How to Check PR Values in PVSyst and 5 Cautions

In practical work for designing and simulating photovoltaic power generation, you often need to check PR values not only for the final generation amount but also as an indicator to judge system health and the plausibility of losses. When using PVSyst, many numbers appear in the report, so it can be difficult to know which value to regard as the PR, and under which assumptions you should evaluate it. Especially for purposes like internal review, explaining to the project owner, design comparisons, and reconciliation with actual performance, merely looking at the PR value is insufficient — you need to know where to check it, how to interpret it, and what points to watch out for.

This article explains the basic method to check PR values in PVSyst and organizes five easy-to-overlook cautions in practical work. It is useful not only for those who are starting to use PVSyst but also for those already using it in daily operations who want to improve their checking accuracy.

Table of contents

• First, clarify what the PR value is

• Basic flow for checking PR values in PVSyst

• Check method 1: View the PR value on the report screen

• Check method 2: Read the PR value together with the loss breakdown

• Check method 3: Verify PR values from monthly trends

• Caution 1: A high PR value is not always good

• Caution 2: Do not confuse meteorological conditions with assumption settings

• Caution 3: PR values change substantially depending on shading and temperature settings

• Caution 4: Clarify whether to include grid constraints and output curtailment

• Caution 5: Align measurement conditions when comparing with actual performance

• Practical tips for handling PR values in PVSyst

• Summary

First, clarify what the PR value is

Before checking PR values in PVSyst, it is important to first clarify the meaning of PR itself. PR stands for Performance Ratio and is an indicator of how efficiently a photovoltaic system converted the received solar irradiation into electrical power. In other words, it is a ratio that makes it easier to see how much the equipment is performing relative to ideal conditions, rather than judging the quality of the site itself.

The reason this indicator is emphasized is that it makes it easier to compare equipment performance, which is hard to judge from generation output alone. For example, a site with high annual irradiation tends to have higher generation, but that does not necessarily mean the equipment conditions are good. Conversely, even at a site with poor irradiation conditions, good design and loss management can yield a high PR. In short, PR is a representative way to evaluate the equipment side of a plant while partly separating out site differences.

However, in practice it is important to note that the PR value on its own is not easily used as an absolute evaluation metric. The appearance of the value changes depending on which losses are included, which meteorological data are used, and whether it is a simulation or actual performance. Therefore, it is risky to extract a number and judge it without context. PVSyst makes it relatively easy to check PR values, but you must understand both where the value is shown and the evaluation assumptions together.

Basic flow for checking PR values in PVSyst

The basic flow for checking PR values in PVSyst is to review the result screens or reports output after a simulation completes. First set the project conditions, input meteorological data, array configuration, azimuth, tilt angle, loss conditions, shading conditions, etc., and run the calculation. Then read the value corresponding to PR from the main indicators displayed on the result screens or reports.

In practice, do not stop after viewing the number just once; it is basic to check both annual and monthly values. Annual values are good for grasping overall performance trends, but without looking at monthly values you may miss seasonal dips or biased influence factors. Seasonal factors such as low solar altitude in winter, increased module temperature in summer, and seasonal changes in impacts cannot be fully understood from the annual average alone.

Furthermore, when looking at PR values, it is important to check the loss diagram and loss breakdown together. PR is a final result indicator, so when a value is low you need to check at which stage the losses are large. You must distinguish whether the issue is solar input, temperature loss, wiring loss, inverter loss, or shading impact in order to arrive at meaningful improvement measures.

Thus, checking PR values in PVSyst is best thought of not as a one-point check of results but as reading annual values, monthly trends, loss structure, and assumptions together to make it practical for real work.

Check method 1: View the PR value on the report screen

The most basic check method is to view the PR value on the report screen output after the simulation. In practice, reports are often used for internal sharing and external explanations, so you should be sure to master this check method first.

The report displays the generation, irradiation, installed capacity, various losses, specific yield, and a metric corresponding to PR alongside these. By checking this value you can immediately grasp the equipment performance on an annual basis for the project. If you want to compare before and after design changes, first looking at this annual PR value gives you a rough judgment whether the performance has improved overall or become worse.

However, avoid concluding your evaluation by looking at the annual PR value in the report alone. Annual values are convenient, but because they are averaged results they can hide seasonal bias or issues under specific conditions. For example, a project that shows large efficiency degradation at high temperatures in summer and comparatively good performance in winter may obscure problems if you only look at the annual average.

Also, when comparing multiple projects internally, you must not rank them simply by PR magnitude without confirming that the assumptions are the same. If the type of meteorological data, loss settings, treatment of output curtailment, or the presence of shading differs, the number labeled PR can mean different things. Viewing PR in the report is a fundamental action, but always confirm the conditions under which that value was calculated as well.

Check method 2: Read the PR value together with the loss breakdown

To correctly understand PR values, it is very important to read them together with the loss breakdown. PVSyst results are structured so you can see not only the final number but also how losses accumulate from irradiation to electrical output. If you only look at the PR value without checking this, you will not know why that value occurred.

For example, if the PR is lower than expected, whether the dominant cause is losses due to module temperature rise, large DC or AC wiring losses, conversion efficiency decline, or strong local shading leads to entirely different countermeasure directions. When considering design changes, identifying which loss items are dominant can be more important in practice than the PR number itself.

Getting into the habit of checking loss breakdowns also helps validate whether the PR value is plausible. For instance, if PR is extremely high despite site conditions with a lot of shading, the shading settings may be insufficient. Conversely, if PR is unnaturally low on an open site, the loss settings may be overly conservative. PR is a result and the loss breakdown provides clues to the cause. Only by looking at both can you increase confidence in the design and simulation.

This is particularly important for practitioners when responding to accountability. When a project owner or stakeholder asks why the PR for a project is at a certain level, simply showing the number may not be convincing. If you can explain the factors such as temperature conditions, shading, electrical losses, and conversion losses based on the loss breakdown, it becomes easier to communicate the validity of the design.

Check method 3: Verify PR values from monthly trends

To capture information not visible from the annual PR alone, it is essential to check monthly trends. Viewing monthly values makes it easier to see whether performance dips in specific seasons or weather conditions, or whether a particular month shows abnormal behavior.

For example, while summer has high irradiation, module temperatures tend to rise and temperature losses increase. As a result, even if the generation amount is large, the PR appearance can change. In winter, irradiation decreases but temperature conditions may be favorable. Additionally, the impact of nearby obstacles changes with seasonal solar altitude, so problems hidden in the annual value can appear as large declines in winter monthly data.

One advantage of monthly checks is that you can more easily find opportunities for design improvement. For instance, if PR is clearly low in only one month, inspect whether shading or weather conditions unique to that month are affecting performance. This is also true for comparisons with actual performance: two results can look similar on an annual basis but show large monthly discrepancies. In such cases suspect measurement errors, downtime causes, soiling, local shading, or unexpected curtailment.

In practice, an effective workflow is to first check the annual value and then dig into monthly data. If you start by examining too many details you can lose the big picture, so first identify major trends on an annual basis and then search monthly data for anomalies or biases. Checking PR values in PVSyst is not just finding a number, but reading its time-series behavior to improve judgment accuracy.

Caution 1: A high PR value is not always good

PR is a convenient indicator, but a high value is not unconditionally good. Misunderstanding this can lead to incorrect reading of simulation results. PR indicates the equipment’s efficient performance, but it does not directly represent absolute profitability or the magnitude of generation.

For example, even if PR is high, annual generation may not be large if the site’s irradiation is weak. Conversely, even with a modest PR, a site with abundant irradiation can produce a large annual generation. PR is only part of the plant evaluation and not everything. When judging a project, you need to look at PR, annual generation, specific yield, loss composition, and business conditions together.

Also, if PR seems too high, you should suspect the settings. If shading is not sufficiently reflected, losses are overly optimistic, or temperature conditions are set more favorably than reality, the PR can look artificially high. Such figures may look good on paper but pose risks in practice. Large discrepancies with later actual performance will erode trust in design accuracy.

Therefore, when looking at PR values, consider not only their magnitude but whether they are consistent with site conditions. Confirming that realistic losses and operational conditions are incorporated to yield a plausible PR helps stabilize design quality.

Caution 2: Do not confuse meteorological conditions with assumption settings

One common misunderstanding when reading PR values in PVSyst is conflating differences in meteorological conditions with differences in equipment assumptions. PR is a performance indicator relative to irradiation, so it is less directly dragged by meteorological conditions than generation, but results still change according to the meteorological data used and the assumption settings.

For example, if PR looks high for a project, you must separate whether that is due to good equipment conditions or the meteorological assumptions input favoring that equipment. Similarly, when comparing different projects, comparing numbers alone while the meteorological data type or correction method differ can lead to incorrect judgments.

In practice, it is common to compare multiple patterns in internal or proposal materials. In such cases, clearly indicate which conditions were changed and which were fixed. If you do not organize whether only racking conditions were changed, azimuth was also changed, loss settings were revised, or meteorological data changed, you will not understand what PR differences mean.

This caution is also important when inheriting past projects or another person’s data. If only PVSyst results remain but records of assumptions are lacking, you cannot correctly interpret PR values. Managing input conditions and calculation settings, not just the numbers in reports, prevents confusion downstream.

Caution 3: PR values change substantially depending on shading and temperature settings

Typical elements that strongly affect PR values are shading and temperature. These two are closely tied to site conditions, and lax or overly optimistic settings directly affect results, so special attention is required.

For shading, handling of nearby shading as well as distant obstacles is important. How far you reflect equipment layout, row spacing, surrounding structures, and terrain impacts PR considerably. If shading settings are overly simplified, PR tends to be higher than reality. Conversely, if shading is set more severely than necessary, the design can appear unduly unfavorable.

Temperature is similar. PV system efficiency decreases with rising module temperature, so results change depending on how you account for mounting configuration, ventilation conditions, and the surrounding environment. If you do not properly reflect rooftop vs. ground-mounted, ventilation quality, and installation spacing, temperature losses will deviate from reality, and PR perception will change accordingly.

The important point here is that shading and temperature often cannot be determined by desk-based numeric settings alone. You need to set realistic assumptions by integrating drawings, on-site checks, experience from past similar projects, and construction conditions. PVSyst is a powerful simulation tool, but if the input assumptions are insufficient, the reliability of results decreases. When checking PR values, focus less on the number itself and more on how closely shading and temperature settings reflect reality.

Caution 4: Clarify whether to include grid constraints and output curtailment

An easily overlooked point when dealing with PR in practice is how to handle grid constraints and output curtailment. In some projects, generation may be curtailed by external factors separate from equipment performance. If you compare PR values without clarifying this treatment, discussions about equipment performance and operational constraints will become mixed.

For example, equipment may be capable of high performance in design, but actual sold electricity will be lower if output curtailment is in place during operation. If you view equipment conversion performance and grid-related constraints on the same footing, evaluating the equipment itself becomes difficult. Depending on whether you are doing a design evaluation, business profitability assessment, or reconciliation with actual performance, you need to decide which losses to include when evaluating PR.

When using PVSyst results, it is important to clarify the purpose of the explanation in advance. If you want to evaluate the design quality, focus on equipment-specific losses. If you want numbers closer to operational performance, include downtime and constraint factors. Neither approach is universally correct; you must organize the interpretation according to the evaluation purpose.

In stakeholder presentations, it is safer not to leave this point ambiguous. Summarizing everything under the single term PR can lead to misunderstandings, so be prepared to explain which range of losses and constraints the reported number assumes to avoid later differences in recognition.

Caution 5: Align measurement conditions when comparing with actual performance

One major purpose of using PVSyst PR values in practice is to compare with post-operation actual performance. However, this comparison is harder than expected and will not be valid unless measurement conditions are aligned. Leaving this vague makes it impossible to know whether the simulation, equipment, or measurement was at fault.

First, confirm the scope of the actual data being compared. The meaning differs depending on whether it is measured on the AC side, at the sales point, whether downtime is included, or whether maintenance shutdowns are excluded. If the definitions of the simulation-side PR and the on-site actual value do not match, differences are inevitable.

Next, meteorological differences are important. Simulations often use representative-year meteorological data, while actual performance is for a specific year’s weather. If actual irradiation and temperature variations are large, the same equipment will produce different results. Therefore, when evaluating PR by comparing with actual performance, clarify whether it is a single-year comparison, a multi-year average, or a corrected comparison.

Site-specific factors cannot be ignored either. Soiling, partial shutdowns, maintenance status, cable faults, shading from weeds, unexpected obstructions — elements not included in the simulation will appear in actual performance. Judging design error simply from the difference between PVSyst PR and field performance without considering these factors is premature. In comparisons with actual performance, evaluate with as much alignment as possible on definition, period, measurement point, meteorological conditions, and causes of downtime.

Practical tips for handling PR values in PVSyst

So far we have covered check methods and cautions, but there are several operational tips to make handling PR values easier in practice. First, do not manage PR values in isolation. Keep annual generation, specific yield, main losses, monthly trends, and a note of assumptions together to greatly improve reproducibility when reviewing later.

Next, when creating comparison documents, explicitly state which conditions were fixed and which were changed. Organize whether the comparison is of azimuth, racking conditions, or loss cases, so the meaning of PR differences is clearly conveyed. If this is ambiguous, PR values can take on a life of their own and lead to wrong decisions.

Also, adopt a habit during internal reviews of checking whether PR values fall within a reasonable range. Check whether PR is not too high for a shaded site, whether losses are too small despite long wiring distances, or whether temperature losses are unrealistically low despite poor ventilation. Since PVSyst has many input items, checking not only numbers but also the consistency of the underlying assumptions helps quality control.

Furthermore, if you intend to compare with actual performance, keep in mind from the design stage what data will be easy to obtain on site. Organizing equipment configuration, stringing rationale, assumed shading conditions, surrounding environment, and installation location information so they can be referenced later will improve the accuracy of post-commissioning evaluations. PR is not only a design-time metric but a common language that connects design, construction, maintenance, and verification, expanding its usefulness.

In that sense, do not complete everything in simulation only; adopt a posture of improving on-site information accuracy. If equipment layout, obstacle locations, actual post-grading shapes, and maintenance check points are ambiguous, no matter how carefully you calculate in PVSyst, reconciliation will be difficult. The better organized the link between design and site information, the closer PR evaluation will be to reality.

Summary

Checking PR values in PVSyst is not difficult, but to use them correctly in practice you must understand not only where to check but also how to read them. The basic flow is to first check the annual PR on the report screen, then look at the loss breakdown to identify causes, and finally check monthly trends to confirm seasonal differences or abnormalities.

At the same time, important cautions are: a high PR value is not always good; do not confuse meteorological conditions with assumption settings; shading and temperature settings strongly influence results; clarify how to handle grid constraints and output curtailment; and align measurement conditions when comparing with actual performance. Observing these points allows you to use PVSyst PR values not just as an output number but as decision support to improve design quality.

To make PR evaluation more practical, it is essential to tightly couple simulation conditions with on-site information. In photovoltaic systems especially, differences between desk-based design values and actual installation conditions easily appear later as performance discrepancies. Accurately grasp equipment locations and surrounding conditions and create a state where the same criteria can be checked after construction; this leads to consistent evaluation across design, construction, and maintenance.

If you want to advance this site-centric management, using LRTK is also effective. LRTK, as an iPhone-mounted GNSS high-precision positioning device, makes it easy to perform high-precision on-site position checks, record equipment layouts, and capture conditions during maintenance. Because it facilitates linking design conditions organized in PVSyst with actual position and management information obtained on site, it is a good option for practitioners who want to increase the verification accuracy of simulation results. To make PR values a more reliable basis for decision-making, consider reviewing operations to include not only design but also improvements in on-site information accuracy.