What can PVSyst compare? Summarizing how to interpret changes when conditions are modified

PVSyst is specialized analysis software used for design studies and energy yield simulations of photovoltaic power systems. It is not simply something that calculates annual energy production once and stops; its major value lies in allowing comparison of multiple calculation results while changing installation conditions, equipment configuration, orientation (azimuth), tilt angle, shading, losses, meteorological conditions, and so on. In practical photovoltaic work, the optimal conditions are rarely determined from the outset, so it is necessary to choose the most appropriate option while considering site conditions, constructability, generation efficiency, future operation and maintenance, and design margins.

Many people who search for "What is PVSyst" want not only the basics of the power generation forecasting software, but also to know which conditions can actually be compared and where on the results screens they should look to make judgments. In particular, if you judge solely by annual energy yield when you change conditions slightly, it becomes difficult to see why the difference occurred, which losses increased or decreased, and whether the design truly improved. This article organizes, from a practical standpoint, the main conditions that can be compared in PVSyst and the views you should check when changing conditions.

Table of Contents

• PVSyst is a design study tool that can be used to compare conditions

• Main items that can be compared when conditions change

• How to interpret results when orientation and tilt angle are changed

• How to interpret results when panel layout and spacing conditions are changed

• Key points to check when shading conditions are changed

• Comparison methods when equipment configuration is changed

• How to interpret changes when loss conditions are modified

• Points to note when meteorological data or site conditions are changed

• Perspectives to avoid judging by annual energy production alone

• Workflow for applying condition comparisons to design decisions

• The accuracy of on-site conditions affects the comparison results

• Summary

PVSyst is a design study tool that can be used to compare conditions

PVSyst is a tool not only for calculating the energy output of a photovoltaic system but also for organizing and comparing the differences when design conditions are changed. In photovoltaic design, even on the same site, energy production and the breakdown of losses change depending on panel orientation, tilt angle, number of panels installed, rack spacing, equipment configuration, cable conditions, how shadows are handled, and so on. By using PVSyst, you can change these conditions one by one to more easily see how much each factor affects the results.

In practice, it is important not to think of PVSyst as software that automatically produces the “correct” answer. PVSyst is a tool that presents calculation results based on the input conditions. Therefore, the accuracy of any comparison depends greatly on the validity of those input conditions. If the on-site slope, nearby obstacles, land topography, orientation, solar radiation conditions, equipment specifications, and so on deviate from reality, the comparison results will also be difficult to use for design decisions.

On the other hand, if you understand the meaning of the inputs and enter them correctly, PVSyst becomes a very effective comparison tool. For example, you can examine whether a slight change in tilt angle increases energy production, how much shading losses change, whether increasing the number of panels will make equipment-side constraints more binding, and whether the effects of wiring losses and temperature losses are within acceptable limits. In other words, PVSyst is not just for looking at generation figures; it is for explaining the differences between design proposals and producing materials that stakeholders can use to make convincing decisions.

Main items that can be compared when conditions change

PVSyst allows comparison of a wide variety of conditions. Typical examples include installation azimuth, tilt angle, panel layout, inter-row spacing, shading conditions, incidence conditions on the module plane, equipment configuration, the capacity ratio between the DC and AC sides, cable conditions, temperature conditions, soiling conditions, various loss rates, meteorological data, and site conditions. These may seem independent of one another, but in fact they interact.

For example, changing the tilt angle not only alters the annual solar energy capture, but also affects inter-row shading patterns, wind exposure, susceptibility to soiling, racking height, and constructability. Increasing the number of panels increases the system capacity, but narrows on-site spacing and can increase shading losses. Changing the equipment configuration not only alters conversion efficiency and capacity constraints, but can also change how partial shading impacts the system.

When comparing conditions, it is important not to change too many variables at once. Changing multiple conditions simultaneously makes it difficult to understand why power generation increased or decreased. In practice, it is desirable to first create a baseline case and then compare while isolating effects—for example, by changing only the orientation, only the tilt angle, only the layout, or only the shading conditions. Even if you ultimately develop a proposal that combines multiple improvements, confirming the effect of each condition individually beforehand will make the analysis easier to explain.

Also, when making comparisons, it is necessary to check not only annual power generation but also monthly generation, loss diagrams, performance ratio, solar irradiance capture, shading losses, temperature losses, equipment-side losses, and so on. This is because even if the annual generation is similar, there can be options that perform better in summer, options that perform better in winter, options that are strong in the morning and evening, or options that drop sharply in certain months. In power generation projects, not only the annual total but also seasonal generation trends, demand, contractual conditions, and alignment with maintenance plans are important.

How to interpret changes in azimuth and tilt angle

Azimuth and tilt angle are typical parameters compared in PVSyst. In solar power systems, the amount of solar irradiance received depends on the direction panels face and the angle at which they are installed. Generally, orientations and tilt angles that receive more irradiance are considered, but on-site constraints such as site shape, roof geometry, site development conditions, wind load, snow accumulation, drainage, and constructability mean the decision cannot be made based solely on theoretically optimal values.

When comparing orientations in PVSyst, it’s important to be aware not only of changes in annual energy production but also of how the timing of generation shifts. Changing the orientation alters whether generation tends to be concentrated in the morning or in the afternoon. Even if the annual total shows little difference, the generation profile by time of day can be meaningful depending on how electricity is used, feed-in conditions, and operational strategies.

When changing the tilt angle, it is necessary to consider the annual solar energy yield, seasonal power generation, shading losses, and the tendency for soiling to persist. Increasing the tilt angle can make it easier to capture sunlight in some seasons, but it can also cause inter-row shading to lengthen. Conversely, reducing the tilt angle tends to improve layout efficiency, but can make it harder to increase power generation during periods of low solar elevation.

When comparing cases, first check the reference case’s annual and monthly energy production, and then look at the differences for cases where the azimuth or tilt angle has been changed; this makes interpretation easier. Determine whether the months showing differences are in summer or winter, and whether the differences occur in the morning/evening or during daytime, so the meaning of the change becomes clear. Also check the loss chart to see whether the differences are due to solar irradiance capture, shading losses, or temperature losses, which makes it easier to judge the validity of the design conditions rather than merely comparing numbers.

How to interpret changes in panel layout and spacing conditions

Comparing panel layouts and inter-row spacing is important when considering the balance between energy production and land-use efficiency. In solar power generation there is a natural tendency to try to install as many panels as possible within a limited site, but packing them too tightly can cause problems such as shading effects, insufficient maintenance aisles, reduced constructability, and difficulty with drainage and mowing. In PVSyst, changing the layout conditions allows you to compare increases and decreases in installed capacity and changes in losses.

If panels are placed more densely, the installed capacity increases, so the simple annual energy output may rise. However, when looking at energy generation per unit capacity or the performance ratio, efficiency may decline. This is because, even if the total energy output increases simply because there are more panels, factors such as shading, temperature, and equipment-side constraints can reduce the generation efficiency per panel or per kilowatt.

On the other hand, widening the row spacing can reduce shading losses and improve maintainability, but it may reduce the number of panels that can be installed on the same site. In this case, the total annual energy production may decrease, but it can be advantageous in terms of equipment health, maintainability, and long-term operational stability. When reviewing PVSyst comparison results, it is important to check not only the total energy production but also the energy yield per unit capacity and the nature of the losses.

When comparing layouts, also check whether shading losses are concentrated in specific seasons or times of day. Design decisions will differ depending on whether large shadows occur only during winter mornings and evenings or whether losses occur widely throughout the year. Short, limited periods of shading may be acceptable, but shading that recurs over long periods can affect not only power generation but also the operation of the equipment.

Points to Check When Changing Shadow Conditions

When comparing scenarios in PVSyst, the treatment of shading is extremely important. In photovoltaic power generation, various shadows—such as those from surrounding buildings, trees, utility poles, mountains, fences, and between rows of mounting structures—affect energy production. Shading does not simply block irradiance; when it falls on part of a module surface it can have a large effect as an electrical loss. Therefore, when comparing different shading conditions, you need to check not only the shading-loss figures but also where, at what times of day, and in which seasons the shading occurs.

When comparing shading conditions, it is helpful to first compare a baseline case with no shading to a case that includes realistic shading, as this makes it easier to grasp the impact of shading. Next, by creating cases that vary obstacle height and position, panel layout, and row spacing, you can see which measures are effective at reducing shading losses. However, note that the no-shading case represents ideal conditions and tends to lead to overestimation in real-world design decisions.

When assessing the impact of shading, check not only the difference in annual energy production but also the extent to which shading-related losses account for within the loss breakdown. Also, by looking at monthly production you can determine whether the shading impact is concentrated in winter or occurs throughout the year. Winter shading is more likely because of the low solar altitude, and at some sites inter-row spacing and nearby obstacles can have a large influence.

Even if changing shading conditions slightly improves power generation, if that improvement leads to a large reduction in the number of modules to be installed or a severe deterioration in constructability, an overall assessment is necessary. The results from PVSyst are only quantitative comparison material, and for the final decision it is important to evaluate site conditions, construction conditions, maintainability, and safety.

How to Compare When Changing Equipment Configuration

PVSyst can also perform comparisons when the configuration of solar panels and power conversion equipment is changed. In practice, even with the same site conditions, changing panel capacity, the capacity ratio between the DC side and the AC side, circuit configuration, number of devices, and connection units will alter the energy production and losses. When comparing equipment configurations, it is not enough to simply increase capacity; you need to assess how efficiently the whole installation can generate power.

What you should particularly check is the balance between DC-side capacity and AC-side capacity. Increasing the DC side makes it easier to increase generation opportunities during periods or seasons with weak solar irradiance, but during periods of strong irradiance the output may be constrained by the AC-side limit. The extent to which this constraint occurs can be understood by checking loss diagrams and items related to output limits. Even if annual generation increases, if constraint losses become too large you will need to reconsider the design balance.

Also, changing the equipment configuration can alter how partial shading and mismatch affect performance. Depending on the circuit-level approach and how connections are arranged, losses when part of the array is shaded can either be larger or be more easily distributed. When comparing in PVSyst, it is important not only to enter differences in equipment specifications but also to consider connection conditions and their relationship to the layout.

In comparing equipment configurations, check annual power generation, performance ratio, conversion losses, output limits, and trends in overloading and underloading. Furthermore, examining how differences appear by month and by time of day makes it easier to understand in which situations changes in the capacity ratio are having an effect. Operational staff need to verify, not only to maximize power generation but also from the perspectives of equipment stability and long-term operation, that conditions have not become excessively aggressive.

How to Interpret Changes in Loss Conditions

One of PVSyst's major features is that it allows you to check how the final energy production is determined through the losses it undergoes. In photovoltaic systems, various losses occur between the moment solar radiation reaches the panel surface and the point when it is extracted as electrical power. These include temperature-related losses, shading losses, soiling losses, wiring losses, equipment conversion losses, and mismatch losses, and changing these conditions will change the results.

When comparing loss conditions, it is important to separate which losses can be improved through design and which losses should be accepted as site conditions. For example, wiring losses may be improved by reviewing cable length, cross-sectional area, and layout planning. Shading losses can sometimes be reduced by revisiting the layout and the relationship with obstacles. Temperature losses are related to installation methods and ventilation conditions, but are also influenced by the local climate and the installation environment. Soiling losses are related to maintenance planning and the surrounding environment.

When changing conditions, it is important not to simply enter a lower loss rate to produce a favorable result, but to set it based on a realistic rationale. Loss assumptions directly affect power generation, so even small changes can lead to different outcomes. Therefore, you should set reasonable values based on in-house standards, past projects, local site conditions, maintenance plans, and design criteria.

When reviewing comparison results, check which differences in losses are responsible for the final difference in energy yield. Whether the increase in energy yield is due to shading countermeasures or merely because the loss-rate inputs were made more optimistic has completely different design implications. Carefully interpreting PVSyst's loss diagram makes it easier to distinguish between the effects of condition changes and apparent improvements in the inputs.

Precautions When Changing Meteorological Data or Site Conditions

When calculating energy production with PVSyst, meteorological data and site conditions are critically important. Because photovoltaic output is strongly affected by solar irradiance and air temperature, the results will vary depending on which location’s meteorological data are used. Site conditions include latitude, longitude, elevation, surrounding terrain, temperature conditions, and irradiance conditions. When comparing conditions, it is important not to confuse differences in design proposals with differences in meteorological data.

For example, even with the same design proposal, using different meteorological data will change the annual power generation. This difference is not due to improvements in design conditions but to differences in the underlying data. Therefore, when you want to compare orientation, tilt angle, equipment configuration, and so on, you need to fix the meteorological data and site conditions for the comparison. Conversely, if you want to compare the candidate sites themselves, you should keep the same design philosophy and vary the meteorological conditions for each site, evaluating them as regional differences.

A point to note when entering site conditions is that the actual site location and the representative point in the data do not necessarily coincide exactly. Even in nearby areas, actual generation conditions can vary due to differences in elevation, distance from the coast, mountain shading, snow cover, fog, wind conditions, and so on. Because PVSyst’s results are based on the meteorological conditions entered, it is important to determine how to correct for or interpret site-specific environmental differences.

When changing conditions, it is advisable to manage separately the cases in which meteorological data are changed and those in which design conditions are changed. If multiple assumptions are changed simultaneously, it becomes difficult to determine whether differences in energy output are due to design improvements or to differences in the meteorological assumptions. By clarifying the purpose of the comparison and separating whether you want to examine site differences or design differences, PVSyst results become easier to use and interpret correctly.

Perspectives to Avoid Judging Solely by Annual Electricity Generation

When reviewing PVSyst comparison results, many people first focus on annual energy production. Annual energy production is an easy-to-understand metric and is important for comparing design proposals. However, judging solely by annual energy production can overlook design risks and the substance of possible improvements. When conditions change, it is necessary to check, in addition to annual energy production, the performance ratio, loss breakdown, monthly energy production, energy production per unit capacity, and the tendency for shading and output limitations to occur.

For example, one proposal may show higher annual power generation simply because the installed capacity has been greatly increased, so the total generation rises as a result. In that case, looking at generation per unit of capacity may reveal a decline in efficiency. Also, even if annual generation is similar, one proposal may see a significant drop in winter generation while another remains stable throughout the year. Which is better depends on the project’s objectives and operating conditions.

The performance ratio is an indicator that shows how efficiently an installation extracts electrical power from the solar irradiance it receives. When the performance ratio changes significantly in comparative conditions, differences in loss conditions, equipment configuration, shading, temperature, and so on are behind it. If annual energy production increases while the performance ratio is declining, the efficiency drop may be hidden by the effect of increased capacity.

Also, by looking at breakdowns of losses, you can identify where there is room for design improvement. If shading losses are large, review the layout and obstacle conditions; if wiring losses are large, review the cable plan; if output limitations are large, reconsider the capacity ratio—this makes it easier to link to the next improvement actions. PVSyst becomes more valuable when used not just to stare at the result numbers but to explore directions for design improvement.

Flow for Using Condition Comparisons in Design Decisions

To make effective use of PVSyst for design decisions, it is important to organize how comparisons will be conducted. First, clarify site conditions and design assumptions as much as possible, and create a baseline case. This baseline case should be prepared using the conditions currently considered most reasonable, and will serve as the foundation for subsequent comparisons. If you produce multiple options while the baseline remains unclear, it becomes difficult to discern what was improved and what was sacrificed.

Next, change the conditions you want to compare one at a time. When comparing orientation, fix all variables except orientation; when comparing tilt angle, fix all variables except tilt angle. When comparing layouts, clearly record how layout changes affect installed capacity and shading conditions. When comparing equipment configurations, focus on checking capacity ratio, conversion losses, and output limits.

Then, review the results of each case from the same perspective. Compare annual energy production, monthly energy production, performance ratio, loss diagrams, major losses, and energy production per unit capacity, and summarize the differences resulting from the changes. What is important here is not only the magnitude of the numbers, but also being able to explain why those differences occurred. Understand whether an increase in energy production is due to improved solar radiation capture, reduced losses, or increased capacity.

Finally, compare the simulation results against the design constraints. Even proposals with high power generation cannot be considered optimal if construction is difficult, maintenance access is hard to secure, they do not match the site's terrain, or there are concerns about future operations and maintenance. The comparative results from PVSyst are important material to support design decisions, but they only become usable for practical decision-making when evaluated together with site conditions and operational conditions.

The accuracy of on-site conditions affects the comparison results

When comparing scenarios in PVSyst, the aspect most often overlooked is the accuracy of the site conditions. No matter how finely you adjust simulation parameters, if the underlying site shape, orientation, elevation differences, obstacle locations, and panel installation area deviate from reality, the reliability of the comparison results will decrease. Accurate site information is especially important for locations with uneven terrain, nearby structures that cast shadows, or constraints on boundaries or allowable installation areas.

In condition comparisons, design decisions are sometimes made based on differences of a few percent. However, if there are large errors in on-site measurements or placement assumptions, those few-percent differences can become meaningless. For example, even if a comparison that changes the tilt angle shows a slight difference in power generation, if the actual ground slope, racking height, or the positions of surrounding obstructions are inaccurate, the simulated difference may not indicate real-world superiority or inferiority.

Therefore, when making comparisons using PVSyst, not only the software input work but also on-site positioning, terrain assessment, obstacle verification, and definition of the installation area are essential. If site coordinates and elevation information can be accurately obtained and reflected in the design model, comparisons of shading and layout conditions will be much closer to reality. Conversely, if site conditions remain ambiguous, even comparing multiple proposals will leave uncertainty in the final decision.

What is useful here is a positioning environment that can acquire high-precision location information on site. When evaluating a solar power plant, minimizing the difference between desktop design and on-site measurements as much as possible is important to make the most of PVSyst comparison results. By utilizing LRTK (iPhone-mounted GNSS high-precision positioning device), you can streamline on-site position checks and measurement point recording, making it easier to organize the coordinate information that forms the basis for design conditions. Even when you want to accurately compare differences after changing conditions in PVSyst, correctly capturing the on-site conditions is indispensable.

Summary

PVSyst is not only a tool for calculating the energy production of photovoltaic systems but also an important tool for comparing differences when conditions change and using those comparisons to inform design decisions. By changing azimuth, tilt angle, panel layout, row spacing, shading conditions, equipment configuration, loss assumptions, and meteorological data, you can observe changes in energy production and losses. However, when reviewing comparison results, it is important not to rely solely on annual energy production; you should also check the performance ratio, loss breakdown, monthly energy production, energy production per unit capacity, and trends in shading and output limitations.

When comparing conditions, it is important to clarify what was changed and what was held constant. If you change many conditions at once, it becomes difficult to determine where differences in the results originated. By creating a baseline case and then comparing orientation, tilt angle, layout, equipment configuration, loss conditions, and so on in sequence, it becomes easier to explain the strengths and weaknesses of the design proposals.

Also, PVSyst results are largely dependent on the input conditions. If the site’s topography, obstacles, installation area, azimuth, and elevation differences are not correctly reflected, the reliability of condition comparisons will be reduced. To improve simulation accuracy, it is essential not only to set the software correctly but also to obtain and organize on-site information. By using LRTK (iPhone-mounted GNSS high-precision positioning device) for field checks and coordinate recording, you can more accurately establish the prerequisites for comparisons in PVSyst. In solar design studies, it is important to combine simulation and on-site surveying so that the numerical basis is clear and design decisions can be explained in practice.