Explaining 10 Terms in the PVSyst Manual That Commonly Cause Confusion

Table of Contents

• Introduction: The PVSyst manual is easier to read once you understand the terminology

• Term 1: Project

• Term 2: Variant

• Term 3: Meteo

• Term 4: Orientation

• Term 5: Albedo

• Term 6: GlobInc

• Term 7: Horizon

• Term 8: Near Shadings

• Term 9: Array Losses

• Term 10: Performance Ratio

• Summary: Grasp the meanings of terms and apply the PVSyst manual in practice

Introduction: The PVSyst manual becomes easier to read when you understand the terminology

When people begin reading the PVSyst manual, what many get stuck on is not so much the operating procedures themselves but the meanings of the technical terms that appear on the screen. Even words that those familiar with the design of photovoltaic systems and energy-yield simulations can understand intuitively may be hard for first-time PVSyst users to grasp — labels such as Project, Variant, Meteo, GlobInc, and PR can be unclear about what they refer to. If you proceed using the software without a clear understanding of the terms, you may lose track of which screen you are entering which data on and which values in the result report you should be checking.

PVSyst is positioned as PC software for the study, sizing, and data analysis of photovoltaic systems, and it handles multiple system types such as grid-connected, stand-alone, pumping, and DC-grid systems. It is also structured to include meteorological data, a component database, and design support tools. The official documentation even notes that pressing the F1 key within the software opens the related help. In other words, the PVSyst manual is not merely an operational guide but also serves as a kind of dictionary for understanding design conditions, meteorological conditions, losses, shading, and energy yield assessment.

This article explains 10 terms that are particularly easy to get confused when reading the PVSyst manual. It covers not only literal translations of the words, but also which screens they appear on in practice, how they should be understood, and which values they are easily mistaken for. The content is useful not only for those using PVSyst for the first time, but also for anyone who feels uncertain about reading reports or who wants to share explanations of design conditions internally or externally.

Term 1: Project

A Project is the basic unit when starting a simulation in PVSyst. In Japanese it can be translated as "プロジェクト", but it is not simply a box for registering a project name. A Project in PVSyst is linked to basic information about the power plant and installation site, geographical conditions, meteorological data, and, if necessary, albedo conditions. Therefore, it is easiest to understand a Project as a set of preconditions for "considering a solar power generation system at this location."

In PVSyst's Project Design, you first define a Project, and within that Project you create multiple Variants to compare. The official documentation also explains that a Project includes geographic location, meteorological data, and optional albedo data, and that multiple system variants can be created as needed. In other words, a Project is not a design proposal itself but a common foundation for comparing design proposals.

In practice, you may perform comparisons on the same site such as changing the module capacity, changing the azimuth, changing the inverter configuration, or adding shading conditions. If you create a separate Project each time, the comparison conditions can easily become inconsistent. As a rule, design proposals to be compared at the same location, with the same meteorological data, and under the same project conditions should naturally be managed within a single Project. If you think of a Project as a "case folder" and a Variant as a "design proposal," the explanations in the PVSyst manual become much easier to read.

Term 2: Variant

Variant is an individual design proposal created within a Project. In Japanese it is close in meaning to "variant," "proposal," or "case," and in PVSyst you can save multiple Variants under a single Project to compare differences in energy production and losses caused by differing conditions. For example, on the same site you can treat a south-facing fixed layout, an east-west arrangement, a design with a different tilt angle, or a design with a different inverter capacity as separate Variants.

When the term Variant appears in the PVSyst manual, it is easier to understand if you think of it as "the design case you are currently working on." Whereas a Project is the container for the entire case, a Variant is the specific set of simulation conditions saved within it. The official documentation shows the flow of defining the plane orientation for each Variant, setting the System properties, running the Simulation when ready, and checking the Report on the results screen. It also advises saving each Variant after the simulation so they can be compared.

If you don't understand the meaning of "Variant", you may overwrite conditions you set in the past or lose track of which file contains the proposal you want to compare. In practice, it's easier to manage if you give Variant names that indicate the different conditions, such as "south-facing 20 degrees", "east-west layout", "with shading", or "after loss revision". When expressions like "save variant", "new variant", or "description of this variant" appear in the PVSyst manual, it's best to view them not as mere save operations but as the task of organizing comparable design proposals.

Term 3: Meteo

Meteo is a term referring to meteorological data. In the PVSyst manual, expressions such as "Weather Data" and "Meteo file" also appear. In solar power generation simulations, meteorological conditions such as solar irradiance, ambient temperature, wind speed, and diffuse irradiance greatly influence the results. Therefore, Meteo is an extremely important element that serves as the starting point for energy yield calculations.

In PVSyst, simulation variables such as GlobHor, DiffHor, BeamHor, Tamb, and Windvel are handled. GlobHor is the global horizontal irradiance read from the meteorological data file, DiffHor is the diffuse horizontal irradiance, BeamHor is the direct horizontal component obtained by subtracting DiffHor from GlobHor, Tamb is the ambient air temperature, and Windvel is the wind speed.

What beginners often get confused about is that Meteo is not simply "weather" but time-series data or monthly data used for numerical calculations. For example, a vague understanding such as "the region has many sunny days, so it generates a lot of power" is not sufficient; in a simulation you calculate how much horizontal plane irradiance there is, how that is converted to the tilted plane, and how much output drops due to temperature conditions. When the PVSyst manual uses the word Meteo, understand it as "the source of the meteorological data that determines the energy production of this Project."

Furthermore, if you choose the wrong Meteo, no matter how detailed your subsequent loss settings are, the overall reliability of the results will be reduced. You need to check whether the site is nearby, whether the dataset has long-term representativeness, whether the values are measured or synthetic, and whether there are missing or anomalous data. When reading the PVSyst manual, it is important not to treat the Meteo as merely an initial setup item to be skimmed over, but to regard it as a core precondition of the simulation.

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Term 4: Orientation

Orientation is a term that describes the direction and tilt at which solar panels are installed. In the PVSyst manual, it appears alongside terms such as Plane orientation, Fixed tilted plane, Tilt, and Azimuth. In Japanese, it is easier to understand if you think of it as "azimuth and tilt settings."

In PVSyst, for a fixed tilted plane you define the Plane tilt and Azimuth. In addition, it supports various Orientation modes such as multiple orientations, seasonal tilt adjustments, racking rows, and tracking. The official documentation indicates that in Fixed tilted plane you define the tilt angle and azimuth, and that in Multi-orientations you can define up to 8 different-orientation PV surfaces.

A common source of confusion here is the difference between Tilt and Azimuth. Tilt is the tilt angle of the panel surface and indicates how much it is tilted up from the horizontal plane. Azimuth is the compass angle and indicates which direction the panel is facing. Because the PVSyst manual often uses the English terms as-is, it can be easier to understand if you replace Tilt with practical terms such as "roof pitch" or "mounting angle," and Azimuth with phrases like "how far it deviates from south toward east or west."

Orientation affects GlobInc, energy yield, shading patterns, and inter-row pitch considerations. Changing the tilt angle alters not only the annual solar irradiation but also the balance of generation between winter and summer. Changing the azimuth angle shifts morning and evening generation tendencies and the timing of peak hours. When you encounter the Orientation setting screen in the PVSyst manual, you should treat it not as a mere angle entry but as an important design parameter that determines the overall generation pattern.

Term 5: Albedo

Albedo is a term that denotes solar radiation reflected by the ground and surrounding surfaces. In Japanese it is often translated as "反射率", and it relates to how much of the solar radiation received by the Earth's surface is reflected and reaches the panel surface. In the PVSyst manual, it appears in Project settings, weather and solar radiation calculations, and in considerations of bifacial modules.

For typical ground surfaces, the impact of albedo on total energy production is often not very large; however, in snowy areas, on white roofs, on light-colored pavement, and with bifacial modules it becomes non-negligible. The official tutorial notes that the albedo coefficient is seldom changed and a standard value of 0.2 is used, whereas examples show setting 0.8 for some months in snowy mountainous regions.

What beginners often confuse is thinking of Albedo as "the solar irradiance itself." Albedo is not the direct solar irradiance from the sun, but the component that arrives after being reflected by the ground or similar surfaces. In PVSyst's result variables, incident components originating from albedo—such as AlbInc—are handled. In other words, the horizontal irradiance read by Meteo, the tilted-plane irradiance determined by Orientation, and the albedo component from ground reflection each have different roles.

In practice, setting the albedo too high can make the estimated energy yield look overly optimistic. This is especially true for bifacial or snowy-site projects, where it is important to verify it together with actual ground conditions, snow duration, ground color, racking height, row spacing, and so on. When albedo appears in the PVSyst manual, read it as a design assumption of “to what extent reflected irradiance from the surrounding environment is expected,” which makes the meaning of the input value clear.

Term 6: GlobInc

GlobInc is an important term that appears very frequently in PVSyst results and calculation processes. Formally, it refers to the collector plane, that is, the global irradiance incident on the solar panel surface. In Japanese, it is easier to understand if you think of it as "global irradiance on an inclined surface" or "irradiance incident on the array surface."

In PVSyst, GlobHor read from the meteorological data is the global irradiance on the horizontal plane, whereas GlobInc is the global irradiance incident on the panel plane. The official documentation describes GlobHor as the horizontal global irradiance read from the weather data file, and GlobInc as the incident global irradiance on the collector plane obtained as the result of the transposition.

What is important here is the conversion from GlobHor to GlobInc. You cannot directly treat the solar radiation incident on the horizontal plane as the solar radiation on a tilted panel surface. Panels have a tilt angle and an azimuth angle, and the sun's altitude and azimuth also change with time. Therefore, in PVSyst, based on meteorological data, solar position, and Orientation conditions, the horizontal-plane irradiance is converted into irradiance on the panel surface. This conversion is called transposition.

In PVSyst's simulation process, at each time step it reads meteorological data, handles global irradiance on the horizontal plane, temperature, and, if necessary, diffuse irradiance and wind speed, and then converts the global irradiance, diffuse irradiance, and albedo irradiance to the collector plane. At this stage, variables such as GlobInc, BeamInc, DiffInc, and AlbInc are defined.

Understanding GlobInc makes it easier to interpret PR and loss diagrams. This is because energy production is evaluated not by "how much solar radiation there was on the horizontal plane" but by "how much effective solar radiation reached the panel surface." When GlobInc appears in the PVSyst manual, think of it as "the amount of solar radiation the panel surface actually receives under these design conditions."

Term 7: Horizon

Horizon is a term that describes shading conditions in which the sun is obscured by distant mountains, buildings, terrain, etc. In Japanese it is sometimes called 「地平線」「遠方影」「ホライズン」. In the PVSyst manual it appears alongside expressions such as Horizon profile and far shadings.

"Horizon" does not refer to situations where nearby fences or adjacent buildings cast shadows on parts of the panels. It deals with conditions in which distant mountains, hills, terrain, or remote buildings cause the sun itself to be obscured at certain solar altitudes and azimuths. In the official documentation, Far shadings are described by a horizon line and are explained as shadows from sufficiently distant objects that determine whether the sun is visible from the entire PV field at a given time.

What is important to understand about Horizon is that the treatment of shadows is overall. If a distant mountain hides the sun for a certain period in the morning, we consider that it will have the same kind of impact across the entire power plant. In contrast, if a nearby utility pole casts a thin shadow over some modules, that falls under Near Shadings or Module Layout rather than Horizon.

In practice, checking the Horizon is important in mountainous areas, valley terrain, urban areas with tall surrounding buildings, and locations with topographical obstructions to the east and west. If you run a simulation without setting the Horizon, you may overestimate generation in the mornings, evenings, and during winter. Conversely, even if you input distant shading in excessive detail, the reliability of the results will not improve if the source data are of low accuracy. When Horizon is mentioned in the PVSyst manual, it is helpful to understand it as “the effect of distant obstructions on the way the sun is seen.”

Term 8: Near Shadings

Near Shadings is a term that refers to shadows cast onto the panel surface by objects located near the power plant. In Japanese, it can be understood as "proximity shading", "vicinity shading", or "shading caused by nearby obstacles". In the PVSyst manual, it appears together with 3D scene, CAD, Shading factor, Module Layout, and similar items.

What distinguishes Near Shadings from Horizon is that the shading does not fall uniformly across the entire PV field, but instead partially affects specific columns, specific modules, and specific times of day. The official documentation explains that Near shadings are those in which nearby objects cast visible shadows on the PV field, and that the Shading Factor is defined as the ratio of the shaded area to the total sensitive area. It also states that handling Near shadings is more complex than far shadings and requires a detailed 3D description of the PV system and the surrounding environment.

A common source of confusion with Near Shadings is that there are broadly two types of losses caused by shading. One is the loss from the reduction in irradiance corresponding to the shaded area. The other is the loss in output that falls more than the shaded area would suggest, due to the electrical connections of modules and strings. PVSyst’s official documentation also explains that for the beam component of near shadings you need to consider irradiance losses, which correspond to a lack of irradiance on the cells, and electrical losses caused by mismatches in the electrical response of series modules and parallel strings.

In practice, nearby buildings, parapets, fences, rows of mounting structures, adjacent rows of solar panels, trees, utility poles, and equipment are considered Near Shadings. Especially for rooftop installations and inter-row shading in ground-mounted systems, how detailed Near Shadings are modeled affects the results. When Near Shadings appear in the PVSyst manual, understand them as “the settings that deal with shadows cast by nearby objects onto parts of the panels and their electrical impacts.”

Term 9: Array Losses

Array Losses is a term that groups the losses occurring on the PV array side. In Japanese it can be expressed as "アレイ損失". In the PVSyst manual it appears in relation to Detailed losses, loss diagram, thermal losses, wiring losses, module quality, mismatch, IAM, soiling, and so on.

In PVSyst's official documentation, "Array losses" are described as all the factors that reduce the array output energy relative to the PV module nominal output specified by the manufacturer under STC conditions. Specifically, these include shading, IAM, reduced efficiency at low irradiance, thermal behavior, actual module performance, mismatch, soiling, and so on.

One key point to understand about Array Losses is that the losses do not have a single cause. For example, in summer when module temperature rises, output falls. High wiring resistance increases electrical losses. Variations in characteristics between modules cause mismatch losses. Surface soiling reduces the irradiance reaching the cells. During periods with large incidence angles, IAM losses occur due to reflections from the glass surface and similar effects. Taken together, these factors reduce the ideal output to the output that can actually be extracted.

When reading the PVSyst manual, it is also important to pay attention to the difference between Array Losses and System Losses. Array Losses are losses that occur mainly in the area from the module to the array output. On the other hand, System Losses is used in the context of losses that occur on the system side, such as inverters and batteries. In the description of the normalized performance indicators, Lc represents array losses, and Ls is described as the system loss that includes inverter losses for grid-connected systems and battery efficiency, etc., for stand-alone systems.

In practice, when looking at a loss diagram it is important to check "which loss is the largest." Depending on whether low power generation is caused by azimuth, shading, temperature, inverter capacity, or soiling, the corrective measures will be completely different. Understanding Array Losses lets you read PVSyst reports not just as generation forecasts but as diagnostic material for design improvement.

Term 10: Performance Ratio

The Performance Ratio is a particularly important evaluation metric in PVSyst result reports. It is abbreviated as PR. In Japanese it is called "性能比" or "パフォーマンス比". It is often used to compare the relative quality of power plants, but it does not simply indicate whether the amount of power generated is high or low.

In PVSyst's official documentation, the Performance Ratio is described as the ratio of the energy actually effectively produced or utilized to the energy that would be obtained if the system were operated continuously at its nominal efficiency under STC. In a standard grid-connected system, PR is defined as E_Grid divided by the product of GlobInc and PnomPV.

One point that often causes confusion about PR is that a project with a larger energy output does not necessarily have a higher PR. In regions with high solar irradiance the energy output itself tends to increase, but PR is an indicator of the efficiency of utilization relative to incident irradiance and system capacity. The official PVSyst documentation also explains that, unlike Specific energy production, PR does not directly depend on meteorological data or the orientation of the plane, making it an indicator that facilitates comparison of system quality across different locations and orientations.

On the other hand, judging the quality of a design solely by PR is risky. Even with a high PR, the plant capacity may be too small or the total energy production may not meet the intended objectives. It is also necessary to check how losses from shading, temperature, inverter constraints, soiling, mismatch, IAM, and so on are accounted for. In PVSyst’s normalized performance indicators, PR is also presented as a global system efficiency obtained by dividing Yf by Yr. Here, Yf can be understood as the effective energy per unit of nominal (rated) power, and Yr as the ideal reference yield based on incident irradiance.

When PR appears in the PVSyst manual, it's helpful to think of it as an indicator of how efficiently the system converted irradiation and installed capacity into useful electricity. When reading reports, it's important to check PR, Specific Production, annual energy production, and the loss diagram together. PR is a useful metric, but it is not universally definitive on its own. When comparing design proposals, it's essential to be able to explain the reasons for a high or low PR together with the loss breakdown.

Summary: Apply the PVSyst Manual to Practical Work by Grasping the Meanings of Terms

The PVSyst manual can feel difficult if you try to understand everything in detail from the start. However, just mastering the 10 terms introduced here makes it much easier to make sense of the interface layout and read the result reports. Project is the foundation of the project conditions, Variant is the design alternative to be compared, Meteo is the starting point for generation calculations, Orientation is the panels’ azimuth and tilt, Albedo is the ground reflectance, and GlobInc is the irradiance incident on the panel surface. Furthermore, Horizon is distant shading, Near Shadings are nearby shadows, Array Losses are the losses on the array side, and Performance Ratio is an indicator of the system’s power generation efficiency.

When using PVSyst in practice, what's important is not just entering numbers and generating reports. It's essential to be able to explain which conditions you assumed, which losses you considered, and which metrics you used to evaluate a design proposal. If you understand the terms that appear in the PVSyst manual, it becomes easier to conduct internal reviews, explain to clients, compare designs, and organize the rationale for the expected energy production.

Beginners in particular do not need to memorize all the detailed settings from the start. First, grasp the relationship between Project and Variant; understand that Meteo and Orientation create the assumptions for energy production, that GlobInc and Albedo represent the solar irradiation conditions, that Horizon and Near Shadings handle shading, and that Array Losses and PR lead to the evaluation of results. Once this flow becomes visible, the PVSyst manual can be used not just as an English operation guide but as a practical manual for logically designing and evaluating photovoltaic power systems.