What is PVSyst? Understand the Power Generation Simulation Process in 5 Steps

Table of Contents

• What is PVSyst?

• Step 1 Decide the location for the calculation and the meteorological data

• Step 2 Define the installation surface and system configuration

• Step 3 Calculate DC-side generation from incident solar irradiance

• Step 4 Reflect losses, shading, and conversion conditions

• Step 5 Interpret the results and use them for comparison and improvement

• Common pitfalls for beginners

• Summary

What is PVSyst?

PVSyst is specialized software for the study, capacity design, performance evaluation, and data analysis of photovoltaic power generation systems. In the official documentation, it is organized as software that handles not only grid-connected systems but also standalone systems, pump applications, and DC-system applications, and is described as a design environment equipped with a meteorological database, an equipment database, various solar energy-related tools, and functions for comparing measured data. In other words, rather than being simply a tool to calculate annual energy production once, its true role becomes clearer if you understand it as practical software for organizing solar projects from their initial assumptions.

When practitioners search "What is PVSyst," what they want to know is less the meaning of the name than what it calculates, how it calculates it, and where it is useful in the design process. A key point in answering that is that this software is not a black box that returns a single answer. The official help explicitly sets out a two-stage approach: in the initial phase it produces monthly estimates with few input conditions, and in the full-scale phase it performs hourly simulations for detailed design. Furthermore, a "project" framework is provided so that multiple simulation conditions can be compared within the same case.

In other words, PVSyst is not only software for producing the numerical values of power generation but also software for organizing the assumptions from which those numbers originate. Because it lets you connect and handle the sequence of site, weather, mounting surface, system configuration, losses, shading, and result comparison within a single environment, a major characteristic is that it makes it easier to explain the design. For beginners who want to understand the flow of generation simulation and for practitioners who want to establish the basis for a design, grasping this first will make later understanding considerably easier.

Step 1 Decide the location for calculation and the meteorological data

The first step in a power generation simulation is to decide where to perform the calculations and to select the meteorological data for that location. In PVSyst’s official documentation, a project is described as a framework that contains geographical conditions and hourly meteorological data. Furthermore, the roles of the meteorological database include creating geographic sites, generating time-series data, visualizing data, comparing data, and importing external files. In other words, the starting point of this software is not the equipment model but “which location and which meteorological conditions to assume.”

The important point here is the obvious fact that the results of photovoltaic power generation are not determined solely by installed capacity. Even with the same capacity, if the installation site differs the solar irradiation conditions change, and annual energy production and seasonal variability can vary greatly. Moreover, even at the same site, the apparent outcome can change depending on the type of meteorological data used and the way representative years are defined. One reason PVSyst is used in practice is that it treats meteorological data not merely as input values but as the foundation of the design. The more a designer wants to explain the basis for their numbers, the more carefully they need to examine this initial step.

What beginners often stumble over here is assuming that selecting a single meteorological dataset finishes the job. In reality, even a slight difference in the site settings can lead to large differences in the results once azimuth and tilt are applied. Also, when using externally imported data, you need to map the columns and verify the data quality. PVSyst provides mechanisms to make those tasks easier, but ultimately it is the user who must judge whether the assumptions for a given project are reasonable. Keep in mind that the first step in power generation simulation is to consciously decide on the site and meteorological conditions before operating the software.

Step 2: Define the installation surface and system configuration

The second step is to define the conditions of the installation surface and the system configuration. In PVSyst project design, you define the orientation of the installation surface, whether tracking is used, the conditions for row-mounted installations, and then select system components and design the number of modules in series and in parallel. This is not simply a step to enter "how many kilowatts to install." It is the process of specifying which direction, at what angle, and in what configuration the modules will be mounted.

One point that beginners in solar design often overlook is that installation surface conditions and equipment configuration are not separate issues. If orientation or tilt changes, the times at which the site receives solar irradiance also change, and if the configuration changes, the voltage and current limits the equipment can tolerate and even the operational efficiency will change. Because PVSyst treats these conditions as an integrated whole, it offers a perspective much closer to practical work than the simplistic thinking of “this capacity will produce this amount of energy.” The major significance of this step is that it lets you proceed while considering how the system will actually be realized.

Another advantage of PVSyst is that you can deal with things in more or less detail depending on the project’s progress. In the early planning stage you can set the rough azimuth and tilt for a preliminary estimate, and in the detailed stage you can refine the configuration and input-side conditions. If you try to create a perfect configuration from the start, you’ll get tired of data entry and lose sight of the overall flow. It’s easier to understand the flow of a power generation simulation if you first create one standard proposal and then refine it while comparing differences in conditions. PVSyst’s design flow is structured so that you solidify assumptions step by step rather than aiming for a finished design from the outset.

Step 3 Calculate DC-side power generation from incident solar radiation

The third step is to convert meteorological data on the horizontal plane into the solar irradiance reaching the installation surface, and to calculate the DC-side power generation from that irradiance. In PVSyst’s official documentation, the conversion of irradiance to a tilted surface is described as the process of calculating the incident irradiance on the installation surface from horizontal-plane irradiance data. Furthermore, the beam, diffuse, and ground-reflected components are treated separately and calculated for each installation surface. In other words, rather than simply thinking “a region with high irradiance will produce more power,” you first organize how that irradiance actually reaches the installation surface and then proceed to the calculations.

Only now does the significance of including the orientation and tilt of the installation plane become apparent. Whether it is south-facing or east/west-facing, and whether the tilt is steep or shallow, the incident irradiance calculated from the same horizontal-plane solar radiation data will change. Because PVSyst performs this conversion for each installation plane, it makes it easy to see how differences in orientation and angle influence the results. What is important for understanding generation simulations is that meteorological data do not directly translate into the final results; they only become meaningful when combined with the installation plane’s conditions. Once you understand this flow, it becomes natural to see why defining the installation plane is important.

Next, PVSyst models the module's power-generation behavior. The official physical model explains that it uses the Shockley single-diode model to describe the module's operation. This model was originally intended to describe cells, but it is generalized and applied to the entire module. Furthermore, not only basic specification values but also additional parameters—such as series resistance and parallel (shunt) resistance—that are not fully listed in typical datasheets are involved. In other words, PVSyst does not determine DC generation by multiplying nameplate values; instead, it calculates the available DC-side energy through the module's behavior in response to changes in irradiance and temperature.

Put simply for beginners, this step is "the stage where the light coming from the sky is converted into the light that reaches the surface, and the amount of electricity that this light generates in the module is calculated." By this point it becomes clear that PVSyst is not just a spreadsheet but is based on physical principles. If you want to understand the flow of a power generation simulation, keeping in mind that in this third step "solar irradiance" and "module behavior" are treated as separate matters will make it easier to understand the meaning of subsequent losses and shading.

Step 4 Account for losses, shading, and conversion conditions

The fourth step is to start from the energy that would be obtained under ideal conditions and then account for the actual losses, shading, and conversion conditions. In PVSyst’s simulation workflow, after calculating the irradiance on the plane of array, corrections are applied to the beam component if there is horizon shading, the effects of near shading are reflected if present, and then incidence-angle losses, attenuation of the diffuse and reflected components, soiling, and so on are applied in sequence to determine the effective irradiance. In other words, the incoming light itself is reduced first, and on top of that losses from the modules, wiring, and conversion side accumulate.

The important point here is that losses are not something you can just subtract all at once at the end. The official overview also explains that in the second stage of detailed design you can analyze fine effects such as thermal behavior, wiring, module quality differences, mismatch, angle‑of‑incidence losses, far shading, and near shading. In other words, the software is built around the idea of incorporating losses into the design from the start. A common practical mistake is to produce high numbers under ideal conditions and then roughly subtract them later as a kind of safety margin. Following the PVSyst workflow makes it easier to check, step by step, where and by how much reductions occur.

More care is required regarding shading. PVSyst’s shading feature not only treats far shading and near shading separately, but can, when necessary, go so far as to account for electrical shading losses. The official module-layout page explains that by defining the position of each module and which string and input it belongs to, electrical mismatch losses caused by partial shading can be calculated in detail. This demonstrates that shading issues are not simply a matter of the “area in shadow.” Even small shadows can increase losses more than expected depending on the circuit connections, so PVSyst considers shading from both spatial and electrical perspectives.

Furthermore, the energy obtained on the DC side does not simply appear unchanged on the AC side. Official models of the power conversion equipment explain that they handle input-side voltage and current conditions, the range of maximum power point tracking, output limitations, changes in efficiency, and so on. In other words, even if you think "we could get this much" on the DC side, the available energy can change further depending on the converter’s conditions. When understanding the flow of a power generation simulation, it is easiest to think of this fourth step as the stage that most "brings it closer to reality." Ideal light does not directly become ideal power; it approaches the actual generated output through shading, losses, and conversion conditions.

Step 5: Interpret the results, compare them, and use them to drive improvements

The fifth step is to interpret the results, compare them, and use them to inform the next improvements. According to PVSyst’s official help, the results include dozens of simulation variables and can be displayed monthly, daily, or hourly. It also explains that the loss diagram is particularly useful for quickly assessing the quality of the system design and identifying the main sources of loss. In other words, the simulation does not end when the numbers are produced. The workflow continues by reading where and how much was lost, comparing different proposals, and, if necessary, revising the assumptions.

What beginners should look at first is not just the annual energy production figure. It is important to look at the loss diagram and check how much of the energy reaching the installation surface is being reduced at each stage. PVSyst makes it easier to tell whether the irradiance conditions themselves are poor, whether shading has a large impact, whether energy is being eaten away by temperature or wiring, or whether losses are occurring on the conversion side. Rather than simply stopping at “low” or “high,” knowing “where the weakness is” leads to the next improvements. This is a major reason why PVSyst is useful as a design software.

As a way of interpreting the results, the performance ratio is also important. The official documentation describes the performance ratio as an indicator that divides the actually effectively obtained energy by the ideal amount calculated from the solar irradiance incident on the installation surface and the nominal output. This is a supplementary metric for assessing how cleanly the system is operating, whereas the generation itself is influenced by site and orientation. When comparing multiple proposals, looking at the performance ratio as well as annual generation makes it easier to distinguish proposals that are simply advantaged by solar irradiance conditions from those with a stable loss structure.

Furthermore, PVSyst has a function that imports measured data to make close comparisons with simulation results. According to the official overview, measured data can be imported from almost any text format, actual performance can be displayed in tables and graphs, and close comparisons with simulation variables can be made. This is a mechanism to review how the assumptions made at the design stage matched reality on site and to feed lessons back into future projects. If you understand the power generation simulation process in 5 steps, remember that this final step is “reading the results, comparing them, and using them for the next project”; doing so takes the use of PVSyst beyond mere calculation to a deeper level.

Common pitfalls for beginners

The most common pitfall for first-time PVSyst users is confusing the rough estimate with the detailed simulation. It is officially stated that the preliminary design function is meant to quickly produce a monthly outlook using only a few general conditions, and should not be used for detailed design. Nonetheless, if you treat the initial rough estimate as a definitive value, you will be caught off guard when large differences appear after you refine the design. It is important to separate the roles: "rough estimates are for getting a sense of direction" and "detailed design is for tightening the supporting evidence."

The second stumbling block is taking the equipment information in the database at face value. PVSyst has a convenient equipment database, but officially it cannot guarantee the included parameters, and users are advised to carefully cross-check them against the latest specifications when using it. Moreover, the module single-diode model involves additional parameters that cannot be fully determined from the datasheet alone. In other words, PVSyst is not software that removes the need for verification, but software that makes verification easier. Without this mindset, you are likely to rely too much on convenience and overlook mismatches in assumptions.

The third stumbling block is assuming you can just apply shading and losses at the end. In reality, PVSyst’s simulation workflow sequentially reflects corrections to incident irradiance, shading, incidence angle, soiling, temperature, mismatch, wiring, conversion conditions, and so on. In other words, losses are not a “final adjustment” but the core of the simulation. Rather than reassuring yourself by looking only at the energy production figure, trying to understand which losses that figure passed through makes your use of PVSyst much more practical.

Summary

PVSyst is a design software that handles photovoltaic project planning as a single workflow, from meteorological conditions through the installation surface, system configuration, losses, shading, and result analysis. When the power generation simulation process is organized into five steps, the sequence is: first decide the location and meteorological data; next define the installation surface and system configuration; then calculate DC-side generation from incident irradiance; reflect losses, shading, and conversion conditions; and finally interpret the results to enable comparison and improvement. Understanding this workflow makes it easier to see that PVSyst is not merely a power-generation calculation tool, but software for building up the rationale behind a design.

In practice, the more thoroughly you refine desk-based power generation simulations, the more important the accuracy of site location data and equipment layout becomes. Even if you properly account for orientation, shading, and losses in PVSyst, unclear on-site positioning or obstacle assessment can easily create gaps between design assumptions and implementation. That is why organizing the power output prediction workflow in PVSyst during the design phase and combining it with an iPhone-mounted high-precision GNSS positioning device like LRTK in the field makes it easier to link design, construction, and maintenance more consistently. The idea of improving desktop accuracy with PVSyst and aligning on-site positioning accuracy with LRTK is well suited to enhancing the overall reproducibility of solar work.