What is PVSyst? A Beginner's Guide to Power Generation Simulation

Table of Contents

• What is PVSyst

• Overview of power generation simulation

• Basic terms to know first

• Simulation flow 1: Choose the location and meteorological data

• Simulation flow 2: Define the mounting surface and system configuration

• Simulation flow 3: Calculate the array's energy production

• Simulation flow 4: Incorporate losses and shading

• Simulation flow 5: Interpret the results

• Common pitfalls for beginners

• How to apply it in practice

• Summary

What is PVSyst?

PVSyst is dedicated software for studying photovoltaic power generation systems, system sizing, performance evaluation, and data analysis. In the official help, it is described as an environment that handles not only grid-connected systems but also stand-alone systems, pumping applications, and DC-system applications, and is positioned as a comprehensive design software that includes a meteorological database, a component database, various solar-energy-related tools, and even functions for comparing measured data. In other words, rather than being a calculator that simply outputs annual generation once, it is easier to understand if you view it as practical software that connects design, generation forecasting, and verification into a single workflow while organizing the project's assumptions.

What beginners in power generation simulation should know at the outset is that PVSyst is not a "black box" that returns the answer in one shot. The official documentation lays out a workflow in which, in the initial phase, monthly approximations are performed with limited conditions, and in the full-scale phase, system design is refined through detailed hourly simulations. Also, the concepts of project and variant are built in from the start so that multiple calculation conditions can be compared within the same case. In other words, PVSyst is software that produces numbers and, at the same time, software that helps organize the reasoning behind those numbers.

Overview of Power Generation Simulation

If you were to describe PVSyst’s energy production simulation in one sentence, it is “the process of sequentially tracking how the light at that location becomes electricity, where it is lost, and ultimately how much is available to use.” In the official simulation workflow, you first read time-step meteorological data, then calculate the solar irradiance incident on the installation surface, reflect optical attenuation from near shading and angle of incidence, and on top of that sequentially build up the array output, power conversion equipment characteristics, and system losses. In other words, it’s not a world that simply ends with “irradiance × capacity”; the result comes from multiple layered assumptions.

If you don't see this overall picture, beginners tend to be fixated on the annual generation figures alone. However, what matters in practice is understanding at which stage and by how much energy was lost. Even the official loss diagram page explains that loss diagrams are useful for quickly assessing design quality and locating the main sources of loss. In other words, a simulation does not end when the numbers are produced; it only becomes meaningful once you read the context behind the results.

Basic terminology to know first

The basic terms you should first learn are: project, variant, project site, weather data file, mounting surface, array, subarray, string, loss diagram, and performance ratio. According to the official project definition, a project is described as the central framework that holds geographic conditions and time-series weather data, within which alternative options called variants are contained. If beginners understand this distinction, it becomes easier to see why project site setup and variant management come first.

Also, in the official system definition, the system is organized as a collection of modules, strings, power-conversion equipment, and grid connections, and a sub-array is treated as a grouping that shares the same configuration conditions. In other words, before looking at the power output figures, you need to know the conceptual configuration of "on which face, in what kind of grouping, and how they are connected." The shortcut to understanding PVSyst is not to memorize terms like a vocabulary list, but to grasp where in the design flow each term appears.

Simulation Flow 1: Select Location and Meteorological Data

The initial process is to decide the location for the calculation and the weather data. The official tutorial shows that when creating a new project, you first define the project name, then select a site from "Site and Weather Data", and, if necessary, choose a different weather data file. The project site also has the latitude and longitude that serve as the reference for solar position calculations, and the weather data file provides time-based environmental conditions. In other words, the starting point of the simulation is not the equipment but the location and the weather.

A common stumbling block here is assuming that “it won’t make much difference which data you choose.” Official comparisons of meteorological data sources show that there are significant differences between available sources, and results can vary depending on the reference years, averaging periods, data processing methods, and the impacts of climate change. In other words, weather data files are not mere inputs but the very assumptions behind the results. If beginners make a point of asking “which meteorological data are these numbers based on,” their interpretation of PVSyst will become much more consistent.

Furthermore, PVSyst manages site information and meteorological data separately. The site is the center of the location information, while the meteorological data are the time-based conditions tied to that location. Because of this distinction, it is easy to try different meteorological data for the same site or to compare nearby candidate sites. What beginners should understand first is that the first step in a power generation simulation is not "choosing components" but "deciding where and under what meteorological conditions to evaluate."

Simulation Flow 2 Define the installation surface and system configuration

The next step is to define the mounting surface and the system configuration. In formal project design, the orientation and tilt of the mounting surface, and, where necessary, tracking or row-mounted conditions are defined; then components are selected within the system definition and the numbers of series and parallel connections are designed. In other words, even under the same site's meteorological conditions, if the orientation and configuration differ, the results will change significantly. The mounting surface and the configuration are inseparable.

At this stage, what beginners tend to do is think only about capacity first. However, in reality, when orientation or tilt changes, the times of day when light is received also change, and when the number of series or parallel strings changes, the input-side conditions and the way conversion-side constraints apply also change. PVSyst treats the mounting surface and equipment configuration as a single unit, so it can evaluate not only "how many kilowatts to install" but also "how to realize that capacity." This is a major difference from simple spreadsheet calculations.

Also, in the official explanation of shading and orientation matching, it is stated that an orientation defined in a variant must be linked to an electrical sub-array for the simulation to run. This means that deciding only the visual orientation is insufficient; a design is only valid when the mapping to the electrical system is included. Beginners may find this a little difficult at first, but if you understand that "PVSyst does not treat orientation and the electrical system as separate things," the meaning of the design will be less likely to become inconsistent.

Simulation flow 3 Calculate the array's power generation

The third stream is to calculate the array’s power generation from the light that reaches the installation surface. In the official simulation procedure, horizontal-plane irradiance is first read from time-resolved meteorological data, and that irradiance is converted into the global, beam, diffuse, and reflected components for the installation surface. After that, optical attenuations due to near shading, angle-of-incidence effects, soiling, and so on are applied to obtain the effective irradiance, and from there the array-side output calculation proceeds. In other words, regional weather conditions do not directly become the generation; generation starts only after being converted into the “usable light that reaches that surface.”

PVSyst uses a single-diode model for its module models. According to the official model description, not only the basic Isc, Voc, Impp, and Vmpp but also additional parameters such as Rshunt and Rseries—which are often not fully specified in typical datasheets—are involved. Because these affect behavior at low irradiance and with temperature changes, PVSyst does not simply multiply nameplate values; it computes the module’s behavior using the model. When beginners understand this, it becomes clear why the response at dawn and dusk or on cloudy days is not simply proportional.

At this stage, among the variables that can be checked, the official list for grid-connected systems includes nominal array energy, reference energy for PR calculation, low-irradiance loss, temperature loss, array MMP energy, and so on. In other words, PVSyst is software that lets you individually check how the array performed. Because you can observe behavior on the DC side, when results are poor on the AC side it becomes easier to distinguish whether the cause is array-related or system-related.

Simulation Flow 4: Accounting for Losses and Shading

The fourth step is to apply losses and shading to the energy obtained from the array. PVSyst's official documentation states that array and system losses are handled in detail, including temperature, low irradiance, module quality differences, mismatch, wiring, downtime, angle of incidence, soiling, and so on. Furthermore, each loss can be reviewed hourly, daily, and monthly, and is reflected in the loss diagrams. In other words, losses are not a single coefficient applied at the end, but are accumulated step by step within the simulation.

The handling of shadows is also extremely important. In the official description of shading relationships, losses from proximity shading are stated to include not only the shortfall in irradiance but also additional losses due to electrical mismatch. In detailed electrical loss calculations, each module’s position and which string or MPPT input it belongs to are used to separately evaluate the linear irradiance shortfall and the additional electrical losses. This makes it less likely to overlook cases where a visually small shadow can have a large electrical impact.

Also, the energy delivered to the AC side is reduced at this stage. The official list of variables includes losses from converter efficiency, losses due to the allowable input voltage range, losses from power thresholds, and so on. In other words, the power obtained on the array side does not directly become usable energy. PVSyst breaks down where and how much was lost, so you’re not left with just “the final result is low” and can more easily revise the design based on the causes.

Simulation Flow 5: Interpreting the Results

The fifth step is to interpret the results. According to PVSyst’s official documentation, the results include dozens of simulation variables and can be displayed monthly, daily, and hourly. Among these, the loss diagram is particularly important as a chart for quickly assessing the quality of the system design and identifying the main sources of loss. In other words, the simulation does not end with producing numbers; the main task is to interpret the reasons behind those numbers.

Another important way to read the results is the performance ratio. The official performance ratio page explains that the performance ratio includes optical losses, array losses, and system losses, and because it is less directly dependent on differences in location and mounting surface, it is useful for comparing system quality. In other words, a proposal with a higher annual energy yield is not necessarily a better design, and by looking at the performance ratio you can check, on a different axis, "how cleanly it is operating." It may seem a little abstract to beginners, but simply knowing this metric will significantly change how you interpret the results.

Furthermore, in PVSyst, comparing alternative scenarios and comparing with measured data are also part of how results are interpreted. The official description of measured data analysis explains that by closely comparing on-site measured data with simulated values, it not only validates the software but also helps analyze the operation of the actual system and detect small anomalies. In other words, reading the results does not mean merely looking at annual values, but involves assessing design quality from multiple perspectives, including loss diagrams, performance ratio, alternative-scenario comparisons, and measured-data comparisons.

Common Pitfalls for Beginners

Throughout this process, the biggest pitfall for beginners is confusing preliminary design with detailed simulation. The official preliminary design is meant to quickly provide monthly estimates using only a handful of general conditions; it is not a detailed design. If you treat the initial numbers as final, you will be confused by the differences once losses and shading are added later. It is important to understand that PVSyst is software where you first create a baseline case and then develop the design by adding conditions.

Another common mistake is to take database entries and default values at face value. Even in official module model documentation, it is noted that the basic values in the specifications alone are not enough and that additional parameters are involved, and values stored in a database are not a substitute for final verification. The fact that convenient initial values exist does not mean they are optimal for a given project. For beginners, it is less confusing to first understand the process using the default values and then, depending on the project, review the assumptions.

Also, a common pitfall is to evaluate shading solely by area ratio. The formula explains that electrical shading losses occur in excess of the linear shortfall. In other words, a shadow that looks small can produce large losses depending on the relationships within the circuit. The point of using PVSyst is that it allows you to see these easily overlooked aspects structurally. You don’t need to understand it perfectly from the start, but simply knowing that “shading is not simple” will greatly change how you interpret the results.

How to apply it in practice

To leverage PVSyst in practice, it's important to keep in mind a workflow of first using it for initial assessments, then refining during detailed design, and finally reviewing against actual performance. The official tutorial also recommends creating the first variant with a minimal configuration, then adding shading and individual losses and comparing them. In other words, rather than getting it right in one go, it's better to start from a baseline scenario and gradually increase accuracy. In practice this approach results in fewer reworks and is easier to explain.

Also, the perspective of linking forecasts with actual performance is important. The official measured data analysis states that close comparisons can reveal the real system’s behavior and even small anomalies. In other words, rather than leaving the design figures as-is, connecting them to post-operation results and learning from them makes it easier to improve the accuracy of the next project. PVSyst is not a one-off estimation tool; the more it is used as a tool to build up design quality, the greater its value becomes.

Summary

Organized for beginners, the things PVSyst can do and that are particularly important are nine functions: preliminary estimate studies in the early planning stage, organization of site and meteorological data, definition of installation surface conditions, verification of system configuration and sizing, time-based generation simulation, checking the breakdown of array losses, evaluation of linear shading losses and electrical losses, comparison of alternative proposals and economic assessment, and comparison with measured data and identification of anomalies. In other words, PVSyst is not software that only looks at the annual energy production number; it is an integrated tool that links design conditions with the reasons for the results.

For beginners, the important thing is not to try to master everything perfectly from the start. First, focus—in this order—on location and weather, the installation surface, the initial configuration, the first simulation, and how to read the loss diagram; mastering just these will let you make solid progress. PVSyst is less a difficult specialist program and more a tool you come to understand step by step. Use it not only to produce numbers but to give those numbers a rationale, and its value becomes much clearer.

The more carefully you verify meteorology, orientation, losses, and shading in the office, the more important the accuracy of on-site positional information and equipment layout becomes. Even if you refine design conditions in PVSyst, if on-site positioning and obstacle identification are unclear, discrepancies between design assumptions and construction reality tend to grow. That is why, at the design stage, organizing desk-based conditions with PVSyst and, at the field stage, combining that with iPhone-mounted GNSS high-precision positioning devices such as LRTK makes it easier to link design, construction, and maintenance more consistently. The idea of establishing design intent with PVSyst and aligning on-site positional accuracy with LRTK is well suited to improving the overall reproducibility of solar PV operations.