7 Revisions to Improve Design Accuracy in the PVSyst Manual

Table of Contents

• The purpose of reading the PVSyst manual is not just to check the operating procedures.

• Review 1 to Improve Design Accuracy: Confirm the Assumptions of Meteorological Data

• Review 2 to Improve Design Accuracy: Align orientation, tilt, and installation conditions with on-site conditions

• Review 3 to improve design accuracy: Reconfirm the specification inputs for modules and PCS

• Review 4 for Improving Design Accuracy: Reevaluate String Design and Voltage Conditions

• Review 5 to improve design accuracy: Clarify the handling of near shadows, distant terrain, and obstacles

• Review 6 to improve design accuracy: Adjust loss settings for each project

• Review 7 to Improve Design Accuracy: Standardize the Reading of Result Reports

• Tips for incorporating the PVSyst manual into internal operations

• To improve design accuracy, it is important to document the rationale for input values.

The purpose of reading the PVSyst manual is not just to review the operating procedures

Many people searching for the PVSyst manual want to check how to operate the interface and what the input fields mean. Practical questions—such as which menu to use to set meteorological data, where to select modules and PCS, and on which screen to enter near shading—are unavoidable when carrying out design work.

However, if you want to leverage the PVSyst manual to improve design accuracy, simply following the procedures is not enough. In photovoltaic system simulations, small changes in input values can change annual energy production, PR, loss rates, monthly results, and behavior at peak times. Even if calculations appear to complete the same way on screen, leaving the assumptions vague means the results will not be reliable enough for use in proposals or design reviews.

In practice, the required level of accuracy changes depending on the stage: the rough estimate stage, the basic design stage, the detailed design stage, and the pre-construction verification stage. In initial studies it may be sufficient to grasp the general layout and output scale, but as you approach documentation for financial institutions, proposals for the client, EPC estimates, component selection, and construction planning, the basis and reproducibility of the input conditions become increasingly important.

When reading the PVSyst manual, it is important to be aware not only of which button to press but also what assumptions each input item represents, which information from site surveys and design drawings it corresponds to, and how much it influences the results. To improve design accuracy, you need to link and review the entire sequence of meteorological data, installation conditions, equipment specifications, electrical design, shading, losses, and result verification.

This article outlines seven key points to review in the PVSyst manual for practitioners who want to improve design accuracy. It is useful not only for people using PVSyst for the first time, but also for those who are already familiar with its operation yet have doubts about the validity of their analysis results.

Review 1 to Improve Design Accuracy: Verify the Assumptions of Meteorological Data

When improving design accuracy in PVSyst, the first thing to review is the meteorological data. In solar power simulations, meteorological conditions such as solar irradiance, ambient temperature, wind speed, snowfall, and humidity have a major impact on energy production. No matter how accurate the module and PCS settings are, if the assumptions in the meteorological data differ significantly from local conditions, the overall reliability of the results will decrease.

The PVSyst manual provides sections on importing and selecting meteorological data. What is important here is to understand which location the data represent, the period the statistics cover, and the approach used to convert horizontal-plane irradiance to tilted-plane irradiance. Even when using a nearby observation site, solar radiation and temperature trends can differ in mountainous areas, coastal areas, basins, snowy regions, and urban areas.

To improve design accuracy, it is necessary not simply to choose the nearest data but to compare candidate meteorological datasets and adopt the one that most closely matches the project's site conditions. For example, if a planned power plant site is on a mountainside, observation data from a plain may not adequately reflect morning and evening solar irradiance or the effects of fog. In coastal areas, cloud cover and salt-corrosion environments should be considered, while in inland areas temperature variations and the impacts of snowfall also need to be taken into account.

Also, judging solely by solar irradiation values can be risky. Even if the annual solar irradiation appears high, whether it is extremely concentrated in summer or remains stable in winter will affect the seasonal variation in power generation. When evaluating monthly generation, PCS capacity, power sales contracts, and consumer-side consumption patterns, it is important to examine monthly trends as well as annual values.

When reading the PVSyst manual, you should treat the meteorological data settings screen not only as an entry point for operation but as the single most important factor in determining the assumptions behind the design results. If multiple people within your organization are performing analyses, recording which meteorological data were adopted, the reasons for adoption, and what comparison candidates were considered will make it easier to explain the results later.

When reviewing meteorological data, confirming consistency with local conditions should take priority over making excessively fine numerical adjustments. By organizing the site’s latitude and longitude, elevation, surrounding topography, climate classification, presence or absence of snow, and differences from past observations—and clarifying the basis for input values—the PVSyst results become easier to use for proposals and design decisions.

Design Accuracy Improvement Review 2: Align Orientation, Tilt, and Installation Conditions with Site Conditions

Next to review are the orientation, tilt, and mounting method of the photovoltaic modules. The PVSyst manual explains the process for setting conditions such as the array’s orientation and tilt, whether it is fixed or tracking, and whether it is roof-mounted or ground-mounted. Because these factors directly affect energy production, they must be carefully cross-checked with drawings and on-site information to improve design accuracy.

Azimuth and tilt are considered basic parameters for solar power generation, but in practice they are surprisingly prone to input errors. If you enter values without checking whether the reference is true south or north, whether angles are measured clockwise, or whether the azimuth definitions on the drawings match those in the software, the calculation results can change significantly.

For roof-mounted installations, the roof pitch and azimuth shown on building drawings may also differ from actual measurements.

For ground-mounted installations, impacts from site development plans, racking pitch, level differences, slopes/embankments, access roads, and drainage planning can make it impossible to adopt the ideal orientation and tilt as-is. Even if standard angles are used in preliminary assessments, they must be reviewed in detailed design to match the actual formed terrain and racking layout. This is especially important on sloped sites, where the inclination of the ground surface and the tilt of the racking are easily confused, so it is crucial to clarify what the input values represent.

Also, in projects where multiple orientations and tilts coexist, accuracy changes depending on whether you calculate everything under a single set of conditions or split it into sub-arrays for separate calculations. If a roof is divided into multiple planes, or mounting angles vary by block to follow the terrain, processing with only representative values can cause monthly energy production estimates and shading impacts to deviate from reality.

When verifying installation conditions while consulting the PVSyst manual, do not rely solely on screen inputs; it is essential to cross-check them against the plan view, section view, layout drawing, site photographs, and survey data. If the designer can explain which area on the drawings the entered azimuth and tilt correspond to, you will reduce rework in later stages.

Reviewing orientation, tilt, and installation conditions affects not only the accuracy of predicted energy production but also the persuasiveness of design explanations. When clients or internal approvers ask, "Why this angle?" or "Isn't this roof surface subject to different conditions?", being able to explain by linking PVSyst's input screens to the drawing information increases the reliability of the analysis results.

Review 3 to Improve Design Accuracy: Reconfirm Module and PCS Specification Inputs

To improve design accuracy in PVSyst, entering the specifications for the modules and the PCS is also essential. The photovoltaic module's nominal output, temperature coefficient, voltage, current, efficiency, low-irradiance characteristics, and the PCS's rated output, MPPT range, input voltage, and conversion efficiency, among others, are directly reflected in the simulation results.

The PVSyst manual shows how to select and register equipment in the component database. In practice, you should not simply select equipment listed in the database; you must also verify that the intended model, datasheet revision, output class, temperature coefficient, and tolerances match. When multiple devices with similar model numbers exist, slight differences can affect string design and energy yield.

Particularly important to watch for are cases where the equipment adopted changes between the estimation phase and the detailed design phase. In initial proposals, simulations are run using representative modules and PCS, and these may later be changed to different models to match procurement conditions or inventory status. If, in such cases, you issue a report under the old conditions without updating the equipment settings in PVSyst, the design documents and estimate conditions will diverge from the analysis results.

Module temperature characteristics are also important. In solar power generation, while greater irradiance increases power output, module output decreases as module temperature rises. The tendency for temperature rise varies depending on the installation method, ventilation conditions, roofing material, and whether it is ground-mounted or rooftop-mounted. In PVSyst settings, you should check not only the nominal output but also the assumptions regarding temperature.

Regarding PCS, it is important not to judge solely by the rated capacity; check the MPPT range, maximum input voltage, number of input circuits, the oversizing strategy, and the conversion efficiency curve. Increasing the DC-side capacity can sometimes increase annual energy production, but you must also consider clipping at peak times and voltage variations caused by temperature conditions. Rather than deciding only by the ratio of PCS capacity to module capacity, checking monthly and hourly behavior in PVSyst leads to improved accuracy.

When reviewing the specification inputs for modules and PCS, it is essential to ensure that the specification document, single-line wiring diagram, equipment selection list, quotation conditions, and PVSyst settings all match. When conducting an internal review, recording the equipment model numbers, date entered, version of the specification referenced, and change history will make later verification easier.

Review 4 to Improve Design Accuracy: Reassess String Design and Voltage Conditions

One of the items that practitioners often struggle with in the PVSyst manual is string design. How many modules to connect in series, which PCS input to connect them to, and how to allocate the number of strings per MPPT all affect power generation efficiency, safety, and constructability. To improve design accuracy, the string settings in PVSyst need to match the actual electrical design.

In string design, the open-circuit voltage at low temperatures, the operating voltage at high temperatures, the PCS maximum input voltage, and the MPPT operating range are checked. In cold regions, module voltage rises at low temperatures, creating a risk of exceeding the PCS allowable voltage. Conversely, at high temperatures the operating voltage drops and may fall outside the MPPT range. These aspects are easy to overlook if you only look at annual power generation, but they are important checks related to design safety and performance.

In PVSyst, warnings and cautions may appear when there are problems with a string configuration. When reading the manual, you should understand the meaning of any warnings and, instead of merely proceeding with the calculations, take care to determine why the warnings are being issued. If you ignore the warnings and proceed, you may obtain results in the simulation that are not valid as an actual design.

The input balance for each MPPT is also an important point to review. Even strings connected to the same PCS can experience reduced power generation efficiency if strings with different orientations, tilts, or shading conditions are grouped on the same MPPT. When roof surfaces differ or shading differs significantly between morning and afternoon, the electrical grouping should be carefully considered.

String design is not something that can be completed solely within PVSyst. It is linked with the single-line wiring diagram, PCS specifications, junction boxes, cable routes, constructability, and maintainability. A configuration that looks optimal in simulation may result in overly complex wiring on site or make fault isolation difficult during maintenance. To improve design accuracy, it is important to verify not only the energy production but also the implementability.

When reviewing string design using the PVSyst manual, check the combination of voltage conditions, MPPT range, number of strings, point of connection, and shading conditions as a whole. In particular, after design changes you must recalculate the entire string configuration rather than merely changing the number of modules.

Revision 5 to Improve Design Accuracy: Organize the Handling of Near Shadows, Distant Terrain, and Obstacles

How shadows are handled is one of the factors that can produce large differences in solar power generation simulations. In the PVSyst manual, topics such as near shading, distant terrain, 3D scenes, and horizon profiles are highlighted as important. The level of detail used to input shadows can greatly change the accuracy of estimated energy production.

Proximity shading refers to the effect of shadows cast by objects located near power generation equipment, such as buildings, utility poles, trees, fences, surrounding equipment, and adjacent arrays. For rooftop installations, roof penthouses, chimneys, HVAC equipment, railings, and parapets can cause shading. For ground-mounted installations, self-shading between arrays, slopes, adjacent buildings, forests, and elevation differences of developed land affect shading.

Distant terrain refers to conditions in which solar irradiance around sunrise and sunset is blocked by obstacles such as mountains, hills, or obstructions along the horizon. In mountainous or sloping terrain, ignoring distant terrain can lead to an overestimation of morning and evening power generation. The influence of distant terrain is relatively greater in winter because the solar altitude is lower.

When setting shading conditions in PVSyst, you need to decide how detailed the modeling should be. You do not have to enter every obstacle in fine detail. An overly complex model takes time to create and verify and increases the likelihood of input errors. Conversely, omitting important obstacles reduces the reliability of the results. To improve design accuracy, it is important to prioritize and organize the obstacles that are most likely to affect power generation.

When reviewing near-field shading, using on-site photographs, point cloud data, survey results, architectural drawings, and site/layout plans improves accuracy. If the height, position, distance, and bearing of obstacles are correctly identified, they can be more easily reflected in the 3D scene in PVSyst. If estimated obstacles are added without sufficient on-site verification, a model that appears precise may still produce results that differ from reality.

Also, it is important to assess the impact of shading not only on annual figures but also by month and by time of day. Even if the effect on annual energy generation appears small, significant losses can be concentrated in winter mornings or during specific time periods. In self-consumption projects for end users, time-of-day generation is critical, so shading checks need to be carried out more carefully.

When reading the PVSyst manual, it is important not only to learn the procedures for operating shading settings, but also to align company-wide criteria for which shading to input and which not to input. If the handling of shading conditions differs between personnel, results can vary even for the same project. To improve design accuracy, standardizing the rules for shading input and the methods for verification is effective.

Design Accuracy Improvement Review 6: Adjust Loss Settings for Each Project

Another factor that significantly affects PVSyst results is the loss settings. In a solar power generation system, various losses occur not only from irradiance and equipment performance but also from temperature losses, wiring losses, mismatch losses, soiling, degradation, PCS losses, IAM, shading losses, and downtime rate. How these are set will change the annual energy production and PR.

The PVSyst manual provides multiple input items for loss settings. What should be noted here is that using the initial values as they are is not necessarily appropriate. The initial values can serve as a starting point for consideration, but they need to be reviewed according to the project's installation environment, design conditions, equipment used, and maintenance plan.

For example, soiling losses vary depending on the region and environment. Around farmland, in industrial zones, along the coast, in snowy regions, and in areas with a lot of dust, the way the module surface becomes soiled differs. The actual situation also varies depending on whether regular cleaning is performed and on rainfall conditions. Setting the same soiling loss for all projects makes it difficult to reflect local conditions.

Wiring losses also vary depending on cable length, cable cross-sectional area, voltage, current, and wiring route. Approximate values may be acceptable in the early stages, but in detailed design they should be reviewed based on the actual wiring plan. Especially for large-scale ground-mounted installations, wiring distances can change significantly depending on the placement of PCS and junction boxes, so the impact on losses cannot be ignored.

Mismatch losses and degradation rates are also related to module quality, string configuration, orientation differences, shading conditions, and assumptions about long‑term operation. If loss settings are overly optimistic, the proposed energy yield may be overestimated. Conversely, if they are made overly conservative without sufficiently reflecting maintenance conditions and equipment specifications, the project viability assessment may appear worse than it actually is.

To improve design accuracy, it is important not to treat loss settings as mere numeric inputs but to organize them as part of the design philosophy for each project. Deciding which losses to use as standard values, under what conditions they should be changed, and where to record the rationale when changes are made will make reviews and explanations easier.

When using the PVSyst manual, go back and forth between the loss diagram, the results report, and the input screens to determine which losses are having the greatest effect on the results. If energy production is lower than expected, rather than simply replacing equipment, examine the breakdown of losses and isolate whether the cause is shading, temperature, wiring, clipping, soiling, or something else.

Review 7 for Improving Design Accuracy: Standardize How to Read Result Reports

When calculations in PVSyst are complete, you can review a report that includes energy production, PR, a loss diagram, monthly results, system conditions, and other items. To improve design accuracy, it is necessary not only to enter inputs correctly but also to interpret the results correctly. Many readers of the PVSyst manual are often unsure which figures in the report they should focus on.

First, what I want to stress is not to judge solely by annual energy production. Annual energy production is an important metric, but you cannot fully assess the validity of the design without looking at month-to-month variability, winter generation, summer clipping, the timing of shading losses, PCS losses, and temperature losses. Even if the energy production appears high, losses may be concentrated in specific seasons or the balance with PCS capacity may be poor.

PR is also an important metric. However, PR is not simply better the higher it is. Because it varies with meteorological conditions, installation angle, temperature conditions, and loss settings, when comparing across projects it is necessary to align the underlying assumptions. If you isolate PR and compare it alone, you may actually overlook differences in weather data and shading conditions.

A loss diagram is particularly useful for obtaining hints for design improvements. By tracking where and to what extent losses occur—from solar irradiance to the final AC output—you can see which points need improvement. Whether shading losses are large, temperature losses are significant, or PCS losses and wiring losses stand out will determine which design conditions should be reviewed.

When presenting a results report internally or externally, it is important not to paste numbers alone but to explain them together with the input conditions. Specify which meteorological data were used, the module and PCS model types, the azimuth and tilt angles, the extent to which shading conditions were accounted for, and whether the loss settings are standard values or project‑specific values, so that the results are easier to interpret.

When reading the PVSyst manual, standardizing the procedure for checking reports reduces oversights by the person in charge. Establish a fixed sequence for reviewing annual energy production, monthly energy production, PR, the loss diagram, system conditions, warning messages, equipment settings, and shading settings to stabilize the quality of reviews.

Design accuracy is not determined solely by the calculation results themselves. It is determined by how those results are interpreted, how they are explained, and how they are used to inform subsequent design decisions. It is important to use PVSyst reports not merely as output documents but as materials for design verification.

Tips for implementing the PVSyst manual into in-house operations

There are limits to improving design accuracy by reading the PVSyst manual alone. In practice, multiple people are involved in a project, and staff in sales, design, construction, procurement, maintenance, and business feasibility assessment all refer to the same simulation results. Therefore, it is important to embed how to use PVSyst into internal operations.

The first thing to work on is templating the input conditions. Preparing a format that can record, for each project, meteorological data, azimuth, tilt, equipment model, string configuration, shading conditions, loss settings, and report check items will make reviews easier. Sometimes, just looking at the PVSyst screen does not reveal why a particular value was entered. By organizing the rationale for inputs separately, it becomes easier to respond if design changes occur later.

Next, it is effective to establish accuracy criteria for each design stage. Clarify whether, in the initial proposal, approximate meteorological data and representative losses are sufficient; whether, in the basic design stage, shading studies based on site conditions should be performed; and whether, in the detailed design stage, wiring losses and string configurations must be made to match the drawings. If the required levels for each stage are ambiguous, you may end up doing unnecessarily detailed work or, conversely, omitting important checks.

Also, it is important to designate a reviewer. Establishing a process in which a person experienced with PVSyst checks the input conditions and result reports leads to early detection of mistakes. In particular, the selection of meteorological data, consistency of equipment model types, string warnings, shading settings, and the plausibility of losses are items where third-party review is likely to be most effective.

It's helpful to organize standard values and exception conditions for settings frequently used within the company. For example, for soiling loss, wiring loss, downtime rate, degradation rate, etc., set standard values while defining the conditions under which to review them—such as snowy regions, mountainous areas, salt-damage areas, factory roofs, low-voltage projects, and high-voltage projects—to reduce variability between personnel.

The PVSyst manual is both a resource for learning how to use the software and a foundation for creating in-house design rules. By translating the knowledge gained from the manual into checklists, input templates, review procedures, and training materials, you can build a design process that does not depend on individual experience.

To improve design accuracy, it is important to retain the rationale for input values

The most important thing for improving design accuracy in PVSyst is to preserve the justification for the input values. Meteorological data, orientation, tilt, modules, PCS, strings, shading, losses, and report results may appear to be independent, but in reality they are closely interconnected. If any one assumption changes, the appearance of the energy yield and losses will also change.

By reading the PVSyst manual, you can check how to operate each screen and the meaning of the settings. However, what is required in practice is not just the ability to enter numbers on the screen. You must be able to explain why those numbers were chosen, how they correspond to site conditions and the design drawings, and how they affect the results.

We organized seven reviews to improve design accuracy: meteorological data, orientation and tilt, equipment specifications, string design, shading conditions, loss settings, and how to read result reports. Improving just one of these is not enough; they should be checked repeatedly according to the project's phase.

Particular care is required when design changes occur. If the module model changes, the PCS capacity changes, the layout changes, the shading conditions change, or the racking angle changes, the PVSyst input conditions must also be reviewed and updated accordingly. Even when reusing past simulation results, you should always confirm that the assumptions match the current design.

PVSyst can be a powerful tool to support decision-making in photovoltaic system design when used correctly. On the other hand, if the basis for input values is unclear, even a well-presented report will not improve the accuracy of design decisions. It is important not only to learn the software operations by reading the manual, but also to establish a process of checking input conditions, interpreting the results, and feeding improvements back into the design.

The purpose of using the PVSyst manual is not to run the software, but to carry out design studies that are closer to actual site conditions, explainable, and reproducible. By carefully reviewing the entire process from meteorological data to the results report, you can improve not only the accuracy of power generation forecasts but also the persuasive power of proposal materials, the efficiency of internal reviews, and the quality of pre-construction checks. If you want to raise design accuracy, a shortcut is to start by treating each PVSyst input item not as a "work procedure" but as a "design rationale."