【How to Compare Simulation Results in PVSyst｜4 Steps】

Table of Contents

• Situations Where Result Comparison in PVSyst Is Important

• Step 1: Align the simulation conditions to be compared

• Step 2: Compare annual and monthly energy production

• Step 3: Identify causes of differences from the loss diagram and PR

• Step 4: Translate comparison results into practical decisions

• Common mistakes and checkpoints when comparing

• Perspectives required to correctly reflect site conditions

• Summary

Situations Where Comparing Results in PVSyst Is Important

The purpose of comparing simulation results in PVSyst is to evaluate the merits of multiple proposals numerically rather than by intuition. In studies of photovoltaic power generation systems, candidate site conditions, system capacity, panel orientation, tilt of the mounting structure, series-parallel configuration, PCS capacity, shading effects, loss conditions, and other factors are interrelated in a complex way. Changing just one of these conditions can alter the annual energy production, monthly generation, PR, and the breakdown of losses, so if the comparison methodology is mistaken you may end up judging a plan that is actually disadvantageous as advantageous.

For example, changing the tilt angle may slightly increase annual generation while altering the generation trends between winter and summer. Changing the PCS capacity can cause differences in equipment utilization rate and clipping losses. Modifying the shading settings may seem to make only a small difference on an annual basis, but can have a large impact in specific months or time periods. To correctly interpret these kinds of differences, it is important not just to look at simulation results one by one, but to place them side by side and compare them from the same perspective.

Common comparison targets in practice include the baseline plan and an improved plan, different tilt angles, different orientations, different panel capacities, different PCS capacities, different layouts, with or without shading consideration, different loss conditions, and different meteorological data. All of these are conditions that affect power generation, but the metrics to look at change depending on the purpose of the comparison. Sometimes the emphasis is on maximizing annual energy generation, other times on winter generation, on minimizing output curtailment during peak periods, or on prioritizing maintainability and constructability.

What is important when comparing PVSyst results is to first decide "what the comparison is intended to judge." Depending on whether you want to see differences in energy production, analyze loss factors, confirm the validity of design changes, or organize the evidence to use in proposals or internal explanations, the screens and indicators you need to check will differ. If you compare only the results without defining a purpose, you may understand the numerical differences but will find it difficult to reach a decision.

Also, because PVSyst can save multiple simulation results, the number of result files and variations grows as the project review progresses. Even if there are only a few options at the initial stage, design changes, customer requests, field survey findings, and changes to grid conditions can make it difficult to tell which result is the most recent and which conditions were modified. For that reason, it is also very important in practice to organize case names and notes on conditions before starting any comparisons.

Result comparisons cannot be completed by operating PVSyst alone. They need to be judged together with design intent, site conditions, construction conditions, surveying accuracy, surrounding obstructions, operational policies, and so on. PVSyst’s numerical outputs are a powerful resource to support design decisions, but if their underlying assumptions diverge from the actual site, the comparison results will also deviate from reality. Therefore, when performing comparisons, you should not only look at the on‑screen energy production figures but also verify, one by one, the conditions from which those numbers arise.

Step 1: Standardize the simulation conditions to be compared

The first step when comparing simulation results in PVSyst is to align the conditions of the cases to be compared. "Align" here does not mean making everything identical. It means keeping all conditions other than the items you want to compare as similar as possible to make it easier to identify the reasons for any differences.

For example, when you want to compare differences in tilt angle, you need to keep the location, weather data, panel capacity, PCS capacity, azimuth, loss conditions, shading conditions, and so on the same. If not only the tilt angle but also the weather data or PCS capacity have changed, you will not be able to determine whether the difference in power output is due to the tilt angle or to some other condition. The basic rule for comparison is to limit the conditions you change at one time as much as possible.

In practice, it is clearer to duplicate an existing simulation case, modify only the items you want to change, and save it as a separate case. For case names, assign labels that make the changes obvious at a glance so they are easier to check later. For example, basic case, tilt-angle-change case, PCS-capacity-change case, case reflecting detailed shadows, and case reviewing loss conditions—naming them to show what was changed makes it less likely you’ll be confused when comparing results.

When aligning conditions, particular attention should be paid to weather data, site information, equipment capacity, loss settings, and shading settings. If the weather data differ, assumptions about solar irradiance and temperature change, so you cannot tell whether differences in power generation are due to equipment design or meteorological conditions. If site information is misaligned, it also affects assumptions about latitude, longitude, elevation, solar radiation conditions, and solar altitude. In comparative cases, the basic step is to first confirm that the site and weather data are the same.

Care must also be taken regarding system capacity. When comparing options with different numbers of panels or nominal capacities, looking only at the absolute annual energy production can make the larger-capacity option appear advantageous. However, when capacities differ, you also need to consider generation per unit capacity and PR. Even if increasing capacity raises annual generation, efficiency may have declined due to shading effects or constraints on the PCS side.

When comparing differences in PCS capacity, pay attention to the relationship between DC-side capacity and AC-side capacity. If PCS capacity is reduced relative to DC capacity, under certain conditions the equipment can be used more efficiently, but output curtailment is more likely to occur during periods of strong solar irradiance. Conversely, even if PCS capacity is increased, if the increase in generated energy is limited, the design rationale should be examined separately. In comparing PVSyst results, it is important to look not only at annual energy production but also at the energy lost on the PCS side and the impact of output curtailment.

Loss settings also significantly affect comparison results. When loss conditions—soiling, wiring, mismatches, temperature, equipment efficiency, aging, and availability—differ, results can change even for the same layout. In particular, because loss assumptions are often revisited between the initial feasibility stage and the detailed design stage, it is important to be explicit about which stage’s conditions are being used for the comparison.

Regarding shading settings, results can vary depending on whether shading is considered in a simplified way or in detail. The appearance of generation output and losses changes depending on how much shading from surrounding buildings, trees, terrain, and between pieces of equipment is reflected. If the accuracy of shading settings differs among the cases being compared, a straightforward comparison of which is better cannot be made. If you want to compare shading conditions, you need to clearly separate cases with and without shading settings and keep all other conditions the same when reviewing the results.

The important thing in this procedure is to confirm the assumptions of the items to be compared before creating a comparison table. The numbers shown on PVSyst's result screen are aggregates of the input conditions. If the input conditions are inconsistent, the comparison results will also be inconsistent. Before comparing simulation results, review the settings for each case and verify whether they are in a state suitable for comparison; doing so leads to more accurate judgments.

Step 2: Compare annual power generation and monthly power generation

Once the conditions are aligned, the next step is to compare the annual energy production and the monthly energy production. When reviewing PVSyst simulation results, many persons in charge first focus on the annual energy production. Annual energy production is an easy-to-understand indicator for grasping the expected generation for the entire project. When comparing multiple proposals, listing the annual energy production first lets you confirm which proposal is larger in total.

However, it is dangerous to judge based solely on annual power generation. Even if the annual generation is similar, the monthly generation trends can differ greatly. For example, one option may perform strongly from spring to summer, while another may be relatively stable from autumn to winter. Depending on feed-in conditions, consumer-side consumption patterns, and the operational purpose of the facility, generation during specific periods can be more important than the annual total. Therefore, after checking the annual generation, always review the monthly generation to determine in which months the differences occur.

Looking at monthly power generation makes the effects of changing conditions easier to see. If the tilt angle is changed, seasonal changes in solar altitude alter how differences appear between summer and winter. If the azimuth (orientation) is changed, not only do morning and afternoon output patterns change, but monthly generation can also be affected. When shading effects are included in detail, losses tend to increase at the low solar altitudes in winter, and differences that appear small on an annual basis can become concentrated in specific months.

When comparing PVSyst results, a practical workflow is to look at the difference in annual energy production and then check in which months that difference occurs. Even if the annual difference is only a few percent, if it drops significantly in a particular month, you need to investigate the cause. Conversely, if the annual difference is small and there is no large monthly bias, you may decide to prioritize factors other than energy production, such as ease of construction, ease of maintenance, or the clarity of the system configuration.

When comparing cases with different capacities, it is important to check not only the absolute annual generation but also the generation per unit capacity. Increasing capacity will naturally increase generation, but it does not necessarily increase proportionally. If adding panels causes the layout to extend into locations that are more prone to shading, or if constraints on the PCS side increase, the generation efficiency per unit capacity can decline. In such cases, looking only at the annual generation may make it appear that output has increased, but the design efficiency may not have improved.

When comparing monthly power generation, you need to pay attention to the assumptions behind the meteorological data. If you compare cases using different meteorological datasets, differences in solar radiation and temperature will be reflected as differences in power generation. If you want to see differences due to equipment design, the basic approach is to compare using the same meteorological data. If you want to compare the meteorological data itself, you need to keep the equipment conditions the same and change only the meteorological conditions.

When comparing annual generation with monthly generation, it is important not only to see “which is larger” but also whether “the pattern of differences matches the design intent.” If you changed the tilt angle to favor winter but winter generation has not increased as much as expected, shading, orientation, or constraints of the mounting surface may be involved. If you changed the PCS capacity but annual generation hardly changes, output limitation may not have been the main factor. In this way, testing hypotheses while reviewing results is crucial to mastering PVSyst in practical work.

When explaining comparison results to stakeholders, supplementing annual energy production with a verbal description of monthly trends makes them easier to understand than showing only yearly totals. For example, if you can explain, "The improved proposal exceeds the other in annual energy production, but the difference mainly appears in winter," "The difference between the two proposals is small in summer, and the effect of shading is concentrated in winter," and "The option that increases capacity raises total energy production, but energy production per unit capacity is slightly lower," it will be conveyed not as a mere numerical comparison but as a basis for design decisions.

Step 3: Interpret the causes of the differences from the loss chart and PR

After checking the differences in annual and monthly energy production, next examine the loss diagram and PR to determine why the differences occurred. When comparing PVSyst results, what matters is not only the magnitude of the results but being able to explain the causes of any differences. Even if one option shows higher annual energy production, it is insufficient for a practical decision unless you verify whether that is due to more effective use of solar irradiance, differences in loss conditions, or omitted inputs.

A loss diagram is essential information for checking where and how much solar energy is lost in the process of becoming the final output. In photovoltaic simulations, the final energy yield is determined by the accumulation of various losses such as plane-of-array irradiance, reflection, shading, temperature, panel characteristics, wiring, mismatch, PCS conversion, output limiting, and so on. When comparing multiple simulation results, examining each item in the loss diagram allows you to identify the main causes of differences in energy production.

For example, when systems with the same capacity produce significantly different amounts of power, first check whether there are differences in shading losses, temperature losses, losses on the PCS side, wiring losses, and so on. If shading losses are large, suspect the layout, surrounding obstacles, terrain, or the effect of solar altitude. If temperature losses are large, check the installation method, ventilation conditions, meteorological conditions, and assumptions about module temperature. If PCS losses or output limitations are large, it is necessary to review the balance between DC-side capacity and AC-side capacity, the equipment configuration, and the operating conditions.

PR is a useful indicator for comparing the overall performance of a system. PR is a concept that indicates how efficiently a system converts incident solar irradiance into electrical energy, and it is also useful when comparing projects or proposals with different capacities. However, PR should not be judged on its own. A high PR does not necessarily mean a better option; it must be considered together with energy production, capacity, losses, and design objectives.

For example, a proposal with high annual generation but a declining PR may mean that although the total output increased because capacity was increased, efficiency has actually fallen. Conversely, a high PR can coincide with small installed capacity and insufficient annual generation. In practice, annual generation and PR are evaluated together to judge both whether the total output is advantageous and whether the efficiency is reasonable.

When comparing loss diagrams and PR, be aware that apparent improvements can result from differences in input conditions. For example, if a case assumes a low soiling loss, the energy yield and PR will look better. However, if that does not match the on-site reality, the comparison is not appropriate. Similarly, if you simply compare a case with simplified shading conditions to one that reflects shading in detail, the detailed case may appear worse. That does not mean the design is poor; it may be the result of using conditions closer to reality.

Therefore, when looking at a loss diagram, you should check not only “which losses are large” but also “whether those loss assumptions are realistic.” In practical comparisons, results that appropriately reflect on-site conditions are more valuable than results close to ideal conditions. Even a proposal that appears to have higher power generation can lead to incorrect expectations in later stages if the loss assumptions are overly optimistic.

When explaining a comparison of results, it is easier to understand if you organize the differences in losses in prose. For example, "In the improvement scenario the annual energy yield has increased, but the primary factor is a reduction in shading losses," "In the scenario with changed PCS capacity, losses due to power clipping have decreased, but the increase in annual energy yield is limited," "In the layout-change scenario winter shading losses have improved, but losses due to increased cable length should also be checked." By linking numerical differences to their causes in this way, PVSyst results become more usable for design decisions.

Step 4: Apply the comparison results to practical decision-making

The final step is to translate the PVSyst comparison results into practical, operational decisions. Comparing simulation results is not simply a matter of checking the numbers. Based on the comparison results, you need to decide which design option to adopt, whether additional study is required, whether on-site verification is necessary, and how to explain the conclusions to stakeholders.

In practical decision-making, we comprehensively evaluate annual generation, monthly generation, PR, loss diagrams, installed capacity, layout conditions, constructability, maintainability, and site constraints. Even if a plan yields the highest annual generation, it may be difficult to adopt if there are issues such as difficult construction, insufficient maintenance space, uncertain shading assumptions, incompatibility with terrain conditions, or being excessive relative to grid conditions. Conversely, a proposal that produces slightly less generation but offers better constructability and maintainability and lower risk is often chosen in practice.

When organizing the comparison results from PVSyst, it is important to verbalize which proposal is superior according to which metrics. Rather than simply writing "Plan A is good" or "Plan B has lower energy production," list both advantages and caveats, for example: "Plan A has higher annual energy production, but still exhibits shading losses in winter" and "Plan B is inferior in annual energy production but has smaller month-to-month variability and a layout that makes maintenance access easier."

When explaining comparison results to colleagues or clients, you need to convey the meaning of the numbers clearly. For stakeholders who do not use PVSyst regularly, detailed items such as PR and the loss diagram can be difficult to understand. Therefore, it is useful to be able to concisely explain "how large the difference in generation is," "which change in conditions caused that difference," and "how much it will affect the adoption decision."

Also, you should always include the assumptions with comparison results. Be explicit about which meteorological data were used, under what site conditions the calculations were performed, to what extent shading was modeled, whether the loss conditions are standard values or project-specific values, and whether the results of on-site surveys were incorporated. Comparison results with unclear assumptions become difficult to use later as a basis for judgment.

When selecting a design option, consider not only the magnitude of the difference in power output but also whether that difference is meaningful in practice. If the simulated difference is very small, the errors in input conditions or variations in site conditions may be larger. In that case, it is more reasonable to emphasize constructability, maintainability, safety, and room for future modifications rather than to make fine distinctions of superiority based solely on power output.

On the other hand, if a clear difference appears in the loss diagram, assess whether there is room for design improvement. If shading losses are large, review the layout and height; if PCS losses are large, reconsider the capacity balance; if wiring losses are large, reconsider equipment placement and cable routing. Comparisons in PVSyst are not merely for confirming results but are a process to drive the next design improvements.

When using comparison results for a final decision, recheck that the simulation conditions in PVSyst match the actual conditions on site. In photovoltaic installations, the planned layout on paper may not perfectly match the site's topography, boundaries, obstacles, existing structures, maintenance access routes, and construction yards. If the on-site conditions are misaligned, no matter how carefully you make comparisons in PVSyst, the accuracy of your judgment will decrease. Therefore, it is important to treat simulation comparisons and on-site verification as a set.

Common Mistakes and Points to Check When Comparing

A common mistake when comparing simulation results in PVSyst is looking only at energy production while the comparison assumptions are not aligned. Even if case names are similar, the weather data, loss conditions, system capacity, or shading configuration may actually differ. Comparing only annual energy production in that situation means you are comparing differences in assumptions rather than differences in design.

Another common mistake is judging solely by the annual energy production. Annual production is important, but if you don't look at monthly generation, PR, and loss diagrams, you won't understand why the results occurred. In particular, the effects of shading, output limitations, and temperature losses can be difficult to see from annual figures alone. When comparing, making a habit of checking in the order of annual, monthly, losses, and PR will reduce the chance of overlooking something.

A common mistake when comparing proposals with different capacities is to look only at total generation. Proposals with larger capacities tend to produce more generation, so they may appear advantageous at first glance. However, if the generation per unit capacity or PR is lower, the added portion may be inefficient. When comparing proposals with different capacities, you need to consider both total output and efficiency.

Care must also be taken in how shading conditions are handled. Cases that reflect shading in detail may show lower power generation than cases that treat shading in a simplified manner. However, that is not necessarily a bad result. Rather, it may be a result that more accurately reflects the on-site conditions. When comparing cases that differ in whether shading settings are applied or in their accuracy, it is necessary to clearly distinguish whether it is a "comparison of design proposals" or a "comparison before and after reflecting shading conditions."

Loss condition settings can sometimes be changed unintentionally. Soiling loss, wiring loss, availability, and degradation over time are items that tend to vary depending on initial values and project-specific assumptions. If you reuse settings from past projects, they may not match the site conditions of the current project. Before making comparisons, confirm that the loss conditions are appropriate for the current project and that they have not unintentionally changed between the comparison cases.

Managing the storage of results is also important. As a project progresses, estimates, revised proposals, re-revised proposals, final versions, and so on accumulate, and it can become unclear which one is the official reference for comparison. Organizing the case name, creation date, changes made, and intended use so they are clearly identifiable makes it easier to verify later. In particular, results used for internal sharing or customer presentations should be kept in a state where the conditions under which they were produced can be traced.

Another mistake is judging site conditions solely from PVSyst results. PVSyst is software for conducting high-precision analyses based on input conditions, but if the site’s topography, obstacles, boundaries, existing equipment, and surrounding environment are not entered correctly, the comparison results will deviate from reality. If the accuracy of on-site surveys or measurements is insufficient, uncertainty remains in the very assumptions underlying the comparison of results.

Perspectives Necessary to Accurately Reflect On-Site Conditions

To improve the accuracy of comparing simulation results in PVSyst, it is essential to correctly reflect site conditions. In particular, for photovoltaic installations, the slope of the terrain, elevation differences of the installation surface, surrounding structures, trees, fences, existing equipment, and boundaries with adjacent land all affect energy yield and construction planning. If these factors are only roughly estimated, the reliability of the comparison results may decrease.

Among on-site conditions, shadow factors have a large impact on comparative results. Shadows do not occur in the same way throughout the year; their effects vary with the season, time of day, and solar altitude. At the low solar altitudes of winter, shadows from distant obstacles or terrain can have an impact. Even if a layout looks fine on paper, when you visit the site surrounding structures or changes in level can affect things more than expected.

In addition, differences in terrain elevation are also important. There can be differences in panel-row shading, constructability, drainage, and maintenance access between a plan calculated assuming flat ground and one that reflects the actual undulations. For sloped or developed sites, it is advisable to verify on-site measured elevation data in addition to the height information on the design drawings. When comparing simulations, it is necessary to explicitly state, as a premise, the extent to which terrain conditions have been reflected.

If on-site location and elevation information remain ambiguous, comparing multiple scenarios in PVSyst will leave the basis for decision-making unstable. Accurate relative positions are especially important when comparing layout changes or the effects of shading. If the positions of panels, PCS, surrounding obstacles, boundaries, or maintenance access routes differ from reality, it will affect not only energy yield but also construction planning.

Therefore, alongside comparative work in PVSyst, it is effective to utilize on-site positioning and survey data. If high-precision positional information and point cloud data obtained on site are available, it becomes easier to verify the validity of design conditions. Handling positional information consistently—from layout planning and checking shading factors to terrain assessment and post-construction verification—can reduce discrepancies between simulation results and the actual site.

What is useful here is an iPhone-mounted high-precision GNSS positioning device such as LRTK. By attaching it to an iPhone and acquiring high-precision location information on site, it can be used for confirming candidate sites for photovoltaic power generation facilities, recording positions of existing structures, checking planned installation ranges, managing locations of on-site photos, and understanding terrain using point clouds. When comparing multiple simulation results in PVSyst, having a more accurate grasp of the site’s position and elevation makes it easier to improve the reliability of input conditions.

The comparison of simulation results is not just a matter of comparing numbers on a screen; it is a task performed while imagining what will happen on site. By checking energy yield, PR, and losses in PVSyst and confirming local positioning and topographical information in LRTK, it becomes easier to bridge desktop studies and on-site verification. For practitioners who want to improve the accuracy of power generation simulations, advancing software-based comparisons together with organizing on-site data will become increasingly important.

Summary

The method for comparing simulation results in PVSyst is not simply lining up multiple result reports and looking at annual energy production. First, align the conditions of the cases being compared and clarify what was changed. Next, check the annual and monthly energy production to identify differences in total output and seasonal variations. Then, review the loss diagram and PR to analyze the causes of the production differences. Finally, translate the findings into practical decisions by considering not only the numbers but also constructability, maintainability, on-site constraints, and ease of explanation.

What matters in using PVSyst is not producing results, but becoming able to interpret them. Being able to explain why the annual energy production increased, why the PR changed, why losses increased, and why there were month-by-month differences will improve the accuracy of comparing design proposals and of internal and customer explanations. Conversely, comparing only the results without checking the assumptions can lead to incorrect conclusions.

When performing comparison work, you must always be mindful that the input conditions in PVSyst match the actual site. Only when the meteorological data, location, shading, terrain, equipment layout, and loss conditions are appropriate will the comparison results become information usable in practice. In particular, for projects where on-site positional relationships and elevation information are important, the accuracy of positioning and surveying determines the reliability of the simulation.

To compare multiple options in PVSyst and make design decisions that are closer to reality, it is important to link desk-based simulations with high-precision on-site data. By using an iPhone-mounted GNSS high-precision positioning device like LRTK, you can efficiently obtain on-site location information, photographic records, and point cloud data, which helps verify design conditions and compare before-and-after construction. By comparing energy generation and losses in PVSyst and accurately capturing site conditions with LRTK, the evaluation of photovoltaic power systems becomes more aligned with practical field work.