What does PVSyst check? Explaining its practical uses in the field

Table of Contents

• What is PVSyst used for?

• Main items that can be checked in PVSyst

• Situations where PVSyst is used in practice

• Key points to check in power generation forecasting

• Key points to check in loss analysis

• Importance of validating the reasonableness of input conditions

• Use cases in design studies

• Use cases in business decision-making

• Commonly overlooked points when reviewing reports

• Points to be careful about when using PVSyst

• How to connect site conditions with the simulation

• Summary

What is PVSyst software used for?

PVSyst is simulation software used to verify the expected energy production, losses, and the validity of the equipment configuration of solar photovoltaic installations. It is not merely a tool for calculating energy output; it is used to evaluate how much power a planned installation can be expected to produce by combining solar irradiance, installation tilt, orientation, shading, temperature, equipment configuration, wiring conditions, and various losses.

Many practitioners who search "What is PVSyst" have heard the name but remain unclear about what the software is specifically used to check, which tasks require it, and where to look on the results screen. In solar power system design and project feasibility studies, looking only at panel capacity is not sufficient to make an adequate judgment. Even with the same installed capacity, actual energy generation varies depending on the installation site, tilt, azimuth, surrounding obstructions, temperature conditions, and the combination of equipment. Simulations like PVSyst are used to quantify those differences.

What is important in practice is not to think of PVSyst as a piece of software that automatically provides the answers. If the input conditions are not appropriate, the output values for energy production and losses will also deviate from reality. Conversely, if you carefully organize the site conditions and design parameters and then run simulations, it becomes extremely useful as material for decision-making at the planning stage. By checking the predicted energy yield, the breakdown of losses, the effects of oversizing, the effects of shading, electrical constraints, and monthly generation trends, you can identify design weaknesses and risks to the business plan at an early stage.

PVSyst is not intended to evaluate a power plant’s performance by a single number. It is used not only to determine how much the annual energy production will be, but also to verify why that value occurs, where losses are occurring, and how much the results change when conditions are altered. In practice, being able to confirm these "reasons" is particularly important. PVSyst plays a significant role in whether you can explain the basis for the generation forecast, compare the effects of design changes, and produce materials that convince stakeholders.

Main items that can be checked in PVSyst

PVSyst can be used to check a wide variety of aspects, but the practical focus is on energy production, losses, design conditions, equipment configuration, shading effects, and monthly generation trends. By reviewing these together, you can determine whether the planned solar power installation will deliver realistic performance.

First, check the expected annual power generation. This is the figure that many people in charge pay the most attention to, but it is insufficient to look at it in isolation. To judge whether the annual generation is high or low, you need to consider it together with the system capacity, installation conditions, local solar irradiance conditions, and the magnitude of losses. By confirming whether the generation is reasonable relative to the system capacity and whether it shows any inconsistency compared with installations in the same region or under similar conditions, you can detect input errors or design problems.

The next important point is the breakdown of losses. In photovoltaic power generation, various losses occur between the solar radiation striking the panels and the electricity being used. These include losses due to incidence angle, shading losses, losses from temperature rise, losses from equipment conversion, wiring losses, and mismatch losses; the accumulation of these determines the final power output. In PVSyst, because these losses can be checked step by step, it is easier to identify which factors are reducing the power output.

Monthly power generation is also an important item to check. Even if the annual generation looks reasonable, an unnatural bias in monthly variations may indicate problems with shading settings, orientation, tilt, weather data, or input conditions. If generation drops sharply only in particular seasons, the solar altitude or nearby obstructions may be responsible. Examining monthly trends can reveal design issues that are not apparent from annual values alone.

Furthermore, it is also used to check the system configuration. By checking the capacity ratio of the photovoltaic panels to the power conversion equipment, the number of series and parallel connections, the voltage range, and the occurrence of output limiting, you can determine whether the design falls within an electrically acceptable range. In particular, for designs that increase the capacity ratio, it is important to verify the balance between increased energy generation and losses due to output limiting. PVSyst is used as a practical tool to compare such design decisions numerically.

Situations in which PVSyst is used in professional practice

The situations in which PVSyst is used range from initial feasibility studies for solar power projects to detailed design, business viability assessment, stakeholder briefings, and post-completion comparison and verification. In particular, for projects where expected power generation is directly tied to the project plan, reviewing the simulation results becomes a critical step.

In the initial assessment phase, it is used to determine how much generation potential a candidate site has. Assuming the land area and shape, installable capacity, orientation, tilt, and surrounding environment, an estimated power output is checked. Because detailed design is often not yet finalized at this stage, the results should not be treated as overly precise but rather used as a guideline for comparing multiple conditions. For example, you can compare how generation and losses change when the tilt is altered, the orientation is adjusted, or the capacity is increased.

At the detailed design stage, you input more specific equipment configurations and layout conditions to verify the validity of the design. Here, it is important to check not only the power generation but also the breakdown of losses and the electrical constraints. You confirm how much shading in the layout plan affects performance, whether the capacity ratio is appropriate, whether wiring losses are excessive, and the extent of output reduction due to temperature conditions. This allows you to identify performance issues that are difficult to judge from drawings alone.

In commercial feasibility assessments, PVSyst’s energy yield predictions are sometimes used as assumptions for financial projections. If the estimated energy yield is overstated, expected revenue from power sales and the projected benefits of self-consumption will also be overstated, which can lead to incorrect business decisions. Therefore, in practice, one checks not only the energy figures themselves but also whether the input conditions and loss settings underlying them are reasonable. In particular, meteorological conditions, the treatment of shading, equipment performance, and assumptions regarding degradation should be reviewed carefully, as they significantly affect business plans.

PVSyst is also useful when explaining matters to stakeholders. When presenting a power generation forecast, simply saying “it will generate this much per year” can sometimes appear insufficiently substantiated. By showing the breakdown of losses, monthly generation figures, and the design conditions, it becomes easier to explain why that level of generation is expected. A major practical advantage is that stakeholders in different roles—construction companies, designers, owners, financiers, and maintenance personnel—can discuss the project on the same assumptions.

Points to check in power generation forecasts

When looking at power generation forecasts, first check whether the annual energy production value is reasonable relative to the system capacity and installation conditions. In PVSyst results, the annual energy production is displayed in an easy-to-understand way, so it is easy to focus only on that. However, in practice you should always verify under what conditions that value was derived.

The basic approach to power generation forecasting is to estimate the energy incident on the panel surface from solar irradiance, then subtract various losses to obtain the final alternating-current (AC) energy output. In this process, meteorological data, installation tilt, azimuth, ground reflectance, shading, temperature, equipment efficiency, wiring conditions, and other factors all have an impact. If any one of these conditions deviates from the actual site conditions, the results will change. In particular, because the selection of meteorological data and the input of installation conditions directly affect the estimated generation, they should be checked first.

Monthly power generation is also important. Even if the annual generation looks reasonable, if the monthly generation trend seems odd you should review the input settings. If generation is extremely low in winter, the solar altitude or shading effects may be significant. If generation in summer is lower than expected, temperature-related losses may be large. If azimuth or tilt deviate from a standard design, seasonal generation patterns will also show distinctive characteristics. In practice, checking monthly values as well as annual values is used to judge the plausibility of simulation results.

Also, it is necessary to understand the units of power generation and the evaluation metrics. If you look only at total generation, the figures will be larger for systems with greater installed capacity. Therefore, it is important to check metrics such as generation per unit of capacity and the performance ratio together. By looking at generation per unit of capacity, it becomes easier to compare projects with different system sizes. By looking at the performance ratio, you can understand how efficiently the system is generating power relative to the solar irradiation conditions.

In power generation forecasts, it is important to avoid overestimation. During the planning stage, one may be tempted to choose conditions that make generation look higher, but in practice it is necessary to adopt conservative and defensible assumptions. Verifying whether local shading has been adequately accounted for, whether loss assumptions are overly optimistic, and whether equipment performance figures are being handled conveniently makes it easier to prevent problems in later stages.

Key Points to Check in Loss Analysis

A major value of PVSyst is that it lets you check not only the energy yield but also the breakdown of losses. By looking at the loss analysis, you can understand why the energy yield took that value and where there is room for improvement. In practice, loss diagrams and loss breakdowns are reviewed to assess the validity of design conditions and to consider directions for improvement.

The first thing to check is losses due to shading. In PV systems, shading is caused by nearby buildings, trees, terrain, and spacing between equipment. Because shading changes with the time of day and season, it can be difficult to accurately assess its impact from a single site visit. By setting the shading effects in PVSyst, you can check how much loss occurs on an annual and monthly basis. If shadow losses are large, you should consider changing the layout, revising the installation angle, or adjusting the spacing.

Another important factor is temperature loss. Solar panels generate more electricity the more solar irradiance they receive, but their output decreases as temperature rises. Especially in summer or under installation conditions with poor ventilation, temperature losses can become non-negligible. If temperature losses are large, check whether the installation method, ventilation conditions, and the assumptions made in equipment selection are appropriate. Because seasons with higher power generation are also more susceptible to temperature effects, it is important not to judge generation solely by solar irradiance.

Electrical losses also need to be checked. These include wiring losses, equipment conversion losses, mismatch losses, and losses due to output limitations. If wiring losses are large, it may be necessary to review cable length, cross-sectional area, and wiring routes. If conversion losses are large, check whether the equipment capacity and operating range are appropriate. If output limitations are large, it is necessary to reconsider the balance between panel capacity and converter capacity.

One point to note in loss analysis is that having fewer losses is not necessarily better in a simple sense. For example, increasing the capacity ratio can increase losses due to output clipping while the annual energy production itself may still increase. Widening array spacing to reduce shading losses can, however, reduce the installable capacity. In practice, it is more important to balance energy production, plant capacity, constructability, business viability, and safety than to try to reduce individual losses toward zero. PVSyst is used to evaluate that balance numerically.

The importance of validating input conditions

To correctly interpret PVSyst results, it is essential to verify the validity of the input conditions. No matter how sophisticated the simulation, if the input conditions deviate from the actual site conditions, the output results cannot be trusted. In practice, before viewing the results screen, you should first confirm that the assumptions are correctly specified.

Particularly important are the conditions of the installation site. Latitude, longitude, elevation, meteorological conditions, and surrounding topography affect solar irradiance and generation trends. If the installation location is entered only roughly, the regional weather characteristics may not be adequately reflected. In mountainous areas, coastal areas, snowy regions, and urban areas, the actual environment can differ greatly even under the same place name. If you intend to use power generation forecasts in practice, it is important to select conditions as close to the planned site as possible.

Installation tilt and orientation are also conditions that must always be checked. Even a difference of a few degrees in tilt or orientation can change the annual energy yield and seasonal generation patterns. For rooftop installations, the building orientation and roof pitch can impose constraints, so achieving the ideal angle may not be possible. For ground-mounted installations, you need to consider not only energy yield but also site preparation, drainage, maintenance access, avoidance of shading, and constructability. In PVSyst you input tilt and orientation as numerical values, but it is important to understand the on-site conditions behind those numbers.

Entering equipment parameters is also important. Panel capacity, electrical characteristics, converter capacity, operating voltage range, conversion efficiency, the number of series and parallel connections, and so on directly affect power generation and losses. If there are input errors here, the calculated power output can be significantly off, or a design that would be unlikely to be feasible in reality may appear to be viable. In particular, capacity ratios and voltage ranges are important for assessing the design’s validity.

Loss conditions should not be overlooked. Soiling, degradation, wiring, shading, mismatch, and the risk of stoppage—all of these can change the results depending on how they are accounted for. It is difficult to predict everything precisely, but in practice you should set values within a range you can justify. Unsupported optimistic assumptions make it hard to explain large discrepancies from actual performance later. Input conditions should be defined not to make generation appear larger, but to enable judgments that are close to reality.

Where to Use in Design Considerations

The appropriate use of PVSyst in design studies is to compare multiple conditions while checking the balance between energy generation and losses. In the design of photovoltaic power systems, there is not a single correct answer determined from the outset. There are various options, such as increasing capacity, changing the angle, adjusting the layout, or altering the equipment configuration. By using PVSyst, you can verify how each option affects energy generation and losses.

For example, you might consider changing the installation angle. Changing the tilt angle affects not only the annual energy output but also the balance of generation between summer and winter. When prioritizing self-consumption, it is important not only to maximize annual generation but also to consider how much can be generated during demand-heavy times and seasons. By comparing conditions with different angles in PVSyst, you can more easily evaluate designs that match your project objectives instead of simply choosing the theoretical optimal angle.

It is also useful for layout planning. Narrowing panel spacing can increase installed capacity, but it may increase the impact of shading. Conversely, widening the spacing reduces shading losses, but it may reduce the capacity that can be installed on the same land. These kinds of trade-offs can be difficult to judge from drawings alone. By changing layout conditions in PVSyst and comparing energy yield and shading losses, you can evaluate whether to prioritize capacity or loss reduction.

It is also used for examining equipment configuration. How to set the ratio between panel capacity and converter capacity affects power generation and output limitations. Increasing the capacity ratio can increase generation during low irradiance, but it makes output limitations more likely during high irradiance. PVSyst lets you check how often these output limitations occur on an annual basis. In practice, rather than trying to avoid output limitations altogether, decisions are made by balancing the additional generation from extra capacity against the losses caused by those limitations.

When using PVSyst for design studies, it is important to organize the comparison conditions. If you change many conditions at once, it becomes difficult to determine what caused the differences in the results. If you are comparing angles, keep conditions other than the angles as consistent as possible; if you are comparing capacity ratios, keep conditions other than the equipment configuration consistent. You need to clarify the focus of the study. Doing so makes it easier to apply the simulation results to design decisions.

Use Cases in Business Decision-Making

PVSyst plays an important role not only in design but also in business decision-making. In solar power projects, estimated energy production directly affects profitability and investment decisions. If energy production is overestimated, a plan may appear viable on paper but fail to deliver the expected results once operational. Therefore, in business decisions the plausibility of the estimated production and its associated risks are checked based on PVSyst results.

When evaluating a project's viability, you need to check not only the annual power generation but also how conservative the assumptions behind that generation are. The selection of meteorological data, the treatment of shading, loss rates, assumptions about degradation, and expectations for equipment downtime all affect long-term generation forecasts. Rough estimates are acceptable in the early planning stages, but as the project moves closer to commercialization, you must make the basis for those assumptions clear.

It can also be used to compare multiple proposals. By comparing options such as increasing installed capacity, reducing capacity to avoid shading, changing the tilt angle, or altering capacity ratios, you can determine which option best meets the project’s objectives. Rather than pursuing maximum energy generation alone, you need to consider installation costs, maintainability, output limitations, land use, and ease of future management. PVSyst at least provides a basis for comparison from the standpoint of generation performance.

Simulation results are important even when explaining to financial institutions and investors. Whether the generation forecast is supported by evidence, whether losses have been appropriately considered, and whether site-specific conditions have been reflected are all focal points when assessing project risk. When using the results as explanatory material, it is important not only to present the numeric outcomes but also to organize the input conditions, breakdown of losses, monthly generation, and key assumptions. The better the supporting rationale is organized, the easier it is to build consensus among stakeholders.

In business decision-making, it is also important not to treat PVSyst results as absolute values. Simulations are forecasts based on assumptions, and actual energy production will vary depending on weather, equipment condition, maintenance, downtime, soiling, aging, and other factors. Therefore, in practice it is necessary to consider not only a single predicted energy output but also the range of variation and the risks associated with differing assumptions.

Commonly Overlooked Points When Reviewing Reports

When reviewing a PVSyst report, it is important not to stop at the large power generation figures alone. The report contains information relevant to design and business decisions, including input conditions, equipment configuration, loss breakdowns, monthly generation, and performance indicators. Practitioners should review these items in sequence and check for any anomalies in the results.

An easy-to-overlook point is checking the input conditions. Even if the report’s power generation looks reasonable, if the installation angle, orientation, capacity, equipment configuration, or meteorological conditions are incorrect, the results cannot be considered valid. In particular, when reusing data from past projects, some location details or conditions may have been left unchanged. When reviewing a report, the basic step is to first confirm that the assumptions match those of the current project.

Be alert to abnormal values in the loss breakdown. If shading loss is larger than expected, temperature loss is extremely small, wiring loss is unnaturally low, or output limitation is larger than assumed, you need to review the settings. Because loss values vary depending on project conditions, you cannot say that any specific percentage is correct across the board; however, it is important to be alert to inconsistencies based on practical experience and comparisons with similar projects.

The balance of monthly power generation is also an important point to check. If generation is unusually low in a particular month, shading, weather conditions, or input errors may be involved. By checking whether seasonal trends align with the region and installation conditions, you can uncover issues that annual values alone won’t reveal. Monthly checks are especially important in areas affected by winter shading, summer temperature losses, snowfall, or high-temperature environments.

When submitting a report to a third party, you must also keep explainability in mind. If you cannot explain why the generated energy takes that value, what the major losses are, and what conditions are being assumed, the credibility of the report will decline. Because PVSyst reports contain a large amount of information, in practice it is necessary to organize the key points to be reviewed and explain them according to the stakeholders’ objectives.

Precautions when using PVSyst

The main caveat when using PVSyst is not to regard the simulation results as identical to actual power production. PVSyst is software that supports detailed analysis, but it cannot perfectly predict future weather or the operational condition of equipment. The results are estimates based on the input conditions, and actual power generation will vary due to a range of factors.

First, there is uncertainty in weather conditions. Even if power generation is forecast based on past weather data, future weather will not necessarily be the same. Some years have many clear days, while others have more rain and cloudiness. It can be viewed as a long-term average, but it will not exactly match a single year’s performance. When using it for business planning, the impact of weather variability must be taken into account.

Next, there are limits to reproducing on-site conditions. It can be difficult to fully input all surrounding obstacles, terrain, snow cover, dirt, vegetation growth, reflections, and localized weather conditions. In particular, the effects of shadows are influenced by the accuracy of on-site surveys. Relying on simplified shadow settings can lead to underestimating the actual impact. The more complex the site conditions, the more important it is to conduct surveys and verifications before inputting data.

It is important to note that results can change depending on the judgment of the person providing the inputs. Power generation will vary depending on how the loss rate is set, which meteorological conditions are used, the extent to which shading is accounted for, and how degradation is treated. Therefore, in practice it is effective to establish internal standards and verification procedures to reduce subjective judgments. To ensure that multiple people handling the same project do not produce significantly different results, it is necessary to clarify how to set the underlying assumptions.

Also, it is important not to finalize a design based solely on PVSyst results. Even if a design appears to have good power generation performance, it cannot be considered appropriate in practice if there are problems with constructability, safety, maintainability, regulatory compliance, drainage, ground conditions, equipment delivery/access routes, or future inspection work. PVSyst is a powerful tool for evaluating power generation performance, but it should be used as part of the overall site design.

Approach for Linking Field Conditions and Simulations

To use PVSyst effectively in practical work, it is essential to have an awareness of connecting on-site conditions with simulation conditions. Simulations are a desk-based task, but their premise lies in the field. If you cannot accurately grasp the site’s location, topography, obstacles, mounting surface, azimuth, tilt, shading, maintenance access routes, and so on, the conditions you enter into PVSyst will be vague.

It is especially important to accurately understand the shapes of the land and the roof. Overestimating the area available for installation can lead to simulations of a capacity that cannot actually be accommodated. Conversely, being overly conservative without fully understanding on-site conditions can result in underestimating the usable area. To improve the accuracy of power generation forecasts, it is necessary to correctly measure on-site dimensions and positional relationships before running simulations.

Even in shadow studies, the accuracy of on-site information affects the results. If the positions and heights of surrounding buildings, trees, and structures remain unclear, the assessment of shadow losses will also be uncertain. Even areas thought to have little shading can experience shadows that extend farther than expected at the low solar angles of winter. Understanding the site's three-dimensional situation and reflecting it in the simulation conditions increases the explanatory power of generation forecasts.

Also, the results of on-site surveys and PVSyst can lead to decisions to change the design. For example, if field surveying reveals that the gradient is steeper than assumed, the layout, tilt, and construction methods will need to be reviewed. If the positions of obstacles are identified accurately, configurations that avoid the impact of shadows can be considered. By comparing candidate equipment layouts in PVSyst and refining the design while cross-checking with site conditions, the gap between desk-based studies and actual site conditions can be reduced.

In practical solar PV work, the accuracy of on-site data is just as important as the accuracy of simulations. Mastering PVSyst is not just about becoming familiar with the on-screen settings. It also means understanding what to measure in the field, what to check, and which information should be reflected in the input conditions. The reliability of power generation forecasts depends on both the software calculations and the field information.

Summary

PVSyst is a practical simulation software used to verify the energy production, losses, design conditions, equipment configuration, shading effects, and month-by-month generation trends of photovoltaic power generation systems. It is not simply for producing annual generation figures; it is used to determine why a given generation value occurs, where losses are happening, and how results change when conditions are altered.

Practical uses span a wide range, including initial studies, detailed design, business feasibility evaluation, stakeholder briefings, report preparation, and comparison of design changes. In particular, when using generation forecasts for business decisions, it is essential to verify the validity of the input conditions and the breakdown of losses. Rather than judging based only on annual generation, it is important to comprehensively check monthly generation, performance indicators, shading losses, temperature losses, wiring losses, and output limitations.

On the other hand, PVSyst’s results depend on the input conditions. If the on-site conditions are inaccurate, the simulation results will also deviate from reality. Carefully organizing the installation site, orientation, tilt, surrounding obstructions, topography, equipment configuration, and loss conditions, and establishing well-founded assumptions, leads to reliable generation forecasts. PVSyst only becomes a useful basis for practical decision-making when combined with accurate field information.

To perform solar power system design and generation forecasting in a way that more closely reflects actual site conditions, on-site checks before simulation are also important. If you can accurately grasp the installation area, obstacles, slopes, and positional relationships, the accuracy of the conditions entered into PVSyst will also improve. If you want to use location information obtained on-site for design and simulation, using LRTK (iPhone-mounted GNSS high-precision positioning device) can make on-site positioning and verification tasks easier to streamline. The first step to improving the accuracy of generation forecasts is not just desk calculations but correctly understanding the on-site conditions.