What does PVSyst show? 10 items you can check

Table of Contents

• What is PVSyst?

• Checkable item 1: Calculation site and meteorological conditions

• Checkable item 2: Orientation and tilt conditions of the installation surface

• Checkable item 3: Horizontal plane irradiance and plane-of-array irradiance

• Checkable item 4: DC-side array behavior

• Checkable item 5: Energy delivered to the AC side

• Checkable item 6: Temperature, low-irradiance, wiring, and mismatch losses

• Checkable item 7: Linear shading losses and electrical losses

• Checkable item 8: Loss diagram and performance ratio

• Checkable item 9: Alternative comparisons and economic evaluation

• Checkable item 10: Comparison with measured data and signs of anomalies

• Common points beginners tend to overlook

• Summary

What is PVSyst?

PVSyst is dedicated software for the study, sizing, performance evaluation, and data analysis of photovoltaic (PV) systems. The official documentation describes it as an environment that handles not only grid-connected systems but also stand-alone systems, pump applications, and DC-system applications, and it includes a meteorological database, a component database, various solar-energy related tools, and even features for comparing measured data—making it a fairly comprehensive design environment. In other words, rather than being just a calculator that produces annual energy once, it is easier to grasp the overall picture if you understand it as practical software for linking design and evaluation while organizing project-specific assumptions.

Another characteristic of PVSyst is that it provides a very large amount of information in its results. The official documentation explains that it performs detailed time-based simulations, allows multiple simulation runs within the same project to be compared, and can display dozens of variables by month, by day, and by hour. In other words, PVSyst is software for viewing power generation itself and, at the same time, for checking which conditions produced those figures. What matters to practitioners is this ability to trace back to the background of the results.

Many people who search for "What is PVSyst" are more interested in what they can actually check with the software than in an explanation of the name. In design practice there are numerous items you want to verify: site, solar irradiation conditions, orientation, tilt, component configuration, losses, shading, comparison results, and actual performance after operation. Because PVSyst makes it easy to track these within a single workflow and a single conceptual framework, it serves more as a checking, comparison, and validation tool than as a mere calculation program. In this article, we organize those items into ten that are especially worth reviewing in practical work.

Verification Item 1: Calculation Point and Meteorological Conditions

In PVSyst, the first things you can check are which site is being targeted and under what meteorological conditions the calculations are carried out. The official documentation explains that geographic conditions and time-series meteorological data are at the center of a project, and the meteorological database is said to allow site creation, generation of time-series data, visualization, comparison, and external import. This means that the starting point for power generation forecasts is not the system capacity but the meteorological conditions at the site.

In solar power generation, even with the same installed capacity, solar irradiance conditions differ by location, causing annual energy yield and seasonal variability to change significantly. Furthermore, even at the same location, results can look different depending on the reference year, averaging period, and how the meteorological data are processed. Official comparisons of data sources also show large differences between different meteorological datasets, and it is not easy to determine precisely which is optimal. PVSyst’s strength is that it does not hide that uncertainty and allows users to consciously account for differences in meteorological assumptions.

What beginners often overlook here is that they treat site setup and the selection of meteorological data as merely “initial tasks.” In reality, the foundation of the results is largely determined at this stage. No matter how much you refine components or loss assumptions later, if the meteorological assumptions are off, the results will not become more convincing. To use PVSyst correctly, the item you should look at first is not the annual energy production but “which location and which meteorological conditions are being used.”

Verifiable Item 2: Orientation and Slope Conditions of the Installation Surface

The second thing to verify is the orientation and tilt conditions of the mounting surface. The official documentation explains that, within project design, you define the mounting surface orientation and can handle tracking surfaces and row installations as needed. This is because, even at the same site, which direction it faces and at what angle it is placed changes the amount and timing of solar radiation it receives. In solar design these differences have a direct impact on the results, so mounting surface conditions are a very basic yet important item to confirm.

What makes PVSyst convenient is that it makes it easy to keep alternative proposals with different orientations and tilts within the same project. In the official tutorial, the workflow shown is to first create an initial proposal under minimal conditions, and then save and compare alternative versions after adding shading and losses. The same approach applies to orientation and tilt: you can easily line up the baseline proposal and versions with slightly altered conditions for comparison. In design practice, because it is necessary to demonstrate "which orientation is better" with numbers, this ease of comparison is of great value.

Also, checking the installation surface serves as the foundation for the shadows and losses you will examine later. If you set orientation and tilt carelessly, the way shadows fall, the way temperature is perceived, and the resulting loss structure all become harder to interpret. Beginners tend to focus on capacity and components, but what you should really look at first in PVSyst is "how each surface is defined." If this remains ambiguous, all subsequent results tend to become unclear.

Verifiable Item 3: Horizontal-plane Solar Irradiance and Installed-surface Solar Irradiance

The third thing you can check is the difference between irradiance on a horizontal plane and irradiance incident on the actual installation surface. In PVSyst’s simulation variables, meteorological data such as global horizontal irradiance and diffuse horizontal irradiance are organized separately from the global, beam, diffuse, and reflected components incident on the installation surface. This means that, rather than using the local meteorological conditions as-is, it converts them—according to the orientation and tilt of the installation surface—into the light that the surface actually receives.

Being able to check this difference is highly important in practice. A project that looks promising when you only examine the area's annual solar irradiance can receive less light than expected once the orientation of the installation surface and surrounding conditions are taken into account. Conversely, a site that does not stand out based on regional averages alone may, depending on the installation surface conditions, achieve stable light reception. PVSyst lets you view the values after that conversion, making it easier to separate "regional conditions" from "the conditions experienced by the installation."

For beginners, this section also serves as the gateway to grasping the essence of PVSyst. This is because solar power generation is determined not only by the "location" but by the "relationship between the location and the plane." Once you develop the habit of comparing horizontal-plane irradiance with plane-of-array irradiance, the implications of changing orientation and tilt become clear, and interpreting subsequent losses and energy yield becomes much easier. This section is crucial for understanding that PVSyst is not merely software for region-based generation estimates.

Verifiable Item 4 DC-side Array Behavior

The fourth aspect you can check is the DC-side array behavior. PVSyst's simulation variables for grid-connected systems organize the nominal installed capacity, the reference array energy for performance ratio calculations, the nominal array energy, array-side low-irradiance losses, temperature losses, and so on. In other words, you can check not only the final AC-side energy sold to the grid and the available energy, but also how the array performed in the preceding stage.

This item is important so that you do not take the quality of the results seen on the AC side as a direct indicator of the overall system performance. For example, even when the AC-side results are low, the array side may be producing sufficiently and losses may be occurring on the conversion side or elsewhere in the system. Conversely, if the array side is not performing well, you should first suspect factors such as irradiance conditions, temperature conditions, module behavior, or the effects of low irradiance. PVSyst includes DC-side information in its results to help with such root-cause analysis.

Also, the official explanation of the loss diagram states that the starting point of the loss diagram uses the array's nominal energy as seen from global effective irradiance and nominal efficiency, and that the PV model's behavior according to environmental conditions is then built up on top of that. In other words, the DC-side array behavior is the key to interpreting the first half of the loss diagram. Mastering PVSyst means not only looking at the final AC-side values but also interpreting the array-side behavior. Being able to examine this makes a considerable difference in the accuracy of design improvements.

Verifiable Item 5: Energy Transferred to the AC Side

The fifth thing you can check is how much of the energy produced on the DC side ultimately made it to the AC side. The official simulation variables for grid-connected systems organize items related to converter behavior, energy output and utilization, and efficiency. These include losses due to converter efficiency, output limiting, losses from input voltage being outside the allowable range, threshold-related losses, and night-time consumption. In other words, PVSyst does not assume that the electricity produced by the array is immediately usable; it allows you to examine the conditions separately up to the point where it reaches the AC side.

In practice, this check is extremely important. That is because there are actual cases in which the array side is harvesting enough energy but the AC side is not producing as much as expected. When the converter’s efficiency curve, rated limits, mismatched input conditions, nighttime consumption, and the like overlap, the discrepancy from the estimate can widen. In PVSyst it is easy to check not only the total but also which items are causing losses, so you don’t need to infer the cause from the AC-side figures alone.

One thing beginners should learn here is that discussions about generation do not end with "the electricity produced by the modules." In practical design work, what matters is the energy that ultimately leaves the system and the energy that can actually be used. Because PVSyst lets you check how energy is reduced along the way, it makes it easier to identify measures when reviewing the configuration or operating conditions. Being able to confirm the energy delivered to the AC side is one reason it is seen not merely as generation-forecasting software but as a system-wide design tool.

Checklist Item 6: Temperature, Low Light, Wiring, and Mismatch Loss

The sixth item that can be identified is the minor losses such as temperature, low irradiance, wiring, and mismatches. The official array/system losses page states that it deals in detail with losses such as soiling, incidence angle, low irradiance, thermal effects, module quality variations, mismatch, wiring, and downtime. Also, in the simulation variables for grid-connected systems, low irradiance losses and temperature losses are organized as independent items. In other words, PVSyst is software that does not just return total losses but allows you to see their breakdown.

Beginners, in particular, often overlook low irradiance and temperature. During periods of low solar irradiance, generation does not scale proportionally; module efficiency can decrease. Also, when ambient or module temperatures are high, output falls. Wiring losses and mismatch losses are similarly inconspicuous, but when they accumulate they cannot be ignored. PVSyst treats these losses as separate variables, so you can go beyond simply noting that "production is low" and more easily identify which losses are at work.

Also, officially these loss parameters are expected to be set to reasonable default values for the initial simulation and then refined according to the project in subsequent stages. In other words, you can use it to gradually approach reality while keeping sight of the overall picture, without having to set perfect loss values from the start. Being able to examine losses in detail is a major advantage not only for bringing the design closer to reality but also for making it easier to explain the differences between the initial concept and the detailed proposal.

Verifiable item 7 Linear shading loss and electrical loss

The seventh item you can identify is linear shading loss and electrical loss. In the official terminology, electrical shading loss is described as the additional loss obtained by subtracting the linear loss due to reduced irradiance from the actual shading loss. In other words, the effect of shading does not necessarily reduce output in direct proportion to the darkened area. When part of a cell or module is shaded, the I-V characteristics become distorted, the string current is limited by the weakest cell, and losses can increase beyond the linear deficit.

In PVSyst, the effects of shading are easy to view separately. Because it can treat the irradiance deficit caused by linear shading and the additional losses from electrical mismatch separately, you don’t have to judge shading issues solely by "area percentage". In the official index, items such as electrical shading loss, module layout, the effects of thin obstacles, and string splitting are provided independently, allowing you to delve deeper as needed. For projects where shading is severe, this can make a huge difference.

For beginners, the important thing is not to take shading lightly. Even shadows that appear small can increase losses within the electrical connections. PVSyst is supported because it treats shading not as a mere appearance issue but as an issue affecting power generation behavior. If you can confirm this, mistakes in judgment at the design stage are greatly reduced, and it becomes easier to provide evidence-based explanations even for projects with severe shading conditions.

Checkable Item 8: Loss Diagram and Performance Ratio

The eighth thing you can check is the loss diagram and the performance ratio. The official loss-diagram page explains that the loss diagram is a chart for quickly getting an overview of the quality of a PV system design and for finding the main sources of loss. Moreover, because it can be viewed not only annually but also monthly, it is easy to grasp how losses vary, including seasonal differences. A major strength of PVSyst is that it lets you check not just whether the energy production result is high or low, but also how much was lost at each process.

Regarding the performance ratio, the official definition describes it as an indicator obtained by dividing the actually and effectively delivered energy by the ideal amount based on the irradiance incident on the installation surface and the nominal power. Furthermore, in its interpretation, the performance ratio is said to include optical losses, array losses, and system losses. In other words, the performance ratio makes it easier to confirm the "cohesion as a system" that is difficult to perceive from annual power generation alone, which is influenced by site differences. This indicator is also very useful for comparing alternative proposals and for benchmarking actual performance.

Beginners tend to focus only on the annual energy production figure, but that makes it hard to see weaknesses in the design. By looking at the loss diagram and the performance ratio together, you can more easily tell whether a proposal merely benefits from favorable irradiance conditions or whether it is a clean proposal that also has a solid loss structure. What makes PVSyst strong as a "verification software" is that it allows you to assess not only the results themselves but also the quality of those results.

Verifiable Item 9: Comparison of Alternatives and Economic Evaluation

The ninth item to check is comparison of alternative scenarios and economic evaluation. In the official project design, it states that you can create different simulation runs within a project and compare them. The tutorial also recommends saving the initial baseline scenario, then creating scenarios that incrementally add far shading, near shading, loss conditions, etc., and comparing them. In other words, PVSyst is not software that simply calculates a single scenario and stops; it is also software for checking "how things change when conditions are varied."

This is extremely important in design practice. Comparisons such as what happens if you change the orientation, what happens if you assume stricter losses, or what happens if you make shading conditions more realistic occur on a daily basis. With PVSyst, you can view these side by side within the same project framework, which makes it easier to explain “what changed and by how much” when you alter something. For designers, there are many situations where how differences in conditions are presented is more important than the numbers themselves, so this ease of comparison is of great value.

Furthermore, PVSyst includes detailed economic assessment capabilities. The official overview states that detailed economic assessments can be carried out using actual component prices, additional costs, and investment conditions. In other words, you can check not only differences in energy production but also how those differences affect economic viability. Because a proposal with higher energy production is not necessarily the optimal one, the ability to easily view both performance and economic aspects is extremely helpful for improving the quality of design decisions.

Verifiable Item 10: Comparison with Measured Values and Signs of Abnormalities

The tenth item you can verify is measured comparisons and signs of anomalies. The official overview explains that PVSyst has the capability to import measured data from almost any text format, display actual performance in tables and graphs, and perform comparisons that closely match simulation variables. Furthermore, this allows for analysis of operational parameters and serves as a means to detect even very small irregularities. In other words, PVSyst is software that can be used not only for pre-installation forecasting but also for post-installation verification and improvement.

This feature is effective in practice because it means the difference between forecast and actual does not have to be dismissed as a mere hit-or-miss. When a discrepancy appears, it provides an entry point for considering whether it was due to different weather conditions, overly lax loss settings, or a small equipment fault. Official analyses of measured data explain that, through close comparisons, it helps not only to validate the software but also to analyze on-site systems and detect faults. In other words, PVSyst is not software just for producing a design and stopping there; it is also software for continuously improving the design.

The official measured-data file verification page also explains that for imported data you can view monthly, daily, and hourly tables and graphs, and even check data synchronization. This makes it easier not only to line up results but also to see whether the measured data used for comparison is itself valid. If you want to seriously analyze discrepancies between predictions and actuals, you must check the quality of the measurement data as well as the results. That PVSyst exposes that level of detail becomes an increasingly significant advantage the longer you use it.

Points Beginners Easily Overlook

Looking at the ten items so far, it becomes clear that what PVSyst can check is quite broad. However, what beginners often overlook is trying to check everything at once. The official tutorial also recommends first creating a baseline case with minimal conditions and then gradually adding shading and individual losses. In other words, it is more natural to use PVSyst as software that starts with a basic scenario and incrementally increases the items to check, rather than as software that perfectly checks all items from the outset.

Another important point is that, while PVSyst is strong for design and evaluation, it does not replace on-site verification itself. Detailed shading assessments and refinement of module layouts require precise definitions of positions and interconnection relationships. In other words, the more that is visible from desk-based work, the more important the accuracy of on-site information becomes. To use PVSyst effectively, you need to consider not only the verification items within the software but also what should be recorded on site.

Summary

In one sentence, PVSyst is software for checking the design conditions of a solar power system and the reasons for its results. Items that can be checked include site and meteorological conditions, mounting surface conditions, horizontal-plane solar irradiance and plane-of-array solar irradiance, array behavior on the DC side, energy delivered to the AC side, detailed losses, linear shading losses and electrical losses, loss diagrams and performance ratio, comparisons of alternatives and economic evaluation, and comparisons with measurements and signs of anomalies. In other words, it can be said to be software for checking not only the annual energy production figure but also "what is happening where."

From a practitioner's perspective, it's important not to use PVSyst as a black box. The more you verify which weather conditions, which mounting surface, which configuration, and which losses are being assumed—and thereby determine at which stage the energy was reduced—the more valuable the software becomes. If you use it not as software to produce numbers but as software to give reasons for the numbers, the quality of your design and explanations will improve significantly.

And the more carefully you check weather, orientation, losses, and shading at the desk, the more important the accuracy of on-site positioning and equipment layout becomes. Even if you refine design conditions in PVSyst, if on-site positioning or obstacle identification is vague, discrepancies between design assumptions and construction reality tend to grow. That is precisely why organizing desktop conditions in PVSyst during the design stage and combining them at the site stage with an iPhone-mounted high-precision GNSS positioning device like LRTK makes it easier to link design, construction, and maintenance consistently. The more items you verify in PVSyst, the better they pair with on-site positioning methods that support location accuracy, such as LRTK.