5 Basic Items for Handling Sloped Roofs in the PVSyst Manual

Table of Contents

• Concepts to understand before working with pitched roofs in the PVSyst manual

• Basic item 1: Correctly organize the azimuth and tilt angle of the roof surface

• Basic Item 2: Confirm the installation area and module placement conditions

• Basic Item 3: Examine the impact of shadows from roof shape and surrounding obstacles

• Basic Item 4: Set temperature and ventilation conditions realistically

• Basic Item 5: Keep track of the numerical values to verify in the results report

• Input mistakes that commonly occur in pitched roof projects and how to prevent them

• How to proceed when using the PVSyst manual in practical work

• Summary

Concepts to Understand Before Working with Sloped Roofs in the PVSyst Manual

Many people who consult the PVSyst manual have concerns such as wanting to perform solar power generation simulations correctly, wanting to know how detailed the design conditions should be entered, and wanting to organize how to interpret the losses and energy output that appear in the reports. In particular, for sloped-roof projects, unlike ground-mounted or flat-roof installations, there are many factors that influence simulation results, such as the roof’s angle, azimuth, how the roof surfaces are divided, shadows from ridges and adjacent buildings, and temperature conditions caused by roofing materials.

Sloped roofs may appear simple at first glance. If you are merely placing panels on a south-facing roof, it might seem sufficient to enter the azimuth and tilt angles. However, in practice roof surfaces are often divided into multiple planes, combine south-facing with east- and west-facing surfaces, and have obstacles on the roof such as ridge vents, chimneys, skylights, antennas, and parapets. Furthermore, when there are neighboring houses, trees, utility poles, or mountain shadows, not only the annual energy production but also the time-of-day generation patterns can differ.

When using the PVSyst manual, it is important not just to follow the on‑screen procedures but to understand why each field is entered and which numerical values have a strong effect on the results. For example, changing the roof tilt slightly may not produce a large difference in some cases, but entering the azimuth angle incorrectly can cause the estimated annual energy production to be significantly off. Also, oversimplifying the treatment of shading can lead to an overestimation of energy production.

For inclined roof simulations, it is important to carefully proceed through the steps of site survey, drawing review, organizing input conditions, reflecting them in PVSyst, and checking the results report. The PVSyst manual is useful as a resource for confirming operational procedures, but the validity of the assumptions entered must be judged by the user. In other words, a correct simulation is not determined solely by the software’s capabilities, but by how accurately site conditions are interpreted and translated into an appropriate model.

In this article, we organize five basic items to keep in mind when handling pitched roofs in the PVSyst manual, and clearly explain points that commonly cause confusion in practice. For those who are about to consider solar PV projects for residential, retail, factory, and warehouse roofs, this provides an overview of the approach from initial setup through report review.

Basic Item 1: Correctly organize the azimuth and tilt angles of roof surfaces

When handling sloped roofs in PVSyst, the basic items you should check first are the roof surface's azimuth angle and tilt angle. The azimuth angle indicates which direction the modules are facing. The tilt angle indicates how much the roof surface is inclined relative to the horizontal plane. These two determine the angle at which sunlight strikes the modules and are therefore fundamental to power generation simulation.

For sloped roofs, the roof pitch may be shown on the architectural drawings as dimensions or pitch notations. For example, if the roof pitch is indicated on a dimensioned drawing, convert it to an angle and use it as an input condition. On the other hand, when confirming it solely by an on-site survey, verify it by combining a smartphone inclinometer, a laser distance meter, roof drawings, construction photos, and so on. The important thing is not to judge it by a rough, intuitive "about this much," but to organize it in a way that preserves the basis for the input.

Care must also be taken with the azimuth. Even if the front of a house or building appears to face south, it may actually be tilted toward the southeast or southwest. If you enter an orientation without confirming that map north, drawing north, and the on-site verified orientation all match, this can lead to discrepancies between simulation results and reality. When entering the azimuth while referring to the PVSyst manual, check the software’s definition of azimuth and make sure it does not conflict with the notation in your company’s design documents or on-site survey records.

Also, on pitched roofs it is not uncommon for a single building to have multiple roof planes. For a gable roof there are south- and north-facing planes, and for a hip roof there are several planes close to south, east, west, and north. Even with a mono-pitched roof, depending on the building’s orientation it may not be ideally south-facing. When placing modules on multiple planes, organize the azimuth and tilt angle for each plane, and determine which planes can be treated as the same condition and which should be handled separately.

When you force all roof surfaces to be entered as a single average value, the result may not accurately reflect reality. For example, if you group the southeast and southwest surfaces together as “south-facing,” differences in generation trends between morning and afternoon become difficult to see. That may be acceptable for a simple assessment that only looks at annual energy production, but when considering battery integration, self‑consumption, peak shaving, or time‑of‑use electricity usage, the generation profile for each surface becomes important.

When reading the PVSyst manual, it's important not to simply follow the input fields on the interface, but to consciously check how the azimuth and tilt angles are reflected in energy production. If the initial input conditions are correct, subsequent shadow analysis, loss settings, and report evaluation will proceed smoothly. Conversely, if there is an error at this stage, no matter how detailed the later settings are, the overall reliability of the simulation will be reduced.

Basic Item 2: Confirm the installation area and module placement conditions

Next, it is important to check how much of the pitched roof can be used for module placement. PVSyst can simulate power generation, but if you lay out modules over areas that cannot actually be installed, the output becomes merely theoretical numbers. On a pitched roof, the entire roof surface is not necessarily available for installation.

First, what you should check is the clearance from the roof perimeter. Depending on conditions such as eaves, verges, ridges, valleys, hip ridges, gutters, snow guards, and inspection walkways, there will be areas where modules cannot be placed. Considering building codes, construction standards, manufacturer guidelines, ease of maintenance and inspection, and safety, there are places that may look like they fit on the drawings but should actually be avoided. Before entering data into PVSyst, it is necessary to define the usable installation area on the design and construction drawings.

Next, check the orientation and arrangement of the modules. On pitched roofs, whether modules are placed vertically (portrait) or horizontally (landscape) along the roof surface affects the number of modules that can be installed and the wiring routes. If the module size does not match the roof dimensions, wasted space can occur at the edges. Also, if the roof surface is trapezoidal or triangular, a neat rectangular layout may not be possible. Ignoring these conditions and calculating capacity based only on area can lead to an overestimate of the actual installable capacity.

For sloped roofs, it is also necessary to check the structural conditions for each roof plane. Depending on the type of roofing material, the substrate, the positions of rafters and purlins, and the mounting hardware attachment conditions, there may be constraints on module layout. Because PVSyst itself is not a structural design software, it does not directly assess the adequacy of the roof’s strength or attachment methods. Therefore, even at the stage of evaluating energy production using the PVSyst manual, it is important not to confuse the range that is structurally feasible for installation with the range that is advantageous for energy production.

In pitched-roof projects, maximizing capacity alone is not always the right approach. If you forcibly add modules in heavily shaded areas, the installed capacity may increase but generation efficiency can suffer. In particular, adding even a small number of modules near roof edges, close to the ridge, around chimneys or antennas, or where shadows from neighboring roofs fall can affect the generation characteristics of the entire system. Depending on module series connections and string configuration, a localized shadow can sometimes lead to a wide-area drop in output.

When modeling pitched roofs in PVSyst, it is important not to simply input the panel capacity, but to organize which roof surfaces that capacity is on, their orientations, and what constraints apply. Carefully documenting the installation conditions makes subsequent loss assessment and report explanations more persuasive. It also makes it easier to clearly explain to clients or internal stakeholders why that capacity was chosen and why some roof surfaces were not used.

Basic Item 3: Evaluating the Impact of Shadows from Roof Shape and Surrounding Obstacles

In PVSyst simulations of pitched roofs, the way shading is handled is particularly prone to producing differences. Even if the roof azimuth and tilt angle are appropriate, overlooking the effects of shading tends to lead to an overestimation of energy production. Shadows do not occur in the same way throughout the year. In winter, when the sun’s altitude is low, during morning and evening hours, in locations where adjacent buildings are close, and where there are mountains or trees, the way shading occurs changes greatly depending on the season and time of day.

On pitched roofs, shadows to check include near-field shadows caused by on-roof obstructions and far-field shadows caused by the surrounding environment. Near-field shadows include chimneys, vents, skylights, antennas, ridge ornaments, parapets, adjacent roof planes, stepped roofs, and rooftop equipment. Even small obstructions can cast strong shadows at certain times if they are close to the modules. Especially in winter, when the sun's altitude is low, shadows can extend much longer than one might expect.

On the other hand, distant shading sources include neighboring houses, buildings, trees, utility poles, mountains, and terrain undulations. In densely populated residential areas, shadows from adjacent buildings are an issue; in mountainous areas, terrain can limit sunlight hours; and in factories and warehouses, shadows from adjacent blocks or equipment supports tend to be problematic. When consulting the PVSyst manual, you need to judge—based on the project's objectives—not only the shading analysis screens and input procedures but also how accurately the shapes should be modeled.

It is not necessary to create detailed 3D models for every project. In the initial assessment phase, roof orientation, tilt, approximate capacity, and simplified shading conditions may be sufficient. However, for investment decisions, proposal preparation, documents for financial institutions, explanations that approach guaranteed energy production, and projects that include complex roof shapes, overlooking shading can be a major risk. When using PVSyst’s shading analysis function, it is important to decide in advance which obstacles to model and which to simplify.

On pitched roofs, roof planes can cast shadows on one another. For example, on hip roofs or staggered roofs, at certain times of day an adjacent roof plane's shadow may fall on modules. In buildings with multiple closely spaced blocks, even a south-facing roof can be shaded by an adjacent block. Because these conditions can be easily overlooked from plan views alone, it's advisable to check them by combining elevation drawings, section drawings, site photographs, and aerial photographs.

When dealing with shading, what matters is not just the power generation figures but being able to explain the reasons for any losses. If a report shows a certain amount of shading loss, you need to determine whether the cause is a neighboring house, rooftop equipment, or the terrain; otherwise you cannot use that information to improve the design. Conversely, even if shading loss appears to be very small, it may simply mean that important obstacles were not entered.

To make practical use of the PVSyst manual, it is important to regard shadow analysis not as an "operational interface" but as the task of quantifying on-site risks. For pitched-roof projects, assess the plausibility of the projected energy yield by comprehensively considering roof surface usage, module placement, string configuration, and the times when shadows occur.

Basic Item 4: Set realistic temperature and ventilation conditions

Temperature conditions are also an important basic factor when considering power generation from sloped roofs. Solar modules will generate more power when solar irradiance is strong, but their output decreases as module temperature rises. Therefore, even under the same irradiance conditions, differences in roof ventilation and installation methods can lead to differences in power generation. When consulting the PVSyst manual, it is important to select conditions that closely match the actual situation of sloped roofs rather than merely entering settings related to temperature losses as a formality.

When installing modules on a pitched roof, it is common for there to be a certain gap between the roofing material and the modules. If this space is sufficiently maintained and allows for good airflow, heat on the back side of the modules can dissipate more easily. Conversely, when modules are installed close to the roof surface or when the roof shape inhibits ventilation, module temperatures are more likely to rise. It is also necessary to consider that different roofing materials—such as metal roofs, slate roofs, and tile roofs—retain heat differently and require different installation methods.

In projects that place particular emphasis on generation in high-temperature regions or during the summer, how temperature-related losses are handled affects the results. Even if differences do not appear large when looking only at annual generation, output reductions can become pronounced during peak hours in midsummer. For self-consumption projects, because the overlap between daytime electricity demand and generation output is important, it is essential not to underestimate the output decline caused by temperature.

In PVSyst, you can set conditions related to module temperature and reflect temperature-related losses. However, the input values depend on site conditions. With reference to the general guidance in the manual, clarify whether the installation is rooftop-mounted or ground-mounted, whether there is sufficient ventilation, and whether it is close to the roof. If you are unsure, it is easier to explain by simulating not only optimistic conditions but also somewhat conservative conditions and comparing the differences in energy yield.

Also, on sloped roofs the way wind moves varies with the surrounding environment. In densely built residential areas wind may not flow through easily, while on high ground or along the coast wind can pass strongly. However, it is risky to simply assume that stronger winds will always lead to favorable temperature conditions. From the perspectives of wind loads and construction safety, separate considerations are required, and these need to be treated independently from the temperature conditions used in power generation simulations.

Temperature conditions are not as visually apparent as shading analysis. For that reason, they are sometimes overlooked in the inputs. However, in PVSyst result reports, temperature losses clearly appear as a factor reducing energy yield. If the installation conditions of a pitched roof are estimated more favorably than they actually are, the energy yield may be overestimated; conversely, if overly strict conditions are applied, the yield may be assessed lower than it actually is.

In practice, there are conditions that have not been finalized during the design phase. When elements such as the type of roof fittings, module installation height, wiring routes, or the ventilation condition of the roof surface are undecided, it is important to perform simulations after clearly stating the assumed conditions. By referring to the PVSyst manual, understanding the meaning of the input values, and documenting the conditions in a way that can be explained later, it becomes easier to accommodate design changes and estimate adjustments.

Basic Item 5: Identify the key figures to check in the results report

Simulating a sloped roof doesn't end with simply entering the inputs. The value of PVSyst lies in the ability to review the calculation results and judge the validity of the estimated energy production and losses. When using the PVSyst manual, it's important not only to know how to configure the settings but also to understand which parts of the results report you should check.

The first thing to check is the annual energy production. This is the figure most often examined in proposal documents and feasibility assessments. However, annual generation alone cannot determine whether the simulation is valid. To understand why the generation reached that level, you need to review solar irradiance, system capacity, performance ratio, the breakdown of losses, and monthly generation together.

Next important is the performance ratio and the breakdown of various losses. In sloped-roof projects, incidence conditions due to azimuth and tilt, shading losses, temperature losses, wiring losses, inverter losses, and so on affect power generation. If any one of the losses is extremely large, it is necessary to review the input conditions and design conditions. For example, if shading losses are large, there is room to reconsider obstacle modeling, module layout, and string design. If temperature losses are large, it is necessary to check the installation method and ventilation conditions.

Monthly power generation is also important. On sloped roofs, roof orientation and surrounding shading affect seasonal generation patterns. Roofs that face close to south tend to be more stable throughout the year, but using east- or west-facing surfaces changes the distribution of generation toward morning or evening. Using a north-leaning surface generally reduces annual generation, and in some cases it may be necessary to decide to exclude it from installation. Checking monthly generation lets you identify imbalances that are not visible from the annual total alone.

In self-consumption projects, the generation profile by time of day is also important. For example, at facilities where electricity demand is high in the morning, east-facing generation can be advantageous. For facilities with high afternoon demand, west-facing generation may be more suitable. The layout that maximizes annual generation does not necessarily match the layout that fits demand. When interpreting PVSyst results, it is important to clarify whether the project's goal is prioritizing power sales, prioritizing self-consumption, or integrating battery storage, and to evaluate accordingly.

Also, the figures displayed in the report are influenced by the quality of the input conditions. If accurate roof surface information, appropriate meteorological data, reasonable loss settings, and realistic shading conditions are not all in place, even an attractive-looking report will not be reliable. While consulting the PVSyst manual to understand the meaning of the result screens, check whether any values deviate from what you expected.

In practice, you should be particularly careful not to take the numbers in a report at face value. If the estimated power generation is high, you need to check whether the input assumptions are overly optimistic. If the estimated generation is low, review whether excessively strict shading conditions or loss assumptions have been applied. A simulation does not automatically produce the correct answer; it returns results based on the input conditions. That is why it is important to be able to explain the relationship between the inputs and the results.

Common Input Mistakes in Pitched Roof Projects and How to Prevent Them

A common mistake when entering data into PVSyst for pitched roofs is confusing the azimuth direction. If the north on the drawings, true north, the software’s azimuth definition, and the azimuth measured on site are mixed, the southeast and southwest faces can be treated in reverse. This mistake can be hard to notice from annual energy production alone, but it shows up as an unnatural result when looking at generation trends by time of day. Before inputting data, it is important to standardize the azimuth reference and verify it against drawings and site photos.

The next most common mistake is errors in converting roof pitch. On architectural drawings, the pitch is sometimes expressed as a dimensional ratio rather than as an angle. If that value is entered directly as an angle, the resulting slope condition will differ from the actual one. When converting roof pitch to an angle, standardize the conversion method in-house and make it possible to check.

Overestimating the number of modules that can be installed is also a common mistake. If you estimate module capacity based only on roof area, you can overlook areas where modules cannot actually be installed due to separation distances, obstacles, maintenance clearances, mounting hardware, and roof-edge constraints. This is especially true for houses and small buildings, where a difference of just a few modules can significantly affect capacity and energy production, so it is necessary to specifically match the roof dimensions to the module dimensions.

Insufficient shading input is also a major problem. Omitting small rooftop equipment or underestimating the height of neighboring houses can cause predicted energy output to be higher than actual. Conversely, entering overly strict data for distant objects that have little to no impact can make the predicted energy output too low. For shading conditions, it is important to prioritize and organize the items that affect energy output based on on-site photos, drawings, and surrounding maps.

Care must be taken to avoid duplicate loss settings. If a loss is also accounted for under another item, the estimated energy production will be excessively low. For example, setting wiring losses, mismatch losses, soiling, or temperature conditions too conservatively can make a project assessment unduly strict. Check the PVSyst manual to understand what each loss represents and make sure you are not counting the same risk twice.

To prevent input errors, it is effective not to have the task completed solely by the PVSyst operator, but to have the site surveyor, design engineer, construction manager, and sales staff share the same assumptions. Power generation simulation is not merely software operation; it is the work of converting site conditions into a numerical model. Creating a pre-input conditions sheet that lists orientation, tilt, roof area, number of panels to be installed, shading conditions, loss conditions, and assumptions about meteorological data makes later verification easier.

How to Use the PVSyst Manual in Practice

When using the PVSyst manual in practice, you don't need to master all of its features from the outset. For pitched-roof projects, it's realistic to first correctly input the basic conditions that strongly affect energy production, and then progressively refine the detailed settings as needed.

In the initial stage, organize the building location, meteorological data, the azimuth and tilt of the roof surfaces, installed capacity, and the basic specifications of the modules and inverters. At this point, the goal is to grasp the project's rough power generation potential rather than to fine-tune the accuracy of the simulation results. If multiple roof surfaces are used, determine whether conditions should be separated for each surface or can be treated together.

In the next phase, we check shading conditions and loss assumptions. While reviewing site photos and drawings, we identify obstacles that could affect power generation and model them as needed. At the same time, we verify assumptions such as temperature loss, wiring loss, soiling, and mismatch. The important point here is not to pursue precision for its own sake, but to align the conditions to the level of accuracy appropriate for the project's purpose. The required accuracy differs for initial proposals, detailed design, and investment decisions.

When verifying results, check the annual energy production, monthly energy production, breakdown of losses, and the performance ratio. If production is lower than expected, confirm whether orientation, shading, temperature conditions, or system configuration might be the cause. If production is higher than expected, also verify that the input assumptions are not overly optimistic. It is important to read the PVSyst report not as a list of numbers but as the basis for design decisions.

To continue using the PVSyst manual in practice, it is also useful to record the input conditions and results for each project. Once you can compare with past projects, it becomes easier to assess how much energy generation is likely under similar roof conditions and which losses tend to be larger. In particular, for residential roofs, factory roofs, warehouse roofs, and store roofs, roof shape, ventilation conditions, and the way shadows fall differ, so experience by project type is helpful.

Also, when presenting PVSyst results to external parties, it is important to explain the underlying assumptions together with the figures in the report. The energy production is calculated based on meteorological data, roof conditions, installed capacity, shading, losses, and equipment specifications. If the assumptions change, the results will change as well. Presenting only the energy production without explaining this point makes misunderstandings more likely when design changes or construction conditions are altered later.

The PVSyst manual serves not only as a reference for checking operating procedures but also as a guide to understanding the meaning of input fields. In pitched-roof projects, it is more important to correctly interpret site conditions and be able to explain the results than to rush through on-screen data entry. By grasping the five basic items, even first-time PVSyst users will be less likely to be unsure where to start checking.

Summary

When handling pitched roofs in the PVSyst manual, it is important to organize, in order, the azimuth, tilt angle, available installation area, shading conditions, temperature conditions, and how to interpret the results report. Pitched roofs are more susceptible to the influence of building geometry than ground-mounted systems or flat roofs, and the differences in conditions between roof surfaces are larger. Therefore, simply entering the capacity will not yield generation estimates that are close to reality.

The first things to check are the azimuth and tilt angles of the roof surfaces. These are basic conditions for power generation, and incorrect inputs will reduce the reliability of the entire simulation. If there are multiple roof surfaces, organize the orientation and angle of each and decide whether to treat them together or separately.

Next, verify the available installation area and the conditions for module layout. Do not determine capacity based solely on roof area; it is important to consider clearances, obstacles, access for inspection and maintenance, roofing material, and installation conditions. If you include areas where installation is actually not possible, the estimated power generation may be overstated.

Shading effects are also an essential check for pitched roofs. Shadows from rooftop equipment, adjacent buildings, trees, and terrain can affect energy production depending on the season and time of day. When using PVSyst’s shading analysis, it is practical to prioritize and organize the elements that affect energy production rather than reproducing everything in detail.

Don't forget temperature and ventilation conditions. On pitched roofs, temperature losses vary with the airflow around the roofing material and behind the modules. Especially in hot regions and for self-consumption projects, you need to properly account for output reductions caused by temperature.

Finally, in the results report, check not only the annual energy production but also the monthly energy production, the performance ratio, and the breakdown of losses. It is important not only to note whether the figures are high or low, but to be able to explain why those results occurred. The purpose of using the PVSyst manual is not simply to learn how to operate the software, but to correctly reflect site conditions and to be able to explain the basis for the energy production.

In pitched-roof solar PV projects, the cumulative effect of many small conditions appears in the simulation results. If you carefully check the five basic items, you will be less likely to get confused when entering data into PVSyst, and the persuasiveness of your proposals and design reviews will increase. To use energy yield simulations effectively in practice, it is important to connect and understand both the manual’s procedures and the on-site conditions.