6 steps to compare multiple cases in the PVSyst manual

Table of Contents

• The purpose of comparing multiple cases in the PVSyst manual

• Align objectives and evaluation criteria before comparison.

• Step 1 Create a baseline case and fix the conditions

• Step 2 Separate the changes you want to compare one at a time

• Step 3 Check meteorological data and terrain conditions

• Step 4 Organize orientation, tilt, and placement conditions

• Step 5 Compare loss settings and system conditions

• Step 6 Read the report results from the same perspective

• Common mistakes when comparing multiple cases

• A Practical Approach to Conducting Comparisons in the Workplace

• Summary

The meaning of comparing multiple cases in the PVSyst manual

When progressing with multiple-case comparisons in the PVSyst manual, what matters is not simply listing simulation results. In photovoltaic system design there are many factors that affect energy production: azimuth, tilt, system capacity, inverter configuration, string design, shading conditions, loss settings, meteorological data, and topography. If you change all of these at once, you will not be able to determine why the results improved or worsened.

The purpose of comparing multiple cases is not just to maximize energy production. In real projects, judgments must take into account factors such as the available installation area, racking/mounting conditions, grid interconnection constraints, construction costs, maintainability, ease of construction, the surrounding environment, and considerations for snow and wind loads. Therefore, when reading PVSyst result screens and reports, it is important not to decide superiority based solely on annual energy production, but to check why the differences occurred, which conditions are realistic, and whether design changes are increasing other risks.

The reason for working while referring to the PVSyst manual is that if you operate by looking only at the on-screen values and field names, it’s easy to confuse similar settings. This is especially the case when creating multiple scenarios, where you often duplicate the first scenario and change only part of it. If, at that time, items other than the ones you intended to change are altered, or conditions from a previous analysis remain, the reliability of the comparison results is reduced.

For example, if you want to compare only the module tilt angle, but one of the cases has different shading settings or loss factors, you cannot correctly interpret the effect of the tilt angle. If you want to compare PCS capacity but the DC-side capacity or the number of strings are changed at the same time, it becomes difficult to determine which element affected the power generation or losses. When comparing multiple cases, it is essential to clearly distinguish the conditions that are changed from those that are fixed.

This article summarizes six practical steps for carrying out multi-case comparisons while consulting the PVSyst manual. It explains not only how beginners tend to get confused by the interface, but also how to align comparison conditions, how to interpret report results, and key points to watch when making judgments.

Align objectives and evaluation criteria before making comparisons

Before you start comparing multiple cases, first be clear about what you want to compare. If you add cases while that remains unclear, you will be unable to make decisions when viewing the results screens. PVSyst lets you configure many different conditions, so you can create cases on a whim, but in practice the more cases you have, the more checks are required and the greater the risk of errors.

For comparison purposes, there are several typical patterns. These include wanting to see the difference in power generation by changing azimuth and tilt; comparing layout proposals with the same installed capacity; checking clipping losses by changing the capacity or number of PCS; verifying voltage range and mismatch by altering string configuration; and understanding the impact of shading conditions.

The important thing here is to decide in advance which metrics you will compare. Whether you look only at annual generation, specific yield, the breakdown of the loss diagram, the bias in monthly generation, or include economic factors will change the number of cases required and the parameters you need to evaluate. The case with the highest generation is not necessarily the one you should adopt.

For example, in one case, even if the annual energy production is high, large PCS oversizing can increase clipping losses at peak times. In another case, annual energy production may be slightly lower, but the equipment configuration is simpler, installation is easier, and future maintenance is more straightforward. PVSyst comparison results are a basis for design decisions, not the final decision itself.

Also, the way you name comparison cases is important. If case names are ambiguous like "Option 1", "Option 2", or "Revised", you won't be able to tell what was being compared when you review them later. Make case names easier to check by including elements that indicate which conditions were changed. For example, even briefly including comparison axes such as tilt angle, azimuth, PCS capacity, layout conditions, and whether shading settings are applied will make them easier to manage.

When reading the PVSyst manual, it is important not only to follow the operational procedures for each screen but also to be aware of which calculations each setting affects. The more items that can be configured on the screen, the harder it becomes to keep comparison conditions consistent. If you set the objectives and decision criteria up front, you can avoid creating more cases than necessary and reduce misinterpretation of the results.

Step 1 Create the baseline case and fix the conditions

The first step in comparing multiple cases is to establish a baseline case. A baseline case is the standard scenario that serves as the starting point for comparison. Create a single design that reflects the project's basic conditions and that you consider the most appropriate at the current time. If you duplicate the baseline while it is still unstable, it will affect every comparison case created afterward.

In the baseline case, carefully verify the fundamental items such as the project location, meteorological data, ground surface conditions, azimuth, tilt, module type, PCS configuration, string design, loss settings, shading conditions, and so on. While referring to the PVSyst manual, check which values are entered on each screen and confirm that no unset or placeholder values remain.

Be especially careful not to use provisional input values directly as the baseline case. In early-stage evaluations, precise design conditions are often not yet available, and you may begin simulations with tentative equipment capacities or provisional shading conditions. However, if you create multiple cases using those provisional conditions as the baseline, the overall comparison results will be biased by those provisional conditions.

When creating a baseline case, separate the conditions that will not change from those that may change. Conditions that are common across the entire project, such as location and weather data, are fixed conditions. On the other hand, azimuth, tilt, layout, PCS capacity, string configuration, and loss settings may be subjects of comparison. Clearly specifying the fixed conditions makes it easier to interpret the differences between cases.

It is also useful to generate a reference-case report once to check overall consistency. The report consolidates input conditions, system configuration, loss diagrams, annual energy production, monthly energy production, and so on. Items that are easy to overlook when checking only on the screen are more likely to be noticed as anomalous values when viewed in a report.

Once a baseline case is completed, procedures are also needed to prevent that case from being overwritten inadvertently. In comparison work the baseline case is often duplicated to create other cases, so if the original baseline is changed the basis for comparison will become inconsistent. It is safer to make the save point of the baseline case explicit and, if changes are necessary, manage them as a new baseline case.

In the PVSyst manual, when conducting comparisons of multiple cases, this reference case effectively serves as a measuring stick. If the measuring stick is warped, no matter how many cases you create you cannot make valid comparisons. Stabilizing the reference case in the initial stage increases the accuracy of later stages.

Step 2 Separate the changes you want to compare one at a time

The next step is to create a separate case for each change you want to compare. The most common mistake when comparing multiple cases is changing multiple conditions at the same time within a single case. If you do that, even if the results differ, you won't be able to tell which change caused the difference.

For example, suppose you create a case where you change the tilt angle from 10 degrees to 20 degrees, change the azimuth at the same time, and even change the PCS capacity. Even if the annual power generation increases in this case, you cannot determine whether the increase is due to the tilt angle, the azimuth, or the PCS configuration. The basic rule of comparison is that when you change one axis, you keep the other conditions fixed.

Of course, in practice multiple conditions can be interlinked. For example, changing the layout may also change the installed capacity. Changing the PCS capacity may inevitably require altering the string configuration. In such cases, it is difficult to change only a single item in isolation, so it is necessary to clearly document the reasons for the changes.

When duplicating cases in PVSyst, it is important to know which case you are duplicating from. Whether you create all comparison cases from the baseline case or derive additional cases from a particular comparison case changes how conditions are inherited. If you stack derivations, conditions modified in earlier cases tend to persist. For that reason, it is generally easier to manage by duplicating from the baseline case and creating separate cases for each comparison axis.

Give case names that indicate what was changed. For example, for a case where the tilt was changed, include the tilt angle; for a case where the azimuth was changed, include the azimuth condition. When comparing PCS capacities, use names that indicate the DC/AC ratio or the PCS capacity so it will be easier to understand when reviewing the report later.

Also, when creating comparison cases, it's important not to create too many. Since PVSyst allows fine adjustments to conditions, you may be tempted to produce a large number of cases with slightly varied values. However, if the number of cases grows too large, verification work can't keep up and decision-making becomes more difficult. In practice, first grasp trends using broad comparison axes, then narrow the range and add further comparisons as needed.

Separating changes one by one makes it easier to explain differences in the results. When explaining to not only designers but also clients, contractors, maintenance personnel, and internal approvers, it is important to be able to show which condition was changed and how the outcome differed. Comparing multiple cases is not just a calculation task; it is also a process that enables you to justify design decisions.

Step 3 Check meteorological data and terrain conditions

When comparing multiple cases, always verify the meteorological data and terrain conditions. Because these form the baseline assumptions for the entire project, if they differ between cases the meaning of the comparison can change substantially. In particular, when reusing multiple projects or past cases, the selection of meteorological data and ground-surface conditions may have been unintentionally altered.

In PVSyst, weather conditions such as solar radiation, air temperature, and wind speed have a major impact on energy production. Even with the same system configuration, annual energy production will change if the meteorological data used are different. Therefore, when you want to compare azimuth or tilt, you need to use the same meteorological data. Conversely, when you want to compare differences between meteorological datasets themselves, fix the other conditions and compare.

Terrain conditions are also important. On sloped terrain, developed land, rooftops, or ground-mounted installations, the shape of the installation site affects how shadows form and the area available for placement. How much of the terrain and surrounding obstacles you model in PVSyst affects how you should interpret the simulation results. Using a detailed 3D scene versus viewing under simplified shading conditions results in different accuracy and workload.

A common mistake in multi-case comparisons is that the baseline case uses simplified shading conditions while another case includes detailed shading settings. In this situation, the difference in power generation may be caused not by differences in design proposals but by differences in the shading-condition settings. If the factor you want to compare is not the shading conditions, shading settings must be aligned across cases.

Also check the conditions related to ground-surface reflectance and albedo. In snow-covered areas or on bright surfaces, the influence of reflections may not be negligible. That said, unless you are making a comparison, you should not enter different values for each case. If you change input values when the basis for them is unclear, it will be difficult to explain the results.

When using the PVSyst manual, it's reassuring to verify on which screen meteorological data and terrain conditions are managed and to which cases they apply. If you don't understand whether a condition applies to the entire project or can be changed for each variant, unintended differences are likely to be introduced.

Reproducibility of site conditions also affects the reliability of comparisons among multiple cases. If drawings, on-site survey data, heights of surrounding structures, site boundaries, land development plans, and the like are inadequate when making comparisons, conditions may change during the detailed design phase. While rough estimates may be acceptable in initial studies, at the stage of narrowing down candidate schemes it is necessary to clarify the basis for the input conditions.

Step 4 Organize orientation, slope, and placement conditions

Orientation, tilt, and layout conditions are items that are particularly often addressed when comparing multiple cases. Because they tend to directly affect power generation and relate to the available installation area and racking plans, it is common to compare several proposals from the early stages of design.

When comparing orientations, it is important to note that being closer to true south does not necessarily yield higher energy production. The optimal orientation varies depending on site shape, roof shape, grid interconnection conditions, timing of electricity demand, surrounding shading, and constructability. For self-consumption projects, not only the annual energy yield but also whether the timing of demand aligns with generation is important.

Even when comparing tilt angles, it is dangerous to judge based solely on annual power generation. Increasing the tilt can make winter power generation more favorable, but it affects wind loads, rack height, shadow length, row spacing, and construction costs. Decreasing the tilt can make it easier to increase installation density, but you need to consider soiling accumulation, drainage, and the effects during snowfall.

When comparing layout conditions, it is important to look at the relationship between installed capacity and shading simultaneously. Packing more panels will increase the installed capacity, but if row spacing becomes narrower, mutual shading effects can increase. Conversely, widening row spacing reduces shading losses but may lower the installed capacity. When reviewing PVSyst results, check not only the simple annual energy production but also the energy per kW and the breakdown of losses.

When comparing orientation, tilt, and layout, it is important to organize the combinations of cases. Create separate cases that change only orientation, only tilt, and only layout so that the influence of each element is easier to interpret. After that, create integrated cases that combine the conditions that are promising in practice so they can be compared as design proposals.

For example, first compare only the tilts — 10 degrees, 15 degrees, and 20 degrees. Next, choose the tilt that is most likely to be adopted and compare different orientations under that condition. Furthermore, based on the selected orientation and tilt, compare layout density and row spacing. By conducting the review in this step-by-step way, you can keep the number of cases down and make decisions more easily.

When checking the PVSyst manual, verify which units are used for azimuth and tilt inputs and which screens or objects the layout conditions are applied to. When dealing with multiple sub-arrays or different surfaces, the same conditions are not necessarily applied to all surfaces. For roof-mounted installations or projects with complex terrain, conditions may differ from one surface to another.

When reading comparison results, consider whether the difference in energy production is meaningful from a design perspective. If the difference in production is very small, it may be more reasonable to prioritize constructability and maintainability. PVSyst displays figures in fine detail, but it cannot fully predict site conditions, construction tolerances, future soiling, or operating conditions. In practice, it is also important not to overestimate the significance of numerical differences.

Step 5 Compare the loss settings with the system conditions

One thing that is easy to overlook when comparing multiple cases is the loss settings and system conditions. When differences in energy production appear, many people focus on orientation, tilt, and differences in installed capacity. However, in reality various loss factors—temperature losses, wiring losses, mismatch losses, soiling losses, conversion losses, and clipping losses—affect the results.

Loss settings are handled by separating items that should be kept consistent across cases from those that are varied for comparison. For example, if soiling loss is treated as a fixed value, the same value is used in all cases. If wiring distance or cable conditions change depending on the design option, they are explicitly treated as comparison variables. Temperature conditions also affect the results when installation methods or ventilation conditions change.

PCS conditions are also important. Changing the ratio of DC-side capacity to AC-side capacity affects power generation and how losses occur. Increasing the DC/AC ratio can, in some cases, be expected to improve equipment utilization rate, but during periods of strong solar irradiance output limiting or clipping tends to occur. Conversely, leaving too much margin can be disadvantageous in terms of equipment cost and efficiency.

In string design, verify the number of modules, series count, parallel count, voltage range, and current conditions. If the string configuration varies between cases, it will affect not only energy yield but also the PCS operating range, safety, and constructability. It is necessary to check on PVSyst that no errors or warnings are shown and that the voltage range is appropriate.

When comparing multiple cases, we always compare the loss diagrams. If you only look at annual power generation, you cannot tell at which stage the losses become large. By checking the loss diagram, it becomes easier to determine whether the losses are due to shading, temperature, PCS-side constraints, wiring, or mismatch.

For example, even if annual power generation is low in a given case, if the cause is shading losses, revising the layout or row spacing is effective. If the cause is clipping losses, reviewing PCS capacity or the DC/AC ratio should be considered. If the cause is temperature losses, check the installation method, ventilation conditions, and racking height. In this way, unless you examine the breakdown of losses, appropriate improvement measures will not be apparent.

When reviewing the loss items in the PVSyst manual, distinguish and understand whether each loss is determined by an input value or calculated as a simulation result. For losses set as input values, the justification is important. Losses that appear as calculated results are influenced by the design conditions. If you do not understand this difference, you will not know what to correct when you look at the results.

Also check whether any warnings or messages have been issued for each comparison case. Just because only the power output is shown does not mean the design conditions are appropriate. If you compare cases while ignoring warnings, you may end up favoring cases that could not be adopted in reality. When comparing multiple cases, you need to verify not only the numerical results but also the validity of the input conditions.

Step 6 Read the report results from the same perspective

The final step is to read the report results from the same perspective. After creating multiple cases and running the simulations, compare the results of each case. If the items you inspect differ between cases, your judgment will become inconsistent. Always verify using the same metrics, in the same order, and from the same perspective.

First, check that the input conditions match. Verify that everything except the changes you want to compare is the same. Confirm that the conditions that should be fixed—such as location, weather data, modules, PCS, loss settings, shading conditions, and system capacity—are all aligned. If you find any differences here, you need to correct the cases before reading the results.

Next, check the annual energy production and specific generation. Annual energy production indicates the total output of the entire installation, but simple comparisons between cases with different system capacities are difficult. In such cases, also look at the production per kW and the performance ratio. Cases with larger system capacity may appear to have higher total production, but they can have lower efficiency per unit of capacity.

Monthly power generation is also important. Even if there is little difference on an annual basis, seasonal generation patterns can vary. For example, there may be cases where shading is stronger in winter, cases where temperature-related losses are greater in summer, or cases where generation differs between morning and evening. When considering self-consumption systems or integration with battery storage, you need to check not only the annual total but also time-of-day and seasonal trends.

Loss diagrams are essential for explaining results. By comparing loss diagrams across multiple cases, you can identify the causes of differences in power generation. Check whether shading losses are increasing, temperature losses are large, PCS clipping is occurring, or wiring losses are significant. If you cannot explain the reasons for the differences in power generation, the comparison has not yet been sufficiently organized.

Also check the design conditions and system configuration displayed in the report. Even if the case name looks the same, the actual number of modules or the string configuration may differ. Verifying the conditions on the report makes it easier to spot oversights while operating the screen.

When summarizing results, do not choose only the cases with the best numerical values; evaluate them including their feasibility for adoption. Layouts that are difficult to construct, configurations that are difficult to maintain, excessively complex string designs, and shading settings that do not match site conditions may look good in simulations but cause problems in practice. PVSyst reports should be treated only as one part of the decision-making material.

When explaining comparison results, organize which case you recommend, why you recommend it, and what issues exist with the cases you did not adopt. If you can explain comprehensively from the viewpoints of power generation, losses, constructability, maintainability, cost, and risk, it will be easier to build consensus with stakeholders.

Common mistakes when comparing multiple cases

One common mistake when comparing multiple cases in PVSyst is creating too many cases. It's not inherently wrong to compare many conditions in detail, but if you increase the number of cases without a clear objective, you'll end up not knowing which one to choose. The more cases you have, the more time it takes to verify input conditions and organize reports.

Another mistake is that the comparison conditions are not consistent. Even if you think you are comparing tilt, if shading conditions or loss settings differ, you cannot correctly interpret the effect of tilt. Even if you think you are comparing PCS capacity, if the number of modules or the string conditions differ, it is not a simple PCS comparison.

Unclear case names can also cause problems downstream. Even if you remember the details while working, they may become unclear a few days later or when viewed by a different person. When submitting reports, the effort required to reconfirm which case corresponded to which conditions increases. Case names and the changes made should be organized at the time of work.

There are also failures that occur from comparing only the results without checking the warnings. Even if calculation results are displayed on PVSyst, the design conditions may be infeasible or some input values may require attention. If you select cases that ignore warnings or inconsistencies as candidate options, it can lead to having to redo the design later.

You should avoid judging based solely on annual energy production. Even in cases with high annual energy production, the breakdown of losses may have worsened. There are also cases where total energy production has increased simply because installed capacity was increased. When making comparisons, you need to look at specific yield, performance ratio, loss breakdown, monthly trends, and design conditions together.

Moreover, failing to verify consistency with on-site conditions is also problematic. Even layouts that are valid in PVSyst may be infeasible when actual site boundaries, slopes, existing structures, maintenance access routes, drainage plans, construction yards, etc. are taken into account. Optimization should not be done solely within the simulation; it is essential to cross-check against drawings and on-site conditions.

Practical Approaches to Conducting Comparisons in the Workplace

To efficiently compare multiple cases in practical work, it's important not to try to create a perfect case from the start. In the initial stages, it's more efficient to perform rough comparisons to capture major trends and then refine the detailed settings once promising conditions become apparent. Trying to reflect all minor losses and complex shading conditions from the outset will take too much time before the direction of the analysis is established.

First, create a baseline case and determine the main comparison axes. Compare items such as orientation, tilt, layout, PCS capacity, and string configuration, starting with those most likely to affect decision-making for the project. Next, exclude clearly unfavorable conditions and narrow down the candidates. Finally, for the narrowed conditions, examine shading, losses, construction conditions, and maintainability in detail.

When summarizing the comparison results, make sure you can explain not only the proposal you adopted but also why you did not adopt the other proposals. If you clarify reasons such as lower power generation, greater losses, difficult construction, maintainability issues, or a more complex equipment configuration, it will be easier to answer questions from stakeholders.

In internal reviews and client briefings, it is more important to clearly show the comparison criteria and the reasons for your judgments than to explain every detailed simulation condition. PVSyst reports contain detailed information, but they can be difficult for those who are not familiar with them. Therefore, it is necessary to provide supplementary explanations about which parts of the report to look at and which figures are relevant to decision-making.

Also, it is important to organize cases by each stage of consideration. If cases for initial review, detailed review, and final proposal are mixed together, you will not know which one is the latest. To prevent confusion, make old cases that are not candidates for adoption identifiable by name or manage them separately.

The PVSyst manual is useful not only for checking how to operate the software but also for verifying the meaning of settings. When comparing multiple cases, managing the conditions is often more important than screen operations. If you understand which settings affect which results, it becomes easier to interpret the differences between cases.

Coordination with on-site surveys and design drawings is also important in practice. If information such as site shape, obstacles, ground elevation, surrounding structures, and roof pitch is inaccurate, the comparison results in PVSyst will diverge from reality. Especially for ground-mounted systems or projects with complex roof geometries, proper characterization of on-site conditions prior to simulation determines the reliability of the results.

Comparing multiple cases is not an exercise in competing energy yields, but an exercise in determining which design proposals can be adopted. By effectively using PVSyst’s calculation results, you can quantitatively grasp the impact of design changes and make it easier to build consensus among stakeholders.

Summary

In the PVSyst manual, the six steps for progressing through a multi-case comparison are: first create a reference case, then separate the changes you want to compare one by one, verify the meteorological data and terrain conditions, organize the orientation, tilt, and layout conditions, compare the loss settings and system conditions, and finally, it is important to read the report results from the same perspective.

The most important thing when comparing multiple cases is to make clear what was changed and what was held constant. If the conditions are not aligned, even if differences appear in power generation you will not be able to correctly explain the reasons. The more cases you add, the more important the management of input conditions, the way cases are named, and the procedures for reviewing reports become.

Also, rather than deciding which proposal to adopt based solely on annual energy production, it is necessary to evaluate the breakdown of losses, specific yield, monthly trends, PCS operation, string conditions, constructability, maintainability, and consistency with site conditions. PVSyst results are extremely useful, but they are not something that can be concluded from numbers alone. By reading them in light of actual design conditions, they become a comparison that can be used in practice.

By using the PVSyst manual, you can organize the rationale behind comparison results while checking the meaning of each setting item. By stabilizing the baseline case, narrowing the comparison axes, and carefully reading the loss diagram and reports, you can see not only differences in energy yield but also the characteristics and risks of each design option.

Comparing multiple cases is useful both for confirming the direction in the early stages of design and for organizing candidate options before detailed design. What matters is not creating the cases themselves, but extracting from the comparison results the information that leads to design decisions. When using PVSyst, managing conditions and checking results in a consistent workflow while confirming the meaning of settings in the manual leads to more accurate solar power system design.