4 Ways to Read PVSyst's Power Generation Coefficient | How to Use It for Estimates

Table of Contents

• What the generation factor in PVSyst represents

• Prerequisites to check before looking at the generation factor

• Interpretation 1: Normalize by dividing annual energy production by the installed capacity

• Interpretation 2: Examine the causes of the generation factor together with PR and loss rates

• Interpretation 3: Use the monthly generation factor to assess seasonal variation and risk

• Interpretation 4: In estimates, use the generation factor conditionally rather than directly

• Practical procedures for applying the generation factor to estimates

• Points to check when the generation factor is too high

• Points to check when the generation factor is too low

• How to organize PVSyst reports for internal sharing

• Approach to linking on-site verification with the generation factor

• Summary

What does the generation coefficient in PVSyst indicate?

When applying PVSyst results to estimates, the first concept you should grasp is the specific yield. By "specific yield" we mean a practical indicator of how much a solar power plant will generate annually relative to a given installed capacity. In general, it is treated as the annual energy generation divided by the PV capacity, and the units are expressed as kWh/kW or kWh/kWp.

For example, if the PV capacity is 1,000 kW and the annual energy production in PVSyst is 1,250,000 kWh, the specific yield is 1,250 kWh/kW. Looking at this number makes it easier to compare projects even when the scale of the power plants differs. Although the absolute values of annual generation differ greatly between a 2 MW project and a 50 MW project, converting to specific yield makes it easier to compare differences in solar irradiance conditions, design conditions, and loss conditions.

However, the generation factor is not a number that can be judged good or bad on its own. A high generation factor does not necessarily mean an excellent design, and conversely a low generation factor does not necessarily indicate a problem. Solar irradiance and temperature conditions differ in Hokkaido, Tohoku, Kanto, and Kyushu. Tilt angle, azimuth angle, shading, snowfall, PCS capacity, overloading ratio, output control, and electrical loss conditions also vary from project to project. Therefore, the generation factor should be read not as the result itself but as an entry point for verifying the validity of an estimate.

In PVSyst reports, information related to generation coefficients appears in multiple places, such as annual energy production, Specific production, Performance Ratio, Normalized productions, and the Loss diagram. When explaining internally in Japanese, it is easier to understand if you describe Specific production as the generation coefficient, or as the annual energy production per 1 kW of installed capacity.

What’s important in an estimate is not only using the generation coefficient to calculate revenue from power sales and the effects of self-consumption. It is also confirming under what assumptions those figures were produced, whether design risks have been accounted for, and whether there is any inconsistency compared with other companies’ simulations or past projects. Once you can correctly read PVSyst’s generation coefficients, the persuasiveness of your estimates increases, and they become easier to use when explaining generation guarantees, materials for financial institutions, EPC estimates, and O&M plans.

Prerequisites to Confirm Before Reviewing the Power Generation Coefficient

Before reading the generation coefficient, what you must always check is which capacity is being used as the divisor. In solar power generation, multiple capacities appear, such as solar cell capacity, PCS capacity, interconnection capacity, and contracted capacity. The generation coefficient is generally based on the solar cell capacity, but in internal documents or materials from other companies it may be presented based on PCS capacity. If this differs, the impression of the numbers can change significantly even for the same power plant.

For example, suppose a project has a DC capacity of 1,200 kW, an AC capacity of 1,000 kW, and an annual generation of 1,320,000 kWh. On a DC-capacity basis it is 1,100 kWh/kW, while on an AC-capacity basis it is 1,320 kWh/kW. Both calculations are valid, but if the reference for comparison differs, the meaning changes. Since PVSyst's Specific production is usually read as annual generation per PV capacity, it is important to specify the reference capacity when using it in estimates.

The next thing to check is at which point the generation is measured. In PVSyst, generation is divided into stages such as array output, PCS output, and grid injection. What should be used for estimates is, in many cases, the final AC-side energy that can be sold or used for self-consumption. Energy produced on the DC side becomes the final grid injection after PCS losses, AC wiring losses, transformer losses, auxiliary equipment losses, and output limitations. If you choose the wrong value as the annual generation, the estimated revenue and payback period will be incorrect.

Furthermore, it is necessary to check the type of meteorological data. PVSyst can use various meteorological data such as Meteonorm, SolarGIS, Japan Meteorological Agency data, and local measured data. Because the generation coefficient is strongly affected by solar irradiance, the results will change when the meteorological data change. Especially for estimates submitted to banks or used for investment decisions, it is necessary to confirm which meteorological data were used and whether they are long-term averages or specific-year data.

Also, loss settings are directly linked to the specific yield. The final specific yield will vary depending on how losses such as soiling loss, snow loss, IAM loss, temperature loss, mismatch loss, DC wiring loss, AC wiring loss, PCS loss, transformer loss, and auxiliary equipment loss are configured. Rather than judging whether the specific yield is high or low based only on that number, checking these assumptions together is fundamental to making PVSyst results useful for estimates.

Interpretation 1 Normalize annual power generation by dividing it by installed capacity

The most basic way to read the generation factor is to divide the annual energy generation by the installed capacity and view it as the annual generation per 1 kW. PVSyst's results display the annual generation, but when project sizes differ, it becomes difficult to compare them as-is. Converting to the generation factor removes the influence of project size and makes it easier to discern differences in design and regional conditions.

For example, if Project A is 2,000 kW with an annual generation of 2,500,000 kWh, and Project B is 10,000 kW with an annual generation of 12,000,000 kWh, looking only at annual generation makes Project B appear larger. However, when converted to generation per unit of capacity, Project A is 1,250 kWh/kW and Project B is 1,200 kWh/kW. In this case, Project A may have higher generation performance per unit of capacity.

This approach is extremely important for EPC estimates and project financial analysis. Using the generation factor makes it easier to compare with past projects, check regional differences, and verify the effects of design changes. For example, if a project in the same region with similar tilt and azimuth produced about 1,180 kWh/kW in the past, yet a new project shows 1,350 kWh/kW, you need to check whether there are differences in the solar irradiance data, loss settings, shading conditions, or overloading conditions.

In PVSyst, a value equivalent to kWh/kWp/year may be displayed as "Specific production". This value can be used as an indicator similar to the generation factor. However, it is necessary to check which stage of the energy chain it is referenced to. When using it for estimates, it is practical to adopt a generation factor based on the amount of electricity that is ultimately available for sale or for self-consumption.

When looking at the generation factor, also be aware that the solar panel capacity refers to the nominal capacity under STC conditions. In actual power plants, temperature, solar irradiance, module degradation, soiling, shading, wiring resistance, and other influences mean the plant does not always generate according to the nameplate capacity. Therefore, the generation factor should not be read as merely the result of a simple division, but as an indicator summarizing realistic power generation performance over the course of a year.

When using it for estimates, it's easier to explain if you present the calculation basis together rather than showing the generation coefficient as a single number. For example, organizing side by side the solar panel capacity, annual grid injection, generation coefficient, the meteorological data used, and the main loss conditions makes it easier to convey the reliability of the figures for internal approvals and customer explanations.

How to Read 2: Examine the Reasons for the Power Generation Coefficient Alongside PR and Loss Rate

The capacity factor is a useful metric, but the number alone doesn't reveal the cause. That's why you should also look at PR, the Performance Ratio. PR is a performance indicator that shows how much of the theoretically obtainable energy was actually delivered as useful electrical energy. While the capacity factor indicates results relative to solar irradiance and installed capacity, PR can be read as an indicator of how small the system losses are.

There are two main reasons a project can have a high generation factor. One is that the amount of solar irradiation is high. The other is that losses are small and the PR is high. Conversely, projects with a low generation factor can be due to poor solar irradiation conditions or large system losses. To distinguish between these two, it is necessary to look at the generation factor and PR together.

For example, in regions with high irradiation the specific yield can be high even if the PR is somewhat low. Conversely, in regions with low irradiation the specific yield may not be very high even if the PR is high. In estimates, a project may look profitable if you only look at the specific yield, but if the PR is low there may be room for design improvements. It is necessary to check whether shading losses, temperature losses, PCS clipping, wiring losses, transformer losses, and so on are significant.

By looking at the Loss diagram in PVSyst, you can see at which stages and by how much the generated energy is reduced. First there is the conversion from horizontal-plane irradiance to tilted-plane irradiance, and then losses stack up from near shading, IAM, soiling, module temperature, low-irradiance characteristics, mismatch, DC wiring, PCS, AC wiring, transformer, auxiliaries, and so on. If the value of the generation coefficient seems off, inspect the Loss diagram from the top and check where the large drops occur.

What you should pay particular attention to in estimates is whether the high power generation coefficient is due to design improvements or merely overly optimistic loss assumptions. Conditions such as soiling loss being near zero, snow loss not being considered despite being in a snowy region, DC wiring losses or AC wiring losses being set too low, or PCS output limits not being reflected can make the power generation coefficient appear higher. If such assumptions are adopted in the estimate as-is, there is a risk of a large discrepancy with actual generated energy.

On the other hand, a low generation factor does not necessarily warrant pessimism. When conservative loss settings, conservative meteorological data, the accounting of snow and output curtailment, and adjustments to bring estimates closer to measured values are included, the generation factor will tend to appear lower. For financial institutions and long-term business planning, an explainable, conservative generation factor can be more practically useful than an overly optimistic one.

How to Read 3: Observing Seasonal Variations and Risks with Monthly Generation Coefficients

The annual generation factor is useful for getting an overall sense of an estimate, but in practice monthly generation factors are also important. By looking at them month by month, you can identify seasonal generation trends, the effects of snowfall and the rainy season, temperature-related losses in summer, insufficient solar radiation in winter, and periods prone to output curtailment.

Even if the annual capacity factor is the same, a different monthly distribution changes the business implications. For self-consumption projects, it is important whether periods of high electricity demand coincide with periods of high generation. Even for power sales projects, monthly generation is indispensable when considering monthly cash flow, seasonal output curtailment risk, O&M planning, and the timing of weeding and snow removal.

For example, in snowy regions the generation factor can drop significantly during winter. Even if a certain amount of annual generation is secured, if generation falls sharply from December to February, winter feed-in revenue will be reduced. Conversely, in regions where solar radiation increases in early spring while temperatures are still low, module temperature losses are small and generation efficiency can be higher. These seasonal characteristics are easy to overlook when looking only at annual values.

In PVSyst's monthly results, you can view GlobInc, EArray, EGrid, PR, and other parameters. If you want to use a generation factor for estimation, you can organize monthly generation factors by dividing the monthly EGrid or the final available energy for each month by the installed capacity. This will show which months concentrate generation and which months experience declines.

When examining the monthly generation coefficient, it is important to separate variations in irradiance from variations in losses. If a month shows low generation, confirm whether it is due to insufficient irradiance, shading, snowfall, temperature-related losses, or output restrictions. In particular, shading effects vary with the season and solar altitude, so shading losses can become larger in winter. The design of the tilt angle and the spacing between mounting racks also affects the monthly generation coefficient.

In estimates, using monthly generation coefficients allows you to create not only annual revenue projections but also monthly income forecasts. When explaining to financial institutions or operators, presenting the monthly distribution of generation as well as the annual generation makes it easier to convey the realism of the revenue plan. Especially for self-consumption solar power, because the temporal alignment of power demand and generation is important, monthly generation coefficients are not merely reference values but fundamental data for assessing the benefits of installation.

Reading 4: Use the power generation coefficient conditionally in estimates, not as-is

The power generation coefficient obtained from PVSyst is very useful for estimates, but it should not be used unconditionally as-is. In estimates, you must also consider factors not included in PVSyst’s basic simulation, such as design changes, construction conditions, operating conditions, long-term degradation, output curtailment, and shutdown risks.

The first thing to consider is whether PVSyst's generation coefficient represents a first-year value or is intended to be treated as a long-term average. Solar PV modules degrade over time. If you use the first-year generation coefficient unchanged for 20- or 25-year financial calculations, you may overestimate long-term generation. In practice, it is common to use first-year generation as a baseline and apply an annual degradation rate to calculate long-term financials.

Next, we will confirm how curtailment and interconnection constraints are handled. In PVSyst you can set PCS capacity and grid injection limits, but the actual curtailment rules applied by utilities and region-specific curtailment records may need to be examined separately. In particular, in regions with high renewable penetration, reductions due to curtailment are sometimes adjusted for on the project economics side in addition to PVSyst’s generation factor.

Also, at the estimation stage the design is often not finalized. If site grading, racking layout, PCS location, cable lengths, substation equipment, shading conditions, maintenance access, drainage plans, etc. change later, the generation coefficient will also change. For a preliminary estimate, it is preferable to use PVSyst's generation coefficient as a reference value, and to perform a recalculation reflecting the design conditions for the detailed estimate and before contract signing.

When applying a generation factor to an estimate, it is important to attach conditions to the figures. For example, rather than simply stating a generation factor of 1,230 kWh/kW, specify assumptions such as: first‑year expected value according to PVSyst, meteorological data from a specific database, module capacity standard, based on grid injection amounts, output control considered separately, and degradation reflected in the financial calculations. This makes the use of the numbers clear and makes it easier to explain if conditions change later.

The purpose of using a generation coefficient in estimates is not simply to make electricity sales revenue look larger. It is to present a realistic amount of power generation that customers and investors can accept, and to reconcile design assumptions with revenue assumptions. For that reason, rather than transcribing PVSyst results as-is, it is necessary to separate and organize what is simulation output and what are adjustments made for the business plan.

Practical Procedures for Applying the Power Generation Coefficient to Estimates

When applying the generation coefficient to estimates, first check the final annual energy production in the PVSyst report. In many projects, the electricity injected into the grid or the AC energy available on the demand side is used. Next, confirm the reference PV capacity and calculate the generation coefficient by dividing the annual energy production by the capacity.

After that, check whether the power generation coefficient is appropriate as a project condition. While reviewing the area's solar irradiance conditions, tilt angle, azimuth, overloading ratio, PCS capacity, shading conditions, and loss settings, compare with past projects and similar cases. If it differs significantly from projects in nearby areas or with similar design conditions, recheck the PVSyst settings. In particular, module capacity, PCS capacity, meteorological data, loss settings, whether shading is present, and output limit settings have a large impact on the power generation coefficient.

Next, include the generation coefficient in the revenue-and-expenditure calculation. For power-sale projects, multiply the generation coefficient by the installed capacity to determine the annual amount of electricity sold, then multiply by the feed-in unit price to calculate annual sales. For self-consumption projects, separately set how much of the generated electricity will be self-consumed, and calculate the reduction in purchased electricity costs and the amount of surplus electricity sold. If batteries are present, charging/discharging losses and control conditions also need to be taken into account.

In this case, instead of using the PVSyst generation coefficient directly for long-term financial projections, reflect degradation over time. Set the first-year generation, the annual degradation rate, and the assumed operational lifetime, and calculate the generation for each year. Additionally, decide to what extent to treat risks such as maintenance downtime, equipment replacement, curtailment, and variability in snowy years.

In estimates and proposals, including a brief explanation of the generation factor makes it easier for clients to understand. For example, explain that the generation factor is the annual expected generation per 1 kW of installed capacity, that it is calculated from PVSyst simulation results, and that actual generation varies depending on weather, equipment condition, output control, and maintenance status. This clarifies that the generation figures are not a fixed guarantee but simulation values based on certain conditions.

Points to check when the power generation coefficient is too high

If PVSyst's power generation coefficient is higher than expected, the first thing to check is the meteorological data. Verify whether the solar irradiation is being overestimated, whether the site is correct, and whether there are errors in the elevation or latitude/longitude. Even when using data from a nearby site, actual conditions can differ in mountainous areas, coastal areas, or regions with snowfall.

Next, verify that the loss settings are sufficient. Check that soiling losses are not set too low, that snow losses are being considered in snowy regions, that DC wiring losses and AC wiring losses are realistic, and that transformer losses and auxiliary losses have not been omitted. In particular, in early-stage simulations losses may remain unrealistically low as provisional settings, which can make the generation factor appear high.

The PCS output limit is also important. If the PCS capacity is smaller than the DC capacity, clipping will occur on sunny days. If PCS capacity and the grid injection limit are not correctly set in PVSyst, the generation factor can be overestimated. In oversized projects, even if the DC-side generation is high, the AC side will be limited by the PCS capacity, so it is necessary to judge based on the final grid injection amount.

Check the shadow settings as well. If surrounding terrain, trees, buildings, utility poles, or shading between mounting structures are not configured, the power generation coefficient will be overestimated. In particular, for projects where shading occurs during periods of low solar altitude, the annual impact may be only a few percent, but the monthly impact can be significant. Since shadow conditions are often undetermined at the estimation stage, it is important not to treat a power generation coefficient calculated without considering shadows as a definitive value.

A high power generation factor is not a bad thing in itself. In regions with favorable conditions, an appropriate tilt angle, layouts with little shading, low losses, and cool climates, a high power generation factor can occur. What matters is whether you can explain the reasons for it. The figures used in estimates should not be simply high numbers; they need to be numbers you can justify when asked.

Points to check when the power generation coefficient is too low

If the generation coefficient is lower than expected, first check the solar irradiation conditions. If the area's solar irradiation is low, the azimuth deviates significantly from south, the tilt angle is not appropriate, or mountain shading and surrounding obstacles have a large impact, the generation coefficient will be low. Check GlobInc and the effective irradiation in the PVSyst results, and distinguish whether it is low at the irradiation stage or at the loss stage.

Next, check the major loss items in the Loss diagram. If temperature losses are large, review the mounting method, ventilation conditions, and the module temperature model settings. If shading losses are large, reconsider rack spacing and layout, terrain, and surrounding obstructions. If wiring losses are large, there may be room for improvement in cable length, cable size, PCS placement, and junction box placement.

PCS clipping can sometimes make the generation coefficient appear low. In projects with a high oversizing ratio, even if the DC side produces more power, the portion that exceeds the PCS capacity is clipped. This loss is not necessarily bad, because oversizing can increase generation in the morning and evening and during periods of low irradiance, which can improve overall profitability. However, for estimation purposes you must understand clipping losses and be able to explain the advantages and disadvantages of oversizing.

Also, if auxiliary losses or transformer losses are set high, the generation coefficient will decrease. In high-voltage and extra-high-voltage projects, transformer and substation equipment losses may not be negligible. Also check how nighttime no-load losses and auxiliary power are being handled. It is important to review whether the settings in PVSyst match the actual substation equipment specifications.

Even when the power generation factor is low, it can actually be a more realistic estimate. When snow accumulation, output control, maintenance shutdowns, shading, and soiling are properly accounted for, the power generation factor will be lower than in optimistic simulations. The problem is not the low value itself but the inability to explain why it is low. In estimates, it is important to organize the factors that reduce the power generation factor and to separate items that can be improved from conditions that should be accepted.

How to organize PVSyst reports for internal sharing

When sharing the PVSyst generation coefficient internally, it is easier to understand if you organize the information by focusing on the items related to the estimate rather than listing technical terms as-is. First, summarize the project name, solar panel capacity, PCS capacity, annual generation, generation coefficient, PR, meteorological data used, and the main loss conditions. Even this alone makes it easier for sales, design, accounting, and management to discuss while looking at the same numbers.

Next, explain the basis for the generation coefficient. Rather than simply saying it is the number produced by PVSyst, clearly state which generation figure was adopted, by which capacity it was divided, and which losses were taken into account. Because the generation coefficient is directly linked to revenue calculations in estimates, it is important to clarify the origin of the numbers.

For internal comparisons, comparing with past projects is effective. Compare projects in the same region, with similar tilt angles and similar capacity ranges to see whether the power generation coefficient is higher or lower. If there is a difference, leave a comment explaining the reason. If you can identify reasons — different irradiation data, different shading conditions, different PCS capacity, inclusion of snow loss, taking wiring losses conservatively, etc. — the explanatory power of the estimate improves.

When organizing PVSyst results in Excel, it is useful to include not only annual values but also monthly values. Organizing monthly energy production, monthly generation coefficient, and monthly PR makes it easier to spot seasonal variations and anomalies. This monthly view is especially important in snowy regions and for self-consumption projects. Even if the annual figures look fine, if generation is low during months with high demand, the effectiveness of the installation may be smaller than expected.

What you should avoid in internal communications is allowing the generation factor to stand alone. If only the figure 1,250 kWh/kW is shared, its conditions and caveats are omitted. It is important to always share, as a set, the meteorological data, loss assumptions, capacity criteria, the adopted energy, and how output control is handled.

Concept for linking on-site verification with the power generation coefficient

PVSyst’s generation coefficient is a simulation result, but actual power plants are affected by on-site conditions. Therefore, to improve estimation accuracy, it is important to connect the desk-based generation coefficient with on-site verification. In particular, shading, terrain, snow accumulation, drainage, vegetation, surrounding structures, and construction errors are items that tend to cause differences between simulation assumptions and actual conditions.

On site, the first thing to check is factors that block solar radiation. Surrounding mountains, buildings, trees, utility poles, fences, slopes, etc., can cast shadows in the morning and evening and during winter. If PVSyst does not account for shading, on-site verification may require adjusting the power generation coefficient.

Next is the relationship between topography and racking layout. On sloped or irregular land, the layout shown on drawings can differ from the actual construction layout. Changes in rack orientation, tilt, or row spacing will alter the power generation coefficient. Even if calculations at the estimation stage assume an ideal layout, reflecting access ways, drainage, maintenance space, and ground conditions in the detailed design can change the installed capacity and shading conditions.

This kind of on-site verification is effective using smartphone RTK, GNSS positioning, and AR-based overlay of drawings. For example, using a system like LRTK that combines an iPhone with a high-precision GNSS to verify positions on site makes it easier to check racking positions, site boundaries, obstacles, survey points, and the current site topography. If you can reconcile the assumptions in PVSyst with the actual field conditions, you can improve the accuracy of estimates for the energy generation coefficient.

The generation coefficient is a desk-based figure, but its accuracy depends on the quality of on-site information. By confirming on site the presence or absence of shading, the feasibility of the layout, terrain conditions, maintenance access routes, and the effects of snow and vegetation—and reflecting these in PVSyst—you can approach a generation coefficient that is usable for estimates. Even when perfect on-site information is not available at the estimation stage, it is important to organize which conditions remain uncertain and keep them in a form that can be updated later.

Summary

PVSyst's generation coefficient is an important indicator that normalizes annual generation by system capacity, making it easier to compare the generation performance of projects. In estimates, because it forms the basis for revenues from power sales, self-consumption benefits, project cash flow, and investment payback, it must be interpreted correctly.

However, the generation factor is not a number that can be judged on its own. Only by checking it together with annual generation, reference capacity, PR, loss rate, monthly generation, meteorological data, shading conditions, output control, degradation over time, and so on, does it become a figure that can be used for estimates. If the generation factor is high, confirm whether the reason is solar irradiation conditions, good design, or overly optimistic loss assumptions. If it is low, it is also important to separate whether it is a design issue, conservative settings, or regional conditions.

When using PVSyst results in estimates, rather than transcribing them as-is, organize them as conditional generation factors. Clarifying whether the values are first-year figures, whether to include degradation rates in long-term financials, whether to consider output curtailment separately, and which generation figures to adopt will increase the reliability of the numbers.

Also, confirming on-site conditions is indispensable for improving the accuracy of the generation coefficient. Check shadows, terrain, racking layout, obstacles, snow accumulation, maintenance access routes, etc., and by aligning PVSyst’s assumptions with on-site realities you can increase the credibility of the estimate. Using iPhone-compatible high‑precision GNSS like LRTK and AR-based overlay of drawings can streamline on-site position verification and checks of design assumptions, and help substantiate the generation coefficient.

PVSyst's generation coefficient is not merely a simulation result but a decision-making input to make estimates realistic. By reviewing not only the annual values but also PR, losses, monthly trends, and site conditions, you can improve the accuracy of energy generation estimates and produce practical documentation suitable for client explanations and internal approvals.