Five basic shading conditions to check in the PVSyst manual

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Table of Contents

• What it means to check shading conditions in the PVSyst manual

• Basic shading condition 1: Understand shadows cast by surrounding obstacles

• Fundamental shading condition 2: consider nearby and distant obstructions separately

• Shade Conditions Basic 3: Check how shadow movement changes with the seasons and time of day

• Shading Conditions Basics 4: Examining the Impact on Module Layout and String Design

• Shaded Conditions Basics 5: Interpreting Loss Rates from Simulation Results

• Shading-related terms that are often confusing when reading the PVSyst manual

• Common mistakes when setting shade conditions

• Workflow for verifying shade conditions in practical work

• Summary

The significance of checking shading conditions in the PVSyst manual

When estimating the power output of a solar power system, looking only at solar irradiance and installed capacity is not enough to make an assessment close to the actual generation. On site, various things—buildings, trees, utility poles, fences, mounting structures, and adjacent photovoltaic modules—cast shadows. Whether those shadows are temporary or occur for long periods every day can greatly change the outlook for annual energy production.

The purpose of reading the PVSyst manual is not simply to learn how to operate the interface. It is important to understand which input items affect energy production and which results to examine to judge design risks. In particular, shading conditions are sensitive to how inputs are specified, and they tend to cause confusion for designers and analysts.

When configuring shading conditions, you need to consider how to represent the objects that cast shadows, how far to model them, and which losses to prioritize when checking. Reproducing every detail is not always best; you should enter data at the level of accuracy required by site conditions and design objectives. If you oversimplify, you may overlook losses, and if you overcomplicate, you increase the chance of input or interpretation errors, so it is important to handle this with a solid grasp of the fundamentals.

In this article, we organize into five basic points the fundamentals that are particularly easy to overlook in practice when checking shading conditions in the PVSyst manual. The explanation is intended not only to prevent beginners from getting lost in the interface, but also to enable them to determine, when looking at analysis results, "why this loss is occurring" and "what should be corrected in the design."

Basic Shade Condition 1: Understand shadows from surrounding obstacles

The first thing to check when considering shading conditions is what kinds of obstacles exist around the power generation equipment. In solar power generation, shadows tend to lengthen in the mornings and evenings and during winter when the sun's position is low. Therefore, obstacles that may appear harmless when seen on site can cast shadows on the generation surface depending on the season and time of day.

Surrounding obstructions include adjacent buildings, roof upstands, parapets, ventilation and exhaust equipment, signs, trees, utility poles, and hills or slopes. For ground-mounted installations, the surrounding terrain and structures on adjacent plots also have an influence. For roof-mounted installations, chimneys, antennas, air-conditioning equipment, and steps in the roof profile on the same roof surface are prone to cause shading.

When checking shading conditions in the PVSyst manual, it is easier to understand if you read with the perspective of “how much of the obstacles should be entered.” You do not need to model every small obstruction in detail, but anything that could cast a shadow on the generating surface should be considered when judging the magnitude of its impact. In particular, obstacles near the module rows and those that create long shadows at the low solar elevations in winter should be prioritized for review.

Organizing obstacle heights, positions, distances, and azimuths based on on-site photos and drawings from the field survey makes data entry into PVSyst easier. Entering heights and distances while they are still ambiguous can cause the extent of shadows to be larger or smaller than in reality. As a result, loss rate estimates become unstable. Shading conditions should not be entered based on intuition; it is important to treat them, as much as possible, based on drawings and measured values.

Also, obstacles whose condition changes with the seasons and growth, such as trees, require caution. For deciduous trees, the nature of shadows changes with the seasons, and for trees that grow, you must also consider the future increase in shading. PVSyst settings represent the conditions at the time of analysis, but in practice you must also make decisions that take the future operational period into account.

When assessing nearby obstacles, it is important not only to note whether shadows occur but also to be aware of the times when shadows appear and the areas they cover. Whether a shadow briefly falls on an edge or shadows affect multiple rows for long periods in the morning has different design implications. When reading the PVSyst manual, deepen your understanding by thinking not of each input field in isolation but of how on-site shading will be reflected as losses in energy production.

Basic Principle of Shading Conditions 2: Consider Near Obstructions and Distant Obstructions Separately

One thing that often causes confusion under shaded conditions is treating nearby obstructions and distant obstructions the same way. Even if the causes of a shadow appear similar, their effects on power generation and the way you treat the inputs are different.

Nearby obstructions refer to building upstands, equipment, adjacent racking rows, rooftop structures, and similar items located close to the modules. These can cast distinct shadows on parts of the generating surface and, depending on the time of day, locally affect specific modules or cells. Shadows from nearby obstructions can cause not only a simple reduction in solar irradiance but also electrical mismatch, so it is necessary to verify their relationship with the layout and string design.

On the other hand, distant obstructions are mountains, hills, distant groups of buildings, and obstacles near the horizon. Distant obstructions often affect solar irradiance by blocking sunlight when the sun is at a low position, and they alter the irradiance conditions not only for part of the power-generating surface but for the entire installation. Rather than locally shading specific modules like near-field obstructions, it is easier to understand them if you think in terms of whether the sun is visible or not.

The PVSyst manual presents several approaches to inputting and modeling shading conditions. What is important here is not to learn which feature to use first, but to classify the nature of the shadows. By distinguishing whether the shading is partial shadows from nearby obstructions or horizon masking from distant terrain or buildings, you can organize the information that needs to be entered.

Nearby shading objects need to be represented fairly specifically in terms of their shape and positional relationships. For example, if there is an outdoor air-conditioning unit on a rooftop, the extent of its shadow changes depending on its height and the distance to the module. When an adjacent row of modules casts a shadow, row spacing, tilt angle, azimuth, and racking height become important. In other words, nearby shading objects are closely tied to design dimensions.

For distant obstructions, the important factor is not the detailed shape of the obstacle but the range that is blocked relative to the sun's altitude and azimuth. At sites with mountain ridgelines or surrounding terrain, this can affect generation in the morning and evening. In particular, in mountainous areas, valley topographies, and near slopes on developed sites, underestimating distant obstructions can cause discrepancies between measured performance and simulations.

Separating near shading and far shading when considering obstructions is also effective for reducing input effort. In practice, rather than modeling everything in detailed three dimensions, prioritizing the representation of the parts that have the greatest impact makes the results easier to interpret. When consulting the PVSyst manual, it is important to review the shading-conditions screens and items while consciously asking, "Is this an assessment of near shading?" or "Is this an assessment of far shading?"

Shade Condition Basics 3: Check How Shadow Movement Changes with Seasons and Time of Day

Shade conditions cannot be determined from a single on-site photograph taken at one moment. Because the sun’s position changes with the season and time of day, the direction, length, and timing of shadows also vary. Even if a site appears to have short shadows and seems to pose no problem when viewed in summer, the sun’s altitude is lower in winter and the same obstructions can cast long shadows.

When checking shading conditions in the PVSyst manual, it is important to be aware of shadow movement throughout the year. The impact of shading is evaluated not simply by whether there is shade, but by when, how much, and which parts are shaded. In particular, shadows tend to be longer in the mornings and evenings during winter, and the effects of buildings and terrain can be significant.

However, shadows in the early morning and late evening do not necessarily pose a major problem. During periods of low solar elevation, the solar irradiance may already be low. Therefore, it is necessary to consider how much the irradiance during the times when shadows occur contributes to power generation. Overestimating short-duration shadows can make the design more conservative than necessary. On the other hand, if shadows fall during periods of high irradiance, even a short duration can cause non-negligible losses.

When checking shadow movement, it is important not to look only at a representative day but to grasp the annual trends. For example, confirming the differences in shadows near the winter solstice, around the vernal and autumnal equinoxes, and near the summer solstice will show which seasons the effects of obstacles are concentrated in. Whether shadows occur in seasons with high power generation or are limited to seasons with low power generation will change the priority of countermeasures.

For rooftop installation projects, the orientation and pitch of the roof change how shadows appear. Even with the same obstacle, a south-facing roof and an east–west-facing roof have different durations of shadow impact. For ground-mounted projects, the row spacing and tilt angle change the times of day when the front row casts shadows on the rear row. In cases with unusual mounting heights or installation conditions, such as agrivoltaic systems or snowy regions, seasonal shadow checks are indispensable.

When reviewing PVSyst analysis results, it is important not to base conclusions solely on annual energy production. Even if losses look small in the annual figures, shading impacts can be concentrated in particular months or times of day. Depending on how the generated power will be used—power sales plans, self-consumption plans, peak shaving, or battery storage integration—the actual timing of shading events can itself be important.

As a basic premise for shading conditions, understanding that shadows change with the seasons and time of day lets you read the PVSyst manual’s explanations not merely as operating procedures but as knowledge that informs on-site decision-making. Shadows are not fixed conditions; they change with the movement of the sun. Grasping this premise is the first step to preventing configuration errors in practice.

Shading Basics 4: Examining the Impact on Module Layout and String Design

Under shaded conditions, particular attention should be paid to the effects when a shadow falls on part of the power-generating surface. In solar power generation, the impact on power output differs between cases where the shadow is cast uniformly over the whole and cases where it is localized on some modules or cells. Partial shading does not necessarily reduce output simply in proportion to the shaded area.

Modules are electrically connected in groups and configured as strings. Therefore, if a single module or part of a cell is shaded, it can affect the power generation of the same string. This is a major reason why shading conditions are complex. When examining shading conditions in the PVSyst manual, you need to understand not only the shape of the shadow but also the relationship between module layout and string design.

For example, if a building's shadow falls on the edge of the same row every morning, the way losses occur varies depending on which string the shadow falls into. If the shadow is concentrated on a particular string, that string's power output will drop significantly. Conversely, by adjusting the area affected by the shadow and the string configuration, the impact can be reduced to some extent.

In module placement, the basic principle is to arrange modules so as to avoid locations where shading is likely to occur. However, when roof area is limited or, for ground-mounted systems, the site shape imposes constraints, it may not be possible to avoid shading completely. In such cases, you should identify the times and areas when shading has the greatest impact, and consider the number of modules, row spacing, tilt angle, and string grouping.

When reading the PVSyst manual, keep in mind that entering shading conditions is not a standalone task but is linked to the system design. After configuring the shading, you do not just stop at viewing the results. In practice, it is important to use the results to decide whether to change the module layout, review the string configuration, or adjust the system capacity.

Shadows from rooftop equipment and parapets in particular tend to fall on module edges and certain rows. How losses appear depends on whether you group shaded modules into the same electrical system or arrange strings prioritizing less‑shaded areas. Rather than simply seeing shading as “generation decreases because of shade,” it is important to confirm “which electrical system is being shaded.”

For ground-mounted installations, the design of row spacing is a major point. Narrowing the row spacing can increase installed capacity, but it raises the risk that shadows from the front rows will fall on the rear rows. Widening the row spacing makes it easier to limit shading losses, but it may reduce the capacity that can be installed on the same site. Here, it is necessary to decide—taking economics into account—whether to prioritize maximum capacity or generation efficiency.

In practical work assessing shading conditions, it is important not only to aim to maximize power generation but also to consider the stability of the design. A design that suffers a large drop in output from a small amount of shade can lead to unexpected reductions in generation during actual operation. Verifying, through PVSyst analysis, how much margin the layout has against shading contributes to a more reliable design.

Shading Conditions Basics 5: Interpreting Loss Rates in Simulation Results

After entering the shading conditions, what becomes important is interpreting the simulation results. Even if you set things up while referring to the PVSyst manual, if you cannot understand what the results mean, they will not lead to design decisions. In particular, for shading losses you need to check what type of loss they are reported as and under which conditions they become large.

When looking at loss rates, the first thing you should check is what proportion of the annual power generation is accounted for by shading losses. Even if shading losses are small, they can affect generation when combined with other losses. Conversely, if shading losses are large, you should consider re-examining the layout and obstruction conditions.

However, it is dangerous to judge based only on the loss rate number. The result showing what percentage the shading loss is is important, but unless you check what kind of shadow produced that number, concrete improvement measures will not become apparent. Countermeasures vary depending on whether the loss is due to distant obstructions in the morning and evening, partial shading from nearby obstructions, or inter-row shading.

When reading PVSyst results, it's easier to understand them by looking at a combination of annual values, monthly trends, and time-of-day effects. Even if the annual figures don't appear to show a major problem, losses may be concentrated in winter, or generation may drop during specific times of day. For self-consumption projects, it's also important to check whether shading coincides with periods of high demand.

Also, if the inputs for shading conditions are not appropriate, the resulting loss rate will deviate from reality. If obstacle heights are entered too large, losses may be overestimated. Conversely, if shadow‑casting obstacles are omitted too much, the predicted energy output may appear better than it actually is. When reviewing the results, you must always revisit the input assumptions you entered.

In practice, you are expected not only to place simulation results directly into a report, but also to be able to explain why those results occurred. When explaining to the client or stakeholders, a number alone—such as “the shading loss is X percent”—is insufficient. It is desirable to be able to explain, “which obstacle affects which area during which seasons and times of day, causing this expected loss.”

Once you develop the ability to interpret loss rates, the way you read the PVSyst manual changes. Rather than merely following operating procedures, you will be able to understand inputs, results, and design improvements as a continuous sequence. Shading conditions are among the analysis factors that most directly lead to design improvements. It is important not to stop at the magnitude of the numbers, but to link them to what should be reviewed on site.

Shading-related terms that are easily confused when reading the PVSyst manual

When checking shading conditions in the PVSyst manual, you encounter terms that look similar — solar irradiance, shading, losses, near shading, distant shading, mismatch, and so on. If you read these ambiguously, it's easy to become unsure of what you're entering on the settings screen.

First, terms related to solar radiation describe how sunlight reaches the power-generating surface. Direct solar radiation is light that comes directly from the sun and is highly susceptible to shading. Diffuse solar radiation is light that reaches the surface after being scattered in the atmosphere and differs in nature from direct solar radiation. Because shading does not completely eliminate all solar radiation, understanding the different types of solar radiation makes it easier to grasp what is meant by losses.

Shading refers to the blocking of sunlight by obstacles. Far-field shading is the condition in which terrain or distant buildings make the sun difficult to see, while near-field shading is easiest to understand as the condition in which objects near the power generation equipment cast shadows on the generating surface. If you configure settings without understanding this difference, you may evaluate the same shadow twice or omit shadows that should be included.

Mismatch is the loss that occurs when output conditions are not aligned between modules or strings. When shading occurs, the power-generating conditions change between shaded and unshaded areas, creating an electrical imbalance. This is why, when considering shading conditions, it is not just a matter of area but also of electrical connections.

The term "loss" should be understood by distinguishing what kind of loss it refers to. There are multiple causes that reduce power generation, such as temperature loss, wiring loss, conversion loss, and shading loss. When checking shading condition settings, be careful not to confuse losses caused by shading with other losses.

When reading the PVSyst manual, it's more important to be aware of at which stage the power output is declining than to memorize terminology perfectly. By distinguishing whether sunlight is being blocked before it reaches the PV surface, whether electrical imbalances occur after it reaches the PV surface, or whether losses are occurring in equipment or wiring, you can clarify how to interpret the results.

Common Mistakes When Setting Shading Conditions

A common mistake in shading conditions is to start entering data without sufficient on-site verification. If you judge obstacles only from drawings, you may fail to notice that tall equipment or surrounding buildings are actually having an impact. Conversely, if you rely solely on on-site photos, you may not know precise distances or heights, causing the input values to become ambiguous.

Also, omitting obstacles that appear to have little impact can be a cause of failure. Even small obstacles, if they are near a module, can create local shading and lead to electrical losses. In particular, rooftop equipment and parapets are easy to overlook, yet depending on their placement they can have a significant impact.

Conversely, entering overly detailed information for items that have almost no impact is also problematic. Models that are too detailed increase the risk of input errors and make interpreting the results more difficult. In practice, it is important to prioritize entering factors that affect power generation and to handle those with minor impacts according to design judgment.

Not taking seasonal differences into account is also a common mistake. If you judge that "there is little shading" based only on a site inspection in summer, you may overlook the possibility of substantial shading in winter. In particular, when the sun's altitude is low, obstacles cast long shadows. When checking shading conditions, you need to consider separately the timing of the site inspection and the changes in shadows throughout the year.

You can also overlook the relationship with string design. Even if you check the extent of shading, if you don’t determine which string the shading affects, you cannot fully evaluate its impact on power generation. Rather than handling the layout drawings, electrical design, and shading analysis separately, it is important to verify them under the same design conditions.

Furthermore, there are also failures caused by judging solely based on the numerical results. After deciding it is not a problem because shading losses are small, one may later discover that reductions in generation during specific time periods were actually important. Especially for self-consumption projects or those involving battery integration, not only the annual energy output but also the time of day when generation occurs is important.

When using the PVSyst manual, what matters is not simply following the on-screen input steps but understanding how configuration errors translate into deviations in results. Shading conditions are an area where the relationship between visible shadows and energy production is not intuitively clear. That is why you need to make it a habit to verify the underlying assumptions at each stage: before input, during input, and after reviewing the results.

Workflow for checking shading conditions in practice

In practical work, when checking shading conditions, we start by organizing documentation. We gather site plans, floor plans, elevation drawings, surrounding photographs, on-site survey results, roof shapes, the locations of equipment and devices, etc., and identify elements that could cast shadows. If information is lacking at this stage, accurate input in PVSyst is not possible.

Next, classify the causes of shading. Organize whether they are nearby obstructions, distant obstructions, or shading between module rows. By classifying them, it becomes clear which information should be entered in detail. For nearby obstructions, height, distance, and shape are important, while for distant obstructions, azimuth and the relationship with solar altitude are important.

Then set the shading conditions in PVSyst. At this stage, rather than making things too detailed from the start, it is easier to check if you enter the elements with the greatest impact first. Handle elements that are likely to directly cause losses—large buildings, parapets, inter-row shading, etc.—first, and add finer details as needed so you can more easily understand how the results change.

After configuring the settings, check the shadow display and simulation results. Verify that shadows appear in the expected directions, that seasonal variations align with local conditions, and that shadows caused by specific obstacles are not over- or under-estimated. If anything seems off, review the entered height, azimuth, distance, tilt angle, and placement conditions.

Next, check the loss rate. After assessing how much shading loss is occurring, also check trends by month and by time of day. If losses are larger than expected, review module layout, row spacing, string design, and clearance from obstructions. Even if losses are small, it is important to confirm that there are no omitted settings.

Finally, organize the results into a form that can be explained. In practice, there are occasions to share analysis results within the company, with the client, and with design stakeholders. When doing so, rather than simply presenting power generation and loss rates, make sure you can explain which shading was considered, which shading was judged to have only a minor impact, and which conditions require special attention, as this will increase the reliability of design decisions.

The PVSyst manual is useful as a reference for checking procedures, but in practice it is important to connect on-site information, design conditions, and result interpretation. Shading conditions in particular need to be handled while understanding the relationship between inputs and results. By not only memorizing the procedures but also thinking about why those procedures are necessary, the accuracy of analyses and the ability to explain them will improve.

Summary

The basics of shading conditions to check in the PVSyst manual are understanding surrounding obstacles, distinguishing between nearby and distant shading objects, seasonal and time-of-day variations in shadows, the impact on module layout and string design, and interpreting the loss rates in simulation results. By mastering these five points, you can treat shading condition settings not as mere screen operations but as practical work for energy-yield assessment and design improvement.

Shading conditions are one of the parameters in solar power generation simulations that most strongly influence the results. If the height or position of obstacles that cast shadows is recorded incorrectly, the estimated loss rate may deviate from reality. Confusing near-field shading with far-field obstruction can lead to overlooking shadows that should be accounted for or, conversely, to overestimating them. That is why organizing on-site information before input and verifying the results afterward are important.

Also, the effects of shading cannot be judged by annual energy production alone. By checking in which seasons shadows occur, at what times of day generation drops, and which modules or strings are shaded, you can make more specific design decisions. This is especially true for rooftop installations, ground-mounted systems, mountainous areas, and locations with many surrounding buildings, where how shading conditions are handled can determine the reliability of energy production.

When reading the PVSyst manual, it's important not only to follow the item names and operating procedures but also to consider "which shadow this setting represents" and "which design conditions produced this result." If you correctly understand the shading conditions, you can improve not only the estimates of power generation but also the accuracy of layout planning, equipment capacity, string design, and explanatory materials.

In solar PV design, many sites cannot completely eliminate shading. Even in such cases, understanding the conditions that cause shading, properly assessing the losses, and considering necessary countermeasures bring the design closer to being realistic and reliable. Grasping the basics of shading conditions while using the PVSyst manual is an important first step to improve the accuracy of energy-yield simulations.