【How to Simulate Energy Production with PVSyst in 8 Steps】

Table of Contents

• Overview of power generation simulation

• Step 1 Clarify the purpose of the simulation

• Step 2 Prepare the project site and meteorological conditions

• Step 3 Enter installation orientation and tilt conditions

• Step 4 Match equipment configuration and capacity balance

• Step 5 Bring loss conditions closer to reality

• Step 6 Reflect the impact of shading

• Step 7 Run the simulation

• Step 8 Interpret the results and return to the design

• Common mistakes in using PVSyst

• Summary

Overview of Power Generation Simulation

PVSyst simulations of power generation are easier to understand if you consider them not as rough single-month estimates but fundamentally as detailed time-series evaluations based on site and meteorological data. In practice, the basic workflow is to prepare the project itself and then create multiple comparison cases with different conditions within that project for analysis. For example, even for the same planned site, creating and comparing separate cases that vary the tilt angle, alter the capacity distribution, or assume stricter shading conditions makes it easier to make design decisions based on evidence rather than intuition. The official PVSyst documentation also describes a structure in which detailed time-step simulations are managed on a per-project basis and multiple comparison cases are created for optimization and comparison.

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Also, the value of power generation simulations is not limited to the final annual energy yield. What matters is being able to grasp which losses have what effect, how they vary seasonally, and which conditions are acting as bottlenecks. Because the final output is the accumulation of factors such as the solar irradiance reaching the installation surface, optical losses, temperature-related degradation, electrical mismatch, wiring losses, and shading effects, it is difficult to identify improvements by looking only at the final result. Once you can read and interpret the intermediate logic, your understanding of how to use PVSyst deepens considerably.

Therefore, beginners especially should not rush the input tasks; first, it is important to grasp the overall flow. If you understand which data should be finalized first, which can be left as placeholders, and which should be carefully refined to match on-site conditions, both the accuracy and reproducibility of the simulation results will improve. The eight steps in this article are ordered to make that judgment easier.

Step 1 Clarify the purpose of the simulation

The first thing to do is to clarify why you are running the power generation simulation. If you begin entering inputs while this is unclear, you may end up spending time on unnecessarily detailed conditions or, conversely, overlooking important conditions. For example, the required level of detail differs depending on whether it is an initial rough estimate, a comparative document for internal presentation, or a detailed study prior to construction.

When organizing objectives, first define the scope of the evaluation. Whether it is ground-mounted or roof-mounted, whether it has a single orientation or multiple orientations, and whether it leans toward surplus power sales or toward self-consumption — when these assumptions change, the input items to prioritize also change. Furthermore, decide in advance whether you want to look only at annual generation, check monthly variations, or emphasize the impact of particular seasons.

In practice, the recommendation here is not to try to produce a perfect single plan from the outset. Rather, it becomes easier to make decisions by creating one baseline plan under standard conditions and then adding a conservative plan and an optimistic plan for comparison. The baseline plan should include representative conditions; the conservative plan should assume somewhat stricter losses and impacts; and the optimistic plan should assume favorable conditions. Looking at the range in this way helps avoid overreliance on a single number.

A common pitfall for practitioners using PVSyst is that filling in the software’s input fields becomes an end in itself. The true objective is to perform an explainable energy yield assessment based on reasonable assumptions. Simply adopting this perspective from the outset greatly improves the quality of subsequent inputs.

Step 2: Prepare the site and weather conditions

Next, it is important to organize the project site and meteorological conditions. The foundation of a power generation simulation is solar irradiance and weather conditions, so if this is handled roughly, no matter how carefully you refine other parameters later the credibility of the results will be weak. In PVSyst outputs, meteorological data such as global horizontal irradiance, the diffuse component, temperature, and wind speed are used, and values converted from these into the irradiance incident on the installation surface are used in the calculations. In other words, site location settings and meteorological conditions are not mere address inputs but the entry point to the entire calculation.

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In practice, it is important to first grasp how atypical the planned site’s environment is. Whether the location is flat with few tall obstructions nearby, in a mountainous area, along the coast, or in a region where snowfall, salt damage, or wind effects should be considered, simply applying average conditions may be insufficient. In particular, on sites that include developed land or slopes, terrain changes how solar radiation is received and the installation conditions, so if the site is not well understood the entire simulation can easily become inaccurate.

Also, when dealing with meteorological conditions, it is important not to be reassured by annual averages alone. Even if annual power generation is similar, locations that perform better in summer and those that perform better in winter will have very different monthly generation curves. For projects where you want to assess alignment with demand, you should take monthly trends and seasonal deviations into account. As a practitioner, proceed with inputs on the assumption that you will definitely check the monthly results later; doing so makes failures less likely.

Furthermore, the impact of distant terrain cannot be ignored. Even if they are less conspicuous than nearby buildings or trees, obstructions along mountain ridgelines or near the horizon affect morning and evening solar radiation. Grasping these conditions early on improves the accuracy when you later incorporate shading conditions. When you are just beginning to learn how to use PVSyst, developing the habit of carefully checking the site and meteorological conditions first is the most effective way to improve.

Step 3 Enter the installation orientation and tilt conditions

In power generation simulations, the orientation and tilt angle of the installation surface are directly linked to the amount of generated power. Even at the same site, changing the direction and angle can greatly alter the seasonal distribution of incident solar radiation. Therefore, it is important here not merely to enter the values from the drawings, but to understand what those values mean from the perspective of power generation.

With rooftop installations, orientation and tilt angle are often almost fixed by the building conditions, whereas ground-mounted installations offer some room for optimization. However, it is not always sufficient to pursue generation output alone. In practice, multiple constraints interact — such as site preparation volume, maintenance access routes, racking conditions, impacts on surrounding areas, aesthetics, and constructability. The role of simulation is not to produce the theoretical maximum, but to compare reasonable options within the constraint conditions.

Also, in projects that combine multiple orientations, it is important not to treat them crudely as a single surface. For east- and west-facing roofs or ground-mounted installations with multiple tiers of inclined surfaces, evaluating the conditions of each surface separately will be closer to reality. Because the time series of incident solar radiation differs for different installation surfaces, averaging them together can lead to misjudging peak times and monthly characteristics.

A practical tip here is to first perform the calculation using the design proposal’s conditions as-is, and then create comparison cases in which you slightly change the tilt angle and the orientation. This reveals whether the current design is in a high-sensitivity condition or whether small deviations have little impact. If it’s the latter, it becomes easier to justify prioritizing constructability and maintainability. Rather than simply seeking a single optimal solution, using PVSyst to evaluate robustness against changes in conditions is also an important use.

Step 4: Align equipment configuration and capacity balance

The next step is to align the equipment configuration with the capacity balance. Here we check whether the generation-side configuration and the conversion-side receiving capacity are well matched without strain. If the generation-side capacity is made too large, output may be curtailed during certain time periods; conversely, if it is too conservative, the equipment may not be fully utilized. In practice, the capacity ratio often becomes a subject of debate, so it should be set with a clear design intent.

How you choose the number of series and parallel strings is also important. If you configure the system without accounting for voltage rises at low temperatures, the operating range at high temperatures, and input current constraints, you may end up with a non-viable configuration or with setups that are inefficient during certain periods of the year. PVSyst is designed to verify the consistency of input conditions and will display warnings when there are problems, so it is important not to ignore those warnings and to understand why they appear.

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Furthermore, the equipment configuration affects not only power generation but also how losses manifest. There are many points that directly influence the interpretation of simulation results, such as how multiple installation surfaces are electrically combined, whether to leave capacity margins or to push the capacity, and whether the configuration is prone to partial shading. If these aspects are left ambiguous and you later only fine-tune the loss settings, the overall study will not be highly accurate.

What practitioners should be mindful of is not to treat the equipment configuration as merely a component selection. In power generation simulations, the equipment configuration is central to the input conditions and influences the results as much as the installation conditions. First ensure feasibility, and then it is important to consider—balanced—annual power generation, whether output curtailment will occur, design margins, and ease of handling during operation.

Step 5: Make loss conditions more realistic

One of the biggest factors that determines the accuracy of power generation simulations is the settings for loss conditions. Beginners tend to leave this section at the default values, but in practice the reliability of the results can change significantly depending on how this is set. Typical examples include output reduction due to temperature rise, wiring losses, mismatch caused by variations between modules, and degradation due to soiling. In PVSyst’s official documentation, conversion from incident irradiance to effective irradiance, temperature losses, module quality, mismatch, wiring losses, and soiling are organized as simulation processes and loss items.

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Temperature losses become harder to ignore the clearer and stronger the solar irradiance. In the field, it is common to assume that higher irradiance will simply increase power generation, but in reality cell temperature rises and reduces output, so the discrepancy from the ideal value tends to be larger during clear midsummer conditions. Because the rate of temperature rise also depends on the mounting method and ventilation conditions, it is important to check the actual installation—such as whether the panels are closely adhered to the roof surface or allow for good airflow.

Soiling losses are another factor that is easy to underestimate. In relatively calm environments, such as residential areas, the impact may be small, but in places prone to dust, locations with heavy traffic, coastal areas, or regions susceptible to pollen or yellow sand, they can be significant even on an annual average. Furthermore, because the month-to-month decline varies depending on whether regular cleaning is performed, it is important to set this according to actual operation.

Wiring loss and mismatch loss may look like minor differences at first glance, but they definitely have an impact over the course of a year. Especially for projects with multiple rows or complex wiring routes, it’s easier to explain later if you enter values using an approach that reflects the actual wiring layout rather than setting a single uniform value carelessly. Even when you can’t measure every detail, it’s important to be able to explain why you adopted those values.

The point here is that it's not a simple matter of "the stricter, the safer." An excessively large loss assumption makes project evaluations unnecessarily pessimistic, while an overly small assumption creates a divergence from expected values later. Using standard values for the baseline case and creating a conservative scenario as a sensitivity check will result in a simulation that's easier to use for internal explanations and decision-making.

Step 6 Reflect the effects of shadows

Handling shading conditions is one of the areas in PVSyst where practical results often diverge. If there are nearby buildings, trees, rows of racking, parapets, or terrain undulations, ignoring shading tends to lead to an overestimation of energy production. Even shading that occurs only in the morning or evening can be significant in winter or at low solar elevations, so it’s safer not to treat it lightly based on appearance alone.

In PVSyst, the approach of using a shading-factor table for near shading is adopted to reduce the computational load for each time step, and the effects of shading are mainly reflected in the components of solar radiation. Furthermore, near shading affects not only the direct component but also the diffuse and ground-reflected components, and as a result it appears as an overall loss of solar radiation. The official documentation also explains that using a shading-factor table speeds up simulations and treats shading losses on direct, diffuse, and total solar radiation as outputs.

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In practice, the important thing is to strike a balance between not over-modeling shadows and not being too careless. In initial assessments it is more efficient to include only the major obstructions to capture the trend, and to refine the surrounding conditions during detailed studies. Conversely, at sites with many obstructions, discussing only annual energy production without considering shadows at all will make it difficult to provide explanations later. It is realistic to improve the accuracy of shading conditions by iterating between on-site inspections and drawing reviews.

Also, it is important to note that partial shading cannot always be represented by a simple area ratio. Because the electrical connections can amplify the effect, you should not judge solely by what percentage is shaded. In particular, depending on the string configuration and how circuits are grouped, the impact can be greater than it appears. If you want to improve the reliability of power generation simulations, shading should be treated not as an afterthought but as an element considered together with the design.

Step 7 Run the simulation

Once these conditions are in place, you finally run the simulation. However, in practice it is important not to treat this stage as merely executing a calculation. In PVSyst, after the project, comparison cases, mounting surfaces, equipment configuration and other conditions have been set, input consistency is checked, and warnings are issued if any problems remain. The official documentation also states that input consistency checks are performed before the simulation, that warnings are issued according to the severity of any problems, and that you proceed to the results screen once preparations are complete.

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Therefore, before execution, double-check that there are no inconsistencies in the site settings, azimuth and tilt, equipment configuration, loss conditions, and shading conditions. Beginners in particular should be careful, because placeholder values entered partway through tend to remain. Common examples are leaving the loss values entered for the initial estimate unchanged, calculating for a single plane when there are actually multiple planes, and forgetting to add shading conditions later as intended.

Also, it is important not to stop after a single calculation. Power generation simulations do not become meaningful by producing one baseline scenario and ending there; they gain value by lining up comparison cases and examining the differences. By running multiple simulations while slightly varying factors such as tilt angle, capacity ratio, and soiling conditions, you can see which conditions influence the results. In practice, this accumulation of comparisons forms the basis for design decisions.

Step 8 Interpret the results and return to design

After the simulation ends, it is important not to be satisfied with looking only at the annual energy production. In PVSyst’s results, in addition to a printable report, many views are provided, such as monthly tables, graphs, time-step behavior, and loss diagrams. The official documentation also explains that, in addition to the report summarizing the main results, you can check monthly tables, monthly and daily graphs, time-step displays, and loss diagrams.

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The first thing to check is the balance between annual generation and monthly generation. Even if the annual figure seems reasonable, if there are extreme drops in particular months you should suspect shading, mounting surface conditions, or seasonally dependent loss settings. In projects where you want to align generation with demand, monthly imbalances can be more important than the annual figure. For example, the desired generation curve differs between projects that prioritize self-consumption in summer and those with high demand in winter.

Next, what we want to check is the loss diagram. The loss diagram clearly shows where energy is being lost, making it extremely useful for finding starting points for improvement. The official documentation also explains that the loss diagram is effective for quickly assessing design quality and identifying the major loss factors. By seeing whether temperature loss is large, shading loss is significant, or soiling and mismatches are accumulating, it becomes clear which conditions should be reviewed next.

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Furthermore, when interpreting results, it is essential to revisit the input conditions. A simulation does not provide the final answer in a single run; its essence is a cycle of taking the results, modifying the design, and recalculating. If shading losses are larger than expected, options include changing the layout, reviewing row spacing, or adjusting the clearance to obstacles. If temperature-related losses are large, it may be necessary to reconsider ventilation conditions or the installation method.

Also, when using the results as explanatory materials, it is important to verbalize not only the final figures but also why those figures came about. In practice, supervisors, salespeople, construction staff, owners, etc., each emphasize different points. Rather than showing only the annual energy generation, it is better to explain it together with the major losses, monthly trends, and differences from comparison cases to create more convincing materials.

When learning how to use PVSyst, the important skill is the ability to read the results screen. The correctness of the inputs can only be judged by checking the consistency of the results. In other words, completing the simulation is not the goal but the starting point for design decisions.

Common Mistakes When Using PVSyst

One common mistake is setting meteorological conditions too generally. If calculations are performed without adequately accounting for site-specific differences in solar radiation and temperature characteristics, annual figures may look plausible while showing large deviations from actual operation. Especially at locations with pronounced surrounding topography or strong local environmental conditions, it is necessary to deepen understanding of the site from the initial stages.

The second issue is being overly optimistic about loss conditions. If you take dirt, wiring, temperature, mismatches, and so on too lightly, the calculations will tend to produce attractive numbers, but they become difficult to explain later. Conversely, setting everything too conservatively can unnecessarily lower the project's evaluation. What’s important is to input values in a state where you can explain why you chose them.

The third is delaying consideration of shading for too long. At some sites, shading can become a major source of losses. Moreover, shading is not simply a matter of getting slightly darker in the morning and evening; depending on the season and the electrical connections, its impact can be amplified. It is dangerous to proceed with decision-making based solely on draft standards that underestimate shading.

The fourth is drawing conclusions based only on annual energy production. If you don't examine monthly imbalances, the shape of the loss diagram, and the differences from comparative cases, you'll miss opportunities for improvement. Energy production simulation is not merely an exercise in producing a single number; it is also a process for identifying which parts of the design need to be corrected. With this perspective, PVSyst becomes not just calculation software but a tool that supports design review.

Summary

When performing power generation simulations in PVSyst, the basic workflow is to start by clarifying the objectives, then define the site and meteorological conditions, decide the orientation and tilt of the installation surface, ensure consistency of the equipment configuration, adjust loss parameters and shading to approximate reality before running the simulation, and finally interpret the results and feed them back into the design. Thinking in this order makes it easier to reduce input omissions and judgment errors, and also increases the explanatory power of the results.

In real-world projects, the accuracy of power generation simulations is not determined solely by desk-based inputs. The more on-site information—local topography, obstacles, available installation area, slope conditions, photographic records, and coordinate data—you have, the easier it becomes to align the simulation conditions with reality. In other words, the deeper you go into using PVSyst, the more you will appreciate that the precision of acquiring on-site information is equally important.

In that sense, having a means to connect on-site verification with design review makes the practical work of power generation simulation significantly easier to carry out. For example, when you want to capture coordinates while confirming candidate installation positions on reclaimed land, sloped terrain, or large sites, or when you need to accurately convey obstacle locations to the design team later, the speed and accuracy of field measurements can make a big difference.

If you want to make power generation simulations more practical for field work, it is important to organize not only the operation of design software but also how on-site information is collected. LRTK, as an iPhone-mounted GNSS high-precision positioning device, is an effective means to streamline on-site position acquisition, photo documentation, and simple surveying. To improve the accuracy of desk-based simulations, having a system that enables seamless progress from on-site verification to the creation of design conditions will further enhance the quality of power generation simulations.