Introduction to Reading PVSyst｜5 Items to Check First

When you're not familiar with it, a PVSyst report can be confusing as to where to start reading. Because similar-looking numbers are listed—energy production, ratios, losses, irradiance, array output, grid-side output, etc.—trying to chase everything from the outset can actually make it harder to grasp the overall picture. In practice, rather than memorizing every term one by one, it's far quicker to have an order of "what to look at first." The official PVSyst tutorial likewise organizes a flow for focusing the report: main results, specific yield, PR, loss diagram, and supporting graphs.

Also, a PVSyst report is not simply a document that shows the total annual energy production. On the main results page you can see the energy conclusions, and the loss diagram shows where energy was lost on the way to that conclusion. Moreover, by looking at meteorological and irradiance-related variables you can confirm whether the original input conditions and the incident irradiance conditions are reasonable. In short, reading PVSyst is not about memorizing numbers, but about sequentially grasping the "conclusion", the "cause", and the "background conditions".

This article explains, in order and for beginners, the five items you should check first when reading a PVSyst report. To help practitioners quickly organize “what to look at first” and “which numbers are easy to misinterpret” immediately after receiving a report, I summarize them in a way that makes the relationships between terms as visible as possible. This content is useful not only for those who are about to start using PVSyst but also for those who receive and review the results.

Table of Contents

• Prerequisites to understand before reading PVSyst

• 1 The first thing to look at is Main results

• 2 Check the values related to solar irradiance

• 3 Follow how energy production decreases in the Loss Diagram

• 4 Understand the differences between EArray・EOutInv・E_Grid

• 5 Search for anomalies in the monthly results and Normalized productions

• Practical reading order to avoid confusion in actual work

• Summary

Prerequisites to Understand Before Reading PVSyst

Before reading PVSyst, the key point to grasp is that the numbers in the report are divided into "result numbers" and "intermediate numbers." For example, figures such as Produced Energy, Specific production, and PR are numbers that are close to the final conclusions. On the other hand, figures such as GlobInc, GlobEff, and EArray are intermediate numbers used to understand under what conditions those conclusions were reached. If you look only at the intermediate numbers from the start, you can lose sight of which numbers are important. That is why, in PVSyst, it is better to look at the conclusions first and then trace the causes. In the official tutorial as well, Main results are positioned first, followed by the Loss diagram and various graphs.

Another important point is that PVSyst's results consist of multiple stages, such as irradiance conditions, optical losses, array losses, inverter losses, and wiring losses. In PVSyst’s official documentation, the simulation variables for a Grid-connected system are defined in sequence as GlobInc, GlobEff, EArrMPP, EArray, EOutInv, E_Grid, and so on. In other words, PVSyst is designed so you can track not only "how much power was generated" but also "where and by how much it was reduced on the way to that generation."

Therefore, what beginners should be aware of at first is not to try to understand everything at once. First grasp the conclusions in the main results, then proceed to the solar irradiance conditions, the loss diagram, the energy flows, and the month-by-month variations — doing so makes it much easier to read. In practice, the ability to read PVSyst is not about memorizing all the abbreviations, but about having an order in which to read the report.

1 The first thing to look at is the Main results

The first item to look at is "Main results." By looking here you can get a preliminary grasp of the project's conclusion. The official tutorial also explains that the report's fourth page shows "energy production, specific production and performance ratio." In other words, the basic approach is to first check here how much generation is expected annually, what that generation looks like per unit of installed capacity, and how the system performs overall.

The three metrics to pay particular attention to here are Produced Energy, Specific production, and PR. Produced Energy is the central figure for the annual energy production ultimately obtained under the simulation conditions. Specific production is an indicator showing how much is produced annually per installed capacity of 1 kWp, and PVSyst’s official documentation describes it as "system’s annual production per unit of installed capacity, expressed in kWh/kWp/year". In other words, it is a useful figure when you want to understand not just the absolute total energy production but how easily the system generates power relative to its installed capacity.

PR is even more important. In PVSyst, PR is described for grid-connected systems as the ratio of E_Grid to GlobInc × PnomPV. This is an indicator of "how effectively the entire system was able to extract energy under the site's incident irradiance conditions." Moreover, the official documentation states that PR includes optical, array, and system losses such as shading, IAM, Soiling, array conversion losses, degradation, mismatch, wiring, and inverter efficiency. In other words, PR is not the module efficiency itself but a rough indicator of the overall system's performance.

A common misreading here is judging good or bad based solely on PR. PR is a useful metric, but it is not a number that replaces the annual energy production itself. Even if PR is high, the total energy production will be small if the installed capacity is small, and conversely there are projects where PR is slightly low but a large capacity secures sufficient energy production. In other words, in Main results it is essential to always read Produced Energy, Specific production, and PR as a set.

When you receive a PVSyst report in practice, first look at these three items to grasp "how much electricity this project will generate annually," "how good it is relative to the system size," and "what the system looks like overall including losses." Doing so makes subsequent detailed checks much easier. In short, the Main results are both the entry point to the report and a map that keeps you from getting lost until the end.

2 Verify the values related to solar radiation

The second item to check is the values related to solar irradiance. After grasping the conclusions in Main results, if you want to know "why this amount of generation occurred," the next thing to check is the irradiation conditions. In PVSyst's official documentation, variables related to weather and irradiance are defined as GlobHor, DiffHor, Tamb, Windvel, and, for the collector surface, GlobInc, BeamInc, DiffAInc, etc. In other words, the report's results are determined primarily by how much irradiance reached that surface.

The first thing to understand here is the difference between GlobHor and GlobInc. GlobHor is the global horizontal irradiance — the solar radiation on a horizontal plane — and is the base value entered as meteorological data for that location. By contrast, GlobInc is the incident irradiance converted to the actual receiving surface, such as a roof or mounting structure. In other words, GlobHor is the basis of the solar radiation coming from the sky for that area, while GlobInc is the amount of solar radiation that the surface actually receives after accounting for orientation and tilt. Distinguishing these makes it easier to understand why results differ between south-facing and east/west-facing surfaces in the same region.

Another thing to look at is GlobEff. In PVSyst's simulation results, the concept of GlobEff — which takes into account optical losses and the like — is placed after GlobInc. If you follow the Main results table and the simulation variables, you can see that irradiance does not simply end once it is incident; it is transformed, after being affected by IAM, shading, Soiling, etc., into conditions that can actually be used for power generation. In other words, even if GlobInc is sufficient, if GlobEff isn’t increasing as much as expected, you should suspect optical losses after incidence.

A common misreading at this stage is to assume, “If the energy output is low, the equipment’s performance must be poor.” However, in reality it may simply be that the amount of solar radiation incident on that surface was low to begin with. For north-facing or east–west installations, or sites where solar radiation tends to be lacking in winter, it can be better to check the incident irradiance conditions before the equipment conditions. In other words, in PVSyst reports it is very important to verify the assumptions about solar radiation before the energy output.

In practice, by examining the solar irradiation data you can more easily judge whether the site conditions are reasonable, whether the orientation and tilt settings are appropriate, and whether optical losses are not too large. When reading PVSyst, keeping the sequence of checking the solar irradiation right after the Main results makes it much easier to grasp the context behind the results.

3 Tracking the Decline in Power Generation with a Loss Diagram

The third item to look at is the Loss Diagram. One of PVSyst's major strengths is that it allows you to visually trace not only the final annual generation result but also where energy was lost along the way. The official documentation also explains that the Loss Diagram is "a diagram for quickly gaining insight into the quality of the system design" and is intended to identify the main sources of loss. Moreover, it is always displayed in the annual report and can be checked on a monthly basis. In other words, if you are unsure how to read PVSyst, the Loss Diagram is the most effective intermediate reference.

In the Loss Diagram you can see, step by step, at which stages the solar irradiance is reduced, at which stages it is lost in the array, and at which stages it is lost in the inverter and wiring. Looking at the official simulation variables, loss variables such as GIncLoss, TempLoss, ShdElec, MisLoss, OhmLoss, and InvLoss are defined. In other words, PVSyst lets you track not only "how many kWh were lost" but also "what caused the loss."

Beginners shouldn't try to memorize every loss in detail. First, it's important to get a rough sense of whether optical losses, temperature losses, shading-related losses, or inverter losses are dominant. For example, if GlobInc is sufficient but GlobEff drops significantly, you should suspect optical losses such as IAM, shading, or Soiling. If there is a large drop from EArrMPP to EOutInv, you should suspect the inverter or operating constraints. In other words, the Loss Diagram is a chart that tells you "where to look."

One useful thing to know when reading the Loss Diagram is that EArray does not appear in the Loss Diagram as-is. According to the official explanation, EArray is the effective energy of the array output and includes shifts in the inverter operating point, but it is not represented in the Loss Diagram. If you don't know this and assume "it's not in the Loss Diagram, so it's not important," you may overlook constraints on the inverter operating point. In other words, the Loss Diagram is very powerful, but you also need to distinguish between what it includes and what it does not.

In practice, after checking the conclusions in the Main results, identifying "where the main causes are" on the Loss Diagram greatly deepens your understanding of the entire report. When reading PVSyst, it is far more efficient to first grasp the largest loss areas on this diagram and then examine the detailed variables, rather than immediately going through every page.

4 Understand the differences between EArray・EOutInv・E_Grid

The fourth item to check is the difference between EArray, EOutInv, and E_Grid. When you start reading a PVSyst report, you'll encounter many similar energy figures. If you read it without distinguishing them, it's easy to lose track of which number represents the actual energy production. In practice, simply grasping the differences among these three greatly reduces misinterpretation of the generation figures.

First, EArray is the effective energy on the array output side. According to the official description, it is the array-output energy that takes into account shifts in the inverter's operating point, and it is stated that it does not appear in the Loss Diagram. In other words, it is the figure that shows how much energy actually came out at the module or array stage.

Next, EOutInv is the energy available on the inverter’s output side. It’s helpful to think of it as the amount that, having passed from the array side through the inverter, appears on the AC side. In other words, by examining the difference between EArray and EOutInv, you can more easily discern the effects of inverter efficiency and operational constraints.

And E_Grid is the energy injected into the grid. In the official variable definitions, E_Grid is also defined as “Energy injected into the grid.” Therefore, this number is the central figure when you want to see the energy sold to the utility or exported to the grid side. However, what should be noted here is that in projects that include self-consumption, E_Grid alone should not be regarded as the system’s total generation. The PR’s official explanation likewise states that, while E_Grid is used for normal grid-connected systems, when there is E_Solar internally consumed within the system, evaluation should use E_Grid + E_Solar. In other words, in self-consumption projects, looking only at E_Grid can cause part of the generated energy to be overlooked.

A common misreading here is to look at E_Grid and conclude that the generation is low. If the project is a self-consumption type, E_Grid may not include the portion used inside the building. Conversely, if the project prioritizes only the amount sold to the grid, E_Grid is very important. In other words, you must read PVSyst's numbers with an awareness of "where the energy was measured."

In practice, looking at EArray, EOutInv, and E_Grid in that order makes it much easier to see where differences appear on the panel side, the inverter side, and the grid side. If you find the numbers in PVSyst overwhelming, first clarifying the roles of these three will let you see the overall flow of energy.

Search for anomalies in the monthly results for May and in Normalized productions

The fifth item to check is the monthly results and Normalized productions. Even if you understand the annual conclusions and the flow of losses, it can still be difficult to see "which seasons are strong" and "which periods are weak." In PVSyst, in addition to the main results, you can make seasonal variations and any abnormalities easier to see through Specific production, PR, and normalized indicators. In other words, by taking a monthly and normalized perspective, you can identify many features that are not apparent from annual totals alone.

Specific production is, as the official description states, the energy yield per installed capacity expressed in kWh/kWp/year. This lets you understand not the simple total energy output but how much a system tends to produce per 1 kWp. In PVSyst’s description of the Normalised performance index, Specific production corresponds to Yf and can be checked on the main results page. In other words, it is a convenient metric for comparing proposals with different system capacities.

Also, understanding the concept of the Normalized Performance Index makes the relationships among PR, Yf, and Yr easier to see. In the official explanation, Yr is defined as an ideal reference based on the solar irradiance incident on the receiving surface, and Yf is organized as the effective energy production divided by the installed capacity. In other words, by looking at Yf and PR, it becomes easier to understand "how much generation is achieved independent of capacity size" and "how efficiently the system is operating relative to irradiance conditions."

Furthermore, it is officially stated that the Loss Diagram can also be viewed by month. This is very important, because issues that appear small on an annual basis may be concentrated in specific months. For example, you can see patterns such as shading losses being large only in winter, temperature losses being large only in summer, or effective irradiance dropping only during the rainy season; when such patterns are visible, it becomes easier to determine directions for design and operational improvements. In other words, a monthly view is useful not only for anomaly detection but also for identifying root causes.

In practice, after confirming the annual conclusions in the Main results, checking the monthly PR and Specific production, and, if necessary, the monthly loss diagrams will considerably increase the level of detail. Rather than being reassured by the annual figures alone, examining month-by-month where the weaknesses are is the final step to fully mastering PVSyst.

Reading Order to Avoid Confusion in Practical Work

When reading a PVSyst report for practical work, first look at Main results and grasp the conclusion from the three items: Produced Energy, Specific production, and PR. Next, check irradiance-related values, especially GlobInc and GlobEff, to confirm the assumptions and how the optics are working. After that, use the Loss Diagram to identify where large losses occur, and, if needed, follow the differences between EArray, EOutInv, and E_Grid. Finally, examine monthly results and normalized indicators to look for seasonal variations and signs of anomalies. The structure of the official tutorial is also quite close to this flow.

The advantage of this order is that it allows you to proceed from the conclusion to the causes. Instead of immediately chasing all the abbreviations, structuring the report as first the conclusion, then the background conditions, then the losses, and finally the monthly variations makes PVSyst reports much easier to read. What is needed in practice is not to memorize all of PVSyst’s variables, but to quickly grasp “what determines whether this project is good or bad.”

Summary

If you want an introduction to reading PVSyst, the five items you should look at first are: Main results, radiation-related values, the Loss Diagram, the differences between EArray, EOutInv, and E_Grid, and the monthly results with Normalized productions. Grasp the conclusion from the Main results, confirm the assumptions with the radiation values, trace causes with the Loss Diagram, understand the flow with the energy variables, and finally check for anomalies or biases in the monthly and normalized indicators. Simply following this order makes PVSyst reports considerably easier to read.

The important thing is not to see PVSyst as a “report that’s difficult because it has a lot of numbers.” PVSyst is designed so that you can follow the conclusions about energy production, the irradiation conditions, losses, energy flow, and seasonal variations within a single report. In other words, if you can just organize how you read it, it becomes a highly practical tool. Rather than trying to understand everything from the start, by checking five items in order you can capture much of the necessary information.

Also, if you truly want to improve the accuracy of reading these reports, it is essential to capture site conditions precisely. If the roof edges, positions of obstructions, elevation differences, or the way nearby shading occurs are ambiguous, no matter how carefully you read PVSyst’s outputs, the underlying assumptions can easily shift. In particular, conditions related to shading and effective area tend to appear directly in the Loss Diagram and as differences in actual energy generation.

In that respect, LRTK, an iPhone-mounted GNSS high-precision positioning device, is extremely effective as a means of accurately grasping the positional relationships on site. Because it makes it easier to record the positions of roof edges and obstacles accurately in the field, it helps improve the accuracy of the assumptions entered into PVSyst. If you want to make PVSyst interpretation truly usable in practice, properly capturing site conditions with a method like LRTK is a major advantage that raises the precision of result interpretation.