4 Ways to Read PVSyst's E_User | How to Check Self-Consumption

When working on the design and generation forecasting of solar power systems in practice, it's important not only to look at figures related to the amount of electricity sold to the grid but also to know how to interpret numbers related to self-consumption. In particular, for self-consumption projects, if you only consider how much was generated and don't break down how much of that was used on-site by the facility and how much of the shortfall was supplied by the grid, you won't be able to judge the validity of the design or identify directions for operational improvements. A representative item to check in this regard is E_User.

However, E_User is a number that can be easily misinterpreted from its name alone. If you confuse whether it refers to the amount generated, the solar energy actually used, or the facility’s total demand, its relationship with E_Solar, EFrGrid, and SolFrac becomes ambiguous. In PVSyst’s self-consumption calculation, because energy exchanges are evaluated on a time-step basis, E_User should be interpreted not as a mere reference value but as a figure that effectively forms the basis of the self-consumption simulation.

A reading that is truly useful in practice is not to view E_User as a single numerical value. Position E_User as the reference value on the demand side, and from there read how it connects with E_Solar, EFrGrid, E_Grid, and SolFrac. Doing so reveals things that a simple check of annual generation would not, such as how easy self-consumption is, the validity of the load profile, and time‑of‑day mismatches.

This article explains how to read PVSyst’s E_User in practical work by organizing the discussion from four perspectives. First, it clarifies the meaning of E_User; next, it examines the relationship with E_Solar and EFrGrid; then it checks the assumptions of the load profile; and finally it summarizes the flow by connecting the analysis to month-by-month results and operational improvements. As a method for verifying self-consumption, the content is organized in a form that can be used directly for design, comparison, and explanation.

Table of Contents

• Start by clarifying what E_User is

• 読み方1｜Interpret E_User as "demand" rather than "generation"

• 読み方2｜Consider it together with E_Solar・EFrGrid・SolFrac

• 読み方3｜First confirm the assumptions of the load profile

• 読み方4｜Use monthly E_User to assess deviations in self-consumption

• Numbers you should check together with E_User

• Common misinterpretations of E_User in practice

• The accuracy of site conditions influences confidence in self-consumption assessments

• Summary

Clarify at the outset what E_User is

In PVSyst's self-consumption calculation, E_User is treated as the user's electrical demand, that is, the energy the user needs to consume. In the official documentation, E_User is defined as the user's needs, or the energy the user will consume, and the self-consumption calculation proceeds based on this demand. The important point here is that E_User is not the energy produced by solar PV generation itself. E_User is a demand-side figure, not a supply-side figure.

If we first organize this definition, the role of E_User becomes much clearer. In solar power self-consumption calculations, you first determine how much demand there is on the user side; of that demand, the portion covered by solar is E_Solar, and the portion that was unmet and supplied by the grid is EFrGrid. In other words, E_User is the total amount of demand, and its breakdown is divided into self-consumption and purchased electricity.

PVSyst's official explanation is organized as E_Solar = E_User - EFrGrid, SolFrac = E_Solar / E_User. As can be seen from this, because E_User serves as the denominator or reference value, misreading E_User will shift the interpretation of SolFrac and the self-consumption rate. If you want to look at self-consumption but read E_User as if it were generated energy, the relationships between the numbers all become ambiguous.

Also, because self-consumption calculations are evaluated as instantaneous exchanges at each time step, E_User is essentially defined not just by how it appears as an annual total but as a time-of-day profile. Even if the annual totals are the same, a load with higher daytime demand and a load with higher nighttime demand will differ completely in how easily self-consumption can be achieved. Therefore, E_User should be read not as mere annual energy consumption but as a representative value of demand that includes a time-of-day profile.

Reading 1｜Read E_User as "demand" rather than "generation"

The first point when reading E_User is to read it as demand rather than generation. This may seem simple but it is extremely important. In self-consumption projects, attention naturally tends to focus on the solar-side generation, so it’s easy to perceive all the figures in the report as supply-side numbers. However, E_User is not on the supply side; it represents the amount of electricity the user needs.

If you don't understand this difference, you may, for example, mistakenly interpret a large E_User as "high self-consumption." In fact, a large E_User only means that the facility's or building's demand is high. How much of that demand was covered by solar can only be known by looking at E_Solar or SolFrac. Even if E_User is large, if most of it is supplied from the grid, it may not be functioning adequately as a self-consumption system.

The reason this way of reading is important in practice is that it allows you to separate total demand from total self-consumption. For example, in cases such as factories, warehouses, or offices where daytime loads are large, a large E_User can itself be interpreted as indicating a large capacity to absorb solar power. On the other hand, in residences or facilities that operate mainly at night, even if E_User is large it may not align with solar generation hours and therefore may not lead to self-consumption. In other words, you need to consider not only the magnitude of E_User but also its temporal pattern.

An easy-to-grasp example is two facilities with the same annual consumption. Assume one operates mainly during the daytime and the other has a larger load at night. Even if their annual E_User is similar, the former will tend to see higher E_Solar, while the latter will tend to have a larger EFrGrid. This difference stems more from differences in the time-of-day profile of E_User than from differences in the performance of the generation equipment. Therefore, when examining E_User, it is essential to first understand it as a quantity of demand and to be aware of when that demand occurs.

How to Read 2｜Read Together with E_Solar, EFrGrid, and SolFrac

E_User is not a number to be viewed in isolation. If you want to confirm self-consumption, you must read it together with E_Solar, EFrGrid, and SolFrac. In PVSyst’s official breakdown, E_User is split into E_Solar and EFrGrid, and SolFrac is calculated as E_Solar / E_User. In other words, E_User is a reference value for evaluating self-consumption, not a standalone evaluation metric.

First, by looking at E_Solar you can see the portion of E_User that was covered by solar. This is the energy that was self-consumed. If E_User is large but E_Solar is small, the case can be interpreted as having high demand but not making sufficient use of solar. Conversely, even if E_User is not very large, a high E_Solar ratio makes it easier to view the case as having a high level of self-consumption. In other words, E_User is the total demand, and E_Solar is the amount of that demand met by solar.

Next, by looking at EFrGrid you can see the portion of E_User that was supplied by the grid to cover shortfalls. This is the energy that occurs at night, during cloudy periods, or at times when demand exceeds generation. If EFrGrid is large, it may indicate that the timing of demand does not align with solar generation, that solar capacity is insufficient for demand, or both. Looking at E_User alone does not reveal how easy self-consumption is, but examining EFrGrid together makes the degree of grid dependence apparent.

SolFrac is the ratio that indicates how much of the total demand was covered by solar power. Because SolFrac assesses E_Solar using E_User as the denominator, if the interpretation of E_User is off, the meaning of SolFrac will also shift. For example, a high SolFrac does not, on its own, mean that the entire project is superior, but it can at least be read as indicating a high contribution of solar to demand. Conversely, if SolFrac is low, solar power can be considered not to have become the primary supply source for the demand.

In practice, reading these four side by side makes it much easier to organize. If E_User is large, E_Solar is also large, EFrGrid is kept low, and SolFrac is high, it is clearly structured as a self-consumption type. If E_User is large but E_Solar does not increase and EFrGrid is large, you can read that there is demand but a strong time-of-day mismatch, or that equipment capacity or operating conditions may warrant reconsideration. In this way, E_User only gains practical meaning when read in relation to the other figures.

How to Read 3｜Confirm the assumptions of the load profile first

To use E_User correctly in practice, it is essential to confirm the assumptions behind the load profile before considering the numerical value. In PVSyst's official description, the evaluation of self-consumption deals with instantaneous energy exchanges, so the user's needs profile must be defined as an input. In other words, E_User is not a number that simply appears after the calculation; it is a value that strongly depends on the original load settings.

Furthermore, PVSyst can import load profiles from hourly or sub-hourly CSV files and rescale them to match annual consumption as needed. This is a convenient feature, but conversely it also means that the meaning of E_User can change significantly depending on how the load profile is positioned. If you only match the annual consumption while the time‑of‑day distribution is far from reality, E_User, E_Solar, and EFrGrid can all end up looking plausibly correct on the surface.

In actual practice, a common situation is that the annual consumption is known, but there is insufficient time-of-day measurement data, so representative load patterns are used as substitutes. In this case, even if the annual total of E_User does not look out of place, if the proportion of daytime load, holiday operation, seasonal variations, and so on differ from reality, the expected self-consumption can change significantly. In other words, the accuracy of interpreting E_User can be considered to be roughly proportional to the accuracy of the load profile.

For example, if you simulate using a typical office load that is concentrated during daytime, the proportion of E_Solar to E_User tends to be higher. However, in reality, if HVAC and equipment start-ups are concentrated in the mornings and evenings, or if there is little operation on weekends, the viability of self-consumption changes. Conversely, in facilities with relatively steady loads, such as factories or refrigeration equipment, the temporal concentration of E_User can more easily support self-consumption. In other words, E_User is not just the total amount of demand; essentially, it is the way that demand is distributed.

The perspective practitioners should adopt here is that, even if the E_User numbers look clean, they should first ask themselves, "Does this load profile really represent the actual site conditions?" When verifying self-consumption, it is fair to say that the first thing to do is not to stare at the resulting numbers but to question the assumptions about demand that underlie them.

Interpretation 4 | Reading discrepancies in self-consumption with monthly E_User

Even if E_User is viewed only as an annual value, you cannot fully understand how likely self-consumption is to be realized. Therefore, a method that is useful in practice is to read the deviations in self-consumption using monthly E_User. By looking at monthly demand levels, it becomes easier to see in which seasons demand is strong and in which it is weak, and where the match with generation is good or poor.

What you should look at here is not the absolute size of monthly E_User itself, but how it combines with the generation side's seasonal variability. For example, facilities with higher demand in summer tend to overlap with the seasonal characteristics of solar power generation, making self-consumption more likely. Conversely, at facilities where demand concentrates in winter and the share is higher in the morning/evening or at night than during the daytime, E_User may be large but E_Solar is unlikely to grow much, and EFrGrid tends to increase. In other words, monthly E_User should not be compared to generation alone, but used as material to read demand seasonality and time-of-day trends.

A clear example is the difference between facilities with strong cooling demand and those with strong heating or hot-water demand. The former tend to have heavy daytime demand in summer and may be well suited to self-consumption. The latter tend to have large loads in winter and during mornings and evenings, and even if annual E_User is large, the E_Solar ratio may not increase easily. Even if the annual total E_User is similar, the monthly pattern of demand can significantly affect the viability of self-consumption.

Also, reviewing monthly E_User can provide hints for operational improvements. If the annual E_User is sufficient but self-consumption does not grow as expected, there may be room for load shifting. By operating equipment that can be moved to daytime, changing operating hours for air conditioning, thermal storage, and charging equipment, and other demand-side measures, it may be possible to increase E_Solar. In PVSyst’s official documentation, demand-side management—i.e., DSM—is also stated to be important for optimizing self-consumption.

If you can interpret it this way, E_User can be used not merely as a measure of consumption but as an indicator to identify opportunities for improving self-consumption. Rather than stopping at annual values, reading deviations in monthly E_User and considering how to reduce those deviations is a practical way to verify self-consumption.

Numbers to review when viewing E_User

Instead of looking at E_User in isolation, there are figures you should check together. The most important is E_Solar. This is the portion of E_User covered by solar power, so simply looking at how much E_Solar there is relative to E_User reveals a lot about actual self-consumption. If E_User is large but E_Solar is small, you can interpret that there is room for growth as a self-consumption model, or that the timing doesn't match.

Next to check is EFrGrid. This is the portion of E_User that was made up by the grid. In self-consumption projects, looking at how much EFrGrid remains reveals the level of dependence on the grid. Projects with strong daytime demand tend to have suppressed EFrGrid, while projects with strong nighttime demand tend to have larger EFrGrid.

Furthermore, SolFrac is also important. Because it is an indicator that evaluates E_Solar with E_User as the denominator, it reveals the contribution of solar to total demand. Whether E_User is large or small alone does not indicate the feasibility of self-consumption, but by looking at SolFrac you can more easily see to what extent demand is being met by solar.

Additionally, checking E_Grid makes it easier to determine time-of-day mismatches with self-consumption. If E_User is large while E_Grid is also large, it may indicate that there is demand but the timing does not align, resulting in a large daytime surplus. In other words, by placing E_User and E_Grid side by side, you can see the surplus that could not be used for self-consumption. This perspective can also inform considerations for operational improvements and the introduction of battery storage.

Common misinterpretations of E_User in practice

There are several common misinterpretations of E_User in practice. The most frequent is to assume E_User is "the amount supplied by solar power." In reality, E_User is the user's total demand, and the amount supplied by solar is E_Solar. If this confusion occurs, interpretations of the self-consumption rate and views on grid dependence will all be skewed.

Another common mistake is to simply assume that projects with larger E_User are more favorable for self-consumption. It is true that having a larger demand sink is advantageous, but that is only the case when the timing aligns. If demand is skewed toward nighttime or early morning, even with a large E_User EFrGrid tends to increase and E_Solar is less likely to grow. It is risky to judge the suitability of self-consumption based solely on the size of E_User.

Also, it is a common mistake to assume the load settings are reasonable by looking only at the annual E_User. In PVSyst you can use hourly or sub-hourly load profiles and rescale them to match the annual consumption. Therefore, even if the annual total alone looks plausible, if the hourly or holiday patterns differ from reality, the self-consumption calculation results will be far from accurate.

Also, being satisfied with checking E_User and not looking at E_Solar, EFrGrid, and SolFrac is another misinterpretation. E_User is a reference value, not an evaluation metric in itself. If you draw conclusions based only on the reference value, you will end up without understanding whether self-consumption will be successful. In practice, when you look at E_User it is important to always proceed to its breakdown.

The accuracy of on-site conditions influences confidence in evaluating self-consumption

E_User itself is a demand-side figure, but the overall confidence in evaluating self-consumption is greatly influenced by the accuracy of understanding on-site conditions. This is because the viability of self-consumption is not determined by demand alone; it also varies significantly with the generation side’s orientation, tilt, shading, installation location, and relationship with nearby obstructions. No matter how reasonable E_User is, if the assumptions about the generation side are misaligned with the actual site, the way E_Solar and E_Grid appear will change, and the assessment of self-consumption will become inconsistent.

For example, even if a facility with strong daytime demand appears suitable for self-consumption, if surrounding obstructions cast significant shadows and generation is reduced for part of the daytime, the energy available for self-consumption will be less than expected. Alternatively, depending on the installation location and orientation, the way it overlaps with demand can change. In other words, to make practical use of E_User readings, it is necessary not only to consider the demand side but also to accurately understand the site’s positional relationships and then set up the generation-side conditions.

In practice, even if something appears fine on the drawings, slight positional shifts or elevation differences at the site can change the irradiation conditions. Those differences ultimately show up as differences in E_Solar, E_Grid, and SolFrac. Therefore, if you want the method for verifying self‑consumption to be truly practical, you should pay as much attention to the accuracy of assessing site conditions as to the accuracy of the load profile.

In that regard, in practical work that requires highly accurate understanding of on-site positional relationships, one naturally turns to LRTK — an iPhone-mounted, high-precision GNSS positioning device. By making it easier to carry out high-precision on-site position checks, distance measurements to surrounding objects, and confirmation of orientation and layout, it becomes easier to organize the assumptions on the generation side, and it also makes self-consumption evaluations that start from E_User more convincing. Correctly reading demand-side figures and accurately capturing on-site conditions are inseparable in self-consumption assessments.

Summary

When reading PVSyst's E_User, first make clear that it represents demand rather than generation; then review it together with E_Solar, EFrGrid, and SolFrac; also question the assumptions behind the load profile; and analyze monthly E_User to identify deviations in self-consumption and opportunities for improvement. With these four perspectives, E_User stops being just a number and becomes a practical benchmark for judging self-consumption.

The important point is not to stop at looking at E_User. E_User is the baseline, from which it splits into E_Solar and EFrGrid and ultimately connects to how SolFrac and E_Grid are perceived. In other words, reading E_User correctly is also reading the entire structure of self-consumption. If you consider not only the total demand but also time of day, seasonality, and the validity of the load profile, PVSyst’s self-consumption calculation becomes a quite practical tool.

And to make that interpretation even more certain, it is indispensable to grasp the on-site positional relationships with high accuracy. If you want to organize the generation-side assumptions more precisely, the perspective of utilizing LRTK in iPhone-mounted high-precision GNSS positioning devices is also effective. By combining an E_User-based interpretation of self-consumption with the ability to accurately pinpoint site conditions, it becomes easier to arrive at more convincing design decisions and operational improvements.