the effects of shading or temperature appear—doing so makes design issues easier to identify. This is especially important in regions where snow or surrounding shading are expected; don't judge by the annual total alone, but examine seasonal variations.

Point 3: In shadow analysis, creating shapes is not enough—the interpretation of the results is important

One of the features often used in design studies with PVSyst is shadow analysis. It is used to assess the impact on energy production by taking into account shadows from nearby buildings, trees, terrain, and between racking rows. Because shadow effects directly affect the power output of solar power installations, they are an important check in layout reviews and design decisions.

However, shadow analysis is not just about creating three-dimensional shapes on the screen. Even if surrounding obstacles can be placed to look convincing, if their shapes, heights, or positional relationships differ from reality, the analysis results will be off. It is important to model them with the level of accuracy required for design, based on on-site survey information, drawings, photographs, and the results of checks of the surrounding environment.

Be particularly careful not to underestimate the impact of shading. When the sun’s altitude is low—during certain times of day or in winter—shadows from obstacles tend to extend further. Even if you visit the site for only part of the daytime and judge that “there is little shading,” the way shadows appear can change with the season or time of day. PVSyst can assess the impact of shading over the course of a year, but if the positions or shapes of the obstacles you enter are insufficient, the results will not adequately reflect the actual site conditions.

On the other hand, estimating shadows too conservatively can lead to unnecessarily low predicted energy output and constrain the flexibility of layout options. In practice, rather than excessively including every minor obstruction, it is necessary to identify which elements affect energy output and design decisions. Shadow analysis is not necessarily more correct the more detailed it is; what matters is securing the precision required for the purpose.

Care must also be taken regarding shading between rows of mounting structures. The times of day and seasons when shadows from the front row fall on the rear row vary depending on row spacing, tilt angle, azimuth, and differences in ground elevation. If row spacing is reduced to increase installed capacity, the installed capacity will grow but shading losses may also increase. PVSyst can be used to examine these kinds of layout trade-offs, but simply choosing the option with the largest capacity is not necessarily the right approach.

When reviewing shading analysis results, check not only the impact on annual energy production but also which time of year, which times of day, and over what areas shading occurs. Even if the impact on energy production appears small, shading concentrated on specific circuits or sections can lead to electrical imbalances and operational challenges. Confirming the relationship between shading locations and equipment configuration improves the accuracy of design decisions.

Also, in shading analysis, you need to separate losses caused by the blocking of solar irradiance from the electrical effects resulting from how modules and strings are connected. When a shadow covers only part of a module, the reduction in energy generation cannot always be judged simply by the shaded area. When reading PVSyst reports and settings, it is important to check which shading conditions are handled by which calculation methods.

The results of the shading analysis are also used when explaining matters to stakeholders. When explaining reasons for layout changes, the need to ensure row spacing, how surrounding obstacles are handled, and the potential need for tree felling or removal, the PVSyst analysis results provide useful material. However, it is important not to show only the figures from the report but also to explain the obstacle conditions that were input and the modeling assumptions.

Shading analysis is easy to understand visually, but it is an area where the assumptions behind the inputs are often overlooked. Before using it for design studies, you need to be aware of obstacle heights and positions, ground elevation differences, racking layout conditions, and the seasonal movement of the sun. You can check the effects of shading using PVSyst, but correctly interpreting the results requires a solid understanding of the site conditions.

Note 4: Using standard loss conditions as-is can diverge from on-site conditions

In PVSyst simulations, you set various loss conditions that affect energy production. These include temperature-related losses, wiring losses, equipment conversion losses, soiling losses, shading losses, and conditions related to downtime and aging, among others—elements used to realistically estimate energy production. These settings influence the resulting energy yield and the performance ratio.

A common mistake beginners make is to use loss parameters as-is, leaving them at default values or the values from previous, different projects. Standard values can be useful as a reference for preliminary studies, but they are not necessarily appropriate for site-specific conditions. Appropriate loss parameters vary depending on the installation site's climate, system size, cable length, mounting structure type, maintenance plan, susceptibility to soiling, and the surrounding environment.

For example, in locations with heavy dust, areas prone to bird activity, or places affected by snowfall or falling leaves, the approach to soiling and temporary shading needs to be considered carefully. Conversely, if regular inspections and cleaning are planned, they can be organized based on those operational conditions. What matters is not choosing convenient values, but using values that can be justified in light of site conditions and operational policies.

The same applies to wiring losses and equipment conditions. During the preliminary estimation stage, detailed wiring routes may not be determined; even in such cases you should explicitly state that they are undetermined and assume they will be updated in later stages. If the loss conditions used in the initial study continue to be used after detailed design has progressed, they will no longer be consistent with the actual design.

Also, loss conditions cannot be assessed by looking at only one. Multiple losses accumulate to determine the final energy output. Even if individual values appear small, their total can make a significant difference. Since PVSyst’s result reports allow you to check the breakdown of losses, it is important to identify which factors have the greatest impact.

When checking loss assumptions, prioritize whether the assumptions are robust enough to support design decisions rather than lowering values to make generation appear higher. In practice, overly optimistic generation forecasts affect business plans and evaluations after operation begins. Conversely, excessively conservative assumptions can make design comparisons and investment decisions appear unduly strict. A balance appropriate to the objective is necessary.

Before using PVSyst for design studies, it's advisable to clarify who will determine the loss conditions, which documents will serve as the basis, and at what stage they will be updated. For items that designers cannot decide on alone, confirming them with construction, maintenance, and business-planning personnel will make the assumptions closer to reality.

Loss conditions are important input parameters for bringing simulation results closer to reality. However, manipulating them without justification undermines the reliability of the results. When using PVSyst, it is important not simply to enter numbers, but to understand what phenomenon each loss represents and to cross-check them against site conditions.

Note 5: Read the results report as material for design decisions

When you run calculations in PVSyst, you can view a report that includes annual energy production, monthly energy production, the performance ratio, and a breakdown of losses. In design studies, this report is sometimes used to judge the merits of a proposal. However, the results report is not merely a report card. As material for design decisions, you need to read it in a way that links the assumptions to the results.

The first thing to check is not to focus too much on annual energy production alone. Annual energy production is an easy-to-understand metric, but that number by itself does not reveal design issues. By examining monthly generation trends, how shading losses manifest, temperature effects, losses from wiring and equipment, and how these align with the input conditions, you can understand why the result occurred.

The performance ratio is also a frequently used indicator, but it should not be evaluated on its own. A high performance ratio does not necessarily indicate a superior design; the result can vary depending on installation conditions, weather conditions, capacity design, and loss settings. When comparing design proposals, the performance ratio should be checked together with energy yield, installed capacity, layout conditions, and shading effects.

Also, PVSyst reports are compiled in a format that is easy to share with stakeholders, but misunderstandings can arise if readers do not understand the input conditions. For example, results intended for preliminary estimates may be treated as finalized values for detailed design, or unresolved loss conditions may be mistaken as already reflected. When submitting a report, it is important to clearly indicate the stage of the study, the conditions that are not yet finalized, and the items that should be updated in the future.

When evaluating the impact of design changes, reading the results report is important. If you changed the panel layout, adjusted the tilt angle, increased system capacity, or revised shading conditions, you should check not only the difference in energy production but also how much each loss category has changed. Even if energy production increases, an increase in shading losses or wiring losses may indicate other issues.

The results of PVSyst are not the only answer for deciding on a design proposal. There are various decision factors in the design of photovoltaic power generation facilities, such as constructability, maintainability, land use, regulations, grid connection, drainage, ground conditions, and the surrounding environment. Even if PVSyst results are favorable, a layout that is difficult to construct on site or a design that is hard to maintain may not be appropriate overall.

Therefore, the results report should be treated not as a document for choosing the option with the highest figures, but as a document for quantitatively verifying differences in design conditions. By checking power generation, losses, shading, and monthly trends, and comparing them with site and operational conditions before making a judgment, it will become a study document usable in practice.

When saving reports, it is also important to manage them together with the input conditions. If, when you look back later, you cannot tell which meteorological data was used, which layout option it was, or which loss conditions were applied, reusing the results becomes difficult. In design studies, linking and managing result files, input conditions, drawings, and review notes can reduce rework.

How to Use PVSyst for Design Studies

To use PVSyst in design studies, it is important not to build out every detail from the outset but to adapt its use to the stage of the study. In the initial phase, based on approximate installation conditions and system size, you identify trends among multiple options. Because detailed loss assumptions are often not yet finalized at this stage, treat the results not as definitive values but as material for comparative evaluation.

Next, when the layout proposals and equipment conditions become more concrete, update the input conditions. Review the tilt angle, azimuth, row spacing, shading conditions, equipment capacity, wiring conditions, and so on, and run simulations in a state that more closely reflects the actual design. At this stage, check the impact of shading and the breakdown of losses, and identify design issues.

As the project approaches detailed design, PVSyst results become increasingly important as explanatory materials for stakeholders. They provide material to explain why this layout was chosen, why this angle was selected, why a consistent row spacing was maintained, and which losses are being anticipated. It is important to use them not only for the numbers but also to organize the reasons behind design decisions.

In practice, the person responsible for simulations and the person responsible for design may be different. In that case, if the person operating PVSyst does not fully understand the meaning of the input conditions, results that differ from the design intent may occur. Conversely, if the designer does not understand the assumptions behind the simulation, they may place too much confidence in the results. It is advisable to establish a process for confirming assumptions between the parties involved.

Also, when creating PVSyst data, it is easier to manage if you establish rules for each project. By recording the case name, creation date, purpose of the study, changes, and unresolved conditions, it will be less confusing when comparing them later. Especially for projects where the design proposal changes repeatedly, if you do not clarify which results are the latest and which are for reference, there is a risk that old figures will be used by mistake.

When using PVSyst, verifying the validity of the results is essential. If you see extremely high energy production or unusually low losses, check for any inconsistencies in the input conditions. Simply reviewing basic items such as system capacity, meteorological data, shading conditions, loss assumptions, panel surface orientation, and the handling of units can often reveal input errors.

Furthermore, to tie PVSyst results to on-site design and operations, it is important to feed simulation issues back into the drawings and on-site inspections. If there are locations where shading has a large effect, review the layout; if a soiling-prone environment is expected, consider a maintenance plan; if wiring losses are high, review routing and equipment placement. In this way, link the results to concrete actions.

PVSyst is not just a tool for calculating energy production; it is a tool for organizing design conditions, visualizing issues, and enabling discussions among stakeholders on the same assumptions. If used improperly, the figures can end up taking precedence, but when used appropriately it can improve the quality of design studies.

Summary: Connecting PVSyst Results to On-site Decision-Making

PVSyst is a simulation tool for checking the energy production, losses, and shading effects of photovoltaic power generation systems. In design studies, it is useful for comparing layout options, predicting energy production, performing shadow analysis, organizing loss conditions, and preparing explanatory materials for stakeholders. However, using PVSyst does not automatically yield the correct answer. Because results change depending on the input assumptions, managing the assumptions and interpreting the results are extremely important.

Before using it for design studies, the key points to keep in mind are to align the assumptions of the input conditions, handle meteorological data and solar irradiation conditions carefully, interpret shading analysis not only superficially but in terms of what the results mean, verify loss assumptions to match on-site conditions, and read the result reports as material for design decision-making. By keeping these in mind, PVSyst’s results become usable information that serves as the basis for design rather than mere numbers.

What is especially important is not to separate simulation results from the field. Solar irradiation conditions, shading, soiling, maintainability, constructability, and the surrounding environment are all tied to the site. Even if PVSyst shows good results on screen, they are meaningless if they do not match the actual design and operation. Conversely, if you can identify issues from the results and link them to on-site verification and design improvements, the simulation can provide great value.

Practitioners new to PVSyst should, rather than trying to understand every setting perfectly from the start, first focus on "what you want to compare," "which conditions are affecting the results," and "whether you can explain those assumptions." In design studies, the ability to organize the assumptions that lead to the numbers is more important than the numbers themselves.

In studying solar power generation systems, combining desktop simulations with on-site information is indispensable. By comprehensively checking expected power output, shading effects, the appropriateness of layout, and ease of maintenance, the accuracy of design decisions is improved. The analysis results organized in PVSyst become more useful as practical decision-making material when linked to site verification, construction planning, maintenance planning, and post-commissioning performance checks.