Six steps to align analysis conditions in the PVSyst manual

Table of Contents

• How to approach the analysis conditions you should grasp first in the PVSyst manual

• Why result comparisons break down if analysis conditions are not kept consistent

• Step 1: First, finalize the project information and the evaluation objectives

• Step 2: Standardize meteorological data and solar radiation conditions

• Step 3: Align orientation, inclination, and layout conditions

• Step 4: Match equipment configuration and string conditions

• Step 5: Standardize loss conditions and detailed settings

• Step 6: Read the result report and the comparison values using the same criteria

• Key points for internal operations to standardize analysis conditions

• Summary

How to Approach the Analysis Conditions You Should Master First in the PVSyst Manual

Many people searching for the PVSyst manual are not simply trying to learn the meanings of the interface screens; they are also troubled by how to consistently compare the simulation results of solar power generation systems. In particular, for designers comparing multiple proposals, sales-engineering staff preparing proposal materials, and managers conducting internal project reviews, standardizing the analysis conditions is extremely important.

Even for plans of the same power plant, simply changing the weather data, azimuth, tilt, number of modules, PCS capacity, loss rates, how shading is treated, or how the report is read will alter the annual energy generation, the PR, and the appearance of the loss diagram. Therefore, when using PVSyst, it is as important to be clear about which conditions you will hold fixed and which you will change for comparison as it is to learn how to operate it.

Aligning analysis conditions does not mean using the same numerical values for every case. It means keeping all conditions other than the items you want to compare to as consistent a standard as possible, so that you can explain where differences in the results originated. For example, if you want to compare differences in azimuth, you should keep meteorological data, equipment configuration, loss conditions, and shading conditions as identical as possible. Conversely, if you change even the meteorological data, it becomes difficult to determine whether the effect is due to the azimuth or to differences in solar irradiance data.

When reading the PVSyst manual, it's easier to understand if you not only follow the individual setting items on each screen, but also keep in mind how the analysis conditions for the entire project are connected. Meteorological data sets the assumptions for energy generation, layout conditions affect incident light and shading, equipment configuration determines the electrical operating range, and loss settings apply corrections that approximate real-world operation. Finally, the report lets you verify how those conditions were reflected in the results.

By keeping this flow in mind, even someone using PVSyst for the first time will be less likely to be unsure about the order in which to check settings. Also, when taking over an existing project, it will be easier to identify which conditions have changed. The important thing is to organize the conditions before analysis and to read the results by the same criteria afterward.

Why Comparisons of Results Break Down When Analysis Conditions Are Not Aligned

In PVSyst simulations, the input conditions are directly reflected in the results. This is obvious, but it is a point that is often overlooked in practice. Even when you think you have created multiple cases and are comparing them, it can turn out that the source of the meteorological data is different, the loss rate has been changed in only one case, or the shading settings are enabled only partially. In such cases, it is dangerous to treat the difference in generated energy as a design difference.

For example, if you want to compare only the module layouts between Plan A and Plan B, the other conditions should be the same as much as possible. However, if Plan A has proximity shading calculations enabled while Plan B only includes a simplified shading loss, the comparison results will reflect not only layout differences but also differences in the shading evaluation method. In that situation, it becomes difficult to explain which plan is truly advantageous.

Also, during the proposal stage, multiple staff may run simulations independently. If each person has a different approach to loss rates or selects different meteorological data, comparing results in an internal review will not lead to productive discussion because the assumptions are not aligned. Although PVSyst’s output reports contain detailed information, they do not automatically explain the intent behind the parameter settings. That is why internal rules are necessary to align the analysis conditions.

Problems tend to surface when analysis conditions are not aligned, particularly when the generated power is higher or lower than expected. Looking only at the results, it may appear that there are issues with equipment selection or layout, but in reality the cause can be the choice of meteorological data, the handling of terrain shading, temperature losses, wiring losses, soiling losses, etc. To isolate the cause, it is necessary to verify that each condition is consistent.

Furthermore, inconsistent conditions become a major burden when a project is revisited in the future. Even if you try to recompute a simulation created a few months earlier, you cannot reproduce the same results unless it is documented which meteorological data were used at the time, by what rationale the loss values were set, and what was changed for comparison. Organizing the analysis conditions is indispensable, also for preserving the design rationale.

If you want to apply the PVSyst manual in practice, it is important not only to learn how to operate the interface but also to consider the management of conditions required for comparisons as a set. From here, I will explain six steps to align the analysis conditions, following the practical workflow.

Step 1: Fix the project information and evaluation objectives first

The initial step in aligning analysis conditions is to establish the project information and the evaluation objective up front. Rather than opening PVSyst and immediately starting to configure modules and PCS, first clarify what you are trying to evaluate with the simulation. If this stage is vague, when you later create multiple cases you will not be able to determine which conditions should be changed.

What should be confirmed as project information are the power plant location, equipment capacity, installation method, assumed grid interconnection conditions, stage of study, and items for comparison. For example, whether it is at the initial proposal stage, the detailed design stage, or the final check before construction will change the required level of precision and the degree of detail in the settings. In the initial stage, emphasize approximate comparisons, whereas in the detailed design stage it is necessary to verify shading and the handling of losses more strictly.

The purpose of the evaluation is also important. Depending on whether you want to get a rough estimate of annual power generation, compare differences in orientation or tilt, confirm the appropriateness of PCS capacity, or check for shortages or excesses in the string configuration, the conditions that should be fixed and those that should be varied will differ. If the objective is clear, it will be easier to explain the differences in the analysis results.

For example, if the purpose is to compare azimuth and tilt, the basic approach is to keep the weather data, modules, PCS, and loss conditions the same and change only the azimuth and tilt. If the purpose is to compare PCS capacity, fix the module layout and weather conditions and change only the PCS configuration and conditions related to the DC/AC ratio. By isolating the elements you want to compare one by one in this way, you can explain which conditions are responsible for differences in the results.

When finalizing project information, it's useful to establish rules for file names and case names as well. If you include the project name, review date, comparison details, version, and so on, it will be easier to infer the contents when you look back later. Rather than managing everything only on the PVSyst interface, record it together with your internal project management sheet and design notes to reduce confusion during handovers.

Also, when multiple people are working on the same project, it is important to establish a single base case. A base case is the standard-condition case that serves as the foundation for comparison. If everyone duplicates this base case and proceeds with their analyses, discrepancies in conditions can be kept to a minimum. Conversely, if each person creates a new case from scratch, the underlying assumptions may change without anyone noticing.

What is important in this procedure is to articulate the objective before the analysis. Before proceeding with the settings while consulting the PVSyst manual, decide what to compare and what to hold constant; doing so will make the subsequent work much more stable.

Step 2: Standardize meteorological data and solar radiation conditions

Next to check are the meteorological data and solar irradiance conditions. In simulations of solar power generation, meteorological data form the basis for the power output. If conditions such as solar irradiance, air temperature, and wind speed change, the results will vary even with the same system configuration. Therefore, when comparing multiple cases, it is extremely important to standardize the meteorological data used.

PVSyst runs simulations by setting location information and meteorological data. What should be noted here is that even data from nearby locations do not necessarily show identical trends in solar irradiance and temperature. In mountainous areas, coastal areas, urban areas, and snowy regions, meteorological conditions can change with only small differences in distance. You need to have internal criteria for deciding which data to adopt for a project site.

To standardize analysis conditions, you should first decide on the baseline meteorological data and use that data consistently across all cases. If the meteorological data differs between cases when comparing module layout proposals or PCS configurations, the causes of differences in the results become unclear. In particular, when annual power generation differences are on the order of a few percent, differences in meteorological data can have a large impact on the comparison results.

In solar irradiance conditions, you should also check the conversion from horizontal-plane irradiance to tilted-plane irradiance, the treatment of diffuse (scattered) irradiance, albedo, ground-surface reflection, and the presence or absence of terrain shading. Although these settings appear as separate options on the screen, they are important factors that affect energy production and loss assessment. When creating comparison cases, you need to verify that the solar irradiance settings are the same.

Albedo is another item that is easy to overlook. Ground reflectance varies depending on the condition of the ground surface. Because typical assumed values differ for general ground, gravel, grassland, snow cover, and so on, set it to match the actual conditions of the project. However, if you change the albedo while comparing multiple proposals, differences will arise that are separate from the effects of layout or equipment configuration. Unless you specifically want to compare albedo, the basic practice is to keep it consistent within the same project.

Temperature data also affects power generation. Because solar photovoltaic (PV) modules’ output varies with temperature conditions, temperature losses will also change when temperature conditions differ. In high-temperature regions and cold regions, output trends can differ even with the same irradiance. When selecting meteorological data, it is important to verify the validity not only of irradiance but also of temperature.

To standardize meteorological data and solar radiation conditions, it is effective to record the name of the dataset used, the location, the period, whether corrections were applied, the albedo, and how terrain shading was handled. When consulting the PVSyst manual, be sure to check not only how meteorological data are imported but also which conditions influence the results.

Step 3: Align orientation, tilt, and layout conditions

The third step is to align orientation, tilt, and layout conditions. In solar power generation, the amount of solar radiation received varies depending on the direction the modules are installed and the angle at which they are tilted. Furthermore, power generation also varies depending on the spacing between modules, the number of rows, the layout area, terrain conditions, and the positions of obstructions.

Orientation and tilt tend to be the focal points of comparisons. For example, comparisons between south-facing and east–west-facing orientations, between a 10° tilt and a 20° tilt, or between layouts that follow the roof pitch and layouts where the angle is adjusted with mounting racks. In such evaluations, conditions other than orientation and tilt should be kept as consistent as possible.

When assessing layout conditions, we check not only the number of modules arranged but also inter-row spacing, aisles, separation distances, maintenance space, and distance from site boundaries. Increasing the number of modules raises the DC capacity and therefore increases power generation. However, at the same time the effects of shading, wiring conditions, and the capacity balance with the PCS may change. A proposal that simply yields higher power generation is not necessarily optimal.

When handling 3D scenes or near shading in PVSyst, the input conditions for obstructions and terrain also need to be standardized. If the modeling of buildings, trees, fences, slopes, adjacent equipment, and so on differs from case to case, comparisons of shading losses will be distorted. If Proposal A includes obstructions in detail while Proposal B simplifies them, the difference in losses between the two will include not only layout differences but also differences in input accuracy.

Also, when reflecting terrain conditions, confirm how the survey data and elevation data to be used are handled. Whether the site is treated as flat or sloped, and how much of the terrain's irregularities are reflected, can change shadowing and incident conditions. Especially for large-scale ground-mounted projects, because the way terrain is handled can easily affect energy yield assessments, it is important to use the same terrain conditions across multiple cases.

When aligning layout conditions, clearly state what was changed for each comparison case. For example, manage changes one at a time: Case A is the baseline layout, Case B is the layout with increased row spacing, and Case C is the layout with a changed PCS capacity. If there are too many changes, it becomes difficult to explain the causes of differences in the results.

Settings for azimuth, tilt, and layout are areas where the design engineer’s judgment tends to be reflected. Therefore, in addition to checking the operating procedures in the PVSyst manual, establishing standardized input rules in-house can reduce variability between projects. In particular, separating simple inputs for preliminary studies from detailed inputs for in-depth analysis makes it easier to balance work efficiency and analysis accuracy.

Step 4: Align equipment configuration and string conditions

The fourth step is to align the equipment configuration and string conditions. In a photovoltaic power generation system, conditions such as modules, PCS, strings, number of circuits, and the DC/AC ratio affect power generation and losses. When comparing multiple proposals in PVSyst, if these settings are not matched, it can lead to misinterpretation of the analysis results.

The first thing to confirm is the specifications of the modules to be used. Nominal output, temperature characteristics, voltage, current, degradation rate, and the number of modules installed are basic parameters that determine the system output. If the module model changes, the DC capacity and operating voltage will change even with the same installation area. Therefore, when comparing layout proposals, you need to keep the module conditions fixed.

Next, confirm the PCS conditions. PCS capacity, number of input circuits, MPPT configuration, input voltage range, maximum current, conversion efficiency, and so on affect the operation of the entire system. If the PCS capacity is small relative to the DC capacity, clipping may occur under certain irradiance conditions. Conversely, if the PCS capacity is too large, you need to consider the balance with equipment costs and operational efficiency.

String conditions are also important. The number of modules in series per string, the number of parallel strings, the allocation per MPPT, and the mixing of surfaces with different azimuths or tilts all affect electrical mismatch and the operating range. In particular, if arrays with different azimuths or tilts are connected to the same MPPT, differences in generation characteristics can manifest as losses.

To align analysis conditions, decide whether to fix or change the equipment configuration depending on what you want to compare. If you only want to compare layouts, keep the module and PCS configurations as identical as possible. If you want to compare differences in PCS capacity, fix module placement and weather conditions and change only the PCS configuration. If you want to compare string design, fix the number and placement of modules and vary the number of modules in series and the MPPT allocation.

One point to note here is that changing the equipment configuration will have effects that propagate to other conditions. Increasing the number of modules increases the DC capacity and changes the capacity ratio relative to the PCS. Changing the PCS alters conversion efficiency and input constraints. Changing the string configuration changes the voltage range and the assessment of mismatch losses. Therefore, even if a modification appears to be a single change, you should understand that it will actually affect multiple result items.

When configuring equipment while consulting the PVSyst manual, it is important not to ignore warnings and error messages. Warnings about voltage ranges, current limits, PCS input conditions, and so on are not mere operational cautions but information related to the validity of the design conditions. Proceeding with comparisons while ignoring warnings can lead to overestimating design proposals that are not realistic.

Equipment configuration and string conditions are critical factors that affect the reliability of simulation results. Beyond simply standardizing the settings, recording why a particular configuration was adopted and which conditions were changed for comparison will make the analysis easier to explain later.

Step 5: Standardize Loss Conditions and Detailed Settings

The fifth step is to standardize the loss conditions and detailed settings. In PVSyst's analysis results, not only the energy production but also various loss items are displayed. These include many items important for assuming actual operation, such as temperature losses, wiring losses, mismatch losses, soiling losses, shading losses, PCS losses, and conditions related to degradation.

Loss conditions are necessary to make a project more realistic. However, because there is a high degree of freedom in setting them, values often vary between the persons responsible. For example, annual energy production will change depending on how much soiling loss is assumed, which criteria are used to set wiring losses, and whether mismatch losses are treated as standard values or as project-specific values.

To standardize analysis conditions, it is effective to first establish internal standard loss assumptions. Organizing standard values according to purpose—such as for initial proposals, detailed design, submissions to financial institutions, and internal comparisons—can reduce variability between staff. However, standard values should not be applied unconditionally to every project. Because appropriate values vary with region, installation environment, equipment specifications, and maintenance plans, it is necessary to leave room to reflect project-specific conditions.

Conditions that affect temperature losses include the module installation method and ventilation conditions. Roof-mounted, ground-mounted, close-mounted, and rack-mounted installations cause the module temperature to increase in different ways. When comparing cases with different installation methods, you need to be aware that differences in temperature conditions are reflected in the results. Conversely, if you want to compare only the layouts, set the temperature conditions to the same baseline.

Wiring losses are also an easy item to overlook. If wiring length, cable size, or circuit configuration change, losses will change as well. In early studies these are often handled using standard values, but in detailed design they need to be brought closer to the actual wiring plan. Deciding in advance at which stage and to what extent to reflect them makes the interpretation of the analysis results clearer.

Soiling loss assumptions vary depending on local environmental conditions and maintenance frequency. The effects of soiling differ by site conditions such as dust, snowfall, pollen, bird droppings, and sea salt particles. However, if soiling losses are changed partway through comparative cases, effects other than differences in layout or equipment configuration will be mixed into the results. When considering soiling loss as a variable, it is important to clarify the objective and separate the cases.

For shadow losses, we will standardize whether to treat them using a simplified loss rate or to calculate them in detail using a 3D scene. Performing detailed shadow calculations in only one case would compromise the fairness of the comparison. In particular, when dealing with near-field or terrain shadows, it is also necessary to ensure consistent input accuracy for occluders and terrain models.

A practical way to standardize loss conditions is to create analysis templates. Prepare a base case that organizes commonly used weather conditions, loss settings, and report checklist items in advance, and adopt an operating procedure that changes only the necessary parts for each project; this reduces input omissions and configuration differences. In practice, it is far more meaningful to not only read the PVSyst manual as an operating procedure but also to translate it into your company's standard conditions.

Step 6: Read the result report and the comparison values using the same criteria

The sixth step is to read the result reports and the comparison figures using the same criteria. PVSyst simulations output a lot of information, such as annual energy production, monthly energy production, PR, loss diagrams, energy flow, and equipment losses. To compare these correctly, you need to decide which figures to use as the reference.

First, what we want to check is the annual energy generation. In proposal documents and internal reviews, annual generation tends to be the metric that attracts the most attention. However, looking at annual generation alone does not necessarily allow a fair comparison between cases with different system sizes. If the number of modules or the DC capacity differs, it is natural that the annual generation will be larger. Therefore, it is necessary to also check the generation per unit of installed capacity and the PR.

PR is an important indicator for understanding the overall performance of a system. However, PR values are also influenced by input conditions. If weather data, loss settings, shading conditions, or temperature conditions differ, the PR comparison results will also change. A high PR does not necessarily mean a design is superior; it may simply reflect that the input conditions were simplified.

It is also important to look at monthly results. Even if annual values do not show large differences, a month-by-month view can reveal summer temperature losses, winter shading, and the effects of snow or low-insolation periods. In particular, when comparing orientation and tilt, seasonal generation trends change, so it is safer not to rely solely on annual values.

Loss diagrams help to understand where energy is being lost. By checking the flow from solar irradiance to effective irradiation, module output, PCS output, and supply to the grid, you can identify items with large losses. However, when comparing loss diagrams, it is assumed that the input conditions are the same. If shading loss or wiring loss is large, it is necessary to confirm whether that is a design issue or a difference in setting conditions.

If you want to standardize comparison figures within the company, it is advisable to treat items such as annual energy production, generation per unit capacity, PR, shadow losses, temperature losses, PCS losses, whether clipping occurs, and trends in monthly generation as common items. The indicators required vary by project, but deciding which items to check each time will stabilize the quality of reviews.

Also, when saving reports, it is important to retain not only the results but also the analysis conditions. If you transcribe only the power generation figures into a separate document, you may later be unable to determine the underlying assumptions. When using numbers in proposal materials, you should also make sure it is possible to trace which case the results came from and under which conditions they were calculated.

When mastering the PVSyst manual, knowing how to read the results screens is as important as knowing how to operate the software. Even if analysis conditions are aligned, if different people interpret the results differently, their judgments will become inconsistent. Standardizing input conditions and output metrics as a set makes simulations easier to explain and more reproducible.

Internal operational points for standardizing analysis conditions

To ensure consistent analysis conditions, you need operational procedures that do not rely solely on individual vigilance. PVSyst has many settings, so even experienced users find it difficult to verify every condition perfectly each time. For stable, reliable use in practice, it is important to establish templates, check procedures, naming rules, and review methods.

First, an effective approach is to prepare templates by project type. If you create base cases for frequently used conditions—roof-mounted, ground-mounted, low-voltage, high-voltage, large-scale projects, initial proposals, detailed designs—you won’t have to set everything up from scratch each time. It’s also useful to include in the templates standard loss conditions, report checklist items, and case naming conventions.

Next, it is important to separate pre-analysis checks and post-analysis checks. Before analysis, verify that the weather data, azimuth, tilt, layout, equipment configuration, and loss conditions are appropriate for the intended purpose. After analysis, review the energy production, PR, loss diagram, warnings, and monthly results to check for any anomalous values. Separating the pre- and post-analysis checks makes it easier to detect input errors and irregularities in the results, respectively.

You shouldn’t overlook rules for case names. For example, making the name descriptive of the change—baseline proposal, orientation-change proposal, tilt-change proposal, PCS-change proposal, shadow-condition-change proposal—makes later comparisons easier. It’s also effective to include the date, the person responsible, and a version number. In projects that undergo multiple revisions, it often becomes unclear which case is the latest, so naming rules prevent operational confusion.

During reviews, it is important to check the changes as well as the results. Even if you find a proposal with high annual power generation, it is insufficient as a basis for recommendation if you cannot explain why it is high. You need to confirm whether there are more modules, whether shading losses are lower, whether PCS capacity has changed, or whether loss settings are looser. In review meetings, organizing the discussion so that you first explain the changes for each comparison case and then look at the results helps keep the discussion orderly.

For internal sharing, wording that is easy to understand for people who are not familiar with operating PVSyst is necessary. Rather than explaining every setting item using technical terminology, organizing them into broad categories—meteorological conditions, layout conditions, equipment conditions, loss conditions, and result indicators—makes it easier to share among sales, design, construction, and management departments.

Moreover, to improve the accuracy of representing on-site conditions, it is important to integrate survey data and field investigation results. If site boundaries, topography, obstructions, existing structures, and the surrounding environment are correctly captured, the layout and shading conditions in PVSyst can be brought closer to reality. If site information remains ambiguous and only the simulation is refined, the reliability of the results will not improve if the underlying assumptions are incorrect.

Setting up operational procedures to standardize analysis conditions may feel like extra work at first. However, the benefits of standardization grow as the number of projects increases. It reduces input errors, shortens review time, clarifies the basis for proposals, and makes handovers easier, so organizations that use PVSyst on an ongoing basis will find it worthwhile to put in place a system for managing conditions.

Summary

To align analysis conditions in the PVSyst manual, simply memorizing each screen operation is not sufficient. The important thing is to first decide the project information and evaluation objectives, and to manage meteorological data, solar irradiance conditions, azimuth, tilt, layout, equipment configuration, strings, loss conditions, and result indicators according to the same standards.

If the analysis conditions are aligned, it becomes easier to explain the comparative results of multiple proposals. Because you can separate whether differences are due to orientation, PCS capacity, shading losses, or loss-setting differences, internal reviews and customer explanations become more persuasive. Conversely, if you compare only the results while conditions are not aligned, you may be swayed by apparent generation figures and end up making incorrect judgments.

In practice, the basic approach is to create a base case, fix everything except the conditions you want to compare, and clearly record the changes. Weather data and loss assumptions tend to vary between analysts, so establishing internal standards helps ensure consistency. When reviewing reports, checking not only annual energy production but also PR, monthly results, loss diagrams, and warning messages together makes it easier to judge the validity of the analysis.

A PVSyst simulation only becomes information that can be used for design and proposals when both the organization of input conditions and the interpretation of results are in place. Getting used to the operations is of course important, but even more so, managing conditions in a reproducible way improves the quality of professional work.

Also, to improve the accuracy of analysis conditions, it is essential to correctly understand the local topography, obstructions, and site conditions. If you can utilize positioning data and topographic information obtained on site, it becomes easier to better align the assumptions in PVSyst with reality. If you want to streamline site surveys and measurements, it can also be effective to use tools such as LRTK (iPhone-mounted high-precision GNSS positioning device) to organize on-site information as the basis for design and analysis.