What is PVSyst? Basic knowledge to prevent misinterpretation of results

PVSyst is a specialized simulation software used to predict the energy production of photovoltaic power systems and to organize design conditions and loss factors. In power generation projects and equipment design practice, many figures are checked, such as annual energy production, monthly energy production, loss diagrams, performance ratio, shading effects, temperature losses, and wiring losses. However, simply reading the numbers displayed on the results screen may not allow a correct assessment of the design’s validity.

Misreading PVSyst results can lead to overestimating energy production, misidentifying the causes of losses, and leaving assumptions unclear when explaining to stakeholders. Beginners in particular are prone to misunderstandings such as feeling reassured by looking only at annual energy yield, evaluating the performance ratio in isolation, or assuming that smaller losses are necessarily more correct. In this article, aimed at practitioners who search for "What is PVSyst", we explain the basic knowledge you should grasp to prevent misinterpreting the results.

Table of Contents

• PVSyst is analysis software that requires the ability to interpret the results

• Reasons why misinterpretation of results is likely to occur

• Basics for avoiding decisions based only on annual energy production

• Approach to interpreting seasonal variations from monthly energy production

• Essential sequence to follow when reading the loss diagram

• How to interpret the performance ratio to avoid misinterpretation

• Checkpoints to avoid overlooking shading and temperature losses

• Importance of cross-checking input conditions with results

• Methods to prevent misinterpretation by comparing multiple cases

• Organizing PVSyst results for practical explanation

• Enhancing reliability by combining PVSyst with on-site information

PVSyst is analysis software that requires the ability to interpret results

PVSyst is software for predicting the power output of solar power generation systems and for checking the effects of design conditions and losses. You input site solar irradiation, temperature, panel orientation, tilt, system capacity, equipment configuration, shading, wiring, soiling, and so on, and it provides annual energy production, monthly energy production, a loss breakdown, performance ratio, and other results. In solar power system design, these figures serve as the basis for business planning and design decisions.

However, PVSyst does not automatically interpret results correctly. While it displays calculation results, users must interpret whether the figures are reasonable, which conditions produced them, and how they should be used for practical decision-making. Even if the results screen shows annual energy production, it is insufficient as a basis for judgment unless you verify that the value is realistic, that shading and losses are correctly reflected, and that the meteorological conditions match the site.

Being able to read PVSyst results is not simply knowing what the numbers mean. It is the ability to understand which assumptions the generation figures are derived from, at which stages losses occur, and whether the system as a whole is generating efficiently. For example, annual energy yield may be high because the loss assumptions are overly optimistic. A performance ratio that looks good may not fully reflect shading or soiling. Conversely, an energy yield that looks low may be a conservative forecast that correctly reflects site conditions.

In practice, PVSyst results are often used as explanatory materials for stakeholders. Therefore, the person reading the results must be able to explain the relationship between the input conditions and the output results. Clarifying which meteorological conditions were used, whether the azimuth and tilt match the site, how shading was taken into account, and what level of losses was assumed will increase the reliability of the generation forecast.

To use PVSyst correctly, basic knowledge to avoid misinterpreting results is as important as learning how to operate it. Especially for beginners, rather than memorizing each number shown on the results screen, it is important to understand the process by which energy production is determined and to check the results along that process.

Why Results Are Easily Misinterpreted

The reason PVSyst results are easy to misinterpret is that the screen displays many numbers, each of which has a different meaning. Annual energy production, monthly energy production, irradiance, loss rates, performance ratio, power clipping, shading losses, temperature losses, and so on all relate to energy production, but they are not the same type of values. Confusing them can lead to a mistaken understanding of what the results mean.

The most common misreading is judging the quality of a design based solely on the annual energy production. Annual energy production is an important figure, but it is only the total for the year. You cannot tell from annual production alone which seasons have higher output, which losses are large, or whether the system is efficient relative to its installed capacity. Even if annual energy production is high, it may simply be due to a large installed capacity, resulting in low efficiency per unit of capacity.

Another common mistake is judging simply by the loss figures alone. If losses are small, the estimated power generation will look high, but that means nothing if those loss settings are not realistic. If a site with shading shows almost no shading losses, it may not be that the design is excellent but that the shading-condition inputs are insufficient. Likewise, if wiring distances are long but wiring losses are unrealistically small, the input conditions need to be reviewed.

Misinterpretation of the performance ratio is also common. The performance ratio is an important indicator for assessing the overall efficiency of a system, but it should not be judged simply as good if high or bad if low. The performance ratio is affected by solar irradiation conditions, shading, temperature, wiring, equipment configuration, and loss settings. Even when the performance ratio is high, if the loss assumptions are overly optimistic, it may appear better than the actual situation.

Moreover, viewing the input conditions and the results separately is another cause of misinterpretation. PVSyst’s results are predictions based on the input conditions. If the installation site, meteorological conditions, azimuth, tilt, shading, losses, or system capacity change, the results will change as well. Instead of judging based only on the results screen, you must always return to the input conditions and verify that the assumptions match the site and the design intent.

Basics for Not Judging by Annual Power Generation Alone

The first thing that tends to catch the eye in PVSyst results is the annual energy production. In power generation projects, annual energy production is undeniably an important metric because it relates to revenue and project feasibility. However, if you judge based only on annual energy production, you may overlook issues with design conditions or the causes of losses.

Annual energy generation is the total value indicating how much electrical energy is expected to be obtained over one year. Because it is a total value, seasonal changes and time-of-day characteristics become difficult to see. For example, even if generation drops significantly in winter due to shading, if summer generation is high the annual total may not look like a major problem. Conversely, an annual generation that appears somewhat low may still have stable month-by-month variations, resulting in a design that is easier to handle in practice.

When evaluating annual generation, it's important to examine its relationship with installed capacity. It's natural that a larger installation will have greater annual generation. However, that alone doesn't tell you whether the installation is efficient. By looking at generation per unit of capacity and the performance ratio together, you can assess how efficiently the installation is generating power relative to its installed capacity.

Also, the higher the displayed annual energy output, the more important it is to check the input conditions. If shading is not considered, soiling losses are set too low, wiring losses are lower than in reality, or the meteorological conditions do not match the site, the estimated output will appear higher. Rather than being reassured by high figures, you must verify the assumptions under which those figures were produced.

Annual energy yield is the entry point for reading PVSyst results. It is not the final judgment; from there, you should expand your checks to monthly energy yields, the loss diagram, the performance ratio, and the input conditions. Simply being aware not to judge based solely on the annual energy yield can greatly reduce misinterpretation of the results.

How to Read Seasonal Variations from Monthly Power Generation

Monthly energy production is a very important indicator for correctly interpreting PVSyst results. While annual energy production shows the total for the year, monthly energy production indicates seasonal generation trends. In solar power generation, solar irradiance, temperature, shading, snowfall, soiling, solar altitude, and other factors change with the seasons, so if you do not look at the monthly results it becomes difficult to grasp the characteristics of the design conditions.

When examining monthly power generation, first check whether the seasonal increases and decreases appear natural. Generally, during periods of high solar irradiance, power generation tends to increase, and during periods of low solar irradiance, power generation tends to decrease. However, in seasons with high temperatures, thermal losses grow larger, and even with abundant solar irradiance power generation may not increase as much as expected. In winter, the sun’s altitude is lower, and the effects of surrounding obstacles and inter-row shading can become significant.

If power generation drops significantly in specific months, you need to check the cause. Determine whether it is due to weather conditions, shading, tilt or orientation, or loss settings. In PVSyst you can check not only monthly generation but also the breakdown of losses, so you can identify which factors are causing the drop in generation.

Monthly power generation is also useful for comparing design proposals. Even if two proposals have nearly the same annual power generation, their monthly generation patterns can differ. One proposal may perform strongly in summer, while another may be relatively stable in winter. Which is preferable depends on the project's objectives and on the way electricity will be used. Rather than judging designs to be the same because their annual generation is the same, it is important to examine and compare the monthly trends.

Monthly generation is also a convenient metric for comparing actual performance after operations begin. When comparing actual generation with PVSyst predictions, looking only at the annual total can sometimes make it difficult to identify the cause. By comparing month by month, it becomes easier to determine whether differences occur during specific periods or persist throughout the year. To make long-term use of PVSyst results, it is important to understand how to interpret monthly generation.

The flow to keep in mind when reading a loss diagram

The PVSyst loss diagram is something you should always check to avoid misreading the results. The loss diagram shows how much the energy from the sun is reduced at each stage — from reaching the panel surface, being converted into electricity, to being output as the final energy yield. It may look complicated to beginners, but following the flow of energy from top to bottom makes it easier to understand.

The first thing to look at is the stage where solar irradiance is translated into irradiance on the panel surface. The site's solar radiation conditions, together with the panel's orientation and tilt, shading, and reflections, determine the actual amount of solar irradiance that reaches the panel surface. If losses at this stage are large, it is necessary to check the orientation, tilt, shading, terrain, and reflection conditions.

Next, we look at the stage where panels convert solar radiation into electricity. Here, effects such as temperature losses, panel characteristics, and mismatch losses come into play. In particular, temperature losses vary depending on ambient temperature, mounting method, and ventilation conditions. Even in regions with high solar radiation, temperature losses can be significant under conditions where ambient temperatures are high and panel temperatures tend to rise.

After that, we check the electrical losses. Wiring losses, equipment conversion losses, and output limitations are related to the system configuration and wiring plan. If wiring distances are long, equipment capacities are poorly balanced, or output limitations are significant, the final power output will be affected. The loss diagram allows you to see to what extent these losses are occurring.

One thing to be careful about when reading a loss diagram is that smaller losses are not necessarily correct. If there is shading on site but the shading loss is small, the shading conditions may not have been reflected. If the wiring is long but the wiring loss is small, the input conditions may not match reality. A loss diagram is not a document to make losses look small, but a document to explain a reasonable power generation estimate given the on-site conditions.

To read a loss diagram correctly, it is essential to compare the results with the input conditions. If there is a large loss, look for potential improvements; if a loss is too small, suspect missing inputs. By adopting this perspective, you will be able to interpret PVSyst's results in a more practical way.

How to interpret performance ratios without misunderstanding

The performance ratio is an important indicator often checked in PVSyst results. The performance ratio is a metric that shows how effectively the system converts the received solar irradiation into electrical power. While annual energy production is affected by system capacity and irradiation conditions, the performance ratio helps understand the overall efficiency of the system.

However, the performance ratio should not be judged simply as “higher is always better” or “lower is always worse.” The performance ratio is affected by loss conditions such as shading, temperature, wiring, equipment configuration, soiling, and output limits. Even if the performance ratio is displayed as high, if shading, soiling, or wiring losses are not adequately reflected, it may appear better than it actually is.

Even when the performance ratio is low, you should not immediately conclude that the design is poor. There may be losses that are difficult to avoid because of local site conditions. Conditions such as many obstacles nearby, terrain constraints, being prone to high temperatures, or longer wiring routes can cause the performance ratio to drop. What is important is to check the reasons for the low performance ratio from loss diagrams and input conditions.

When looking at the performance ratio, it's easier to understand if you check not only the annual value but also the month-by-month changes. If the performance ratio drops in summer, the effect of temperature losses should be considered. If it drops in winter, you need to check for impacts such as shading, solar altitude, and snowfall. By examining the monthly performance ratio, you can identify which times of the year the system is more likely to experience efficiency declines.

The performance ratio can also be used to compare design proposals. However, it is important to ensure consistent comparison conditions. Simply comparing cases with different installation locations or different weather conditions can lead to misunderstandings. Within the same project, checking how the performance ratio changes when orientation, tilt, layout, capacity, and loss conditions are varied makes it easier to interpret the influence of the design conditions.

The performance ratio is a useful metric for interpreting PVSyst results, but it should not be used alone to draw conclusions. By examining it together with annual energy production, monthly energy production, the loss diagram, and the input conditions, you can correctly understand what the performance ratio means.

Points to check to avoid overlooking shading and temperature losses

To avoid misreading PVSyst results, checking shading and temperature losses is indispensable. These factors can greatly affect energy production, yet they are easy to overlook if the results are misinterpreted. In particular, if you only look at annual energy production, the seasonal effects of shading and temperature can be difficult to discern.

Shading effects are caused by surrounding buildings, trees, slopes, terrain, equipment and structural elements, and the relationships between rows of panels. Because shading changes with the seasons and time of day, a single site visit is not sufficient to determine its annual impact. In PVSyst results, check how much shading loss is occurring and whether there are any unnatural drops in monthly energy production.

Even when shading losses are small, you should check the input conditions before becoming complacent. If there are obstacles on site but the shading loss is small, the obstacle positions or heights may not be correctly reflected. Conversely, if shading losses are large, consider whether they can be improved by changing the layout or reviewing the installation area. Shading loss is not a number to invalidate a design, but information to look for potential improvements.

Temperature loss is the phenomenon in which output decreases due to an increase in panel temperature. In solar power generation, while higher solar irradiance tends to increase power generation, high ambient temperatures that raise panel temperature can reduce efficiency. If, during summer, power output or the performance ratio does not increase as much as expected despite high irradiance, temperature loss may be having an effect.

When assessing temperature losses, consider not only the local ambient temperature but also the mounting method and ventilation conditions. The way the panel temperature rises can vary depending on ground mounting, roof mounting, the distance from the roof, and the surrounding airflow. If PVSyst indicates large temperature losses, it is necessary to verify whether they are reasonable by comparing them with the on-site installation conditions.

Shading and temperature losses are both factors that greatly influence energy production. Rather than just checking the numbers on the results screen, reading them while cross-checking with on-site conditions makes it easier to avoid misinterpretation.

The Importance of Verifying Input Conditions Against Results

To read PVSyst results correctly, you must always cross-check the input conditions with the results. PVSyst outputs are predicted values calculated based on the conditions you entered. Therefore, looking at the reported energy production or loss figures alone does not allow you to judge their validity. Only after confirming the conditions under which the results were calculated can they be used as information for practical work.

The first things to check are the installation site and the meteorological conditions. Verify that the candidate site and the location of the meteorological data match, and that assumptions about solar irradiance and temperature do not deviate significantly from the site’s characteristics. If estimated power generation is unusually high or low, the choice of meteorological conditions may be affecting it. This is especially true in mountainous areas, along coasts, or in regions with snow, where meteorological conditions can differ even between nearby locations.

Next, check the azimuth and tilt. The direction and angle at which the panels are installed directly affect the amount of solar radiation reaching the panel surface. If there is a discrepancy between the azimuth and tilt shown on the design drawings and the actual on-site conditions, it will also affect the power generation forecast. If the results differ from what you expected, it is important to review whether the azimuth and tilt inputs are correct.

Shadow conditions are also important when validating input results. If there are buildings, trees, slopes, or equipment structures on site but shadow losses are almost nonexistent, the shadow conditions may not have been reflected. Conversely, if shadow losses are excessively large, check whether the positions or heights of obstacles have been overestimated. Because shadows greatly affect power generation, the basis for the input conditions should be clearly documented.

Checking the loss assumptions is also essential. Confirm that conditions such as soiling, wiring, temperature, equipment conversion, and output limits match the site and the design. If losses are set too low, the energy yield will appear higher; if losses are set too high, the yield will appear lower. To make the results reliable, it is important to be able to explain the rationale behind each loss assumption.

When reading PVSyst results, it is standard practice to go back and forth between the results screen and the input screen. If something about the results feels off, return to the input conditions, correct them, and then recheck the results. By repeating this back-and-forth, you can prevent misinterpretation and increase the reliability of the power generation forecast.

How to Prevent Misinterpretation When Comparing Multiple Cases

In PVSyst, comparing multiple design cases makes it easier to avoid misinterpreting the results. Looking at only a single case can make it difficult to judge whether the energy production is reasonable or which conditions are affecting the results. By creating a baseline case and then creating cases that change only the conditions you want to compare, the relationship between input conditions and results becomes clear.

When comparing multiple cases, first decide on a baseline case. The baseline case is the set of design conditions considered most realistic at that time. From there, change one condition at a time—change the orientation, change the tilt, change the system capacity, introduce shading, or change the loss conditions—and compare. If you change many conditions at once, it becomes difficult to determine what is causing the differences in power generation.

For example, if you want to check the impact of shading, compare a case that does not consider shading with a case that reflects the on-site shading. This comparison allows you to understand to what extent shading affects annual and monthly energy production. If you want to see the effect of orientation, fix the tilt and capacity and change only the orientation. If you want to see the effect of tilt, fix the orientation and capacity and change only the tilt.

When reviewing comparison results, check not only the annual energy generation but also monthly generation, loss diagrams, and the performance ratio. Even if generation increases in a given case, shading losses or output curtailment may have grown substantially. In cases where installed capacity has been increased, total generation may rise while generation per unit capacity and the performance ratio fall. In comparisons, it is important to interpret not only changes in generation but also changes in efficiency and losses.

When dealing with multiple cases, managing case names and conditions is also important. If you lose track of which case corresponds to which condition, you cannot compare the results. You need to make the changes for each case clear and organize them so they remain understandable later. To make the most of PVSyst's comparison feature, it is essential not only to produce numbers but also to manage the assumptions behind the comparisons.

Comparing multiple cases not only prevents misinterpretation but also helps when explaining to stakeholders. Because it allows you to show numerically why a particular design was adopted and how it differs from alternative conditions, it makes sharing the rationale behind design decisions easier.

Organizing PVSyst Results for Practical Explanation

PVSyst results are used in practice not only for personal verification but also as materials for explaining to stakeholders. Therefore, it is important not just to read the results but to organize them in a form that can be explained. You need to communicate not only the energy generation figures, but also the conditions under which they were calculated, which losses were anticipated, and what kinds of decisions they lead to.

The first thing to clarify in the explanation is the input conditions. Make clear what the installation location, meteorological conditions, system capacity, orientation, tilt, shading conditions, and loss assumptions are. The power generation results only become meaningful with these assumptions. If you present only the annual generation without explaining the input conditions, the figures can easily be taken out of context.

Next, we will describe the annual and monthly energy production. The annual energy production presents an overall outlook, while the monthly energy production supplements this with seasonal trends. If production is low in a particular month, explain it by considering solar irradiance conditions, shading, temperature, and other loss factors together. By presenting monthly trends, you can share design features that are not apparent from the annual total alone.

Loss diagrams and loss breakdowns are effective for explaining the reasons behind power generation levels. In the flow from solar irradiance to the final generated output, clarify which losses are large, which losses are due to site conditions, and which losses have room for improvement. If shading losses are large, explain the causes of the shading and possible countermeasures. If wiring losses or output restrictions are large, explain their relationship with the equipment configuration and wiring plan.

When explaining the performance ratio, it is important to present it not as a standalone number but together with energy generation and losses. Even if the performance ratio is high, you need to show that the input conditions are realistic. If the performance ratio is low, explain which losses are affecting it. The performance ratio is a convenient indicator for conveying system efficiency, but it must be considered together with the underlying assumptions.

When explaining in a professional context, in addition to the PVSyst report it is important to record site conditions. If you document and organize items such as obstacles that cause shading, the installation area, azimuth, tilt, and elevation differences, it becomes easier to explain the rationale behind the simulation results. PVSyst results only become persuasive materials when they are tied to on-site information.

Enhancing reliability by combining PVSyst with on-site information

PVSyst is simulation software for evaluating the energy production, losses, and performance ratio of photovoltaic power systems. However, to avoid misreading the results, you should not look only at the annual energy production; you need to comprehensively check monthly production, loss diagrams, performance ratio, shading and temperature losses, and the input conditions. The results from PVSyst are predictions based on the assumptions entered, and if those assumptions do not match the site, the outputs will also diverge from reality.

The basic way to avoid misreading results is to understand the process that determines energy generation. The installation site and weather conditions set the assumptions for solar irradiance and temperature, orientation and tilt affect the irradiance reaching the panel surface, and shading, soiling, temperature, wiring, and system configuration are reflected as losses. As a result, annual generation, monthly generation, and the performance ratio are displayed. If you grasp this flow, you can read the numbers on the results screen not in isolation but by tracing back their causes and assumptions.

Particular attention should be paid to verifying the input conditions against on-site information. If buildings or trees causing shading, terrain elevation differences, the installation area, orientation, tilt, or wiring routes are inaccurate, PVSyst results will be difficult to trust. Misreading results can arise not only from how the screens are interpreted but also from insufficient on-site verification before data entry. To obtain correct results, it is essential to gather accurate on-site information and reflect it in the input conditions.

Also, PVSyst results are used to explain matters to stakeholders. Rather than simply presenting the generation figures, it is important to be able to explain under which conditions the calculations were performed, which losses are large, and where there is room for improvement. By combining input conditions based on on-site information with PVSyst results, the reliability and explanatory power of the generation forecast are increased.

If you want to streamline verification of on-site installation boundaries, recording obstacle locations, and understanding orientation and elevation differences, using LRTK (iPhone-mounted GNSS high-precision positioning device) is effective. Incorporating the high-precision location data collected on site into PVSyst's assumption setup makes it easier to make the input conditions for shading, terrain, and installation boundaries more realistic. By correctly interpreting PVSyst simulation results and linking them with the on-site information obtained via LRTK, you can avoid misreading power generation forecasts and further improve the accuracy and explanatory power of solar PV system design.