4 Ways to Read PVSyst's Reference Yield | For PR Comparison

PVSyst's Reference Yield is the metric that serves as the foundation for PR comparisons

When reading a PVSyst report, if you evaluate it by looking only at energy production and the Performance Ratio, you may not be able to correctly compare differences between projects. Especially when comparing PRs across multiple sites, or reconciling another company's analysis with your own, it is important to understand how to read the Reference Yield.

Reference Yield is used in Japanese to mean something close to standard yield, reference generation time, and reference irradiance. In the context of PVSyst, it is easier to understand it as the value obtained by dividing the solar irradiance incident on the photovoltaic array plane by the reference irradiance under standard test conditions. The unit corresponds to time, and because kWh/m2 (kWh/ft2) is divided by kW/m2 (kW/ft2), it has a meaning similar to h.

Simply put, Reference Yield is a value that converts how much solar energy a power plant received into a form that is easy to use for evaluating the performance of the generation equipment. It is an input-side metric indicating the solar irradiation conditions before looking at how much the plant actually generated.

PR is an indicator that shows how effectively the actual generated electricity has been converted from solar irradiance conditions. Therefore, to read PR you need to understand the meaning of the Reference Yield in the denominator. A year with a large Reference Yield is a year with favorable irradiance conditions, while a year with a small Reference Yield is a year with harsh irradiance conditions. However, a large Reference Yield does not necessarily mean a high PR. In fact, the stronger the irradiance, the more temperature losses and clipping increase, which can lower PR.

If you understand this point, you will be able to interpret PVSyst results not merely as differences in total energy generation, but as the relationships among solar irradiance conditions, system performance, and loss structure. In particular, for generation assessments submitted to banks, EPC design comparisons, O&M performance evaluations, and checking differences against other companies' reports, starting from the Reference Yield greatly increases the precision of the discussion.

Reference Yield is a value representing solar irradiance conditions converted for power plant evaluation

When first reading Reference Yield, it is fundamental to consider it not as the performance of the generation equipment itself but as an indicator representing the solar irradiation conditions applied to the power plant. In PVSyst, several solar radiation-related items appear, such as Global horizontal irradiation, Global incident in collector plane, and Effective irradiation. Among them, Reference Yield is used as the baseline value connected to PR and yield assessment.

The power output of a solar power plant is, first and foremost, greatly influenced by solar irradiance. In Hokkaido and Kyushu, on flatlands and in mountainous areas, and with south-facing fixed racking versus east-west-facing racking, even with the same panel capacity the amount of solar irradiance received differs. Therefore, simply comparing annual power output alone cannot determine the quality of the installation. This is because locations with favorable solar irradiance tend to generate more electricity, while locations with poor solar irradiance tend to generate less.

Reference Yield serves as a baseline for organizing differences in solar irradiation conditions. For example, if one site's Reference Yield is 1,400 h per year and another site's is 1,200 h per year, the former means that more solar energy is entering the power plant. What you should look at here is not what the installed capacity in kW is, but how much solar irradiation the facility received.

Keeping this value in mind makes interpreting Specific Yield and PR more consistent. Specific Yield is the annual energy generation divided by the installed capacity. Its unit is kWh/kWp. On the other hand, Reference Yield is the solar irradiation condition converted into time units. PR can be considered as Specific Yield divided by Reference Yield. In other words, Reference Yield is an important value that appears in the denominator of the PR calculation.

A point to note here is that a high Reference Yield does not necessarily mean a good design. Because Reference Yield represents solar irradiation conditions, it does not directly indicate the design quality of the power plant. If the array faces south with an appropriate tilt angle, Reference Yield can be high. However, if subsequent losses—such as temperature losses, mismatch losses, wiring losses, inverter losses, clipping losses, and shading losses—are large, the final PR will decrease.

Conversely, at sites where the Reference Yield is somewhat low, PR can still be high if the loss design is good. In such cases, even if the absolute power output is small, the conversion efficiency relative to the incident solar radiation can be considered high. Therefore, it is important to treat Reference Yield as an indicator of the plant’s potential and PR as an indicator of how much of that potential has been realized.

When reviewing PVSyst results, first look at the Reference Yield to determine whether the project's solar irradiation conditions are high or low. Then, by checking Specific Yield, PR, the final Grid Injection, and the Loss Diagram in sequence, it becomes easier to explain where differences in energy production originate.

In PR comparisons, treat Reference Yield as the denominator

The reason Reference Yield becomes important in PR comparisons is that PR is an indicator showing power generation performance relative to solar irradiance conditions. PR alone is a useful indicator of a plant’s overall performance. However, to judge whether a PR is high or low, you need to check the underlying Reference Yield.

For example, suppose Project A has a PR of 82% and Project B has a PR of 80%. Looking only at these numbers, Project A appears better. However, if Project A has a low Reference Yield and Project B has a high Reference Yield, the evaluation is not straightforward. Projects with a high Reference Yield tend to experience stronger solar irradiance and therefore higher energy generation, but module temperatures also tend to rise, increasing temperature losses. In designs where PCS capacity is small relative to DC capacity, clipping losses can also increase during periods of strong solar irradiance.

Therefore, a project with a high Reference Yield appearing to have a slightly lower PR does not necessarily mean the design is poor. Rather, under high solar irradiance conditions, increased temperature losses and output limiting may naturally lower the PR. Conversely, for projects with a low Reference Yield, weaker irradiance can reduce temperature losses and clipping, resulting in a relatively higher PR.

Therefore, when comparing PRs, you must always check the Reference Yield as the background condition. PR is a useful metric, but it cannot completely separate the influence of irradiance conditions. In particular, when comparing projects side by side that differ in region, orientation, tilt angle, snow cover, shading, and overloading ratio, judging performance based on PR alone can be misleading.

When comparing PVSyst reports, it's easier to organize things if you look at Reference Yield, Specific Yield, and PR together. Reference Yield represents the solar irradiation conditions on the input side, Specific Yield indicates the energy production per unit of installed capacity, and PR is the conversion efficiency with respect to solar irradiation. By checking these three simultaneously, you can distinguish whether differences in energy production are due to irradiation conditions, design losses, or differences in simulation conditions.

When comparing another company's analysis with our own, Reference Yield should be the first item to check. If the Reference Yield differs significantly despite analyzing the same power plant, the input conditions—such as meteorological data, tilt angle, azimuth, albedo, horizon shading, nearby shading, and the transposition model—may be different. In this situation, comparing only PR or annual generation does not constitute a proper comparison, because the analysis conditions are not aligned.

In PR comparisons, first check whether the Reference Yield is similar. If it differs significantly, you should check differences in solar irradiance conditions before the PR difference. If the Reference Yield is close but PR differs, the flow is to look at loss settings, equipment configuration, wiring losses, temperature losses, IAM, mismatch (losses), inverter efficiency, auxiliary equipment losses, and so on.

Differences in Reference Yield arise from meteorological data and in-plane solar irradiance conditions

If you understand where differences in Reference Yield originate, it becomes easier to compare analyses in PVSyst. Reference Yield is not determined solely by the region's solar irradiance; in PVSyst, meteorological data, tilt angle, orientation, terrain shading, nearby shading, albedo, and the conversion of irradiance onto inclined surfaces all play a role.

The biggest factor is the meteorological data. Even at the same site, the annual solar irradiation can vary depending on which meteorological dataset is used—Meteonorm, SolarGIS, satellite data, measured data, etc. Monthly irradiation trends can also differ. In some datasets winter irradiation is higher, while in others summer irradiation is higher. Therefore, if the Reference Yield differs from another company's report, you should first check the source and period of the meteorological data.

The next important step is converting to irradiance on the tilted surface. Solar panels are installed not on a horizontal plane but at a fixed tilt angle and azimuth. In PVSyst, a process converts horizontal-plane irradiance into the irradiance incident on the panel surface. If panels face south with an appropriate tilt angle, the in-plane irradiance can be more favorable than the horizontal-plane irradiance. On the other hand, east–west orientations, low tilts, northward azimuths, or complex terrain conditions will alter the Reference Yield.

Also, the way shading is treated affects how Reference Yield is interpreted. When horizon shading or near-field shading is taken into account, the solar irradiance reaching the panel surface is reduced. This is especially true for solar plants located in mountainous areas, near forests, on slopes of developed land, or with surrounding structures, where shading in the mornings and evenings and during winter tends to be more pronounced. If you compare Reference Yield without confirming at which stage shading losses are reflected, you may confuse differences in irradiance conditions with differences in shading conditions.

Albedo is also a non-negligible factor in cold or snowy regions. When ground-reflected solar irradiance increases, the irradiance incident on tilted surfaces can rise. In particular, for bifacial modules and in snowy regions, the impact of albedo settings on energy generation becomes larger. However, because setting the albedo higher can sometimes increase the Reference Yield and energy output, it is important to clearly document the rationale for the setting.

In this way, differences in Reference Yield arise not only from the weather data but from the entire set of input conditions in PVSyst. When looking at Reference Yield for PR comparisons, you should not simply compare numeric magnitudes; you need to check which conditions produced that value.

In practice, when the Reference Yield is higher than another company's analysis, it tends to bias the results toward higher energy production. Therefore, it is necessary to distinguish whether the cause of the difference in energy production is the superiority of the design or differences in solar irradiance conditions. Conversely, if the Reference Yield is low yet the energy production is high, PR or loss settings may be favorably biased. In either case, using Reference Yield as the starting point for comparison makes discussions quantitative rather than subjective.

Examine the relationship between Reference Yield and Specific Yield

One thing that's easy to confuse when reading PVSyst is the difference between Reference Yield and Specific Yield. Both include the word "Yield," and the units of the values—such as time or kWh/kWp—give a similar impression. However, their meanings are clearly different.

Reference Yield is a value that represents irradiance conditions. It can be thought of as the solar energy incident on the power plant divided by a standard irradiance. This is an input-side metric. On the other hand, Specific Yield is the electrical energy actually produced by the plant divided by its installed capacity. This is an output-side metric.

When you look at the relationship between these two, the performance of the power plant becomes easier to understand. If the Reference Yield is 1,400 h and the Specific Yield is 1,120 kWh/kWp, then for the given irradiance conditions the system produced 1,120 kWh per kWp of installed capacity. In this case, PR can be understood as approximately 80% by dividing the Specific Yield by the Reference Yield.

Thus, the difference between Reference Yield and Specific Yield can be regarded as the result of various losses occurring within a photovoltaic system. Solar irradiance reaches the panel surface, but not all of it is delivered to the grid as electrical power. It goes through module temperature losses, low-irradiance losses, IAM losses, mismatch losses, wiring losses, inverter losses, transformer losses, auxiliary equipment losses, and output limitations, resulting in the final energy output.

If you understand this structure, the meaning of PR becomes clearer. PR indicates how efficiently power was generated during the conversion from Reference Yield to Specific Yield. A high PR means that losses are relatively small compared with the input solar irradiance. A low PR suggests that some losses are large, or that output is being curtailed due to design conditions or control settings.

However, a high PR does not necessarily mean a superior project. In projects with a low Reference Yield, temperature losses and clipping losses can be smaller, which may make PR appear high. Also, in designs with a low oversizing ratio, clipping is reduced and PR can be higher; however, a different assessment may be required from the standpoint of investment efficiency. PR is the central metric for performance evaluation, but for business feasibility assessment you also need to consider energy generation, installed capacity, PCS capacity, land conditions, construction costs, grid conditions, and so on.

By reading Reference Yield and Specific Yield together, you can explain differences in energy production more accurately. This is because you can distinguish whether a high energy output is due to favorable irradiance conditions or to strong system performance. This is extremely useful when using PVSyst reports for customer presentations or internal reviews.

Looking at the monthly Reference Yield reveals seasonal factors

Looking only at the annual Reference Yield reveals the site's overall solar irradiance conditions. However, for PR comparisons and analyses of generation differences, it is also important to look at Reference Yield by month. Viewing it on a monthly basis allows you to identify which seasons' irradiance conditions are affecting power generation and PR.

In photovoltaic power generation, solar irradiance, solar altitude, ambient temperature, snow accumulation, and shading effects change significantly with the seasons. In summer, solar irradiance tends to be higher, but higher ambient temperatures raise module temperature and increase temperature-related losses. In winter, lower temperatures are favorable for module efficiency, but solar irradiance is reduced and the solar altitude is lower. In regions with snowfall, the effects of snow-induced shading and reflection are also added.

By checking the monthly Reference Yield, you can analyze the causes of generation differences in greater detail. For example, even if the annual generation is lower than another company's analysis, a month-by-month view may show that the difference is large only in winter. In that case, winter solar irradiance from the meteorological data, snow losses, albedo, horizon shading, nearby shading, and the like can be considered causes. If the difference is large only in summer, you should check summer solar irradiance from the meteorological data, temperature conditions, PCS clipping, and output control settings, among other factors.

When examining monthly variations in PR, Reference Yield is also important. Generally, months with strong solar irradiance and high temperatures tend to show lower PR, while months with weak irradiance and low temperatures can appear to have higher PR. This is not a system malfunction but can naturally occur as a characteristic of photovoltaic power generation. Therefore, when evaluating monthly PR, it is important to view Reference Yield together with temperature.

Reading the monthly Reference Yield makes it easier to explain the generation trends shown in PVSyst’s graphs and tables. Even if the annual PR is the same, different monthly breakdowns imply different risks and characteristics for a plant. Project-specific features become apparent, such as plants that perform well in summer, plants that tend to drop in winter, plants that are susceptible to morning and evening shading, and plants that are heavily affected by snow.

In internal reviews, checking monthly Reference Yield as well as annual values makes it easier to assess the validity of the analysis conditions. For example, if solar irradiation in a particular month differs greatly from nearby projects in the same region, you should check whether there are any anomalies in the meteorological data or import settings. Verifying that the monthly trends align with the region’s climate also contributes to the quality control of PVSyst analyses.

Verification procedure when comparing with other companies' reports

When comparing other companies' reports with PVSyst results, Reference Yield is the item that should be checked first. Even if you compare only annual energy production or PR, the evaluation will be off if the input conditions differ. In reviews aimed specifically at PR comparison, it is more efficient to check the degree of agreement of Reference Yield before moving on to the loss items.

The first thing to check is whether the same power plant, the same installed capacity, and the same layout are being assumed. If the installed capacity differs, the interpretation of Specific Yield and energy production changes. If the layout, orientation, or tilt angle differ, the Reference Yield will also change. Before comparing PR alone, verify that the items being compared are actually under the same conditions.

Next, check the source of the meteorological data. The meteorological data used in PVSyst influence solar irradiation, temperature, wind speed, and so on. Reference Yield is mainly influenced by solar irradiation conditions, but PR is also affected by temperature conditions. Therefore, even for the same site, using different meteorological data will change the energy production and PR. When creating a comparison table, organizing the meteorological dataset name, the target year(s), horizontal plane solar irradiation, and tilted plane solar irradiation will make explanations easier.

Next, check the tilt angle and azimuth. In PVSyst, even with the same horizontal-plane irradiance, the in-plane irradiance changes depending on the panels' orientation. A difference of just a few degrees in azimuth may not make a large difference, but east–west orientation, low tilt, high tilt, or a mix of multiple orientations can affect the Reference Yield. Be especially careful in mountainous areas and land development sites, where racking orientations may become complex to match the terrain.

Next, check the shading and albedo. Whether horizon shading or nearby shading is included, and how detailed the shading calculations are, will affect the Reference Yield and the effective irradiance. Albedo usually does not vary much under typical ground conditions, but it is important in snowy areas and for bifacial modules. If albedo settings differ from those used in other companies' analyses, this can impact energy production as differences in winter or reflected irradiance.

Finally, after confirming that the Reference Yield is roughly the same, we look at the causes of the PR difference using a Loss Diagram. From here we compare temperature loss, IAM loss, mismatch loss, DC wiring loss, AC wiring loss, transformer loss, inverter loss, auxiliary losses, output limitation, and so on. If the Reference Yield is aligned, these differences in losses can more easily be explained as the main causes of the PR difference.

Looking at them in this order organizes the explanation of differences from other companies' reports. Rather than immediately discussing PR differences, first look at Reference Yield, then Specific Yield, and finally the loss items; this clarifies at which stage the differences arise.

When Reference Yield is high but PR is low

A common occurrence in PVSyst results is when the Reference Yield is high while the PR is relatively low. At first glance, it may seem that performance is poor despite favorable irradiance conditions. However, this is not necessarily abnormal.

A high Reference Yield indicates that a large amount of solar irradiance is reaching the panel surface. When there are many hours with strong irradiance, module temperature tends to rise. Because the output of photovoltaic modules decreases as temperature increases, thermal (temperature) losses increase. As a result, even if Reference Yield is high, PR may decrease.

Also, in designs with a high oversizing ratio, the PCS output limit is more likely to be reached during periods of strong solar irradiance. In such cases, even if there is capacity to generate on the DC side, the output is constrained on the AC side, resulting in clipping losses. The higher the Reference Yield at a site, the more pronounced this output constraint may appear. Therefore, if Reference Yield is high and PR is low, it is natural to first check temperature losses and inverter output limits.

Furthermore, in regions with high solar irradiance, the absolute amount of power generation can be larger. Even if the PR is slightly low, if the annual generation or Specific Yield is high, the project may still be commercially viable. PR is an indicator of efficiency, not the electricity sales volume itself. In project evaluation, it is necessary to consider not only the PR level but also annual generation, equipment utilization rate, electricity selling price, construction costs, and operating costs together.

In such cases, care is needed in how this is communicated to customers. If you simply explain that the PR is low, it may be perceived as poor design quality. In reality, the PR may appear lower simply as a result of increased temperature losses and clipping under high irradiance conditions. Explaining, as a set, that the Reference Yield is high, that sufficient energy is being produced, and that the breakdown of losses is reasonable from a design perspective can prevent misunderstandings.

When the Reference Yield Is Low but PR Is High

Conversely, there are cases where Reference Yield is low but PR appears high. In this situation, although the incident solar irradiance is low, the conversion efficiency relative to that irradiance looks high. This does not necessarily mean it is a good design.

At sites with low Reference Yield, solar irradiance is weak and module temperature may not rise easily. Therefore, temperature losses become smaller and PR may appear higher. Also, if there are many periods of weak irradiance, the time during which the PCS reaches its output limit is shorter and clipping losses are also reduced. As a result, PR tends to be higher.

However, a high PR does not necessarily mean that annual power generation will be sufficient. If the solar irradiance conditions themselves are low, the absolute amount of power generated is unlikely to be high. This is particularly important when evaluating the profitability of commercial solar projects. Even projects with a high PR may have limited Specific Yield or annual electricity sales if the Reference Yield is low.

Therefore, it is risky to judge a project as good based solely on PR. If Reference Yield is low and PR is high, you need to check why PR is high. Check whether temperature losses are small, whether there are few output limitations, whether loss settings are being made favorable, and whether wiring losses or auxiliary losses are set low.

When comparing analyses from other companies, reports in which the Reference Yield is low but only the PR is high can make the performance look good at a glance. However, what matters to operators is the final energy production and revenue. If the reason for a high PR cannot be explained, the report is insufficient for interpretation. By checking Reference Yield, Specific Yield, and PR together, you can balance performance evaluation and energy production assessment.

Reading Alongside PVSyst's Loss Diagram

Reference Yield is easier to interpret in practical terms when read together with PVSyst's Loss Diagram. The Loss Diagram is a chart that shows how much loss occurs at each stage, from solar irradiation to the final energy injected into the grid. The Reference Yield can be understood as a reference value positioned upstream of that diagram.

In the Loss Diagram, solar irradiance conditions are shown first; from there it proceeds through optical losses, module conversion, temperature losses, electrical losses, inverter losses, AC-side losses, and so on, to the final energy yield. Reference Yield can be regarded as the baseline before these losses are applied.

In PR comparisons, differences can arise partway through the Loss Diagram even when Reference Yield is the same. For example, even with the same Reference Yield, one analysis may have larger temperature loss while the other has larger wiring loss. In this case, the final PR may be similar, but the loss structures differ. Conversely, even when there is a large PR difference, the Loss Diagram can be used to determine whether the primary cause is a difference in Reference Yield or a difference in loss settings.

Specifically, what we want to check in practice is the magnitude of the decrease from Reference Yield to Specific Yield. If this difference is large, there is a significant loss somewhere. We will examine, in order, whether the temperature loss is large, whether the shading loss is large, whether the IAM is large, whether the DC wiring losses are large, or whether the inverter output limitation is large.

Also, even for the same PR, the types of losses can differ. In one project temperature losses may be large, while in another clipping losses may be large; the improvement measures will differ accordingly. If it is temperature loss, racking ventilation and verification of module characteristics are relevant; if it is clipping, examination of the DC/AC ratio and PCS capacity is relevant. For wiring loss, the key issues are cable length, conductor cross-sectional area, junction/connection box placement, and PCS placement.

Reference Yield alone does not reveal the specific improvement points of a power plant. However, by using Reference Yield as a starting point and reading the Loss Diagram, you can attribute a plant's performance differences to specific loss items. This is an important way of interpreting PVSyst to use it not merely as an energy yield calculation tool but as a tool for design review and PR comparison.

How to explain Reference Yield to customers

PVSyst's Reference Yield is a specialized metric, so it should be rephrased when explaining it to customers. If you present the term "Reference Yield" by itself, it can be difficult to distinguish it from actual energy production. When explaining, it is easier for customers to understand if you say that it is the value obtained by converting the solar irradiation conditions incident on the power plant into a form that is easy to use for performance evaluation.

What customers often want to know is why the energy generation is higher, why the PR is higher, and how it differs from other companies' reports. Reference Yield serves as the entry point for that explanation. For example, if generation is higher than in another company's analysis and the Reference Yield is higher, you can first explain that the assumptions about solar irradiance are higher. If the Reference Yield is similar but generation is higher, the difference can mainly be explained by loss settings or equipment efficiency.

For customers, it's helpful to briefly explain Reference Yield, Specific Yield, and PR separately. Reference Yield refers to the solar irradiation conditions, Specific Yield is the energy produced per unit of capacity, and PR is the ratio that indicates how effectively the solar irradiation was converted into electricity. Placing these three side by side naturally explains where differences in generation come from.

Also, when explaining differences in Reference Yield, referring to assumptions such as meteorological data, tilt angle, orientation, shading, and albedo makes the explanation more persuasive. However, because explaining too much detail can become difficult, it is important to present the information stepwise according to the client's level of understanding. In internal reviews, verify the detailed loss items, while for client-facing materials it is practical to focus the explanation on the key points.

In PR comparisons, rather than simply stating how many percent the PR differs, it is effective to first confirm whether the Reference Yield is under the same conditions and then explain the differences in losses. This can demonstrate the fairness of the comparison. Instead of describing differences in generation or PR intuitively, separating the explanation into input conditions and loss structure increases technical credibility.

A Reference Yield Is Needed Even When Comparing with Field Data

The Reference Yield in PVSyst is relevant not only to simulation results but also to performance evaluation after the start of operation. When comparing measured generation with PVSyst predictions, simply comparing annual energy yields will be affected by differences in weather. If solar irradiation in a given year is lower than the long-term average, it is natural for generation to be lower than predicted. Conversely, if irradiation is higher, generation may exceed the prediction.

In that case, checking the measured irradiance conditions corresponding to the Reference Yield makes it easier to isolate the causes of generation differences. If the solar irradiance is lower than predicted, the low generation is likely mainly due to weather. If the solar irradiance is about the same as predicted but generation is low, you should suspect equipment-side losses, faults, soiling, shading, curtailment, downtime, etc.

Even when evaluating PR on site, the concept of Reference Yield is important. Measured PR is assessed by dividing the actual energy production by the actual irradiance conditions. Therefore, the pyranometer’s installation location, tilt angle, calibration status, missing data, and the presence or absence of shading affect the results. When comparing PVSyst’s Reference Yield with the reference value derived from measured irradiance, an accurate comparison cannot be made unless the measurement conditions are the same.

In O&M, daily and monthly PRs are sometimes managed. At such times, looking only at generation output without checking the solar irradiance conditions corresponding to the Reference Yield can lead to incorrect anomaly judgments. A month with prolonged cloudy weather will see reduced generation, but that alone does not indicate an abnormality. Only by comparing how much generation is produced relative to the irradiance conditions can you determine whether there is performance degradation or a malfunction.

As such, Reference Yield is not a concept confined to PVSyst. It is a fundamental concept that relates to the overall performance assessment of solar power generation—from design-stage simulations and comparisons with other firms to evaluations for financial institutions and post-operation performance management. Once you can correctly read the Reference Yield in PVSyst, discussions about energy production and PR become that much deeper.

Points to note when viewing Reference Yield

When looking at Reference Yield, there are a few points to be aware of. First, Reference Yield is not the same as actual energy production. It is an indicator of solar irradiation conditions and differs from the final amount of electricity sold or the amount of energy injected into the grid. A high Reference Yield does not necessarily mean that final energy production will be high. If losses along the way are large, the final energy output can be lower than expected.

Secondly, Reference Yield depends on the analysis conditions. Even for the same power plant, changes in settings such as meteorological data, azimuth, tilt angle, shading, and albedo will alter the value. Therefore, when comparing with analyses from other companies, differences in Reference Yield should not be treated merely as errors but should be checked as differences in input conditions.

Third, do not misunderstand the relationship with PR. PR indicates the power generation performance relative to the Reference Yield, but a higher Reference Yield does not necessarily mean a higher PR. Under high insolation conditions, temperature losses and output limitations can increase, which may lower PR. Conversely, under low insolation conditions, losses may appear smaller and PR may be higher.

Fourth, do not judge based solely on annual values. Even if the annual Reference Yield is the same, generation trends change if the monthly distribution differs. Whether there is more irradiance in summer or in winter, whether snowfall has an impact, or whether morning and evening shading is significant will alter how you interpret energy output and PR. Monthly checks are especially important in cold regions and mountainous areas.

Fifth, you should also pay attention to the difference between Reference Yield and effective solar irradiance. In PVSyst there are multiple items related to solar irradiance. You need to confirm which stage of irradiance is being used—whether it is before or after effects like shading and the IAM are applied—otherwise you may misinterpret the meaning of the values. It is important to determine which stage the value represents by looking at the item names in the report.

By keeping these points in mind, Reference Yield can be used not merely as a number on a report but as a benchmark for PR comparisons.

4 ways to read PVSyst's Reference Yield

When reading PVSyst's Reference Yield in practice, it's easier to understand if you organize it into four perspectives.

The first way to interpret it is to assess the strength of the solar irradiation conditions. Reference Yield indicates how well positioned the plant is to receive solar irradiation. Because it is affected by region, weather data, azimuth, tilt angle, shading, albedo, and other factors, it serves as an entry point for checking the plant’s input conditions. By checking the Reference Yield before looking at annual generation, it becomes easier to determine whether the scale of generation is due to solar irradiation conditions.

A second interpretation is to view PR in terms of its denominator. PR is close to the concept of dividing Specific Yield by Reference Yield, and indicates how much generation was achieved relative to solar irradiation conditions. Therefore, when comparing PRs you must always check the Reference Yield. Comparing PR alone between projects with substantially different Reference Yields can cause you to overlook differences in conditions.

The third way to interpret it is to look at the causes of differences with other companies' analyses. If the Reference Yield is different for the same project, the meteorological data, tilt angle, azimuth, shading, albedo, transposition conditions, etc. may be different. If the Reference Yield is different, both energy generation and PR will change. Before discussing differences in PR or energy generation, you can clarify the assumptions of the comparison by checking the differences in Reference Yield.

The fourth way to interpret the data is to look at seasonal factors by month. Annual values alone do not reveal which season the differences occur in. By examining monthly Reference Yield, it becomes easier to interpret the impacts of summer solar irradiance, winter solar irradiance, snowfall, shading, temperature losses, and clipping. If generation differences or PR differences are concentrated in specific months, you can narrow down the cause by checking the Reference Yield and loss items for those months.

With these four perspectives, the way you read a PVSyst report will change significantly. Instead of looking at energy production, PR, and loss rates separately, you'll be able to understand them as a flow from solar irradiance conditions to the final energy production.

How to proceed with reviews starting from Reference Yield

When reviewing a PVSyst report, it is efficient to start from the Reference Yield and check items in sequence. First, look at the annual Reference Yield to confirm whether the irradiation conditions are reasonable. Compare it with nearby projects and past analyses to ensure it is not significantly different and does not contradict regional characteristics.

Next, check the monthly Reference Yield. If a particular month is unusually high or low, verify there are no anomalies in the meteorological data or the import conditions. In snow-covered regions, examine the winter values; in mountainous areas, also check morning/evening and winter shading; and in coastal or high-temperature regions, consider the summer temperature conditions as well.

Next, check the Specific Yield. Look at how much generation per unit of capacity is achieved relative to the Reference Yield. If the Reference Yield is high but the Specific Yield is not correspondingly high, there may be large losses. If the Reference Yield is low but the Specific Yield is relatively high, losses may be small, or the PR may be appearing higher.

Next, review the PR. When judging whether the PR is high or low, consider factors such as the magnitude of the Reference Yield, temperature conditions, the oversizing ratio, output limitations, shading, and wiring losses. Do not judge good or bad based solely on the PR number; check the Loss Diagram to understand why the PR has that value.

Finally, check the breakdown of losses in the Loss Diagram. Review temperature loss, IAM, mismatch, wiring loss, inverter loss, auxiliary losses, transformer loss, output limitation, etc., and organize the causes of the PR difference. By doing this, the flow from Reference Yield to the final energy output becomes clear, making it easier to present in internal reviews and customer explanations.

This sequence is also effective for standardizing how PVSyst is interpreted. If each person looks at items in a different order, the review results become subjective. By checking in the order Reference Yield, Specific Yield, PR, and Loss Diagram, it becomes easier for anyone to evaluate from the same perspective.

Approach to Verification by Combining LRTK and Field Data

PVSyst is a powerful tool for simulating power generation, but at actual power plants, design drawings, site topography, construction accuracy, equipment layout, and shading conditions also affect generation performance. To correctly interpret Reference Yield and PR, it is also important to verify that the desk-based analysis conditions align with the on-site conditions.

For example, even if the mounting structure is configured in PVSyst as south-facing with a consistent tilt, if the actual azimuth or tilt at the site varies, plane-of-array irradiance and shading conditions may change. On reclaimed sites or in mountainous areas, terrain undulation, slopes, trees, and surrounding structures can cause shading that is larger than assumed. To explain differences in Reference Yield or PR, these site conditions should also be checked.

As with LRTK, having a system that uses an iPhone and GNSS to handle on-site location information, point clouds, and drawing overlays makes it easier to reconcile PVSyst analysis parameters with actual site conditions. If racking positions, graded surfaces, surrounding terrain, point cloud data, and drawing information can be confirmed on site, it helps verify whether assumptions about solar irradiance and shading match the real situation.

In particular, when comparing PR or explaining differences in energy production, consistency with on-site conditions is as important as the numbers themselves. Even if the Reference Yield in PVSyst is reasonable, actual site generation may decline if shading increases in the field. Conversely, if site conditions are better than assumed in the analysis, actual generation can exceed predictions. Combining desk-based analysis with on-site verification can increase the reliability of power plant evaluation.

Reference Yield is a numeric value in PVSyst that represents solar irradiation conditions. However, in practice it only becomes easy to use for PR comparisons and energy production assessments after you confirm that the value is consistent with the site’s orientation, tilt, topography, shading, and construction status. Combining the ability to read PVSyst figures with the ability to inspect the site is important for design reviews and operational evaluations of solar power plants.

Summary

PVSyst's Reference Yield is a very important benchmark in PR comparisons. It is an indicator that expresses the solar irradiation conditions reaching the power plant in a form that is easy to use for performance evaluation, and can be understood as the concept on the denominator side of PR.

Viewing the Reference Yield makes it easier to distinguish whether differences in energy production are caused by solar irradiance conditions or by system losses. In particular, when comparing against analyses from other companies, if the Reference Yield differs, the underlying assumptions—such as meteorological data, azimuth, tilt angle, shading, and albedo—may be different. Comparing only PR in that situation does not provide a fair evaluation.

Reference Yield should be read together with Specific Yield and PR. Reference Yield describes the input solar irradiation conditions, Specific Yield indicates the energy produced per unit of installed capacity, and PR represents the conversion efficiency relative to the irradiation conditions. By combining these three, you can describe a power plant's performance more accurately.

By looking at the monthly Reference Yield as well as annual values, you can also grasp seasonal factors and characteristics of the weather data. You can analyze in greater detail factors that affect PR and energy production, such as summer temperature losses, winter shortages of solar irradiance, snow, shading, and clipping.

Once you learn to read PVSyst's Reference Yield correctly, you can understand energy production, PR, and loss items not as separate numbers but as a continuous flow from irradiation to final energy output. This is useful for internal reviews, explaining to customers, comparing other companies' reports, and post-operation performance evaluation. Reading PVSyst starting from the Reference Yield is the foundation for making accurate PR comparisons.