4 Ways to Read PVSyst's E_Grid | How to View Sold Electricity Amounts

In practical work on designing photovoltaic systems and forecasting power generation, alongside annual energy production and PR, it is important to know how to interpret the figures that directly relate to electricity sales. Among these, E_Grid is often checked in PVSyst reports. Although the numbers may look straightforward at first glance, treating them in the same way as the actual amount of generated electricity can lead to incorrect conclusions.

Especially for practitioners searching for "how to read PVSyst", it is easy to remain unclear about what E_Grid means, how it differs from annual generation, which losses affect E_Grid, and how it should be interpreted on a month-by-month basis. Because the figure is close to the amount of electricity sold, there is a tendency to judge it simply by whether it is large or small, but E_Grid is a number that emerges as the result of accumulated assumptions and losses. Therefore, using it without examining that background can easily lead to misreading the actual sales forecast and the validity of the design.

What really matters in practice is not to view E_Grid as a single result value, but to understand the flow by which that figure is produced. There are solar irradiation conditions, incident-light conditions, and generation on the DC side, and from there, through wiring and conversion, E_Grid appears as the amount of electricity ultimately delivered to the grid. In other words, while E_Grid is an output figure, it is also a comprehensive result that reflects the overall design state of the project.

This article explains how to read PVSyst’s E_Grid in practical work, organized from four perspectives. After first clarifying the role of E_Grid, it sequentially explains the difference from annual energy production, the relationship with losses, how to view it month by month, and how to use it for business decisions. It is aimed at those who want to correctly understand how to view sold electricity and to organize an interpretation that can be used directly for design, comparison, and explanation.

Table of Contents

• What does the E_Grid value indicate?

• Reading 1｜Do not interpret E_Grid as the same as annual power generation

• Reading 2｜Follow the factors that reduce E_Grid in order from the earlier stages

• Reading 3｜Interpret seasonal differences in power sales using monthly E_Grid

• Reading 4｜Cautions when using E_Grid for business decisions

• Items to check together when reviewing E_Grid

• Common misinterpretations of E_Grid in practice

• The precision of on-site conditions affects the credibility of E_Grid

• Summary

What does the value E_Grid represent?

E_Grid is easiest to understand when thought of as a representative figure indicating the amount of electrical energy sent to the grid. The power produced by a solar power system is not all sold to the grid as-is. After factors such as irradiance conditions, shading, temperature, DC-side losses, wiring losses, and conversion losses, the amount that is ultimately sent to the grid is what E_Grid represents. Therefore, E_Grid is not an interim generation value but a number close to the final output.

It's very important to understand this positioning beforehand. This is because E_Grid, at first glance, looks like a value close to the amount of electricity sold to the grid, so it's easy to treat it with the same sense as the generated output itself. However, in reality, E_Grid is not the total amount generated but the value that arrives after losses. In other words, you need to read it as a result that includes not only how much the installation was able to generate, but also how much of that power was delivered to the grid.

Also, E_Grid is a number that is easy to use in practical explanations. Because it is closer to the perspective of electricity sales and grid interconnection than annual generation, it is more commonly referenced when examining project viability and financial assessment. However, precisely because it is easy to use, it is important not to over-rely on it. If you judge a project solely by E_Grid, it becomes difficult to see whether that figure is the result of specific losses, whether there is room for improvement in the design, or whether it stems from inherent differences in natural conditions.

Furthermore, E_Grid may look useful for comparative evaluation, but a simple comparison is risky if the underlying assumptions differ. Differences in solar irradiation, orientation, tilt, shading conditions, equipment configuration, or grid-side conditions mean that differences in E_Grid will reflect a mix of multiple factors. Therefore, although E_Grid is a convenient figure that is close to the final result, it must always be read together with its background. This is the starting point for interpreting E_Grid.

Interpretation 1｜Do not view E_Grid as the same as annual power generation

The first thing to keep in mind when reading E_Grid is not to interpret it as having the same meaning as annual electricity generation. Because both appear to represent annual amounts of electricity, beginners tend to treat the two as essentially the same. However, in practice their roles are different. Annual electricity generation is an entry figure for grasping how much a facility was able to generate, whereas E_Grid is closer to an exit figure showing how much of that was sent to the grid.

If you don't understand this difference, the interpretation of the results will be ambiguous. For example, even if the annual energy production looks sufficient, E_Grid may not increase as much as expected. In that case, the upstream solar irradiance or light-receiving conditions may not be bad, but losses in the downstream stages may be taking effect. Conversely, even if the annual energy production isn't that large, if downstream losses are well controlled, E_Grid can still show a solid result. In other words, E_Grid is not simply another way of saying energy production; it is a number that reflects the quality of the generation and how it is delivered.

What often happens in practice is that people look only at the annual generation figures, judge that things are broadly fine, and then treat E_Grid with the same mindset. However, if you consider the volume of electricity sold or the grid-side outlook, E_Grid is actually more directly relevant. By seeing how much E_Grid differs from the annual generation, the significance of downstream losses becomes apparent. If you take comfort in the annual generation alone without checking this difference, it can lead to mistaken expectations in practice.

Also, this distinction is important when explaining things. When presenting numbers to internal teams or clients, describing annual generation and E_Grid in the same way will mix up their meanings for the audience. Annual generation is an indicator of the overall generation scale of the installation, while E_Grid is better framed as a resultant value closer to electricity sold or transmitted to the grid; organizing your explanation this way makes it easier to understand. This distinction is especially important in discussions of commercial viability and operational planning.

What beginners should first internalize is the awareness that when they look at E_Grid, the value is not the total amount generated but a figure closer to the amount ultimately delivered. Simply having this awareness will markedly change how E_Grid appears.

Reading 2｜Tracing the factors that reduce E_Grid sequentially from upstream stages

The next important point when reading E_Grid is to trace, in sequence from the upstream stages, how those numbers were produced. E_Grid is an output number, but looking only at the output won’t tell you why. In practice, what matters is considering, in the order of solar irradiance conditions, incident light conditions, DC-side losses, and subsequent conversion and wiring losses, where and by how much reductions occur. Viewing it in this order will considerably deepen your understanding of the E_Grid number.

First are the solar irradiation conditions. The foundation is how much solar resource is available at the site. Next comes how that solar radiation is actually received by the installation surface — that is, azimuth, tilt, irradiance conditions, and shading conditions. This is the preliminary stage. Then the power obtained there suffers losses on the DC side, and after wiring and conversion reaches the AC side, it ultimately appears as E_Grid. In other words, E_Grid is the result of passing through all of these stages.

This perspective is useful in practice because it makes it easier to pinpoint causes that cannot be determined by looking only at the magnitude of E_Grid. For example, when E_Grid is lower than expected, the countermeasures differ depending on whether the cause is upstream influences, thermal losses on the DC side, or downstream conversion and wiring. If there is a large reduction upstream, it may be necessary to reconsider the layout or on-site conditions. If the reduction occurs downstream, there may be room to review the equipment configuration or grid-side conditions.

What is important here is not to treat all losses as having the same weight. Losses in earlier stages reduce the foundation for all subsequent stages. In other words, shading and deterioration of irradiance conditions are losses that are hard to recover through later-stage efforts. Conversely, losses in later stages act on the energy that has already passed through the earlier stages. Therefore, even with similar percentages, the practical implications differ between early-stage and late-stage losses. When reading E_Grid, it is very important to be aware of this sequential relationship.

As a practical reading method, after looking at E_Grid you should make a habit of returning to the annual generation, the DC-side results, the loss diagram, and the loss breakdown. Rather than simply staring at the E_Grid numbers themselves, by reading them in reverse — tracing back the flow that led to them — it becomes easier to see which parts of the design should be reviewed. When you can read it this way, E_Grid ceases to be just a result value and becomes a figure that serves as the starting point for finding problems.

How to Read 3 | Using Monthly E_Grid to Analyze Seasonal Differences in Electricity Sales

E_Grid is often checked as an annual value, but to improve accuracy in practice it is essential to look at it on a monthly basis. The annual E_Grid alone does not reveal which seasons support that figure or when the largest drops occur. By examining monthly E_Grid, seasonal differences in electricity sales become apparent, revealing project-specific quirks that are not visible in the annual value.

First, what you want to focus on are the peaks and troughs over the year. Look at which seasons E_Grid rises and which seasons it falls. This is similar to viewing monthly generation, but E_Grid also reflects downstream losses and the amount reaching the grid, so it conveys more information than generation alone. For example, if there is abundant solar radiation in summer but E_Grid doesn’t increase as much as expected, temperature losses or downstream losses may be at work. If it drops sharply in winter, shading or orientation effects may be strongly impacting the amount sold to the grid.

The purpose of looking at monthly E_Grid is not simply to grasp which months have higher or lower values. What matters is whether those ups and downs look natural, and considering the loss factors behind them. For example, if values are stable in spring and autumn but plateau in midsummer, you should suspect temperature effects. If there is a sudden drop from autumn to winter, you need to consider shading or problems with light-receiving conditions at low solar elevations. Being able to read these seasonal differences lets you use E_Grid as more than just a single annual number.

In practice, the monthly E_Grid is extremely useful as explanatory material. Annual power sales projections alone tend to be abstract, but by showing monthly power sales trends you can convey the characteristics of a project to stakeholders concretely. In particular, indicating which seasons have strong power sales and which seasons warrant a cautious outlook makes it easier for them to gain a sense that cannot be conveyed by annual figures alone.

One thing beginners often overlook is that, because E_Grid is close to the amount of electricity sold, they assume annual values alone are sufficient. However, in practice, it is only when you look at how that sold electricity varies by season that the results become more convincing. If you want to master E_Grid, it is important to make a habit of examining monthly trends as well as the annual value.

How to Read, Part 4 | Points to Note When Using E_Grid for Business Decision-Making

E_Grid is a figure close to the amount of electricity sold, so it’s easy to use for business decisions, but that also requires caution. In practice, there are occasions when you may be tempted to take E_Grid at face value as an assumption for financials or planning. However, while E_Grid is a useful final output, you must remember that it is a simulation result based on assumptions. Getting this wrong can lead to overly simplified premises for business decisions.

First, be careful not to treat E_Grid as an absolute value. The figure is produced by the accumulation of various factors—solar irradiation conditions, orientation, tilt, shading, system configuration, temperature, conversion conditions, and so on—so if those assumptions change, E_Grid will change as well. Therefore, when using E_Grid for business decisions, you should not simply extract the numbers; you must also confirm the conditions behind them.

Next, it is important to align the assumptions when comparing multiple scenarios. Just because a scenario has a higher E_Grid does not, by itself, mean that scenario is better. If site conditions, shading, or system configuration differ, the meaning of the comparison changes. If you use E_Grid for business decisions, you need to read it with a clear understanding of what was changed in the comparison and what was held constant. If this is not done, it becomes easy to misunderstand the reasons for differences in E_Grid.

Also, although E_Grid is convenient for explanations, presenting it alone can actually lead to misunderstandings. For example, if you show only the annual E_Grid and say "this is the amount of electricity sold," the other party may perceive that number as definitive. In practice, however, it is more honest to also explain under which conditions that figure applies, how seasonal differences affect it, and where the uncertainties lie. E_Grid can serve as the centerpiece of an explanation, but it is not the whole story.

The basic approach for reading it for business decision-making is to use E_Grid as the entry point for the final expected electricity sales, and then check monthly trends, the loss structure, and the assumptions. By following this order, E_Grid becomes easier to use as a practical figure for financials and planning.

Items to Check When Viewing the E_Grid

To read E_Grid correctly, there are items you should check together rather than viewing it in isolation. First and foremost is the annual generation. By comparing the annual generation with E_Grid, you can get a sense of how much of the total generated energy is ultimately delivered to the grid. If this difference is larger than expected, you need to look into downstream losses and revisit the operating conditions.

Next, what I want to check are the specific yield and PR. These are not E_Grid itself, but they help capture the overall project's performance and coherence. Even if E_Grid appears large, if PR and specific yield are not that high, it may simply reflect favorable site conditions. Conversely, even if E_Grid is not particularly large, if specific yield and PR are stable, the design may be well balanced.

Even more important are the loss diagram and the loss breakdown. E_Grid is an output figure, so you cannot tell why it has that value unless you look at the losses. By checking items such as shading, temperature, array losses, wiring, and conversion, you can see why E_Grid is being reduced and where there is room for improvement. In practice, only by looking at both E_Grid and the losses do you gain confidence in the results.

Also, monthly results cannot be omitted. Because seasonal differences cannot be seen from the annual E_Grid alone, checking the monthly peaks and troughs makes it easier to determine in which seasons the effects of shading and temperature are strongest. Especially from the perspective of assessing power sales, looking not only at annual values but also at monthly trends contributes to practical accuracy.

In this way, E_Grid is a central figure, but it only becomes meaningful when viewed together with related parameters. The basic way to read PVSyst is not to take E_Grid in isolation, but to read it in connection with the surrounding numbers.

Common Misreadings of E_Grid in Practical Work

There are several common misinterpretations of E_Grid in practical work. The most frequent is treating E_Grid the same as power generation. As mentioned above, E_Grid is a figure closer to the amount of electricity ultimately delivered to the grid, and its meaning differs from the total electricity generated by the equipment. Using it without being aware of this difference can make the interpretation of results ambiguous.

Another common mistake is to assume that a project is fine if E_Grid is high. Even if E_Grid looks high, you cannot tell whether that is due to favorable solar irradiance conditions or because the design is excellent. If you are reassured by E_Grid alone without examining the loss structure, you may overlook projects that have room for improvement. Conversely, even if E_Grid is somewhat low, the design may be entirely reasonable given harsh conditions.

Also, evaluating E_Grid solely by its annual value is a common misunderstanding. Even if it appears fine on an annual basis, there can be significant monthly disparities. Features such as a large drop in winter or sluggish growth in summer cannot be seen from annual E_Grid alone. When assessing electricity sales, it is important to check trends down to the monthly level.

Moreover, it is risky to compare only E_Grid in a comparative review. If you simply compare proposals that differ in site conditions, shading conditions, and equipment configuration, the meaning of those differences becomes ambiguous. If you decide superiority based solely on E_Grid without organizing what was changed and what was held constant in the comparison, decision-making in practice tends to become inconsistent.

To avoid such misinterpretations, it is important to treat E_Grid not as a standalone answer but as a resultant value for tracing causes. Once this way of thinking is adopted, E_Grid becomes a much more manageable number.

The accuracy of on-site conditions influences how convincing E_Grid is

To use E_Grid figures in practice as numbers that inspire confidence, the accuracy of on-site condition assessment is critically important. E_Grid is a figure close to the final electricity sales volume, but it incorporates many site-level details such as orientation, tilt, spatial relationships to obstacles, shading, and installation conditions. In other words, if the understanding of on-site conditions is vague, the interpretation of E_Grid will also be vague.

For example, when E_Grid in winter is lower than expected, determining whether this is truly due to insufficient solar irradiance or the effect of shading at low solar altitude requires accurately understanding the site's spatial relationships. Likewise, when E_Grid underperforms in summer, you need to consider not only temperature conditions but also the influence of installation methods and the surrounding environment. The accuracy of such judgments depends on how precisely the site is understood.

In practice, an arrangement that looks fine on drawings can produce different shadowing on site because distances to obstacles and differences in elevation change how shadows appear. Those differences ultimately show up as differences in the E_Grid. Therefore, if you truly want to make full use of the E_Grid, it is essential to be mindful of consistency with the actual site rather than just reading the numbers on the screen.

In that sense, for practical work where you want to grasp on-site positional relationships with high accuracy, it naturally leads to using LRTK with an iPhone-mounted GNSS high-precision positioning device. Making it easier to carry out high-accuracy on-site position checks, distance measurements to obstacles, and orientation confirmations helps organize the prerequisites to enter into PVSyst and makes the E_Grid figures more convincing. In practice, it is very important not to leave the assessment of expected power sales to desk calculations alone, but to include the precision of on-site understanding.

Summary

When reading E_Grid in PVSyst, it is important first not to view it as having the same meaning as annual generation. From there, follow the flow in order from upstream to downstream — from solar irradiation conditions to incident irradiance conditions, to the DC side, and to downstream losses — check seasonal differences using monthly E_Grid, and finally clarify the assumptions when using it for business decisions. Simply mastering these four ways of reading E_Grid will make it not just a result value but a strong practical clue for assessing electricity sales volume.

What's important is to use E_Grid as a convenient final figure while not losing sight of the losses and design conditions behind it. By thinking about why the E_Grid figure is what it is, rather than focusing on the number itself, you can improve the quality of design refinement, comparative assessments, and explanatory materials. Interpreting the amount of electricity sold is not about reading the final output figure, but about reading the structure that leads to it.

And to make that interpretation more reliable, it is essential to grasp the site’s positional relationships with high precision. If you want to organize the relationships among shadows, orientation, and obstacles more accurately, the perspective of leveraging an iPhone-mounted GNSS high-precision positioning device, LRTK, can also be effective. By combining the ability to correctly read PVSyst’s E_Grid with the ability to accurately capture site conditions, it becomes easier to arrive at more convincing estimates of expected electricity sales and to make sound design decisions.