How to Check Shading Losses in PVSyst | 5 Key Points for Interpreting Results

Table of Contents

• Basics to understand before viewing shading losses in PVSyst

• How to read the screens and reports for checking shading losses

• Approach 1: See the impact of annual shading losses on energy production

• Approach 2: Check whether shading effects are skewed by month or season

• Approach 3: Verify the validity of the 3D scene and obstruction settings

• Approach 4: Distinguish electrical losses from near-field shading when interpreting results

• Approach 5: Compare shading losses before and after design changes

• Conditions to review in practice to reduce shading losses

• Common mistakes and countermeasures when checking shading losses

• Importance of combining on-site verification with high-precision positioning

• Summary

Fundamentals to Understand Before Analyzing Shading Losses in PVSyst

When performing a photovoltaic system simulation in PVSyst, one of the items you should always check on the results screen is losses due to shading. In solar power generation, the irradiance reaching the panels is directly tied to the power output. Consequently, if irradiance is obstructed by surrounding buildings, trees, utility poles, slopes, rows of racking, fences, or mountain ridgelines, it leads to a reduction in generated energy. For practitioners learning how to use PVSyst, understanding how to interpret shading losses is important not only for reading the numbers, but also for judging whether the design conditions match the site and whether the power production estimates are being overestimated.

Shadow losses can be broadly divided into far shading and near shading. Far shading refers to obstructions that affect the site during periods of low solar altitude, such as the horizon, mountain ranges, or distant buildings. Near shading, on the other hand, refers to shadows that obstacles on or around the plant site cast onto the panel surface. Examples include shadows from adjacent panel rows, building façades, trees, equipment, embankments, and rooftop protrusions. When checking shadow losses in PVSyst, it is important not to confuse these two.

In professional practice, it is particularly insufficient to judge shading losses simply as “good or bad” based on a percentage. Even with the same annual loss rate, the design implications change depending on whether the losses are concentrated in the morning and evening, in winter, or during high-generation periods. Also, when shading affects only some panels, not only simple blocking of irradiance but electrical mismatch losses can become significant. When reviewing PVSyst results, you need to check, in sequence, where, when, and to what extent shading occurs, and how that is reflected in the system’s overall energy production.

In PVSyst you can create a 3D scene to set obstructions and panel layouts and simulate the effects of shading based on those conditions. The result report displays not only the final energy yield but also loss diagrams, monthly values, and loss items related to shading. Being able to read these correctly makes it easier to compare design proposals, explain them internally, and prepare materials for clients. Conversely, if you submit results without understanding the meaning of shading losses, you may later receive comments such as “there is more shading on site,” “the energy yield is too optimistic,” or “the obstruction inputs are too coarse.”

In this article, I organize and explain how to check shading losses in PVSyst into five practical viewpoints that are easy to use in the field. Following the workflow you should use in actual projects, I cover how to read the result screens that often confuse beginners, how to approach monthly checks, how to cross-check with the 3D scene, the difference between near shading and electrical losses, and how to compare before-and-after design changes.

Screen for Checking Shading Losses and How to Read the Report

The basic procedure for checking shading losses in PVSyst is, after running a simulation, to review the loss items in the results screen and the output report. When examining the results, rather than looking only at annual energy production and the performance ratio, check the shading-related items in the loss diagram. The loss diagram shows step by step the flow from incident irradiance to effective irradiance, module output, and system output, making it easy to understand at which stages and by how much losses occur.

Shadow losses may display different items depending on the settings. For example, if you enter obstruction from a distant horizon, losses related to distant shading will be reflected. If you set proximate obstructions in the 3D scene, solar losses due to near-field shading and, depending on conditions, electrical impacts will also be reflected in the results. What is important here is not to look only at the numbers shown in the results, but to verify which input conditions produced those numbers.

In practice, there are many situations where you must submit result reports internally or to clients. In those cases, simply stating what percentage the shading loss is is insufficient. You need to be able to explain which obstructions were included, whether shadows between panel rows were considered, to what extent surrounding terrain was reflected, and whether electrical losses caused by shading were evaluated. Because PVSyst’s results are calculations based on the input conditions, if the input conditions are coarse, the results may look neat but will be weak as a basis for practical decision-making.

When checking shading losses, first look at the annual energy production in the simulation results summary. Next, check the shading-related items in the loss chart. Then review the monthly values and detailed results to determine during which periods the impact of shading is greatest. Furthermore, return to the 3D scene to inspect the obstructions and panel layout that are causing the shading. By going back and forth between the results screen and the input screen in this way, you perform an analysis that leads to design improvements rather than merely verifying numbers.

One point beginners should be particularly careful about is not to judge shading losses by a single number. Even if the loss is small on an annual basis, it may be large during winter mornings and evenings. Conversely, even if the annual loss rate is somewhat high, it can be acceptable in design if the impact is concentrated in time periods that have a limited effect on overall generation. When using PVSyst, it is important not to look at only a part of the results screen but to take a comprehensive view of annual, monthly, and hourly results and the consistency of the input conditions.

Perspective 1: Examining the impact of annual shading losses on power generation

The first point to check is how much the annual shading loss affects the total energy production. PVSyst results display various losses alongside the annual energy production and the performance ratio. By looking at the proportion of losses caused by shading here, you can roughly grasp the impact that obstructions and layout conditions have on the generation plan.

When assessing annual shading losses, first determine at which stage the shading affects power generation. Shading is a factor that reduces the solar irradiance reaching the panel surface; therefore, it can appear as a loss at the irradiation stage. Conversely, when partial shading affects some panels or circuits, it may manifest as a different loss in the form of reduced electrical output. In other words, the impact of shading is not necessarily confined to a single item. When reading a loss diagram, it is important to check whether there are multiple items related to shading.

Even when the annual loss rate is small, it’s premature to be immediately reassured. For example, although it may appear to be less than a few percent on an annual basis, if shadows concentrate in certain seasons or times of day, they can cause problems when explaining power sales schedules or generation guarantees. Also, if shaded areas are biased toward specific rows of panels, they can cause variability in output or lead to abnormality determinations during maintenance inspections. Annual values are an entry point for grasping the overall picture and should be regarded as the starting point for detailed verification.

Conversely, if the annual losses are large, first check the input conditions. Review whether the obstruction height, position, orientation, distance to the panel surface, racking row spacing, tilt angle, azimuth angle, and so on match the on-site conditions. In particular, if the position or height of obstructions were entered as rough estimates, the shadow extent may end up larger or smaller than in reality. Because PVSyst results depend on input accuracy, when the annual losses come out large, it is important to first verify the validity of the input data rather than immediately changing the design.

When assessing annual shading losses, also check the absolute amount of energy generation. Not only the loss rate, but knowing how much generation is lost annually makes it easier to determine the priority of design changes. For example, measures to avoid shading—reducing the number of panels, increasing row spacing, changing the installation area, or increasing distance from obstructions—should be judged by balancing energy generation, constructability, and land use efficiency. Therefore, in practice it is necessary to review from an overall optimization perspective rather than simply trying to reduce shading losses to nearly zero.

Perspective 2: Check whether the effects of shadows are unevenly distributed across months or seasons

Next, what we want to check is the monthly trend of shading losses. Because the sun's elevation and azimuth change with the seasons, the impact of shading is not constant throughout the year. In particular, during winter the sun's elevation becomes lower, so shadows from buildings, trees, and rows of mounting structures tend to extend longer. Conversely, in summer the sun's elevation is higher, so the same obstructions may have a smaller shading effect. When looking at shading losses in PVSyst, it is important to check not only annual values but also monthly outputs and losses.

In a monthly review, first check whether shading losses become large in winter. It's natural for shadows to lengthen when the sun is low in the morning and evening, but if shadows persist into periods of high generation, the impact on the design can be significant. In particular, if low-angle sunlight is blocked, winter generation is more likely to be lower than expected. In snowy or cold regions, the importance of winter generation varies by project, so being able to explain any seasonal bias in shading losses will make the plan more persuasive.

When examining monthly shading losses, you should not simply look for months with high loss rates; you should also consider the total generation for those months. Even if a month with low generation has a high shading loss rate, its impact on annual generation may be limited. Conversely, if shading losses occur in months with high generation, the impact on the annual financial balance can be significant. Therefore, it is important to read the monthly loss rates together with the monthly generation.

Seasonal bias can also provide clues for estimating the type of obstruction. Shadows that appear prominently on winter mornings and evenings are likely caused by surrounding buildings, trees, or terrain. If shadows occur only during a specific time period, obstructions with a fixed azimuth may be responsible. If an effect is present consistently throughout the year, shading between panel rows or nearby structures may be involved. Comparing the timing of shadow occurrence with the positions of obstructions while reviewing PVSyst results makes it easier to isolate the cause.

When operational staff explain things internally, rather than saying “what percentage is the annual shading loss?”, it is easier to convey the message by saying things like “the shading impact is concentrated in the mornings and evenings during winter,” “the shading impact is limited in summer because the sun altitude is high,” and “large shading losses are not observed during periods of high power generation.” As for using PVSyst, monthly checks are a basic operation for gaining a deeper understanding of the results. Even if the annual values seem reasonable, it is important to make a habit of always breaking them down and checking them by month.

View 3: Verify the validity of the 3D scene and occlusion settings

After checking the shadow loss figures, next verify that the 3D scene settings match the on-site conditions. In PVSyst, panel layouts and obstructions are modeled in 3D to evaluate near shading. If this 3D scene is not constructed correctly, the shadow loss shown in the results cannot be considered accurate. In other words, verifying shadow loss is not completed by simply looking at the results screen; you must always go back and check the input 3D model and obstruction conditions.

In a 3D scene, the first things to check are whether the panel orientation, tilt angle, layout extent, and row spacing match the design drawings. Even a slight deviation in panel azimuth can change shadow patterns and solar irradiance. If row spacing is set narrower than actual, inter-row shading may be overestimated. Conversely, if row spacing is set too wide, you may overlook shadows that will actually occur. Verifying that the dimensions on the drawings match the layout in PVSyst is a prerequisite for checking shading losses.

Next, check the height and position of obstructions. If the heights of buildings, trees, fences, equipment, slopes, and so on are entered as estimates, they will significantly affect the extent of shadows. In particular, trees require careful input because not only tree height but also the spread of branches and foliage and seasonal changes influence shading. For buildings, you must accurately reflect the height of roofs and walls, the distance from the panel surface, and their orientation. In projects with slopes or undulating terrain, not only horizontal distances but also elevation differences affect shadow formation.

When checking the validity of a 3D scene, it is effective to verify whether it matches the real on-site perception by watching shadow animation and how shadows are cast according to the sun’s position. Visually confirm whether long shadows appear on winter mornings, whether buildings on the south side affect shading around midday, or whether obstacles to the east and west affect conditions in the mornings and evenings. Causes of shadows that are hard to understand from numbers alone also become easier to grasp when viewed in a 3D scene.

It is also important not to oversimplify obstructions. In practice, you do not need to reproduce every shape in detail, but you should model the primary surfaces and heights that affect shading. Conversely, modeling fine details that have little effect on energy production will increase work time and make model management more difficult. The key is to input the elements that influence shading losses with appropriate accuracy. When using PVSyst, the mindset should be to include the shading conditions necessary for energy yield assessment—neither more nor less—rather than recreating site conditions as a complete model.

Perspective 4: Read electrical losses and proximity shading separately

When interpreting shadow losses, what beginners often stumble over is the difference between losses due to blocked solar irradiance and electrical losses. If part of a panel is shaded, not only does the irradiance on that portion decrease, but it can also affect the output of the entire circuit. Photovoltaic systems are composed of multiple panels and circuits connected together, so a reduction in output from one panel can sometimes affect the outputs of neighboring panels. This effect cannot be judged by a simple area ratio alone.

In PVSyst, there is a concept of treating irradiance losses from near shading separately from the electrical effects of shading. Irradiance loss refers to loss caused by solar radiation being blocked from reaching the panel surface. On the other hand, electrical loss is the additional reduction in system output that occurs when shading is concentrated on some panels or circuits. For example, even if it appears that only a very small part of a panel surface is shaded, the output reduction can be large depending on the connection configuration.

When explaining shading losses in practice, it is more persuasive to separate "losses from reduced solar irradiance caused by shading" and "losses that are electrically increased by partial shading." If you simply judge that it is not a problem because the shaded area is small, you may misjudge the actual reduction in output. Especially on rooftops and in small-scale projects, ventilation equipment, railings, walls, and surrounding structures can cast shadows on some panels. For this kind of partial shading, not only the area but also which panels are affected, at what time of day, and from which direction the shadow falls are important.

When reviewing PVSyst results, check how much electrical impact is being taken into account in the near-shading settings. If you evaluate detailed electrical effects, the panel layout and connection configuration will influence the results. When inputs are simplified, you need to be cautious in interpreting the results. For example, even if shading losses appear small, if the connection configuration differs from reality, the actual output reduction may not match.

This check is useful not only during the design phase but also for verifying power generation after construction. If the actual power generation is lower than the simulation, you should suspect not only differences in insolation conditions but also the effects of partial shading and the electrical connection configuration. By checking in advance with PVSyst where shading will occur and its electrical impact, it becomes easier to isolate the causes of reduced power generation. When looking at shading losses, it is important to be aware not only of the visible shadows but also of how they affect the system electrically.

Perspective 5: Compare shading losses before and after design changes

For practical purposes, the important part of checking shading losses is comparing before-and-after design changes. PVSyst lets you review energy yield and losses while comparing multiple design conditions, so when you change panel layout, tilt angle, azimuth, row spacing, installation area, distance to obstructions, and so on, you can see how shading losses change. Understanding how to interpret shading losses allows you to use them as input for design improvement decisions rather than merely to confirm results.

For example, increasing the spacing between rows may reduce inter-row shading, but it can also reduce the number of panels that can be installed on the same site. If the number of panels decreases, even if the shading loss rate falls, the total annual energy generation may decline. Conversely, allowing some shading and increasing the number of panels can sometimes be advantageous for annual energy generation. Therefore, rather than minimizing shading loss alone, it is necessary to compare annual energy generation, land use efficiency, constructability, and maintainability together.

When comparing design changes, it is important to check the changes one by one. If you change the tilt angle, azimuth, row spacing, installation area, and obstruction inputs significantly at the same time, it becomes difficult to determine which change affected the shading losses. First create a baseline scenario, then a scenario that changes only the row spacing, then a scenario that changes the placement area, and then a scenario that revises the distance to obstructions; managing them in a way that makes comparison easy will make explaining the results simpler.

When comparing designs, we check not only the shading loss rate but also the annual energy production and the monthly energy production. In some designs, the annual shading loss may be small, yet winter generation can drop significantly. In other proposals, the annual shading loss may be slightly larger, but the overall energy yield and constructability may be superior. The purpose of comparing PVSyst results is not to choose the option with the least shading, but to choose the most reasonable option for the project's conditions.

When explaining to customers or internal teams, clearly state the reasons for the comparison. Being able to say things like, "Widening the row spacing reduced shadows in the winter mornings and evenings, but because installed capacity decreased, the increase in annual energy generation is limited," and "By reducing the number of panels located close to obstructions, we have reduced the risk of output loss due to partial shading," helps give confidence in the design decisions. It is important to treat the verification of shading loss not as a mere checklist task but as an evaluative process to improve design quality.

Conditions to Review in Practice to Reduce Shading Losses

If PVSyst shows large shading losses, the first thing to review is the panel layout. Especially for ground-mounted systems, the balance between row spacing and tilt angle has a major impact on shading losses. Increasing the tilt angle can be beneficial for solar energy capture, but it can also lengthen the shadows cast onto rear rows. Widening the row spacing can reduce shading, but it may decrease the capacity that can be installed on the site. For this reason, you need to judge based on shading losses, installed capacity, and annual energy production together.

When installing on a roof, check the shadows cast by surrounding structures. On rooftops there are many elements that can cause shading, such as parapet walls, equipment bases, piping, handrails, lightning protection devices, and inspection walkways. Even if these appear small on drawings, they can cast long shadows when the sun is at a low altitude. In particular, if a narrow shadow falls on part of a panel, the electrical output reduction can be significant, so it is important to verify their relative positions in PVSyst.

Shadows cast by terrain are another factor that’s easy to overlook. In mountainous areas, developed or graded sites, and properties with slopes, the horizon and surrounding inclines can block morning and evening sunlight. Even if a site appears open on location, terrain effects can appear during periods of low solar altitude. Properly accounting for distant shading and terrain conditions can improve the accuracy of power generation forecasts.

Attention must also be paid to how trees are treated. Because trees grow, even if shading is small at the design stage, its impact may increase after a few years. Whether trees are deciduous or evergreen also changes the seasonal effects of shading. When entering data in PVSyst, it is necessary to decide on a case-by-case basis to what height and over what area trees should be considered. For photovoltaic systems intended for long-term operation, it is important to consider not only current shading but also future changes.

Measures to reduce shading losses are not necessarily limited to removing obstructions. There are several approaches, such as shifting panel placement, avoiding heavily shaded areas, optimizing circuit configurations, leaving space where shadows fall that also serves as maintenance access, and adjusting tilt angles. Because PVSyst allows you to compare these changes by scenario, in practice it is more realistic to evaluate with the perspective of “keeping the impact of shading within acceptable limits” rather than “eliminating shading.”

Common Mistakes and Countermeasures When Checking Shadow Losses

One common mistake when checking shading losses in PVSyst is judging only by the annual loss rate. Annual values are convenient, but they can hide when and at what time of day shading occurs. In particular, shading that happens in the mornings and evenings during winter, or shading that occurs only in specific seasons, can be difficult to notice from annual values. As a countermeasure, always check the monthly values and how shadows appear in the 3D scene, and make sure to link the numbers with the actual phenomena to understand them.

Another mistake is trusting the results without verifying the input accuracy of the 3D scene. PVSyst’s calculation results are based on the obstructions and layout conditions you enter. If the heights or distances of obstructions are incorrect, the results will be off. In particular, when dimensions read from drawings differ from on-site measurements, the assessment of shading loss is affected. As a countermeasure, for important obstructions you should cross-check their position, height, and distance to the panel surface against on-site information or survey data.

Also, far-field shading and near-field shading are often confused. The impacts of mountain ranges and the horizon versus those of on-site buildings and rows of mounting racks are checked on different screens and require different input methods. If you include only one and assume you have accounted for all shading, the power generation forecast may not match reality. Depending on the project, you may need to check both far-field and near-field shading.

One point to be careful about is not to underestimate the electrical effects of partial shading. Even shadows that look small can, depending on panel and circuit connections, have a large impact on output. In particular, when a thin shadow crosses a panel, when shading is concentrated on specific columns, or when part of a circuit is continuously shaded, losses greater than the simple shaded area can occur. When reviewing results, it is important to make a habit of checking electrical effects as well as solar irradiance losses.

Furthermore, there are cases where recalculation is forgotten after design changes. Even small modifications to the panel layout or obstruction inputs can change the shading losses. If the 3D scene on the PVSyst side remains outdated after drawing revisions, the result report will not match the actual design. In practice, it is essential to verify the consistency of the design drawings, the 3D scene, the simulation results, and the submission documents.

The Importance of Combining On-site Verification and High-Precision Positioning

To correctly assess shading losses in PVSyst, the accuracy of site information is as important as the software settings. Shading simulations are only meaningful when the positions and heights of obstructions, the panel layout, and the topographical conditions are entered correctly. In particular, for projects installed near existing buildings, projects where the topography changes before and after land development, projects with slopes or steps, and projects with many trees or structures, accurately understanding the on-site spatial relationships increases the reliability of power generation forecasts.

On-site inspections should not only document the presence or absence of obstructions with photographs, but also record where they are, at what height, and how far they are from the panel surface. Photos alone can make distance and orientation ambiguous when entering data into PVSyst later. Having coordinates and height information collected on-site makes it easier to improve the input accuracy of the 3D scene. It also makes it easier, during design changes or internal reviews, to explain "which obstructions were entered under which conditions."

For obtaining such on-site information, high-precision positioning using a smartphone is effective. LRTK, as a GNSS high-precision positioning device that can be attached to an iPhone, can be used for on-site position logging and simple surveying. During the planning stage of a solar power plant, if you record with high precision the locations of obstructions, site boundaries, reference points for racking layout, and the positions of slopes and level differences, it becomes easier to organize the input basis when checking shading losses in PVSyst.

The simulation results from PVSyst are, at best, predictions based on the input conditions. Therefore, instead of relying solely on desk-based settings, combining them with position information, photographs, and survey point data obtained on-site will increase the reliability of the results. In particular, when explaining shading losses, it is a significant advantage not just to say "obstructions are taken into account" but to be able to explain "obstructions are set based on position information confirmed on-site." The use of on-site positioning data is also important for connecting design, construction, generation output evaluation, and maintenance.

Summary

Checking shadow losses in PVSyst is not just a matter of reading the numbers on the results screen. First, look at the annual shadow losses to understand the overall impact, then check monthly and seasonal trends. After that, return to the 3D scene to verify that obstructions and panel layouts match on-site conditions, and read the irradiation losses and electrical losses caused by near-field shading separately. Furthermore, by comparing results before and after design changes, you can use shadow losses as a basis for design improvement decisions.

In practical work, the important thing is not to treat shading losses as a single standalone number. By combining when the shading occurs, the time of day, the location, the cause, and the impact on the circuits, the meaning of the results becomes clear. Even if the annual loss rate is small, caution is needed if it is biased toward particular seasons or times of day. Conversely, even with some shading loss, a proposal can be reasonable when balanced against installed capacity, annual energy production, and constructability. When using PVSyst, both the ability to interpret the numbers and the ability to judge them against on-site conditions are required.

Additionally, the accuracy of shading loss assessments is greatly influenced by the accuracy of the input data. If the heights and positions of obstructions, the spacing between panel rows, and terrain conditions remain ambiguous, the reliability of the results will be limited. By using coordinates and height information obtained from on-site verification and reflecting them in PVSyst’s 3D scene, it is possible to perform simulations that more closely match actual conditions.

In the design and energy yield assessment of solar power systems, it is essential not only to operate software but also to accurately understand the site. By utilizing an iPhone-mounted GNSS high-precision positioning device such as LRTK, you can efficiently record obstructions and site conditions on-site, making them easy to use as reference data when checking shading losses in PVSyst. By combining PVSyst simulations with high-precision on-site position records, the explanatory power of energy yield forecasts is enhanced, enabling consistent quality control from design review through post-construction verification.