What is PVSyst? A basic explanation of how to evaluate the impact of shading

PVSyst is a specialized simulation software used to predict the energy yield of photovoltaic power installations and to organize design conditions and loss factors. In solar power generation, not only system capacity and solar irradiance, but also shading from surrounding buildings, trees, terrain, and adjacent panel rows can greatly affect energy output. If the effects of shading cannot be accurately assessed, the energy yield prediction may appear higher than reality, or unexpected generation shortfalls may occur after the design.

For practitioners searching for "What is PVSyst," shading assessment is an unavoidable and crucial consideration. In power generation projects and system design in particular, it is necessary to understand not only whether shading exists, but when, where, and how much shading occurs, and how that is reflected in annual energy production, monthly generation, and the breakdown of losses. This article explains, from the basics and from a practical perspective, how to evaluate the effects of shading in PVSyst.

Table of Contents

• PVSyst is an analysis software that reflects the effects of shading on power generation

• Why shading affects power generation in solar power systems

• Types of shading evaluated in PVSyst and the underlying concepts

• On-site information required for shading assessment

• Basic workflow for assessing shading in PVSyst

• Key points when interpreting shading loss results

• How to leverage shading assessment in layout planning

• Common pitfalls beginners encounter in shading assessment

• Why you shouldn’t rely solely on PVSyst and should prioritize on-site verification

• Improving the accuracy of shading assessment by combining PVSyst with high-precision on-site information

PVSyst is analysis software that accounts for the effects of shadows on power output

PVSyst is analysis software for simulating the power output of photovoltaic systems and for checking the generation and losses under different design conditions. The energy output of a solar power system cannot be calculated simply by choosing the installed capacity. The final generation is determined by a combination of site solar irradiance conditions, panel orientation, tilt angle, surrounding shading, topography, temperature, wiring, equipment configuration, and other factors. Among these, the impact of shading in particular is an element that, if overlooked during the design stage, can easily lead to large discrepancies in predicted energy output.

In PVSyst, you can account for situations where shading reduces the solar irradiance reaching the panel surface and assess the impact on energy production. At sites with shading, results may differ between simulations that ignore shading and those that include it. By comparing these differences, you can understand to what extent local obstacles and layout conditions affect energy production.

What beginners should understand first is that shading assessment is not a task to make estimated power generation look lower, but a task to grasp power generation that is close to reality. If you ignore shading effects, simulated generation can sometimes appear higher. However, if shading actually occurs on site, failing to reflect that effect may cause the actual generation performance after operation to differ from the predicted values. In generation forecasts, it is more important to provide explainable figures that match local site conditions than to produce optimistic numbers.

Also, PVSyst's shading analysis is not just for checking the total generation. By checking which seasons shading is most pronounced in, how it affects monthly generation, and how much it accounts for in the breakdown of losses, you can use that information to change the layout or review the installation area. PVSyst does not automatically solve shading issues, but it helps organize the effects of shading numerically and serves as material for design decision-making.

Why Shadows Affect Power Output in Solar Power Generation

In solar power generation, the sunlight that reaches the panels is converted into electricity. Therefore, if shadows fall on the panel surface, the solar energy received decreases and power generation drops. The effect of shadows is not determined solely by the area that is shaded. The impact on power output varies depending on the time of day when shadows occur, the season, the panel connection configuration, equipment control, and the density and extent of the shadows.

What you should pay particular attention to is that the sun's position changes with the seasons and the time of day. Even in locations where shadows are hardly a problem during summer daytime, in winter mornings and evenings the sun's altitude becomes low and shadows can extend long. The reach of shadows cast by surrounding buildings, trees, slopes, and equipment structures can change greatly with the season. A single site visit may not be sufficient to judge the effects of shadows throughout the year.

Also, shadows can be non-negligible even when only partial. Even if only part of a panel is shaded, depending on the circuit configuration it can affect the overall output. In power generation systems, because multiple panels are electrically connected, a local drop in generation can also affect the output of surrounding panels. When evaluating shading in PVSyst, you need to consider not just the simple area loss but also the impact that shading has on the entire generation system.

Shadows can arise not only from external factors but also from the equipment itself. When panels are arranged in rows, the front-row panels or racking can cast shadows on the rear rows. If you try to install many panels on limited land, inter-row shading can increase. Even if increasing installed capacity appears to boost power output, increased shading losses can keep generation from rising as much as expected.

In the design of solar power generation systems, there are sites where it is difficult to eliminate shading completely. Surrounding buildings, differences in terrain elevation, constraints in land shape, the need to secure maintenance access routes, and other real-world conditions vary. What is important is not to judge the presence or absence of shading by intuition, but to use PVSyst to check the impact on power generation and to distinguish between shading that should be accepted and shading that should be mitigated.

Types of shading evaluated in PVSyst and how they are treated

When evaluating shading in PVSyst, it is easier to understand if you organize the different types of shading. Shading can come from surrounding obstacles, from terrain, from within the installation itself, or vary with season and time of day. If you lump these together without distinguishing them, it becomes difficult to determine which shading is affecting power generation.

Shadows from surrounding obstacles are caused by buildings, trees, utility poles, tower-like structures, adjacent equipment, and similar objects. These shadows change in length and direction depending on the sun’s position. In particular, tall obstacles can cast shadows even from a distance. Even if there are no obstacles immediately near the panels when you inspect the site, shadows from distant obstacles can reach them during periods of low solar elevation.

Shadows caused by terrain are generated by mountains, hills, slopes, embankments, excavations, and sites with elevation differences. Terrain shading can block solar radiation over wide areas and can have particularly large effects in the mornings, evenings, and during winter. Because the influence of terrain is difficult to discern from plan views alone, height information and on-site verification are important. When reflecting terrain conditions in PVSyst, how accurately the local topography is captured will affect the results.

Shadows that occur within a facility include shading between rows of panels, and shadows caused by the racking, equipment components, and surrounding equipment. When panels are placed densely, inter-row shading is more likely to occur. Even if you want to make maximum use of the land area, if inter-row shading increases, the energy generation per unit of capacity may decrease. In PVSyst, by checking shading losses while varying layout conditions, you can evaluate the balance between installed capacity and energy production efficiency.

In assessing shading, it is also important to be aware of the times of day and seasons when shading occurs. The impact on power generation varies depending on the timing of the same shading. If shading occurs during periods of high generation, the effect tends to be greater. Even shading in the mornings and evenings, when generation is low, can accumulate depending on the season and affect annual losses. When reviewing PVSyst results, it is important to check not only the annual value of shading losses but also monthly trends and their relationship to total generation.

On-site information required for shadow assessment

To evaluate shading in PVSyst, the quality of on-site information is critically important. PVSyst performs calculations based on the conditions entered, so if information about obstacles or terrain that cause shading is inaccurate, the shading loss assessment will also be inaccurate. To improve the accuracy of the shading assessment, it is necessary to accurately identify not only the location where the panels will be installed but also the surrounding obstacles, terrain, elevation differences, orientation, tilt, and installation area.

First, what you need is the location information for the installation area. Confirm where the panels will be placed, which areas are available for installation, and where the property boundaries and roof surfaces lie. If you evaluate shading while the installation area is still ambiguous, you may overlook spots that would actually be shaded and could have been avoided, or conversely find that locations you assumed would have little shading actually have obstructions.

Next, the position and height of obstacles are important. Determine where buildings, trees, columnar structures, and surrounding equipment are located and how tall they are. Shadows change in length depending on an obstacle’s height and the sun’s angle, so if height information is ambiguous it becomes difficult to correctly assess the extent of the shadows. Trees in particular require consideration of their seasonal leaf conditions and future growth. Even if a problem appears small at the time of an on-site inspection, shadows may increase in the future.

Topography information is also indispensable. For ground-mounted solar PV installations, site elevation differences and slopes affect how shadows form. If there are embankments or steps around the site, shadows can extend during times when the solar altitude is low. Even for roof-mounted systems, roof pitch, adjacent roof planes, upstands or parapets, and equipment areas can cause shading. Accurately capturing the on-site geometry is a prerequisite for shading assessment in PVSyst.

Orientation and tilt also affect shading assessment. Depending on which direction the panel surface faces and at what angle it is installed, the way it is affected by shading changes. Even if shadows are in the same position, the impact on power generation can vary depending on the panel’s orientation and tilt. When evaluating shading in PVSyst, it is important to check installation conditions and shading conditions together rather than considering them separately.

When collecting on-site information, it is also important not to rely too heavily on drawings and photographs. Drawings may contain information that differs from the current conditions. Photographs alone can make it difficult to accurately determine heights and distances. By verifying location, height, orientation, and tilt on site and reflecting that information in PVSyst's input conditions, the reliability of shading assessment is increased.

Basic procedure for evaluating shading in PVSyst

The basic procedure for evaluating shading in PVSyst is to first organize the reference design conditions, then input the information that causes shading, and finally compare the differences between cases without shading and with shading taken into account. For beginners, it is important to grasp the impact of shading step by step rather than trying to handle complex conditions all at once.

The first step is to create a baseline case that does not account for shading. Input the installation location, weather conditions, system capacity, orientation, tilt, equipment configuration, and basic loss conditions, and check the energy production when there is no shading. This baseline case is intended to capture the generation close to ideal conditions. Even when shading will be present in the actual design, confirming the baseline value first makes it easier to understand the difference after including shading.

Next, reflect on-site obstacles and terrain conditions. Incorporate into the input conditions elements that can cause shading, such as surrounding buildings, trees, slopes, equipment structures, and the relationships between rows of panels. At this stage, the accuracy of the site information is critical. If the positions or heights of obstacles are incorrect, the extent and timing of shading will also be offset. Before evaluating shading in PVSyst, you need to confirm whether the information collected on site is sufficient.

After creating a case that accounts for shading, check the differences from the reference case. Examine how much the annual power generation changed, what differences appear in the monthly generation, and how much shadow loss contributes to the loss breakdown. If the impact of shading is large, consider changing the layout or reassessing the installation area. Even if the shading impact is small, it is important to confirm there is no seasonal bias.

Furthermore, comparing multiple layout cases is also effective. Change the spacing between panel rows, slightly shift the installation area, avoid portions close to obstacles, adjust the tilt and orientation, and check how shading losses change under different conditions. This comparison allows you to consider the balance among power generation, installed capacity, shading losses, constructability, and maintainability.

Shade assessment in PVSyst is not something you calculate once and forget. As site surveys progress, design conditions change, or new information emerges during pre-construction checks, shading conditions must be updated and reassessed. Shading evaluation should be continuously reviewed from the early planning stages through detailed design and pre-construction verification.

Key points when interpreting shading loss results

After evaluating shading in PVSyst, interpreting the results is important. Even if shading losses are displayed, it is not sufficient to judge them by that number alone. You need to check how much shading losses affect energy production, in which seasons the impact is greatest, whether they are large compared to other losses, and whether they can be improved.

First, what you should check is the difference in annual power generation between the case that does not consider shading and the case that does. By looking at this difference, you can grasp how much shading affects total power generation. However, annual values alone do not provide a full understanding of shading characteristics. Because shading varies by season and time of day, even if the annual loss appears small, it may be concentrated in specific months.

Checking monthly generation is very important. If generation drops significantly in winter, the cause may not only be a reduction in solar irradiance but also shading effects caused by the lower solar elevation angle. In locations where shadows appear in the morning and evening, the generation profile can change seasonally. When reviewing PVSyst results, it is important not only to look at annual generation but also to infer shading patterns from the monthly trends.

In loss diagrams and loss breakdowns, check what proportion of the total is accounted for by shading losses. If shading losses are large compared with temperature losses or wiring losses, it is worth reviewing the layout and the impact of obstructions. Conversely, even if shading losses are small, you should verify that the underlying assumptions are correct. If there are obvious on-site obstructions but shading losses are almost non-existent, the shading-condition inputs may be insufficient.

When assessing shading losses, it's important not to make eliminating losses completely the only goal. Depending on site conditions, some shading may be unavoidable. Considering the terrain, surrounding environment, maintenance access routes, and construction constraints, it can be more rational to balance energy yield against installed capacity rather than trying to remove all shading. PVSyst results can be used not only to eliminate shading but also to determine how much shading can be tolerated.

Also, even if shading losses are large, you do not need to immediately reject the entire design. Separate the causes of the shading and classify those that can be improved and those that are difficult to improve. By distinguishing shading that can be mitigated by panel layout, shading that can be avoided by adjusting the installation area, and shading that is hard to avoid due to the surrounding environment, realistic countermeasures become clear. The shading loss figures are a starting point for evaluating the design, not the final judgment itself.

Approach to Leveraging Shadow Assessment in Layout Planning

PVSyst's shading assessment is only meaningful when used to improve the layout plan. Once shading losses are identified, use those results to consider the balance of panel arrangement, row spacing, installation area, orientation, tilt, and system capacity. The purpose of shading evaluation is not to estimate generation conservatively, but to provide material for creating a more realistic and easier-to-operate design.

When planning the layout, the first thing to consider is whether the causes of shading can be avoided. If shading losses are large in areas close to obstacles such as buildings or trees, avoiding installation in those parts can improve power generation efficiency. Sometimes simply changing the installation area slightly can reduce the impact of shading. By comparing multiple layouts in PVSyst, you can check which areas will incur larger shading losses.

Next, consider adjusting inter-row shading. Increasing the spacing between panel rows can reduce the shading on rear rows. However, widening the spacing may reduce the capacity that can be installed on the same land. Conversely, tightening the spacing increases capacity but may increase shading losses. Comparing cases with different row spacing in PVSyst makes it easier to evaluate the balance between capacity and shading losses.

Adjustments to orientation and tilt also relate to shading assessment. Changing the tilt angle can affect how inter-row shading occurs and seasonal energy production. Altering the orientation can change the times when shading occurs and the relationship between shading and energy production. However, adjustments to orientation and tilt affect not only energy production but also racking design, wind impacts, constructability, and maintenance. It is important to judge based on PVSyst results combined with site conditions.

In layout planning, the case with the highest power generation is not necessarily the optimal one. If the layout is changed significantly to avoid shading, construction can become more difficult and maintenance access routes may be harder to arrange. Also, reducing installed capacity to minimize shading losses can put you at a disadvantage in terms of total annual energy production. PVSyst’s shading assessment should be used to consider the balance among energy production, efficiency, constructability, and maintainability.

In power generation projects, future maintenance must also be considered. If the cause of shading is trees, confirm their future growth and whether they can be managed. If surrounding land use is likely to change, there is also a risk that new shading will occur. By conducting a shading assessment at the layout planning stage and allowing for some future changes, it becomes easier to reduce problems after operations begin.

Pitfalls beginners often encounter in shadow evaluation

When evaluating shading in PVSyst, there are several points where beginners tend to stumble. The most common is treating shadows too roughly. Even if you know there will be shadows on site, entering data without accurately determining the position and height of obstacles makes the shading loss results difficult to trust. In shading assessment, you need to verify not only visual impressions but also distance, height, azimuth (direction), and seasonal variations.

Another common pitfall is judging the annual shading based on a single on-site inspection at one moment in time. Even if there is little shade when you check the site on a summer day, large shadows can appear on winter mornings and evenings. Because the sun’s position changes with the seasons, it is risky to assess shading impacts from a single visual check. To evaluate shading effects over the year in PVSyst, it is important to set conditions that take solar altitude and seasonal variation into account.

A point to watch out for is becoming reassured simply because the shading loss is small. Even if PVSyst shows a small shading loss, that presumes the shading conditions were entered correctly. If there are obstacles on site that have not been reflected in the inputs, the shading loss will appear small. The smaller the result, the more important it is to verify that nothing was omitted from the inputs.

On the other hand, it is premature to conclude that the design is poor just because shading losses are large. Depending on site conditions, certain shading may be unavoidable. What matters is to identify the causes of the shading losses and separate those that can be mitigated from those that must be accepted. If the shading can be significantly improved by changing the layout, it is worth considering. If the shading is difficult to avoid due to terrain or the surrounding environment, it is necessary to assess the project's viability assuming those losses.

Also, it is important to be aware of a common misunderstanding about the relationship between shading assessment and installed capacity. Increasing the installed capacity tends to increase annual energy generation, but packing the layout more tightly can increase inter-row shading and reduce efficiency. If you design based only on capacity, shading losses can become large and the energy generation may not increase as much as expected. In PVSyst, it is important to check capacity, layout, shading losses, and performance ratio together.

In shading assessment, it is also important to be able to explain the calculation results to stakeholders. Rather than simply saying "the shading loss is about this much," you should be prepared to explain which obstacles are causing the shading, which seasons are most affected, which layouts were compared, and whether mitigation measures were considered. PVSyst results are documentation for explanation, and their credibility is enhanced when used together with the rationale for the input conditions.

Reasons to prioritize on-site verification rather than relying solely on PVSyst

PVSyst is a useful tool for assessing the impact of shading, but it cannot replace on-site verification. Because PVSyst performs calculations based on the conditions entered, if the site conditions are inaccurate, the results will also diverge from reality. In shading assessment, accurately understanding the site’s obstacles and terrain is more important than the mere operation of the software.

During on-site inspections, you should first survey a wide area around the installation site. Not only the area immediately around the planned panel installation, but also buildings, trees, slopes, and structures located a short distance away can cause shading. Especially during periods of low solar elevation, shadows from distant obstacles can reach the site. By recording the positions and heights of obstacles on site and reflecting them in the inputs to PVSyst, you can improve the accuracy of the shading assessment.

Checking the terrain is also important. For ground-mounted installations, elevation differences within the site, surrounding slopes, and level differences with adjacent properties can affect shading. For roof-mounted installations, you need to confirm the roof surface orientation and pitch, upstand or parapet details, equipment placement areas, and the relationship with surrounding roofs. Even where drawings appear flat in plan, there may in reality be elevation changes or obstacles that alter how shadows are cast.

On-site inspections must also include verification of orientation and tilt. If there is a discrepancy between the orientation shown on the design drawings and the actual orientation, the timing of shadow occurrence and the impact on energy production will change. If the panel tilt angle differs from what was assumed, it will also affect inter-row shading and the amount of solar irradiation received. To perform an accurate shading assessment in PVSyst, it is necessary to determine the site’s location, orientation, height, and angles as precisely as possible.

Also, on-site verification information is necessary to explain the results of PVSyst. If stakeholders ask for the basis of shading losses, the credibility of the simulation will not increase unless you can explain which obstacles you confirmed on site and which conditions you entered. By organizing photos, positioning information, field notes, and cross-checking with design drawings, you can link the PVSyst report to the actual on-site conditions.

Shadow assessment cannot be completed with PVSyst alone; it becomes a practical, usable evaluation only when combined with on-site verification. The basic process of shadow assessment is to gather accurate information in the field, reflect that information in PVSyst, and then review and revise the layout and design after examining the results.

Improving Shading Assessment Accuracy in PVSyst with High-Precision On-Site Data

PVSyst is analysis software for predicting the power output of photovoltaic systems and for organizing various loss factors, including shading. To evaluate the effects of shading correctly, it is necessary to check not only whether shading is present, but also which obstacles cast shadows, in which seasons, at which times of day, and over what extent. Using PVSyst, you can compare cases with and without shading and assess the impact on annual generation, monthly generation, and the breakdown of losses.

What is important in a shading assessment is not just looking at the numerical results, but verifying the assumptions behind them. If shading losses are large, it is worth considering changes to the layout, a review of the installation area, or adjustments to row spacing. Even when shading losses are small, you need to confirm that on-site obstacles and terrain are accurately reflected. PVSyst results become a basis for practical decision-making only when the input conditions match the actual site.

Shadow assessment is neither intended to make projected power generation appear higher nor to underestimate it unnecessarily. Its purpose is to accurately reflect on-site conditions and to determine how much shading can be avoided and how much should be accepted. Because solar power systems are operated for long periods, carefully checking the effects of shading during the planning stage helps reduce discrepancies in post‑operation power generation and the need for additional explanations.

To do this, not only the operation of PVSyst but also the accuracy of on-site information acquisition is important. If you can ascertain as accurately as possible the installation area's location, orientation, tilt, elevation differences, the positions and heights of obstacles, and changes in the surrounding environment, the reliability of the shading conditions entered into PVSyst will be enhanced. If on-site verification remains ambiguous, no matter how detailed the simulation is, the basis for the results will be weakened.

If you want to streamline on-site position checks, obstacle recording, and determining installation extents, using an iPhone-mounted GNSS high-precision positioning device like LRTK makes it easier to incorporate on-site information into design and simulation. If obstacles and installation extents can be organized based on high-precision positional information, the assumptions underlying shadow assessment in PVSyst become clearer and the explanatory power of power generation forecasts improves. By combining PVSyst's shadow simulations with high-precision positioning information obtained on site, shadow assessment in solar power design can be brought closer to real-world practice.