How to Check the Self-Consumption Rate in PVSyst | 4 Points for Interpreting the Results

Table of Contents

• What the self-consumption rate indicates

• Conditions to prepare before checking the self-consumption rate in PVSyst

• How to interpret results 1: examine the temporal overlap between generation and load

• How to interpret results 2: look at self-consumed energy and surplus electricity

• How to interpret results 3: see the difference between self-consumption rate and self-sufficiency rate

• How to interpret results 4: examine monthly and time-of-day variations

• Design conditions to check when the self-consumption rate is low

• How to interpret results when considering batteries and control strategies

• Points to note when explaining the self-consumption rate in a report

• Methods to improve the accuracy of the self-consumption rate by reflecting site conditions

• Summary

What does the self-consumption rate indicate?

The self-consumption rate is an indicator that shows the proportion of the electricity generated by solar power that is used directly within a building, factory, or facility. If all the generated electricity can be consumed on site, the self-consumption rate is high; if generation exceeds demand and a large surplus occurs, the self-consumption rate is low. When considering self-consumption type solar power systems, this self-consumption rate greatly influences system sizing and investment decisions.

For example, even if the annual power generation is large, if much of it is exported as surplus power, it may not sufficiently reduce the building's electricity purchases. Conversely, even if the generation itself is moderate, if daytime load and generation timing overlap well, the generated electricity can be used efficiently and the practical benefits increase. The purpose of checking the self-consumption rate in PVSyst is not only to increase the output of the generation equipment, but to determine whether the system size is appropriate for the demand.

One point to note here is that the self-consumption rate is not an indicator that can be simply judged as "the higher, the better." If system capacity is reduced, a larger share of the generated electricity can be used on-site, so the self-consumption rate can appear high. However, if the system capacity is too small, the amount of purchased electricity that can be reduced is also limited. Conversely, increasing system capacity raises annual electricity generation, but can increase surplus electricity and lower the self-consumption rate. In other words, the self-consumption rate should not be viewed in isolation; it needs to be considered together with annual generation, electricity load, surplus electricity, and the reduction in purchased electricity.

Also, there is a metric that is often confused with the self-consumption rate: the self-sufficiency rate. The self-consumption rate is a metric that looks at “of the electricity generated, how much was used by the site.” On the other hand, the self-sufficiency rate is a metric that looks at “of the electricity consumed by the facility, how much was covered by solar power generation.” It is easier to organize your thinking if you consider that the self-consumption rate views things from the generation side, while the self-sufficiency rate views them from the demand side. When checking PVSyst results, if you do not make clear which metric you are looking at, misunderstandings can arise in internal explanations or when explaining to customers.

When using the self-consumption rate in design practice, there are three main objectives. The first is to verify that the capacity of the photovoltaic system is not excessive relative to demand. The second is to consider how to handle surplus power. The third is to determine whether additional measures such as batteries, output control, or load shifting are necessary. PVSyst is software that is easy to use from the early design stages through detailed analysis because it enables relatively systematic verification of the results needed for these decisions.

Conditions to Prepare Before Verifying Self-Consumption Rate in PVSyst

To correctly verify the self-consumption rate in PVSyst, you must prepare the input conditions before viewing the results screen. The self-consumption rate is not determined by generation alone. It can change significantly depending on load data, system capacity, installation azimuth, tilt angle, meteorological conditions, loss settings, whether a battery is present, and the approach to feed-in or surplus handling. Therefore, rather than judging solely by the numerical results, it is essential to always confirm under what conditions the results were calculated.

First and foremost, the load conditions are important. To calculate the self-consumption rate, you need the temporal relationship between generation and demand. If you only input annual electricity consumption, you will not know how much electricity is used during the daytime, how much the load drops on holidays, or how the load changes with the seasons, and the accuracy of the self-consumption rate will not improve. In practice, it is desirable to prepare load data at as fine a time resolution as possible—at minimum data that reveal monthly trends or representative-day patterns.

In factories, warehouses, offices, shops, and public facilities, load profiles vary greatly. In factories, weekday daytime operating loads are high, which can make them well suited to self-consumption solar systems. Conversely, facilities that cease operations on holidays or during long vacations tend to see increased surplus power during those periods. In schools and public facilities, seasonal usage patterns, air-conditioning loads, and closed days have an impact. When checking the self-consumption rate in PVSyst, the starting point is to confirm whether these facility-specific load characteristics are being reflected.

Next, configure the generation-side conditions. The power output of a solar PV system is affected by the site’s solar irradiance, the panel surface’s azimuth and tilt, shading, temperature conditions, wiring losses, equipment losses, and other factors. If the resulting self-consumption rate is lower than expected, it may not only reflect poor overlap with the load but also that the generation peak is skewed toward specific time periods. For example, a design with south-facing panels whose generation peak is concentrated around noon and a design that spreads generation into morning and evening by orienting panels east–west will differ not only in annual energy yield but also in how the self-consumption rate appears.

Also, setting the system capacity is important. If the generation system is too large relative to demand, large surpluses tend to occur during sunny daytime hours and the self-consumption rate is likely to fall. Increasing system capacity will raise generation, but it can also increase the amount of time when the generated electricity cannot be fully used. In self-consumption-oriented designs, it is important to consider capacity in balance with the load rather than simply filling the entire available installation area with panels.

When battery storage is included, charging and discharging conditions also affect the self-consumption rate. Using a battery can increase the self-consumption rate because excess power generated during the day can be shifted to the evening or nighttime. However, if the battery capacity is too large or too small, it may be difficult to achieve the expected effect. It is necessary to check the charge/discharge efficiency, discharge time periods, seasons when the battery tends to become fully charged, and time periods when it cannot be fully discharged.

The results from PVSyst are calculated based on the input assumptions. Therefore, when verifying the self-consumption rate, it is important to review not only the result screens but also the load settings, power generation system conditions, loss assumptions, battery conditions, and the handling of surplus power together. In particular, for internal reviews and materials submitted to clients, rather than showing only the numerical results, being able to explain the assumptions used for the calculations as a set will increase the reliability of the assessment.

How to Interpret Results 1: Observe the Temporal Overlap between Power Generation and Load

When checking the self-consumption rate, the first thing to look at is how much generation and load overlap in the same time periods. Solar PV generates during daytime, but if the facility's electricity demand does not occur in those same periods, it is unlikely to translate into self-consumption. In PVSyst results, by examining the relationships between generation and load not only on an annual basis but also by month, by day, and by time of day, the background behind the self-consumption rate becomes clear.

For example, at facilities with high daytime loads, generation and demand are more likely to overlap. If air conditioning, lighting, production equipment, pumps, or refrigeration and cold-storage equipment are operating during the day, there is a higher likelihood that solar power can be used on site. In this case, if the system capacity is appropriate, the self-consumption rate tends to be relatively high. Conversely, at facilities with large loads at night or in the early morning, the generation hours of solar power and the demand hours are misaligned, so much of the generated power tends to become surplus.

When viewing results in PVSyst, it is important not to judge solely by the annual total generated energy and the annual total load. Even if generation and load appear close on an annual basis, generation may actually be concentrated at noon on sunny days while loads occur at night or in the early morning. In such cases, looking only at the annual energy balance may seem acceptable, but the actual self-consumption rate will be low. When evaluating self-consumption, not only the total amount of energy but also the temporal alignment is important.

What you particularly want to check is how much load exists at the power generation peak. While generation reaches its maximum around noon on sunny days, if the facility load during that period is small, surplus power will increase. Conversely, if air conditioning or production equipment is operating around noon, the generated power is more likely to be consumed. Check representative days and monthly trends in PVSyst’s result screens and output data to see whether the generation peak and the load peak overlap.

Also, the difference between weekdays and holidays is important. Even if weekday load is high and the self-consumption rate is large, if a facility is shut down on holidays, the generation during those days tends to become surplus. In annual results, such holiday effects can be averaged out and become less visible. For factories, schools, public facilities, offices, and the like, the load difference between business days and non-business days is large, so it is necessary to confirm that holiday patterns are reflected in the load data.

Seasonal differences should not be overlooked. In summer, cooling loads are high and generation is also large, so self-consumption tends to increase. By contrast, in spring and autumn generation can be high while cooling loads are low, causing surpluses to grow. In winter, generation falls in regions with low solar insolation, but facilities with daytime heating loads can still expect a certain level of self-consumption. In this way, by examining the monthly relationship between generation and load, you can identify which seasons influence the annual self-consumption rate.

When reviewing the results, it is easier to organize them by separating periods when power generation exceeds load from periods when load exceeds power generation. During periods when power generation exceeds load, surplus power occurs. During periods when load exceeds power generation, you need to purchase from external sources the portion that cannot be covered by solar power. To increase the self-consumption rate, consider reducing periods when power generation greatly exceeds load or implementing a mechanism to utilize the excess power in other time periods.

Thus, when checking the self-consumption rate in PVSyst, the first step is to examine the temporal overlap between generation and load. Rather than only noting whether the resulting figure is high or low, being able to explain on a time axis why that figure occurred will clarify the points for improving the design proposal.

How to Read the Results 2: Viewing Self-Consumption and Surplus Electricity

The next items to check are self-consumption and surplus electricity. The self-consumption rate is a percentage indicator, but it always corresponds to an amount of energy. In practice, it is important to check not only the percentage but also how many kWh are used within the facility each year and how many kWh are surplus. Looking only at the percentage can prevent a proper comparison of differences in system capacity and load scale.

For example, even if a design has a high self-consumption rate, the self-consumed energy itself may be small if the system capacity is small. Conversely, even if a design's self-consumption rate is somewhat lower, if the system capacity is large and the amount of electricity available for use within the facility is large, the reduction in purchased electricity can be greater. Therefore, in PVSyst results, it is necessary to check not only the self-consumption rate but also the self-consumed energy, surplus energy, and total generation together.

Surplus electricity is the portion of the electricity generated that could not be consumed within the facility. How surplus power is handled depends on the project policy. Design decisions vary depending on whether it is assumed to be exported externally, whether output will be curtailed, whether it will be used to charge batteries, or whether it will be redirected to other loads. If PVSyst results show a large surplus of electricity, we assess whether that surplus is acceptable or whether additional measures are required.

In particular, for self-consumption projects, there are often requests to minimize surplus power as much as possible. Depending on the incoming power equipment, contractual terms, and operational policies, there may be cases where you do not want to—or cannot—export surplus to the outside. In such cases, rather than designing solely to maximize annual energy production, it is necessary to limit the capacity to a level that is less likely to generate surplus. Comparing multiple system capacities in PVSyst and checking how much surplus energy increases makes it easier to grasp an appropriate capacity guideline.

When looking at surplus electricity, check not only the annual total but also which months have large surpluses. If surpluses are high in spring or autumn, generation may be exceeding demand during periods of low air-conditioning load. If surpluses are high on holidays, the cause is the load difference between operating days and non-operating days. If surpluses are high on sunny summer days, the system capacity may be too large or daytime load may be smaller than assumed. Examining monthly surpluses can reveal directions for design improvement.

Additionally, surplus electricity directly affects considerations for battery storage. If a surplus occurs during the daytime, charging that surplus into a battery and discharging it from the evening onward can potentially increase the self-consumption rate. However, the effectiveness of a battery depends on the time of day the surplus occurs, the magnitude of the surplus, and whether there is nighttime load. In projects with small surpluses, even if a battery is installed, there may be insufficient power to charge it. In projects with excessive surplus, increasing battery capacity may still not be able to absorb all of it.

Self-consumption and surplus electricity are metrics that are easy to use when comparing design proposals. For example, when the system capacity is increased slightly, check how much self-consumption increases and how much surplus electricity increases. If self-consumption increases only a little while surplus mostly increases, that capacity increase may be inefficient. Conversely, if increasing the system capacity greatly boosts self-consumption, you can judge that the facility has sufficient daytime load and that there is room for capacity expansion.

When reviewing PVSyst results, it is important not to be swayed by impressions based on percentages. Rather than evaluating only that the self-consumption rate is high or low, checking how much actual energy was consumed and how much was left over makes design decisions more concrete. For self-consumption solar PV systems, the basic way to interpret results is to understand the relationship between generation, load, self-consumed energy, and surplus energy as a single flow.

How to Read Result 3: Comparing the Self-consumption Rate and the Self-sufficiency Rate

When checking self-consumption results in PVSyst, the difference between the self-consumption rate and the self-sufficiency rate is something you should pay particular attention to. These two indicators may look similar, but their meanings are completely different. The self-consumption rate is a generation-side metric that indicates the proportion of generated power that was used within the facility. On the other hand, the self-sufficiency rate is a demand-side metric that indicates the proportion of the facility's power consumption that was covered by photovoltaic generation.

For example, if the generated power is small and the facility’s daytime load is large, most of the generated electricity is used within the facility, so the self-consumption rate becomes high. However, if the generated amount is small relative to the facility’s total power demand, the self-sufficiency rate is low. In this case, it can be interpreted as “the generated electricity is being used without waste, but it covers only a small portion of the facility’s total power.”

Conversely, if the generation capacity is large and a lot of surplus occurs during the daytime, the self-sufficiency rate may be somewhat high. This is because it can cover a wide range of the facility's daytime load, reducing the amount of purchased electricity. However, because part of the generated power cannot be used and remains unused, the self-consumption rate may decrease. In this case, it should be read as "it is effective in reducing the facility's electricity use, but it does not mean that all the generated electricity is being fully consumed."

If you do not understand this difference, you may misinterpret the results from PVSyst. For example, when a customer says "I want to increase the self-consumption rate," you need to confirm whether what they really want is to reduce surplus or to reduce the amount of purchased electricity. If they want to reduce surplus, the self-consumption rate is important. If they prioritize cutting electricity costs or reducing the amount of externally purchased electricity, the self-sufficiency rate and the reduction in purchased electricity are also important.

When you check the self-consumption rate and the self-sufficiency rate side by side in PVSyst results, it becomes easier to assess the appropriateness of the system size. If the self-consumption rate is very high while the self-sufficiency rate is low, there may be room to increase system capacity. If the self-consumption rate is low and the self-sufficiency rate is not as high as expected, there may be a large temporal mismatch with the load. If the self-consumption rate is low but the self-sufficiency rate is high, the generation system is contributing to demand reduction; however, you may need to consider surplus management or capacity adjustments.

These two indicators should be explained separately in internal briefings and proposal documents. "What percentage of the generated electricity can be used" and "what percentage of the facility's electricity consumption can be covered" mean different things to the audience. Presenting only the self-consumption rate can make a proposal with smaller installed capacity appear advantageous. Presenting only the self-sufficiency rate can make a proposal with large surpluses appear highly effective. Showing both allows you to convey the advantages and cautions of a design option in a balanced way.

Also, the self-consumption rate and the self-sufficiency rate are useful for assessing the impact of adding a storage battery. When a storage battery makes it possible to use surplus power at night, the self-consumption rate increases. At the same time, if the amount of electricity purchased at night decreases, the self-sufficiency rate also increases. However, depending on the battery capacity and operating conditions, there may be cases where the self-consumption rate rises but the improvement in self-sufficiency is small. This occurs when the battery cannot be sufficiently charged or when the nighttime load available for discharge is small.

In practice, when reviewing results it is important not to confuse the self-consumption rate and the self-sufficiency rate, and to be able to explain the meaning of each. Although PVSyst can perform detailed calculations, it produces many output metrics, so you need to read the results while clarifying what each number represents. The self-consumption rate is the degree to which generation is utilized, while the self-sufficiency rate is the degree to which demand is satisfied. By grasping this basic distinction alone, misinterpretation of the results is greatly reduced.

How to interpret the results 4: Viewing variations by month and time of day

When evaluating self-consumption rate results, it's dangerous to rely solely on the annual average. Solar PV generation and facility loads vary greatly by season, day of the week, and time of day. Even if the annual self-consumption rate appears to be above a certain level, excess can be concentrated in particular seasons, be large only on holidays, or occur only during certain daytime hours. To make practical use of PVSyst results, it is important to check monthly and time-of-day variations.

In monthly checks, we first look at the balance between power generation and load. Months with high solar radiation see increased generation, but that does not necessarily mean facility load also increases. In summer, many facilities experience higher air-conditioning loads, so generation and load may overlap more. Conversely, in spring and autumn, despite favorable solar conditions and higher generation, air-conditioning loads are relatively small, so surpluses tend to occur. In winter, generation may decline in some regions, but in facilities with heating and lighting loads, a certain amount of daytime self-consumption can be expected.

By looking at the monthly self-consumption rate, you can identify which months are driving the annual result. For example, even if the annual self-consumption rate is low, there may be only a few specific months with large surpluses while the other months are used relatively well. In this case, rather than judging the entire installation as inappropriate based solely on the annual value, there is room to consider operational changes or load shifting for the months prone to surplus. Conversely, if surpluses are large in every month, the installation’s capacity may be too large relative to demand.

When checking by time of day, we look at the mismatch between the generation peak and the load peak. In general, solar power generation produces electricity during the daytime, but a facility’s load varies by industry. Facilities with high morning loads, facilities with high afternoon loads, and facilities whose loads persist into the evening will have different self-consumption rates even with the same installed capacity. Because adjusting the installation orientation can slightly shift the generation period, time-of-day results can provide hints for design improvements.

For example, if surpluses are concentrated around noon, options to consider include slightly reducing equipment capacity, distributing generation in the east–west direction, increasing loads that can be operated during the daytime, and using batteries. If loads are high in the morning and surpluses occur in the afternoon, reviewing the orientation of generation and load operation can be effective. If the amount of purchased electricity from the evening onward is large, it is worth considering the effect of time-shifting with batteries.

Variations by day of the week are also important. In facilities where the load changes significantly between weekdays and holidays, the annual average alone makes it difficult to see the actual situation. There may be cases where the self-consumption rate is high on weekdays but there is a large surplus on holidays, which pulls down the annual figure. For such projects, it is necessary to decide on an operational policy: whether to accept the holiday surplus, to reduce the system capacity, or to redirect the surplus to loads that also operate on holidays.

When reviewing PVSyst results internally, it's easier to understand if you look at the annual values, monthly values, and the representative day's hourly graphs and outputs in that order. Use the annual values to grasp overall trends, the monthly values to check seasonal factors, and the hourly results to identify mismatches between generation and load. Viewing the results in these three stages makes it easier to clarify why the self-consumption rate is high or low and to pinpoint areas for improvement.

Variability in the self-consumption rate is also related to equipment operation planning. If you can identify months or time periods with large surpluses, you may be able to adjust the operating hours of electrical equipment. For example, if there are pumps, air conditioning, charging equipment, or parts of the production process that can be run during the daytime, operating them to coincide with the peak of solar power generation can improve the self-consumption rate. The results from PVSyst can be used not only for design but also as a basis for considering operational improvements.

Design conditions to verify when the self-consumption rate is low

When PVSyst results show a self-consumption rate lower than expected, it is important to review the basic conditions before immediately considering batteries or additional equipment. There is not a single cause for a low self-consumption rate. The system capacity may be too large, or the load data may not reflect actual conditions. The generation peak can also be misaligned with the load due to the installation azimuth or tilt angle. To improve the results, you need to break down and check the causes.

First, you should check the system capacity. If the generation equipment is too large relative to demand, on sunny days during the daytime generation will exceed the load and surplus will increase. If you set capacity only with the goal of increasing annual generation, the system can be oversized for self-consumption installations. Developing cases with stepwise changes in capacity and comparing how self-consumption and surplus energy vary makes it easier to assess the suitability of the capacity.

Next, verify the validity of the load data. In actual facilities, loads change with the day of the week, season, operating hours, equipment upgrades, and operational plans. If simplified load patterns are used, the self-consumption rate may appear higher or lower than in reality. In particular, check whether it appropriately reflects holiday loads, long vacations, lunch breaks, nighttime standby power, and seasonal air-conditioning loads.

Installation orientation and tilt angle are also key points to check. The direction that maximizes annual power generation is not necessarily optimal for the self-consumption rate. If generation is concentrated around noon and results in a large surplus, a design that slightly spreads the generation hours can be effective. If a facility’s load is biased toward the morning or afternoon, consider the layout while examining its relationship to the generation peak.

The effects of shading cannot be ignored. If shading reduces generation, the self-consumption rate may appear to increase, but this only indicates lost generation opportunities and is not necessarily a good outcome. A high self-consumption rate does not mean that a design with a lot of shading is desirable. Check shading losses, annual generation, and self-consumed energy together to determine whether surplus has merely decreased or whether actual effective utilization has increased.

Loss settings should also be reviewed. If temperature loss, wiring loss, equipment loss, mismatch loss, etc. are set too high or too low, the estimated generation will change and the self-consumption rate will be affected. If generation is calculated too low, the self-consumption rate can appear relatively high. Conversely, if generation is calculated too high, the surplus can appear large and the self-consumption rate can be low. In practice, you need to confirm that the loss assumptions are reasonable before evaluating the results.

Also, verify that the handling of surplus power is correctly reflected in the calculation assumptions. The interpretation of the results changes depending on whether the surplus is assumed to be exported externally, curtailed, or stored. If the handling of surplus is left ambiguous when comparing results, you cannot correctly assess the differences between options. When explaining to customers in particular, it is important to clarify what assumption is being made about how surplus will be handled if it occurs.

When the self-consumption rate is low, check not only the figures on the results screen but also the input and operational conditions in order. Reviewing system capacity, load data, installation orientation, seasonal variations, holiday loads, loss settings, and surplus handling will reveal the reason for the low rate. Once the cause is understood, it becomes easier to move on to further considerations such as capacity adjustments, layout changes, load shifting, or adding battery storage.

How to Read When Considering Battery Storage and Control Systems

As methods to increase the self-consumption rate, battery storage, output control, and load control may be considered. When evaluating a system that includes battery storage in PVSyst, it is not sufficient to look only at whether the self-consumption rate has increased. It is necessary to check how much the battery is being charged, during which time periods discharging occurs, how often full-charge or empty states occur, and how much surplus power has been reduced.

The basic role of a storage battery is to bridge the time gap between power generation and load. When generation exceeds load during the daytime, the surplus can be stored in the battery. Then, when there is demand in the evening or at night, using the stored energy can reduce the amount of electricity purchased. If this process works well, both the self-consumption rate and the self-sufficiency rate will improve.

However, battery storage is not effective in every case. If very little surplus power is generated, there will be insufficient power to charge the battery. In such cases the self-consumption rate may already be high, but the additional effect of the battery will be small. Conversely, even if there is a lot of surplus power, if the night or evening load is low, there may be nowhere to discharge the stored energy, and the battery may not be used effectively.

When evaluating a battery using PVSyst results, first compare the cases with and without the battery. Look at how the self-consumption rate, self-sufficiency rate, surplus energy, and purchased energy have changed. If only the self-consumption rate increases but the reduction in purchased energy is small, the practical effect may be limited. Conversely, even if the improvement in self-consumption rate is moderate, if it reduces purchased energy during peak hours or is effective for nighttime use, it may have operational value.

Comparing battery capacities is also important. Increasing capacity may seem to allow you to absorb more surplus, but in reality there will be days when the battery cannot be fully charged and days when it cannot be fully discharged. If capacity is too small, it cannot adequately absorb surplus on sunny days. If capacity is too large, the portion that goes unused over the year increases. By comparing multiple capacities in PVSyst and checking changes in surplus reduction and reduction in purchased electricity, it becomes easier to judge whether capacity is excessive or insufficient.

When considering output control, confirm how much generation opportunity is being suppressed. Under conditions where surplus cannot be exported externally, it may be necessary to reduce generation. In such cases, the self-consumption rate may appear high, but there is a possibility that electricity that could have been generated is being discarded. Therefore, in addition to improving the self-consumption rate, check the curtailed amount of energy and determine whether the system capacity is excessive.

Load control can also be effective. If there are systems that can be operated during the daytime, you can increase the self-consumption rate by shifting their operation to periods of high generation. For example, pre-cooling air conditioning, running pumps, operating charging equipment, or moving parts of manufacturing processes to daytime can potentially reduce surplus. By identifying the time periods when surplus occurs in the PVSyst results and considering whether there are loads that can be run during those periods, you can find improvement measures other than adding equipment.

When evaluating battery storage and control, it is important to look not only at annual averages but also at representative days and seasonal behavior. Batteries may be used often in summer but hardly charged in winter; in spring there is a large surplus and batteries tend to become fully charged; and on holidays there are fewer opportunities to discharge — these are issues that cannot be seen from annual values alone. By carefully examining PVSyst results, you can avoid overestimating the effects of batteries and control and arrive at realistic design decisions.

Points to note when explaining the self-consumption rate in a report

When you check the self-consumption rate in PVSyst, there are occasions when you need to explain the results to internal staff or clients. Presenting only the numbers can cause misunderstandings. Because the self-consumption rate varies depending on the assumptions, it is essential to explain it together with the calculation conditions. In particular, you should clearly specify the type of load data, the system capacity, how surplus power is handled, whether battery storage is present, and the period considered.

In the report, first briefly explain the definition of the self-consumption rate. Making it explicit as "the proportion of generated electricity that was used within the facility" will make it easier for the reader to understand. Also, explaining the difference from the self-sufficiency rate will make later discussions smoother. If you clarify that the self-consumption rate is a generation-side indicator and the self-sufficiency rate is a demand-side indicator, you will reduce the risk of misinterpreting the meaning of the figures.

Next, showing monthly trends in addition to annual values makes the argument more persuasive. Even if the annual self-consumption rate is high, surpluses can be concentrated in particular months. Even if the annual self-consumption rate is low, it may simply be due to months with low load or strong holiday effects, and weekdays may still achieve adequate self-consumption. Explaining monthly trends makes it easier to identify design challenges and directions for operational improvements.

Also, when comparing design proposals, it is important to compare them under the same assumptions. When comparing proposals that change installed capacity, add a battery, or change orientation or tilt, if load conditions or weather conditions differ, you cannot determine what caused the difference in results. In comparison reports, clearly separate and explain the common conditions and the changed conditions. This makes it easier to explain which design changes affected the self-consumption rate.

Even when results indicate a high self-consumption rate, it is important not to overemphasize it. It is necessary to explain whether the high self-consumption rate is due to a small system capacity or to a good match between load and generation. Even with a high self-consumption rate, if the total generation is small the effect on reducing purchased electricity is limited. Therefore, it is important to look at the self-consumed energy and the reduction in purchased electricity alongside the self-consumption rate.

Even if the self-consumption rate is low, we do not simply treat it as a bad result; we explain the reasons. The appropriate measures differ depending on whether the system capacity is large and surplus generation has increased, holiday loads are small, surpluses are seasonal, or the load is concentrated at night. If the reason for the low rate is clear, it can lead to consideration of capacity adjustment, battery storage, load shifting, or surplus utilization.

What you should avoid in a report is an explanation that merely lines up PVSyst's output numbers as they are. What practitioners and decision-makers want to know is, "how much can be used with this design," "how much surplus electricity will there be," "is the plant capacity appropriate," and "if improvements are needed, what should be changed." Therefore, rather than the superficial numerical results, it is important to supplement them with written explanations of the design judgments that the numbers imply.

In explanatory materials, it is easier to understand if you summarize in the order: assumptions, results, interpretation, and next items to examine. In the assumptions, explain the load conditions and equipment conditions; in the results, show the self-consumption rate, self-sufficiency rate, self-consumed energy, and surplus energy. In the interpretation, state why those results occurred. Finally, organize the items to be checked next, such as capacity adjustments and battery (storage) considerations. By explaining in this sequence, it becomes easier to link PVSyst results to practical decision-making.

How to Improve the Accuracy of Self-Consumption Rate by Reflecting Local Conditions

To make PVSyst’s self-consumption rate yield results closer to real-world practice, reflecting on-site conditions is indispensable. Because simulations depend on input conditions, the more accurately you capture the site’s building geometry, the available roof and site areas, orientation, tilt, shading, equipment layout, incoming service equipment, and the actual load, the more reliable the results become. Conversely, if calculations are performed while on-site conditions remain ambiguous, you may obtain seemingly detailed figures that diverge from actual operation.

First and foremost, confirm the available installation area. How many solar panels can be installed on the roof or on the premises affects the self-consumption rate. A larger available area doesn't necessarily mean it's optimal to cover it entirely with panels. While increasing system capacity raises energy production, it also increases surplus during periods when generation exceeds demand. Based on the usable installation area determined by the site survey, it's practical to create several capacity scenarios and compare them using PVSyst.

Next, assess the shading conditions. Shadows from nearby buildings, towers, trees, equipment, railings, steps, and so on affect power generation. When shading reduces generation, the apparent self-consumption rate may increase, but that represents a loss of generation opportunities and is not necessarily a desirable outcome. You need to account for the effects of shading and examine how generation, self-consumption, and surplus electricity change.

It is also important to understand the actual on-site load conditions. If detailed electricity usage records or metered data are available, use data with as high a temporal resolution as possible. Monthly usage alone limits the accuracy of the self-consumption rate. Using data that shows weekdays and holidays, daytime and nighttime, and seasonal variations allows a more accurate assessment of the overlap between generation and load. If detailed data are not available, it is important to interview about the facility’s operating hours, main equipment, closed days, and seasonal usage trends, and to develop a reasonable load profile.

We also check the power receiving equipment and operational constraints. Whether surplus power can be exported offsite, whether reverse power flow must be avoided, or whether output control is required will change the design approach. The optimal system capacity differs depending on whether surplus is acceptable or whether surplus must be minimized. When reviewing PVSyst results, you need to confirm not only how many kWh of surplus there are, but also how that surplus can be handled on site.

To reflect site conditions in PVSyst, the accuracy of positioning and assessment of current conditions is also important. If you can correctly determine the dimensions of the roof and site, equipment locations, obstacle positions, and elevation differences, it becomes easier to plan layouts and evaluate shading. If drawings are outdated or equipment has been installed on-site afterward, desk-based design alone can differ from reality. Using on-site acquired positional data, photos, and point clouds can bring the simulation assumptions closer to reality.

At this stage, a useful option is a positioning tool that can easily acquire on-site location information and be used for design and record-keeping. LRTK is a GNSS high-precision positioning device that can be attached to an iPhone; it acquires high-precision location data on site and helps you understand current conditions by linking photos, point clouds, and positioning records. Even when considering photovoltaic power generation facilities, accurately recording candidate installation areas, obstacles, equipment locations, and on-site verification points makes it easier to organize the input assumptions for PVSyst.

Especially when considering self-consumption solar PV systems on the roofs or premises of existing facilities, it is important to accurately record on-site conditions. The positions of rooftop equipment, structures that cause shading, inspection walkways, areas where installation is not possible, and the distance to the main electrical service all affect design conditions and construction planning. By utilizing LRTK, position information acquired on site makes it easier for designers, construction staff, and facility managers to share a common understanding. Linking PVSyst analyses with on-site information also makes simulations of self-consumption rates a more practical basis for decision-making.

Summary

In PVSyst, when checking the self-consumption rate, it is important not to look only at the percentage shown on the results screen, but to interpret generation, load, self-consumed energy, surplus energy, self-sufficiency rate, and monthly and hourly trends together. The self-consumption rate is an indicator of how much of the generated electricity was used within the facility, but it alone cannot determine whether the system is good or bad. If the system capacity is small, the self-consumption rate tends to appear high, and if the capacity is large, surplus increases and the self-consumption rate may decrease.

When reviewing results, the basic approach is first to check the temporal overlap between generation and load. Next, look at self-consumption and surplus energy to understand how much electricity was actually used and how much remained. Then separate and understand the self-consumption rate and the self-sufficiency rate to clarify the utilization on the generation side and the degree to which demand was satisfied on the consumption side. Furthermore, by checking not only annual averages but also monthly and time-of-day variations, you can identify the causes of surplus and the directions for improvement.

If the self-consumption rate is low, do not immediately add a storage battery; instead, review in order the system capacity, load data, installation azimuth, tilt angle, shading, loss settings, and the handling of surplus power. When considering batteries or control strategies, it is important to check not only the amount by which the self-consumption rate can be improved but also the amount of surplus reduced, the reduction in purchased electricity, and the actual charge/discharge behavior. PVSyst is well suited for comparing multiple scenarios, so by varying capacity and operating conditions you can evaluate which option best matches local demand.

Furthermore, to improve the accuracy of simulations, it is essential to correctly understand on-site conditions. If the feasible installation area, causes of shading, equipment locations, service equipment, and the actual load conditions remain unclear, PVSyst results may deviate from reality. By obtaining accurate position information, photographs, and point clouds on site and reflecting them in the design conditions, evaluations of the self-consumption rate will become more reliable.

LRTK is a GNSS high-precision positioning device that can be attached to an iPhone, allowing you to easily record on-site location information and apply it to pre-design surveys and current-condition checks of solar power installations. When checking self-consumption rates in PVSyst, combining accurate on-site positioning data and records with desk-based simulations makes it possible to more clearly understand installation boundaries, obstacles, and equipment locations. When considering self-consumption solar power systems, an important point for avoiding practical failures is to keep generation simulations and on-site surveys integrated and make design decisions based on site-specific conditions.