What kind of software is PVSyst? Organizing the prerequisite knowledge before using it

Table of Contents

• What is PVSyst used for?

• Concepts of energy yield forecasting to understand before using PVSyst

• Initial planning conditions and basic information about the plant

• How to consider meteorological data and solar irradiance

• Prerequisite knowledge of solar panels and electrical equipment

• Understanding layout planning and the impact of shading

• What you should know before entering loss parameters

• Basic indicators for interpreting simulation results

• Practical perspectives required of PVSyst users

• Verification points to avoid relying solely on PVSyst

• Summary

What is PVSyst used for?

PVSyst is a specialized software for simulating and forecasting the power output of photovoltaic systems while organizing design conditions and loss parameters. Many of those who search for "PVSyst とは" are likely practitioners who have heard the name but want to know what to input, what to check, and how much knowledge is required. It is easier to understand if you think of it not simply as a convenient tool that automatically produces generation figures, but as a design support tool for numerically organizing a solar power plant’s planning conditions and reflecting equipment specifications and layout, irradiation conditions, and loss parameters to evaluate expected generation.

What PVSyst can do is not limited to predicting annual energy production. You can check a plant’s performance from multiple angles: monthly generation trends, the process by which irradiance is converted into electrical energy, output reductions due to temperature rise, losses from shading, losses from wiring and conversion, and generation efficiency relative to system capacity. In other words, it is important not to look only at the energy production figures displayed as the result, but to verify the assumptions from which those figures were derived.

On the other hand, PVSyst is not a magical piece of software that will always produce the correct answer simply by entering assumptions. If the meteorological data, equipment specifications, tilt angle, azimuth, shading conditions, loss rates, and so on that you input deviate from the actual site conditions, the simulation outputs will also be off. Therefore, before using PVSyst, you need to have a certain amount of prior knowledge about the basic principles of solar power generation, how to read design conditions, how to organize site conditions, and how to interpret result reports.

In practical applications, the results of energy production forecasts are often used for feasibility evaluations, design comparisons, internal briefings, procurement decisions, and post-construction verification. Therefore, rather than just learning how to operate the software, it is important to aim to be able to explain which changes in conditions will alter the results, which losses have the greatest impact, and which input values carry uncertainty. PVSyst becomes a tool that is useful in real-world practice only when used with an understanding of the relationship between inputs and results.

What to Understand About Energy Yield Forecasting Before Using PVSyst

Before using PVSyst, the first thing to understand is that a solar power system’s energy production is not determined by capacity alone. Even if you install solar panels of the same capacity, annual generation will vary depending on the installation site, orientation (azimuth), tilt, solar irradiation conditions, temperature, shading, system configuration, and loss conditions. Forecasting energy production means organizing each of these conditions and estimating how much of the energy arriving from the sun can ultimately be extracted as electricity.

As a basic procedure, first check how much solar irradiance is available at the installation site and calculate how much of that irradiance reaches the surface of the solar panels. The solar irradiance on a horizontal surface and the irradiance incident on a tilted panel surface are not the same. The amount of irradiance a panel receives varies with its orientation and tilt. Furthermore, shadows from surrounding mountains, buildings, trees, or rows of mounting racks will reduce the irradiance available for power generation.

Next, solar panels convert solar irradiance into direct current (DC) power, but at this stage losses due to temperature and incident light conditions also occur. Because panels have the characteristic that output decreases as temperature rises, in hot regions or under poorly ventilated installation conditions the generation efficiency can be lower than expected. After that, the DC power passes through power conversion equipment to become alternating current (AC) power, and losses also occur in the wiring and conversion processes.

In PVSyst, the process leading to power generation is handled in stages. To correctly understand energy yield forecasts, it is important to look not only at the final value but also at where losses occur along the path from solar irradiance to energy production. Even if the energy yield is low, the measures to take depend on whether the cause is irradiance conditions, shading, temperature, the combination of equipment capacities, or the loss settings.

Also, power generation forecasts do not perfectly predict future weather. They estimate the average expected power generation based on past weather data and standard solar irradiance data. Therefore, it is natural that the actual power generation in a given year and the simulation values do not match exactly. In practice, simulation results should be used not as absolute values but as a basis for comparing conditions and making design decisions.

Initial Planning Conditions and Basic Power Plant Information

Before you start using PVSyst, you need to clarify the basic conditions of the power plant. The first requirement is the installation site. Latitude, longitude, elevation, and the surrounding environment affect solar irradiance and temperature conditions. In particular, solar irradiance varies greatly by region, and the same installed capacity can result in different energy production. If you run a simulation while the installation site remains vague, the meteorological conditions will not match reality and the reliability of the results will decrease.

Next, let's clarify the concept of equipment capacity. In solar power generation, multiple capacities are involved, such as the capacity on the panel side, the capacity of the power conversion equipment, and the grid connection capacity. If you do not understand which capacity is being used as the basis for evaluating generation, you can misread the results. For example, in a configuration where panel capacity is designed to be larger and the power conversion equipment limits output above a certain level, you can increase generation opportunities, but output may be curtailed during specific periods. To understand these relationships, it is necessary to grasp not only the numerical values of capacity but also the electrical meaning of the configuration.

Furthermore, the installation method is also important. Ground-mounted, roof-mounted, slope-mounted, or floating installations, among others, will affect the mounting height, ventilation, temperature conditions, shading patterns, and maintainability depending on the installation conditions. Even though PVSyst often treats these as generic conditions, it is necessary to understand the differences in installation methods in order to judge how to reflect the actual site conditions in the inputs.

In the planning stage, the required input accuracy varies depending on whether the plant in question is a new installation, a retrofit of existing equipment, a site-comparison, or a rough estimate for financial evaluation. In initial studies, approximate conditions can be used for comparisons, but at stages related to contracts and detailed design you need to verify equipment specifications, layout, shading, and loss conditions more carefully. Before using PVSyst, it is important to clarify what decision this simulation will be used to inform.

How should we consider meteorological data and solar radiation?

When performing energy yield predictions with PVSyst, meteorological data is extremely important. Solar power is driven by solar irradiance, and if irradiance is low, no matter how high-performance the equipment is, the generated energy will not increase. Therefore, understanding the types, locations, periods, and representativeness of the meteorological data you will use is important prerequisite knowledge before using PVSyst.

Weather data includes solar irradiance, air temperature, wind speed, and other parameters. Solar irradiance is the primary input for power generation, and air temperature affects output through panel temperature. Wind speed can be related to panel cooling. These conditions reflect regional climatic characteristics, but they do not necessarily fully represent the actual site. When using nearby observation stations or standard meteorological data, discrepancies with actual conditions can occur in mountainous areas, coastal areas, urban areas, or snow-prone areas.

Also, there is a difference between the solar irradiance that reaches a horizontal plane and the irradiance that falls on a tilted panel surface. In PVSyst, the irradiance on the panel surface is calculated according to the installation surface’s tilt angle and azimuth. Therefore, it is necessary to understand the concept that, rather than directly linking meteorological data values to power output, the received irradiance is transformed by the installation conditions.

Furthermore, in solar power generation, the difference between direct irradiance and diffuse irradiance is also important. Direct irradiance is the component that arrives directly from the sun, while diffuse irradiance is the component that reaches the surface after being scattered in the atmosphere. In regions with frequent cloudy skies or locations with surrounding shading, this difference affects generation trends. In detailed analyses, because the treatment of irradiance components influences the results, it is necessary when selecting meteorological data to confirm what assumptions the data are based on.

What practitioners should be careful about is that, once the meteorological data is selected, the foundation of the simulation results is almost determined. Even if you input detailed equipment and loss conditions, if the meteorological conditions are far from those at the site, the overall reliability of the results will not improve. Before using PVSyst, it is important to understand that meteorological data is not merely an initial setting but the very basis for power generation forecasts.

Prerequisite Knowledge of Solar Panels and Electrical Equipment

Using PVSyst requires the ability to read the basic specifications of solar panels and electrical equipment. Solar panels include information such as nominal output, voltage, current, temperature coefficient, efficiency, and dimensions. These are not merely catalog values but are directly linked to the simulation’s calculation conditions. In particular, the temperature coefficient indicates how much the output decreases when the panel temperature rises, and thus it affects the annual energy yield.

Also, the string configuration—how panels are connected in series and how they are connected in parallel—is important. If the number of panels in series is not appropriate, problems with the voltage range may occur. Increasing the number of parallel strings will affect current and the wiring configuration. The electrical configuration entered into PVSyst must align with the actual design. It is not enough that the capacity simply matches; you must consider voltage, current, and the input ranges of the power conversion equipment.

It is important to understand the rated capacity, input range, conversion efficiency, and behavior under overloading of the power conversion equipment. In configurations where the panel-side capacity is larger than the capacity of the conversion equipment, some output may be limited during periods of strong solar irradiance. However, this is not necessarily a poor design—sometimes that capacity ratio is chosen deliberately to increase generation opportunities in the mornings, evenings, and during low-irradiance periods. In PVSyst you can simulate the effects of such configurations, but to read the results correctly you need to understand the meaning of the capacity ratio.

Furthermore, wiring, junction boxes, protective devices, transformer equipment, and grid interconnection conditions also affect power generation and losses. PVSyst does not complete the detailed electrical design itself, but it is important to know where losses occur and which equipment conditions are reflected in the simulation.

Even if the person operating PVSyst is not a specialist in electrical equipment, they need to at least understand that solar panels generate DC power, which is then converted to AC power for use or fed into the grid. If numbers are entered without understanding the meaning of the input fields, a report may appear to be produced, but it may not be usable for design decisions.

Understanding Layout Planning and Shadow Impacts

In solar power generation, how equipment is arranged has a major impact on the amount of energy generated. Before using PVSyst, it is necessary to understand how tilt angle, azimuth, row spacing, installation height, surrounding obstructions, and terrain conditions relate to energy yield. In particular, the effect of shading is a point that beginners tend to overlook.

Solar panels generate electricity by receiving sunlight. Therefore, if sunlight is blocked by buildings, trees, utility poles, mountains, adjacent rows of mounting racks, or the like, power generation decreases. Shading does not just reduce generation in the shaded area; depending on the electrical connections of the panels, it can affect the output of surrounding panels as well. Even if the shaded area looks small, when these effects accumulate across times of day and seasons they can lead to a significant difference in annual energy production.

In layout planning, the balance between orientation and tilt is also important. Generally, selecting an orientation and angle that are more likely to receive sunlight relative to the sun’s movement makes it easier to increase power generation. However, on actual sites, conditions such as area, topography, constructability, maintenance access, drainage, local regulations, snow accumulation, and strong winds also come into play, so the optimal layout cannot be determined by generation output alone. PVSyst is useful for comparing multiple layout scenarios, but judgment that takes site-specific conditions into account is indispensable.

Also, narrowing the row spacing allows you to install more panels on the same site, but shadows from the front rows are more likely to fall on the rear rows. Widening the row spacing makes it easier to mitigate shading effects, but the installed capacity may decrease. In this way, layout planning involves a trade-off between increasing capacity and reducing shading. Before using PVSyst, understanding these design relationships will help you interpret simulation results more practically.

In shadow analysis, on-site surveying and an understanding of the surrounding conditions are also important. If site boundaries, building heights, tree locations, or changes in ground elevation are inaccurate, the assumptions underlying the shadow analysis will be misaligned. Even if settings in PVSyst appear to be configured precisely, if the underlying field information is coarse, the accuracy of the results is limited. The quality of power generation forecasts depends not only on software operations but also on the accuracy of how site conditions are obtained.

What you should know before entering loss conditions

When using PVSyst, many practitioners find the loss conditions confusing. Losses refer to the portions of solar irradiance that are lost during the process of being converted by the solar panels into the final generated electricity. Major losses include output reduction due to temperature, shading losses, soiling losses, variability between panels, wiring losses, conversion losses, and losses due to system downtime.

Before entering loss conditions, it is important not to treat loss rates as mere conventional values. For example, the effects of soiling vary with regional rainfall, dust, bird damage, proximity to farmland or roads, and cleaning frequency. Wiring losses are related to cable length, current, voltage, conductor size, and wiring route. Losses from equipment downtime are also influenced by maintenance and monitoring arrangements. In this way, loss conditions reflect site-specific and operational characteristics.

Regarding temperature losses, it is insufficient to simply assume that power generation is lower because the region is hot. Panel temperature varies depending on the mounting method, rear ventilation, distance from the roof surface, condition of the ground surface, how the wind flows, and so on. For ground-mounted and roof-mounted installations, the way panel temperature increases can differ even at the same ambient temperature. When handling temperature conditions in PVSyst, it is necessary to be aware of the actual installation environment.

Also, making the loss assumptions either too large or too small is problematic. If you set them overly optimistically, the estimated power generation will appear high and there is a risk of overestimating the project’s viability. Conversely, if you set them overly conservatively, the results may be worse than reality and could impede reasonable planning decisions. What matters is understanding the meaning of each loss and setting explainable conditions according to the project’s purpose.

The loss diagram in PVSyst allows you to see at which stages and how much loss occurs. By looking at it, you can more easily identify the main factors that are reducing energy production. However, to read the loss diagram correctly, you need to understand what each loss item means. In practice, it is important not to follow the item names alone but to consider them in connection with site conditions and design conditions.

Basic Indicators for Interpreting Simulation Results

To read the results produced by PVSyst, you need to understand several basic indicators. Typical ones include annual energy production, monthly energy production, specific yield, performance ratio, and breakdown of losses. By viewing these indicators together, you can judge not only whether the energy production is high or low, but also whether the system is generating efficiently as an installation.

Annual energy generation is the expected total amount of electrical energy produced over a given period. It is a very important figure in project feasibility assessments, but on its own it does not determine the quality of the design. Because larger installed capacity tends to yield higher annual generation, it is necessary to look at generation per unit of capacity. Specific yield indicates how much electricity can be generated relative to installed capacity, making it useful when comparing projects of different sizes.

The performance ratio is an indicator that shows how effectively a system actually generates power compared with the theoretically available energy. If the performance ratio is low, there may be significant loss factors somewhere—temperature, shading, wiring, conversion, soiling, system configuration, and so on. However, it is also risky to judge performance solely by the performance ratio, because its interpretation changes depending on local solar irradiance conditions, ambient temperature, installation conditions, and the approach to oversizing.

Monthly power generation is also important. Even if annual values do not reveal problems, generation can be low in specific seasons. By looking at monthly trends, it becomes easier to understand a plant’s characteristics—such as longer shadows in winter, the effects of snow, greater temperature-related losses in summer, or impacts from the rainy season or wet season. In design comparisons, it is important to check seasonal generation patterns as well as the annual total.

Also, the results report presents the input conditions and the output results as a set. In practice, rather than extracting and using only the numerical results, you need to verify together which meteorological data were used, which equipment specifications were assumed, and which loss rates were set. Simulation results are not meaningful when separated from their assumptions. Users of PVSyst are expected to be able to explain the result values together with the input assumptions.

Practical perspectives required of PVSyst users

Those who use PVSyst in professional practice need not only software operation skills but also the ability to interpret design conditions and explain the results. Personnel responsible for solar power generation may share information with people in a variety of roles—design, construction, project planning, maintenance, financial evaluation, and administrative/regulatory matters. In that context, how PVSyst results are communicated is extremely important.

For example, when explaining a power generation forecast internally, simply saying "we will generate this much power annually" is insufficient. You need to be able to explain which weather conditions the forecast assumes, what equipment capacity was used for the calculation, what losses are expected, and to what extent the impact of shading has been reflected. Numbers without clear assumptions are hard to use as a basis for decision-making.

Also, in design comparisons, simulations are sometimes performed while changing multiple conditions. When examining changes such as altering the tilt angle, changing the azimuth, varying panel capacity, modifying row spacing, or adjusting loss conditions, the ability to see differences in the results is important. Even if energy production increases, if there are problems with constructability, maintainability, land use, or equipment load, it is not necessarily a good proposal. PVSyst provides material for comparison, but the final decision requires a comprehensive practical perspective.

Moreover, the results from PVSyst highlight different points of interest depending on the stakeholder. Design engineers emphasize system configuration and the breakdown of losses, business personnel emphasize annual energy yield and impacts on profitability, and maintenance personnel may emphasize soiling, downtime losses, and shading effects. To make use of energy yield forecasts, it is important to be aware of what the other party wants to assess and to organize and communicate the necessary information.

As prerequisite knowledge for using PVSyst, in addition to technical knowledge of solar power generation, practical skills such as collecting site information, reading drawings, checking electrical specifications, preparing reports, and creating explanatory materials are also useful. Power generation forecasting may appear to be a desk calculation, but in reality it is the work of linking site conditions and design conditions. The more someone understands the site, the more likely they are to notice the validity of input conditions and any anomalies or inconsistencies in the results.

Points to Verify to Avoid Relying Solely on PVSyst

PVSyst is software that helps predict power generation, but you shouldn't rely on it for everything. One point to be especially careful about is that the software does not fully guarantee that the conditions you entered are correct. Even if you enter incorrect coordinates, incorrect orientation, incorrect equipment specifications, or overly optimistic loss rates, it will still produce a report that looks plausible. For that reason, verifying the input conditions is essential before reviewing the output results.

The first thing to check is the consistency between the installation site and the meteorological data. Even when using data from nearby stations, actual solar irradiance conditions can differ due to elevation differences, topography, sea breees, snow cover, fog, and the surrounding environment. If the candidate area is large or terrain changes are significant, care must be taken in how representative points are selected. As a basic step, verify that the location settings in PVSyst match the actual planned site.

Next, verify consistency between the design drawings and the on-site information. Check that the panels' azimuth and tilt angles, inter-row spacing, mounting structure height, and the positions of obstacles match the drawings. In particular, when assessing shading effects, inaccurate heights or positions of nearby obstacles can cause the shading loss evaluation to be off. Even a site that appears simple on the drawings can, in reality, have level changes, slopes, existing structures, vegetation, or boundary conditions that affect energy generation.

Furthermore, consistency of equipment specifications is also important. The specifications of solar panels and conversion equipment involve not only model numbers and capacities, but also voltage ranges, current ranges, temperature characteristics, conversion efficiency, and so on. Even equipment with similar capacities can affect simulation results if their detailed specifications differ. Even when using data registered in PVSyst, it is necessary to confirm that it matches the specifications adopted in the plan.

Finally, it is also important to check the plausibility of the results from other perspectives. Compare them with past similar projects, simple calculations, regional solar irradiation trends, and typical energy production per unit of installed capacity to ensure the results are not unusually high or low. If something feels off, review the input conditions, loss settings, shading conditions, and capacity settings. To trust PVSyst’s results, you should not accept the software’s output at face value; adopt a practitioner’s approach and perform independent checks.

Summary

PVSyst is specialized simulation software for predicting the energy production of photovoltaic (PV) systems and for organizing design conditions and loss conditions. What is required before using it is not merely the operating procedure. You need to understand prerequisite knowledge such as solar irradiance, meteorological data, panel characteristics, electrical equipment, layout planning, shading, losses, and performance indicators, and you need the ability to link input conditions with output results.

In particular in practical work, you must take care that the power generation forecast figures do not stand alone. Only when you can explain which location’s meteorological data was used, what plant capacity was assumed, and how shading and losses were estimated do PVSyst’s results become information that can be used for design and business decisions. PVSyst is a convenient software, but verifying the validity of the input conditions and interpreting the results is ultimately the responsibility of the practitioner.

If you're just starting to use PVSyst, it's more important to get a broad grasp of how the energy production is determined than to try to understand every detail perfectly from the outset. Check the site's solar irradiance conditions, consider the irradiance reaching the panel surface, understand how that irradiance is converted to electricity by the equipment, and recognize the various losses that occur along the way until the final energy output is reached—this flow will make the meaning of the input fields and the results reports much easier to understand.

Additionally, improving PVSyst's accuracy requires a thorough understanding of on-site conditions. The more accurate the information on orientation, tilt, site shape, surrounding obstacles, terrain, and equipment layout is, the closer the simulation assumptions will be to reality. In solar power planning, linking desk-based generation forecasts with on-site location information is a key factor in improving design quality.

If you want to streamline on-site inspections and the acquisition of location information, leveraging LRTK (an iPhone-mounted GNSS high-precision positioning device) can make obtaining the planned site's coordinates and recording field information smoother. As a preliminary step before evaluating power generation with PVSyst, accurately organizing the site's location and surrounding conditions is effective in enhancing the reliability of input parameters. If you want to apply photovoltaic simulations in practice, it's important to consider not only the software settings but also the workflow of correctly obtaining field information and reflecting it in the design conditions.