How to speed up slow recalculation in PVSyst | 6 points to review

Table of Contents

• Main reasons why PVSyst recalculations become slow

• Improvement 1: Review 3D scene and shading analysis settings

• Improvement 2: Organize array configuration and string settings

• Improvement 3: Check handling of meteorological data and time resolution

• Improvement 4: Limit loss settings to the necessary and sufficient scope

• Improvement 5: Organize file management and storage locations

• Improvement 6: Separate working models from submission models

• Practical workflow to speed up recalculations

• Summary: A system that can reflect site conditions quickly and accurately is important

Main reasons PVSyst recalculations become slow

When using PVSyst to simulate solar power generation systems, recalculations can sometimes take a long time even if you only change the conditions slightly. In particular, in practical work where mounting structure conditions, shading analysis, array configuration, loss settings, meteorological data, and comparisons of generation results are performed repeatedly, slow recalculation alone can bring the entire workflow to a halt.

There are broadly two situations in which PVSyst's recalculation feels slow. One is when the calculation itself takes a long time. The other is when loading, saving, screen updates, report generation, or result display before and after the calculation take a long time. Both give the user the impression that "PVSyst is sluggish" or "recalculation is slow," but if the causes differ, the countermeasures will also differ.

Typical factors that cause calculations to slow down include a 3D scene being too complex, shadow analysis conditions being set too finely, arrays and subarrays being excessively subdivided, and time-series data or loss-condition settings being more detailed than necessary. Also, if the project file becomes too large or the storage location is unstable, wait times are more likely to occur each time you recalculate or save.

PVSyst is a professional software for performing high-accuracy energy yield simulations and can accept many input parameters. However, the more parameters you enter, the greater the computational load becomes. The important thing is not to enter every parameter in detail, but to prioritize the conditions that affect design decisions. If recalculations are slow, don’t simply blame the computer’s performance; instead, you need to review how the model itself is constructed.

This article explains six improvement points to check when recalculations are slow, aimed at practitioners searching for "how to use PVSyst". It is organized as an approach that can be used at any stage—initial study, basic design, detailed design, internal review, and final checks before submitting to clients.

Improvement measure 1: Review the conditions for 3D scenes and shadow analysis

A particularly common cause of slow recalculation in PVSyst is 3D scenes and shading analysis. If you input buildings, trees, fences, surrounding structures, adjacent arrays, terrain undulations, and so on in detail, the number of items subject to shadow calculation increases. Furthermore, if you evaluate in detail the movement of shadows for each sun position and how shadows fall on the array, the computations tend to take longer.

In practice, when trying to accurately reflect site conditions, it is common to over-detail surrounding structures. For example, reproducing distant buildings in fine shapes that have little impact, or placing numerous objects that cast almost no shadow on the generation surface, can make the appearance closer to reality but will increase the computational load. In PVSyst's 3D scenes, it is important to separate visual fidelity from the information required for calculations.

First, what should be reviewed is whether objects with little impact can be simplified. For distant buildings, it is often unnecessary to reproduce fine irregularities; simple rectangular blocks or wall-like shapes may be sufficient. Trees are also more practical to treat as simple shapes representing their area of influence rather than reproducing the shapes of branches and foliage. The purpose of obstructions is not to recreate the scenery but to understand the conditions under which they cast shadows on the power-generating surface.

Next, confirm the scope of the shadow analysis. Structures that are sufficiently distant from the array and have little effect throughout the year can be omitted during stages when recalculations are repeated. For the initial assessment, include only elements that have a major impact, and add necessary surrounding conditions during the final check before submission; this workflow makes it easier to reduce recalculation time during the work.

Also, be careful when placing a large number of similar structures within a 3D scene. Modeling each racking row in fine detail increases the number of elements to compute. Organize your placement approach and simplify parts that can be treated as representative blocks or repeating structures. In particular, if the main objective of the impact assessment is to observe trends in inter-row shading, it is effective to examine representative cross-sections or representative areas before modeling every row in detail.

When recalculations are slow, duplicate the 3D scene and create a simplified version to compare; this makes it easier to identify the cause. If simply simplifying greatly reduces computation time, you can conclude that the primary cause of the slowness is shadow analysis or the 3D geometry. Based on that, decide how much detail is sufficient for design decisions to avoid unnecessary refinement.

Shade analysis is an important setting that significantly affects power generation, but making it more detailed does not necessarily produce better results. It is important to choose the appropriate level of granularity according to survey accuracy, on-site information, the design stage, and the purpose of submission. If you are having to wait a long time for each recalculation, the basic step is to first suspect the complexity of the 3D scene.

Improvement 2: Organize Array Configuration and String Settings

When PVSyst recalculations are slow, you should also review the array configuration and string settings. As the scale of a solar power plant increases, the number of modules, strings, PCS units, and sub-arrays rises. It is important to split these more finely to align with the actual electrical design, but over-dividing during the study phase will make setting checks and recalculations time-consuming.

Particular attention should be paid to cases where subarrays are divided more than necessary. It makes sense to separate subarrays when azimuth, tilt angle, module type, PCS conditions, shading patterns, or the installation area differ. However, if the conditions are almost the same and subarrays are split finely only for management convenience, this can merely increase the complexity of the simulation.

For example, in areas with the same tilt angle, the same orientation, the same module, and the same PCS conditions, it may be possible to treat them collectively during the initial study phase. Even if the detailed design is brought closer to the actual circuit configuration, consolidating into representative configurations for rough comparisons of generation and for examining layout patterns allows recalculations to proceed more quickly.

Regarding string configuration, before reflecting every minor difference you need to consider how much those differences will affect the simulation results. If string lengths differ substantially, if they affect the input voltage range, if shading is uneven, or if the PCS input conditions differ, it is worth configuring them in detail. On the other hand, when the final circuit has not yet been determined during the study phase, it is more efficient to perform calculations using a provisional standard configuration and refine the details later.

When the array configuration becomes complex, not only does recalculation become slower, but it can also cause errors and warnings. Verifying the consistency of input voltage, current, PCS capacity, DC/AC ratio, oversizing ratio, number of strings, number of inputs, and so on takes time, and you need to check warnings every time you make a change. The more detailed the settings, the harder it becomes to track which change caused the results to change.

In practice, it is effective to first create a simple baseline array configuration. From there, change the tilt angle, change the azimuth, change the PCS capacity, change the number of strings—separating and comparing each change one by one. If you include all elements in a complex way from the start, recalculations will not only be slow but interpreting the results will also become difficult.

Also, if you change conditions repeatedly within the same project, it’s a good idea to save the state before each change under a different name. If you keep directly editing a complex model, you’ll lose track of when the calculations started to become heavy. It’s important to be able to determine whether it slowed down after adding a subarray or after making the string settings more detailed.

The array configuration is a crucial setting at the heart of power generation simulations. However, you do not always need to enter it at a final design level if doing so would slow down your workflow. The basic approach to using PVSyst efficiently is to switch between a simplified model, a detailed model, and a submission-ready model depending on the stage of analysis.

Improvement Measure 3: Confirm the handling of meteorological data and temporal resolution

In PVSyst calculations, the way meteorological data are handled also affects recalculation time. Because power generation is calculated based on data such as irradiance, ambient temperature, wind speed, the diffuse component, and the direct component, the amount of processing varies depending on the types of data loaded, the period, and the time resolution. In a typical annual simulation, standard meteorological data are often used, but when using custom detailed time-series data or comparing multiple meteorological datasets, recalculation and loading can take longer.

First, what I want to confirm is whether highly detailed meteorological data are truly necessary at the current stage of study. In initial assessments, representative annual data may be sufficient. If you repeatedly recalculate using fine-grained time-series data or multi-year data while deciding the overall design direction, work efficiency will decrease. It is more efficient to examine detailed meteorological conditions after the candidate options have been narrowed down.

Next, verify that the weather data files are properly organized. Data imported from external sources may contain unnecessary columns or inconsistencies, which can slow down loading and conversion. Missing timestamps, outliers, differences in units, time zone offsets, and mismatches in solar radiation entries can make pre-calculation checks and corrections time-consuming. Even if recalculations seem slow, you may actually be spending time on loading and validating the weather data.

When changing and comparing meteorological data, it is important to clarify the purpose of the comparison. The required data granularity depends on whether you want to see large trends in annual power generation, monthly fluctuations, or the impact of a particular season. Instead of calculating every scenario at the same level of detail each time, it is effective to first check trends using coarse conditions and then examine only the important cases in detail.

Also, when you increase the detail of both meteorological data and shadow analysis at the same time, recalculations can suddenly become much heavier. For example, if you have a complex 3D scene, use detailed time-series data, and also set loss parameters finely, it becomes difficult to determine which element is increasing calculation time. In such cases, first simplify the shadow analysis and compare only the differences in meteorological data, then add the shadow conditions afterward; dividing the items to be examined like this makes it easier to identify the cause.

What’s important when using PVSyst is not always choosing the most detailed settings. It’s about ensuring sufficient accuracy for the purpose of the study while avoiding unnecessary computational load. Meteorological data must be handled carefully because it forms the basis for energy yield estimates, but it is not always necessary to use detailed data for every recalculation.

In practice, efficiency improves if you choose a single reference meteorological dataset and build a standard model using it. In addition, comparisons with other datasets, checks under conservative conditions, and assessments of long-term variability are performed as separate models. This keeps routine recalculations lightweight while allowing detailed investigations when necessary.

Improvement 4: Restrict loss settings to a necessary and sufficient range

In PVSyst, you can set various losses such as temperature losses, wiring losses, mismatch losses, soiling losses, degradation, PCS losses, shading losses, and conditions related to availability. These are important for bringing the estimated energy production closer to reality, but if recalculations are slow you should review whether the loss settings have become overly detailed.

Loss settings affect not only the calculation time itself but also input verification and result checking. For example, if you set everything—monthly soiling losses, multiple temperature-condition patterns, detailed wiring conditions, and losses for finely divided subarrays—the number of items to check increases every time conditions are changed. As a result, not only do recalculations take longer, but the entire workflow slows down.

First, identify which losses will influence the current design decision. For example, if you are comparing different racking systems, temperature conditions and shading conditions become important. On the other hand, if you are still at the stage of considering a preliminary layout, precisely accounting for wiring length and minor mismatch losses may have only a limited impact on design decisions. Treat lower-priority losses using standard values or assumed conditions, and focus comparisons on the critical factors to improve efficiency.

A common mistake in loss settings is copying and using the settings from past projects as-is. Past models may include conditions specific to that project. For example, unusual soiling conditions, a particular mounting system, long wiring distances, or special temperature conditions. Using these unchanged in a new project makes the model more complex than necessary, which not only slows recalculations but also reduces the validity of the results.

When you change loss settings, it is important to check their impact on power generation. Even if you detail a particular loss item, if its effect on annual energy production is negligible, it may be acceptable to simplify it in preliminary studies. Conversely, items whose results change significantly with small adjustments should be set carefully. To shorten recalculation time, you need the ability to distinguish between settings that have a large impact and those that have a small impact.

When organizing loss settings, it is helpful to note the assumptions in the model for later reference. If you clearly indicate which losses are assigned provisional values, which losses are set based on site conditions, and which items need to be reviewed before submission, you can avoid repeating unnecessary detailed calculations during the work.

When you feel that PVSyst recalculations are slow, it is important to confirm what purpose the current model was created for before adding more settings. For a preliminary assessment, keep loss settings to the minimum required; for detailed analysis, refine the key items; for deliverables, organize the conditions with an emphasis on accountability. Applying these distinctions lets you reduce recalculation wait times while producing high-quality simulations.

Improvement 5: Organize File Management and Storage Locations

The cause of slow recalculations in PVSyst is not limited to model settings. File management and the condition of the storage location can also make the software sluggish. In particular, as project files, weather data, output reports, backup files, and comparison files increase, saving and loading tend to take longer.

First, what I want to confirm is whether the project you are working on is placed in a stable local environment. If you are saving and working directly in a company-shared location or a synchronized location, communication and synchronization occur every time you save, which can make operations feel slow. In particular, in workflows that perform automatic saves or report saves after recalculation, a slow response from the save destination can make the entire operation appear to be stalled.

In practice, it is more reliable to keep files you are working on temporarily in a local working folder and copy them to the shared location only after calculations or edits are complete. This reduces the risk of synchronization processes interrupting while recalculations or saves are in progress. Even when sharing is necessary, separating working files from shared files prevents the model you are editing from becoming sluggish or bloated.

Next, let's organize version control for project files. If you save under a different name every time you change conditions, you'll end up with a large number of similar files. This can be convenient for comparison, but without a file-naming convention you won't know which is the latest, which is for submission, or which is still in progress. As a result, you may open unnecessary files or load heavy models repeatedly, increasing the time spent on work.

Including the project name, analysis conditions, date, and purpose in file names makes them easier to manage. For example, if you use names that indicate their purpose—such as preliminary assessment, shading details, loss review, or for submission—you can avoid opening unnecessary models. To speed up PVSyst recalculations, it is important not only to shorten the calculations themselves but also to reduce peripheral tasks such as searching, opening, saving, and comparing.

If you keep placing a large number of output reports and result files in the same folder, management becomes cumbersome. It's a good idea to save past output results organized into categories such as verified, submitted, and for comparison. Even just cleaning up unnecessary temporary files can make your working folder easier to navigate and reduce accidental operations.

If you continue editing a project over a long period, unnecessary settings and past analysis conditions may remain. Copying and reusing old models repeatedly can mix in data that isn’t needed for the current case and make the model more complex. If recalculations start to slow down, consider creating a new project and carrying over only the necessary conditions. This may seem like extra work, but organizing and removing unnecessary settings makes it easier to explain the results.

Problems with storage locations and file management are often overlooked, but they have a significant impact on work efficiency. To improve how PVSyst is used, it is important to review not only the settings within the software but also the structure of working folders, file names, save locations, and sharing methods.

Improvement 6: Separate the working model and the submission model

One of the root causes of slow recalculations in PVSyst is trying to make a single model serve all purposes. If preliminary evaluations, internal comparisons, detailed design, client explanations, and the preparation of submission materials are all handled in the same file, the model becomes increasingly complex. As a result, recalculations slow down and it becomes harder to change conditions.

To avoid this issue, it is effective to separate a working model from a submission model. The working model is a lightweight model for quickly changing and comparing conditions. Keep the 3D scene to the bare minimum, consolidate array configurations to representative conditions, and focus loss settings on items relevant to the purpose of the analysis. By contrast, the submission model reflects the final conditions and is configured with the settings necessary for explanation. Even if re-computation is somewhat slower, prioritize the rationale for the conditions and reproducibility.

In working models, it is important to clearly specify which items will be changed. For example, separating models by purpose—such as a model for comparing tilt angle, a model for comparing azimuth, a model for comparing PCS capacity, and a model for comparing shading conditions—keeps recalculations light and makes differences in results easier to interpret. If you change all conditions at once, it becomes difficult to tell which setting affected energy output.

In the submission model, add the necessary detailed settings based on the conditions determined in the working model. It is only at this stage that the 3D scene accuracy, shadow analysis, loss conditions, report output, and result checks for explanatory purposes are carefully performed. Ideally, the submission model should be created after frequent trial-and-error is complete so that long computation times are less problematic.

If you don't make this division, you'll end up re-running heavy models many times from the very early stages of study. For example, even when you're still deciding the orientation of the layout, running calculations each time with a model that includes detailed shadow analysis and complex loss settings will greatly reduce work efficiency. Conversely, if you keep a simplified model up until just before submission, insufficient explanations and omitted conditions can occur. By separating models according to the stage, you can achieve both speed and quality.

It's also useful to create a separate model for internal review. In internal reviews, it is not always necessary to check every detailed setting. Because comparisons of power generation, differences in assumptions, and the effects of design changes are often sufficient, preparing a lightweight model and a summary of results makes discussion easier. Finalizing the submission model after the review has settled on a direction reduces unnecessary recalculations.

As you become more familiar with PVSyst, you may be tempted to build a highly polished model from the start. However, in practice the conditions often change repeatedly during the review phase. If you keep modifying a heavy model every time the site boundary, number of modules, mounting system, PCS capacity, shading conditions, loss assumptions, submission format, etc. change, your work time will increase. Establishing a workflow in which you quickly make decisions using a lightweight working model and then reflect them in the final submission model is extremely important for minimizing delays from slow recalculations.

Practical workflow to speed up recalculation

To apply the six improvement measures discussed so far in practice, it is important to organize the order of tasks. When PVSyst recalculations are slow, changing individual settings ad hoc is unlikely to lead to fundamental improvements. If you create a lightweight model first, add conditions incrementally, and finalize the details at the end, you can reduce unnecessary recalculations.

Initially, we create a preliminary model. At this stage, input the installed capacity, azimuth, tilt angle, basic array configuration, and representative weather conditions, and check the rough trends in power generation. Keep 3D scenes and detailed shading conditions to the minimum necessary. The goal is not to produce perfect results but to narrow down candidate conditions.

Next, change the conditions you want to compare one at a time. If you change the tilt angle, change only the tilt angle; if you change the azimuth angle, change only the azimuth angle; if you change the PCS capacity, change only the PCS conditions. By doing this, not only will recalculation be faster, but it will also be easier to understand what the differences in the results are attributable to. Changing multiple conditions at the same time reduces the efficiency of the analysis and makes explanations more difficult.

Once the candidates have been narrowed down, add the shadow conditions. Even then, rather than immediately adding all surrounding structures in detail, add them in order from the elements that most significantly affect the power-generating surface. Proceed while checking which of the buildings, adjacent rows, terrain, fences, surrounding objects, etc., are influencing the results. If recalculation suddenly becomes slow immediately after adding shadow conditions, that 3D scene may be too heavy.

Then, detail the loss settings. Check temperature conditions, wiring losses, soiling losses, mismatch losses, degradation conditions, etc., and align them with the project's assumptions. Here too, rather than detailing everything, prioritize items that affect energy production and accountability. If you subdivide items down to those with small impact, you not only increase workload but also complicate the explanation of the assumptions.

Finally, prepare it as the submission model. Organize file names, remove unnecessary analysis conditions, and confirm that the information required for report output is present. Before submission, verify that the input conditions, simulation results, loss breakdown, monthly generation, shading losses, array configuration, and PCS conditions are consistent. At this stage, even if recalculation is somewhat slow, the overall impact on the work is small because the main analyses have already been completed.

Standardizing this workflow within the company reduces variations in work between staff members. When one person creates a detailed model from the start while another proceeds with a simplified model, comparing results and conducting reviews becomes difficult. If you clearly define the stages—preliminary study, detailed study, and submission—you can shorten not only PVSyst recalculation time but also the time required for internal approvals and customer explanations.

The most important factor in speeding up recalculations is not making the model lighter per se, but making it an appropriate size for the purpose of the study. A model that is too coarse can lead to incorrect judgments, while a model that is too heavy will hinder progress. Gradually adding detail while balancing the required accuracy and working speed leads to a PVSyst workflow that is practical and easy to use.

Summary: It is important to have a system that can quickly and accurately reflect on-site conditions

When PVSyst recalculations are slow, it is important not to blame the computer’s performance alone but to comprehensively review how the model is built, the 3D scene, shading analysis, array configuration, meteorological data, loss settings, file management, and workflow. In particular, if the 3D scene is overly complex or sub-arrays are divided too finely, the recalculation load tends to increase.

The basic principle of improvement is to vary the level of model detail according to the stage of work. In the initial review, use lightweight models to compare quickly and determine the direction by changing only the important conditions. Once candidates are narrowed down, add shading conditions and loss settings, and finally refine the model for submission. By following this order, you can reduce unnecessary recalculations while ensuring the accuracy required in practice.

Also, PVSyst calculation results are greatly influenced by the quality of the input conditions. No matter how well you refine the calculation settings, if the site’s topography, rack positions, obstacles, installation area, azimuth, tilt, or surrounding conditions are unclear, the reliability of the simulation results will decrease. While organizing the model to speed up recalculations is important, it is equally important to have a system in place to accurately obtain on-site conditions.

In designing photovoltaic systems, a key consideration is how to reflect location and terrain information obtained from on-site surveys in PVSyst’s configuration settings. If you can accurately capture the site boundaries, the positions of racking rows, the locations of obstructions, ground elevations, and the relationships with surrounding structures, you can reduce unnecessary assumptions and minimize the need to re-run simulations. In other words, to speed up recalculations you need to review not only the settings in the software but also the accuracy of on-site data acquisition and the methods used to organize that data.

On that point, LRTK, a GNSS high-precision positioning device that can be attached to an iPhone, is a good fit for on-site inspections and pre-design surveys of solar power plants. If you can organize the high-precision positional information obtained on site—such as racking layout, site conditions, obstacles, point cloud data, and photographic records—you can make the assumptions entered into PVSyst clearer. Being able to grasp site conditions quickly and more easily reflect them in the design parameters will also help reduce iterations of rework and recalculation in PVSyst.

When you find PVSyst recalculations slow, it is important to start by simplifying the model, then streamline your workflow, and finally review how you collect on-site data. Speeding up calculations is not merely a time-saver; it is a practical improvement that enables quick responses to changing conditions, accelerates design decisions, and leads to more accurate generation estimates. By combining PVSyst with high-precision on-site positioning, you can more easily improve the speed and reliability of solar power system design evaluations.