How to Read PVSyst Design Conditions: 5 Things to Check Before Viewing Results

PVSyst should read the design conditions before the results

When looking at a PVSyst report, many people first go to the result pages such as Annual Energy Generation, Performance Ratio, Specific Yield, Grid Injection, and the Loss Diagram. Of course, the final energy output and PR are important. For business feasibility evaluations, quotes, materials for financial institutions, explanations to clients, and confirming terms with the EPC, the final numerical results serve as the basis for decision-making.

However, when reading PVSyst, the first thing to grasp is not the results themselves but the assumptions that produced those results. No matter how neatly a report is presented, if the design conditions differ from the actual project situation, comparisons of energy yield or PR become less meaningful. Conversely, if you confirm the design conditions first, it becomes easier to judge whether the resulting figures are high or low, reasonable, or simply the result of differing conditions.

PVSyst is software for simulating solar power plants, but it is not something that will simply produce generation just by entering the location. Meteorological data, azimuth, tilt angle, module capacity, PCS capacity, string configuration, wiring losses, transformer losses, temperature conditions, near shading, far shading, albedo, soiling, output limits, grid injection conditions, and many other input parameters combine to produce the results.

Therefore, when reading PVSyst results, it is important to first check "under what design conditions these results were calculated." If you judge the magnitude of energy output by looking only at the results page, the differences may simply be due to differences in design capacity, PCS capacity, loss conditions, or meteorological data. Especially when comparing analysis reports from multiple companies, comparing only PR or annual energy production without confirming differences in design conditions can lead to incorrect evaluations.

In this article, we outline five perspectives you should pay particular attention to when reading the design conditions in PVSyst. The intended readers are designers, construction managers, power producers, O&M personnel, estimators, and those responsible for preparing materials for financial institutions who need to read PVSyst reports in their work. By checking the design conditions before moving on to the results pages, the way you read PVSyst becomes much more stable.

What does the "Design Conditions" page in PVSyst show?

Design conditions in PVSyst refer to the power plant specifications, equipment configuration, installation conditions, and loss conditions that serve as the assumptions for energy production calculations. In the report, they appear as pages or items related to Project, Variant, System, Orientation, PV Array, Inverter, Detailed losses, Near shadings, Horizon, Albedo, Grid, and so on.

The purpose of reading the design conditions is not merely to verify the input values. The purpose is to determine whether those conditions align with the actual plan, whether they are based on the same assumptions as the report being compared, and whether the conditions that significantly affect the results are appropriately set.

For example, even for the same solar power plant, you cannot directly compare annual generation between a report calculated with a module capacity of 100 MWdc and a report calculated with 98 MWdc. A report with a tilt angle of 10 degrees and one with 15 degrees will show differences in monthly solar irradiation and shadowing patterns. If PCS capacity differs, the oversizing ratio, clipping, grid injection, and the apparent PR will also change.

Furthermore, even with the same capacity, different loss conditions will change the results. DC wiring losses, AC wiring losses, transformer losses, Auxiliary loss, Module quality loss, LID, Mismatch, IAM, Soiling, Albedo, etc., may appear to be only a few percent numerically, but they make a large difference in annual energy generation. Especially in large-scale projects, a 1 percent difference can affect revenue and warranty terms.

The design conditions in PVSyst form the foundation for judging the reliability of the results. Rather than simply interpreting a report as good because it shows high annual energy production or a high PR as indicating an excellent design, the practical way to read PVSyst is to look at the conditions under which those results were produced.

By mastering how to read the design conditions, you will be able to make judgments such as the following: distinguish whether differences in power generation are caused by meteorological conditions, design capacity, loss settings, shading conditions, or PCS output limitations. This is extremely important for internal reviews, explanations to the client, queries with the EPC, and comparisons with third-party reports.

How to Read Design Conditions 1: Check Project Information and Meteorological Data

The first things to check in PVSyst's design conditions are the project information and the meteorological data. If you overlook these, all subsequent result comparisons will become unstable. In PVSyst, factors such as the installation site, latitude and longitude, elevation, the meteorological data source and period, monthly solar irradiance, ambient temperature, horizontal plane irradiance, and irradiance on a tilted surface greatly influence the results.

The first thing to check is the project's location. Check whether the actual location of the power plant and the coordinates set in PVSyst are significantly offset. A difference on the order of hundreds of meters (hundreds of ft) to several kilometers (several mi) may have little effect in some cases, but in mountainous areas, snowy regions, coastal areas, basins, and areas with large elevation differences, differences in location and elevation can affect solar radiation and temperature.

Next, review the types of meteorological data. In PVSyst, multiple meteorological data sources may be used, such as Meteonorm, SolarGIS, satellite data, measured data, and data from nearby observation points. Even at the same location, annual and monthly solar radiation can vary depending on the meteorological data source. Therefore, when comparing multiple PVSyst reports, you must always check not only the energy production but also which meteorological data were used for the calculations.

Particularly important is checking Global horizontal irradiation, Diffuse horizontal irradiation, and Ambient temperature. Horizontal-plane global irradiation, diffuse irradiation, and ambient temperature affect tilted-surface irradiation, module temperature, and power generation efficiency. If annual irradiation is high, energy yield tends to increase, and if ambient temperature is low, module temperature losses tend to be smaller. In cold climates, not only irradiation but also improvements in power generation efficiency due to low temperatures, losses from snow accumulation, and increased albedo come into play, so simple comparisons cannot be made.

Monthly weather data are also important. Even if the annual values are similar, a different monthly distribution can change how power generation, temperature losses, shading losses, and snow impacts appear. For example, datasets with high solar irradiance in summer versus datasets with high irradiance in spring and autumn can yield different generation results even with the same annual irradiance. Because temperatures are higher in summer and module temperature losses tend to be larger, the conversion efficiency from irradiance to energy production can change even with the same irradiance.

When looking at meteorological data, it is important not to focus on the goodness or badness of the calculated results, but to assess whether they are reasonable as design conditions. Compare with surrounding measured data, past power generation performance, Japan Meteorological Agency data, and external sources such as SolarGIS and Meteonorm, and check whether irradiance is unreasonably high or temperatures unreasonably low.

Especially in reports for submission to banks or for investment decisions, it is easier to explain if you clarify whether the meteorological conditions are conservative, average, P50-equivalent, or closer to a P90-type assessment.

One aspect that is easy to overlook when using PVSyst is the correction and import conditions of meteorological data. For meteorological data imported from external sources, units, time stamps, time zone, missing-data handling, conversion from the horizontal plane to the tilted plane, and the treatment of diffuse irradiance can all affect the results. When using Hourly data, a time offset can influence calculations of morning and evening irradiance and shading.

Before viewing the results page, first check the project name, Variant name, site name, coordinates, elevation, weather data source, annual irradiation, monthly irradiation, and ambient temperature. If these match the actual design, it then makes sense to read the equipment configuration and loss conditions. Conversely, if there is a major inconsistency here, you should verify the validity of the meteorological conditions before examining the annual power generation or PR in detail.

How to read Design Condition 2: check the azimuth and tilt angle

The next design parameters to check are the module azimuth and tilt angles. In PVSyst they appear as items related to Orientation, and conditions corresponding to the plant’s installation type—fixed tilt, tracking, multiple azimuths, multiple tilts, east-west installation, etc.—are set.

Azimuth and tilt angles are important parameters that determine the amount of solar radiation incident on an inclined surface. In photovoltaic power generation, it is not the irradiance on the horizontal plane itself but the irradiance on the module surface that directly determines power output. Therefore, even if the meteorological data are the same, changes in tilt or azimuth will alter the Plane of Array irradiance and the Effective irradiation.

The first thing to check is whether the tilt angle on the design drawings and racking specifications matches the tilt angle in PVSyst. If the plan calls for 15 degrees but PVSyst is calculated at 10 degrees, or if some areas have different tilt angles but are represented by a single angle, the results will differ. In snowy regions in particular, the tilt angle affects snow shedding, albedo, and winter energy production, so the impact on results can be significant.

The same applies to azimuth. Confirm whether the array faces due south, is tilted to the southeast or southwest, or has multiple orientations to match the terrain. If it is tilted east or west, not only the annual energy yield but also the time-of-day generation curve will change. Azimuth affects generation patterns — for example, designs that are stronger in the morning, stronger in the afternoon, or that suppress the peak.

When handling multiple orientations or multiple tilts in PVSyst, you need to confirm that the capacity allocation for each surface is correct. For example, at a plant where south-facing and southwest-facing areas coexist, if PVSyst is set to calculate everything as south-facing, the results may appear better than reality. Conversely, if a conservative representative angle is set, the results may come out lower.

The tilt angle also affects shadow calculations. Depending on the relationship between row-to-row spacing, racking height, terrain gradient, and solar altitude, the conditions for near shading change. In PVSyst, Near shadings or the 3D scene are sometimes used to evaluate shading, but if azimuth or tilt angle differ, shading losses will also change. You should not consider the tilt angle in isolation; it is important to interpret it together with the shading conditions.

When evaluating azimuth and tilt angles, we consider not only their effect on annual energy production but also their impact on month-by-month generation. Low tilt tends to increase solar gain in summer, while it can be disadvantageous in winter. High tilt can be advantageous for winter solar gain and snow shedding, but may be disadvantageous in summer and with respect to installation density. Thus, tilt must be assessed as a balance among energy production, land use, shading, snow, and constructability.

When checking the Orientation in PVSyst's design conditions, don't simply read it as "south-facing 15 degrees"; verify that it is consistent with the actual site layout, mounting structure specifications, terrain, PCS blocks, and string configuration. If it doesn't align, it will affect everything from the conversion of solar irradiance to the resulting power output.

How to Read Design Conditions 3: Confirm Module Capacity and PCS Capacity

One of the most important parameters in PVSyst design conditions is the module capacity and PCS capacity. These are related to the System, PV Array, and Inverter pages. They are the basic conditions for determining the plant size, oversizing ratio, clipping, voltage range, string configuration, number of PCS units, and so on.

The first thing to check is the nominal capacity of the PV array. Verify that the module model, output per module, number of modules, and total DC capacity match the planned values. In PVSyst this is often shown as kWp, and if this differs it will affect how you interpret Specific Yield and PR. Even if the annual energy generation is large, you cannot simply say it is better if the DC capacity is also large.

Next, what you should check is the capacity of the PCS or inverter. Check the PCS model, rated output, number of units, and the total AC capacity. From the relationship between DC capacity and AC capacity, determine the Pnom ratio, the DC/AC ratio, and the oversizing rate. In solar power plants, it is common to design the module capacity on the DC side to be larger than the PCS capacity on the AC side. While this design increases power generation, during periods of strong solar irradiance the PCS may impose output limits, resulting in the so‑called clipping.

What's important when reading PVSyst is distinguishing whether differences in energy production are because the plant actually generates more power, or simply because it has a larger DC capacity. When comparing multiple reports, you should look not only at annual energy production but also at Specific Yield, Performance Ratio, DC capacity, AC capacity, and the Pnom ratio.

We also check the string configuration: whether the number of modules per string, the number of parallel strings, the number of MPPTs, and the number of connections per PCS match the equipment specifications. It is important to confirm that the string voltage falls within the PCS’s MPPT range, that the open-circuit voltage at low temperatures does not exceed the maximum input voltage, and that it does not drop below the MPPT lower limit at high temperatures. PVSyst may warn about electrical mismatches, but report readers should also verify these as design conditions.

Module model and PCS model also affect the results. If a module’s temperature coefficient, low-irradiance characteristics, IAM characteristics, degradation conditions, size, rated output, and voltage–current characteristics differ, the energy yield can change even with the same capacity. The PCS likewise changes the results depending on its conversion efficiency curve, MPPT range, maximum input current, output limitations, and power factor conditions. Therefore, it is important to confirm whether the model is a provisional setting or the finalized actual unit.

What requires particular attention is the definition of PCS capacity. It is necessary to confirm whether the AC capacity shown in the report is the upper limit of active power, how its relationship with apparent power is treated, and, if a power factor setting exists, how the output limit is handled. In projects with power factor conditions or grid requirements, misreading the PCS rating and output limits can lead to incorrect interpretations of Grid Injection and losses.

Also, when output limits are set in PVSyst, check whether those limits are for an individual PCS or are restrictions caused by the plant’s overall grid interconnection capacity. For example, if the total PCS capacity is large but the grid injection capacity is separately limited, the way losses and energy yield are read on the report will change. If you can see Grid limitation or Inverter loss over nominal power on the Results page, it is necessary to go back and check the capacity settings in the design conditions.

Misreading module capacity and PCS capacity will lead to misunderstanding the overall PVSyst results. Before looking at the final energy yield, confirming DC capacity, AC capacity, the DC/AC ratio, string configuration, PCS model/type, and output limiting conditions is central to verifying the design conditions.

How to read design conditions 4: Confirm the loss conditions

In PVSyst, the loss conditions in the design settings have a major impact on the results. Loss conditions appear in Detailed losses and the Loss Diagram, but rather than only looking at the resulting loss rates, you should first check how they were entered as design conditions.

Typical loss conditions include Module quality loss, LID, Mismatch loss, DC ohmic loss, AC ohmic loss, Transformer loss, IAM loss, Soiling loss, Auxiliary loss, Thermal loss, Unavailability, Ageing. Depending on the project, MV transformer loss, MV line loss, Grid limitation, Battery loss, Self consumption loss may also be relevant.

The first thing to check is the DC wiring loss. DC wiring loss is caused by the wiring resistance from the module to the junction box, from the junction box to the PCS, or from the string to the PCS. In PVSyst it can be set as a loss rate for standard test conditions or for operating conditions. Appropriate loss rates vary depending on wiring length, cable size, current, voltage, and PCS placement.

In a distributed PCS design that places the PCS close to the racking, the DC wiring distance is shorter, so losses may be relatively small. On the other hand, designs where the distance from the combiner box to the PCS is long, or designs that route large-capacity DC trunk lines, can result in larger losses. If DC loss is set to, for example, 1.5 percent in a PVSyst report, confirm whether that value is reasonable for the project's wiring design.

Next, check the AC wiring losses. These may include the wiring losses from the PCS to the transformer, from the transformer to the receiving/substation equipment, and up to the point of interconnection. AC wiring loss values vary depending on whether they include the low-voltage side, the medium-voltage side, or the high-voltage side. When comparing PVSyst reports with each other, you must confirm whether the scope of AC loss is the same; otherwise, you cannot compare the loss rates.

Transformer losses are also important. Transformers have no-load losses and load losses, comprising a component that occurs continuously and a component that increases with load. In PVSyst, these may be configured as Transformer loss. In large-scale projects, the treatment of transformer losses affects energy yield and PR. In particular, caution is needed when the handling of transformers for PCS, transformers for grid connection, and MV line differs between reports.

Soiling loss relates to how you assess dirt, sand, pollen, ash fallout, snow accumulation, cleaning frequency, and so on. In PVSyst it can also be set on a monthly basis. Results differ depending on whether you apply a uniform annual loss rate or vary it seasonally. In snowy regions, it is important not only to consider soiling but also how to handle generation outages due to snow and increases in reflection. Verify whether soiling is applied conservatively or based on actual performance.

Thermal losses must not be overlooked. Solar modules' output decreases as temperature rises. In PVSyst, thermal loss coefficients such as Uc and Uv, the mounting method, and ventilation conditions are relevant. Appropriate thermal conditions vary depending on whether the modules are roof-mounted, ground-mounted, or rack-mounted, and on the quality of rear ventilation. If temperature losses are large on the results page, check the thermal loss coefficients used as design conditions as well as the ambient temperature.

IAM loss is the reflection loss of light entering at oblique angles. It varies depending on glass properties, the module surface, and the angle of incidence. Because it is also related to azimuth and tilt angles, it should be evaluated together with the design conditions. If IAM loss is large, it may be affecting power generation in the mornings and evenings and during winter.

Auxiliary loss may represent auxiliary consumption such as PCS, monitoring devices, air conditioning, trackers, and communication equipment. Which items are included in auxiliary consumption varies by project. It is necessary to check whether it reflects the power plant's actual auxiliary power, uses standard values, is constant throughout the year, or applies only during generation hours.

When reading loss conditions, the basic rule is to distinguish whether each loss is a value based on the actual design, a standard value, or a conservative assumption. Instead of interpreting a small loss rate as good and a large one as bad, verify whether there is a basis for the figure. In practice, it is important to be able to explain the rationale for the loss conditions.

If PVSyst results show a high energy production, it may simply mean the loss assumptions are too lenient. Conversely, if the energy production appears low, it may simply mean conservative loss assumptions were used. Checking the loss assumptions before reviewing the results lets you correctly interpret the numbers' background.

How to Read Design Conditions 5: Check Shadows, Topography, and Grid Conditions

Finally, the design conditions that should be checked are shadows, terrain, and grid conditions. These are important items that reflect the on-site conditions of the power plant. In PVSyst, they relate to Horizon, Near shadings, 3D scene, Electrical shading, Grid limitation, and so on.

First, check the Horizon. Horizon represents distant shading. It describes conditions in which obstacles far from the plant—such as mountains, hills, buildings, or forests—block the sun from the plant’s perspective. Especially in mountainous areas and basins, distant shading can affect mornings, evenings, and the winter season. If Horizon is not set in the PVSyst report, shadow losses may not be reflected even though mountain shadows actually exist.

Next, check the Near shadings. Near shadings are shadows caused by nearby racking rows, buildings, trees, utility poles, fences, slopes, equipment, and the like. For utility-scale solar, shading from preceding and following rows, shading due to terrain undulation, racking height, and row spacing are important. If you are using a 3D model in PVSyst to calculate shading, verify how well the 3D scene reflects the actual layout.

With near shading, there are not only simple solar shading effects but also electrical impacts. When part of a module is shaded, losses can spread at the string level or the MPPT level. PVSyst handles Linear shading and Electrical shading, and the way losses manifest changes depending on the settings. Even if shading losses appear small, it is necessary to verify whether the electrical effects are being adequately reflected.

Topographic conditions are also important. Whether PVSyst is calculated as flat terrain or reflects the terrain gradient affects shading and solar exposure. On sloped sites, racking orientation, row spacing, ground elevation, and site development plans change the inter-row shading. Even with the same slope angle on the design drawings, actual shading conditions differ greatly depending on whether the terrain slopes downward to the south or to the north.

Also, system conditions should be checked before reviewing the results. In PVSyst, PCS output, transformers, Grid injection, Grid limitation, Power factor, Export limitation, and so on are involved. If the grid interconnection capacity is smaller than the PCS capacity, output curtailment of the entire plant will occur. If the generation on the results page is low, it may be due to grid injection limits rather than insufficient irradiance or losses.

The power factor setting also requires careful attention. If the grid side requires specific power factor conditions, the active power that can be delivered may change depending on the PCS apparent power capacity, the active power limit, and how reactive power supply is handled. Check how the power factor is configured in PVSyst and how it affects PR and Grid Injection.

For projects subject to output control or curtailment conditions, you need to verify how fully these are reflected in PVSyst. Whether it is a continuous grid capacity limit, curtailment during specific time periods, or whether output control by the utility will be evaluated separately will change how it is treated as a design condition. If output control is not included in the PVSyst report, the actual amount of electricity sold in operation may differ.

Shading, terrain, and grid conditions are factors that impose site-specific impacts on PVSyst results. These aspects are hard to see in standard-condition simulations, but they are crucial for explaining discrepancies with actual power generation. Before examining the results, confirming how fully these conditions have been reflected makes it easier to assess the report’s reliability.

Misunderstandings that arise from looking only at the results without reading the design conditions

A common misunderstanding when interpreting PVSyst is judging the quality of a design solely by the annual energy yield or PR figures. However, results are the accumulation of the conditions. If you look only at the results without reading the design conditions, many misunderstandings will arise.

The first is mistaking differences in capacity for differences in performance. Even if you see a report showing higher annual energy production and judge it to be superior, it may simply have a larger DC capacity. In such cases, you cannot make a correct comparison without looking at Specific Yield, PR, and the capacity conditions.

The second is mistaking differences in meteorological data for differences in design. Even for the same power plant, annual generation will vary depending on the meteorological data source. If you use data with higher solar irradiance, the estimated generation will tend to be higher. It may not be because the design is better, but simply because the input irradiance is higher.

The third is mistaking differences in loss assumptions for differences in actual performance. If you set losses low, the reported energy yield will be higher. Conversely, if you use conservative loss assumptions, the reported energy yield will be lower. When comparing PVSyst reports from multiple companies, if you compare only PR without aligning the loss assumptions, you cannot determine which design is appropriate.

The fourth is overlooking whether shadow conditions are considered. Reports that include 3D shadow calculations and reports that include almost no shadows can produce different results even with the same layout. This difference is especially pronounced on slopes and in mountainous areas, where whether shadow conditions are accounted for makes a big difference.

The fifth point is mistaking grid constraints for generation performance. If Grid Injection is low, it may not be that the modules or the PCS are underperforming, but rather that grid injection limits or PCS output limits are the cause. Unless you check the design conditions, you won't know where the restriction is occurring.

To avoid such misunderstandings, the order in which you review PVSyst is important. Instead of looking at the results first, check the project conditions, meteorological data, azimuth and tilt, equipment capacity, loss assumptions, shading conditions, and grid conditions before reviewing the results. Doing just this will significantly change your understanding of the PVSyst report.

How to Read Design Conditions When Comparing Multiple PVSyst Reports

In practice, you often need to compare multiple PVSyst reports—your company's analysis, the EPC's analysis, third-party evaluations, assessments for financial institutions, and manufacturer-provided materials. In these cases, the first thing to compare should be the design conditions, not the energy production.

First, align and verify the DC capacity and AC capacity. If the capacities differ, you should compare using kWh/kWp or PR rather than annual generation. However, since PR is also affected by meteorological data and loss conditions, it is risky to draw conclusions based on PR alone.

Next, we compare the meteorological data. We check how much the annual solar irradiance, monthly irradiance, and ambient temperature differ. If irradiance differs by a few percent, it can sometimes explain the majority of the difference in power generation. When the weather conditions differ between reports, the difference in power generation cannot be conclusively attributed to design differences.

Next, check the azimuth and tilt angles. Confirm whether the layout conditions are the same, whether multiple azimuths are treated consistently, and whether calculations are performed using representative angles or divided into detailed cases. Even for the same project, the granularity of modeling may differ depending on the report author.

Next, compare the loss conditions. Listing DC wiring losses, AC wiring losses, transformer losses, Soiling, Auxiliary, Thermal, Mismatch, and so on makes it easier to see the reasons for differences in energy production. In particular, the approach to setting loss conditions differs between conservative reports and optimistic reports.

Finally, compare the shading and grid conditions. Check whether a 3D shading model is being used, whether Horizon is included, whether output limits are applied, and whether power factor conditions are applied. If these conditions differ, the differences in the results cannot be explained by design performance alone.

When comparing multiple reports, simply placing the PVSyst results side by side is not sufficient. You need to place the design conditions side by side, organize the differences between them, and then analyze the differences in energy production and PR. This allows you to explain to the client or your supervisor concretely, for example: "This difference is due to irradiance conditions," "This difference is due to the setting of DC wiring losses," and "This difference is due to how PCS capacity and output limiting are handled."

How to Communicate Design Requirements When Explaining to Clients or Supervisors

Because PVSyst's design conditions include many technical items, explaining them as-is to a client or supervisor can be hard to understand. When explaining, it is important to prioritize communicating the conditions that affect the results, rather than listing every detailed input value.

First, you should state which location's meteorological data were used for the calculations. Since these are the basis for the power generation assumptions, explain the data sources for solar radiation and temperature. If necessary, add whether the annual solar radiation is typical, conservative, or how it compares with other datasets.

Next, convey the scale of the power plant. Briefly explain DC capacity, AC capacity, number of PCS units, and the overloading ratio. Because power generation tends to be proportional to capacity, sharing the capacity conditions first makes it easier for people to understand the resulting figures.

Next, provide the installation conditions: explain the azimuth, the tilt angle, whether it is fixed or tracking, and whether there are multiple orientations. Because these affect generation patterns and seasonal generation output, sharing them before reviewing the monthly results will aid understanding.

Next, convey the main loss conditions. You don't need to describe every loss in detail, but explain those that have a major impact on the results, such as wiring losses, transformer losses, soiling, temperature, shading, and output limits. Whether the loss conditions are conservative or standard is also important.

Finally, communicate the site-specific conditions: shading from mountains, nearby shading, topography, snow, grid constraints, and other factors unique to the project. Being able to explain these makes it easier to convey that PVSyst is not just a desk calculation but a simulation that reflects actual site conditions.

In explanations, before saying "PVSyst's result is an annual energy production of X," state as a premise "which meteorological data, which capacity, which installation angle, and which loss conditions were used to calculate this result" — this reduces misunderstandings. If you present only the result first, you'll need to explain differences in conditions afterward, and the discussion will tend to circle back.

Practical sequence for confirming design conditions

When checking the design conditions in PVSyst, it's more efficient to follow the same order each time. In practice, standardizing the sequence of checks reduces oversights, even if item names or page layouts vary slightly between reports.

First, check the project name, Variant name, creation date, author, and the PVSyst version used. If there are multiple Variants, be careful not to mistake which Variant’s results you are looking at. Confusing an older Variant with the latest one can lead to viewing results that do not reflect design changes.

Next, we will check the site and meteorological data. We will look at the coordinates, elevation, meteorological data source, annual solar radiation, monthly solar radiation, and outdoor air temperature. If anything seems off here, we will stop before proceeding to later result checks.

Next, check the Orientation. Examine the azimuth, the tilt angle, whether it is fixed or tracking, and the capacity allocation among multiple surfaces. Confirm that it matches the design drawings.

Next, confirm the System: module model, number of modules, DC capacity, PCS model, number of PCS units, AC capacity, string configuration, and Pnom ratio. These are the core conditions that determine the scale of the results.

Next, check the Detailed losses. Review DC wiring losses, AC wiring losses, transformer losses, soiling, thermal, mismatch, module quality, auxiliary, and so on. In particular, confirm whether they remain at the default values or have been adjusted to match the project conditions.

Next, we check Horizon and near shadings. We examine distant shadows, near shadows, 3D models, electrical effects, and terrain representation. For projects where shading is important, we review this in detail.

Finally, check the grid conditions. Review the grid injection capacity, output limits, power factor, transformers, and the losses up to the interconnection point. Before looking at the amount of electricity sold or Grid Injection, confirm what is included in PVSyst.

By reading in this order, it becomes easier to trace why the PVSyst results are what they are. Rather than working backwards from the results to identify the conditions, understanding the conditions first and then looking at the results improves both the accuracy of the review and the ease of explanation.

Items in PVSyst design conditions that are particularly easy to overlook

There are several items in PVSyst's design conditions that are easy to overlook. They may not be noticeable as numbers, but they can influence the results.

The first is albedo. Albedo is the reflectivity of the ground surface and is particularly important in snowy regions and for bifacial modules. Even if its impact is limited under typical ground conditions, reflected solar radiation can increase on snow or white surfaces. Check whether albedo is set on a monthly basis or as a single uniform value.

The second point is the monthly settings for Soiling. A uniform annual soiling loss may not capture seasonal variations. Appropriate settings vary depending on periods of heavy rainfall, periods with high yellow sand or pollen, the snowy season, and whether cleaning is scheduled.

The third is auxiliary consumption. Even if the Auxiliary loss appears small, the results change depending on how much you include monitoring devices, communication equipment, PCS standby power, air conditioning, tracker power, etc. In particular, whether nighttime consumption is included affects the evaluation of electricity sales and on-site consumption.

The fourth is the transformer no-load loss. Because losses occur even during periods when no generation is taking place, it differs from simple load-proportional losses. While it may look small as a percentage of annual generation, it can make a difference in comparisons.

The fifth point is the handling of output limits. When the PCS rating, grid interconnection capacity, contracted capacity, and power factor conditions are mixed together, it can be difficult to tell where active power is being limited. Before looking at Grid Injection, it is important to verify the input of the limiting conditions.

The sixth is the electrical effects of shading. It’s not just about what percentage of solar radiation is blocked; losses can propagate depending on the configuration of strings and MPPTs. Check how PVSyst treats the electrical effects of shading.

The seventh point concerns degradation and first-year conditions. Verify whether the report refers to first-year generation, generation for a specific year that includes degradation over time, or a long-term average. For financial institutions and business plans, it is necessary to avoid confusing first-year figures with long-term averages.

These items are parts that are easy to overlook if you only look at the beginning of the report. By reading the design conditions carefully, you can interpret the numerical results more accurately.

Approach to Linking PVSyst Design Conditions and On-site Verification

Reading PVSyst's design conditions only as desk-based input values is insufficient. Verifying them against actual field conditions increases the reliability of the simulation.

For example, azimuth and tilt angles can be checked on the design drawings, but actual angles may differ due to on-site construction tolerances or terrain. If you can confirm whether the mounting racks are installed as planned or whether some angles have been adjusted to fit the terrain, you can verify consistency with the PVSyst conditions.

On-site verification of shading conditions is also important. Even if drawings appear to show little shading, there may be trees, utility poles, slopes, temporary structures, or surrounding buildings on site. Using drone surveys, point cloud data, site photographs, and shadow checks makes it easier to confirm the validity of PVSyst's Near shadings and Horizon.

It is also important to ensure that wiring losses are consistent between the design drawings and the actual site. If the actual wiring routes are longer than in the design, cable sizes have been changed, or the PCS layout has been altered, the loss parameters in PVSyst also need to be reviewed.

Snow accumulation and soiling also need to be considered in conjunction with site conditions. Surrounding environment, wind direction, ground surface, snow-removal policy, cleaning frequency, bird damage, dust from farmland or roads, and other site factors affect Soiling and winter losses. It is important not only to rely on uniform settings in PVSyst but also to be able to explain them based on the actual site conditions.

For such on-site verification, simple surveying using a smartphone and a high-precision GNSS is also effective. Using a system that combines an iPhone and GNSS, like LRTK, to confirm site position, elevation, point clouds, photos, and overlaid drawings makes it easier to identify discrepancies between the design conditions set in PVSyst and the actual site conditions. For example, you can record rack locations, prepared ground surfaces, slopes, nearby obstructions, inspection routes, and structures likely to cast shadows on site, and use them for design reviews and to explain differences in power generation.

PVSyst is a powerful tool for simulations, but the validity of input conditions is supported by on-site information. By combining the ability to read design conditions with the ability to inspect the site, the explanatory power of generation forecasts is enhanced.

Flow for Viewing the Results Page After Confirming Design Conditions

After checking the design conditions, next read the results page. When doing so, it is important to keep in mind the items you verified in the design conditions.

First, check the annual power generation. Confirm which point's generation you are looking at, such as Grid Injection or Produced Energy. The figures vary depending on the evaluation point—module output, PCS output, after the transformer, the grid injection point, etc.

Next, we check the Specific Yield. This is a metric for looking at the annual energy production per unit of DC capacity. It is useful when comparing reports with different capacities, but a simple comparison cannot be made if weather conditions or loss assumptions differ.

Next, check the Performance Ratio. PR is an indicator of how much the system generated relative to the solar irradiance conditions. However, PR is also affected by temperature, losses, power curtailment, auxiliary consumption, and differences in definitions. Rather than assuming a high PR is necessarily good, you need to interpret which loss conditions produced that PR.

Next, review the Loss Diagram. Check to what extent the losses identified in the design conditions are affecting the results. Verify DC losses, temperature losses, IAM, Soiling, Inverter loss, Transformer loss, Grid limitation, etc., against the design conditions.

Next, review the monthly results. Look for seasonal variations that annual values alone don't reveal. If generation is low in winter, solar irradiance, snow cover, shading, tilt angle, albedo, and temperature conditions may be contributing factors. If PR is low in summer, temperature losses or PCS clipping may be contributing factors.

In this way, the results page becomes meaningful when read after confirming the design conditions. The basic way to read PVSyst is to proceed from the conditions to the results.

Benefits of Making PVSyst Design Condition Verification an In-House Standard

Standardizing the verification of PVSyst design conditions within the company stabilizes review quality. When each reviewer checks different items, oversights and differences in interpretation are more likely to occur. Deciding the order of checks and the key items streamlines the quality review of reports.

The primary benefit of internal standardization is that it makes comparisons easier. You can compare analysis results across multiple projects, reports, and authors from the same perspective. If you check meteorological data, capacity, azimuth and tilt, losses, shading, and grid conditions in the same order, it becomes easier to organize the differences.

Next, it becomes easier to explain. When explaining to your supervisor, the client/owner, financial institutions, EPC, or O&M personnel, you can present the assumptions in the same structure each time. This prevents the numbers in the results from being taken out of context.

Furthermore, it becomes easier to check the impacts when design changes are made. For example, if you change the tilt angle, change the PCS capacity, change the wiring route, reassess soiling, or update the shadow model, it becomes easier to track which conditions changed and to what extent they affected the results.

It is also useful for comparing with third-party reports. If another company's report shows higher power generation, you can clarify whether the reason is the weather data, the loss settings, or the capacity conditions. Instead of simply judging "the other company is higher" or "our company is lower," you can explain it as a difference in conditions.

Reviewing the design conditions in PVSyst is useful not only for analysts but also for sales, design, construction management, O&M, and strategic business decisions. To make power generation simulations useful across the company, it is important to foster a culture of sharing not only the results but also the underlying assumptions.

Summary

When reading PVSyst, the first thing you should check is the design conditions, not the annual generation or PR. The results are produced by the accumulation of meteorological data, azimuth, tilt angle, module capacity, PCS capacity, string configuration, loss conditions, shading conditions, terrain conditions, and grid conditions. If you look only at the results without reading the assumptions, you may misinterpret differences in capacity, weather, loss settings, shading conditions, or output limits.

When interpreting the design conditions, first check the project information and meteorological data. Examine the coordinates, elevation, meteorological data source, annual solar radiation, monthly solar radiation, and ambient air temperature to assess whether the basis for the power generation calculation is appropriate.

Next, check the azimuth and tilt angles. Verify that they match the design drawings and racking specifications, and that multiple azimuths and multiple tilts are properly reflected. This affects irradiance on tilted surfaces, shading, and monthly energy output.

Next, verify the module capacity and PCS capacity. By examining the DC capacity, AC capacity, number of PCS units, string configuration, Pnom ratio, and output limit conditions, you can understand the implications for power generation and clipping.

Next, confirm the loss conditions. Verify whether DC wiring losses, AC wiring losses, transformer losses, Soiling, Thermal, IAM, Auxiliary, etc., are values based on the actual design, standard values, or conservative assumptions.

Finally, verify shadows, terrain, and grid conditions. By confirming whether Horizon, Near shadings, 3D models, electrical impacts, grid injection limits, power factor conditions, etc. are reflected, you can understand site-specific impacts.

PVSyst is useful as a practical document not simply by looking at the numerical results, but by reviewing the conditions that produced those results. By making it a habit to verify the design conditions before reviewing the results, you can make more accurate judgments for internal reviews, client briefings, competitor comparisons, materials for financial institutions, and O&M performance evaluations.