【Where should you look on PVSyst's results screen? 6 indicators important for practical work】

Table of Contents

• Key concepts to check first on PVSyst result screens

• Indicator 1: Use annual energy production to assess the project's overall viability

• Indicator 2: Read seasonal variations and anomalies from monthly energy production

• Indicator 3: Evaluate the overall validity of the design using the Performance Ratio

• Indicator 4: Compare generation efficiency relative to system size using Specific Production

• Indicator 5: Decompose causes of reduced generation using the loss diagram

• Indicator 6: Check assumptions with solar irradiation and effective irradiation

• Practical points to watch for when reviewing result screens

• Connect PVSyst result checks to on-site surveys and construction management

• Summary

Key considerations to check first on the PVSyst results screen

One of the moments where beginners tend to struggle when learning how to use PVSyst is the results screen after running a simulation. After entering design conditions, setting meteorological data, registering modules, PCS, layout, and loss conditions, and running the simulation, various numbers and graphs are displayed. However, because so much information is shown, many people find it difficult to know which parts to look at to inform practical decisions.

The results screen of PVSyst is not simply a screen for viewing annual energy production. Annual energy production is of course important, but in practice it is crucial to understand from what assumptions that figure was calculated, at which stages how much loss occurs, and what the seasonal generation trends are. In solar power system design, you must check not only the magnitude of the generation but also whether the figure is reasonable, whether there are errors in the input conditions, and whether it is consistent with site conditions.

When viewing the results screen, it is important to grasp the overall picture first rather than chasing detailed items one by one from the start. Begin by checking the annual generation, then look at the monthly generation to observe seasonal variations. Next, use aggregate indicators such as the Performance Ratio and Specific Production to assess the efficiency of the entire system. Furthermore, review the loss diagram to identify which factors are reducing generation, and check the solar irradiance and effective irradiance to see whether the underlying meteorological conditions or layout present any anomalies.

What's important in practice is not to paste the numbers from the result screen directly into a report, but to be able to understand and explain what those numbers mean. If you can explain why the annual power generation ended up at that level, why generation was low in a particular month, which items account for the largest portions of the losses, and whether the results are reasonable compared with on-site conditions, the results will be easier to use for design studies, internal reviews, explanations to clients, materials for financial institutions, and pre-construction checks.

This article explains where to look and how to interpret the six indicators on PVSyst’s results screens that are particularly important in practical work. It is organized to be useful not only for those who are just starting to learn how to use PVSyst, but also for practitioners who can produce results yet feel uncertain about how to read them.

Indicator 1: Confirm the overall business viability based on annual power generation

The first indicator to check on PVSyst’s results screen is the annual energy production. Annual energy production is the basic figure that indicates how much electrical energy the photovoltaic system in question is expected to generate over one year. In practice, it serves as the starting point for various decisions, such as project feasibility assessment, estimation of revenue from electricity sales, evaluation of self-consumption benefits, and verification of the appropriateness of the system size.

When evaluating annual generation, it is important not to judge solely by the magnitude of the numbers. For example, even with the same installed capacity, annual generation can vary depending on the site's solar irradiance conditions, orientation, tilt angle, shading effects, temperature conditions, PCS capacity, wiring losses, and settings for soiling and degradation. Therefore, even if annual generation is higher than expected, you should not immediately conclude it is a good result; you need to check whether the input assumptions are overly optimistic. Conversely, if it is lower than expected, it is important to distinguish whether the reduction is reasonable given site conditions or caused by a mistake in the settings.

In practice, annual electricity generation is evaluated in combination with installed capacity. This is because if installed capacity increases, generation also increases, making it difficult to compare the quality of designs using annual generation alone. For example, when comparing multiple proposals, the proposal with the highest annual generation is not necessarily the optimal one. In some cases generation is higher simply because installed capacity is larger, and in other cases increasing the degree of oversizing raises annual generation while also increasing output curtailment at peak times.

Annual electricity generation is first checked against the overall business plan. Compare it with the assumed annual generation, contracted capacity, self-consumption demand, electricity selling price, and assumptions about the equipment utilization rate, and verify there are no extreme discrepancies. If large discrepancies appear here, it is often better to reconfirm the input conditions before looking at other indicators on the results screen. Errors in site settings, meteorological data, system capacity, orientation, tilt, or loss settings can significantly affect annual electricity generation.

Also, when looking at annual generation, it is important to distinguish whether the figure refers to the final grid-side output or the array-side generation. PVSyst’s results display the energy at each stage, such as the energy produced by the photovoltaic array, the energy after PCS conversion, and the energy sent to the grid. In practice, when considering revenue or available usable energy, you need to look at the energy that is ultimately available. On the other hand, when analyzing design loss factors, it is useful to examine the array-side generation and the difference before and after conversion.

Annual generation is the starting point for checking results. By catching any major anomalies here and then moving on to monthly generation, Performance Ratio, Specific Production, the loss diagram, and irradiance conditions, it becomes easier to understand the context behind the numbers.

Metric 2: Reading Seasonal Variation and Anomalies from Monthly Power Generation

After annual power generation, the next thing you should check is monthly power generation. If you only look at the annual total, you can understand the total amount generated over the year, but seasonal variations and abnormalities in specific months become difficult to see. Solar power generation is affected by factors such as solar irradiance, temperature, solar altitude, and the occurrence of shading, so examining it on a monthly basis allows you to verify the validity of the design conditions in more detail.

For monthly power generation, you first check whether the shape of the seasonal variation looks natural. In general, generation increases in seasons with good solar irradiance and decreases in seasons with poor solar irradiance. However, during periods of high temperature the efficiency of solar cells falls because of temperature rise, so months with high solar irradiance do not necessarily correspond to the months with maximum generation. In addition, regions with heavy snowfall, mountainous areas, coastal areas, or high-temperature regions may exhibit patterns that differ from the typical seasonal variation.

When reviewing monthly power generation in practice, it is important to check the continuity with adjacent months. If only one month shows an extremely low or high generation, you should suspect that there may be unnatural settings in the meteorological data, shading configuration, operating conditions, output limits, soiling factor, or similar. Of course, when based on actual meteorological data, site-specific seasonal variations may be reflected. However, during the early design or preliminary estimate stages, anomalous values caused by input errors can slip in, so graphs and tables of monthly generation are items that should always be checked.

Monthly power generation is also important when considering self-consumption solar power systems. Even if annual generation appears sufficient, if months of high demand do not coincide with months of high generation, the self-consumption rate and economic benefits may fall short of expectations. For example, for facilities with high air-conditioning demand in summer, it is important to estimate how much generation can be expected in summer. Conversely, for facilities where electricity demand increases in winter, it is necessary to assess the supply–demand balance assuming lower winter generation.

Monthly power generation is also useful for checking the effects of shading. Shadows from surrounding objects and terrain can have seasonally varying impacts. Especially during periods of low solar elevation, shadows from distant obstacles or adjacent rows are more likely to affect power generation. If you review monthly generation and losses and find that production drops significantly only in winter, it is worth rechecking the shading settings and terrain conditions.

Monthly power generation is also an indicator that is easy to explain in reporting materials. Even when annual power generation alone is difficult for clients or stakeholders to visualize, showing monthly trends makes it easier for them to intuitively grasp seasonal variations in generation. Practitioners should treat monthly generation not merely as a table but as important information for checking seasonal variation, the relationship with demand, the impact of shading, and the validity of meteorological data.

Indicator 3: Use the Performance Ratio to assess the overall validity of the design

Performance Ratio is a representative indicator for evaluating the overall performance of a photovoltaic power generation system. In Japanese it is sometimes referred to as 性能比. Simply put, it indicates how much of the electricity that would be expected under ideal conditions is actually produced in the simulation. On PVSyst’s results screen, checking this Performance Ratio as well as the annual energy yield allows you to grasp the overall efficiency of the system.

What makes the Performance Ratio useful is that it allows comparisons by normalizing, to some extent, differences in system capacity and solar irradiation. Annual energy production is heavily influenced by system capacity and the site's solar radiation conditions, whereas the Performance Ratio is suited to checking the effects of internal system losses and design conditions. When comparing multiple design options or looking at trends between past projects and the current one, the Performance Ratio serves as a practical metric for decision-making.

However, Performance Ratio is not a simple metric that is always better the higher it is. If an extremely high value appears, it may indicate that loss settings are insufficient. For example, if temperature loss, wiring loss, mismatch loss, soiling loss, conversion loss, or shading effects are not adequately reflected, the Performance Ratio may look overly optimistic. Conversely, if it is too low, there may be significant loss factors such as shading, output limitations, temperature conditions, PCS capacity, or wiring conditions.

In practice, when looking at the Performance Ratio, we first compare it with the typical expectations for our company or by project type. Whether roof-mounted, ground-mounted, on sloped terrain, on heavily shaded sites, in high-temperature environments, or in snowy environments, the acceptable range varies depending on project conditions. Therefore, instead of judging solely by the numerical value, it is necessary to interpret it taking site conditions and design parameters into account. In particular, if the Performance Ratio is excessively high in projects with severe shading or terrain conditions, it may indicate that the shading settings have not been properly reflected.

The Performance Ratio is an easy-to-use metric for explaining matters to stakeholders. When explaining why the annual energy generation ended up at this level, if the Performance Ratio is maintained to a certain extent, it becomes easier to argue that there is little major waste in the system design. On the other hand, if the Performance Ratio is low, it is necessary to combine it with a loss diagram to explain which losses are having an effect. In other words, the Performance Ratio is not a standalone metric; its meaning becomes deeper when viewed together with a loss diagram.

When learning how to use PVSyst, it's easy to focus on annual energy production, but in practice it's important to develop the habit of always checking the Performance Ratio. Even if the annual energy production meets expectations, if the Performance Ratio seems off, there may be problems hidden in the input conditions or loss settings. On the results screen, checking the Performance Ratio as an indicator of overall system efficiency after annual energy production makes it easier to verify the quality of the design.

Indicator 4: Compare power generation efficiency relative to plant size using Specific Production

Specific Production is an indicator showing the annual electricity generation per 1 kW of installed capacity. In Japanese it is sometimes called 比発電量. Whereas annual electricity generation indicates the total output of the entire installation, Specific Production is an indicator for evaluating how efficiently the installation generates electricity relative to its size.

This metric is particularly useful when comparing multiple design proposals or different projects. For example, even if Proposal A has a larger annual power generation and Proposal B has a smaller annual power generation, Proposal B may have a higher generation per unit of capacity simply because Proposal A’s installed capacity is larger. Looking at Specific Production makes it easier to compare while taking differences in installed capacity into account.

In practice, during the design proposal review stage we check how Specific Production changes when the module layout is increased. Increasing the number of installed modules can raise annual energy production, but if shading effects increase, PCS output limitations grow, or the layout is extended into areas with unfavorable azimuth or tilt, the energy production per unit of capacity can decline. Instead of simply placing more panels, Specific Production is useful for judging how far it is reasonable to extend the installation.

Specific Production is also useful for understanding differences in site conditions. It tends to be higher in regions with favorable solar radiation and lower in regions with poor solar radiation. However, because not only solar radiation but also temperature, shading, orientation, tilt, loss settings, and output limits affect it, it is risky to judge based solely on regional differences. Even within the same region, Specific Production will change if the roof orientation or the surrounding environment differs.

When looking at Specific Production, it is useful to understand the difference from Performance Ratio. Performance Ratio is an indicator that shows how efficiently the system converts solar irradiation into electrical energy. Specific Production, on the other hand, is an indicator that shows how much electricity can be generated per unit of installed capacity over a year. Both are measures of efficiency, but they take different perspectives. In practice, it is effective to use Performance Ratio to assess the reasonableness of system losses and Specific Production to compare energy yield per unit of capacity.

If Specific Production is lower than expected, first check the solar irradiation conditions, then review azimuth, tilt, shading, temperature, output limits, wiring losses, and so on. In particular, if the energy produced per unit of capacity has decreased as a result of increasing the layout, it may be necessary to reconsider the installation area. Maximizing energy production and maximizing investment efficiency are not necessarily the same. Specific Production is a practical metric for identifying that difference.

Metric 5: Break down the causes of power generation decline with a loss diagram

On PVSyst's results screen, the loss diagram is extremely important. The loss diagram shows, in the process from sunlight striking the module to becoming the final usable electrical energy, at which stages and to what extent losses occur. It allows you to break down and verify the causes of reduced energy production that cannot be understood from the annual energy production or the Performance Ratio alone.

When viewing a loss diagram, inspect it with the sense of tracing the flow of energy from the top downward. First there is the solar irradiance incident on the horizontal or tilted plane, and from there it is converted into the final output while being affected by near shading, far shading, reflection, angle of incidence, temperature, module characteristics, mismatch, wiring, PCS conversion, output limiting, and so on. By examining the losses at each stage, you can identify where the main factors reducing power generation lie.

In practice, particular attention should be paid to shading losses, temperature-related losses, PCS-related losses, wiring losses, and settings for soiling and degradation. If shading losses are large, it may be necessary to review the layout, nearby obstructions, and terrain conditions. If temperature losses are large, verify the mounting method, ventilation conditions, and assumptions about module temperature. If PCS-related losses are large, it is necessary to reconsider PCS capacity, the oversizing ratio, and the approach to output limiting.

Loss diagrams are also useful for detecting input errors. For example, if wiring loss is extremely large, there may be an error in the cable length or electrical condition settings. If shadow loss is almost nonexistent while there are large obstructions at the actual site, the shadow settings may be insufficient. If temperature loss is unnaturally small, the temperature condition or installation method settings may be more optimistic than reality. In this way, loss diagrams can be used as a checklist to verify the plausibility of results.

When reading a loss diagram, the important thing is not to set eliminating losses entirely as the sole goal. Photovoltaic systems have unavoidable losses. Efficiency degradation due to temperature and PCS conversion losses, for example, occur to some extent in real installations. What matters is to separate which losses can be addressed by design or construction improvements and which losses should be accepted as site conditions.

Loss diagrams are also very effective when explaining to clients or internal stakeholders. When explaining why annual power generation is lower than expected, it is more persuasive to show, based on a loss diagram, at which stages and to what extent reductions are expected, rather than simply saying "there is an effect from shading." Also, when comparing multiple proposals, looking at the loss diagrams side by side makes it easier to explain which proposal suppresses which losses.

When reviewing the results screen in PVSyst, the loss diagram is one of the most practical pieces of information. If you are not satisfied with the annual energy production figures, if the Performance Ratio seems off, or if there are unusual month-to-month variations in generation, checking the loss diagram makes it easier to identify the causes.

Indicator 6: Confirm assumptions with solar radiation and effective solar radiation

To correctly interpret PVSyst results, it is essential to check not only the energy production but also the solar irradiance. In photovoltaic simulations, how much solar energy reaches the site is the starting point for estimating energy production. Therefore, if the annual energy production looks suspicious, you should first verify whether the assumptions about solar irradiance are reasonable.

On the results screen, you can check information such as horizontal irradiance, tilted-surface irradiance, and effective irradiance. Horizontal irradiance is the concept of irradiance incident on a horizontal surface. Tilted-surface irradiance is the irradiance that reflects the tilt and azimuth of the module surface as actually installed. Effective irradiance is easiest to understand if you think of it as the irradiance that contributes to power generation after being affected by shading, reflection, angle of incidence, and similar factors.

In practice, mistakes in site location settings or in selecting meteorological data can have a major impact on solar radiation. Using weather data for a region different from the target site, entering incorrect latitude and longitude, or having inconsistencies in how elevation or time zone are handled can undermine the assumptions about expected energy production. Checking the solar radiation on PVSyst's result screen is also part of verifying the foundation of the simulation.

In addition, irradiation on tilted surfaces is important for verifying the validity of the orientation and tilt angle. When comparing multiple options with different orientations and tilts, looking not only at annual power generation but also at how the irradiation on tilted surfaces changes makes it easier to understand where the differences in power generation originate. For example, if one option has a lower annual power generation, it is necessary to determine whether that is due to the way it receives solar radiation or to losses.

Effective solar irradiance is useful for checking the effects of shading and reflections. Even if it appears that sufficient sunlight is reaching the module surface, nearby shading and the angle of incidence can reduce the solar radiation actually available for power generation. Confirming effective solar irradiance is especially important for building roofs, slopes, sites with densely packed equipment, and locations with many surrounding obstacles.

Checking solar irradiation is directly linked to explaining power generation. When explaining why generated power is low, it is not sufficient to look only at losses. You need to distinguish whether the site's solar irradiation conditions are poor, whether the irradiation received is reduced due to the orientation or tilt of the installation surface, or whether effective solar irradiation is reduced by shading. Therefore, solar irradiation and effective solar irradiation are essential baseline indicators that should always be checked on PVSyst's results screen.

Practical points to be aware of when viewing the results screen

When using PVSyst's result screens in practice, it's important not only to look at each indicator individually but also to examine the connections between them. Annual energy yield, monthly energy yield, Performance Ratio, Specific Production, loss diagram, and solar irradiation may appear to be independent pieces of information, but in reality they are different perspectives on the same simulation results.

For example, if the annual power generation is lower than expected, looking at the monthly generation will tell you whether the decline is concentrated in a particular season or is low throughout the year. By looking at the Performance Ratio you can check whether the system efficiency is low for the given irradiance conditions. By looking at the Specific Production you can judge whether the generation relative to the installed capacity is reasonable. By looking at the loss diagram you can see where losses are large — shading, temperature, PCS, wiring, etc. By looking at the irradiance you can confirm whether the underlying meteorological conditions and the installation surface conditions are appropriate.

What you most want to avoid on the results screen is drawing conclusions based solely on the annual energy production. Annual energy production is important, but that number alone won’t tell you whether the design is good, the conditions are optimistic, losses are excessive, or the meteorological data are appropriate. When using PVSyst, it’s important to adopt a workflow that treats annual energy production as the entry point and corroborates it with other indicators.

Also, in practice it is important to make a habit of comparing the figures on the results screen with internal standards and past projects. Rather than starting from scratch each time, compare them with similar past projects to check whether there are significant differences in energy production, Performance Ratio, Specific Production, and loss items. If there are differences, verify whether you can explain the reasons. Differences in terrain, orientation, shading, weather conditions, or oversizing ratio are acceptable if there are reasonable explanations. However, if there are differences that cannot be explained, you need to review the settings.

When viewing the results screen, keep the objectives of the design stage in mind. In initial studies, the focus may be on comparing multiple options and obtaining a rough estimate of power generation rather than on detailed loss conditions. By contrast, in detailed design or pre-contract reviews, loss conditions, shading conditions, wiring conditions, PCS settings, and other factors need to be made more realistic. Depending on the objective, the items emphasized on the results screen will change.

When using this as a report, descriptive text for the figures is also important. Simply listing the numbers displayed on the results screen makes the document difficult for readers to evaluate. By adding explanatory text about how much the annual power generation is, what the monthly trends look like, what the main loss factors are, and what design considerations should be noted, it becomes more useful as a practical document.

Linking PVSyst Result Verification to On-site Surveys and Construction Management

The PVSyst results screen is intended for reviewing desk-based simulation outputs, but in practical work it is important to use it in conjunction with on-site surveys and construction management. Because simulations are calculated based on input conditions, the reliability of the results decreases if on-site conditions are not correctly reflected. If you find any anomalies on the results screen, you should go back and verify the on-site conditions.

It is particularly important to verify the terrain, orientation, tilt, shading, obstructions, and installation area. If the layout set in PVSyst does not match the actual site topography, the assessment of shading effects and available solar irradiance may be inaccurate. If there are nearby buildings, trees, equipment, slopes, racking, or existing structures, it is necessary to check at what times of day and in which seasons they will cast shadows.

Also, during the construction phase it is important to verify that the layout and tilt assumed in the design are being reproduced on site. Positional shifts at the site, differences in racking height, changes in ground topography after land development, and the addition of surrounding structures can cause the conditions used in the simulation to differ from the actual conditions. To make practical use of PVSyst results, it is necessary to manage and correlate the figures obtained from the simulation with the on-site conditions.

Such on-site inspections benefit from a system that can acquire location information with high precision. As a GNSS high-precision positioning device that can be attached to an iPhone, LRTK can be used for on-site location checks, point cloud acquisition, photo documentation, and verification against design positions. For site surveys and construction management of solar power plants, recording site boundaries, planned racking locations, obstacles, terrain changes, and objects that cause shading with accurate location information makes it easier to improve the accuracy of the parameters set in PVSyst.

By calculating power generation with PVSyst and not only checking the annual generation and losses on the results screen but also reviewing design conditions based on accurate location information and point cloud data obtained on site, you can reduce discrepancies between the simulation and the actual site. In particular, on large sites, sloped sites, or sites with many surrounding obstacles, there are many conditions that are difficult to judge from plans alone. Using LRTK to record site information with high accuracy makes it easier to check shadows, consider layouts, compare before-and-after construction, and explain the situation to stakeholders.

Verifying PVSyst results cannot be completed solely through operations within the software. By confirming on site the issues that appear on the results screen and feeding the information obtained in the field back into the design, you can achieve a power generation assessment that is more grounded in practical operations. Connecting simulations with on-site measurements is an important workflow for improving the accuracy of solar power projects.

Summary

When looking at the PVSyst results screen, it's important not to judge solely by the annual energy production but to check multiple indicators together. First use the annual energy production to get a broad sense of the project's viability, and use the monthly energy production to check seasonal variations and anomalies. Then look at the system's overall efficiency with the Performance Ratio, and compare generation per unit of installed capacity using Specific Production. Finally, break down the causes of generation losses with the loss diagram and check the validity of the assumptions with irradiance and effective irradiance.

To acquire practical-level skills in using PVSyst, it is important to understand the meaning of the numbers displayed on the results screen and to be able to explain the relationships between those numbers. Rather than just judging whether the annual energy yield is high or low, checking why that result occurred, which losses are having an effect, and whether it is consistent with site conditions will increase the reliability of the simulation results.

Also, PVSyst results are greatly affected by site conditions. If the entered location, meteorological data, azimuth, tilt, shading, terrain, or loss conditions differ from reality, the numerical values on the results screen will also diverge from actual conditions. For that reason, it is important not to separate desk-based simulations from on-site surveys and to reflect accurate site location and terrain information in the design conditions.

By using iPhone-mounted high-precision GNSS positioning devices like LRTK, it becomes easier at solar power plant candidate sites and construction sites to record geotagged photos, acquire point clouds, verify design positions, and assess obstacles and terrain. By reviewing results in PVSyst and accurately recording on-site conditions with LRTK, it becomes possible to produce more practical and easier-to-explain solar power plant designs that connect power generation simulations with actual site conditions.