What is PVSyst? 7 Basic Points to Check Before Implementation

PVSyst is a specialized analysis software used for simulating the power output of photovoltaic systems, organizing loss factors, and comparing and evaluating design conditions. It is sometimes used in practical work related to solar power generation, such as system planning, design studies, preparing technical documentation, and explaining to stakeholders. On the other hand, because it requires many input items, if meteorological data, module parameters, wiring, orientation, tilt, shading, loss rates, and other factors are not checked thoroughly before use, a report that looks well-prepared may still produce results that differ from actual site conditions.

This article organizes and explains seven basic points that practitioners searching for "What is PVSyst" should check before adopting it. It not only provides an overview of the software, but also summarizes perspectives useful for making an adoption decision: when it is used, where input errors are likely to occur, and how to interpret the results.

Table of Contents

• What PVSyst is used for

• Usage objectives to verify before adoption

• Input data quality determines the results

• Key items shown in power generation simulations

• Considerations for shading analysis and loss settings

• Do not take report results at face value

• Rules and verification framework required for internal operations

• Summary: Preparations to put in place before using PVSyst

What is PVSyst used for?

PVSyst is simulation software for evaluating photovoltaic power generation systems’ annual and monthly energy production, various losses, and the appropriateness of system configurations. It is used in the planning stage before constructing a solar power plant, for verifying conditions of existing installations, for comparing design changes, and for preparing explanatory materials for power output forecasts.

Solar power generation can vary even for systems with the same installed capacity depending on factors such as the installation location, azimuth (orientation), tilt angle, surrounding shading, weather conditions, equipment configuration, wiring conditions, and temperature conditions. Therefore, it is insufficient to judge simply that “a larger installed capacity means more generation.” In PVSyst, you can input these conditions and numerically verify how much power a photovoltaic system is expected to generate.

A major practical role is that it makes it easier to compare design conditions numerically. For example, you can check the differences in power generation when changing the tilt angle, changing the azimuth, adjusting the number of modules, or taking shadow effects into account. This makes it easier to provide explanations based on certain assumptions rather than relying solely on subjective judgment.

However, PVSyst is not a tool that will necessarily produce the correct answer simply by entering inputs. If the input conditions do not match the actual on-site situation, the output results will also diverge from reality. In particular, the selection of meteorological data, installation conditions, equipment specifications, loss rates, and shading conditions require the responsible person’s understanding and verification. It is easier to understand PVSyst as a professional tool for evaluating the performance of solar power generation systems under appropriate assumptions, rather than as software that guarantees power generation.

Before implementation, it is necessary to clearly define who will use it, what decisions it will be used to make, and the level of accuracy and accountability required. It is important to treat it not merely as a tool for producing reports, but as a foundation for verifying the validity of design conditions and for establishing a common understanding among stakeholders.

Intended Uses to Confirm Before Implementation

Before introducing PVSyst, the first thing to confirm is the intended purpose. Even within solar power work, the required functions and how you use the software vary depending on your scope of responsibility—development, design, construction, maintenance, investment decisions, document preparation, etc. If you introduce it with an unclear purpose, learning how to operate it can become the goal itself, and you may not be able to use it effectively in actual practice.

When used for planning a new power plant, the primary objective is to assess the candidate site's meteorological and topographical conditions, orientation, tilt, and the influence of surrounding obstructions, and to produce an estimate of annual power generation. In the initial stages, the focus is on rough comparative estimates, but as the plan becomes more concrete it is necessary to increase the precision of the input conditions. Because simulation assumptions change each time land conditions or layout plans are altered, it is important to record which set of conditions a given calculation is based on.

When used for design studies, the focus is on equipment configuration, circuit configuration, wiring conditions, differences in orientation and tilt angles, the approach to oversizing, and the organization of loss factors. For designers, it is important not only to know the amount of power generated but also to be able to explain why the results turned out that way. Because PVSyst results are used as part of the basis for design decisions, it is necessary to understand the meaning of each input item.

When using it to create internal documents or customer presentation materials, it is useful to be able to organize the results in a report format. However, a well-formatted report is not the same as accurate content. Reports created when the basis for the input conditions is weak may cause trouble if you are later asked to explain them. Before implementation, it is reassuring to decide not only how to handle the output numbers but also how thoroughly to manage the input conditions and assumptions.

Also, when using it to analyze existing installations, comparison with actual generation is important. If simulation results differ from actual values, multiple factors need to be considered, such as differences in weather conditions, downtime, soiling, equipment degradation, shading, measurement conditions, and data gaps. Rather than attributing the cause to PVSyst alone, it is important to verify by combining on-site data and operational records.

In other words, introducing PVSyst is not merely a decision about whether to install the software. It is important to consider where in your company’s operations it will be used, which decisions it will inform, who will review the results, and how records will be kept. When the purpose of implementation is clear, it becomes easier to determine the necessary scope of training and the operational rules.

The quality of input data determines the results

One of the key basic points in PVSyst is the quality of the input data. Simulation software performs calculations based on the conditions entered. Therefore, if the input data are inaccurate, no matter how familiar one is with operating the software, the results will not be reliable. Before introducing PVSyst, it is necessary to clarify what data need to be prepared and who within the company will verify them.

First and foremost, information about the installation site is important. Latitude, longitude, elevation, and meteorological conditions form the assumptions for energy generation. In photovoltaic power generation, solar irradiance and ambient temperature greatly affect output. If the selection of meteorological data is not appropriate, the projected annual energy generation may be overestimated or underestimated. Even when using nearby meteorological conditions, differences in topography and environment—such as mountainous areas, coastal zones, snowy regions, and urban areas—can cause discrepancies from actual conditions.

Next, entering the equipment specifications is important. The rated output of the solar modules, temperature characteristics, number of modules, tilt and orientation of the mounting surface, capacity of the power conditioner, circuit configuration, and so on form the basis for power generation calculations. Misreading values on the specification sheet or entering a number of modules that differs from the design drawings will affect the overall results. In particular, when design changes occur during the planning process, care is necessary because it is easy to mistakenly recalculate using the old conditions.

Wiring and loss conditions must not be overlooked. The final power output will vary depending on how you account for DC-side and AC-side wiring losses, conversion losses, temperature-related losses, soiling, mismatch, and degradation over time. These loss rates should not be treated as fixed values without consideration; it is preferable to verify them according to the project conditions and internal company standards. Using figures with unclear justification will weaken your persuasiveness when explaining.

Also, reflecting on-site conditions is important. Surrounding buildings, trees, shading between racking rows, and terrain undulations can all affect power generation. If simulations are carried out without sufficient site investigation, it may look fine on paper but in reality shading can have a major impact. Before introducing PVSyst, it is advisable to decide how you will collect design drawings, site photos, survey data, and information about shading.

Maintaining the quality of input data requires a system that does not rely solely on the experience of the person responsible. By defining the documents to check before input, the items to verify after input, and the rules for updating when changes occur, you can reduce errors. PVSyst is software capable of detailed calculations, but if the management of the data that underlies it is inadequate, it is difficult to obtain the expected results.

Main Items Observed in Power Generation Simulations

In PVSyst's power output simulations, you can examine not only the annual generation but also monthly generation, irradiance, system losses, the performance ratio, and the energy flow at each stage. Before implementation, it is important to understand which figures to check and what conclusions to draw from them. If you only look at the final annual generation, you may overlook important loss factors and design issues.

The figure that tends to attract attention first is the annual energy production. This is an indicator showing how much electrical energy the target facility is expected to generate over the course of a year. It is a figure often used in business plans, financial assessments, and explanations to stakeholders. However, annual energy production is the result of stacking multiple assumptions and cannot be judged as correct on its own. You need to check together which meteorological data were used, which losses were anticipated, and under which design conditions the calculation was made.

Monthly power generation is also important. Because solar power output varies with seasonal changes in solar radiation and temperature, there are differences in generation from month to month. In summer, output can drop due to high temperatures even when solar radiation is abundant, while in winter, conditions may be favorable temperature-wise but generation is affected by shorter sunlight hours and lower solar elevation. By looking at monthly figures, you can identify generation trends that are not apparent from the annual total alone.

Performance ratio is also a metric frequently used in practice. It is a way of assessing how efficiently an actual system can generate power under a given set of reference conditions. Although one might be tempted to assume that a higher performance ratio is simply better, the apparent value changes depending on input conditions and loss settings, so when comparing different projects you must align the underlying assumptions. Comparing projects with different conditions based only on their numbers can lead to misunderstandings.

The breakdown of losses is also something you should always check. In PVSyst, you can organize various loss factors step by step, such as incident solar irradiance, temperature, shading, equipment conversion, wiring, and mismatch. If energy production is lower than expected, identifying which stage shows significant losses can lead to a review of the design conditions. Conversely, if losses appear extremely small, you need to check for missing inputs or overly lax condition settings.

Also, it is important to show the validity of the system configuration. The combination of modules and conversion equipment, the number of circuits, the voltage range, and the operating range under temperature conditions are all design verification points. Even if the purpose of the simulation is to predict power generation, an impractical equipment configuration can lead to operational problems in practice.

When reviewing PVSyst results, don’t focus solely on the final values—be mindful of the intermediate results leading up to the energy production. If you understand what the numbers mean, it will be easier to explain to stakeholders which conditions affected the results.

Precautions for shadow analysis and loss settings

Shadow analysis and loss settings are easy to overlook in solar power generation simulations, yet they can have a significant impact on the results. Before introducing PVSyst, you need to consider how detailed the treatment of shadows will be and on what basis the loss rates will be set.

The effects of shading vary greatly depending on the type of power plant and the installation environment. When installed on a building roof, nearby buildings, roof penthouses, railings, equipment, and trees can be sources of shading. For ground-mounted installations, surrounding terrain, adjacent structures, shading between racking rows, and site grading affect shading. Because shadows change throughout the day and across seasons, failing to properly reflect on-site conditions can lead to inaccurate power generation forecasts.

PVSyst can perform analyses that consider three-dimensional shading and the effects of nearby shading. However, creating a model does not automatically reproduce the site perfectly. If inputs such as dimensions, position, height, orientation, and ground slope do not match the actual site, the results of the shading analysis will change. In particular, in early stages when on-site survey information is lacking, care must be taken not to underestimate the impact of shading.

The same applies to loss settings. In solar power generation, output is reduced by various factors such as increased module temperature, wiring resistance, conversion efficiency, equipment-to-equipment variability, soiling, reflection, aging, and downtime. The extent to which you account for these factors will change the simulation results. Simply using initial/default values or values from past projects as-is may not sufficiently reflect the realities of each project.

One thing to watch out for is that setting the loss rate low makes projected power generation look higher. When there is a desire to make the generation appear larger, settings tend to underestimate realistic losses. However, if the gap compared with actual performance later becomes large, it will be difficult to explain. Before implementation, it is important to organize, within the company, the standard approach to loss rates and the items to be reviewed for each project.

Shadow analysis and loss settings are areas where a designer’s judgment tends to be reflected. Precisely for that reason, it is necessary to record the basis for the inputs. If you document which sources were used to create the shadow model and under what assumptions the loss rates were set so they can be checked later, you will have peace of mind during internal reviews and when explaining things to clients.

When implementing PVSyst, it is essential not simply to memorize the operational procedures but to understand the meaning of shading and losses. Rather than merely producing power output numbers, building up assumptions that closely reflect the site conditions leads to simulations that are trusted in practice.

Do not take the report results at face value

PVSyst allows you to organize simulation results into a report format. Because energy production, losses, input conditions, graphs, and so on are presented together, the reports are convenient for internal review and for explaining results to stakeholders. However, it is risky to assume that the contents are entirely correct just because a report has been generated.

The report is merely an organized summary of calculation results based on the input conditions. If the entered meteorological data, equipment specifications, installation conditions, loss rates, or shading conditions are not appropriate, the results will not be highly reliable even if the report appears well-presented. Before implementation, it is necessary to establish a system to verify the contents of the report, rather than making the creation of the report the goal.

What I particularly want to check is the consistency of the input conditions. I verify whether equipment capacity, number of modules, converter capacity, orientation, tilt, installation location, meteorological data, loss rates, and so on match the design drawings, specifications, and on-site conditions. In projects with frequent plan changes, values from old documents may remain. Before submitting the report, it is important to confirm that the calculations have been performed using the latest conditions.

Next, verify the validity of the results. If the annual energy production is unusually high, losses are unreasonably small, monthly generation patterns do not match local conditions, or the impact of shading is much smaller than expected, there may be input errors or omitted settings. Do not assume there is no problem just because the numbers are close to your expectations; take a careful stance of checking whether the results feel inconsistent.

Also, when comparing multiple options, it is important to align the comparison conditions. If one option takes shading into account while another does not, the comparison of power generation is not fair. The same applies when meteorological data or loss rates differ. When presenting comparison results to stakeholders, you need to make clear what was changed and what was kept constant.

Report-reading skills are important when using PVSyst. If only the operator understands the content, internal checks will not function adequately. Sharing the points to check for each relevant role—such as design personnel, project personnel, construction personnel, and maintenance personnel—makes it easier to prevent incorrect interpretations.

PVSyst reports are useful deliverables, but they should not replace final decision-making. Use the report as a starting point to verify the relationship between input conditions and results, and revise the conditions as necessary—that is the correct way to use it in practice.

Rules and verification system required for internal operations

To effectively use PVSyst in practice, you need not only individual operational skills but also internal operational rules. If each person uses different input methods or has a different approach to loss rates, it becomes difficult to compare results between projects and can cause confusion when presenting them. It is desirable to establish at least a minimum set of operational rules before implementation.

The first thing to decide is how to manage the input conditions. Recording the project name, calculation date, person responsible, drawings used, specifications used, meteorological data, installation conditions, loss rates, shading conditions, and so on makes it easier to trace results later. If you only save the calculation files, you may not know under which assumptions they were created. Version control is especially important for projects that undergo repeated design changes.

Next, it is important to establish a review system. Rather than having the person entering the data check everything by themselves, create a process in which another staff member verifies the key items to reduce simple input errors. Items to check include installation location, system capacity, orientation, tilt, equipment configuration, loss rates, shading conditions, and the validity of output results. Even if it is difficult to check everything in detail, be sure to focus on the items that have a major impact on the results.

Another point to clarify is our approach to standard conditions. Regarding loss settings such as soiling, wiring, mismatch, temperature, and downtime, we need to decide whether to set them freely for each project or to establish company-wide standard values. Even when using standard values, it's important not to apply them mechanically to every project; there should be room for revision based on site conditions.

A training program is also essential. PVSyst is specialized software, and it is not easy for staff using it for the first time to fully understand it in a short period. If you provide progressive learning of basic operations, the meaning of input items, how to interpret results, common mistakes, and internal company rules, you can more easily prevent reliance on specific individuals. Using files from past projects as teaching materials to check which conditions affect which results is also effective.

Furthermore, when the materials are to be submitted externally, you need to be mindful of accountability. The recipient may question the basis for the meteorological data, the rationale for the loss rates, the treatment of shading, and the validity of the design conditions. In such cases, credibility is enhanced if the person responsible does not rely solely on verbal explanation but ensures that the information is documented and retained.

To increase the effectiveness of introducing PVSyst, simply increasing the number of people who can use the software is not sufficient. By establishing internal workflows for input, verification, storage, explanation, and updates, simulation results become easier to utilize as business assets.

Summary: Preparations to Make Before Using PVSyst

PVSyst is specialized simulation software for evaluating the energy production, loss factors, and design parameters of solar photovoltaic installations. If introduced, it can be useful for energy production forecasting, design comparisons, and preparing explanatory materials; however, to use it correctly, understanding the input conditions and having a verification process in place are essential.

Before implementation, the first thing to confirm is the intended use. Whether it will be used for predicting power generation for a new project, for design comparisons, for analysis of existing facilities, or for internal or external briefing materials, the items to prioritize will vary. If the purpose is clear, it becomes easier to organize the necessary data, the figures that need to be checked, and the operational rules.

Another important factor is the quality of the input data. Each input condition—installation location, weather conditions, equipment specifications, orientation, tilt, shading, loss rates, etc.—affects the results. In particular, if calculations are performed without reflecting on-site conditions or design changes, the numbers in the report can diverge from reality. Personnel using PVSyst need to understand not only how to operate the software but also the meaning of the input items.

How to interpret the results is also important. Rather than judging based only on annual generation, you should verify monthly generation, performance ratio, breakdown of losses, the impact of shading, and the appropriateness of the system configuration to understand the context behind the results. Reports are convenient, but since they present calculation results based on input conditions, you must always check the assumptions and consistency before submitting.

If you plan to use it continuously in-house, operational rules and a verification system are also necessary. Record file names, calculation conditions, reference materials used, loss rates, shading conditions, and change history, and have a different staff member check them to help prevent mistakes and reliance on particular individuals. PVSyst is a powerful piece of software, but if usage varies by person in charge, the reliability of the results will decline.

In the practical work of solar power generation, it is important to consider the entire workflow—not only generation simulations but also obtaining on-site information, organizing design conditions, post-construction verification, and monitoring generation performance during operation. When introducing PVSyst, rather than using the software in isolation, taking the perspective of integrating it with site information and operational data will make it more useful in practical work.

If, before deployment, you establish the objectives, input data, the handling of shading and losses, report review procedures, and internal rules, PVSyst can become an effective tool to support decision-making in solar power projects. For final decisions, it is important not to rely solely on simulation results but to adopt an approach that cross-checks them against site surveys, design documents, equipment specifications, and operational performance to make generation forecasts more realistic.