What Do You Need to Know About PVSyst? 10 Essential Basics for Beginners

When you start getting involved in the design, energy-yield forecasting, and feasibility assessment of solar power plants, you encounter questions like "What is PVSyst?" and "How much do I need to understand to use it in practice?" It has many specialized configuration items—such as solar irradiance, temperature, losses, shading, equipment configuration, energy production, and reports—so it can be hard for a beginner to know where to start learning. However, what you need at the introductory stage is not to memorize all the detailed formulas. First, it's important to grasp what PVSyst is used for, which input conditions affect the results, and how to read the outputs.

In this article, aimed at practitioners who search for "PVSyst とは" ("What is PVSyst"), we organize and explain the ten basic pieces of knowledge you should know first. From a practical standpoint, we summarize the minimum points that designers, those responsible for verifying generation forecasts, those reviewing business plans, and those involved in pre-construction studies should understand.

Table of Contents

• PVSyst is design support software for predicting the electricity generation of solar power systems

• The primary objective beginners should first understand is to validate the predicted energy production

• Basic knowledge 1: Solar irradiance data forms the foundation of the prediction results

• Basic knowledge 2: Installation conditions greatly affect the power output

• Basic knowledge 3: Entering the equipment configuration determines the behavior of the entire system

• Basic knowledge 4: The impact of shading is an important factor that affects annual energy production

• Basic knowledge 5: Understanding the concept of losses makes the results easier to interpret

• Basic knowledge 6: Do not overlook output reduction due to temperature

• Basic knowledge 7: Performance ratio is a basic indicator for assessing the health of a PV plant

• Basic knowledge 8: Monthly energy production is used to assess seasonal variations and check for anomalies

• Basic knowledge 9: Read reports by considering the input conditions and the results together

• Basic knowledge 10: Judge PVSyst results by cross-checking them with on-site conditions

• Common stumbling points for beginners

• Verification steps when using PVSyst in practice

• Summary

PVSyst is design support software for predicting the power generation of photovoltaic (solar) systems.

PVSyst is a specialized design support software used for forecasting power output and conducting design studies for solar power generation systems. By entering the power plant location, solar irradiance, meteorological conditions, PV module layout, equipment configuration, azimuth, tilt angle, shading effects, various losses, and so on, it simulates how much electrical energy can be produced over a year.

When evaluating solar power generation, simply deciding on the installed capacity is not sufficient. Even power generation systems with the same capacity can have greatly different actual energy output depending on the installation region, roof or terrain conditions, surrounding obstacles, combinations of equipment, temperature environment, and wiring conditions. PVSyst is used to organize these conditions and quantitatively estimate the energy production.

What’s important for beginners is not to think of PVSyst as a tool that automatically produces the correct power generation. PVSyst is software that performs calculations based on the assumptions you enter. In other words, if the input conditions deviate from reality, the output power generation will also deviate from reality. Conversely, if you carefully reflect site conditions and clearly document the basis for your inputs, you can create materials that are useful for design comparisons and business decision-making.

In practice, you should not just look at PVSyst results; you need to verify the conditions under which the results were calculated. It is important to read the annual energy production figures, the performance ratio, the breakdown of losses, the monthly generation, the effects of shading, and so on, and to judge whether the plant plan is reasonable.

The first objective beginners should understand is verifying the validity of power output

When you start learning PVSyst, you may feel overwhelmed by the number of input screens and settings. However, the objective that beginners should understand first is simple: to check how much energy the planned solar power system can be expected to generate under the assumed conditions.

In evaluating the feasibility and design decisions of solar power projects, the expected annual energy production is extremely important. If production is overestimated, project cash flows and investment decisions will become overly optimistic. Conversely, if production is underestimated, a plan that is actually promising may be judged unfavorably. PVSyst is a tool for producing the energy production forecasts that form the basis of these judgments.

However, the results from PVSyst are only simulations. Actual power generation will vary due to year-to-year weather, equipment degradation, soiling, downtime, maintenance status, changes in the surrounding environment, and other factors. Therefore, when reading PVSyst results, they should be treated as "predicted values calculated under these conditions."

Beginners should focus first on grasping the flow of power generation forecasting rather than trying to perfectly understand all the detailed loss settings from the outset. Simply checking which region’s solar irradiance data was used, what orientation and tilt the installation assumes, what system capacity was assumed, and which losses were anticipated can greatly change how you read a report.

Basic Knowledge 1: Solar irradiance data forms the foundation of forecast results

In PVSyst, the first thing that becomes important is solar irradiance data. Because photovoltaic generation converts sunlight from the sun into electricity, how much solar irradiance a location receives forms the basis for generation forecasts. Regions with high irradiance tend to produce more electricity, while regions with low irradiance tend to produce less electricity even with the same installed capacity.

Solar irradiance data use average weather data for each region. The point to note here is that solar irradiance data are not "meant to predict future weather accurately." Generally, they are based on past weather and statistical data and are treated as conditions approximating long-term averages. For that reason, if you look at only a single year, the actual power generation and the simulation results may differ.

The points beginners should check are which location’s meteorological data are being used, whether those data do not significantly contradict the site’s elevation and topography, and whether substituting a nearby representative location is reasonable. If data from a point distant from the planned power plant site are used, actual conditions can differ in coastal areas, mountainous regions, basins, and snowy areas.

In addition to solar irradiance, temperature and wind speed also affect power output. In particular, temperature influences the output of photovoltaic cells, so in hot regions temperature-related losses can increase even when solar irradiance is high. When using PVSyst, you should not simply select solar irradiance data; you need to verify how well that data represents the meteorological conditions at the project site.

Basic Knowledge 2: Installation Conditions Greatly Affect Power Generation

In PVSyst, you enter the installation conditions for the solar panels. Typical items include orientation, tilt angle, mounting method, row spacing, and layout conditions. Because these determine the angle at which sunlight is received, they have a major impact on power generation.

Azimuth is a parameter that indicates the direction a solar panel faces. In general, orientations that allow panels to receive sunlight more efficiently relative to the sun’s path are advantageous, but due to the shape of the land or roof, surrounding obstructions, and installation conditions, it may not be possible to install them in the ideal orientation. In PVSyst, you can compare differences in energy production caused by such azimuth variations.

The tilt angle is also important. When the tilt angle changes, the way solar radiation is received in each season changes. A shallow angle tends to be advantageous in summer, while a steeper angle can make it easier to receive winter sunlight. However, the optimal angle varies depending on the region and the installation purpose. The choice also differs depending on whether you prioritize annual power generation or winter generation.

When entering installation conditions, the point to be careful about is whether the assumptions on the drawings match the actual conditions on site. Even slight differences in roof pitch, racking angle, terrain slope, or the orientation of the installation surface can affect power generation forecasts. This is especially true for ground-mounted power plants, where the entire site is often not level, so it is important to reflect the results of on-site surveys and terrain checks.

Basic Knowledge 3: The overall behavior of the system is determined by the equipment configuration input

In PVSyst, you enter the equipment configuration such as solar modules, conversion devices, connection configuration, number of circuits, number of modules in series, and number of parallel strings. This allows calculation of how the generated electricity is converted and over what range it operates.

What beginners should understand is that the equipment configuration is not merely a list of components but an important input that determines the operating conditions of the entire power generation system. If the number of solar panels, the number of series connections, the capacity of the conversion equipment, the input voltage range, and so on are not appropriate, power generation losses or design inconsistencies may occur.

For example, the relationship between the solar array capacity and the converter capacity affects how generation and losses are assessed. If the converter capacity is smaller than the solar array capacity, output may be limited during periods of strong irradiance. Conversely, making the converter capacity larger is not always beneficial; decisions need to be made while considering the overall design balance of the system.

Also, lower temperatures tend to increase voltage, while higher temperatures tend to decrease it. Therefore, when considering combinations of equipment, it is necessary to take into account temperature variations throughout the year. In PVSyst inputs, you can reflect these conditions to check whether the system will operate properly.

In practice, what matters is entering the values from the equipment specification correctly. If there are input errors, the results can change significantly. Model, output, efficiency, temperature coefficient, operating range, number of connections, and so on are items that readers of the report should also verify.

Basic Knowledge 4 The impact of shading is an important factor that influences annual power generation

In solar power generation, shading is a very important source of losses. Buildings, trees, utility poles, fences, mountains, surrounding equipment, and adjacent PV rows can cast shadows, reducing the power produced during those periods. PVSyst can perform simulations that account for nearby obstacles and shading between rows.

What beginners should pay particular attention to is that the effects of shading cannot be judged by a simple area ratio alone. Even if only part of a solar panel is shaded, depending on the circuit configuration the power output can decrease by more than the shaded area would suggest. Also, whether the shading occurs only in the morning and evening or persists for long periods in winter will change its impact on annual energy production.

For ground-mounted installations, attention must also be paid to inter-row shading, where the front row of solar panels casts shadows on the rear rows. Narrowing the row spacing allows more solar panels to be installed on the same site, but it can increase losses due to shading. Conversely, widening the row spacing reduces shading but can decrease the installable capacity. PVSyst is useful for comparing such layout conditions.

For roof-mounted installations, shadows from rooftop equipment, guardrails, penthouses, and adjacent buildings can be problematic. In particular, when placing many solar panels in a limited area, even small obstructions can cast shadows at specific times of day. Beginners should not omit shading settings; it is important to verify them using on-site photographs, drawings, and survey results.

Basic Knowledge 5 Understanding the Concept of Loss Makes Results Easier to Interpret

When reading PVSyst results, an essential concept is the consideration of losses. In photovoltaic power generation, not all of the light that reaches the solar cells can be used as electricity. Power output is reduced by various factors such as the angle of incidence of solar irradiance, temperature, shading, soiling, wiring, conversion, equipment characteristics, and downtime.

In PVSyst reports, these losses are organized and presented in stages. It may look difficult for beginners at first, but it becomes easier to understand if you basically think of it as "the energy that would be obtained under ideal conditions becoming the final output after passing through the losses at each stage."

The important thing is not to make losses look small, but to adequately account for realistic losses. If you understate losses in order to make power generation appear larger, the discrepancy with actual operational results will be significant. In business planning and design decisions, explainable, reproducible figures are more important than optimistic numbers.

Losses due to soiling vary depending on the region and the installation environment. Factors such as sand and dust, pollen, bird damage, snowfall, salinity, and the effects of nearby construction must be taken into account for the local environment. Wiring losses vary depending on wiring length, cross-sectional area, and equipment layout. Conversion losses are affected by the efficiency of the conversion device and operating conditions.

Beginners should aim to be able to look at a loss chart and determine which losses are large, whether the configured values are justified, and whether they deviate significantly from the typical range.

Basic Knowledge 6 Don't Overlook Output Reduction Due to Temperature

In solar power generation, it’s often assumed that the more sunlight there is, the more electricity is produced, but systems are also affected by temperature. Solar cells tend to lose output as they become hotter. Therefore, in hot regions or in installation environments with poor ventilation, temperature-related losses can be significant.

In PVSyst, based on meteorological data and the mounting method, it accounts for output loss due to the temperature rise of the solar cells. Installations that are closely attached to a roof tend to trap heat, so their temperature conditions differ from those of ground-mounted systems with good ventilation. If the mounting method is not correctly reflected, estimates of temperature losses may deviate from actual conditions.

What beginners should remember is that places with higher solar irradiance do not necessarily have higher power generation efficiency. Even if solar irradiance is high, if the output drop due to high temperatures is large, the amount of power generated may not grow as much as expected. Conversely, in regions where temperatures are low and solar radiation is stable, the system may operate more efficiently.

Temperature losses are also important when reading monthly generation and the breakdown of losses. In summer, even if solar irradiance is high, temperature losses can reduce the performance ratio. Understanding this tendency will help you interpret seasonal variations in reports more naturally.

Basic Knowledge 7: The Performance Ratio Is the Fundamental Indicator for Assessing a Power Plant's Health

One of the metrics often checked in PVSyst results is the performance ratio. The performance ratio is an indicator of how effectively the theoretically available energy can actually be extracted as usable electrical power. For beginners, it is easiest to understand if regarded as a metric for roughly grasping the overall efficiency of the plant and the magnitude of its losses.

If the performance ratio is high, it can be interpreted that losses are relatively small and the equipment is operating efficiently. However, the performance ratio is not simply better the higher it is. Because it varies depending on input conditions and calculation assumptions, superficially comparing different projects can lead to misunderstandings.

For example, designs with little shading, favorable temperature conditions, and low wiring losses tend to have a higher performance ratio. On the other hand, in hot regions, sites with shading, complex wiring, or roofs with many installation constraints, the performance ratio can decrease. This does not necessarily mean the design is poor; it may simply reflect the actual site conditions.

When evaluating the performance ratio, it is important to check it together with annual energy production, the breakdown of losses, and monthly variations. Rather than judging good or bad solely by the performance ratio, you need to interpret why that value has occurred. Beginners should use the performance ratio as a "summary indicator of results" while making a habit of checking the causes in the loss breakdown.

Basic Knowledge 8 Monthly power generation is used to check seasonal variations and detect anomalies

In PVSyst reports, you can view not only the annual energy production but also the monthly energy production. The monthly breakdown is useful for interpreting seasonal variations in irradiance, solar altitude, temperature, and shading effects.

Looking only at annual generation, you cannot fully understand a plant’s characteristics. For example, even if the annual generation appears reasonable, if winter generation is extremely low, shading due to low solar altitude, snow accumulation, or the effects of orientation and tilt may be involved. If summer generation falls short of expectations, temperature-related losses or output limitations may be affecting it.

By reviewing monthly power generation, you can assess whether the design conditions reflect natural seasonal variations. In some regions, generation may drop during the rainy season or in winter, and in areas affected by snow you should be cautious when forecasting winter output. It is important to verify that the local climate and the monthly generation trends are not in significant contradiction.

Beginners should read monthly generation not only as "a breakdown of annual generation" but also as "a way to verify the validity of input conditions." If a particular month is extremely high or low, check whether the cause lies in solar irradiance, temperature, shading, loss settings, or equipment configuration.

Basic Knowledge 9: Read reports as a set of input conditions and results

When you look at a PVSyst report, it's easy to focus on the results—energy production, performance ratio, loss diagrams, and monthly data. However, in practice the most important thing is to read the input conditions together with the results.

Even if the annual energy production is the same, its meaning changes if the input conditions differ. Unless you verify whether site-specific meteorological data are being used, whether shading is taken into account, how soiling losses are set, whether the equipment configuration matches the actual design, and whether the azimuth and tilt angles match the drawings, you cannot assess the reliability of the results.

In particular, the input conditions may change between the early stages of design and after detailed design. Initial studies typically run simulations using estimated conditions, while detailed design commonly involves re-calculating to reflect site surveys, equipment specifications, and layout drawings. Therefore, the recipient of a report needs to check which stage of study the report pertains to.

When beginners read a report, they first check the project name, location, system capacity, azimuth, tilt, meteorological data, equipment configuration, loss settings, and whether shading is present. After that, they read the annual energy production and the performance ratio. Simply following this order reduces the risk of misunderstanding that comes from looking only at the numbers.

Basic Knowledge 10: Cross-check PVSyst results with on-site conditions

The most important factor when using PVSyst results in practice is verifying them against actual site conditions. Even if the software produces a polished report, the reliability of the energy production forecast cannot be considered sufficient unless the site’s topography, obstacles, slopes, drainage, snow accumulation, surrounding environment, and construction constraints are reflected.

For example, even if drawings appear to show no shading, shadows can occur on site due to trees or buildings on adjacent properties, utility poles, or changes in terrain elevation. For ground-mounted installations, slight ground tilt or steps can also affect the arrangement of mounting frames. For roof-mounted installations, equipment, upstands, lightning protection devices, and inspection walkways can pose layout constraints.

PVSyst is not a substitute for on-site inspection or surveying. Rather, it is a tool for organizing site conditions and reflecting them in energy-yield predictions. Conditions entered without verifying the site are merely assumptions. Beginners need to understand that gathering the evidence to support input conditions is also part of professional practice, not just operating PVSyst.

Especially when using power generation forecasts for business decisions or proposal documents, it is important to verify on-site conditions. If the design values differ from actual site conditions, layout changes may be required during construction, which can change the assumptions of the power generation forecast. Accurately understanding the site's location information, elevation, boundaries, obstacles, and the condition of the installation surface brings PVSyst results closer to being reliable.

Common pitfalls for beginners

What beginners to PVSyst tend to stumble over is not the sheer number of settings, but the inability to picture how each item influences energy production. Even if they can work through the inputs on the screen, if they don't know whether a value is large or small or how much it will affect the results, they cannot judge the validity of the report.

A common pitfall is to judge based only on annual energy production. Annual energy production is the most readily understandable result, but that number alone does not reveal whether the calculations are sound. You need to check that solar irradiance, system capacity, losses, performance ratio, and monthly generation are naturally consistent with each other.

Moreover, over-adjusting loss items in excessive detail can make the underlying justification unclear. In practical work, input values need to have an explainable basis. Even when using standard values, it is desirable to be able to explain why those values were adopted.

Another stumbling block is putting site conditions off. If you become so focused on operating PVSyst that you proceed with simulations without adequately checking on-site shading, slopes, obstacles, and the surrounding environment, you may need major revisions later. From the introductory stage, it is important to treat software inputs and on-site verification as a single set.

Verification procedures when using PVSyst in professional practice

When using PVSyst in practice, instead of jumping straight into the detailed settings, deciding on a verification procedure in advance can reduce mistakes. First, confirm the location of the planned site and the meteorological conditions. Next, identify the orientation and tilt of the installation surface, the usable area, and any surrounding obstructions. Then enter the system capacity, equipment configuration, and layout conditions, and verify the shading and loss settings.

When the simulation results are available, check not only the annual energy production but also the performance ratio, loss breakdown, and monthly generation. If any item shows large losses, trace the cause back to the input conditions. If shading losses are large, review the layout and obstructions; if temperature losses are large, check the mounting method and ventilation conditions. If there are significant output limitations, check the balance of the equipment configuration.

When submitting or sharing a report, it is important to clearly state the assumptions behind the input conditions. Clarifying whether it is based on design information at which stage, whether a site survey has been carried out, whether it reflects approximate conditions, and to what extent shading considerations have been incorporated will prevent misunderstandings among stakeholders.

Beginners do not need to understand everything perfectly from the outset. What is important is that when they look at the results they can explain "why this amount of energy was generated" based on the input conditions and losses. With this perspective, PVSyst becomes not just calculation software but a practical tool that supports design decisions.

Summary

PVSyst is design-support software for predicting the energy production of photovoltaic power systems and for checking the effects of design conditions and losses. What beginners should learn first is not to memorize every detailed function, but the basic workflow: solar irradiance, installation conditions, equipment configuration, shading, losses, temperature, performance ratio, monthly energy production, how to read reports, and comparing results with site conditions.

The results of PVSyst are highly dependent on the input conditions. Rather than judging solely by the energy yield figures, it is important to verify the assumptions used in the calculations and determine whether they are consistent with the actual site conditions. In particular, the site location, topography, mounting surface, surrounding obstacles, and shading conditions directly affect the accuracy of energy yield forecasts.

When assessing solar power generation projects, it is essential to accurately understand the on-site information that forms the basis for simulations. Verifying the planned site's location and boundaries, the condition of the installation surface, and surrounding obstructions on site—and reflecting them in the PVSyst input conditions—enhances the credibility of the generation forecasts.

If you want to streamline on-site position checks and positioning, using LRTK, an iPhone-mounted GNSS high-precision positioning device, makes it easier to smoothly acquire site coordinates and record location information. By combining PVSyst power generation simulations with the accurate location information obtained on site, you can reduce discrepancies between desk-based studies and actual field conditions and achieve more reliable solar power generation plans.