What does PVSyst compare? A case-by-case beginner's guide to using it

PVSyst is a specialized simulation software used to predict the energy production of photovoltaic systems and to compare differences among design conditions. When evaluating photovoltaic power generation, it is necessary to consider not only the system capacity but also a combination of installation site, azimuth, tilt, shading, terrain, wiring, equipment capacity, loss conditions, and other factors. Even for the same power plant, slight changes in conditions can affect the annual energy production, monthly generation profile, loss patterns, and the ease of operating the equipment.

For practitioners searching "What is PVSyst", it is important to understand PVSyst not merely as power generation calculation software but as a tool for comparing multiple design cases and clarifying which conditions affect energy yield and project economics. This article explains, case by case, what can be compared in PVSyst and in which situations its use is most effective.

Table of Contents

• PVSyst is software that supports design decision-making through comparative analysis

• Fundamentals to grasp before making comparisons in PVSyst

• Case 1 Compare installation site and meteorological conditions

• Case 2 Compare orientation and tilt

• Case 3 Compare panel layout and installed capacity

• Case 4 Compare shading and terrain conditions

• Case 5 Compare equipment capacity and output limitations

• Case 6 Compare wiring losses and electrical conditions

• Case 7 Compare loss conditions to assess sensitivity of energy yield

• Points to note when interpreting PVSyst comparison results in practice

• Combine PVSyst with on-site information to improve comparison accuracy

PVSyst is software that supports design decisions through comparison

PVSyst is analysis software that simulates the energy yield of photovoltaic installations and verifies how differences in design conditions are reflected in the results. It is easier to understand if you consider it not as a tool for calculating energy yield just once, but as a tool for exploring more appropriate design conditions by comparing multiple cases. In solar power practice, while you want to maximize energy yield, you must also take into account land conditions, constructability, maintainability, system configuration, shading effects, and wiring plans. PVSyst helps confirm the energy yield and losses when these various conditions are changed, and assists in establishing the rationale for design decisions.

The output of a solar power system is not determined simply by the panel capacity. Even in regions with high solar irradiance, if the installation angle is not appropriate, surrounding shading is significant, or wiring losses are large, the expected generation may not be achieved. Conversely, even if the installed capacity is slightly smaller, if there is little shading and the layout and equipment configuration are appropriate, it can generate power efficiently. Because it is difficult to judge these differences by intuition alone, comparing conditions with PVSyst is worthwhile.

Comparisons in PVSyst are not just about looking at which system produces more energy. They comprehensively check annual energy production, monthly energy production, performance ratio, breakdown of losses, output clipping, shading losses, temperature losses, and so on. In one design proposal, annual energy production may be high, but large losses could occur in specific seasons. In another design proposal, annual energy production may be slightly lower, but shading impacts might be smaller and maintainability and constructability may be superior. PVSyst can be used to organize these comparisons numerically so stakeholders can make decisions more easily.

What beginners should be aware of first is that PVSyst comparison results only make sense when it is made clear "which condition was changed." If you change multiple conditions at the same time, it becomes difficult to determine what caused the differences in energy yield. If you change the azimuth, change only the azimuth; if you change the tilt, change only the tilt; if you change the shading conditions, change only the shading—clarifying the purpose of the comparison is important. PVSyst can perform advanced calculations, but the design of the comparison itself must be organized by a person.

Basic Points to Keep in Mind Before Comparing in PVSyst

Before performing a case comparison in PVSyst, it is important to first decide on a baseline case. The baseline case is the one in which you enter the design conditions that you currently consider most realistic. Organize the installation location, meteorological conditions, orientation, tilt, system capacity, layout, equipment configuration, shading conditions, wiring conditions, loss conditions, and so on, and first create a single standard simulation. Then change only the items you want to compare and check how the results change.

The important thing in comparisons is to clarify the purpose of changing the conditions. For example, if the comparison changes orientation, the purpose is to confirm "to what extent differences in direction affect annual power generation and seasonal power generation." If the comparison changes tilt, you will look at "which angle is advantageous for annual power generation" and "how the difference between winter and summer power generation changes." For comparisons of shading conditions, you can confirm "how much difference in generated power there is between considering obstacles and not considering them." By clarifying the purpose in this way, it becomes easier to interpret the results.

When comparing results, it is important not to focus solely on annual generation. Annual generation is an easy-to-understand metric, but unless you also check monthly generation, loss breakdowns, and the performance ratio, you cannot fully grasp the characteristics of a design. For example, two cases with almost the same annual generation may differ: one may perform strongly in summer while the other is stable in winter. Which is preferable depends on the purpose of the power generation project and how the electricity will be used.

Also, when making comparisons in PVSyst, attention must be paid to the accuracy of the on-site conditions. If the site's orientation, tilt, obstructions, terrain, and available installation area are inaccurate, the comparison results are likely to deviate from reality. The accuracy of on-site information has a particularly large impact when comparisons include shading and terrain. Even if the software allows you to create multiple cases, if the underlying assumptions are ambiguous, the reliability of the comparison results will not improve.

The basic approach to making comparisons in PVSyst is to create a reference case, change each condition you want to compare one at a time, and check not only the annual energy production but also losses and seasonal variations. By following this workflow, even beginners will find it easier to interpret the meaning of the comparison results.

Case 1: Comparing installation locations and weather conditions

One of the typical items that can be compared in PVSyst is the installation site and meteorological conditions. Solar power generation is greatly influenced by local solar irradiance and ambient temperature. Even with the same system capacity, the annual energy yield differs between regions with high irradiance and those with low irradiance. In addition, in areas with high temperatures panels are more likely to heat up, which can lead to greater temperature-related output losses. Because PVSyst can calculate energy production based on the installation location and weather conditions, it is useful for comparing candidate sites.

In the initial assessment of a power generation project, there are situations where multiple candidate sites are compared. Even if the land areas are similar, differences in regional solar irradiance conditions, topography, surrounding environment, and shading conditions can change the outlook for power generation. By using PVSyst, you can set the same equipment conditions for each candidate site and check the differences in power generation and losses. This makes it easier to understand which candidate site is advantageous in terms of power generation.

When comparing weather conditions, it is important to consider the effects of temperature as well as solar irradiance. Regions with high irradiance tend to have higher energy yields, but they may also experience increased losses due to high temperatures. Conversely, regions with relatively low temperatures may see reduced temperature-related losses, but if irradiance is low, energy yield may not increase much. In PVSyst results, checking temperature losses and monthly generation together with the energy yield makes it easier to identify regional characteristics.

When comparing installation sites, monthly power generation trends are also important. Even if annual power generation is similar, the seasonal distribution of generation can differ. Regional characteristics—such as periods with frequent snow or overcast skies, high temperatures in summer, or insufficient solar radiation in winter—are reflected in monthly power generation. In business planning, it is useful to check not only the annual total but also which seasons the generation is concentrated in.

However, the meteorological data are only representative conditions and do not fully guarantee future weather. Actual power generation will fluctuate due to year-to-year variations in weather. Therefore, when comparing installation sites in PVSyst, it is important to use the results not as fixed absolute values but as a reference for understanding the relative trends among candidate sites.

Case 2 Comparing orientation and inclination

A common comparison performed in PVSyst is the panel azimuth and tilt. Azimuth indicates the direction the panels face, and tilt indicates the angle at which the panels are installed. These directly affect the amount of solar irradiance reaching the panel surface. To increase power generation, it is necessary to consider the azimuth and tilt that match the solar conditions at the installation site.

When comparing orientations, you may consider layouts that are close to south-facing, arrangements that take advantage of the east–west axis, or configurations tailored to the shape of the site. Generally, some orientations are advantageous when annual power generation is prioritized, but the optimal direction varies depending on the local land shape and equipment layout. In configurations closer to east-facing or west-facing, the peak hours of power generation can shift. Paying attention not only to annual totals but also to generation trends by time of day and season makes the purpose of orientation comparisons easier to understand.

When comparing tilt angles, you check how annual and monthly energy production change when the angle is altered. A small tilt angle can make it easier to use the installation area efficiently, but it can affect soiling, drainage, snow accumulation, and seasonal solar gain. A large tilt angle can make it easier to receive winter solar irradiance, but inter-row shading, wind loads, and construction conditions need to be considered. By changing and comparing tilt angles in PVSyst, you can evaluate the balance between energy production and site conditions.

When comparing azimuth and tilt, choosing only the condition that yields the highest energy production is not necessarily appropriate. The conditions that can actually be adopted may be limited by site topography, roof orientation, mounting-frame installation constraints, maintenance access, surrounding shading, constructability, and other factors. A case that produces the highest output in PVSyst may be difficult to construct on site. Therefore, use the comparison results as material to narrow down design candidates, and make the final decision after confirming the on-site conditions.

When beginners compare azimuth and tilt, it’s important not to change both too much at once. If you are comparing azimuth, keep the tilt fixed; if you are comparing tilt, keep the azimuth fixed—this makes it easier to determine which condition is responsible for differences in the results. Comparing while organizing the conditions in PVSyst makes it easier to understand the factors that affect energy production.

Case 3: Comparing panel layout and installed capacity

PVSyst is also useful when comparing panel layouts and installed capacity. In solar power generation, the capacity that can be installed changes depending on how land or roof area is used. Installing more panels will increase the installed capacity, but if layouts are packed too tightly, shadows can increase, maintenance access can be insufficient, and construction can become more difficult. By using PVSyst, you can see how differences in layout and capacity affect energy generation and losses.

When comparing installed capacity, there is a general tendency for cases with larger capacity to yield higher annual energy generation. However, a larger capacity does not necessarily mean better generation efficiency. Placing more panels on a limited site can make inter-row shading more likely. Wiring distances may also become longer, and the balance with equipment capacity can worsen. By comparing different capacities in PVSyst, you can confirm the increase in energy production obtained by increasing capacity and the losses that increase at the same time.

When comparing panel layouts, we examine cases that vary row spacing, orientation, and the layout area. For example, comparing an arrangement that maximizes installed capacity with one that leaves extra spacing to reduce shading makes it easier to determine which is more advantageous from a business standpoint. Even if the annual energy generation is higher for the larger-capacity case, if the generation per unit of capacity is lower, there may be issues in terms of efficiency.

Maintainability is also an important consideration when comparing layouts. PVSyst is mainly software for evaluating energy production and losses, but when interpreting comparison results it is necessary to take on-site operations into account. If panels are packed too tightly, there may be insufficient access aisles for inspection and cleaning. If you decide on a layout based solely on energy production, operation and maintenance after commissioning can become difficult. It is important to use PVSyst results in combination with assessments of constructability and maintainability.

In comparing installed capacity, it is important to look not only at generation but also at the breakdown of losses and the performance ratio. If the performance ratio drops even though capacity has increased, there may be stress somewhere—shading, wiring, equipment capacity, or site layout conditions. PVSyst can provide the data needed to confirm such changes. Beginners should avoid the simplistic view that simply increasing capacity is enough, and instead focus on balancing capacity, layout, losses, and operability.

Case 4 Comparing shadows and terrain conditions

In comparisons in PVSyst, shadows and terrain conditions are extremely important. In photovoltaic power generation, surrounding buildings, trees, terrain undulations, slopes, adjacent equipment, and shading between panel rows all affect the energy yield. Because shadows change with the time of day and season, it can be difficult to judge the magnitude of their impact by appearance alone. Using PVSyst, you can compare cases that reflect shadow conditions with those that do not, cases with different layouts, and cases with different obstacle conditions.

The first thing often done in shadow comparisons is to compare an idealized, shadow-free case with a case that reflects the site's actual shadows. This comparison lets you understand how much local obstacles and terrain affect power generation. Even if the shadow-free case shows high output, a large drop in the case reflecting site shadows may mean you need to reconsider the layout or the installation area.

When comparing terrain conditions, you check how land slope and elevation differences affect panel layout and shading. On flat land, panels can be arranged relatively simply, but on sloped or undulating land the relative heights of panel rows and the way shadows fall become more complex. Even slight elevation differences that are not obvious visually can have a large impact from shading during periods of low solar altitude. To perform comparisons in PVSyst that take terrain and shading into account, it is essential to accurately determine the on-site positional relationships and height information.

When comparing shading and terrain, it is important to look not only at annual energy production but also at monthly generation and shading losses. Shadows can be concentrated in specific seasons or times of day. Even if they appear small in the annual total, they can have a large impact on winter generation. For a power generation project's revenue forecasts and operational plans, these seasonal biases also need to be checked.

Shading and terrain conditions are often difficult to change later. You cannot move surrounding buildings or terrain, and there may be restrictions on tree management. Therefore, it is important to use PVSyst during the planning stage to compare the impacts of shading and terrain. Based on the comparison results, you can consider realistic countermeasures such as changing to a layout with less shading, adjusting the installation area, reassessing row spacing, or limiting system capacity to improve efficiency.

Case 5 Comparing equipment capacity and output limits

In PVSyst, it is also important to compare combinations of panel capacity and power conversion equipment capacity. In a photovoltaic power system, the DC power generated by the panels is converted into usable electrical power. At this stage, the balance between panel capacity and power conversion equipment capacity affects the amount of energy produced and how output limits or clipping occur. By using PVSyst, you can compare cases with different capacity balances to check how much loss or difference in energy production will result.

When panel capacity is set large, it can make it easier to use power conversion equipment efficiently even during periods of weak solar irradiance. Conversely, during periods of strong solar irradiance, output can be limited by the upper limit of the power conversion equipment. The extent to which this output limitation occurs varies with system capacity, installation conditions, solar irradiance, temperature, azimuth, tilt, and so on. PVSyst allows you to check the losses from such output limitations.

When comparing equipment capacities, it is important not just to check whether output limiting occurs, but to assess its impact on annual energy production. Even if some output limiting occurs, its effect on total annual generation may be small. Conversely, if output limiting is large and a lot of potential energy is lost during periods when generation would otherwise be possible, the capacity balance needs to be reviewed. By examining the loss breakdown in PVSyst, you can determine to what extent limiting is affecting energy production.

Also, comparing equipment capacities is important not only for power generation but also for assessing the rationality of the overall system configuration. Increasing the capacity of the power conversion equipment tends to reduce output limitations, but it is necessary to consider the balance with the overall system layout, installation space, wiring, and operations management. Conversely, if capacity is made too small, losses due to output limitations increase and may affect the outlook for power generation. PVSyst is useful for numerically comparing this balance.

When beginners compare equipment capacities, it’s good to look at annual energy production, losses due to power limiting, and performance ratio together. By checking how much energy production changes when you alter the capacity balance and which items the losses show up in, it becomes easier to understand the meaning of the equipment configuration. PVSyst is a tool for evaluating equipment configurations by observing their impact on energy production, rather than deciding them by intuition.

Case 6: Compare wiring losses and electrical conditions

In PVSyst, comparing wiring losses and electrical conditions is also important. In photovoltaic systems, the power generated by the panels does not directly become the final output. The generated power incurs losses as it is transmitted through wiring and conversion equipment to the receiving equipment. Electrical losses change depending on wiring distance, conductor capacity, voltage conditions, equipment layout, and so on.

When comparing wiring losses, you check how much the energy yield differs when equipment layout or wiring routes are changed. In installations with large sites or complex layouts, wiring distances tend to become longer and losses may increase. To improve the accuracy of energy yield projections, wiring planning is also an important design element. Comparing wiring conditions in PVSyst makes it easier to understand the overall impact that wiring losses have.

When comparing electrical conditions, we also check the circuit configuration and the combinations with equipment. Changes in how panels are connected or how circuits are separated can alter voltage and current conditions, which can affect generation efficiency and losses. Even if a design appears valid on paper, it can perform poorly under actual operating conditions. Using PVSyst allows you to check how these electrical conditions are reflected in the energy production.

When comparing wiring and electrical conditions, be aware that even if the impact on power generation seems small at first glance, it can become non-negligible over long-term operation. Small losses accumulate over long periods in power generation projects. Wiring plans also affect constructability and maintainability. If wiring is made complex solely to reduce losses, installation and inspection can become difficult. PVSyst comparison results should be used to judge electrical efficiency together with on-site feasibility.

Beginners tend to treat wiring losses as a minor, specialist topic to be left for later, but in practice it is an important item to verify. In particular, when the installation is large, the site is long and narrow, or equipment placement is constrained, wiring conditions are more likely to affect energy production. Comparing wiring losses in PVSyst allows you to make a more concrete assessment of the validity of the layout plan and equipment placement.

Case 7 Compare loss conditions and examine the sensitivity of power generation

PVSyst allows you to compare various loss conditions to determine which factors the energy production is most sensitive to. In photovoltaic systems, various losses occur, such as temperature losses, shading losses, soiling, wiring losses, equipment conversion losses, mismatch losses, and output limitations. By changing these conditions, you can see how much the annual energy production and the performance ratio change.

Comparing loss conditions helps identify weaknesses in a design. For example, if energy production changes significantly when soiling losses are varied, it indicates that cleaning and maintenance planning is important. If results change greatly when shading loss conditions are altered, on-site obstructions and layout planning should be checked more carefully. If wiring losses have a large impact, it is worth reconsidering equipment placement and wiring routes.

When comparing loss conditions, it is important to set the conditions within a realistic range. If losses are set artificially low to make power generation appear higher, or if overly stringent conditions are applied so that power generation is underestimated, the results will be difficult to use for practical decision-making. The purpose of the comparison is not to produce convenient numbers but to understand which losses are most likely to affect power generation.

Comparing loss conditions is also useful for explaining risks. In power generation projects, future uncertainties need to be taken into account during the planning stage. If soiling is greater than expected, shading increases, or wiring conditions change, checking in advance how much these factors would affect energy production makes it easier to explain to stakeholders. PVSyst can be used as a tool for such sensitivity checks.

For beginners comparing loss conditions, it's easiest to change only one loss parameter at a time and observe the results. If multiple loss conditions are changed simultaneously, it becomes difficult to determine which factor affected the power generation. Start by creating a baseline case, then check soiling, shading, wiring, temperature, and output limits individually to better understand what the losses mean.

Practical considerations when interpreting PVSyst comparison results

After comparing multiple cases in PVSyst, how you interpret the results is important. When reviewing the comparison, simply choosing the case with the highest annual energy production may be insufficient for practical decision-making. You need to check how large the difference in energy production is, which conditions caused that difference, whether there are issues with constructability or maintainability, and whether the way losses appear is reasonable.

The first thing to check is whether the differences in the compared conditions are clearly defined. You need to organize which of orientation, tilt, layout, capacity, shading conditions, wiring conditions, or loss conditions were changed in the comparison; otherwise, the meaning of the results becomes ambiguous. If multiple conditions are changed at the same time, it becomes difficult to determine what is causing the difference in power output. In practice, whether or not you create a comparison table, it is important to document the assumptions for each case.

Next, confirm whether the difference in annual energy production is practically significant. If the difference is slight, it may be better to prioritize constructability and maintainability. Conversely, if the difference in energy production is large, you should investigate the causes in detail and consider improvement measures and whether to adopt the option. Because PVSyst outputs numerical values, it’s easy to focus on small differences, but in practice you must also take into account measurement errors, meteorological variability, and uncertainties in site conditions.

Examining the breakdown of losses is also indispensable. Even in cases with high annual generation, you need to be cautious if a particular loss is large. For example, even if annual generation increases because installed capacity was raised, if shading losses or output curtailment have increased significantly, there may be issues with the system’s efficiency. It is also important to check monthly generation to confirm that there are no large drops in specific seasons.

The comparison results from PVSyst are also used as explanatory materials for stakeholders. Therefore, you need to be able to explain not only the results but also why those cases were compared, which conditions were changed, and which outcomes were prioritized. If the purpose of the comparison remains ambiguous, stakeholders may interpret it differently, making consensus-building difficult.

The most important thing when interpreting comparison results is to evaluate PVSyst’s outputs together with on-site feasibility. Even a design with a high energy yield is meaningless if it cannot be constructed on site. If a layout is difficult to maintain or is based on assumptions that do not align with local site conditions, problems may arise after operations begin. PVSyst is a tool that supports design decisions, and final judgments require a comprehensive perspective that includes site surveys, construction planning, and maintenance planning.

Improve comparison accuracy by combining PVSyst with on-site information

PVSyst is software that supports design decisions by not only predicting the energy yield of photovoltaic (PV) systems but also comparing factors such as site location, azimuth, tilt, layout, shading, terrain, equipment capacity, wiring, and loss conditions. For beginners to understand PVSyst, it is important to clarify "what to compare." By creating a baseline case and changing the condition you want to compare one at a time while checking annual energy yield, monthly energy yield, performance ratio, and loss breakdown, you can grasp how design conditions affect the results.

PVSyst lets you compare a wide range of items. When comparing candidate sites and meteorological conditions, you can verify the power generation potential for each region. When comparing azimuth and tilt, you can see how the installation angle affects power output and seasonal variability. When comparing layout and installed capacity, you can consider the balance between increased capacity, shading losses, and maintainability. When comparing shading and topography, you can understand the risks that site conditions pose to power generation. When comparing equipment capacities and wiring conditions, you can check electrical losses and output limitations. When comparing loss conditions, you can identify which factors power generation is most sensitive to.

However, PVSyst comparison results are heavily dependent on the quality of the input conditions. If site orientation, tilt, elevation differences, obstacles, installation area, wiring routes, and so on are inaccurate, the comparison results will also diverge from reality. In particular, for comparisons involving shading and terrain, the accuracy of on-site information has a major impact on the reliability of the results. It is essential not only to create multiple cases in the software but also to accurately acquire the underlying on-site information and reflect it in the design conditions.

In power generation projects and equipment design, it is important to connect desk simulations with on-site realities. By comparing multiple cases in PVSyst and revising the conditions based on information obtained on site, it becomes possible to produce power generation forecasts that are closer to reality. When explaining the comparison results to stakeholders, having assumptions based on on-site information also makes it easier to demonstrate the basis for the estimated generation and losses.

If you want to streamline on-site position verification, positioning, understanding of the installation area, and recording of obstacle locations, using an iPhone-mounted GNSS high-precision positioning device like LRTK is effective. If you can reflect the high-precision location information obtained on-site in design reviews, it becomes easier to set more accurate baseline conditions for the cases compared in PVSyst. By combining PVSyst power generation simulations with high-precision positioning data obtained in the field, you can increase the reliability of comparative studies and further enhance design decisions and explanatory power in power generation projects.