Six Ways to Find the Causes of Large Shading Losses in PVSyst

Table of Contents

• Why it is important to identify the causes of shading losses in PVSyst

• Method 1 Separate shading sources into on-site and off-site factors

• Method 2 Organize the seasons and time periods when shading occurs

• Method 3 Review array layout and row spacing

• Method 4 Examine the relationship between azimuth, tilt, and terrain conditions

• Method 5 Check string configuration and the impact of partial shading

• Method 6 Narrow down causes with comparative simulations and on-site verification

• Thinking to connect shading-loss analysis to practical improvements

Why it is important to identify the causes of shading losses in PVSyst

When you run simulations in PVSyst, you may find that generation does not reach expectations and shading losses appear large. The important point here is not to be satisfied with the result that shading losses are large. In practice, the value lies more in whether you can identify why the losses are large than in the fact that they are large. Without knowing the cause, you cannot decide whether to widen row spacing, revise azimuth or tilt, or reconfigure obstacles, and the design process can become a cycle of trial and error.

In particular, solar power planning always involves a trade-off between using the site efficiently and minimizing shading losses. Packing arrays more densely increases capacity but also increases self-shading. Conversely, leaving more clearance to reduce shading can reduce the number of modules that can be installed. PVSyst is a tool to visualize this balance, but if you misread the causes of shading losses, you may make design changes that sacrifice capacity with little benefit.

Also, shading losses rarely arise from a single cause. It is common for several elements to overlap: self-shading between front and rear rows, shadows from nearby buildings, trees and slopes, and differences in how shadows extend due to small elevation changes. Moreover, these do not manifest with the same intensity throughout the year—some are strong only on winter mornings, others exert a steady, year-round effect. In other words, when shading losses are large, what you need is not just confirmation that shadows exist, but a breakdown of those shadows interpreted as design conditions.

This also makes a big difference when explaining to colleagues or clients. Rather than simply saying shading losses are large so we will change the layout, it is more persuasive to explain which obstacle affects which rows at which times, how that produces the observed annual loss, and why the proposed design change is effective. The real value of handling shading losses in PVSyst is not producing a loss ratio but being able to verbalize the rationale for the design.

Method 1 Separate shading sources into on-site and off-site factors

If you want to find the cause of large shading losses, the first step is to separate shading sources into on-site factors and off-site factors. In practice, people tend to classify shading simply as present or absent, but PVSyst reveals more nuance. Whether the shading is self-shading between front and rear arrays, shadows from on-site retaining walls, slopes, equipment rooms, fences, etc., or from off-site factors such as adjacent buildings or trees, the ease of mitigation and the priorities differ.

For example, if self-shading is dominant, you may improve it by reviewing row spacing, tilt angle, array direction, or access-path planning. These are shadows that designers can relatively easily control. On the other hand, shadows from neighboring buildings or distant tall trees often must be accepted to some extent, and small adjustments in placement may not yield significant improvement. Treating the two types of shading the same mixes shadows you can mitigate with those you must accept, making design actions unclear.

Furthermore, even among on-site factors, it is important to identify which obstacle is the main cause. Clarifying whether it is a building, a slope, or array segmentation created to ensure access paths makes it easier to see what to prioritize in PVSyst. In practice, including too many obstacles can obscure the primary cause, so it is better initially to narrow down the items likely to affect shading and prioritize them.

By performing this work carefully, your perspective on shading losses changes considerably. If one option is dominated by self-shading and another by external building shadows, the meaning of the comparison becomes clear. The first step in finding the cause of large shading losses in PVSyst is not to look at the loss percentage figures but to organize the origins of shadows and separate factors that can be changed in the design from those that are difficult to change.

Method 2 Organize the seasons and time periods when shading occurs

When investigating the causes of shading losses, judging based only on the annual loss rate is risky. PVSyst clearly shows annual energy and annual losses, but shading does not occur uniformly throughout the year. Some shadows are strong only in the winter mornings and evenings, while others are faint but continuous year-round. If you want to find the cause, you must first organize which seasons and which times of day the shading is concentrated in.

For example, if shading is strong only on winter mornings, the low solar altitude in that season may be causing long shadows from buildings or front rows. In that case, slight adjustments to row spacing or layout direction could significantly improve performance. Conversely, if a shading effect steadily affects the mornings throughout the year, the cause may be external obstacles or inherent site conditions that are difficult to improve by simple row-spacing changes. If you take measures without knowing the time-of-day bias, you may waste time on changes that have little effect.

Also, by looking at season and time-of-day patterns, you can weight the shading-loss figures correctly. A loss that appears small on an annual basis may be non-negligible when comparing alternatives, and conversely, a fairly large loss figure might be acceptable for the overall project. To connect PVSyst results to practical work, it is important not only to know what percentage is lost but also how that loss is distributed over time.

In practice, it is useful to make a habit of returning from the annual loss figure to seasonal and time-of-day trends. Knowing in which month the differences open up and in which time periods the impacts concentrate greatly advances cause identification. When finding the causes of large shading losses in PVSyst, the basic approach is not to conclude from the annual total alone but to see what time axes compose that number.

Method 3 Review array layout and row spacing

When shading losses are large, the most often effective practical check is array layout and row spacing. When aiming for high generation in PVSyst, there is a temptation to place as many arrays as possible on the site. However, this often results in overly tight row spacing and increased self-shading. When investigating shading-loss causes, you should first suspect how much self-shading is contributing.

In particular, proposals prioritizing capacity by increasing the number of rows may look favorable at first glance but tend to have large shading in winter or during mornings and evenings. Sometimes simply widening row spacing slightly will greatly reduce shading losses; in other cases, even considerable widening yields little improvement. This difference is tied to azimuth, tilt, and the positional relationship with surrounding obstacles. To find the cause in PVSyst, it is important not only to check whether the layout is packed but also to confirm which time periods those packings actually affect.

Also, revising the layout relates to the placement of access paths and edge clearances. If you reduce clearances to slopes or maintenance paths to add arrays, that proposal may look to have high generation on paper, but when Near Shading and shading losses are included, it may not achieve the expected benefit. In practice, such design compromises often manifest as shading losses, so when shading losses seem large, the first thing to inspect is whether the layout conditions are overly greedy.

As a countermeasure, compare scenarios in PVSyst with different row spacings, slightly different array arrangements, and adjusted access-path positions to check differences in shading losses. Only then will you know how much margin is effective in improving shading losses. In practical work to find shading-loss causes, it is important to read self-shading not merely as a result but as a reflection of array-layout design decisions.

Method 4 Examine the relationship between azimuth, tilt, and terrain conditions

Large shading losses often stem not only from row spacing but from the combination of azimuth, tilt, and terrain conditions. In practice, you may set an ideal azimuth and tilt first, then fine-tune to fit the site. However, if the site has undulation or the slope orientation does not match the array direction, the way shadows form can change even with the same row spacing. To correctly find causes of shading losses in PVSyst, you need to view angle conditions and terrain conditions together, not separately.

For example, increasing the tilt can improve irradiance conditions but tends to lengthen shadows between rows. If terrain slope or slope orientation adds to that, certain rows may receive stronger shading or shading may be more biased than expected. Conversely, slightly reducing tilt can create more spacing between rows and may improve annual losses. In PVSyst, the important thing is not to seek azimuth or tilt as standalone optimal values, but to confirm how shadows appear within the given site conditions.

Also, comparing shading losses without considering terrain conditions can lead to misidentification. What seemed like a row-spacing issue might actually be dominated by slope orientation, or what was thought to be building shadow might be caused by ground elevation differences. In practice, such misreadings lead to rework after design changes. PVSyst is well suited to organizing the relationship between angle settings and terrain because it makes it easy to check layout and shading on the same screen.

As a countermeasure, compare proposals that vary tilt and azimuth slightly within the same site conditions. Looking not only at annual generation totals but also at which conditions produce strong shading helps clarify the causes. When investigating large shading losses in PVSyst, treat angle settings not as fixed values but as conditions to read including compatibility with the terrain.

Method 5 Check string configuration and the impact of partial shading

When searching for shading-loss causes, it is dangerous to judge only by the apparent amount of shadow. PVSyst especially shows differences depending on whether you have confirmed how partial shading occurs on the given string configuration. In practice, one tends to assume that a small shaded area implies a small loss, but the impact depends on which rows are shaded and how those rows are grouped electrically. Partial shading is both a visual issue and an electrical grouping issue.

For example, if rows prone to shading and rows less prone to shading belong to the same string, the effect can spread and appear as a larger loss than visually expected. Conversely, if rows with similar conditions are naturally grouped, the same amount of shading is easier to interpret. If you feel reassured by shaded area alone when viewing PVSyst results, you can easily miss this distinction. In practice, what matters is not whether shading exists but how that shading affects electrical groupings.

Also, adopting this perspective changes possible improvements. In addition to layout adjustments such as moving arrays away from obstacles, other options emerge, such as changing stringing strategies or reallocating blocks. Many projects cannot completely eliminate shading due to site constraints. In those cases, whether you can control which shading is applied to which configuration determines overall system quality. PVSyst should be used not only to evaluate shaded area but also to interpret how shading propagates electrically.

As a countermeasure, for proposals with large shading losses, always check which rows, strings, and blocks concentrate the impact. Looking beyond annual totals and examining both shading patterns and how they group electrically advances cause identification considerably. To find shading-loss causes in PVSyst, you must read partial shading not by area alone but with a perspective that includes electrical impact.

Method 6 Narrow down causes with comparative simulations and on-site verification

The final method for finding shading-loss causes is to combine comparative simulations with on-site verification to narrow down the cause. Looking at only one scenario in PVSyst can make it difficult to judge whether a loss is large or small and whether it should be accepted or mitigated. However, lining up scenarios such as slightly wider row spacing, slight adjustments to array orientation, different access-path positions, and revised clearances from buildings or trees makes it easier to see what is the main cause of losses.

In practice, an option that completely avoids shading is not always the best. Reducing shading may decrease capacity, reduce site utilization, or worsen construction logistics. Conversely, accepting some shading can sometimes produce a more practical and robust overall layout. The purpose of comparative simulations in PVSyst is not only to compare shading-loss magnitudes but to clarify what you gain and what you lose in exchange for shading.

However, it is also dangerous to draw conclusions from comparative simulations alone. If shadows from buildings look stronger on site in the morning, or the slope orientation suggests longer shadows in the evening, you should check for inconsistencies with PVSyst assumptions. Even well-organized desk results can mislead if your understanding of on-site positional relationships and elevation differences is weak. Because PVSyst is a tool that is faithful to its input assumptions, reverse-checking with on-site verification remains important until the end.

As a countermeasure, for proposals with concerning shading losses, always compare multiple improvement patterns, review their differences, and then narrow the causes by cross-checking with site conditions, drawings, photos, and positional information. This iterative process makes numerical comparisons lead directly to design improvements. In practice, when finding the causes of large shading losses in PVSyst, the most important attitude is not to trust a single result but to narrow causes through comparison and on-site verification.

Thinking to connect PVSyst shading-loss analysis to practical improvements

What the six methods above have in common is the refusal to treat shading losses as mere loss-rate numbers. Separate sources, read seasonal and time-of-day biases, review array layout and row spacing, organize the relationship between azimuth, tilt, and terrain, check string configuration and the impact of partial shading, and finally narrow causes with comparative simulations and on-site verification. When you can follow this flow, shading losses in PVSyst become not an explanation of design results but the starting point for design improvements.

What matters for practitioners is not only reducing shading-loss figures. The real value is being able to explain why the loss occurs and decide what to fix. Within the multiple constraints of site utilization, capacity, constructability, maintainability, and generation stability, the essence of practice is to determine which shadows to accept and to what extent, and which shadows to improve. PVSyst supports those judgements with comparisons and numbers rather than intuition.

Also, to improve the accuracy of shading-loss analysis, you must not complete the process with desk simulations alone. If site information such as boundaries, slopes, buildings, trees, paths, and existing conditions is unclear, the basis for shading-loss assumptions weakens. To connect PVSyst results to practice, repeatedly verify numbers against site understanding and simulation inputs. Shading losses are both calculation results and reflections of actual site conditions.

In that sense, when you need more reliable position checks or coordinate acquisition on site, using iPhone-mounted GNSS high-precision positioning devices such as LRTK can be effective. If on-site position information and site conditions are easier to organize, the assumptions for layout and obstacle conditions when analyzing shading-loss causes in PVSyst become clearer. If you can improve desk comparison accuracy with PVSyst and support on-site understanding with LRTK, shading-loss analysis becomes not just loss confirmation but a site-rooted design-improvement process. Carefully finding the causes of shading losses improves not only the accuracy of generation forecasts but also the practical capability to connect desk and field work.