How to Bring PVSyst Closer to Detailed Design｜7 Tips to Improve Accuracy

Table of Contents

• Approach to bringing PVSyst simulations closer to detailed design

• Point 1: Carefully check the meteorological data and site conditions

• Point 2: Match azimuth, tilt angle, and racking conditions to actual conditions

• Point 3: Set module and PCS configurations realistically

• Point 4: Reflect shading effects as concretely as possible

• Point 5: Do not leave loss conditions as a single bulk setting

• Point 6: Confirm string conditions that are close to the electrical design

• Point 7: Use on-site survey data to refine design conditions

• Cautions when using PVSyst results for detailed design

• Summary: Simulation accuracy is determined by the quality of on-site information

Concepts for Bringing PVSyst Closer to Detailed Design

To carry out analyses in PVSyst that approach detailed design, it is important to take a step beyond the view of "software that calculates power generation" and treat it as an "analysis environment for verifying the validity of design conditions." Power generation simulations return results based on the input conditions. In other words, if the conditions are approximate, the results will be approximate, and if the conditions are detailed, the results will approach a detailed analysis.

In practice, the information available at the early stage of a project is limited. Based on the site location, approximate capacity, expected number of modules, racking system, grid interconnection policy, and so on, we often first produce a preliminary design. At this stage, the main purpose is to obtain an indication of power generation and to assess project viability.

However, as the project progresses, topographic surveys, layout drawings, equipment specifications, electrical design, shading factors, surrounding obstructions, maintenance access routes, and construction constraints become more concrete. PVSyst input conditions must also be updated in line with this progress.

When approaching detailed design, the important thing is not to make every item more detailed. Identify the items that have a significant impact on power generation and design decisions, and spend effort on those. For example, deviations in azimuth and tilt angles, shading settings, temperature conditions, wiring losses, equipment selection, string configuration, and the slope of the terrain are elements that tend to affect the results. On the other hand, overly detailing conditions that have little impact can only increase the time spent on analysis and may not lead to meaningful design decisions.

When using PVSyst results for detailed design, it is important not to treat the results themselves as absolute values, but to look at the differences caused by changes in conditions. For example, compare how the annual electricity generation and the breakdown of losses change when you alter the tilt angle, adopt an east-west orientation, change the overloading ratio, or add shading effects. Through such comparisons, you can identify which conditions have the greatest impact on a project's profitability and design quality.

Bringing PVSyst closer to the detailed design is not simply a matter of data entry but a process of validating the design conditions. Linking site information, equipment data, electrical design, and construction conditions, and reducing the gap between the simulation assumptions and the actual system conditions, is the basic approach to improving accuracy.

Point 1: Carefully verify meteorological data and local site conditions

The key items to check first in PVSyst are the meteorological data and the site conditions. In solar PV simulations, solar irradiance, temperature, wind speed, solar altitude, azimuth, and latitude and longitude all have a major impact on energy production. No matter how finely you configure the modules and the PCS, if the underlying meteorological conditions deviate significantly from reality, the overall reliability of the results will be reduced.

In practice, there are often no meteorological observation points that exactly match the target site, so data from nearby locations or wide-area meteorological data are used. In such cases, you need to consider not only simply choosing the nearest location, but also elevation, whether it is coastal or inland, whether it is mountainous or a plain, the presence or absence of snow cover, and the tendency for fog or cloud formation. Even if the distance is short, differences in topography or climatic conditions can alter solar radiation and temperature trends.

To get closer to a detailed design in PVSyst, first set the project's site latitude and longitude correctly and verify the validity of the meteorological data to be used. If multiple candidate meteorological datasets are available, compare annual solar radiation, monthly solar radiation, average temperature, and seasonal variations, and select the one that most closely reflects the actual conditions at the site. Depending on the project, you may use solar radiation data obtained on site or meteorological data specified by the client. Even in those cases, it is important to check the data period, the presence of missing values, and whether it can be used as a representative year.

A particular point to be careful about is continuing to use the meteorological data employed at the preliminary estimate stage unchanged through to the detailed study. Even if there are no problems in the initial proposal, differences in solar irradiance conditions in studies closer to detailed design can affect evaluations of power generation and profitability. As the project progresses, it is desirable to review the basis for the meteorological data and keep it in a state that can be explained in documentation.

Also, for site conditions, check the elevation and the surrounding environment. In high-elevation areas, temperature conditions change and the tendency of temperature-related losses can be different. In snowy regions, winter power generation, soiling, and shading by snow must be considered separately. Along the coast, measures against salt damage and maintenance conditions become important and can affect the design itself. While not everything can be fully represented within PVSyst, at a minimum organizing the site conditions as assumptions for the energy yield simulation is the first step toward detailed design.

Point 2: Align Azimuth, Tilt Angle, and Mounting Conditions with On-site Conditions

The basic conditions that greatly affect power generation are azimuth, tilt angle, and mounting conditions. When using PVSyst, in the initial stage it is common to set the system to south-facing, a fixed tilt, and standard mounting conditions, but to bring the model closer to detailed design, inputs must reflect the actual layout plan.

Azimuth is the parameter that indicates which direction a solar panel faces. In general, south-facing orientations tend to produce more energy, but site shape, grading conditions, roads and fences, the arrangement of electrical equipment, maintenance access routes, and relationships with adjacent properties mean it is not always possible to orient panels due south. Even a small change in azimuth will alter the balance of generation between morning and afternoon and affect annual energy yield. When progressing toward detailed design, it is important to verify the actual angles on the layout drawing and reflect them in the PVSyst input values.

The tilt angle likewise affects both energy production and constructability. Increasing the tilt can be advantageous for winter solar gain, but it affects support structure height, row spacing, wind loading, shading, installation cost, and maintainability. Reducing the tilt can make it easier to increase installation density, but it may impact soiling, drainage, and generation at low solar elevations. Because PVSyst makes it easy to change the tilt angle, it is important to compare multiple cases and judge not only by energy production but also by land-use efficiency and shading losses.

For mounting structure conditions, the approach to setting them changes depending on whether the system is fixed or intended to allow tilt adjustment, and whether it is rooftop or ground-mounted. For rooftop installations, because they are constrained by the roof slope and orientation, conditions must be specified based on building drawings and on-site surveys. For ground-mounted installations, the finished ground surface after site development, row spacing, minimum ground clearance, mounting structure height, gaps between panels, and maintenance access all affect shading and layout.

To get closer to detailed design, rather than consolidating into a single azimuth or tilt angle on PVSyst, it is important to appropriately separate and evaluate each orientation and tilt when multiple ones are present. For example, if installing on the east and west sides of a roof, if the south and north sides have different tilt or shading conditions, or if only part of a site is arranged at a different angle, setting the conditions separately will yield results that more closely reflect reality.

Azimuth and tilt angles may seem like simple input fields, but they are crucial parameters that set the assumptions for the entire design. As a basic practice for improving accuracy, do not leave provisional settings from the rough estimate in place; update them to match the layout drawings and survey results.

Point 3: Set the module and PCS configuration realistically

To bring a PVSyst model closer to a detailed design, the configuration of modules and PCS must be set realistically. In energy yield simulations, module output, temperature characteristics, electrical characteristics, number of modules, PCS capacity, MPPT configuration, and the oversizing ratio all affect the results. In the initial stages it may be acceptable to study with provisional equipment, but as the design approaches the detailed phase it is important to review and update inputs to match the specifications actually planned for adoption.

First, you should check the modules' rated output and the number of modules. Even for the same system capacity, if the output per module differs, the required module count and string configuration will change. If the module count changes, the installation area, wiring, shading impacts, and how the modules pair with the PCS will also change. In PVSyst, it is preferable not to match capacity only, but to enter conditions that are close to the actual number of installed modules.

Next, check the temperature characteristics of the modules. Solar panels lose output as temperature rises. Therefore, even with the same irradiance, energy generation varies depending on ambient temperature and installation conditions. Module temperature assumptions change when ventilation on a roof is poor, when a ground-mounted installation has good airflow, or when the mounting height differs. Because PVSyst has settings for temperature losses, it is important to confirm that the conditions are not overly optimistic for the installation type.

When configuring the PCS, check the rated capacity, input voltage range, number of MPPTs, conversion efficiency, and oversizing ratio. The oversizing ratio is often used in designs where the DC-side module capacity is made larger than the PCS's AC capacity. Oversizing can increase annual energy yield, but under some conditions it can increase peak clipping. In PVSyst you can check the balance between the energy gain from oversizing and clipping losses. To move closer to a detailed design, you must verify the appropriateness not simply by raising the oversizing ratio but by considering the project's grid capacity, contract terms, generation curve, feed-in conditions, and self-consumption conditions.

Also, the number of PCS units and the connection configuration are also important. Even if only the total capacity is matched, if the actual number of PCS units or the MPPT assignment differs, the impact of partial shading and orientation differences can change. For example, combining arrays with different orientations into the same input can make mismatches more likely in actual operation. How finely to reproduce this in PVSyst depends on the project, but it is important to at least check whether major configuration differences affect the results.

The equipment configuration must be consistent not only for simulation but also with the drawings, single-line wiring diagrams, equipment specifications, and construction plans. If the conditions in PVSyst differ from those in the design documents, it becomes difficult to explain the power generation forecast. As you move closer to the detailed design stage, it is important to reconcile the design documents with the PVSyst input values and aim for no inconsistencies in capacity, number of modules, number of PCS units, number of strings, and input ranges.

Point 4: Reflect the effects of shadows as concretely as possible

In PVSyst, shadow configuration is extremely important for improving the accuracy of energy yield. In photovoltaic installations, shadows are caused by surrounding buildings, trees, utility poles, fences, mountains, adjacent panel rows, roof steps, and equipment. Shadows do not simply reduce irradiance; they can affect generation at the string level and can significantly increase reductions in energy production.

At the conceptual stage, shading may be ignored or treated as a simple loss factor. However, as the design approaches the detailed stage, the causes of shading should be organized as specifically as possible, and the extent to which they can be represented in PVSyst should be verified. In particular, shading that occurs at low solar angles in the morning and evening, shadows that extend long in winter, self-shading caused by inter-row spacing, and shadows from rooftop equipment are elements that are likely to affect annual energy production.

For ground-mounted installations, self-shading—where the front row of panels casts shadows on the rear rows—is an important consideration. Increasing the tilt angle can lengthen shadows in winter and during mornings and evenings. Widening row spacing reduces shading but may decrease the capacity that can be installed on the same site. Conversely, narrowing row spacing increases capacity but can raise losses due to shading. In PVSyst, you can vary these layout parameters and assess the balance between energy production and shading losses.

For rooftop installations, rooftop equipment, upstands/parapets, lightning protection equipment, adjacent buildings, railings, roof penthouses/towers, and similar items can cause shading. These may not be fully captured by drawings alone, so on-site inspection, photographs, and survey data are important. Especially for existing buildings, as-built conditions can differ from the design drawings, so it is advisable to verify the positions and heights of obstacles on site and, where necessary, reflect them in the PVSyst shading model.

In shadow analysis, rather than simply checking whether shadows are present or not, you confirm when, over what area, and to what extent they occur. The impact on annual energy production varies depending on the time of day and season when shadows occur. A slight shadow in the early morning of midsummer and widespread shading during the generation hours in winter have very different effects on energy production. In PVSyst results, it is important to determine whether the shading is acceptable for the design by examining not only the percentage of shading losses but also monthly and hourly trends.

Also, making the shading settings excessively detailed significantly increases the workload. Rather than reproducing every small obstacle, it is more practical to prioritize entering the primary shading factors that are likely to affect power generation. The purpose of approximating detailed design is not to create a visually precise model, but to appropriately assess the losses needed for design decisions.

Point 5: Don't configure loss conditions in bulk

Loss conditions have a significant impact on PVSyst results. In photovoltaic power systems, various losses occur, such as temperature losses, wiring losses, mismatch losses, soiling losses, shading losses, PCS losses, degradation due to aging, and downtime losses. To approach detailed design, it is important not to treat these as a single, aggregated safety margin but to consider each item individually as much as possible.

Temperature losses are influenced by the installation environment and ventilation conditions. Module temperature rises differ between ground-mounted installations with good airflow and installations located close to a roof. Underestimating temperature losses leads to overly optimistic power generation estimates. Temperature conditions should be checked carefully, especially in hot regions and rooftop projects.

Wiring losses vary depending on cable length, current, voltage, cable cross-sectional area, and the wiring route. During the estimation stage they are often set to standard values, but as the design approaches the detailed phase, the actual equipment layout and the distances to combiner boxes, PCS, and substation/transformer equipment become clear. In projects with long wiring routes or distributed layouts, the impact of wiring losses can be significant and cannot be ignored. It is important to confirm that the settings in PVSyst are consistent with the voltage drop and cable planning in the electrical design.

Mismatch losses are caused by differences in module performance, shading, soiling, temperature differences, orientation differences, and so on. Because not all modules generate power under the same conditions, some degree of mismatch occurs in real installations. When combining arrays with different orientations or tilts, when partial shading is present, or when string lengths differ, the handling of mismatch must be considered carefully.

Soiling losses vary depending on the region, installation environment, and maintenance schedule. In areas with a lot of wind-blown dust, sites close to agricultural land or roads, locations affected by bird fouling, or regions with low rainfall, losses due to soiling can be large. Conversely, when there is sufficient tilt and regular rainfall or cleaning can be expected, the way losses are considered changes. When setting soiling losses in PVSyst, it is desirable not to use the default values as-is, but to configure them based on the local environment and maintenance policy.

Conditions related to downtime losses and availability are also important. Power generation equipment does not always operate ideally. Inspections, equipment shutdowns, communication failures, grid-side constraints, output curtailment, natural disasters, and other factors can lead to periods when generation is not possible. Even if PVSyst cannot directly reproduce everything in detail, for commercial feasibility assessments and reporting materials it is necessary to separate and organize the scope of the energy yield simulation and the operational risks that should be considered separately.

Loss assumptions are not convenient figures for adjusting power output; they represent the premises for design and operation. To move closer to detailed design, it is important to provide a basis for each loss and ensure that the explanations connect to design documentation and actual site conditions.

Point 6: Check string conditions close to the electrical design

When conducting a study in PVSyst that approaches detailed design, checking the string configuration is indispensable. String design is closely related to the number of modules, voltage, current, the PCS input range, MPPT configuration, and temperature conditions. Even if the capacity appears to match in the energy yield simulation, it cannot be used for detailed design considerations unless it is valid as an actual electrical design.

The first thing to check is the number of modules in series per string. The open-circuit voltage of solar modules rises at low temperatures, and the operating voltage falls at high temperatures. Therefore, the system must be designed so that it does not exceed the PCS maximum input voltage in cold periods and stays within the MPPT operating range in hot periods. Since PVSyst can check voltages taking temperature conditions into account, it is important not to judge solely by the voltage at standard conditions.

Next, verify the number of parallel strings and their assignment to the MPPTs. When multiple strings are connected to the same MPPT, large differences in the number of modules per string, orientation, tilt, or shading conditions can affect power generation efficiency. In detailed design, it is fundamental to make the conditions of strings connected to the same MPPT as uniform as possible. In PVSyst, you also need to set up the model with attention to how arrays with different conditions are handled.

In addition, the string configuration is also related to the effects of shading. The impact on power output varies depending on whether the partially shaded area is concentrated on a particular string or dispersed across multiple strings. By cross-referencing the layout diagram with the string diagram and confirming the connection configuration of areas prone to shading, a more realistic assessment becomes possible.

When using PVSyst results as working documentation, also check that the number of strings in the simulation matches the number of strings on the single-line wiring diagram and construction drawings. Even if only the system capacity is matched, differences from the actual string configuration can change losses and PCS operating conditions. Especially during the detailed design stage, it is important to verify the consistency among PVSyst, the layout, the single-line wiring diagram, and the equipment specifications.

Reflecting string conditions that are close to the electrical design makes PVSyst useful not only for simple energy-yield calculations but also for validating the design. Although entering the data requires effort, checking the string conditions is essential to avoid rework and insufficient explanations in later stages.

Point 7: Use on-site survey data to finalize design conditions

The final critical point for bringing a PVSyst model closer to a detailed design is the use of on-site survey data. In photovoltaic (PV) system design, there are many site conditions that cannot be captured by desk drawings or maps alone. Ground slope, level differences or steps, slope faces, existing structures, trees, surrounding buildings, drainage paths, elevation differences relative to roads, and the locations of rooftop equipment all directly affect energy yield and constructability.

Especially for ground-mounted installations, terrain conditions have a major impact on layout and shading. It is rare for a site to be completely flat; in practice there are gentle slopes and local elevation differences. If the heights of the rows differ, that will affect self-shading, racking height, earthworks volume, and drainage planning. How closely to reproduce the terrain in PVSyst depends on the project, but at minimum, as a basis for layout and shading studies, it is important to have accurate terrain information.

Even on rooftop projects, on-site surveying is important. The roof’s slope, orientation, level differences, equipment foundations, piping, handrails, upstands, lightning protection equipment, and other features may differ from the drawings alone. If you set shadows and layouts in PVSyst without verifying on-site dimensions and positions, you may end up with conditions that differ from the actual construction. This is especially true for existing buildings, where renovations or added equipment can cause the drawings and the current conditions not to match.

By utilizing on-site survey data, you can improve the accuracy of the azimuth, tilt angle, shading factors, and layout conditions entered into PVSyst. For example, based on the coordinates and elevation information obtained from surveys, you can verify the positions and heights of obstacles and model structures that cause shading. In addition, by accurately identifying site boundaries, access ways, and equipment locations that serve as references for panel layout, you can reduce the discrepancy between desktop studies and construction plans.

What's important here is that improving PVSyst's accuracy does not conclude within the software alone. Simulation software calculates based on the input conditions. Therefore, if the accuracy of on-site condition acquisition is low, no matter how finely you configure the settings, there will be limits to the reliability of the results. Conversely, if accurate location and elevation information can be obtained through on-site surveying, it becomes easier to provide a sound basis for the condition settings in PVSyst.

In recent years, there has been a growing trend to acquire high-precision location information on site and combine it with photographs, point clouds, and positioning data to apply to design. In the design of solar power generation facilities, it is important not only to calculate power generation but to consider the entire workflow—from understanding current conditions and layout planning to construction verification and as-built management. To obtain PVSyst results close to detailed design, how accurately and efficiently on-site data can be collected is a major key.

Precautions when using PVSyst results for detailed design

Even if you set conditions in PVSyst in great detail, you should avoid treating the results as definitive values for the detailed design. Simulations are merely predictions based on assumptions. Actual power generation will vary due to year-to-year weather differences, equipment condition, maintenance status, output curtailment, failures, snow accumulation, soiling, changes in the surrounding environment, and other factors. Entering detailed inputs does not fully guarantee future power generation.

In practical work, what matters is not only the numerical results but also making the assumptions clear. Organize which meteorological data were used, what the azimuth and tilt angles were based on, how far shading was accounted for, which approach was used to set loss conditions, and which specifications the equipment configuration is based on. This makes it easier to explain during internal reviews, to the client, in materials for financial institutions, and in discussions with contractors.

Also, when reviewing PVSyst results, it is important not to judge based solely on the annual energy production. Check the loss diagram, monthly energy production, PR, shading losses, temperature losses, PCS losses, clipping losses, etc., and identify where the energy production is being reduced. Even if the annual energy production is lower than expected, the design countermeasures differ depending on whether the cause is shading, temperature, peak clipping due to oversizing, or wiring losses.

Comparing multiple cases is also effective. Create cases with different tilt angles, different row spacing, different PCS capacities, added shading, or more conservative loss assumptions, and compare the differences in energy production and losses. Examining these differences makes it easier to explain the effects and risks of design changes. When using this approach for work closer to detailed design, it is important to assess sensitivity to changes in conditions rather than relying on the result of a single case.

Furthermore, attention must be paid to the consistency between PVSyst settings and other design documents. The layout drawing shows a changed number of modules, yet PVSyst still reflects the old count. The single-line wiring diagram shows the number of PCS units was changed, but the simulation still uses the previous configuration. An obstruction was found during the on-site inspection, yet it has not been reflected in the shading settings. Such inconsistencies frequently occur in practice. It is important to update and manage PVSyst conditions each time the project progresses.

Bringing PVSyst closer to detailed design is not about making the simulation look more complex. It means reflecting the conditions required for design decisions and being able to explain the rationale. Having the result figures, input conditions, design documents, and on-site information linked together leads to simulations that are trusted in practice.

Summary: Simulation accuracy is determined by the quality of on-site information

To bring PVSyst simulations closer to detailed design, it is important to stepwise scrutinize meteorological data, azimuth, tilt angle, racking conditions, equipment configuration, shading, losses, string conditions, and on-site survey data. While approximate conditions may be sufficient at the initial proposal stage, if input conditions are not updated to match the actual design as the project progresses, the gap between simulation results and the installed system will grow.

What's especially important is not to try to improve accuracy solely within PVSyst. The accuracy of power generation simulations is largely determined by the quality of site information. If the exact location, orientation, height, obstacles, terrain, and equipment layout are known, the conditions to input into PVSyst can be specified concretely. Conversely, if site conditions remain ambiguous, no matter how detailed the inputs are, it will be difficult to obtain results that closely match reality.

When conducting studies that approach the level of detailed design, it is effective to first accurately ascertain the on-site conditions and then use that information to configure the conditions in PVSyst. By combining layout drawings and electrical designs with as-built surveys, photographs, point clouds, and coordinate data, you can more concretely confirm factors such as shading, elevation differences, and areas available for installation. This makes it easier to make design decisions that consider not only power generation forecasts but also constructability and maintainability.

As a means to streamline the acquisition of on-site information, you can utilize LRTK, an iPhone-mounted GNSS high-precision positioning device. By using LRTK, you can obtain high-precision positional information in the field and combine it with photos and point cloud data to more easily advance the site assessment necessary for photovoltaic system design studies. If you can record site boundaries, planned racking locations, obstacles, rooftop equipment, and surrounding structures with coordinates, it will be easier to apply that data to condition settings and design reviews in PVSyst.

When deepening your use of PVSyst, it's important not only to learn how to operate the software. You must accurately measure the site, clarify the design conditions, and reflect those conditions in the simulation. By combining high-precision positioning tools like LRTK, it becomes easier to move from preliminary assessments to analyses approaching detailed design, which helps improve the design quality of solar PV systems.