5 Points to Check Near Shading in the PVSyst Manual

Table of Contents

• Basics to understand before checking proximity shading in PVSyst

• Impact of nearby shading on power generation assessment

• Point 1: Exhaustively identify all objects that cast shadows

• Point 2: Accurately reproduce dimensions and spatial relationships in 3D scenes

• Point 3: Check how shadows move by season and time of day

• Point 4: Read the results including electrical effects

• Point 5: Compare in a form that can be used for design changes

• Common mistakes when checking for proximity shadows

• How to Improve Verification Accuracy in Practical Work

• Summary

Basics to understand before checking near shading in PVSyst

When understanding the five points for checking near shading in the PVSyst manual, the first thing to grasp is that near shading is not simply the presence or absence of shade, but an important consideration that affects a photovoltaic system’s annual energy yield, monthly generation trends, string configuration, layout planning, and maintenance planning. In PV simulations people tend to focus on irradiance, module specifications, PCS capacity, orientation, tilt, and temperature conditions, but when there are obstacles close to the site, leaving near-shading settings vague can easily create discrepancies between simulation results and actual energy production.

Proximity shading refers to shadows caused by objects located close to solar panels, such as buildings, rooftop structures, handrails, walls, trees, utility poles, adjacent racks or frames, steps or level differences, slopes, and equipment. Unlike shadows from distant mountains or the horizon, proximity shading often falls locally on the panel surface, and the shape and movement of the shadows become complex. In particular, for rooftop installations, installations on narrow sites, factory and warehouse roofs, low-voltage projects near residential areas, and ground-mounted projects with terrain changes, checking for proximity shading greatly influences design quality.

The purpose of using PVSyst is not just to neatly display near-field shading. What matters in practice is identifying which obstacles cast shadows over which areas at which times, understanding how those shadows affect annual and monthly energy production, and, if necessary, revising the layout and string configuration. In other words, the real purpose of near-field shading assessment is not to stop at creating a 3D model, but to convert it into information that can be used for design decisions.

Additionally, proximity shading cannot be simply judged as “bad” just because there is a little shade. If the shading occurs only in the early morning or late afternoon in winter, the impact on annual power generation may be limited. On the other hand, if shading repeatedly occurs during hours of high solar irradiance or shading is concentrated on only part of a particular string, the impact can be greater than it appears. Therefore, it is necessary to check not only whether shading exists but also the season and time of day when it occurs, the area covered by the shade, the positions of the modules receiving the shade, and the relationship with the string configuration.

Many people who check near shading while referring to the PVSyst manual have concerns such as "where should I start configuring?", "what should I reproduce in the 3D scene?", "which part of the results screen should I look at?", and "how much shading loss is acceptable?". This article organizes and explains the approach to near-shading verification in five key points, focusing on the areas that are easy to get confused about in practical work.

Impact of nearby shading on power generation assessment

The impact of nearby shading on power output assessments is not limited to simple solar irradiation blocking. Solar panels are devices that convert incident sunlight into electricity, but when part of a module is shaded, it is not merely that only that part stops producing power—due to the circuit connections, the shading can also affect the generation of surrounding areas. Therefore, even a shadow that is small in area can lead to substantial electrical losses.

For example, even a narrow shadow falling on only part of a single panel can, due to the action of cell strings and bypass diodes, cause a significant reduction in output from the affected area. Furthermore, if the current of the entire string that includes that panel is limited, panels that are not shaded can also be affected. When checking near shading in PVSyst, you need to be aware not only of the physical area of the shadow but also of its electrical effects.

Also, nearby shading does not occur the same way throughout the year. In winter, when the solar altitude is low, shadows tend to be longer, and during morning and evening hours the shadows of buildings and railings extend considerably. Conversely, during summer daytime, because the solar altitude is high, the shadow extent from the same obstacles can be smaller. In other words, it is risky to judge the annual impact of shading based on a single on-site observation of shadow conditions. The value of simulation tools such as PVSyst lies in their ability to confirm these seasonal and time-of-day variations through calculation.

To correctly assess the impact of nearby shading, it is important not to judge solely by annual losses but also to examine monthly trends. Even if the annual loss appears small, a significant drop in generation during winter can affect demand patterns, power sales plans, battery operation, and maintenance scheduling. This is especially true for self-consumption solar power systems, where not only the annual total but also when generation is possible matters. Therefore, checking nearby shading is not just a layout consideration but also a validation of the overall generation plan.

The challenge in evaluating near shading is that completely eliminating shadows is not always optimal. If you significantly reduce the number of panels to avoid shading, shading losses may decrease but total energy production can decline. Conversely, tolerating some shading and increasing installed capacity can, in some cases, be advantageous for annual energy yield and overall economics. Therefore, when checking near shading in PVSyst, it is important not to aim solely for zero shading loss, but to consider the balance among installed capacity, energy production, cost, constructability, and maintainability.

Point 1: Thoroughly identify all objects that cast shadows

The first step in checking near shading is to comprehensively identify all objects that could cast shadows. No matter how accurately you configure settings in PVSyst, if you overlook obstacles at the site, the simulation results will diverge from reality. When assessing near shading, organizing and clarifying the site conditions is more important than software operation.

The first objects to check are the structures around the solar panels. For rooftop installations, penthouses, chimneys, ventilation equipment, outdoor air conditioning units, antennas, railings, parapets, adjacent buildings, rooftop signs, and similar items can cast shadows. For ground-mounted installations, nearby buildings, fences, trees, utility poles, overhead lines, slopes on developed land, retaining walls, and adjacent solar arrays can be causes of shading. Because these may not be shown on drawings, do not judge based only on plan drawings; using site photographs, field surveys, aerial photographs, and point cloud data to confirm will improve accuracy.

Next important is the height of obstacles. Near-field shading varies greatly not only with an obstacle’s plan position but also with its height. An object that appears distant from the panels on a plan view can cast long shadows if it has height, especially under the low solar altitude in winter. Conversely, low equipment located close to the panels may only produce short shadows during specific times of day. When creating a 3D scene in PVSyst, it is important to match the heights of objects as closely as possible to the site conditions.

Also, care must be taken when dealing with trees. Unlike buildings, trees have irregular shapes and the amount of foliage can change with the seasons. For deciduous trees, the intensity of shadows may change in winter, and as they grow the extent of shaded areas can increase after several years. It can be difficult to reproduce trees exactly on PVSyst, but as a practical approach, at minimum trees likely to have a large impact should be evaluated conservatively, taking into account their height, location, and future growth.

One thing that is easy to overlook is the shadows panels cast on each other. When arranging multi-row arrays, panels in the front rows can cast shadows on panels in the rear rows. Special attention is required when the tilt angle is large, when row spacing is narrow, or when the layout is complex in the north–south direction rather than the east–west direction. In ground-mounted projects, simply changing the array spacing slightly can alter winter shading losses. In PVSyst, it is important to check not only surrounding obstructions but also the self-shadowing between arrays.

When identifying objects that cast shadows, you do not need to model everything in detail. What matters is prioritizing those that are most likely to affect power generation. Reproducing in detail low obstacles that are far away or objects on the north side that have little impact will only increase work time while contributing little to design decisions. In practice, it is efficient to prioritize checking tall objects on the south, east, and west sides of the panels, objects that tend to cast longer shadows in winter, and objects that cast shadows during periods of high solar irradiance.

Point 2: Accurately reproduce dimensions and spatial relationships in 3D scenes

One of the most important tasks in near-shading verification is reproducing the dimensions and positional relationships in the 3D scene. Even when working through the PVSyst manual, simply placing obstacles is not sufficient. If the positions of panels, mounting structures, buildings, trees, walls, and so on are offset from actual site conditions, the timing and extent of shading will change.

When creating a 3D scene, first clarify the reference coordinates and orientation. In solar power generation, orientation is extremely important. Which way the panel surface faces, the building’s longitudinal orientation, and whether obstacles are on the south or west side of the panels greatly affect how shadows fall. Even when importing drawings and placing elements, you must always verify that the north direction is correct. Even a slight deviation in orientation can lead to differences in the assessment of morning and evening shadows.

Next, correctly set the panel height and tilt. The panels are not placed directly on the ground or the roof surface; they are mounted on racking that provides a specific height and angle. Changes to the panel bottom-edge height, top-edge height, tilt angle, and row spacing alter how shadows fall from the front row to the rear row and from surrounding obstacles. This is especially true for low standoffs or low-pitch installations on corrugated metal roofs, where small height differences can affect shadowing.

It's also important not to make obstacle shapes more complex than necessary. If you try to fully reproduce building irregularities, the fine shapes of equipment, piping, and small protrusions, the work can become heavier and it can become difficult to see the points that need to be checked. In practice, it is more effective to simplify the silhouette that casts shadows and reproduce the heights and widths that have the greatest impact. For example, for a large rooftop air-conditioning unit, it is more important to correctly set its position relative to the panels, its height, and its width than to model fine details.

However, oversimplifying can be dangerous in some cases. For example, the shadow of a narrow handrail or fence may be small in area, but if it falls along a panel's cell rows it can have a significant electrical impact. A thin shadow is not necessarily ignorable. Objects that may repeatedly cast shadows on panels should have their position and height preserved even when simplified.

After creating a 3D scene, don't rely on appearance alone; check it from multiple viewpoints. Verify the plan layout as seen from above, the height relationships as seen from the south, the distances to obstacles in the east–west direction, and the spacing between panel rows—checking these makes input errors easier to spot. In particular, confusing units, reversed orientation, omitted height entries, and misplaced obstacles are common mistakes. For near-field shading checks, it is essential to carefully confirm that the 3D scene itself accurately represents the site before looking at the simulation results.

Point 3: Check the movement of shadows for each season and time of day

Proximity shading cannot be assessed by looking at a single moment in time. Because the sun’s position changes with the seasons and times of day, the length, direction, and extent of the shade cast by the same obstacle can vary greatly. When checking proximity shading in PVSyst, it is important to visually confirm the seasonal movement of shadows as well as the results of the annual calculation.

Particularly important to note is the low solar altitude in winter. In winter the sun is low and shadows tend to extend long, so nearby obstructions can have a much larger impact. Obstacles that cast little or no shadow in summer can throw shadows over entire panels on winter mornings and evenings. The effect on annual power generation is determined by the balance with periods of high solar irradiance, but for projects where winter generation is important, winter shadows cannot be ignored.

Shadows in the morning and evening also need to be checked. In solar power generation, output tends to be higher around midday, while in the morning and evening the sun’s altitude is low and shadows are longer. Obstacles to the east in the morning and to the west in the evening can create shadows immediately after generation begins or just before it ends. Even if the impact appears small when looking only at annual generation, for self-consumption systems at facilities with high power demand in the morning or evening the operational implications can be different.

Obstacles on the south side are especially important. In the typical south-facing configurations in Japan, buildings and trees to the south can cast shadows during the daytime power-generation hours. Because southern shadows frequently coincide with periods of high power output, they tend to have a greater impact even for the same shaded area. When checking shadow movement in PVSyst, pay particular attention to how far shadows from south-side obstacles reach the panels during times when the sun is high.

When checking seasons and times of day, it is easier to understand if you set representative days and observe the movement of shadows. By checking around the winter solstice, around the vernal and autumnal equinoxes, and around the summer solstice, you can grasp how differences in the sun's altitude affect shadow patterns. Also, by looking at multiple times in the morning, around noon, and in the afternoon, you can confirm which direction the shadows move. This makes it easier to determine whether a shadow falls only briefly or whether it affects the same string for a long time.

When assessing shadows, not only the "length" of the shadows that occur but also the "way they move" is important. Shadows that pass over the panel surface in a short time may have only a limited impact, but shadows that remain on the same group of panels for a long time tend to cause larger power generation losses. In addition, if a narrow, elongated shadow moves along the string direction, the electrical impact can be greater. In PVSyst's 3D checks, it is important not just to look at a single instant like a still image, but to track the movement of shadows over time.

Point 4: Interpret results including electrical effects

A common misconception in near-field shading checks is to judge the impact solely by how the shadows look in the 3D scene. In reality, power losses due to shading are not determined only by the area of shadow that falls on the panel surface. The way losses manifest depends on electrical factors such as the arrangement of cells within the module, bypass diodes, string configuration, and MPPT assignment.

For example, even shadows with the same area can have different effects on power generation depending on whether they briefly fall on the edge of a panel or stretch across multiple modules. If shading is concentrated on part of a string, the output of that entire string can be limited. Furthermore, if shaded strings and unshaded strings are connected to the same MPPT, losses due to mismatch can also occur.

When checking nearby shading in PVSyst, you should be aware of shading losses not only as physical shading but also as electrical losses. After confirming the shadow positions in the 3D scene, read the simulation results to determine which items and to what extent shading losses appear. If shading losses are large, improvements may be possible not only by simply changing the panel layout but also by reviewing string grouping and MPPT allocation.

In practice, it is important not to mix areas that are prone to shading with areas that are not prone to shading in the same string. For example, if a building's shadow falls on part of the east side only in the morning, treating the panels that receive that shade as a separate string may help limit the spread of the effect. Conversely, if panels with different shading conditions are connected to the same string without planning, partial shading on some panels can lead to a reduction in output across a wide area.

Also, when checking for nearby shading, it is important to understand not only the annual loss rate but also where the losses occur. Even with the same loss rate, the practical assessment changes if the season or time of day when losses occur differs. In projects focused on selling power, annual energy production is often prioritized, but in self-consumption projects the overlap between the facility’s electricity demand and the generation times is important. Considering how morning shadows, midday shadows, and evening shadows affect demand enables more realistic design decisions.

When evaluating electrical effects, it's also important not to become overly focused on excessively precise numerical values. Simulations are the result of modeling site conditions, and in reality there are variables such as tree growth, changes to surrounding buildings, dirt, snow accumulation, and construction errors. Therefore, in practice it is more effective to understand the causes, extent, and potential for improvement of shading and to reflect that understanding in the design, rather than judging solely by the decimal places of the loss rate.

Point 5: Compare in a form that can be used for design changes

The ultimate purpose of checking near shading is to improve the design. Therefore, when you check near shading in PVSyst, you should not just look at the results and stop; you need to compare them in a form that can be used to implement design changes. Near-shading simulations not only uncover the weaknesses of the current proposal but also provide the basis for comparing multiple design options and selecting a more rational layout or configuration.

Representative items to compare are panel layout, row spacing, tilt angle, installed capacity, string configuration, clearance from obstacles, and racking height. For example, if retreating the panels slightly greatly reduces shading losses, compare the resulting reduction in number of installed panels with the improvement in energy production. Conversely, if you significantly reduce the layout to avoid shadows, shading losses may decrease but total energy production can decline. Thus, it is important to consider not only the shading loss rate but also the relationship with annual energy production and installed capacity.

Considering row spacing is also important. If self-shading between arrays is significant, increasing the row spacing can reduce shading losses, but it will decrease the number of panels that can be installed on the same site. To achieve the maximum energy production on a limited site, a proposal that minimizes shading losses is not always optimal. In PVSyst, it is useful to compare multiple scenarios with different row spacings and assess the balance between shading losses and installed capacity.

Response to obstacles also requires comparison. Several measures can be considered, such as relocating rooftop equipment, changing panel layout, adjusting racking height, and excluding areas that receive shading. However, relocating equipment involves costs and construction constraints. Excluding panels reduces shading losses but also reduces installed capacity. Raising the racking may avoid shading in some cases but can affect wind loads, construction costs, and maintainability. Therefore, evaluation of nearby shading should be based not only on energy generation but also on construction conditions and costs.

It is important to compile comparison results in a form that is easy to explain to stakeholders. To ensure designers, contractors, project owners, and maintenance personnel share the same understanding, organize which obstacles are casting shadows, at what times shadows occur, and how much each proposal would improve the situation. Because simply presenting the PVSyst results as-is can be difficult to interpret, it is important in practice to put the key points into writing and make the rationale for decisions clear.

Also, when making comparisons, it is useful to record the reasons for the proposals that were not adopted. For example, a proposal that reduces shading losses but greatly decreases installed capacity; a proposal that increases power generation but has poor constructability; or a proposal that requires relocating obstacles and is therefore costly—these can be helpful when explaining the review process later. Checking near-field shading is not merely a simulation task, but also forms the basis for design decisions.

Common mistakes when checking nearby shadows

One common mistake when checking near shading in PVSyst is becoming reassured just because a 3D model has been created. When you place buildings and obstacles and shadows appear, you may feel you have checked things sufficiently. However, if the orientation, height, dimensions, and panel positions are not correct, the scene may look plausible while the results differ from reality. A 3D scene is only meaningful when the input conditions are correct.

Another common mistake is judging the height of obstacles based only on site photos. Photographs are useful for understanding the situation, but perspective and shooting angle can easily lead to misperception of height and distance. In particular, rooftop equipment and adjacent buildings may appear to have little impact in photos but can actually cast long shadows in winter. Where possible, it is desirable to verify dimensions by combining drawings, survey measurements, point clouds, and on-site checks.

Misalignment of orientation is also a major cause of failure. If the north direction is offset when importing drawings, or if the building layout is rotated, the timing of shadow occurrence will change. In solar power generation, slight differences in orientation affect the results, so you must always verify this at the stage of creating the 3D scene. In particular, when placing elements using images or PDF drawings as a base, be aware that the top of the drawing is not necessarily true north.

Relying solely on the annual loss rate to check for shading is problematic. Even if you conclude there’s no issue because the annual loss rate is small, there can be significant impacts during specific months or times of day. For example, if shading is concentrated around midday in winter, it may look minor over the year but could affect winter self-consumption planning. When evaluating nearby shading, it is important to consider annual, monthly, and time-of-day perspectives.

Furthermore, there are failures to evaluate shading without considering string configuration. Even if the physical shadow is the same, the way the shaded panels are connected changes how losses spread. If panels that are more susceptible to shading and panels that are less susceptible to shading are mixed in the same string, the impact of shading can spread. Rather than considering layout design and electrical design separately, it is important to reflect the results of proximity shading in string design.

Another mistake is being overly afraid of shade and reducing installed capacity too much. Reducing shading losses is important, but cutting the number of modules too much can lower total energy yield and economic performance. When evaluating nearby shading, you need to consider not only shading losses but also the balance of energy generation, capacity, cost, and constructability. Rather than immediately excluding an area because of shade, it is important to compare multiple options and then decide.

How to Improve Verification Accuracy in Practical Work

In practical work, improving the accuracy of near-field shadow assessments requires organizing the workflow. The first thing to do is to sort out the site conditions. Collect site plans, roof plans, elevation drawings, equipment drawings, site photographs, survey data, etc., and compile a list of objects that could cast shadows. If information is missing at this stage, there will be limits to the accuracy even if you configure details later in PVSyst.

Next, prioritize modelling objects that are likely to have a large impact from shadows. It is not necessary to model every object with the same level of detail. Give priority to those close to the power-generating surface, those that are tall, those located on the south, east, or west sides, and those that are likely to cast shadows in winter. Small equipment and distant obstacles may be simplified if you can determine their impact is small. The important thing is not to overlook any objects that would affect design decisions.

After creating the 3D scene, do not proceed immediately to the annual calculation; perform a visual inspection. Check the orientation, panel layout, spacing between rows, obstacle heights, roof slope, and the orientation of the mounting structure. View the scene from multiple viewpoints to ensure there are no unnatural placements or dimension mix-ups. Because input errors are difficult to notice by looking only at the results screen, make it a habit to check the scene after creation.

After that, check the movement of shadows on representative days and at representative times. Check around the winter solstice, the spring and autumn equinoxes, and the summer solstice, and observe shadow changes in the morning, at noon, and in the evening. In particular, confirming which panel groups the shadows fall on from morning to afternoon in winter makes it easier to detect design issues. If shadows remain over the same area for long periods, it is worth considering layout changes or splitting the strings.

When reviewing simulation results, interpret the outcomes as well as the shading loss figures. Clarify which obstacles are the main loss factors, which seasons are most affected, and whether design changes can provide improvements. When preparing improvement proposals, compare the current plan, layout-change proposals, row-spacing-change proposals, and obstacle-avoidance proposals, and verify not only shading loss but also annual energy generation and installed capacity.

Finally, retain the verification results as explanatory documentation. The evaluation of nearby shading is not something that can be completed by the designer alone; it is often shared with the client, contractors, maintenance personnel, and electrical design staff. Making clear under which conditions the calculations were performed, which obstacles were considered, and which option was adopted helps prevent misunderstandings in later stages. In particular, for designs that allow shading, it is important to record why the shading was accepted and the extent of the expected losses.

Summary

To make the five points for checking near shading in the PVSyst manual useful in practice, it is important to understand not only the software operation procedures but also how to read shadows and translate that understanding into design decisions. Near shading is caused by the positional relationships of buildings, trees, equipment, and arrays, and it changes significantly with the seasons and time of day. Furthermore, not only the area of the shadows but also the string configuration and MPPT assignments alter the electrical impact.

The first point is to comprehensively identify all objects that cast shadows. Check not only the drawings but also on-site photos and survey information, and catalog buildings, equipment, trees, fences, adjacent arrays, and so on. Next, accurately reproduce dimensions and positional relationships in the 3D scene. Because errors in orientation, height, distance, tilt, or row spacing will distort the shadow assessment, visual verification after entering the data is essential.

The third point is to check how shadows move by season and time of day. Shadows in winter, in the morning and evening, and those cast by obstacles on the south side require particular attention. The fourth point is to interpret the results including electrical effects. By considering not only which panels are shaded but also which strings are affected, you can make judgments that more closely reflect reality. The fifth point is to compare options in a form that can be used for design changes. Rather than simply reducing shading losses, you need to select the optimal plan while balancing installed capacity, annual generation, constructability, and cost.

Checking near shading is not a task to make simulation results look neat; it is a process to bring power generation forecasts closer to reality and to clarify the basis for the design. When using PVSyst, treating 3D scene creation, shadow visualization, loss assessment, and design comparison as a continuous workflow lets you move from mere operational checks to decisions that can be used in practice. Carefully checking near shading helps avoid overestimation of power generation and is useful for post-construction explanations and for verification during operation.