What is PVSyst? An Easy Explanation of How to Read Shadows, Azimuth, and Tilt

Table of Contents

• What PVSyst is used to analyze

• Why shading, orientation (azimuth), and tilt are important

• An easy guide to interpreting orientation (azimuth)

• An easy guide to interpreting tilt

• An easy guide to interpreting shading

• Understand why results change in a 3D scene

• How to proceed with checks in practice without getting confused

• Common misinterpretations and how to prevent them

• Summary

What is PVSyst used to view?

PVSyst is not a tool for roughly estimating the output of a solar installation. In its official description it is positioned as software for the study, design, and analysis of solar systems—including grid-connected, stand-alone power, and pumping applications—and is not a mere simple calculator. It provides mechanisms to interpret the background of results by taking into account meteorological conditions, system conditions, loss factors, and the effects of shading. What matters for practitioners is not just the final annual energy figure but understanding the assumptions behind that number. If you view PVSyst as “software to translate design conditions into numbers for comparison,” it suddenly becomes much easier to know what to look at.

Among them, shading, azimuth, and tilt are the three elements that form the foundation for interpreting PVSyst. For fixed installations, the basic inputs consist of the orientation and tilt of the installation surface, and, as needed, this can be expanded to multiple orientations, seasonal tilt adjustments, long-row layouts, trackers, and so on. In other words, although many settings may appear on the screen, the central points to grasp first are “which way it faces,” “how much it is tilted,” and “what stands in front of it.” Once these three are understood, PVSyst becomes not a difficult specialist software but a practical tool for sequentially interpreting the conditions that affect power generation.

In practical work, it is not uncommon for a project's direction to be largely determined by site and roof conditions before equipment specifications or wiring methods are considered. In situations where the building's orientation is fixed, an ideal south-facing layout cannot be achieved, there are obstacles in front, or foundation heights are uneven on developed land, differences in power generation are governed more by how shade, azimuth, and tilt are handled than by equipment selection. All the more reason that those who want to understand what PVSyst is should first grasp how to assess these three factors. Knowing which axes to look at before learning how to operate the software is the shortest route to avoiding misinterpretation of the results.

Why Shadows, Orientation, and Slope Are Important

The power output of a solar installation is determined by the amount of solar irradiation it receives and by how much of that irradiation can be converted into electricity without losses. In this context, azimuth and tilt are the conditions that determine how easily sunlight can reach the installation surface in the first place. Shadows, on the other hand, are a condition that reduce the sunlight that would otherwise enter. In PVSyst’s orientation optimization approach, when azimuth and tilt are changed you can roughly check how far the chosen conditions are from the optimal point. This is not a precise final evaluation but merely a guideline to provide an outlook; however, it is extremely useful for visually understanding how the orientation and angle of the installation surface affect power generation.

The important point here is that even if orientation and tilt look favorable, results can be reversed depending on shading conditions. For example, increasing the tilt may improve the incidence of solar radiation on the installation surface, but it can increase shading between front and back rows or worsen installation density, which can be detrimental to the overall final energy yield of the system. PVSyst’s explanation for row layouts also indicates that a lower tilt makes the system less susceptible to the effects of building orientation and helps reduce azimuth dependence. In other words, orientation and tilt are not factors that can be judged good or bad on their own; they need to be evaluated together with shading.

The most common misunderstanding among beginners is assuming that tilting panels to face due south will always maximize energy production. In practice, roof orientation, site width, front-to-back row pitch, obstructions, terrain slope, installation conditions, and so on all interact, so things rarely follow ideal theory. PVSyst is meant to visualize the gap between the ideal and the constraints, so “reading” shading, azimuth, and tilt should be understood not as searching for an ideal value but as finding a compromise that minimizes losses under constraints — a perspective that is more useful in practice. Seen that way, PVSyst is not software that gives a single “correct” answer, but software that lets you check which losses increase under which conditions.

A Simple Guide to Understanding Directions

A common stumbling block when first using PVSyst is the definition of azimuth. With typical drawings or maps people tend to use north as the reference, but in PVSyst the azimuth in the Northern Hemisphere is referenced to south. South is 0 degrees, west is +90 degrees, east is -90 degrees, and north is 180 degrees. In other words, if you enter the opposite sign when you want an east-facing orientation, it will be interpreted as west-facing. This is not just a display difference—it can change whether the system produces a morning-type or afternoon-type power profile, and how shadows fall in the morning and evening. First of all, firmly grasping the single point that "PVSyst's azimuth is south-based" is the first step to reading it correctly.

What matters next when assessing orientation is to look at how far it deviates from the optimal conditions rather than the numerical value itself. PVSyst has an azimuth optimization tool to roughly check where the current azimuth and tilt stand relative to the optimal point. Officially, this is only a rough estimate and is intended for judging the difference from the optimal values. The takeaway is that orientation should not be judged in black-and-white terms of good or bad, but read as a distance from the optimum. In practice, it is far more important to determine whether a slight deviation from true south causes a significant loss or falls within a range of mild impact.

Also, PVSyst is not software that handles only a single orientation. Because it allows multiple orientation settings, it can accommodate roofs divided east-west, multiple buildings, and installations whose orientations vary along the terrain. What matters in practice is not forcing an entire project into a single south-facing model. Considering orientations separately for each roof surface, each zone, or each terrain cluster will yield results closer to reality. The fact that PVSyst supports multiple orientations can help break the assumption that orientation must be fixed to a single direction.

Furthermore, the interpretation of azimuth changes depending on the relationship with shadows. At sites with strong mountain shadows in the morning and sites with strong building shadows in the evening, azimuths near south can be advantageous or disadvantageous in different ways. Because distant shading is treated as horizon conditions and nearby shading is treated as a 3D scene, judging based only on azimuth can lead to misidentifying the cause. When evaluating azimuth you should always consider two aspects together: whether sunlight can easily enter from that direction, and whether that direction will increase shading. Understanding azimuth merely as a number is insufficient; only when you can imagine the time of day and how shadows will fall does the azimuth setting in PVSyst become a practical input for decision-making.

An easy guide to understanding slopes

Tilt is the angle formed between the installation surface and the horizontal plane. In PVSyst’s definition, put simply, it describes how much the panel surface is raised relative to the ground. This explanation may sound straightforward, but in practice this angle carries a great deal of meaning. It influences how the panels receive light, how inter-row shading increases, how many modules can be placed in the same area, how they fit on roofs and mounting structures, and even considerations for ease of cleaning and drainage. Tilt therefore encompasses multiple decision axes in one. For this reason, in PVSyst tilt should be considered not merely as an input value but as a parameter that numerically represents the design philosophy.

What you need to keep in mind here is that the tilt you enter does not necessarily match the actual effective tilt in reality. In PVSyst’s 3D definition, a surface itself has a tilt in its own coordinate system, and the final orientation is determined when it is placed in the global scene. Furthermore, if the table’s reference line has a tilt, the actual surface’s direction and tilt will change. In other words, on sloping terrain or complex roof surfaces, it is dangerous to rely solely on the nominal tilt. If you do not check how the software ultimately interprets each surface, discrepancies will arise between the input values and the results.

In large projects or terrain-following projects, this discrepancy becomes even larger. PVSyst groups surfaces with similar orientations within the same zone and calculates an average tilt, azimuth, and reference-line slope from them, treating that as a single orientation. This is very reasonable computationally, but from a field perspective it is also a pitfall: it’s easy to understand the whole site by a “single tilt angle.” In reality there is variation, and judging only by the average can cause you to overlook surfaces that suffer large local losses. In practice, knowing that averaging is being applied, it is important to check whether there are many surfaces that deviate from the average.

Also, tilt changes how strongly production depends on azimuth. In explanations for row layouts, a lower tilt has been shown to reduce the dependence of energy output on building orientation and make it easier to match the building azimuth. This is quite important in practice: for projects with tight roof or site constraints, slightly reducing the tilt can make the overall plan easier to manage. Even if a higher tilt may look better at first glance, if it becomes disadvantageous due to shading or installation density, it is not truly optimal. When evaluating tilt in PVSyst, you need to consider the three factors together: how solar radiation is received, shading, and the amount installed.

A Gentle Overview of How to Read Shadows

PVSyst officially identifies near shading as the most difficult part. This is not an area that only beginners get confused by; even users with some experience can easily misinterpret the correspondence between settings and results. The first thing to clarify is that shadows can be broadly divided into far shading and near shading. Far shading is the kind of shading—such as from mountains or distant terrain—that is applied to the entire system at a given time depending on whether the sun is visible or not. Near shading is the shadow that previous rows, nearby buildings, trees, fences, etc., cast in a specific shape on part of the installation. Although both are "shading," the way of thinking and the configuration methods differ.

For distant shading, PVSyst provides a method to define the horizon as a polyline, which is suitable for sufficiently distant obstacles. Official guidance indicates that objects roughly ten times the system size or more distant should be treated as distant shading. Conversely, if you represent buildings or trees that are closer than that only by the horizon, you cannot reproduce phenomena in which only part of the installation is shaded. In practice, it is helpful to organize things as “mountain shadows as horizon shading, nearer obstacles as near shading.” If this separation is done incorrectly, the causes of morning and evening losses become unclear, and it becomes harder to identify directions for design improvements.

In near shading, it is necessary to further distinguish between "linear shading" and "electrical shading." According to PVSyst, linear shading is the lack of solar irradiance caused by the visible shadow itself, while electrical shading is the additional loss from mismatches produced by that uneven irradiance. In other words, even if the apparent shaded area is small, depending on how the shadow falls the electrical loss can be large. If you estimate losses based only on simple shaded area without understanding this, you may be surprised by a larger-than-expected drop. PVSyst treats linear losses and electrical losses separately precisely because it reflects this reality.

What is even more important in reading shadows is that the concept of shading applies not only to the direct component but also to the diffuse and ground‑reflected components. PVSyst uses a shading‑coefficient table to account for attenuation of not only the beam component but also diffuse and ground‑reflected components, and in the fast calculation mode it interpolates from precomputed tables. Officially, this table is interpolated from precomputed values at 10° increments of solar altitude and 20° increments of azimuth. What practitioners should understand here is that shading is not just a matter of whether the sun is visible or not, but also affects how light from the whole sky is perceived. Therefore, PVSyst’s shading assessment is much more three‑dimensional than the flat shadow silhouettes of a still image.

Moreover, the treatment of diffuse shading is not something that changes hourly with the sun’s position; rather, it is calculated as an integral based on geometric conditions, and part of it is used as a constant coefficient throughout the year. In the formula, the shading coefficient for diffuse radiation is determined by the system geometry and is considered constant over the year. Knowing this reduces the likelihood of confusion when you look at shading losses in a report and imagine only direct shading. When examining shading in PVSyst, it becomes much easier to interpret if you understand that there are "components that vary with the sun’s position" and "components that act as fixed geometric conditions."

Understanding Why Results Change in a 3D Scene

When PVSyst results differ from expectations, the 3D scene is a high-priority area to review. In the official 3D definition, a surface has its tilt within its own coordinate system, and its azimuth is determined when it is placed in the global scene. In other words, even if you believe you set tilt and azimuth in the input fields, the actual orientation can change depending on how it is positioned in the 3D scene. Simple layouts on flat ground rarely cause problems, but with multiple surfaces, sloping terrain, folded roofs, or staggered-row arrangements, an insufficient understanding of the 3D side can lead to misreading the results. If, when using PVSyst, you ask yourself "Why is the shading so large only at this time?", the safest first step is to suspect whether the 3D scene has been created according to the design intent.

The reason long tutorials on near shading are provided is that the 3D scene directly determines the results. In PVSyst, to check near shading you open the 3D construction window, define obstacles and equipment surfaces there, and inspect the shadows with animations and diagrams. This is not mere drafting; it is the work of creating the very assumptions on which the simulation is based. Put another way, if the accuracy of the 3D scene is low, subsequent shadow assessments become fundamentally vague. Near shading is considered difficult not because the操作 is complicated, but because errors in the geometric conditions directly feed back into the loss evaluation.

Furthermore, in PVSyst’s new orientation management, surfaces with similar orientations are automatically grouped and their average tilt and average azimuth are calculated. This is reasonable for large-scale projects, but conversely it means that what a user thought “they’re all the same orientation” may be handled inside the software as an averaged representative value. In practice, it is important to be aware whether this averaging is valid over the range in question and whether local differences are too large. Distinguishing projects for which averaging is sufficient from those that must be subdivided in detail is the key to mastering 3D scenes.

In projects where nearby shading is significant, a detailed evaluation of electrical shading may be necessary. Officially, to calculate mismatch losses from electrical shading most reliably, you must use a detailed layout feature that defines each module’s position and interconnections. This detailed feature is typically handled at the final stage, after the 3D scene and system definition have been sufficiently finalized. In practice as well, rather than immediately diving into the details during the initial study phase, it is more efficient to first finalize the 3D geometry and basic orientation, and then only detail those projects that require it.

How to Proceed with Verifications in Practical Work Without Getting Lost

When reading PVSyst in practice, it's safer not to start from the results screen. The first things to check are the location and meteorological conditions, then the horizon conditions, then the orientation (azimuth) and tilt, and finally the near-field shading. If you build up the inputs in this order, it's easier to trace where the results changed. Conversely, if you model near-field shading in detail from the start and later make large changes to the orientation or tilt, it becomes hard to see what did and didn't have an effect. PVSyst may seem to have many settings, but the practical way to read it is simply to add assumptions little by little and examine the differences.

When checking orientation and tilt, first set a reasonable direction and angle as the fixed surface, and confirm your current location on the orientation optimization screen. Then create several realistic candidates to match the building’s orientation and site conditions. The important point here is not to try to nail the ideal value in a single attempt. The official guidance also states that this optimization is intended for a rough outlook, so it’s better to use it to narrow down candidates rather than to draw a definitive conclusion here. In practice, it’s useful to verify that a south-based orientation has been entered correctly, and to nudge the orientation and tilt slightly to observe sensitivity.

When checking shadows, treat distant shadows and near-field shadows separately. Include mountain ranges and distant terrain as horizon conditions, and verify nearby objects such as buildings and front-row equipment in a 3D scene. Then, if necessary, consult shadow factor tables, shading contour maps, and temporal variations to determine which seasons and times of day the losses are concentrated. If near-field shading is large but the visually observed shaded area does not match the losses, you should suspect the influence of electrical shading. Simply distinguishing whether the effect can be explained by mere solar irradiance obstruction or whether an explanation must include mismatch effects will greatly improve the accuracy of your interpretation.

In final comparisons, it is important not to judge solely by annual energy production. Even between two proposals with similar output, practical ease of handling can differ because of how morning and evening shading occurs, biases in output time windows caused by differences in orientation, variability from terrain following, and future maintainability. PVSyst is a tool for seeing those differences in advance. Therefore, when interpreting results, rather than extracting a single number, it is important to trace the installation surface conditions, the shadow settings, and the chain of effects leading to the final output as a coherent narrative. Once you can adopt that perspective, PVSyst begins to function not merely as power-production calculation software but as a tool for organizing design decisions.

Common Misreadings and How to Prevent Them

One of the most common misreads in PVSyst is misunderstanding the sign of the azimuth. If you’re not used to the definition that uses south as the reference with east negative and west positive, you can enter east and west swapped and end up interpreting morning and afternoon generation trends in reverse. This is less an operational slip and more a structural error caused by differences between drawing conventions and the software’s azimuth definition. The way to prevent it is simple: after creating a candidate layout, always sense-check whether it favors the morning or the afternoon. If you don’t proceed by looking only at the numbers but instead think about it in terms of the sun’s movement, this mistake is much reduced.

A common mistake is viewing a slope as a single angle. That may not cause problems for simple flat-site layouts, but in projects involving ground slope or roof pitch, the actual orientation and tilt of the surfaces change. Moreover, when multiple surfaces are averaged, relying only on the representative value can give a false sense of security and cause you to miss localized adverse conditions. To prevent this, you need to check the 3D scene and how surfaces are grouped, not just nominal values, and be aware of the effects of averaging. Understanding how directions are organized internally in PVSyst will help you notice anomalies in the results sooner.

Another common misinterpretation is judging shading solely by the visually obstructed area. In PVSyst, the reduction in irradiance caused by visible shading and the additional losses due to electrical mismatch are treated separately. Therefore, it can happen that losses are surprisingly large even though only a small portion appears to be shaded. This is especially the case for projects with row layouts or partial shading; if you don’t understand this difference, you may easily feel that “the calculations are wrong.” To avoid this, it is important to read linear losses and electrical losses as separate items and, when necessary, proceed to a detailed layout evaluation.

Furthermore, caution is necessary when deciding the merits of a proposal based solely on the performance ratio. The performance ratio is a useful indicator, but even in its official definition it expresses the ratio of the actual amount of electricity produced to the solar irradiance incident on the installation surface and the rated output. In other words, while the performance ratio is effective for observing the overall behavior of the system, it is not a dedicated indicator for judging the appropriateness of orientation or tilt on its own. In practice, the performance ratio, energy generation, shading losses, and installation conditions need to be considered together. Instead of simplistically deciding that a high performance ratio means everything is fine and a low one means failure, it is important to trace which design conditions produced that figure.

Summary

Looking at shading, azimuth, and tilt in PVSyst is not simply a matter of typing numbers into input fields. Read azimuth relative to south, understand tilt as the angle from the horizontal plane, separate shading into far-field and near-field shadows, and also be aware of linear losses and electrical losses. Once these basics are in place, the numbers and diagrams that appear on the screen suddenly become much easier to understand. Much of the reason PVSyst feels difficult is not that it has many features, but that it's easy to lose sight of how shading, azimuth, and tilt connect to the results. Conversely, if you view things with these three as the axis, even practitioners can interpret it adequately.

In practice, it is more important to choose the option that minimizes losses within constraints than to search for ideal conditions. By carefully checking shading, azimuth, and tilt in PVSyst while taking into account building orientation, topography, obstacles, installation density, and constructability, the accuracy of the design will increase significantly. If you want to reduce discrepancies between design assumptions and site conditions, stabilizing decisions goes hand in hand with improving the accuracy of on-site positioning and coordinate verification. If you want to streamline such preliminary on-site checks, using an iPhone-mounted GNSS high-precision positioning device like LRTK and organizing installation conditions based on the acquired position information makes it easier to connect desk-based simulations with on-site intuition.