8 Metrics to Check in PVSyst Reports | Practical for Real-World Use

In the work of designing solar power systems and forecasting generation, running a simulation is not the end. What matters more is how you read the resulting report. No matter how carefully the input conditions are prepared, if you cannot correctly interpret the results, neither the quality of the design, the accuracy of comparisons, nor the persuasiveness of explanations to internal and external stakeholders will improve. Especially for practitioners searching for information on "how to read PVSyst," it can be difficult to know which figures in the report should be prioritized.

Actual reports present many numbers, such as annual energy generation, specific yield, PR, solar irradiance, losses, monthly results, grid-side energy, and figures related to self-consumption. Because of this, those who are not familiar tend to pick out only the most conspicuous items and make judgments. However, a report is not merely a list of numbers. There are site conditions, irradiance conditions, losses such as shading, temperature, and mismatch, and the results are the outcome of energy flowing from the DC side to the AC side. In other words, it is important to read the results as a flow rather than view them as isolated points.

Also, in practice, what you want to check differs from project to project. In initial comparisons you want an overview, while in detailed design you need to isolate causes. For client explanations, clarity is essential, and during reviews you need a way of reading that makes opportunities for improvement visible. That is why organizing which numbers to check and in what order to make decisions easier will greatly increase a report’s usability.

This article narrows down the indicators you should look at in a PVSyst report to eight. Rather than simply listing item names, it explains why you should check each indicator, when it is useful, and what is容易ly misunderstood, providing practical ways to read the report for use in the field. The goal is to make it easier to know where to look in the report and to make the results more usable for design, comparison, and explanation.

Table of Contents

• Key concepts to grasp before reading the report

• Indicator 1｜Annual energy generation

• Indicator 2｜Specific yield

• Indicator 3｜Horizontal plane solar irradiance

• Indicator 4｜Effective irradiance on the tilted surface

• Indicator 5｜PR

• Indicator 6｜Shading Loss

• Indicator 7｜System Loss

• Indicator 8｜Final electrical energy (E_Grid or E_User)

• In what order should the indicators be read?

• The accuracy of site conditions determines the reliability of the report

• Summary

Key concepts to grasp before reading the report

When reading a PVSyst report, the first thing to understand is that the numbers listed there are not independent. First, there is the solar irradiation that reaches the site; that irradiation is intercepted by the installation surface and, while affected by shading, reflection, and temperature, is converted into direct-current (DC) power, which then passes through inverters and wiring to become AC-side output. The numbers listed in the report are a breakdown of this entire flow. Therefore, every figure has a sequential relationship.

If you ignore that context, the results table quickly becomes hard to interpret. For example, looking only at annual energy production you cannot tell whether the number is due to favorable site conditions or to good design. Looking only at PR you cannot determine whether shading, temperature, or wiring is having the effect. Looking only at Shading Loss, if you do not know the underlying irradiance conditions, it is difficult to judge whether that loss is significant or minor. That is why, to use a report effectively, you must read the numbers not as isolated points but as a flow.

Another important point is to read a report not as an answer but as material for decision-making. The numbers in a report are built on assumptions such as site conditions, orientation, slope, shading conditions, equipment configuration, and demand profiles. In other words, rather than feeling reassured or alarmed by the numbers alone, it is important to consider why those numbers were produced. In practice, the more a person reads the results in relation to the assumptions, the higher the accuracy of both the design and the explanations.

Therefore, a clear sequence for reading the report is to first look at the numbers that capture the overall picture, next confirm the fundamentals of solar irradiation and incident light, then read about performance and the causes of losses, and finally review the output figures such as electricity sales and self-consumption. Keeping this order makes it less likely you’ll be unsure where to start and makes it easier to translate the report as a whole into practical, operational decisions.

Indicator 1｜Annual Power Generation

The first metric to look at is annual electricity generation. Because it captures the overall scale of the project in a single number, it is very useful as an entry point for a report. By checking how much generation can be expected annually, you can get a rough sense of the project's positioning. In internal comparison materials and in summary explanations to clients alike, this figure is often used first.

However, annual energy production, while convenient, can be dangerous to judge by itself. This is because annual production is the result of a mixture of installed capacity, site conditions, incident light conditions, loss structure, and so on. If capacity is large, the figure will naturally tend to be larger, and in regions with favorable solar radiation the results will also tend to be higher. For that reason, it is premature to take a high annual energy production as direct evidence of an excellent design.

In practice, the point of looking at annual power generation is, first, to get a sense of the project's scale. It becomes useful if you treat this figure as a number for checking how much electricity the project is expected to produce and whether it is unusually large or small compared with past similar projects. After that, it is appropriate to verify why this value was obtained by examining the following indicators.

Also, precisely because annual power generation is a figure that’s easy to explain, you need to be careful how you present it. If you show only the numbers, the other party is likely to feel that they represent the entirety of the design. In reality, however, those figures are the result of accumulated solar irradiation conditions and losses. A practical way to interpret them in professional work is to position annual power generation not as a conclusion but as an entry point, and then always go on to examine the causes.

Indicator 2 | Specific yield

One metric you should look at together with annual generation is specific yield. Specific yield is a handy indicator for understanding how much electricity is generated per unit of installed capacity, and it is especially useful when comparing projects of different scales. Annual generation alone tends to make projects with larger installed capacity look more favorable, but examining specific yield reveals the generation efficiency normalized by capacity.

In practice, this metric is often useful for comparing multiple candidate sites or proposals with different capacities. For example, a proposal with a large annual power output may not be particularly strong in terms of specific yield. In that case, the large output is a matter of scale and does not necessarily reflect superiority in design or site conditions. Conversely, a proposal with modest annual output but a high specific yield is easier to assess as having good performance per unit of equipment.

However, specific power generation is not perfect. When comparing sites with different solar irradiance conditions, looking only at specific power generation will conflate the sites' advantages and disadvantages. Therefore, it is practical to use specific power generation as a supplementary metric to annual energy generation. By first getting a sense of scale from annual energy generation and then checking efficiency with specific power generation, the overall picture of the results becomes much clearer.

The advantage of specific power generation is that it makes comparative discussions easier to structure. In practice, directly comparing projects of different scales can lead to mismatches in the discussion. Including specific power generation allows you to separate scale and efficiency, making differences in design and location easier to see. As indicators to look at in a report, it is easiest to understand if you consider annual generation and specific power generation as the initial set.

Indicator 3｜Horizontal-plane solar radiation

Next, what we want to check is the horizontal-plane solar irradiance. This figure indicates the baseline of the natural conditions at that site. If you only look at outcome metrics such as power generation and PR, you cannot tell whether differences between projects are due to design differences or site differences. Therefore, you first need to confirm how much solar resource is available at that location. The horizontal-plane solar irradiance serves as that benchmark.

This metric is important in practice because it makes it possible to distinguish between the scope of design responsibility and the range of natural conditions. For example, even for a project with high annual energy production, if the reason is the inherently favorable solar resource, it is not appropriate to give full credit to the design alone. Conversely, at a site where solar resource conditions are not particularly favorable, if the results are stable, it is easier to conclude that design measures and loss mitigation are effective.

Also, this figure is important when comparing sites. When there are multiple candidate locations, listing only the annual energy production will make differences in geographical conditions appear directly as differences in results. However, if you first check the horizontal-plane solar irradiance, it becomes easier to determine how much of the difference is attributable to site conditions. This is also important for ensuring fairness in comparisons.

For beginners, it can be difficult to appreciate the connection between horizontal‑plane solar irradiance and power generation. However, grasping this makes the meanings of tilted‑plane irradiance, PR, and losses that you’ll examine later much clearer. To make it less likely you'll get confused when reading reports, it's important to develop the habit of first checking the baseline natural conditions.

Indicator 4｜Effective Solar Radiation on Slopes

When you have checked the solar irradiance on a horizontal surface, the next thing to look at is the effective irradiance on the tilted surface. This is an indicator used to see how much of the solar radiation available at a site is actually received as usable irradiance after accounting for the installation’s actual orientation, tilt, and shading conditions. In other words, it is a number that shows how the installation conditions capture the natural conditions.

Even at the same location, the amount of solar irradiance received by the equipment surface changes if the orientation or tilt differs. Also, if there are nearby obstructions or inter-row shading, the solar irradiance that can actually be used changes further. Therefore, horizontal-plane irradiance alone does not reveal the design's ability to receive sunlight. Only by examining the effective irradiance on the tilted surface does it become clear how well the site conditions are being utilized.

In practice, by looking at this indicator it becomes easier to distinguish whether the issue is poor solar radiation conditions or poor light reception. For example, if the site's solar radiation is sufficient but the amount of light received on the inclined surface is not high, there may be room for improvement in orientation, tilt, shadow conditions, etc. Conversely, even if the site conditions are not particularly favorable, if the light-receiving conditions are straightforward, the result is more likely to be a stable project.

This way of reading is also closely connected to considerations of shading and layout. To understand Near Shadings and Shading Loss, first grasping how solar radiation enters the receiving surface makes the meaning of the losses easier to understand. As indicators to look for in reports, horizontal irradiance and the effective irradiance on the tilted surface are practically useful if considered as a set comprising the basis and the way the surface receives radiation.

Indicator 5 | PR

PR is one of the most commonly used summary metrics in reports. Because it is consolidated into a numerical value and easy to understand, people tend to give it undue weight from the start. Indeed, it is very useful in that it makes it easy to grasp the overall performance of a system with a single number. However, judging the quality of a project solely by PR is risky. PR is a convenient number, but it is not an all-purpose evaluation score.

The purpose of looking at PR is to get a rough sense of the overall coherence of a project. It is most useful if you think of it as an indicator for sensing how cleanly performance emerges as the result of solar irradiation conditions, incident-light conditions, and the loss structure. If PR is high, it likely means losses are being relatively well controlled; if it is low, it is easier to infer that there is some factor depressing performance somewhere.

However, looking at PR alone without seeing the reasons can be misleading. For example, if site conditions are favorable, there is little shading, and temperature conditions are good, PR tends to look better. Conversely, at sites with severe field conditions, PR may not increase as much even if the design is well organized. In other words, PR needs to be read together with the background. As a practical way to use it in the field, after looking at PR you should always return to the loss items and verify what is producing that number.

PR is a figure that is easy to use in reports and explanations. However, if you present only that, the other party may come to understand it in an overly simplified way. Therefore, in practice, using PR as a summary value while also being able to explain the underlying solar irradiation conditions and loss structure will greatly increase persuasiveness.

Indicator 6｜Shading Loss

Shading Loss is a metric that is easily overlooked in practice, yet has a large impact on results. Losses from shading cut energy at a fairly early stage of the power generation process, and therefore affect every subsequent stage. In other words, for projects with high Shading Loss, no matter how much you tighten downstream efficiencies, it is difficult to recover the lost energy. For that reason, checking this metric in reports is of great importance.

When evaluating Shading Loss, it is important not to decide importance based only on the annual loss rate. You need to consider which seasons and times of day the shading takes effect to understand its true significance. Shading that occurs only in the early morning in winter has a different qualitative impact on annual generation than shading that falls during times in spring and autumn when generation contribution is high. Because this is closely linked to the accuracy and placement conditions of Near Shadings, you must be aware not only of the numbers but also of the 3D background conditions.

Also, it is important to recognize that visible shadows and generation losses do not necessarily match. Partial shading can spread electrical effects, causing losses that exceed what the visible shading suggests. In other words, Shading Loss may include not only the visual blocking of light but also the electrical behavior of modules and strings. Without this perspective, it is easy to become confused when losses appear disproportionately large or small compared to what is seen.

When evaluating Shading Loss in practice, it's easier to think of it not as checking whether shadows exist but as assessing their significance. If you use the value as a number to determine which shadows can be avoided and which should be accepted, it also makes it easier to revisit the layout, orientation, and positions of obstacles.

Indicator 7｜System Loss

System Loss is a metric that shows how much of the energy remaining after array-side losses is being eaten up by the inverter, wiring, transformer, auxiliary equipment, shutdown losses, and so on. Unlike losses that occur at the irradiation stage, such as shading and temperature, this is a downstream loss. Therefore, when the array side looks fine but the final result doesn’t improve as much as expected, this metric becomes important.

The reason System Loss is important in practical work is that it makes the quality of downstream equipment configuration and routing plans easy to see. Not only inverter efficiency, but also AC wiring, transformers, auxiliary equipment consumption, downtime, and so on—how the entire system is put together is reflected here. The better the upstream conditions of a project, the more a small difference in downstream System Loss will affect the results.

Also, with System Loss it is important not to confuse the set values with the annual results. Wiring losses and transformer losses do not keep the same actual weight based solely on assumptions at rated conditions; their real significance depends on how they accumulate across the distribution of output over the year. Therefore, the annual results shown in the report should be read not as mere nominal values but as results aggregated under operating conditions.

When looking at System Loss in the results table, it's important to consider it separately from losses on the array side. By distinguishing whether the issue is caused by shading or temperature, or by downstream equipment or routing, the direction for review becomes clearer. A practical way to read it for use in the field is to view Shading Loss and System Loss side by side and determine whether the more significant issues lie in the upstream or downstream side.

Indicator 8｜Final electrical energy (E_Grid or E_User)

Finally, the metrics to look at are those related to the final amount of electricity. In projects that sell power to the grid, the amount of electricity sent to the grid, such as E_Grid, becomes important, while in self-consumption projects E_User and the related self-consumption quantities are important. These are figures close to the outputs of the results table and tend to be directly linked to business and operational decisions.

However, if you see these figures first, you will not understand why they took those values. That is precisely why it makes sense to look at them last. After checking annual generation, irradiation conditions, incident light conditions, PR, losses, and monthly trends, you will feel considerably more convinced by these output numbers. In other words, E_Grid and E_User are conclusions, but it is easier to understand them when positioned at the end.

For projects that sell electricity to the grid, looking at how much of the generated energy is ultimately delivered to the grid makes it easier in practice to capture the effects of downstream losses and output restrictions. For self-consumption projects, reading how much was able to be used on the demand side makes it easier to assess the load profile and the validity of operations. In both cases, organizing them as figures that show the final usage makes them easier to use in practice.

A practical point is not to use output figures as inputs. Output numbers are important, but they are ultimately results. By reviewing them after laying out the underlying conditions and losses, it becomes easier to draw implications for design and operation. When working through the results table, the most orderly approach is to check these output figures last.

In what order should you read the metrics?

To make the eight indicators presented so far more practical for use in the field, it is important to have a defined order for reading them. The recommended sequence is to first grasp the overall picture with annual energy production and specific yield, next confirm the foundation with horizontal irradiance and effective irradiance on the tilted plane, then identify causes using PR, Shading Loss, and System Loss, and finally look at the outputs with E_Grid and E_User. This order makes it easier to interpret the numbers within their contextual relationships.

This order is useful because the flow from the overall picture to the causes and then to the output is natural. If you jump straight into loss items, it becomes difficult to understand what those losses are referring to. Conversely, if you stop at annual power generation alone, you won't see the causes. Looking in the order of input, foundation, causes, and output makes it less likely for beginners to get confused and helps organize practical discussions.

Also, this order can be used as-is for comparative evaluations. When comparing multiple proposals, first look at scale and efficiency, then check solar irradiation and incident light conditions, compare the loss structures, and finally examine the final figures for electricity sales and self-consumption—doing so makes it easier to see what fundamentally explains the differences. Rather than viewing indicators in isolation, arranging them in sequence greatly improves the usability of the report.

The accuracy of on-site conditions affects the reliability of the report

Even if the numbers in a report look tidy, their reliability depends heavily on how accurately site conditions have been assessed. In particular, Shading Loss, the effective irradiance on inclined surfaces, and parts of System Loss are influenced by how precisely on-site information—such as positional relationships with obstructions, orientation, equipment layout, and cable routes—has been incorporated. In other words, if you want the way you read reports to be truly usable in practice, you must also be aware of how accurately the site itself has been understood.

For example, when shading loss is large, determining whether it truly originates at the site or is due to inaccurate input of obstacle positions requires an accurate understanding of the on-site spatial relationships. The same applies to wiring losses and route conditions. Rather than judging based only on the numbers in the results table, considering the site conditions that underlie those numbers will increase the persuasiveness of the report.

In that sense, having a way to capture the on-site positional relationships with high accuracy is of great importance for using PVSyst reports more practically. If the location of equipment, distances to obstructions, orientation, and route conditions can be determined accurately, it becomes easier to refine the assumptions related to shading and layout, and the figures in the report become more convincing.

What naturally fits here is LRTK, an iPhone-mounted GNSS high-precision positioning device. Because it makes on-site position verification, distance assessment to obstacles, and reproducibility of equipment placement easier, it becomes simpler to organize the assumptions for input into PVSyst. By combining the ability to read reports correctly with the ability to capture the site with high precision, you can more readily arrive at design decisions that are stronger in practice.

Summary

As indicators to check in a PVSyst report, reviewing in order the annual energy production, specific yield, horizontal plane irradiation, effective irradiation on the tilted plane, PR, Shading Loss, System Loss, and the final energy output makes it easier to organize the overall picture of results and their causes, and to reach outputs closer to business and operations. The important thing is not to judge based on any single number. Reports are structured as a flow, so reading them in sequence is fundamental.

In practice, simply having the sequence of an overall picture as the entry point, the foundation of solar radiation and incident light, the losses that are the root causes, and the final output greatly changes how a report appears. When you can explain the meaning of the numbers within their context, comparisons, internal explanations, and customer explanations all become much easier to understand.

And to make that interpretation even more reliable, it is essential to grasp the positional relationships on site with high precision. If you want to organize shadows and layout conditions more accurately, the perspective of using LRTK, an iPhone-mounted GNSS high-precision positioning device, is also useful. By combining the ability to correctly read PVSyst reports with the ability to accurately capture the site, it becomes easier to arrive at design decisions and power generation forecasts that are more convincing.