6 Basic Items to Understand How to Read PVSyst｜For Practical Work

In solar power system design and power generation forecasting, the accuracy of your judgments depends greatly on how you read the simulation results. Preparing the input conditions is, of course, important, but if you cannot correctly interpret the results, the quality of the design, the potential for improvement, and how you explain things to stakeholders all become unclear. In particular, many practitioners searching for "how to read PVSyst" are likely to be confused about where to start, since there are so many items on the screen and in the reports.

In the actual field, it is not enough to stop at looking only at the annual energy production. You need to follow in sequence and understand how incident solar irradiance reaches the receiving surface, at what stages losses occur, and how these ultimately translate into output. Furthermore, only after checking monthly variations, the effects of temperature, the impacts of shading and orientation, and the relationship between the DC side and the AC side will the results be in a state usable for practical decision-making.

PVSyst is not merely a tool for lining up numbers. It is a tool for assuming design and site conditions and, on that basis, organizing how to estimate power generation performance. Therefore, once you grasp the basics of how to read it, you can do more than just check outputs: you can identify which items should be improved, which constraints originate from the site, and which figures should be used as explanatory material.

This article organizes how to read PVSyst into six basic items for practitioners. It explains the material in a way that is easy to understand for those reading results for the first time, while making the approach directly usable in everyday practice. Rather than tracing the screen’s field names, it is structured from the viewpoint of the order in which to look at things to make judgments easier. For those who will be performing project comparisons, design checks, or customer explanations, this should provide a clear, reliable foundation for interpreting results.

Table of Contents

• Why It's Easy to Get Confused When Interpreting PVSyst

• 基本1｜First, Look at Annual Energy Production and Specific Yield

• 基本2｜Look at Solar Irradiation and Incident Light Trends

• 基本3｜Correctly Understand the Role of the PR (Performance Ratio)

• 基本4｜Infer Design Issues from the Loss Breakdown

• 基本5｜Check Seasonal Variations Using the Monthly Results

• 基本6｜Check the Difference Between the DC Side and the AC Side

• Checkpoints Easily Overlooked in Practice

• Apply the Interpretation of Results to Comparative Analysis and Explanations

• The Accuracy of Site Condition Assessment Affects the Quality of Interpretation

• Summary

Reasons Why It's Easy to Get Confused When Interpreting PVSyst

The reason it's easy to get confused when viewing PVSyst results is that a large amount of information is displayed and each item appears separate. Annual generation, PR, losses, monthly values, irradiance, DC output, AC output, and so on all look important, so it's easy to be unsure which to prioritize. In practice, with limited time, it's not uncommon to end up picking only the numbers that happen to stand out.

However, in reality each of these items is connected. There are solar irradiance conditions, incident irradiance conditions, losses, and these determine the amount of energy generated. Furthermore, there are DC-side conditions and AC-side conditions that determine the final output. In other words, what’s important when interpreting the results is not to look at each item in isolation, but to read them as a flow. Just understanding this makes PVSyst’s results much easier to comprehend.

Another reason for the confusion is that numerical values need to be interpreted differently depending on the context. In internal preliminary reviews, annual energy production and loss trends are important; in detailed design, the effects of shading and temperature become significant; and when explaining to customers, monthly trends and explanations of losses may be required. Even with the same results, what you emphasize changes depending on the purpose.

Therefore, first, regardless of who you're showing it to or what you're deciding, it's important to have a basic, commonly shared way of looking at things. The six items covered in this article are easy to use as that foundation. With this as your base, you'll be less likely to waver about where to begin when examining the results, even if the scale or conditions of a project change.

Basic 1｜First, look at annual power generation and specific yield

The first thing that is easy to check is the annual power generation. This figure is indispensable for understanding the overall generation scale of the project, and because it is easy for stakeholders to grasp, it serves as the starting point in practice. How much electricity can be expected annually is highly significant for assessing the project's commercial viability and for planning.

However, judging based solely on annual power generation can be crude. For projects with different installed capacities, simply comparing annual generation is of limited meaning. Therefore, in practice, concepts such as specific yield (generation per unit of installed capacity) are also important. By checking how much generation can be expected per unit of installed capacity, it becomes easier to view a project's performance relatively. Because this evens out differences in scale, it is particularly useful for comparative evaluations.

What's important here is to use annual energy production and specific yield not as the final conclusion but as an entry point to grasp the overall picture. Even if annual energy production is high, the loss structure may be unreasonable, and even if specific yield is good, site conditions may be severe and reproducibility may be in doubt. Therefore, at this stage it is important to first get a sense of the scale and performance, and then go on to examine the details.

Annual generation is a number that’s easy to explain, but it can also be misleading. For example, even if two proposals have similar annual generation, one may simply benefit from better solar irradiation conditions while the other may be catching up through measures to reduce losses. It’s dangerous to assume they are similar projects just because the final numbers are close. First grasp the overall picture with annual generation and specific yield, then be prepared to dig deeper.

From a practical standpoint, looking at annual power generation is still only part of the evaluation. What we want to confirm here is whether this project is not significantly off and roughly where it stands relative to the comparison targets. The true meaning of the results becomes concrete only after reviewing the subsequent items.

Basic 2｜Understanding the Flow of Solar Radiation and Light Reception Conditions

After checking the annual power generation, the next thing to examine is how solar irradiance is reflected in the receiving conditions. Solar power generation, of course, cannot produce electricity without sunlight. However, it is not simply a matter of having a large amount of irradiance on a horizontal plane—the outcome changes depending on the angle, the direction, and the manner in which the sunlight is received. Therefore, solar irradiance and the receiving conditions must be considered together rather than separately.

In practical work, it is important to understand, in sequence, how much solar irradiance is available as an input, how it is received on tilted surfaces, and how that then leads to effective light capture. If there is ample solar irradiance but results do not improve, the light-receiving conditions may be poor. Conversely, even if the solar irradiance itself is only average, proper layout and tilt settings can deliver stable power generation performance.

When reviewing this item, you should pay attention not only to the amount of solar radiation but also to how the installation conditions affect the way sunlight is received. It is important to check whether the orientation and tilt settings are appropriate, whether the conditions of the receiving surface are reasonable, and whether the input conditions actually match the site. If these are off, all subsequent evaluations of power generation and losses will be skewed.

Also, checking the incident irradiance conditions is necessary preparation for assessing downstream losses. If you do not know how well the upstream section is receiving solar irradiance, you cannot correctly evaluate the magnitude of downstream temperature losses or electrical losses. For example, in a project that originally receives little irradiance, focusing only on downstream losses is unlikely to lead to fundamental improvement. Organizing the upstream incident irradiance conditions first is therefore very important when interpreting PVSyst.

By adopting this way of looking at things, you will gain a more natural, intuitive understanding of how site conditions affect the results. Rather than viewing the results as a mere list of numbers, you will be able to read them while visualizing how sunlight reaches the equipment and where differences in conditions arise. As a practical method for reading data in the field, this is a basic point you should definitely master.

Basics 3 | Correctly Understand the Positioning of PR

When looking at PVSyst results, many people focus on PR. PR is useful as a value that concisely indicates the overall performance of the system, and it is often referenced in practice. It is easy to understand numerically and convenient for comparing projects and for use in presentation materials, so it tends to attract attention as an indicator.

However, evaluating PR in isolation can be hazardous in practical situations. PR is certainly important, but it is only one result and not a universal metric independent of its underlying assumptions. It is a value that appears after various factors accumulate, such as solar irradiation conditions, temperature conditions, the presence or absence of shading, system configuration, and site characteristics. Therefore, instead of judging good or bad based solely on PR, it is necessary to consider under which assumptions that value was obtained.

For example, even if a project has a high PR, that may simply be because the irradiance conditions were inherently good and the temperature conditions were favorable. Conversely, a project that keeps losses well suppressed under harsh environmental conditions may not have a PR that looks particularly high, yet it can still be excellent from a design standpoint. In other words, PR is convenient for summarizing results, but it is not a single number that can convey the essence of a design.

When operations personnel look at PR, they should first use it as an indicator to grasp the overall picture, and then always check it together with the breakdown of losses and month-by-month fluctuations. If PR is high, look at why it is high. If PR is low, look at what is dragging it down. Reading it in this order prevents you from being swayed by the PR figure.

Also, because PR is useful when explaining things to stakeholders, it is important not to misuse it. If you show only the numbers, people tend to take them as a simple indicator of superiority or inferiority. However, in actual practice, how PR is perceived changes depending on site conditions. Therefore, when explaining PR, you need to be mindful to communicate the background behind the results as well. PR is a useful figure, but only by following the proper order of interpretation does it become a number that is truly useful in practice.

Basic 4 | Identifying design challenges from a loss breakdown

The most directly practical aspect of reading PVSyst is checking the breakdown of losses. If annual energy production and PR are the surface of the result, the loss breakdown is the part that tells you why that result occurred. By understanding at which stages and by how much energy is lost, you can identify design issues and opportunities for improvement.

What matters here is not to see losses as mere negative numbers, but to organize them by their nature. Losses related to how sunlight is received, losses related to shading and layout, losses related to temperature, and losses related to wiring and conversion each have different meanings and countermeasures. By separating what should be accepted as natural conditions from what can be tightened up through design, the breakdown of losses becomes much easier to read.

Losses also occur in a sequential context. A large loss in an upstream stage affects all subsequent stages. Losses in downstream stages act on the quantity remaining at that point. Therefore, judging only by the magnitude of the numbers can lead to incorrect prioritization of improvements. It is important to consider whether a loss takes effect in an upstream stage or a downstream stage.

For example, in projects where shading has a large impact at the front end, tightening the electrical efficiency downstream will yield only limited overall improvement. Conversely, if the front-end light-receiving conditions are good, optimizing downstream wiring and conversion can be more effective. When reading a breakdown of losses, it is practical to look not only at which losses are large but also at which stage they are taking effect.

Furthermore, a breakdown of losses is also useful when explaining differences between projects. In one project temperature may be the driving factor, while in another project shading may be — even when the difference in generated output is the same, the causes can differ. Being able to explain this with a loss breakdown gives stakeholders greater confidence in design decisions. Rather than simply listing numerical results, showing the loss structure makes it easier for stakeholders to gain a deeper understanding.

The loss breakdown is an extremely powerful section once you learn how to read it. You can use it when looking for reasons for low generation, when searching for points to improve, and when comparing design proposals. If you read PVSyst in practical work, this section is one of the basics you should definitely grasp.

Basic 5｜Check seasonal variations with monthly results

If you only look at annual values, it is easy to overlook seasonal differences. In practice, it is essential to check the monthly results to see how power generation trends change with the seasons. A project that looks acceptable on an annual basis may nevertheless experience a sharp drop only in winter or show strong temperature effects in summer. Such behavior only becomes apparent when viewing the data on a monthly basis.

When reviewing monthly results, it is important not just to look at which months are higher or lower, but to verify whether the fluctuations are within a natural range and consistent with installation conditions and loss trends. For example, if the winter decline is unusually large, you should question the relationship between solar altitude and surrounding obstructions or the shading condition settings. If the summer increase is weaker than expected, the impact of temperature-related losses may be strong.

Monthly results also help explain the outcomes. Annual generation alone can be abstract, but showing monthly trends conveys the characteristics of a project more concretely. If you can share how generation varies by season, stakeholders will find it easier to plan and make decisions. Especially in practice, a monthly perspective is indispensable, since not only the annual total but also the stability and timing of peaks by period are important.

Also, checking the monthly results makes it easier to notice inconsistencies in the input conditions. Even if the annual values look plausible, examining them by month can reveal unnatural fluctuations. This may indicate problems with the solar radiation data, shading conditions, or the orientation and tilt settings. In other words, monthly results can be used not only to observe seasonality but also to verify the overall validity of the simulation.

If you want to stabilize your interpretation in practical work, make it a habit to always return to the monthly results after looking at the annual figures. Annual figures show the overall picture, while the monthly results flesh out the details. By going back and forth between the two, you deepen your understanding of the results.

Basic 6｜Confirm the differences between the DC side and the AC side

In PVSyst results, there is a difference between the DC-side output or generated energy and the AC-side final output. Confirming this difference is very important for understanding the system configuration and conversion conditions. The power produced by the solar cells does not become the final output as-is, because it is affected along the way by conversions, wiring, and similar factors. Therefore, evaluating only the DC side is insufficient for practical assessments.

Even if the DC side appears satisfactory, if the AC side shows weak performance there may be issues in the downstream stages. Conversely, in cases where the upstream conditions are severe yet the AC side is well consolidated, the equipment configuration may have been well arranged. By comparing the DC and AC sides in this way, you can identify where the results are changing.

When checking this item, you should consider not only the magnitude of the difference but whether that difference is within a reasonable range and whether it aligns with the design intent. By being aware of how downstream-related factors—wiring conditions, the conditions of conversion equipment, approaches to output control, etc.—are affecting the outcome, your interpretation of the results becomes more practical.

Also, the differences between the DC side and the AC side are useful when comparing options. Even two proposals with similar final power output can differ: one may be strong on the DC side, while the other compensates with higher efficiency in the downstream stages. Understanding this difference reveals which proposal is a more straightforward design and which one depends on downstream conditions. It is not uncommon for designs to differ in character even when their apparent power output is the same.

For practitioners, the AC-side figures that are ultimately exported to the grid are what matter. However, to understand the context behind those numbers, you need to examine their relationship with the DC side. If you want to deepen your understanding of how to read PVSyst, it's important to check these upstream and downstream connections.

Verification Points Easily Overlooked in Practice

Just by covering the six items so far, your way of reading PVSyst becomes considerably more stable. However, in practice there are still points that are easy to overlook. One of these is viewing the result figures separately from the assumptions. When the numbers look plausible you tend to feel reassured, but if the input conditions do not align with the actual site, the interpretation of the results becomes unreliable.

Another common oversight is examining items in isolation. If you evaluate only the annual power generation, only the PR, or only the losses, you won’t see the overall flow. When reviewing results, you must always be conscious of the sequential context. It’s important to connect how the upstream light-receiving conditions relate to downstream output and to identify at which stages losses take effect.

Furthermore, care is required in how comparisons are made. If projects differ, regional conditions and installation conditions will also vary. Therefore, it is risky to judge good or bad based on a single indicator alone. When comparing, you need to look at a combination of annual power generation, specific yield, PR, breakdown of losses, monthly variations, and so on, and clarify where the differences lie. Even if the visible numbers are close, the underlying structure can be quite different.

Also, when explaining to stakeholders, simply lining up the numerical results often does not convey the meaning. Supplementing with words that explain why a value is what it is — which parts originate from the design and which from site conditions — makes the implications of the results easier to grasp. To make use of PVSyst in practice, it is important not only to read the numbers but also to be able to explain the background behind them.

Use comparative examination of result interpretation to inform explanations

The purpose of learning how to read PVSyst is not simply to understand the screen itself. In practice, it is important to be able to apply that perspective to comparisons and explanations. When comparing projects, you need to look structurally at where the differences lie, not just at the final energy yield. If you can identify whether the cause is solar irradiance conditions, the conditions under which the modules receive irradiance, the locations where losses occur, or subsequent conversion, you can make a more convincing decision.

For example, when comparing candidate sites, simply choosing the location with the highest annual energy production can be insufficient. Even if solar irradiation conditions are good, there may be constraints on shading or on layout flexibility that undermine confidence in the reproducibility of the results. Conversely, even if the numbers are not outstanding, a project with a straightforward, easy-to-explain loss structure can be easier to handle in practice. Organizing the way you interpret PVSyst makes these differences easier to see.

This perspective is useful when explaining things to customers or within the company. Rather than showing only part of the results, first convey the scale using the annual generation, then discuss in sequence the irradiance conditions, PR, breakdown of losses, monthly variations, and the relationship between DC and AC so that the audience can understand more easily. By aligning the flow of the explanation with the flow for reading the data, the meaning of the numbers will come across naturally.

Also, standardizing how you review things makes internal decision criteria more stable. If each person looks at different aspects, evaluations can vary even for the same project. However, if there is a common format that starts by checking these six items for every project, comparisons and handovers become easier. The way PVSyst is read can be used not as individual knowledge but as a standard that supports the quality of organizational decision-making.

The Accuracy of Assessing On-site Conditions Determines the Quality of Interpretation

No matter how carefully you read PVSyst results, if your grasp of site conditions is vague, there are limits to the accuracy of your interpretation. In particular, the relationships among shading, orientation, tilt, surrounding obstacles, and the planned installation location strongly influence the preliminary aspects of the results. In other words, the deeper you delve into interpreting PVSyst, the more important it becomes to have accurately captured the on-site positional relationships.

In practice, even if drawings appear problem-free, small positional shifts or changes in elevation on site can affect shading conditions. Such differences also influence how illumination (incident light) conditions are interpreted and how loss breakdowns are understood. If the assumed positional relationships are ambiguous, you may see the resulting numbers but their meaning becomes blurred.

Therefore, if you want to make PVSyst assessments more reliable in practice, it is important to have a means of precisely understanding the spatial relationships at the site. Improving verification of the planned installation location, clearances to surrounding objects, determination of orientation, and on-site reproducibility will increase the validity of input conditions and give you greater confidence in interpreting the results. In particular, for projects where shading and layout have a strong impact on power generation, this difference in precision directly translates into differences in design decisions.

From this perspective, in practical work where a high-precision understanding of on-site positional relationships is required, it naturally leads to LRTK, the iPhone-mounted GNSS high-precision positioning device. By making it easier to perform high-precision on-site position checks and orientation determination, it becomes easier to organize the assumptions entered into PVSyst, and the interpretation of results becomes more practical. Rather than concluding with the numbers on the screen alone, considering the on-site level of positional accuracy as well is extremely important as a practical way to view PVSyst.

Summary

To stabilize the way you interpret PVSyst in practice, it is effective to follow this flow: first grasp the overall picture using annual energy production and specific yield, next check the pattern of irradiance and incident conditions, understand PR together with the assumptions, identify issues from the loss breakdown, observe seasonal variations from the monthly results, and finally check the difference between the DC side and the AC side. Just covering these six items will greatly clarify how the results appear.

The important point is not to judge based on a single indicator alone. The results from PVSyst are the cumulative outcome of multiple conditions and losses. Therefore, reading them in sequence, considering the context, and understanding the background behind the numbers leads to a practical way of interpreting them. Whether for design improvement, project comparison, or explaining to stakeholders, this principle forms the foundation.

And to make interpretation of the results more reliable, it is also important how accurately you can grasp the on-site spatial relationships. If you want to set the assumptions for shadows, orientation, and layout with high precision, considering the use of LRTK from an iPhone-mounted high-precision GNSS positioning device is also effective. By combining the ability to interpret PVSyst results with the ability to accurately capture the site, you can more easily arrive at design decisions that are more robust in practice.