5 Things to Check in the PVSyst Manual Before Recalculation

Table of Contents

• Why Pre-Recalculation Checks in PVSyst Are Important

• Confirmation item 1: Whether the project conditions and site information remain unchanged

• Confirmation item 2: Are the assumptions about meteorological data and illuminance conditions correct?

• Check item 3: Are there any inconsistencies between the array configuration and the string design?

• Check item 4: Are the settings for shadows, terrain, and nearby obstacles reflected?

• Checklist item 5: Are the loss conditions and the comparison axes of the output report aligned?

• Benefits of fixing the verification order before recalculation

• Common Recalculation Mistakes and How to Prevent Them

• Approach to Making the PVSyst Manual Easier to Use in Practice

• Summary

Why pre-recalculation checks in PVSyst are important

Many people who consult the PVSyst manual have concerns such as wanting to correctly handle photovoltaic system energy yield simulations, wanting to be confident in the figures used in proposal documents and design studies, and wanting to be able to explain why results changed significantly after recalculation. PVSyst has many input items, and multiple factors affect the energy yield results, including meteorological data, modules, PCS, strings, azimuth, tilt, shading, losses, and grid conditions. Therefore, if you do not organize the items to check before pressing the recalculation button, only the calculation results will be updated and you will not be able to tell which condition changes had an impact.

Recalculation is not merely a redo. It is an important step for conducting comparative evaluations after changing design conditions. For example, if you slightly change the azimuth, the change in power generation may be relatively easy to understand. However, if you also alter meteorological data, terrain conditions, adjacent shading, temperature losses, wiring losses, and so on at the same time, it becomes difficult to trace what caused the differences in the results. In practice, this untraceable state becomes a major problem. It leads to situations where you cannot explain it in an internal review, have difficulty providing justification in proposal documents for clients, and cannot compare the previous proposal with the current one.

When reading the PVSyst manual, it's important not just to memorize the operating procedures but to understand it from the perspective of what should be checked before recalculation. Simply knowing where the input fields are on the screen will not fully prevent practical mistakes. What is important is to organize the assumptions that affect the calculation results and to separate the items you changed from those you did not.

Pre-checks before recalculation are indispensable, especially when a project is handled by multiple people. If the person in charge changes and a recalculation is carried out without understanding the previous intention behind the settings, the quality cannot be guaranteed even if the results are updated. On PVSyst, settings may remain but it can be impossible to determine whether those settings are based on the latest drawings, are from an older proposal, or are provisional inputs. Therefore, before recalculation it is important to have a workflow that at minimum confirms the five items: input conditions, meteorological conditions, electrical design, shading conditions, and loss conditions.

In this article, using the PVSyst manual, we outline five items to check before recalculation, arranged according to practical points that often cause confusion. The explanations are designed to be useful not only for beginners learning how to operate the software but also for staff who want to formalize verification procedures as an in-house standard.

Confirmation Item 1: Have the project conditions and site information remained unchanged?

Before recalculation, the first things to check are the project conditions and the site information. In PVSyst, the basics for the calculation are the project's location, latitude and longitude, altitude, time zone, and the reference point for the meteorological data. Because these are often set once and then reused, they are items that tend to be overlooked during recalculation. However, if there is any discrepancy here, no matter how meticulously you refine loss conditions or equipment parameters later, the assumptions for power generation will be undermined.

Particular attention should be paid to cases where a project created at a provisional location in the early stages is used unchanged for detailed design. In initial proposals, estimates may be made using information at the city/municipality level or from nearby points. Later, even after the actual site coordinates and design drawings have been finalized, if you re-run calculations without updating the site conditions in PVSyst, the calculations may appear to be complete while the assumptions are not up to date.

When checking site-setting items in the PVSyst manual, it is important not merely to verify that a location can be entered, but to confirm that the chosen location corresponds to the current stage of study. The required level of accuracy differs between the conceptual estimate, basic design, and detailed design stages. For conceptual estimates, nearby data may be acceptable, but for detailed design and proposal documents, the consistency between site conditions and meteorological conditions becomes more important.

Project names and variant names should also be checked. Repeated recalculations can make it unclear which proposal is the latest and which is for comparison. For example, if multiple variants exist within the same project—variants that change the tilt angle, variants that change the number of modules, and variants that change the shading conditions—ambiguous names may lead to accidentally recalculating a different variant.

In practice, before performing a recalculation it is important to clearly define "what this recalculation case is intended to verify." Depending on whether you want to examine maximizing power generation, the impact of changing PCS capacity, or the figures after reflecting shading conditions, the input fields you need to check will differ. If you proceed without confirming the objective before recalculation, even if results are produced the evaluation criteria will be unclear.

Another important point is the consistency between site conditions and the design drawings. If the site, array layout, orientation, and terrain conditions on the drawings have been updated while the project conditions in PVSyst remain outdated, the reliability of the analysis results will decrease. This is especially true for projects with complex terrain or where nearby obstacles have a significant impact, because even slight discrepancies in site conditions can affect the evaluation.

Before recalculation, confirm in one continuous flow the project location, the meteorological data being referenced, the variants under consideration, the design stage, and consistency with the drawings. When reading the PVSyst manual, rather than only understanding each screen’s explanation individually, being aware that these items form the foundation of the recalculation results makes it easier to reduce operational mistakes.

Check 2: Are the assumptions about meteorological data and illuminance conditions correct?

The meteorological data and irradiance conditions are factors that significantly affect the results of recalculations in PVSyst. In photovoltaic simulations, conditions such as solar irradiance, air temperature, wind speed, the diffuse component, and the direct component influence energy generation. When checking the handling of meteorological data in the PVSyst manual, you should verify not only which dataset to select but also whether that dataset matches the purpose of the project.

Meteorological data are items that are easy to overlook before recalculation. The reason is that they are rarely changed after the initial setup. However, as a project progresses from the proposal stage to the detailed design stage, the meteorological data that should be used may change. In the initial stage, data from representative locations that are easy to obtain are used, and later they may be switched to data closer to the site or to data based on internal company standards. If you perform a recalculation after making this switch, the annual power generation will change even if the number of modules and loss conditions have not been altered.

The important thing here is to understand changes in the results by separating them into "changes due to design modifications" and "changes due to changes in meteorological data." If you did not check the meteorological data before recalculation, you will not be able to correctly explain why the power generation increased or decreased. In an internal review, when asked "why did the power generation change compared to last time?", failing to recognize that the meteorological data changed will lead to unnecessary rework.

The same applies to irradiance conditions. In PVSyst, the solar irradiance incident on a surface and the light-receiving conditions on tilted surfaces are taken into account in the calculations. Naturally, if you change the orientation or tilt, the light-receiving conditions will change. However, in practice, you may find that conditions have changed because you copied settings from another variant even though you thought you had not changed the orientation or tilt. Before recalculation, it is important to check that any conditions other than those you intend to compare have not changed unexpectedly.

Also, attention must be paid to the period and type of meteorological data. The meaning of the results differs depending on whether the simulation is an annual-average one or an analysis based on data from a specific year. Simply reading the explanations in the PVSyst manual may not be sufficient to determine which data are appropriate for your company’s projects. Therefore, it is effective to establish internal criteria and to keep a record of the reasons for data selection for each project.

What should be checked before recalculation are the name of the selected weather data, the location, the period, the source, the conversion conditions, and the treatment of tilted-surface solar radiation. Recalculation will be performed only after confirming that these have not changed or that any changes were intentional. Especially when comparing multiple proposals, the comparison becomes meaningless unless the weather data are aligned. If the weather data differ between Plan A and Plan B, you cannot determine whether the difference is due to equipment design or to differences in the underlying data.

Once you get used to PVSyst, pressing the recalculate button itself feels simple. However, if you skip checking the meteorological data, you may have trouble explaining things in later stages. Before recalculation, it is important to make a habit of always checking the meteorological data as an external condition supporting power generation, not just the equipment conditions.

Checklist Item 3: Are there any inconsistencies between the array configuration and the string design?

The third item to check before recalculation is the array configuration and string design. In PVSyst, factors such as module type, module count, number in series, number in parallel, how they are paired with the PCS, and the number of input circuits all affect the calculation results. If there are inconsistencies here, it will impact not only the energy yield but also the overall validity of the system.

A common situation in practice is that after a layout change only the number of modules is updated, leaving the string design outdated. For example, if the module count on the layout has increased or decreased but in PVSyst you recalculate using the previous series and parallel counts, the actual design and the simulation conditions will not match. When checking system settings in the PVSyst manual, it is important not only to follow the numeric input procedures but also to verify consistency with the drawings and the electrical design.

The combination of modules and the PCS is also important. If the module specifications, temperature conditions, voltage range, and the PCS input conditions are not properly matched, this can lead to calculation warnings or abnormal losses. Before recalculating, you should not only check whether any warnings are displayed, but even if no warnings appear, confirm that the setup aligns with the design intent.

When checking the array configuration, first make clear what was changed in this recalculation. Depending on whether you changed the module type, the number of modules installed, the PCS capacity, reviewed the DC/AC ratio, or adjusted the number of strings, the points you need to check will differ. If you do not identify the changes before recalculating, you cannot correctly interpret the changes in the calculation results.

In particular, the DC/AC ratio is an item that is often checked in proposal documents. The relationship between DC-side capacity and AC-side capacity affects annual energy generation, peak shaving, equipment costs, and profitability assessments. Confirming that this ratio is as expected before recalculation makes it easier to judge when viewing the results report. If the numbers have changed significantly, you need to check whether either the number of modules or the PCS capacity has been changed unintentionally.

Also, when dealing with multiple sub-arrays, confirm whether the conditions for each sub-array are aligned or intentionally separated. If orientation or tilt differ due to site conditions, you may set up separate sub-arrays. In that case, if you change only one and forget to update the other, the recalculation results will diverge from reality. Because it’s easy to miss this in PVSyst unless you check each settings screen one by one, it is important to make a habit of verifying at the sub-array level before re-running calculations.

Inconsistencies in string design, which may seem like minor mistakes in the early stages, can lead to major revisions later in the process. If the proposed power output, design drawings, equipment list, and quotation conditions do not match, it becomes impossible to determine which document should be considered authoritative. Checking the array configuration in PVSyst before recalculation is important not only to ensure the accuracy of the simulation results but also to maintain the overall consistency of the design documentation.

Verification Item 4: Are the settings for shadows, terrain, and nearby obstacles reflected?

The fourth item to check is the configuration of shading, terrain, and nearby obstacles. In photovoltaic power generation, surrounding buildings, trees, graded terrain, adjacent equipment, and shading between racking rows, among others, affect energy production. In PVSyst, 3D scenes and near-shading settings can be used to reflect the impact of shading. Before recalculation, you need to verify that these conditions are based on the latest design and on-site information.

Shading conditions are important not only in terms of whether they were entered, but also how extensively they were reflected. For example, in an initial assessment you might include only large surrounding obstructions, while in a detailed assessment you might include shading between racking rows and structures around equipment. If you recalculate without understanding these differences in scope, you will not be able to determine why the power generation decreased compared with the previous calculation. In reality, the shading conditions were only made more detailed, yet it may appear that the design proposal has worsened.

When checking shadow settings in the PVSyst manual, you need a perspective that verifies not only how the 3D scene was created but also which conditions are being used for the calculations. Even if shapes are visible in the 3D scene, certain settings can mean they are not reflected in the calculations. Before recalculating, confirm that shadow calculation is enabled, that the relevant objects are correctly positioned, and that orientation and scale are not misaligned.

Topographic conditions are also easy to overlook. A project initially estimated as flat ground may later be changed to conditions that take grading slopes and level differences into account. Reflecting topographic conditions can change the array layout, tilt, shading between front and rear rows, and the constructible area. After changing terrain or array-surface conditions in PVSyst, it is important to check other related items before recalculating.

When setting nearby obstacles, the position, height, shape, and perceived distance of the object are important. Even when obstacles are added based on site photos, survey maps, or design drawings, errors in units, coordinates, or reference direction can cause the way shadows appear to differ from reality. In particular, a reversed orientation or a scale mismatch can be hard to notice on screen. Before recalculation, check that the shadow shapes seem intuitively reasonable and that winter and morning/evening shadows are not significantly different from what was assumed.

Also, if the array spacing is changed, the conditions for mutual shading must also be reviewed. When the spacing between front and rear rows, the tilt angle, or the height change, the effects of inter-row shading change. If you change only the layout and recalculate without updating the shading calculations, the results may be based on the old shading conditions.

Shadow and terrain settings also affect how well the power generation can be explained. When customers or internal stakeholders ask, "Why does it produce this amount of power?", being able to explain how thoroughly shadow conditions were reflected increases the credibility of the simulation results. Conversely, repeatedly recalculating while shadow conditions remain unclear weakens the basis for the figures.

Before recalculation, clarify whether the shading conditions are unset, set in a simplified manner, or reflected in detail. Based on that, decide whether to treat the present results as rough estimates, use them in proposal materials, or rely on them as the basis for detailed design. The PVSyst manual provides the entry point for operation, but in practice it is essential to manage the granularity of the settings.

Check item 5: Are the loss conditions and the comparison axes of the output report aligned?

The fifth item to check is the loss assumptions and the comparison axes of the output report. PVSyst results should not be evaluated based solely on the annual energy yield. You should judge by looking at multiple items such as the loss diagram, PR, monthly energy yields, system losses, temperature losses, wiring losses, mismatch losses, soiling, degradation, and PCS-related losses. If you don’t confirm the loss assumptions before recalculation, you won’t be able to correctly read the differences from the previous run when you review the result report.

Loss assumptions may be fixed as standard values for each project, or they may be changed depending on the stage of the study. For example, an initial proposal may use general values, while detailed design may review them based on wiring lengths and equipment specifications. Recalculating after making these changes will alter the annual energy yield and PR. If you recalculate without confirming the loss assumptions, you will not be able to tell whether the difference is due to layout changes or to changes in the loss assumptions.

When reviewing loss items in the PVSyst manual, it is important to be aware at which stage each loss is set and which results it affects. The loss conditions include many input fields, and reviewing all of them in detail every time is burdensome. However, before recalculation you should at minimum check whether any items have been changed since the last time, whether any values differ from internal standards, and whether any provisional entries remain.

What you need to pay particular attention to is whether the loss conditions are consistent between the options being compared. If you want to compare module layouts between Option A and Option B, the loss conditions must be the same. If, for example, only Option A has large soiling losses while only Option B has small wiring losses, you cannot correctly judge which layout is superior. For recalculation, the basic rule is to keep everything the same as much as possible except for the elements you want to compare.

The comparison axes of the output report are also important. In PVSyst, the results report displays many numerical values, but which values to prioritize depends on the purpose. In proposal documents, annual energy production and PR tend to attract attention, while in technical reviews, loss diagrams, month-by-month variations, and the effects of peak shaving may be emphasized. Before recalculating, decide how you will use these results so that the necessary items to check are clear.

Also, before saving a report, make sure to record the variant name, comments, and output conditions. If you only look at the report after recalculation and cannot tell which conditions were used, it will be difficult to use later. As a project progresses the number of reports increases, so including condition-identifying information in result files and output names is an effective practice.

Checking the loss conditions before recalculation is the final inspection to maintain the reliability of the results. Even if input conditions, meteorological data, array configuration, and shading conditions are in order, if the loss conditions are outdated it becomes difficult to explain the results. When using PVSyst in practice, loss conditions should be treated not as "minor settings" but as important conditions that form the basis for the energy yield.

Benefits of Fixing the Verification Order Before Recalculation

Before performing a recalculation in PVSyst, fixing the order in which you check items makes it easier to reduce errors. Less experienced staff tend to open screens in whatever order catches their attention. However, because input conditions are interrelated, if the checking order changes each time, oversights are more likely to occur.

A recommended approach is to proceed from external conditions to internal conditions, and from basic conditions to detailed conditions. First, check the site information and project conditions, then check the meteorological data. After that, review the array configuration and string design, and examine shading and terrain conditions. Finally, check the loss conditions and the comparison axes for report outputs. Following this order allows you to verify the calculation results from the ground up, making it easier to trace causes.

The advantage of fixing the order of checks is that it improves reproducibility. If different staff members follow the same sequence, the quality of reviews stays consistent. Also, when results differ, it becomes easier to trace which step caused the change in conditions. When sharing the PVSyst manual internally, compiling not only screen-by-screen explanations but also the pre-recalculation check sequence makes it more practical for day-to-day work.

Pre-recalculation checks may seem like a time-consuming task. However, checking in advance is ultimately more efficient than investigating unexplained discrepancies later. In particular, for projects with tight proposal deadlines or for those that require comparing multiple options in a short time, pre-recalculation checks can affect the overall speed of the work.

Fixing the order of checks makes conversations during reviews easier to organize. If you can explain "the weather data is the same as last time," "only the array configuration has been changed," "the shading conditions have been updated to the detailed version," and "the loss conditions remain at the company standard," it becomes easier to understand changes in the results. Conversely, if you present only the recalculation results without being able to provide these explanations, it becomes difficult to assess the validity of the numbers.

When using PVSyst for simulations, condition management is more important than the operation itself. Fixing the order of checks before recalculation is the first step toward systematizing condition management.

Common Recalculation Mistakes and How to Prevent Them

A common mistake when recalculating in PVSyst is that the settings you think you changed do not match the settings that were actually changed. For example, even if you intended to change only the number of modules, the loss conditions may have been altered when copying conditions from another variant. Also, you may think you updated the shading conditions, but the settings may not be configured to be reflected in the calculation.

To prevent such mistakes, it is effective to separate and check "the items changed this time" and "the items that must not be changed" before recalculating. In comparative analysis, you must fix everything except the parameters whose differences you want to observe. For tilt-angle comparisons, meteorological data, modules, PCS, and loss conditions should be kept consistent. For PCS comparisons, array layout and meteorological conditions should be kept consistent. Simply adopting this mindset makes the results after recalculation easier to interpret.

Another common mistake is mixing up old and new reports. If you repeatedly rerun calculations in PVSyst, you will accumulate results with similar names. If you save them under names that don’t indicate the date or conditions, you won’t be able to tell which one is the latest. Before rerunning a calculation, verify that the variant currently open is the correct one, or include information about the conditions in the output report name to prevent confusion later.

Also, warnings can be overlooked. In PVSyst, warnings may appear when there are inconsistencies in the input conditions, but as you become accustomed to the work, checks can become perfunctory and you may miss important warnings. Before re-running calculations, it is important to check whether any warnings have been issued and, if they have, to proceed only after understanding their content. There are cases where warnings can be ignored, but even then you must be able to explain the reason.

In addition, corporate standard values and project-specific values can become mixed. Soiling losses, wiring losses, operating rates, temperature conditions, and other parameters may be defined as internal standards. Conversely, they may be reviewed individually depending on the project. If you recalculate without confirming which values are being used, the interpretation of the results becomes ambiguous.

To prevent recalculation errors, you should not only read the PVSyst manual as an operational guide but also use it as a checklist. By understanding the meaning of the screens, identifying the items that affect the results, and keeping a record of changes, the quality of recalculations will improve significantly.

Ideas for Making the PVSyst Manual Easier to Use in Practice

The PVSyst manual is helpful for understanding the software's functions. However, to achieve results in practice, it is important not only to read the manual's information as-is but to organize it to match your company's workflow. In particular, items to check before recalculation tend to be judged differently by each person in charge, so standardizing them within the company is effective.

A practical way to organize work is to group items by purpose rather than by screen. For example, organize the items to be checked for each purpose, such as “verify the cause of a change in power generation,” “check before using in proposal materials,” “recalculate after design changes,” and “produce results that reflect shading conditions.” This makes it easier for the person in charge to perform the necessary checks when they are needed.

Also, for people who are not familiar with operating PVSyst, it is easier to teach them centered on the five checks to perform before recalculation than to have them memorize all the items at once. If they remember the sequence of site conditions, meteorological data, array configuration, shading conditions, and loss conditions, it becomes easier to visualize what will change the calculation results.

The results of PVSyst may be shared with multiple stakeholders such as design, sales, construction, and maintenance. Therefore, checks before recalculation are important not only for the person responsible, but also for creating materials that can be explained to stakeholders. If you can explain under which conditions the results were calculated, what was changed since the last time, and what the differences in the results are due to, the credibility of the materials will increase.

When creating a manual for internal sharing, it's effective to include not only explanations of the operation screens but also the intent behind each check. For example, when checking meteorological data, add "to align the assumptions for power generation"; when checking string design, add "to prevent inconsistencies between drawings and electrical design"; and when checking loss conditions, add "to eliminate differences in conditions between the proposals being compared." Adding such reasons makes it easier for the person responsible to understand the importance of the checks.

When applying the PVSyst manual to practical work, it is important to regard recalculation not as a "button to press at the end" but as a step carried out as a result of confirming the conditions. Recalculating while the conditions are not in order will not produce reliable results. Conversely, if the items to be checked are well organized, you can confidently compare, explain, and document the results after recalculation.

Summary

The items to check before recalculation in the PVSyst manual are five: site information, meteorological data, array configuration, shading conditions, and loss conditions. These may each appear to be independent settings, but they have a major impact on final energy production, PR, the loss diagram, and monthly results. If you skip these checks before recalculation, you will be unable to explain why the results changed, and rework is likely to occur during internal reviews and the preparation of proposal documents.

First, confirm the project conditions and site information to ensure the basis of the calculations aligns with the latest project parameters. Next, check the meteorological data and irradiance conditions to make sure the assumptions across the comparison scenarios are consistent. Then, review the array configuration and string design to verify there are no inconsistencies with the drawings and electrical design. Additionally, confirm that the settings for shading, topography, and nearby obstructions are based on the latest conditions, and finally, align the loss conditions and the comparison axes in the output reports.

If you fix this workflow, recalculations in PVSyst become not merely an operation but a well-founded simulation process. Rather than looking only at the numerical results, understanding which conditions influence those results enhances your ability to explain the energy yield.

When using the PVSyst manual, it's important to read it not only for how to operate each screen but also from a practical perspective of what should be checked before recalculation. Sharing the checklist internally, maintaining a change history for each project, and aligning comparison criteria when recalculating will greatly improve the reliability of the simulation results.