What is PVSyst? An easy-to-understand explanation of how solar simulation works

Table of Contents

• What is PVSyst?

• What does a solar PV simulation calculate?

• In what order does PVSyst perform its calculations?

• Key input parameters

• How to read the results and interpret the loss diagram

• Use cases for which PVSyst is suitable and not suitable

• Practical ways to use it to minimize mistakes in real-world work

• Summary

What is PVSyst?

PVSyst is dedicated software for the study, sizing, performance evaluation, and data analysis of photovoltaic (PV) power generation systems. In the official documentation it is described as software that handles PV systems not only for grid-connected applications but also for standalone and pumping uses, and it is positioned as a practical, professional environment equipped with meteorological data, an equipment database, and various solar energy–related tools. In other words, it is easier to understand PVSyst as software for verifying the validity of designs by organizing conditions step by step, rather than merely a quick reference for power output.

To put it more practically, PVSyst is not just a tool for seeing "how much power it is likely to generate." A major feature is that, within the framework of a project, it manages the site, weather, installation angle, equipment configuration, and loss conditions together and allows multiple calculation scenarios to be compared. Even the official help assumes that detailed design is organized on a project basis and that the approach is to compare multiple simulation conditions within the same project. Because of this structure, practitioners can more easily explain "what and how much differs between this layout proposal and an alternative."

PVSyst also offers both a preliminary design for rough assessments and a full-scale design that performs detailed, hour-by-hour simulations. In the preliminary design you can generate quick, monthly-based estimates using only a few general conditions, while the detailed design lets you delve into hourly meteorological data and loss conditions. In practice, because it is uncommon for all conditions to be fixed from the start, beginning with a coarse assessment and progressively refining it as the project becomes more concrete matches the typical workflow—this is one reason PVSyst is widely used.

What does a solar radiation simulation calculate?

Many people who search for "What is PVSyst" ultimately want to know what this software calculates and how. In short, PVSyst first takes meteorological data, organizes how much solar energy is available at that location, converts it into the irradiance incident on the installation surface, and then, while subtracting shading and reflection, temperature effects, equipment conversion efficiencies, wiring losses, and so on, determines the final usable energy. Rather than simply assuming "more irradiance means more generation," it uses an approach that sequentially incorporates the losses that actually occur in photovoltaic power generation.

At this stage, meteorological data are extremely important as the starting point. The official documentation explicitly states that meteorological data are the starting point for project assessment and, at the same time, a primary source of uncertainty. In other words, even if PVSyst’s calculations are excellent, the results can easily be off if the meteorological assumptions entered are inappropriate. Moreover, official comparisons indicate that there are differences among the available meteorological data sources and that the degree of variation differs by location. When using PVSyst, what matters more than the software operation itself is being aware of which meteorological assumptions were adopted.

Also, PVSyst does not greatly simplify the behavior of solar cells. Officially, it represents the electrical behavior of PV modules based on a single-diode model, and it reflects changes due to irradiance and temperature in its calculations. In other words, PVSyst does not treat solar cells as "a box that generates a fixed proportion of the incident irradiance"; rather, it simulates them in a way that follows reality, where output characteristics change as irradiance and temperature change. This is why it is more practical for real-world use than simple calculations.

What is the order in which PVSyst performs its calculations?

To put PVSyst’s calculation flow simply: first it organizes the “light coming from the sky,” then it calculates the “light that reaches the installation surface,” next it determines the “amount the solar cells convert into electricity,” and finally it subtracts the “losses in equipment and wiring.” In the official list of simulation variables, weather data such as horizontal irradiance, diffuse irradiance, temperature, and wind speed are handled, and in the next stage these are converted into the irradiance incident on the installation surface. Rather than using the horizontal-plane data as-is, this includes a conversion step to determine how much irradiance is incident on a generation surface with a given tilt angle and azimuth.

The calculation of the "light reaching the installation surface" is the heart of solar simulation. Even at the same site, whether it faces south or east–west, and whether the tilt is shallow or steep, both the amount and the timing of incoming solar irradiance change. In PVSyst, global and diffuse irradiance on the horizontal plane are used to break down the installation surface's global irradiance, direct irradiance, diffuse irradiance, and ground-reflected components. If practitioners understand this, it becomes much easier to grasp why results differ with installation conditions even when using the same meteorological data.

Next come optical losses and shading corrections. The official help explains that shading calculations are performed on an hourly basis and require different treatment for the direct, diffuse, and reflected components. Moreover, shading not only causes reduced irradiance but also produces additional losses due to electrical mismatch between series-connected modules. In other words, you cannot simply say that a smaller shaded area means a smaller impact. PVSyst is said to be strong in shading assessment because its approach takes these electrical shading effects into account.

Even after light reaches the module surface, not all of it is directly converted into electricity. When the angle of incidence is large, reflection at the glass surface increases and the light reaching the cell decreases. In PVSyst, this is treated as incidence-angle loss, and the insufficient transmittance as a function of incidence angle is modeled. The official documentation also describes the IAM as an optical loss representing the reduction of solar irradiance actually reaching the cell surface. Understanding this stage makes it easier to grasp why generation is lower in the morning and evening and why the glass condition of the installation surface affects output.

After that, PVSyst uses a single-diode model to determine the solar cell’s output characteristics as a function of solar irradiance and temperature. This incorporates efficiency drops at low irradiance and reductions in output at high temperatures. In the official loss descriptions, irradiance losses, thermal losses, module quality differences, mismatch, and so on are organized so you can follow, step by step, how actual power generation falls from the ideal value. PVSyst’s results are closer to reality than a simple multiplication because it accumulates many losses at this stage.

Finally, the DC-side output is converted to the AC side. In this process, PVSyst assumes that the conversion equipment always attempts to follow the maximum power point, but that voltage, current, and output have upper limits, and that conversion efficiency can vary with load factor and input voltage. The official documentation explains that maximum power point tracking operates within an allowable voltage range, that losses occur outside that range, and that conversion efficiency is modeled according to output and input voltage. Because of this, the energy captured on the DC side does not directly become AC energy for sale to the grid or for self-consumption.

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When you start using PVSyst, it's easy to focus solely on equipment parameters, but what matters first are the site conditions and meteorological conditions. The official guidance also states that at the center of a project are geographic information and time-series meteorological data. Which region you are in, which meteorological dataset you use, and which period you treat as the representative year can all greatly change the annual energy yield and seasonal variability. If those points remain unclear and you only refine the equipment details, the results will not become more persuasive. First, it is important to establish the assumptions about location and weather.

Next, the conditions of the installation surface are important. Azimuth, tilt, whether tracking is used, distant shading, near shading, row spacing, and the effects of ground reflection all influence the light reaching the installation surface. In PVSyst, after defining the orientation of the installation surface and the mounting structure conditions, shadows and losses are added progressively. In particular, shadows are treated not only on an hourly basis but also down to electrical mismatch, so if site conditions are not well organized the reliability of the results can easily decline. It is important to input not only the plan view but also the heights and placement of surrounding objects.

Furthermore, equipment configuration also has a major impact on the results. Officially, a grid-connected system is defined as consisting of photovoltaic modules, strings, power converters, and the grid connection, and a mechanism is provided to propose an appropriate configuration based on the input conditions. The number of modules in series and parallel, how the input circuits are divided, and the operating voltage range of the converters affect not only the energy yield but also how losses manifest. PVSyst is software that does not stop at entering the system capacity; it examines how that capacity is actually configured.

And what is easy to overlook is the loss settings. The official documentation states that PVSyst treats incident angle loss, soiling loss, irradiance loss, thermal loss, module quality differences, mismatch, wiring loss, transformer loss, auxiliary consumption, downtime loss, and so on in detail. Moreover, even if reasonable initial values are entered at first, it is recommended to review them after the first simulation to match your own project. In other words, rather than accepting the numbers as they are in the initial settings, aligning the breakdown of losses with the project specifications leads to improved accuracy in practice.

How to Interpret Results and Read Loss Plots

When looking at PVSyst results, the first thing to focus on is the loss diagram. The official documentation states that the loss diagram is a chart for quickly gauging the quality of a system design and is especially effective for identifying where and how much loss is occurring. Because it is shown not only in the annual report but also by month, it serves as an entry point for spotting seasonal differences and time-of-day issues that are difficult to see from the annual energy production total alone. For practitioners who are just starting to use PVSyst, developing the habit of reading this loss diagram first will speed up understanding.

The reason a loss diagram is useful is that you can trace the calculation flow in reverse. You start with the available solar irradiance, and losses such as reflection, shading, temperature, mismatch, wiring, and conversion efficiency are sequentially subtracted until you reach the final energy. If generation is lower than expected, you can look at which losses are large to determine which input assumptions to revisit. Simply knowing that “annual generation is low” doesn’t reveal the cause, but by looking at the loss diagram you can more easily tell whether it’s caused by shading, high temperatures, or losses on the conversion side.

Another important point is the detailed output variables. According to the official documentation, dozens of variables are available as simulation results and can be displayed or exported on a monthly, daily, or hourly basis. In addition to energy production, various items such as plane-of-array irradiance, direct component, diffuse component, ambient temperature, wind speed, and AC-side energy can be viewed, which makes PVSyst particularly strong for root-cause analysis. In practice, rather than judging only by annual values, it is advisable to examine monthly and hourly behavior to confirm alignment with the design intent.

Furthermore, as an indicator of system quality, it is useful to check the performance ratio. Officially, the performance ratio is defined as the ratio of the energy actually usefully delivered to the ideal amount calculated from the plane-of-array irradiance and the nominal output, and it is described as broadly including optical losses, array losses, and system losses. Although the power generation itself depends greatly on location and orientation, the performance ratio serves as an auxiliary indicator of the system’s quality. When comparing multiple proposals, looking at this indicator as well as annual energy production makes it easier to distinguish proposals that merely benefit from favorable irradiance conditions from those that have higher system quality.

Tasks PVSyst Is Suited For and Uses It Is Not Suited For

PVSyst is well suited to workflows that aim to link early-stage design studies through to detailed design in a single process. It is ideal for a workflow in which a rough estimate is made during pre-design, followed by detailed simulations to refine shading, losses, and equipment configuration, and finally the results are compared and compiled into explanatory materials. The official documentation also organizes both preliminary studies and detailed design, and the software is structured to allow optimization while comparing multiple simulation conditions. For that reason, it can be said to be software whose role can easily change to match project progress, from rough estimates at the sales stage to detailed comparisons during the design stage.

Also, PVSyst lets you break down losses, so it pairs well with projects that carry heavy accountability. Decisions such as why a particular orientation was chosen, why the row spacing was widened, or why the capacity ratio was set within a given range can be explained not only by energy yield but also by the breakdown of losses. The official guidance also presents the idea of performing optimization and parameter analysis through variant comparisons, indicating that it is more suited to narrowing down reasonable options while observing differences in conditions than to producing a single definitive answer.

On the other hand, you should avoid treating PVSyst as a universal source of correct answers. Meteorological data are both the starting point for evaluation and a major source of uncertainty, and official comparisons have shown differences between data sources. Therefore, PVSyst results should be treated not as "definitive figures of future actual power generation" but as "an outlook based on the given assumptions." Just because the numbers look neat does not mean you can skip verifying site conditions or checking the validity of the design assumptions.

Furthermore, at minimum the core functions in the official documentation are feasibility assessment, capacity design (sizing), performance evaluation, and data analysis. In other words, PVSyst is not software that automatically replaces on-site surveys, the preparation of construction drawings, or the actual on-site management of equipment locations. No matter how carefully simulations are performed on the design side, if the site’s orientation, obstacle conditions, or equipment-location management are unclear, the assumptions made at the desk will diverge from the actual field conditions. Rather than overestimating PVSyst, it is important to divide responsibilities and use it across design, on-site verification, construction, and operation and maintenance.

How to Use It in Practice with a Low Risk of Failure

To make practical work less prone to failure, it is more important to start from a rough plan and incrementally increase accuracy than to aim for perfect inputs from the outset. PVSyst itself follows a two-step approach: a preliminary design conducted with only a few conditions, and a detailed main design that performs time-step simulations. First get an overall sense using the site conditions, approximate capacity, and rough installation surface conditions, and then refine shadowing, losses, circuit configuration, and operational conditions—this approach minimizes rework. Trying to decide everything in detail on the first attempt leads to large backtracking if assumptions change later.

Next, it's important to cultivate the habit of making comparisons. PVSyst is based on the idea of comparing multiple conditions within the same project. Therefore, if you save and compare separate scenarios—different orientations, different tilts, with and without shading, or options that assume stricter loss conditions—you will see how sensitive the results are. In practice, rather than leaving only the final plan's numbers, grasping which changes to conditions affect which outcomes will improve both your explanatory ability and your judgment.

Also, it is important not to adopt the initial calculation results as-is. In the official guidance, although loss parameters have initial values, it is recommended to carefully review each loss according to the project after the first simulation. In other words, PVSyst’s initial values are a convenient entry point but do not substitute for project-specific conditions. Only by adjusting the losses toward those that are likely to occur in your company’s projects—soiling, wiring, shading, mismatch, temperature conditions, downtime, etc.—do the numbers become convincing.

Finally, when interpreting PVSyst results, it is important not to stop at annual energy production alone. Check the loss diagram for major losses, examine month-by-month changes to see seasonal characteristics, and, if necessary, follow behavior with hourly data; looking in that order makes it easier to pinpoint design weaknesses. By also checking the performance ratio, you can distinguish whether a high energy yield is simply due to favorable irradiance conditions or whether the proposal has high system quality. Mastering PVSyst is, more than learning the operation, about learning how to read and interpret the results.

Summary

PVSyst is not software for simply calculating photovoltaic energy output; it is a practical tool for creating an overview of the entire system by sequentially stacking meteorological data, installation surface conditions, shading, optical losses, temperature characteristics, equipment efficiencies, wiring losses, and so on. Put simply, it is easier to understand if you think of it as software that makes the intermediate steps by which "the sunlight received at a location" becomes "how much of it can be used as electricity" visible as much as possible. For that reason, PVSyst's value lies not merely in producing an annual generation figure but in being able to explain why that number is reached.

In practice, the more you increase the accuracy of simulations, the more important alignment with on-site conditions becomes. Even if you thoroughly refine power generation simulations at the desk, if on-site position checks and understanding of equipment layouts are unclear, gaps can easily arise between design, construction, and operation and maintenance. If you want to connect solar facility planning to on-site operations more reliably, it is effective to consider, in addition to simulation tools like PVSyst, on-site systems that can handle location information with high precision. For example, utilizing LRTK, an iPhone-mounted GNSS high-precision positioning device, can make it easier to improve the accuracy of equipment location verification and on-site records, and help bridge design and on-site operations.