What is PVSyst? An overview of the entire process from design and verification to reporting

PVSyst is simulation software used for forecasting the power output of photovoltaic systems, performing loss analysis, comparing design conditions, and preparing reports. It is used not only to calculate annual energy production but also to organize factors such as solar irradiance, tilt angle, orientation, shading, equipment configuration, temperature effects, wiring losses, and conversion losses, and to assess how reasonable a solar power plant's design is.

Many of those searching for "What is PVSyst" are likely practitioners who will be involved in designing solar PV systems, conducting business feasibility studies, performing technical reviews, preparing proposal documents, or checking generation reports. Even if they have heard the name, if it's unclear what to enter, what to verify, and how to connect it to reporting, they can easily get stuck at the initial stage of understanding.

In this article, we view PVSyst through the flow of "design," "verification," and "reporting," and explain from an overall perspective how it is used in practice.

Table of Contents

• What is PVSyst used for?

• Practical applications of PVSyst

• Input conditions to define during the design stage

• Basic principles of energy yield simulation

• Key points to check in loss analysis

• Items to check during the verification stage

• Contents to include in the report

• Precautions when using PVSyst

• On-site information required to improve design accuracy

• Summary

What is PVSyst used for?

PVSyst is specialized simulation software used to predict the power generation of photovoltaic systems and to analyze the loss factors that lead to those results. In planning solar power generation, equipment capacity alone cannot determine how much will actually be generated. Even when using solar modules with the same rated output, the amount of generation varies depending on the installation site, tilt angle, azimuth, surrounding shading, weather conditions, equipment configuration, wiring distance, and temperature conditions. PVSyst is used to combine these conditions to estimate annual and monthly power generation.

What matters in practice is that PVSyst is not a tool that simply produces a single number for energy generation, but also a tool that explains why that generation occurs. When evaluating the commercial viability of a photovoltaic power plant, the expected annual generation directly ties into the financial plan. However, the generation figure alone does not allow you to judge whether the assumptions are reasonable, which conditions have a major impact on the results, or where the risks lie. PVSyst lets you check, step by step, from solar irradiance, to incidence on the module surface, losses due to temperature, the effects of shading, wiring and conversion losses, and finally the grid-side output.

Also, PVSyst is not software just for designers. It is relevant to people who need to verify the basis for projected energy production—such as power producers, construction companies, maintenance personnel, technical reviewers, and those involved in finance or investment decisions. Even for those who read the simulation results prepared by designers, understanding the basics of PVSyst makes it easier to know which parts of the report to check, whether the input conditions are reasonable, and whether the estimated losses are realistic.

A key feature of PVSyst is that it allows the relationship between input conditions and results to be traced in relatively fine detail. In simplified calculations, annual energy production is sometimes estimated by multiplying system capacity by a regional coefficient and an assumed capacity factor. This method is convenient for initial studies, but may be insufficient for detailed design or explanatory documentation. PVSyst calculates energy production after organizing meteorological data, system configuration, layout, shading, equipment characteristics, and so on. Therefore, it has the advantage of making it easier to compare how changes in design conditions affect energy production and losses.

However, using PVSyst does not automatically produce the correct answer. Simulations are more valid the closer the input conditions are to reality. Conversely, if site conditions or equipment parameters are entered ambiguously, you can end up with a report that looks tidy but yields results that diverge from the actual situation. It is important to understand that PVSyst is not software that automatically guarantees the correct answer, but a practical tool for quantitatively organizing design conditions and evaluating energy production and losses.

Practical use cases for PVSyst

A typical scenario in which PVSyst is used is the planning stage of a solar power plant. It is used when evaluating candidate land or roof sites to determine how much installed capacity can be accommodated, how much electricity can be generated annually, how significant shading effects are, and whether the equipment configuration is appropriate. In preliminary studies it is used to grasp approximate generation amounts, and in detailed design the input conditions are scrutinized to produce forecasts with greater explanatory power.

Next, it can also be used to compare design conditions. For example, if you change the module tilt angle, adjust the azimuth, widen the inter-row spacing, increase the layout density, or alter the capacity ratio of the conversion equipment, you can compare how the energy production and losses change. In designing a solar power plant, you need to consider not only maximizing energy production but also constructability, land-use efficiency, maintainability, cost-effectiveness, and impacts on the surrounding environment. PVSyst serves to provide comparative information from the perspective of generation performance.

In technical reviews and internal approval processes, PVSyst results are also important. If the power generation forecast is overstated, the business plan’s profitability will appear better than it actually is. Conversely, if it is too conservative, plans that might otherwise be viable can be underestimated. Therefore, it is necessary to verify the basis for the input conditions, the appropriateness of the loss settings, and the consistency of the output results, and to be prepared to explain them to stakeholders. PVSyst reports are often used as part of those explanatory materials.

It is also useful for checking the impacts of design changes. In planning a photovoltaic power plant, the initial conditions can change as site surveys, surveying, site development planning, equipment selection, grid connection conditions, and construction planning progress. Changes are not uncommon—layout may change, the number of panels may change, tilt and azimuth may be adjusted, or the impact of surrounding structures may become apparent. Comparing multiple scenarios in PVSyst makes it easier to explain how design changes affect energy production and losses.

Furthermore, the PVSyst approach is useful for post‑completion evaluation and during the operational phase as well. When there is a discrepancy between actual generation and predicted generation, it is necessary to determine whether the difference is due to weather conditions, equipment malfunction, soiling or shading, or downtime. If a reference simulation created with PVSyst is available, it can be used as a comparison target when checking operational performance. However, in performance evaluation it is important to take actual irradiance and operating conditions into account and not to judge performance solely based on the design‑stage annual predictions.

Input Conditions to Be Organized During the Design Phase

Before using PVSyst, the first thing you need to do is organize the design conditions. In solar power generation simulations, the information to be entered spans a wide range. Installation site, latitude and longitude, elevation, meteorological conditions, terrain, surrounding obstructions, module layout, tilt angle, azimuth, equipment configuration, wiring conditions, and operational conditions all affect the results. It is not that any one of these alone is important; the energy output is determined by the combination of multiple conditions.

Information about the installation site is fundamental. Solar power generation is strongly influenced by local solar radiation conditions, so even a slight change in location can alter the predicted values. In particular, in mountainous areas, coastal areas, snowy regions, areas prone to fog, or areas with nearby elevation differences, general regional averages may not adequately represent the actual on-site conditions. The site information entered into PVSyst should be organized not as a mere address but accurately as the exact location where the power generation equipment will actually be installed.

Meteorological data are also important. In forecasting annual power generation, solar irradiance, ambient air temperature, wind speed, and the like are involved. In particular, solar irradiance forms the foundation of generation, so the results change depending on which data are adopted. In practice, it is important to understand the nature of the available meteorological data and to check the distance to the site, the period, representativeness, and maintainability. Meteorological data are not just numbers on the surface; unless you verify the assumptions under which they were created, you may end up with forecasts that are too high or too low for the planned site.

Information on equipment layout is also essential. The orientation, tilt angle, and spacing of photovoltaic (PV) modules affect not only the power output but also shading impacts. Increasing the tilt angle can be advantageous in some seasons, but it can also increase inter-row shading. Increasing the layout density can raise the installed capacity, but may create shading and maintenance space issues. In PVSyst, you can evaluate these design trade-offs from the perspective of energy production.

Careful input of the equipment configuration is also necessary. If the number of modules, the number of series strings, the number of parallel strings, the capacity of the power conversion equipment, and the circuit configuration are not appropriate, this can lead to calculation errors or unrealistic results. In solar power systems, the capacity balance between the DC side and the AC side is also important. Increasing DC-side capacity can, in some cases, increase generation opportunities, but under certain conditions it may also increase output limitations. PVSyst allows you to verify the effects of such capacity design.

Shading conditions are a factor whose input accuracy tends to be reflected in the results. When surrounding buildings, trees, mountains, rows between mounting racks, or structures within the facility cast shadows, energy production decreases. Because shadows vary with time of day and season, they cannot be assessed by simple area alone. Especially during periods of low solar altitude and in winter, shadows can extend farther than expected. In the design phase, it is important to identify on-site obstacles and terrain as accurately as possible and organize them in a form that can be reflected in PVSyst.

Basic Concept of Power Generation Simulation

PVSyst's energy yield simulation starts with the solar irradiance reaching the Earth's surface and, step by step, calculates the irradiance incident on the module surface, the DC power generated by the solar cells, the AC power after conversion, and finally the amount of energy available for use. In other words, it is important not to look only at the final annual energy yield but to track what conversions and losses occur along the way.

First, the solar irradiance on the horizontal plane is calculated to determine how it strikes the surface of the installed module. Photovoltaic modules are not necessarily placed horizontally; in many cases they have a specific tilt angle and azimuth. Therefore, instead of using the horizontal-plane irradiance as-is, it is converted and considered as the irradiance incident on the module surface. The irradiance received varies depending on installation conditions, such as near-south-facing layouts, east–west configurations, low-tilt installations, and placements that follow the roof shape.

Next, the modules produce direct current (DC) power. However, even with high solar irradiance they do not always generate at their rated output. When module temperature rises, output may decrease, and efficiency can change under low irradiance. Variations between modules, soiling, degradation, and wiring conditions are also taken into account. In PVSyst, these are organized as losses, and the factors that reduce energy production are reflected in stages.

Afterwards, DC power is converted into AC power through conversion equipment. At this stage, conversion efficiency, capacity constraints, input voltage range, and output limitations come into play. Even if sufficient power is generated on the DC side, depending on the capacity and conditions of the conversion equipment, it may not be possible to deliver all of it to the AC side. In particular, when the DC-side capacity is designed to be relatively large, output saturation can occur under certain conditions. Such losses need to be examined as the impact of design policy on the amount of power generated.

The final energy production is the result of passing through multiple such stages. When reviewing PVSyst results, we comprehensively check not only the annual energy yield but also monthly trends, specific loss items, the performance ratio, and how plant utilization appears. For example, even if the annual energy yield looks high, if only certain months are abnormally high, losses are extremely low, shading effects are almost absent, or temperature losses are unnaturally small, the input conditions need to be reviewed.

Power-generation simulations do not completely predict future actual performance. Actual generation can vary due to that year’s weather, equipment outages, soiling, maintenance condition, changes in the surrounding environment, and other factors. The role of PVSyst is to produce reasonable forecasts based on certain assumptions and to provide a basis for design and business decisions. Therefore, simulation results should be treated not as "absolute values" but as "predictions based on assumptions."

Points to Check in Loss Analysis

Loss analysis is extremely important when using PVSyst. In solar power generation, the energy arriving from the sun does not directly become electrical energy. Losses occur at each stage: the incident stage on the module surface, the generation stage, the DC wiring stage, the conversion stage, and the AC output stage. By examining the loss analysis, you can understand where generation is being reduced and where there is room for design improvement.

The first thing to check is losses related to solar irradiance. If the installation tilt or orientation does not match the site’s solar conditions, the irradiance received on the module surface can be reduced. When there are constraints such as roof mounting or land topography, it may not be possible to choose the optimal orientation or tilt. Even in such cases, understanding the extent of the impact makes it easier to explain design decisions.

Shading losses are also an important item to check. Shadows from surrounding obstacles and between rows directly affect power generation. The impact of shading can be particularly significant during periods of low solar altitude or in the morning and evening. If shading losses are large, it is necessary to consider measures such as adjusting the layout, reviewing inter-row spacing, and rechecking the extent of obstacle shadows. Conversely, if there are obvious shading factors on site but losses are minimal, the inputs may be insufficient.

Temperature-related losses cannot be overlooked. Solar photovoltaic modules have a characteristic in which their output decreases as temperature rises. During periods of strong solar irradiance in summer, generation tends to increase, but losses due to rising module temperature also become larger. The effect of temperature varies depending on the installation method, ventilation conditions, the distance to the roof surface, and the surrounding environment. Because temperature losses are influenced by regional differences and installation methods, it is important to verify that they match local conditions rather than treating them as a simple fixed value.

DC-side losses include wiring resistance, module variability, soiling, and efficiency reductions during low irradiance. Each of these may appear small when viewed individually, but when they accumulate they can have a non-negligible impact on annual energy production. In particular, for projects with long wiring runs or complex circuit configurations, it is necessary to verify whether the DC-side loss assumptions are realistic.

Regarding losses around conversion equipment, conversion efficiency and capacity constraints are important. If the capacity of the conversion equipment is small relative to the facility capacity, output may be curtailed during periods with good generation conditions. This is not necessarily a poor design and may be intentionally adopted when considering the cost-effectiveness of the entire facility. However, even in such cases, it is necessary to be able to explain how much output curtailment is occurring and to what extent it affects annual power generation.

Loss analysis is insufficient if approached merely from the perspective that smaller losses are better. If losses are unnaturally small, the input conditions may be overly optimistic. Conversely, even if losses are large, they can be reasonable when site conditions and design constraints are taken into account. What matters is whether each loss is consistent with real design conditions and whether there is a rationale that can be explained to stakeholders.

Items to check during the verification phase

When validating PVSyst results, you should not only verify the final energy production but also comprehensively review the input conditions, calculation processes, loss components, monthly trends, and output indicators. In practice, the person who created the simulation is often different from the person who reviews the results, so it is important to maintain a verification perspective.

The first things to check are the installation site and the meteorological conditions. Verify whether data from a location different from the planned site is being used, whether it significantly deviates from the climate characteristics of the target site, and whether there are any inconsistencies in elevation or regional conditions. If the meteorological conditions are off, no matter how carefully subsequent calculations are performed, the overall reliability of the results will decrease. In particular, in mountainous or coastal areas, or regions affected by snowfall or fog, it can be difficult to judge based solely on general regional data.

Next, check the installed capacity and equipment configuration. Verify that the number of modules, the number of modules in series, the number of parallel strings, the capacity of the power conversion equipment, and the circuit configuration match the drawings and equipment plan. If there is any discrepancy here, not only will the calculated power generation change, but the way output limits and losses appear will also differ. If design changes have been made, it is also an important check to ensure that the conditions in PVSyst have not been left outdated.

Placement conditions are also subject to verification. We check whether the tilt angle, orientation, row spacing, the shape of the installation surface, and surrounding obstacles are consistent with the actual plan. Even if there appears to be no problem on the drawings, reflecting the site's terrain and the influence of surrounding objects can change the results. In particular, for ground-mounted installations, differences in land elevation and site development plans can alter the appearance of the mounting structures, so a simple planar layout alone may be insufficient.

We also check monthly generation trends. Annual values alone make it difficult to notice seasonal anomalies. For example, if winter generation is unnaturally high, summer temperature losses are unrealistically small, or losses do not appear during periods when shading effects should be present, it may be necessary to review the input conditions. Monthly trends provide clues for judging whether they are consistent with the site's solar irradiance conditions and the installation tilt angle.

Checking the performance ratio is also useful. The performance ratio is used as an indicator of how efficiently a facility is generating power compared to ideal conditions. However, it is risky to judge solely by the performance ratio. A performance ratio that is too high may indicate that loss settings are insufficient. A performance ratio that is too low may indicate problems with the design conditions, or may reflect harsh site conditions. The performance ratio should be considered together with the breakdown of losses and the design conditions.

During the verification phase, not only the consistency of the results but also their explainability is important. When stakeholders ask, "Why is the energy production this amount?", "Which losses are significant?", or "What happens if conditions change?", you need to be able to answer with supporting evidence. Verification of PVSyst is not work that ends with receiving calculation results; it is the process of checking the connection between design conditions and results and organizing them into a form that can be used for decision-making.

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Content to be organized into a report

PVSyst's results are often compiled into reports and proposal documents. What is important in a report is not just presenting the power generation figures. It is about organizing what assumptions were used for the calculations, which conditions influence the results, the extent of losses being anticipated, and how the results should be interpreted.

First, the report must clearly state the calculation conditions. Basic items include the installation location, installed capacity, module layout, tilt angle, azimuth, meteorological conditions, equipment configuration, shading conditions, and loss assumptions. If these are ambiguous, the validity of the estimated power generation cannot be verified. In particular, when comparing multiple proposals, it is necessary to clarify which conditions are the same and which are different.

Next, organize the annual and monthly power generation. Annual power generation is a convenient metric for project feasibility assessments, but examining monthly power generation allows you to confirm seasonal variations and the impact of design conditions. In solar power generation, solar irradiance and temperature conditions change with the seasons, so showing monthly trends is important for conveying this. Rather than presenting only the annual total, being able to explain which seasons have higher generation and which tend to see lower generation increases the practical usefulness of the report.

Organizing a breakdown of losses is also indispensable. Being able to explain at which stage and to what extent losses are expected increases the persuasiveness of the results. For example, if shading losses are significant, you should indicate whether the cause is surrounding obstructions, inter-row shading, or terrain. If temperature-related losses are large, verify that they align with regional characteristics and the installation method. The loss breakdown also contributes to design improvements and to explanations of risk.

In reports, it is important to appropriately communicate the limitations of the results. PVSyst simulations are predictions based on certain assumptions and do not fully guarantee future actual power generation. Actual generation is influenced by year-to-year weather variability, equipment outages, maintenance conditions, soiling, changes in the surrounding environment, and other factors. By making these assumptions clear, readers of the report can avoid treating the results as absolute.

Also, in the report it is important to present the results in a form that can be used for design decisions. Simply attaching the raw outputs from the software makes it difficult for readers to understand what they should judge. Organizing in prose the expected power generation, the main loss factors, design considerations, the impacts of changes in conditions, and on-site information that should be confirmed going forward will make it easier for stakeholders to use the report for decision-making.

Points to note when using PVSyst

When using PVSyst, the most important thing to pay attention to is the validity of the input conditions. Simulation software performs calculations based on the conditions entered. In other words, if the inputs deviate from reality, the output results may also deviate from reality. Even if the report looks well presented, if the underlying assumptions are insufficient, it will be a weak basis for decision-making.

What requires particular attention is unconsciously incorporating optimistic assumptions. If shadows are not adequately accounted for, if estimates for soiling and downtime are too small, if temperature assumptions are too lenient, if wiring losses are underestimated, or if the meteorological data do not match the target site, estimated power generation tends to be higher. While higher estimated generation may look more attractive during project evaluations, if the gap with actual performance grows large, it will become difficult to explain later.

On the other hand, care must be taken not to introduce overly conservative conditions. If losses are overestimated, the expected power generation may appear lower than it actually is, which can unduly lower the evaluation of the plan. What is important is to place reasonable assumptions based on site conditions and design parameters, rather than optimism or pessimism. Even when adopting conservative settings, you should be able to explain the reasons for them.

Managing design changes is also important. In solar power plant planning, the layout, capacity, equipment configuration, scope of work, and shading conditions may change along the way. If the PVSyst model is not updated to the latest conditions, there is a risk that reports will be produced based on outdated assumptions. It is important to verify the consistency of the report date, the version of the design drawings, and the input conditions, and to clarify which point in time the simulation reflects.

Also, it is necessary to cross-check PVSyst results against other documents. By confirming consistency with the layout plan, single-line diagram, equipment specifications, survey results, site photographs, shading verification results, and grid conditions, it becomes easier to detect input errors and missing assumptions. Rather than treating the simulation as an isolated task, verifying it within the overall design raises the practical quality of the work.

PVSyst is a multifunctional software, but configuring every parameter in detail does not necessarily improve accuracy. Increasing detailed settings can, if their rationale is unclear, actually make explanations more difficult. Judging which parameters should be handled in detail and which can remain at standard conditions requires design knowledge of photovoltaic systems and an understanding of site-specific conditions.

On-site information required to improve design accuracy

To improve the accuracy of PVSyst, not only software operations but also the quality of on-site information is important. Solar power generation simulations strongly depend on the conditions of the installation site. Therefore, correctly understanding the site’s location, topography, surrounding obstacles, condition of the mounting surface, orientation, tilt, existing structures, and factors causing shading leads to more reliable generation forecasts.

Especially for ground-mounted installations, differences in land elevation and the shape after earthworks affect shadows and layout. If there are undulations not visible on a plan view, the rack height and the relationships between rows change, and the way shadows fall also changes. For roof-mounted installations, roof orientation, pitch, level differences, surrounding buildings, equipment, railings, and upstands can also affect power generation. If such information is entered based only on desk-based conditions without confirming it on site, discrepancies with the actual situation are likely to occur.

In shadow assessments, it is necessary to consider not only the area immediately around the target installation but also shadows during periods when the sun is low in the sky. Not only nearby buildings and trees, but distant topography can also cause shading in the mornings, evenings, or in winter. It is important to combine on-site photographs, survey data, and surrounding elevation information to understand shadow conditions as accurately as possible. Because shading affects not only overall power generation but also per-circuit output reductions and uneven generation, it is an item that should be carefully checked during the design stage.

Accurate on-site location information is also relevant to consistency with meteorological conditions and design drawings. If latitude/longitude or elevation are ambiguous, this will affect verification of solar irradiance and topographical conditions. In power plant planning, it is important that the coordinates on drawings, site surveys, installation locations, and equipment layouts are consistent. Especially when handling multiple documents, discrepancies in the understanding of coordinate systems or reference points can affect layout and shadow analysis.

The quality of on-site information directly affects the persuasiveness of the report. In addition to PVSyst results, being able to explain the location data and surrounding conditions confirmed on site clarifies the basis for the power generation forecast. Conversely, if understanding of the site conditions is weak, it becomes difficult to explain the validity of input conditions when questioned. In solar power system design, it is important not to separate simulation and on-site verification, but to combine both in your assessment.

In this respect, an environment that allows efficient acquisition of on-site location information is also a great help when leveraging PVSyst. If it becomes easier to organize the installation location, boundaries, surrounding obstacles, verification points, and the spatial relationships of site photographs, the assumptions for the simulation can be made clearer. The design conditions handled within PVSyst may look like desk-based figures, but their basis lies in the field. That is precisely why the workflow of accurately capturing on-site information and reflecting it in the design is important.

Summary

PVSyst is practical simulation software for predicting the energy yield of photovoltaic power systems, analyzing loss factors, verifying the validity of design conditions, and organizing the results into reports. It does not simply calculate annual energy production; it comprehensively handles irradiance conditions, layout, equipment configuration, shading, temperature, wiring, conversion efficiency, and other factors, and serves to explain under what assumptions the energy yield has been derived.

In the design phase, organize the installation site, meteorological conditions, equipment layout, tilt angle, orientation, equipment configuration, shading conditions, and so on. In the power generation simulation, understand the flow from solar irradiance to the final alternating-current (AC) energy output, and verify the losses that occur along the way. In the verification phase, check the consistency between input conditions and design documents, review monthly generation, performance ratio, and the breakdown of losses to confirm there are no anomalies in the results. In the reporting phase, it is important to clearly organize the calculation conditions, generation figures, loss factors, interpretation of the results, and the limits of the predictions.

To use PVSyst effectively, you need more than just software operation skills; basic knowledge of solar power generation, an understanding of design conditions, and familiarity with site information are indispensable. The closer the input conditions are to reality, the more usable the simulation results become as material for decision-making. Conversely, if site conditions remain ambiguous, no matter how polished the report is, its practical persuasiveness will be weak.

To make the design, verification, and reporting of photovoltaic power generation more reliable, it is important to take a perspective that combines power generation simulation and on-site measurements. If installation location, boundaries, surrounding obstacles, shadow factors, and the positional relationships in site photographs can be accurately understood, the basis for the conditions entered into PVSyst also becomes clear. If you want to streamline on-site position confirmation and positioning, using LRTK, an iPhone-mounted GNSS high-precision positioning device, can make pre-design surveys and field verification of photovoltaic installations proceed more smoothly. By combining desktop studies with PVSyst and on-site information acquisition with LRTK, the flow from design and verification to reporting can be made more practical and easier to explain.