【How to Set the Tilt Angle in PVSyst｜6 Basic Optimization Tips】

Table of Contents

• Understand the significance of setting the tilt angle in PVSyst

• Basic 1: Separate and organize azimuth and tilt angles

• Basic 2: Enter the tilt angle according to the installation type

• Basic 3: Find the optimal angle based on annual energy production

• Basic 4: Check monthly energy production and seasonal variations

• Basic 5: Check consistency with shading, inter-row spacing, and roof conditions

• Basic 6: Compare multiple cases to determine a realistic angle

• Common mistakes and checkpoints when setting the tilt angle

• Required surveying accuracy to correctly reflect site conditions

• Summary

Understanding the significance of setting the tilt angle in PVSyst

In PVSyst, the tilt angle refers to how much the surface of a solar panel is inclined relative to the horizontal plane. The closer to horizontal, the smaller the tilt angle; the more upright it is, the larger the tilt angle. In photovoltaic power generation, the amount of solar irradiance incident on the panel surface is directly linked to power output, so the tilt angle has a significant impact on simulation results.

Changing the tilt angle alters not only the annual solar irradiance gain but also the monthly power generation trends. Generally, a smaller tilt angle tends to be advantageous for the higher sun in summer, while a larger tilt angle tends to be advantageous for the lower sun in winter. However, actual power generation is simultaneously affected by irradiance data, azimuth, temperature, shading, terrain, panel layout, mounting conditions, and other factors, so you cannot draw conclusions based solely on angle.

The purpose of setting the tilt angle in PVSyst is not just to seek the theoretical maximum. In practice, within the range that can be installed, it is necessary to comprehensively assess energy output, constructability, maintainability, structural conditions, and land-use efficiency. For example, for ground-mounted installations, increasing the tilt angle can improve winter energy output, but because the shadows of the front and rear rows become longer, it may be necessary to widen the row spacing. Widening the row spacing can reduce the number of panels that can be placed on the same site.

For roof-mounted installations, it is often necessary to match the existing roof pitch, so you may not be free to choose the optimal tilt angle. In this case, in PVSyst it is important to accurately reflect the roof pitch and then check the azimuth, shading, losses, and output results. Rather than optimizing the angle, the primary objective becomes correctly modeling the site conditions.

Therefore, when setting the tilt angle in PVSyst, it is important not only to seek "the angle that yields the highest energy production" but also to adopt the stance of determining "which angle is the most reasonable among those that can actually be implemented at this site." Simulations are tools to assist design decisions, and if you ignore site conditions and chase numbers alone, rework is likely to occur during the implementation phase.

Basic 1: Separate and organize azimuth and tilt angles

Before setting the tilt angle, you first need to understand the roles of the azimuth and tilt angles separately. The azimuth angle indicates which direction the panel surface is facing, and the tilt angle indicates how much the panel surface is tilted. These two affect power generation together, but their meanings are completely different.

A common stumbling block in practice is that when generation is lower than expected, people try to find the cause by adjusting only the tilt angle. However, if the azimuth is off or the layout is close to an east–west orientation, changing the tilt angle slightly may not lead to a significant improvement. Conversely, even if the azimuth is appropriate, if the tilt angle does not match the site conditions, assessments of monthly generation and shading losses can diverge from reality.

When setting up in PVSyst, first confirm which direction the panel surface faces, and then enter the tilt angle. For rooftop installations, verify the roof surface’s orientation and slope from building drawings and on-site survey results. For ground-mounted installations, clarify the orientation and angle of the panel rows based on design drawings, layout plans, racking specifications, and site development plans. If you enter these ambiguously at this stage, even when comparing later simulation results it will be difficult to identify which differences in conditions are causing differences in energy production.

Azimuth and tilt angles may look like minor input items in a simulation, but they are actually design assumptions. When comparing multiple options in particular, mixing cases that differ only in azimuth, only in tilt, and in both makes it difficult to explain the comparison results. In comparative studies, it is important to clearly specify which conditions will be changed and which will be fixed.

For example, if the objective is to optimize the tilt angle, keep the azimuth, panel capacity, equipment conditions, weather data, and loss settings as consistent as possible, and vary only the tilt angle incrementally to compare. By separating the conditions and examining them in this way, it becomes easier to discern the impact that differences in tilt angle have on energy production and losses.

Basic 2: Enter the tilt angle according to the installation type

When setting the tilt angle in PVSyst, first clarify the type of installation. Typical examples include ground-mounted, roof-mounted, carport-type, slope-mounted, and buildings with roof surfaces facing multiple orientations. Depending on the installation type, the tilt angle may be freely adjustable or fixed to match site conditions.

For ground-mounted installations, the mounting structure’s design angle is entered as the tilt angle. In early studies where the design angle has not yet been decided, multiple candidate angles are prepared and their respective energy production, shading losses, and land use efficiency are compared. Ground-mounted systems may appear to be able to adopt the theoretically optimal angle, but in reality there are constraints such as site grading conditions, mounting structure height, foundations, wind loads, snow loads, surrounding obstructions, and maintenance access. Therefore, the angle that yields the highest energy production in PVSyst does not necessarily become the final design angle.

For roof-mounted installations, it is common to enter the roof pitch directly as the tilt angle. The exception is when angle-adjustable mounting frames are installed on the roof, but in many projects the equipment is installed along the existing roof surface. In such cases, accurately reflecting the roof conditions is more important than allowing the designer to freely choose the tilt angle. If the roof pitch differs between the value on the drawings and measurements taken on site, the simulation results may also differ.

On projects with multiple roof surfaces, it is necessary to treat the orientation and tilt angle of each surface separately. If you combine a south-facing roof surface and an east-facing roof surface, or multiple surfaces with different slopes, into a single condition, the estimate of power generation will be coarse. In practice, because the power-generation characteristics differ for each roof surface, it is desirable to make the input conditions as close to reality as possible.

When installing on sloped terrain, you need to consider not only the panel tilt angle but also the slope of the ground. Be careful not to confuse the angle of the panel surface relative to the horizontal plane with the angle relative to the ground surface. The angle entered into PVSyst must be set with an understanding of which reference it will be treated as in the simulation. For projects involving the site’s slope, the mounting structure, and the finished grade after earthworks, carefully verify using survey data and design drawings.

Basic 3: Finding the optimal angle based on annual power generation

The most straightforward criterion for optimizing the tilt angle is annual energy production. By using the same project conditions in PVSyst and creating multiple cases that change only the tilt angle, you can compare which angle yields the highest annual energy production. This method is commonly used in preliminary studies and during the basic design stage.

When using annual energy generation as the basis, first create a baseline case. For example, enter the planned standard tilt angle and set the weather data, equipment conditions, layout conditions, and loss settings. Then create separate cases in which the tilt angle is changed gradually and compare the annual energy generation and specific yield. The important point here is to avoid changing conditions other than the tilt angle as much as possible. If you change equipment capacity or loss settings at the same time, it becomes difficult to determine the reason for differences in generation.

When comparing tilt angles, there is no need to change the angle in excessively fine increments. In the initial stage, it is sufficient to set a few representative candidate angles and simply grasp the trend in power generation. If power generation hardly changes within a certain range, you can prioritize constructability, cost, structural conditions, and maintainability rather than power output alone when making a decision. Conversely, if differences in angle lead to clear differences in power generation, check why the differences occur using monthly data and loss diagrams.

The tilt angle that maximizes annual power generation varies depending on the region and weather conditions. Because latitude, seasonal variation in solar radiation, temperature, snowfall, and tendencies toward cloudy weather all have an impact, it is not possible to say a single angle is correct. Also, the angle that maximizes annual power generation may not coincide with the angle that maximizes revenue from electricity sales or the benefits of self-consumption. For example, facilities with high power demand during specific times of day or seasons may prioritize a generation profile that matches that demand.

When optimizing the tilt angle in PVSyst, don't just look at the annual energy production figure; check under what solar irradiance conditions, loss conditions, and seasonal distribution that figure is obtained. Even if a case shows slightly higher energy production, it may be unsuitable as a final design if it increases shading losses or requires unrealistic inter-row spacing. Optimization is both a process of searching for the maximum value and a process of narrowing the options to conditions that are feasible on site.

Basic 4: Check monthly power generation and seasonal variations

Changing the tilt angle affects not only the annual energy production but also the balance of monthly generation. Even if there is little difference in the annual total, there can be differences between summer and winter generation. When checking PVSyst results, it is important not to judge solely by annual values, but to examine the trends in monthly generation, irradiance, and losses.

If the tilt angle is set at a smaller value, it tends to receive more solar radiation during periods of high solar altitude. Conversely, setting the tilt angle to a larger value can be advantageous during periods of low solar altitude. Of course, actual results vary depending on local weather conditions and orientation, but by examining monthly variations you can identify which seasons the differences in tilt angle affect.

In practice, proposals that emphasize winter power generation are also considered, not just those that maximize annual power generation. Especially for self-consumption systems, a facility’s electricity demand varies by season, so the seasonal distribution of generation can become important. Even if the annual total decreases slightly, if generation increases during periods of high demand, the overall design can be reasonable.

When examining monthly power generation, you should not only consider the simple difference in generation amounts but also check whether the generation is reasonable relative to the solar irradiance and whether losses are concentrated in specific months. For example, if generation in winter is lower than expected, not only the tilt angle but also shading from nearby obstructions, topographical shading, inter-row shading, snow conditions, and equipment conditions at low temperatures may be involved.

Also, increasing the tilt angle can be advantageous for winter solar radiation capture, but it can also make the front row’s shadow more likely to extend onto the rear rows. In PVSyst, checking the relationship between tilt angle and shading loss together allows you to uncover practical issues that are not visible from a simple angle comparison. Monthly data is also useful when explaining design proposals, because it lets you describe differences that are hard to convey with annual totals by showing seasonal trends.

Basic 5: Check consistency between shadows, row spacing, and roof conditions

One aspect that is easily overlooked when setting the tilt angle is its relationship with shading and inter-row spacing. For ground-mounted installations, increasing the tilt angle raises the rear edge of the panels and can lengthen the shadows cast on the rows in front and behind. To avoid shading you need to widen the row spacing, but widening the spacing can reduce the installable capacity. If you ignore this relationship and optimize only the tilt angle, you may end up with a layout that is not actually feasible.

When changing the tilt angle in PVSyst, check not only the energy production but also the shading losses. In particular, at the low solar elevations in winter, shadows from the front row are more likely to fall on the rear row. Even if increasing the tilt angle appears to improve winter energy production, if inter-row shading has increased you should reassess the overall optimality of the layout.

In rooftop installations, rather than freely deciding the tilt angle, the basic approach is to match the roof conditions. Roof pitch, ridge orientation, surrounding upstands, equipment, parapets, and adjacent buildings all influence shading. Even if the roof surface’s tilt is correct, if the height or position of obstacles is inaccurate, the assessment of shading losses may not reflect reality.

Also, when using angle-adjustable mounting systems for roof installations, increasing the tilt angle can make them more susceptible to wind effects. Even if simulations show increased power generation, if structural constraints or construction difficulties increase, the decision to adopt them should be made cautiously. PVSyst results should not be considered separately from structural assessment and construction planning.

In projects on sloping or complex terrain, the ground surface elevation and slope affect inter-row shading. The way shadows appear can differ between entering the site as flat and reflecting the actual elevation differences. Before optimizing tilt angles, it is important to confirm that the terrain conditions are correctly represented. If on-site elevation data or obstruction information is ambiguous, finely comparing angles will not yield highly reliable results.

Basic 6: Compare multiple cases to determine a realistic angle

A practical way to determine the tilt angle in PVSyst is to create and compare multiple cases. If you run a simulation with only one angle, it becomes difficult to judge whether that angle is good or bad. By setting several candidate angles and comparing them under the same conditions, you can objectively check the energy production, losses, monthly trends, and the impact of shading.

When preparing comparison cases, clearly define a baseline case. The baseline case should be the design condition that currently has the highest likelihood of being adopted. Then prepare cases with a smaller slope angle, a larger slope angle, a case matching the roof pitch, and a case with an angle that is easier to handle during construction, among others. It is important that the angles being compared have design significance. Do not merely list numbers; make sure you can explain why each angle is being considered.

In result comparisons, we check annual energy production, specific yield, loss diagrams, monthly energy production, shading losses, system losses, and so on. Even if one case has the highest energy production, if there are issues such as large shading losses, reduced installed capacity, taller mounting structures, poor constructability, or difficulty providing maintenance access, a different option may be more suitable in the overall assessment.

In internal communications and when explaining to the client, simply saying "we will use this angle because it yields the highest power output" can be insufficient. You need to organize and convey why that angle suits the site conditions, how much difference there is compared to other angles, and—if the power-generation difference is small—why ease of installation should be prioritized. The comparison results from PVSyst can be used as supporting material for that explanation.

In practice, the final tilt angle is determined not only by power generation but also by installable capacity, site constraints, structural conditions, maintainability, aesthetics, regulations, construction procedures, and so on. Optimization in PVSyst is an important consideration at the core of that decision, but it is not the final decision itself. Choosing an angle that can be reproduced on site without difficulty, rather than relying solely on favorable numbers, leads to practical success.

Common Mistakes and Points to Check When Setting the Tilt Angle

A common mistake when setting the tilt angle in PVSyst is misinterpreting the meaning of the angle shown on the drawings versus the input angle. When roof pitch, racking angle, ground slope, and the panel surface tilt are mixed together, it can be unclear which angle should be entered. In particular, on sloped terrain, be careful not to confuse the angle relative to the ground surface with the angle relative to the horizontal plane.

Another mistake is assuming you changed only the tilt angle when other conditions have also been altered. If equipment parameters, installed capacity, loss settings, meteorological data, or azimuth change when you create comparison cases, you will not be able to identify the cause of the differences in energy output. When comparing tilt angles, the basic principle is to minimize the number of conditions you change.

Also, by focusing too much on finding the optimal tilt angle, checks on shading and row spacing may be postponed. Increasing the tilt angle can improve winter solar radiation capture, but it can also increase inter-row shading. If you look only at annual energy production without checking shading losses, you may end up choosing a layout that is impractical for the site.

In roofing projects, it is important not only to read the roof pitch from the drawings but also to verify that it matches the on-site conditions. In older buildings or renovated properties, the drawings and the as‑built conditions may differ. Differences in the pitch of the panel mounting surface, the height of obstacles, the location of equipment, or the shape of the roof edges can affect the reliability of simulation results.

When you are unsure what tilt angle value to enter, first clarify the purpose. The required level of accuracy varies depending on whether it is a rough estimate, basic design, detailed design, or for submission documents. At the rough estimate stage a representative value may be acceptable, but for detailed design and explanatory materials values based on site conditions are required. As a practical approach to using PVSyst, it makes sense to increase input accuracy in line with the project stage.

Survey Accuracy Required to Correctly Reflect Site Conditions

Accurately setting the tilt angle requires a thorough understanding of on-site conditions. No matter how carefully you compare cases in PVSyst, if the site information used as input is inaccurate, the reliability of the results will decrease. In particular, terrain, roof pitch, obstacle locations, height information, site boundaries, and the positions of existing structures directly affect the tilt angle and shading analysis.

For ground-mounted installations, the site is not always perfectly flat. Even small elevation differences can affect inter-row shading, racking height, earthworks volume, and drainage planning. On sloping sites, if the relationship between the ground surface and the panel surface is not properly defined, the interpretation of the tilt angle can be off. When assessing the appropriate tilt angle in PVSyst, it is effective to use not only the design drawings but also the position and elevation data collected on site.

On-site surveying is important even for rooftop installations. If you can accurately determine the roof surface slope, orientation, heights of obstacles, and positions of surrounding buildings, you can make the input conditions in PVSyst closer to actual conditions. Especially in urban areas where shading has a large impact, or on buildings with many rooftop installations, the accuracy of on-site information greatly affects simulation results.

A useful tool here is LRTK, a smartphone-mounted GNSS high-precision positioning device. By using LRTK, it becomes easier to apply position data collected on site to design considerations and site assessments. In planning photovoltaic power installations, there are many situations where you need to organize on-site coordinate information, such as site elevation differences, locations of obstacles, checks around roofs, and records before and after construction. To make tilt angle settings and shadow analysis in PVSyst more realistic, it is important to grasp the on-site shapes and positional relationships with high accuracy, not just rely on desk-based conditions.

The accuracy of a simulation is not determined solely by operations performed within the software. The higher the accuracy of the on-site information entered, the greater the credibility of the design evaluation. By utilizing a high-precision, field-friendly positioning device such as LRTK, it becomes easier to link the processes of survey, design, construction, and record-keeping, and to reconcile the study results produced in PVSyst with actual site conditions.

Summary

When setting the tilt angle in PVSyst, you must first understand that the tilt angle is an important parameter that affects energy generation, monthly trends, shading, row spacing, and constructability. The tilt angle should not be decided in isolation, but should be considered together with azimuth, installation type, roof pitch, terrain, shading, racking conditions, and maintenance and operability.

The basic principle of optimization is to fix as many conditions as possible other than the tilt angle and compare multiple cases. Check the annual energy production, read seasonal differences from the monthly production, and examine consistency with shading losses and row spacing. Based on that, choose the most practical option among the tilt angles that can actually be implemented on site, rather than the angle that produces the maximum generation.

When you are not yet familiar with using PVSyst, it is easy to focus only on the input values on the settings screen, but in practice the basis for those inputs is important. Organizing whether they come from drawings, on-site survey measurements, or rough estimates makes it easier to explain the simulation results. In particular, tilt angles and shading analysis can have their reliability greatly affected by the accuracy of the assessment of on-site conditions.

To make the design study of solar power generation systems more reflective of actual site conditions, it is effective to combine simulations in PVSyst with on-site positioning. LRTK, as a GNSS high-precision positioning device that can be attached to a smartphone, supports acquiring site location and elevation information. If slope angles, terrain, obstacles, and installation locations can be accurately understood and that information reflected in the design review, it becomes easier to improve the accuracy of result checks in PVSyst and internal explanations. Correctly measuring the site, correctly entering the conditions, and comparing results to make judgments are the basics of solar power generation simulations that are usable in practice.