8 Things to Check in a PVSyst Design Review

Table of Contents

• What to check in a PVSyst design review

• 1. Review the basic conditions and project assumptions

• 2. Check the validity of meteorological data and solar irradiance

• 3. Review the design intent for azimuth and tilt angles

• 4. Review the balance between DC capacity and PCS capacity

• 5. Review near-field shading, far-field shading, and terrain impacts

• 6. Review the assumptions behind loss settings

• 7. Review the consistency between energy yield and PR

• 8. Review the differences between reports

• Points to note when using PVSyst for design reviews

• How to connect on-site verification with a PVSyst review

• Summary

What to look for in a PVSyst design review

In a solar power plant design review, it is necessary to comprehensively verify the drawings, equipment specifications, layout plan, wiring plan, terrain conditions, constructability, and projected power generation. In that context, PVSyst is not merely software for producing annual energy estimates, but an important verification document for organizing how design conditions affect generation performance.

When viewing a PVSyst report, many people first check the annual energy yield and PR. Of course the final energy yield is important, but the purpose of a design review is not merely to judge the size of the numbers. It is important to understand why that energy yield is what it is, which conditions are having an effect, and where the design risks and scope for improvement lie.

Especially for commercial solar projects, simulation results can vary greatly even with the same installed capacity depending on tilt angle, azimuth, spacing, shading, PCS capacity, wiring distance, transformer configuration, snowfall, temperature conditions, and output control conditions. PVSyst can quantify and organize these conditions, so it serves as an easy-to-use document and common language for design reviews.

However, PVSyst results are calculations based on the assumption that the input conditions are correct. If the input assumptions deviate from actual conditions, the output results will also deviate from reality. Therefore, in design reviews, it is necessary to interpret the results by sequentially checking not only the energy yield figures but also the input conditions, loss assumptions, design intent, and consistency with site conditions.

This article explains how to interpret PVSyst design reviews, broken down into eight items. It summarizes practical perspectives that can be used for checking design drawings, internal reviews, reviewing materials for financial institutions, discussions with EPCs, and organizing risks from an O&M perspective.

1. Read the basic conditions and project assumptions

The first thing to check is the basic conditions of the PVSyst report. Listed here are the project name, location, meteorological data, installed capacity, module model, PCS model, string configuration, tilt angle, azimuth, system configuration, and so on.

In design reviews, we confirm that these basic conditions are consistent with the drawings and equipment specifications. For example, we verify whether the module model matches the latest specifications, whether the PCS rated capacity corresponds to the actually selected unit, and whether the DC capacity agrees with the capacity calculated from the number of modules shown on the design drawings. If these are off, no matter how closely you examine subsequent power generation estimates or loss rates, the assumptions of the review will be undermined.

Particular attention should be paid to how equipment capacity is handled. In solar power generation, multiple similar terms appear — DC capacity, AC capacity, PCS capacity, interconnection capacity, contracted capacity, etc. If you compare values shown in PVSyst without confirming which capacity they refer to, you can easily misjudge the energy production and the evaluation of kWh/kW.

Also, when a power plant is analyzed by dividing it into multiple sections, it is important that the capacity, tilt angle, azimuth, and PCS configuration of each section are correctly separated. Whether the entire plant is analyzed under a single representative condition or each section is analyzed individually will change the accuracy of the results and their interpretation.

In a design review, you first confirm that PVSyst correctly represents the actual design. Before assessing the quality of the energy yield, the starting point for interpretation is to verify that the input model appropriately reflects the real power plant.

2. Assessing the validity of meteorological data and solar radiation

Next, we check the meteorological data and solar irradiance. PVSyst's annual energy production strongly depends on the assumptions about solar irradiance. Therefore, even with the same system design, the energy production varies depending on the meteorological data used.

In design reviews, we check which meteorological data are being used. In PVSyst, external meteorological data such as Meteonorm or SolarGIS, or measured data, may be imported for analysis. We confirm which data have been adopted, whether they are appropriate for the site in question, and, if data from nearby locations are used, whether the distance or elevation difference poses any problems.

When assessing solar irradiance, it's important to check monthly trends as well as annual values. For example, if winter solar irradiance is unusually high, summer temperatures are unusually low, or a snowy region shows unnaturally high winter power generation, there may be inconsistencies in the meteorological data or the loss settings.

Also, the conversion from horizontal-plane irradiance to tilted-plane irradiance is also important. In PVSyst, the irradiance incident on the module surface forms the basis for energy production calculations. Because the relationship between horizontal irradiance and effective irradiance changes with tilt and azimuth, design reviews verify how much effective irradiance results from the combination of the irradiance data and the chosen design angles.

The validity of meteorological data is important not only for designers but also for investors, financial institutions, and those assessing power output guarantees. Even if projected power generation appears high, if the assumptions for solar irradiance are overstated, the difference may stem from the data assumptions rather than from superior design. Conversely, if projected generation appears low, it may not reflect poor design but rather that the meteorological data are conservative.

3. Reading the design intent of azimuth and tilt angles

In a PVSyst design review, understanding how to read the azimuth and tilt angles is also important. The power output of a solar PV system changes depending on which direction the modules face and at what angle they are installed.

Generally, the closer to south-facing and the more the tilt angle is optimized for the region, the higher the power generation tends to be. However, in actual designs, constraints such as site shape, land development conditions, racking layout, roads, drainage, shading, constructability, wind loads, snowfall, and landowner conditions mean that the angle that maximizes power generation is not always chosen.

In a design review, you need to not only check whether the azimuth and tilt angle are reasonable as numerical values, but also interpret why those angles were chosen. For example, the azimuth may be adjusted slightly to align the racking rows neatly with the site. The tilt angle may be lowered to reduce row spacing and increase the number of panels installed. In snowy regions, the tilt angle may be set larger to allow for snow shedding and to improve winter power generation.

In PVSyst, differences in azimuth and tilt angles are reflected in tilted surface irradiance, shading losses, and energy production. Therefore, during design reviews it is important to consider the angles themselves together with the losses and differences in energy production that result from those angles.

If the azimuth significantly deviates from due south, check how much the energy yield has decreased. When the tilt angle is low, consider not only the impact on annual energy production but also the effects on soiling, snowfall, drainage, and maintainability. PVSyst results focus primarily on energy production, but design reviews should evaluate on-site operational aspects as well.

4. Reading the Balance Between DC Capacity and PCS Capacity

What you must always check in a design review is the balance between DC capacity and PCS capacity. In solar power plants, the ratio between DC capacity, which is the total capacity of the modules, and the AC-side capacity, which is the output capacity of the PCS, has a major impact on power generation and losses.

In PVSyst, you can check the relationship between module capacity and PCS capacity using concepts equivalent to the Pnom ratio and the DC/AC ratio. Designing the DC capacity to be larger than the PCS capacity is common, but if it is made too large, the PCS will reach its output limit during periods of strong solar irradiance and clipping losses will occur. Conversely, if the DC capacity is too small, the PCS’s capability cannot be fully utilized, which may lower the efficiency of the investment.

In a design review, we check whether the PCS oversizing ratio is reasonable. The appropriate balance varies depending on the plant’s location, solar irradiation conditions, temperature conditions, azimuth, tilt angle, whether output control is present, the feed-in tariff, and equipment costs. Therefore, rather than simply focusing on whether the DC/AC ratio is high or low, it is important to look at how much clipping loss is occurring in PVSyst.

Also, when checking PCS capacity, pay attention to power factor conditions and how the active power limit is handled. If the PCS's rated capacity, the grid interconnection limits, and the way output limits are configured in PVSyst are not consistent, you may misinterpret losses and energy production.

For example, even if the PCS rating is presented as a fixed value in the equipment specifications, the way results appear can change depending on whether, in the analysis, it is treated as an upper limit of active power or whether apparent power and power factor are included. In design reviews, it is important to confirm PCS capacity, power factor, output limits, and clipping losses together.

5. Interpreting Near-Field Shading, Far-Field Shading, and Terrain Effects

In PVSyst design reviews, the handling of shading is also an important item to verify. In solar power generation, shadows from buildings, trees, terrain, other mounting structures, utility poles, fences, mountains, and adjacent equipment affect energy production.

In PVSyst, you can define near and far shadows to reflect shading losses. In design reviews, you need to verify not only the shading loss figures but also which shadows are being modeled and which are being ignored.

For near shading, shadows cast between racking rows, nearby structures, and terrain undulations are important. In particular, for ground-mounted systems, the relationship between row spacing and tilt angle tends to produce shading in the mornings and evenings during winter. If PVSyst results show large near-shading losses, there is room to revisit row spacing, tilt angle, racking height, and array azimuth.

Distant shading occurs when mountains, hills, or surrounding terrain block sunlight during periods of low solar altitude. In mountainous areas, on slopes, and in valley topographies, whether distant shading is considered can affect the amount of power generated. In reviews, we check whether distant shading has been left unset for projects with severe terrain conditions.

Shading losses are a factor that is difficult to judge based on annual values alone. Whether the shading is concentrated in winter or occurs throughout the year changes its design implications. Even if shading in winter is significant, its impact on annual energy generation may be limited. Conversely, if shading occurs during key daytime hours, the impact on generation becomes large.

PVSyst's shading settings depend on the accuracy of the 3D model and the layout conditions. If the placement on the drawings does not match the actual terrain or structures, the shading loss assessment will also be off. During design reviews, it is useful to verify the shading assumptions by cross-checking drawings, site photographs, point clouds, and terrain data.

6. Read the assumptions behind the loss settings

What is important in a PVSyst report is the various losses shown in the Loss Diagram. In design reviews, each loss item is checked one by one to determine whether it is reasonable as a design condition.

Typical losses include IAM loss, soiling loss, temperature loss, low-irradiance loss, mismatch loss, DC wiring loss, PCS loss, AC wiring loss, transformer loss, auxiliary equipment loss, output curtailment loss, etc. These are factors that reduce power generation, and even small changes in their settings can affect annual energy production.

In design reviews, we check not only whether loss values fall within typical ranges but also whether they match the project conditions. For example, if a design has long DC wiring distances yet the wiring losses are extremely small, the wiring condition inputs may not reflect reality. Conversely, if PCS units are distributed near the mounting racks but the DC wiring loss is set excessively high, the energy production may be conservatively estimated.

Soiling losses are also important. Under conditions such as a lot of dust in the surroundings, proximity to agricultural land or unpaved roads, low rainfall, or a low tilt angle, soiling losses cannot be overlooked. In snowy regions, it is necessary to confirm whether generation losses due to snow are treated as soiling losses or reflected by other methods.

Temperature losses reflect the decrease in power generation efficiency as module temperature rises. Temperature conditions vary depending on the mounting system, ventilation conditions, installation height, and whether the system is roof-mounted or ground-mounted. It is also important in design reviews to verify that PVSyst’s temperature model matches the actual installation conditions.

The Loss Diagram is a document that visualizes where power generation is being reduced. Rather than simply looking at loss rates, it is important to interpret it by separating losses that can be addressed through design improvements from losses that should be accepted as equipment characteristics or as natural conditions.

7. Assessing the Consistency Between Energy Output and PR

Metrics commonly seen in design reviews are annual energy production and PR. Annual energy production indicates how much electricity a plant generates over a year, and PR is an indicator of how efficiently the system generates power relative to solar irradiance conditions.

High energy production does not necessarily mean the design is good. In regions with high solar irradiance, energy production can appear high even if losses are somewhat large. Conversely, in regions with low solar irradiance, energy production can appear low even if the design is good. Therefore, in design reviews, energy production and PR are checked together.

If PR is extremely high, check whether the loss settings are too lenient and whether shading, soiling, wiring, temperature, and PCS losses are being accounted for appropriately. A high PR in itself is a good thing, but if it is unrealistically high there is a risk of diverging from future actual performance.

On the other hand, if PR is low, we distinguish whether it is due to a design issue or conservative settings. From the Loss Diagram, we check factors causing the PR decline, such as large shading losses, large wiring losses, significant PCS clipping, high temperature losses, or large losses from snow or soiling.

Also, metrics such as kWh/kW, which are obtained by dividing annual energy generation by installed capacity, can be used for comparison. However, the meaning of this metric also changes depending on whether the capacity is based on DC or AC. In design reviews, it is important to standardize the denominator used for comparisons.

When reviewing PVSyst results, rather than looking at energy production, PR, loss rate, and irradiance separately, check whether they are consistent with each other. If irradiance is high but energy production is not increasing, there may be significant losses. If PR is high but energy production is low, conditions such as irradiance, azimuth, or tilt may be affecting output. In this way, it is important to interpret multiple indicators together.

8. Read the differences between reports

In design reviews, there are many situations where multiple PVSyst reports are compared. These include comparisons of initial and final designs, comparisons of multiple proposals, comparisons with analyses from other companies, comparisons between reports prepared for submission to financial institutions and those for internal review, and comparisons of sectional analyses with consolidated reports, and so on.

When comparing differences between reports, you must first standardize the comparison parameters. If the meteorological data used, module type, PCS model, capacity, azimuth, tilt angle, loss settings, shading settings, or output restriction conditions differ, differences in power generation will naturally occur.

In a differential comparison, the important thing is not to jump straight into discussing the difference in final power generation. First, examine the differences in solar irradiance, irradiance on tilted surfaces, shading loss, temperature loss, wiring loss, PCS loss, and output curtailment loss, in that order. By identifying which item is the primary cause of the generation difference, the design issues become clear.

For example, if our in-house analysis shows lower power generation than another company's analysis, before concluding that the design is poor we check for differences in meteorological data, soiling losses, snow considerations, wiring losses, transformer losses, auxiliary equipment (BOS) losses, and shading settings. Sometimes the result is lower because conservative settings were applied, and other times the design actually incurs large losses.

Conversely, when your in-house analysis indicates higher power generation, reviewers need to be more cautious. Higher generation may appear desirable, but if it is only due to lenient input conditions, the discrepancy with actual performance becomes a problem. In design reviews, it is important to adopt an approach of verifying the rationale for both high and low results.

When comparing reports, organizing the differences in a table makes assessment easier. In particular, arranging capacity, solar irradiance, PR, annual energy production, major losses, PCS clipping, wiring losses, and shading losses side by side makes it easier to see where discrepancies arise. However, for the final determination you should verify consistency with the design drawings and site conditions, not just the numbers.

Points to note when using PVSyst in design reviews

PVSyst is a very useful analysis tool, but there are several points to be aware of during design reviews. First, the results from PVSyst depend on the input conditions. The numbers produced by the software are not inherently correct; they are useful as a basis for design decisions only when the input conditions are accurate and the modeling is appropriate.

Next, while PVSyst is strong for energy-yield assessment, it is not a tool that directly evaluates constructability or maintainability. For example, narrowing row spacing can increase installed capacity and thus raise energy production, but it may create problems with aisle widths, mowing, cleaning, inspections, cable laying, racking installation, and heavy-equipment access routes. In design reviews, PVSyst’s energy-yield evaluation should be considered separately from on-site construction and operational assessments.

Also, in PVSyst reports, losses are organized by item, but not all losses are estimated with the same level of confidence. Some items, such as equipment efficiency, are relatively straightforward to assess from specifications, while others—such as soiling, snow, shading, future tree growth, and power curtailment—have much greater uncertainty.

In design reviews, it is important to separate and organize defined conditions, design assumptions, conservative estimates, and uncertain risks. This allows PVSyst results to be used not merely as numbers but as explanatory material for design decision-making.

Furthermore, when explaining to financial institutions or project owners, it is important not to rely solely on overly technical terminology. Terms such as PR, Loss Diagram, clipping, IAM, and mismatch are understood to differing degrees by stakeholders. In design review materials, it is necessary to clearly explain the meaning of the numbers and their implications for the design.

Approach to connecting on-site verification and PVSyst review

To make PVSyst design reviews more practical, it is important to link them with on-site verification. Judging solely from drawings and PVSyst can cause actual site conditions to be overlooked.

For example, even if the plans appear to show little shading, the site may contain trees, slopes, utility poles, adjacent buildings, temporary structures, or structures not shown on the drawings. The ground elevation may change before and after development. The rack orientation shown on the drawings may also differ slightly from the actual placement during construction.

In such checks, high-precision GNSS positioning using a smartphone and on-site AR verification can be helpful. By using a system that combines an iPhone with GNSS, like LRTK, to confirm site positions with high accuracy, it becomes easier to cross-check the rack positions, survey points, boundaries, and installation locations shown on drawings with the actual site. Confirming the azimuth, layout, and shading conditions set in PVSyst not only at the desk but also on-site can improve the accuracy of design reviews.

In particular, shadows, spacing, interactions with boundaries, and conflicts with roads or drainage, which can be difficult to detect during the design phase, are worth verifying on site. If PVSyst analysis results raise concerns about shading losses or layout conditions, confirm their causes at the site and, if necessary, incorporate them into the design or analysis conditions.

A design review is not something that can be completed by simply reading the PVSyst report. By checking the figures in PVSyst, verifying the layout on the drawings, and confirming the actual conditions on site, you can achieve a more reliable review.

Summary

The approach to interpreting PVSyst for design reviews is not limited to looking only at annual energy production or PR. By checking, in order, the basic conditions, meteorological data, azimuth angle, tilt angle, the balance between DC capacity and PCS capacity, shading, loss settings, the consistency between energy production and PR, and the differences between reports, you can organize the design-related issues.

In a design review, the most important thing is not to take PVSyst’s figures at face value but to interpret why those figures are what they are. Whether the energy production is high or low, you need to verify the reasons by reviewing the input conditions and the loss items.

PVSyst is a powerful tool for numerically describing the design of solar power plants. However, a proper review requires cross-checking with drawings, equipment specifications, site conditions, constructability, and maintainability. By using PVSyst results as the central document for design review while tying them to actual site conditions, you can achieve more accurate energy yield assessments and design improvements.