5 Ways to Consider Wind Conditions in the PVSyst Manual

Table of Contents

• Prerequisites to keep in mind before considering wind conditions in PVSyst

• How to view wind conditions 1: Consider wind speed as a condition affecting power generation and temperature loss

• How to Read Wind Conditions 2: Check Whether Meteorological Data Includes Wind Speed

• Understanding Wind Conditions 3: Examining Differences Between Wind Speed Measurement Heights and On-site Conditions

• Interpreting Wind Conditions 4: Do not overestimate wind effects when setting Uc and Uv

• How to Interpret Wind Conditions 5: Comparing Ventilation Performance by Installation Type Using Scenarios

• Practical points on wind conditions to be aware of when reading the PVSyst manual

• Common mistakes when checking wind conditions

• Summary

Prerequisites to Keep in Mind Before Considering Wind Conditions in PVSyst

When considering wind conditions in the PVSyst manual, the first thing to understand is that wind speed in PVSyst is mainly treated not as a condition for directly assessing the structural safety of a solar power installation, but as a meteorological parameter that affects module temperature, thermal losses, and consequently energy production. In practical solar PV design, the word “wind” tends to evoke racking strength, wind pressure resistance, typhoon countermeasures, and the risk of flying debris, but when viewing wind speed on PVSyst’s simulation screens it is important to be conscious of its relationship with temperature behavior in energy-yield assessment.

In PVSyst’s official help, the thermal loss coefficient is described as a primary input for evaluating the temperature-dependent behavior of a photovoltaic array, and it is indicated that this coefficient can change with wind speed. Specifically, the thermal loss coefficient U is treated by splitting it into a constant component Uc and a wind-speed-proportional component Uv, using U = Uc + Uv・WindVel. In other words, when interpreting wind conditions in PVSyst, you should not simply conclude that stronger wind means “increased energy production” or “greater safety”; rather, you need to see how wind speed is reflected in the reduction of module temperature and how, consequently, thermal losses change.

On the other hand, handling wind speed data is a surprisingly difficult area. In PVSyst’s meteorological data tutorial, global horizontal irradiance and air temperature are listed as mandatory inputs for the simulation, while diffuse horizontal irradiance and wind speed are treated as optional items and are explained to be evaluated by models when necessary. Therefore, when considering wind conditions in the PVSyst manual, the starting point is to first distinguish whether the wind speed data is measured, a monthly average, a synthesized value, or not entered at all.

In this article, aimed at practitioners considering wind conditions while consulting the PVSyst manual, we organize the topic into five perspectives: wind speed data, temperature losses, Uc and Uv, installation configurations, and scenario comparisons. Rather than a mere glossary, the article explains these as viewpoints usable for decision‑making in power generation simulations, so that even those unfamiliar with PVSyst’s operation can understand which screens and figures to check and what they mean.

How to View Wind Conditions 1: View wind speed as a condition affecting power generation and temperature loss

The primary way to view wind conditions when checking the PVSyst manual is to regard wind speed as a meteorological condition that affects temperature losses. In photovoltaic power generation, higher irradiance is favorable for power production, but if module temperature becomes too high, output decreases. Especially in summer, for rooftop installations, and for installation configurations with poor ventilation, increases in module temperature affect annual energy yield. Because wind helps dissipate heat from the module’s front and rear surfaces, in PVSyst it is related to the assessment of temperature losses.

The thermal loss model in PVSyst shows a flow in which the steady-state array temperature is calculated first, and then the actual transient array temperature is obtained using a thermal inertia model. It also explains that users can modify the heat transfer coefficient and the module mass in the Detailed Losses and PAN file menus. This implies that looking at wind speed alone is insufficient, and unless the thermal loss coefficient and installation conditions are considered together, it is difficult to correctly assess the impact on energy production.

For example, even with the same solar irradiance in the same area, the way module temperature rises differs between projects installed on the ground with sufficient airflow behind the modules and projects installed close to the roof surface. Even if the wind is blowing, if the structure does not allow air to pass behind the modules, you cannot expect the cooling effect of wind speed data as-is. When evaluating wind conditions in PVSyst, you need to consider not only whether wind speed data have been entered but also whether that wind actually contributes to cooling the modules given the installation conditions.

Also, the influence of wind speed on energy production can be less apparent than that of solar irradiance or air temperature. Therefore, if you only look at the annual energy production on PVSyst’s results screen, you may overlook differences caused by the wind-condition settings. By checking temperature losses, array temperature, monthly losses, and seasonal results together, it becomes easier to identify when the wind conditions are having an effect and how large those differences are.

What's important in this perspective is not to treat wind conditions as a standalone input item. When reading the PVSyst manual, you need to understand wind speed, air temperature, irradiance, the heat loss coefficient, and the mounting configuration as an integrated set. Rather than making the simple judgment that high wind speed is advantageous and low wind speed is disadvantageous, the basic approach to considering wind conditions in PVSyst is to look at how module temperature is being estimated.

How to Read Wind Conditions 2: Check Whether Weather Data Includes Wind Speed

The second thing to check is whether the meteorological data you are using includes wind speed. In PVSyst, the quality of the weather data has a major impact on the simulation results. Solar irradiance and temperature are central to power generation calculations, but wind speed may or may not be included depending on the meteorological dataset. When consulting the PVSyst manual, first check whether the meteo file or site data you are using contains a wind speed field.

In PVSyst’s meteorological data tutorial, monthly meteorological data require global irradiation and temperature, while diffuse irradiation and wind speed are optional. It also explains that if measured hourly data are not available, PVSyst generates hourly meteorological data from the monthly values. In other words, even if wind speed is displayed on the screen, it is important to confirm whether that is measured hourly wind speed, generated from monthly values, or a representative value originating from the data source.

Even if wind speed data are not included, that does not mean a PVSyst simulation itself cannot be run. However, when you actively use thermal loss models that rely on wind speed, you need to carefully check the data source and its granularity. If only monthly average wind speeds are available, hour-by-hour variations in wind are not adequately represented. In particular, in coastal areas, mountainous regions, valley terrains, densely built urban areas, and regions strongly affected by typhoons or seasonal winds, average wind speed alone may not reflect on-site conditions.

Practitioners reading the PVSyst manual are often unsure whether it is acceptable to leave wind speed unentered or whether it must always be entered. The conclusion is that, for typical energy-yield simulations, it is realistic to prioritize the reliability of irradiance and ambient temperature first, and then treat wind speed as auxiliary information to improve the accuracy of temperature-loss estimates. If you give Uv strong influence while wind speed data quality is poor, you risk estimating energy yield too optimistically.

When checking meteorological data, it is useful to use validation features such as PVSyst's Weather Data Tables and Graphs to visually inspect monthly trends and outliers in wind speed. Check whether there are months with unusually high wind speeds, whether values are suspiciously uniform throughout the year, whether the units are consistently m/s, and whether the relationship with solar irradiance and temperature is reasonable. Precisely because wind speed is an optional field, you should not unconditionally trust the values provided; instead, adopt an attitude of assessing whether they are suitable for use in simulations.

How to Read Wind Conditions 3: Examining Differences Between Wind Measurement Height and On-site Conditions

A third perspective is to look at the difference between the wind speed measurement height and the actual module height. PVSyst's official help explains that wind speed according to meteorological standards should be measured on a 10 m (32.8 ft) mast in an unobstructed environment. It also notes that wind speeds measured for PV system monitoring do not necessarily meet those conditions, and that collector-level wind speeds may be lower.

This point is very important when considering wind conditions in the PVSyst manual. For example, while the wind speeds included in meteorological databases are values assuming an open site at a height of 10 m (32.8 ft), if an actual photovoltaic installation is mounted on a roof in a location surrounded by a parapet, or installed in a place with surrounding buildings, trees, or windbreak walls, the effective wind speed around the modules may differ greatly. If you look only at the wind speed data and conclude that it "cools well," you may end up underestimating the module temperature.

Conversely, for ground-mounted systems with open surroundings and sufficiently large array spacing, wind can more easily wrap around to the rear side, making conditions where ventilation cooling effects are relatively likely. However, you should still confirm at what height the wind speed entered into PVSyst was measured and whether it reflects the surface roughness and surrounding obstacles. Wind speed is sensitive to altitude, terrain, and nearby obstacles, and meteorological data that use the same locality name may not match the wind at the array surface on site.

PVSyst's help notes that using the wind-speed-dependent component Uv is difficult, that reliable wind speed information is rare within meteorological datasets, and that when synthesizing hourly values from monthly values the basis or model used becomes an issue. This indicates that handling wind speed in greater detail does not necessarily improve accuracy. Rather, when the origin of the wind speed data or the measurement conditions are unclear, settings that do not strongly reflect wind-speed dependence can be more stable in practice.

When assessing wind conditions, distinguish whether the wind speed in the meteorological data is a "regional representative wind speed", an "observed value near the planned power plant site", or an "on-site monitoring value". Furthermore, even for on-site monitoring values, check the sensor installation height, the effects of racking and buildings, the measurement interval, and whether missing data were imputed. The purpose of reading wind conditions in the PVSyst manual is not to input precise numbers, but to establish assumptions that can be used to explain the simulation results.

How to Interpret Wind Conditions 4: Don't Overestimate Wind Effects When Setting Uc and Uv

The fourth viewpoint is to treat the thermal loss coefficients Uc and Uv with caution. In PVSyst, the thermal loss coefficient U can be handled by separating it into Uc and Uv. Uc is the component that does not depend on wind speed, while Uv is the component proportional to wind speed. Looking only at the equations, it appears that by inputting wind speed data and setting Uv, you can achieve a more realistic, advanced simulation. However, PVSyst's help explains that using the wind-speed dependence via Uv is very difficult.

In the official PVSyst help, when reliable measurement data are not available, PVSyst proposes default values by installation type with no wind dependence, i.e., an approach that assumes an average wind speed. For open-frame racks such as ground-mounted installations where air can circulate freely, Uc = 29 W/m²K, Uv = 0 W/m²K/(m/s) are indicated, and a lower value is suggested when the back is insulated. Also, as general defaults for new projects, Uc = 20 W/m²K, Uv = 0 W/m²K/(m/s) are provided.

The important point here is not to simplistically interpret it as meaning that wind is being ignored simply because Uv = 0. PVSyst's documentation indicates that, in the absence of reliable wind speed data, a single Uc can be used to include an average convective heat transfer corresponding to the site's average wind speed. In other words, even if wind speed is not entered on a time-by-time basis, the thermal loss coefficient can be treated to include an average cooling effect.

On the other hand, if reliable hourly wind speed data are available and Uc and Uv can be appropriately set to match the mounting configuration, there is room to consider a wind-speed-dependent model. The PVSyst help presents, as the PVUSA thermal correlation widely used in open-rack situations where wind speed data are available, Uc = 25 W/m²K, Uv = 1.2 W/m²K/(m/s). However, the same page also notes that reliable measured data under windy conditions may not be sufficient, and that these values should not be adopted mechanically but judged in light of the project conditions.

A practical tip when reading Uc and Uv in the PVSyst manual is to create explainable assumptions rather than aiming for overly precise settings. For example, in large ground-mounted projects with high exposure and relatively reliable wind-speed data, it can be worthwhile to include wind-speed dependence as a case in a sensitivity analysis. On the other hand, for rooftop or semi-integrated installations where ventilation is limited, it may be more appropriate to conservatively set the Uc value according to the mounting configuration rather than heavily weighting wind-speed dependence.

Also, when the energy yield calculated by PVSyst is higher than expected, it is important to check the combination of wind speed data and the Uv setting. With high wind speeds and Uv set to be effective, module temperature may be calculated lower and temperature losses may be reduced. If you use an unexplained increase in energy yield in proposals or financial forecasts, the validity of the assumptions may be questioned in later stages. Wind conditions should be checked as a commonly overlooked factor that can cause upward bias in predicted energy yield.

Interpreting Wind Conditions, Part 5: Comparing Ventilation Across Installation Configurations Using Scenarios

The fifth perspective is to compare the ventilation of each installation type through scenarios. In the official PVSyst help, the U-value is explained to depend on the module installation type, for example open racking, roof installation, façade, floating installations, etc. It also states that there is no simple method to evaluate the U-value in general cases, and that a reliable method is to measure it on site.

As this explanation makes clear, when examining wind conditions in the PVSyst manual it is effective not to pick a single standard value and stop there, but to compare multiple cases according to the project's installation configuration. For example, even with the same module capacity, the rear-side heat dissipation conditions differ between a ground-mounted installation with ample space beneath the racking, an installation on a corrugated metal roof using low-height mounting brackets, and an installation placed close to a pitched roof. Even if the wind speed data are the same, the actual wind hitting the modules and the ways heat escapes will vary.

Especially for rooftop installations, you need to pay attention to the gap between the roof surface and the modules, the presence or absence of parapets, surrounding walls, and wind disturbances caused by ridges and equipment, rather than relying solely on the wind speed data in PVSyst. For installations close to the roof surface, even when wind is blowing, air on the module rear side tends to stagnate, and you may not expect as much cooling effect as with ground-mounted installations. When handling wind conditions in PVSyst, the focus should be not merely on the magnitude of the wind speed but on how to reflect the quality of ventilation in the thermal loss coefficient.

In scenario comparisons, creating three cases—the standard case, the conservative case, and the sensitivity case—makes it easier to explain in practice. In the standard case, use PVSyst recommended values or values close to internal company standards; in the conservative case, assume poor ventilation; and in the sensitivity case, compare situations that include wind-speed dependence or where Uc is set higher. If the differences in results are small, you can explain that wind conditions have a limited impact on the project’s overall energy production. If the differences are large, you need to recheck the validity of the meteorological data and the thermal loss coefficient.

PVSyst's description of NOCT indicates that the NOCT conditions are irradiance 800 W/m², ambient temperature 20 °C, wind speed 1 m/s, and an open-circuit condition. This means that wind speed conditions are included when reading catalog values and standard conditions. Even when referring to NOCT or NMOT in module datasheets, if the difference between actual installation conditions and the standard conditions is not taken into account, the interpretation of temperature behavior may be mistaken.

When mastering the PVSyst manual, it is important to treat wind conditions not as "the numerical values in the input fields" but as "a description of the thermal environment appropriate to the installation type." Ground-mounted, rooftop, agrivoltaic, vertical, floating, etc., each project has different assumptions about ventilation. Even if wind speed data are highly accurate, choosing thermal loss settings that do not match the installation type will reduce the credibility of the simulation.

Practical points about wind conditions to be aware of when reading the PVSyst manual

When examining wind conditions in the PVSyst manual, a clear workflow is to first check on the meteorological data screen whether wind speed is present, then check the Uc and Uv settings on the thermal losses screen, and finally review temperature losses and the monthly results in the report. Rather than making a judgment based solely on wind speed data, the basic professional practice is to verify consistency across the three stages of input, model, and results.

The first thing to check is the type of meteorological data you are using. PVSyst can handle multiple kinds of meteorological data, such as built-in data, external data, and custom files. The tutorial explains that PVSyst can import meteorological data from external sources and convert custom files for use. For projects where wind speed is a critical factor, it’s prudent to verify which data source the wind speed is coming from and, if necessary, compare multiple datasets.

The next thing to look at is the thermal loss settings. PVSyst's default values are convenient, but they are not automatically optimal for every project. For large open-rack power plants, low-tilt rooftop installations, and installations with poor rear ventilation, the way to approach the thermal loss coefficient changes. PVSyst's help also explains that the U-value depends on the installation configuration, and there is no simple method to evaluate it for general cases.

Additionally, on the results screen we check not only the annual power generation but also the magnitude of temperature losses. We examine how much temperature losses change when wind conditions are altered, whether there is a difference between summer and winter, and whether the difference in power generation is large enough to affect profitability decisions. Checking the monthly results makes it easier to see which seasons are influenced by wind conditions. For example, in high-temperature regions temperature losses tend to be larger in summer, and ventilation settings may be reflected in the results.

In practice, we recommend not only submitting the PVSyst report as-is, but also documenting the assumptions about wind conditions in an internal memo or design explanation document. Items to record include the name of the meteorological data used, whether wind speed data were available, the unit of wind speed, the setting of the heat loss coefficient, the rationale for judgments regarding the installation configuration, and the differences between the standard case and the sensitivity analysis cases. Keeping these on record makes it easier to explain later why those settings were chosen when reviewing the assumptions for power generation.

Also, when considering wind conditions, it is important not to confuse PVSyst simulations with structural design. Entering wind speed in PVSyst does not mean that the wind-resistance design of the mounting system or the evaluation of attachment methods is complete. Structural safety, building regulations, regional design wind speeds, safety during typhoons, and the strength of attachments to roof materials must be examined separately by specialists. In PVSyst, the role should be clearly defined as checking how wind affects temperature-related losses within the power generation simulation.

Common Mistakes When Checking Wind Conditions

One common mistake when checking wind conditions in the PVSyst manual is assuming that the mere presence of wind speed data means it is highly accurate. Wind speed is easily affected by regional differences, terrain, height, and nearby obstacles, so having data is a different matter from representing the site. In particular, wind speeds assumed for an open environment at a 10 m (32.8 ft) height may not match the wind speeds around modules close to a roof surface. PVSyst’s help also points out the differences between standard wind speed measurement conditions and the wind speed measurement conditions used for PV system monitoring.

The second mistake is thinking that setting Uv will always produce a more advanced model. Looking at PVSyst’s equations, adding a wind-speed-dependent term appears to make the model more precise. However, without reliable time-resolved wind speed data or coefficients that match the installation configuration, finer settings can actually increase uncertainty. PVSyst’s help clearly describes the difficulty of using Uv and the reliability issues of wind speed data.

The third mistake is treating rooftop and ground-mounted installations under the same thermal conditions. On ground-mounted systems air can circulate more easily behind the modules, whereas on rooftop installations the air layer behind the modules may be limited. Even when using PVSyst’s default values, if you do not understand what installation scenario those values assume, you may underestimate temperature-related losses. For rooftop projects in particular, you should choose settings after checking module-to-roof spacing, tilt, wind pathways, and surrounding obstructions.

The fourth mistake is judging the impact of wind conditions solely by annual generation. The effect of wind conditions may appear as temperature-related losses in summer or in the generation of specific months, even if it looks small in the annual total. In the results screen, you need to consider temperature loss, array temperature, and differences in monthly generation together. Even if the annual difference between the standard case and the conservative case is small, it may still be relevant when explaining losses at the summer peak or the plant's capacity factor.

The fifth mistake is treating PVSyst results as proof of structural safety. The wind conditions discussed in the PVSyst manual should be read in the context of energy yield and temperature behavior. Maximum instantaneous wind speed during typhoons, the wind-pressure resistance of the racking, the fastening strength to roofing materials, and the pull-out resistance of foundations are design areas separate from PVSyst’s energy production simulations. Simply looking at PVSyst’s wind speed entries does not eliminate the need to verify wind-load design.

Summary

When considering wind conditions in the PVSyst manual, it is important to understand wind speed not merely as an item of meteorological data but as a condition that links module temperature, thermal losses, mounting configuration, and the quality of meteorological data. In PVSyst, wind speed is related to the concept of the thermal loss coefficient U, and wind-speed dependence can be expressed by Uc and Uv. However, as indicated in the official help, using the wind-dependent component Uv requires reliable wind speed data and appropriate coefficient settings, and using it carelessly can lead to overly optimistic results.

The basic approach in practice is to first check whether the meteorological data include wind speed, then determine whether that wind speed is measured or synthetic, and further consider differences in measurement height and the surrounding environment. Based on that, set Uc and Uv according to the installation type, and by comparing a standard case with a conservative case you can make PVSyst’s results easier to explain. Especially for roof-mounted installations or projects with limited ventilation, do not over-rely on wind speed data and adopt a conservative stance when verifying thermal losses.

The purpose of checking wind conditions in the PVSyst manual is not to enter detailed numeric values per se. The aim is to verify, as assumptions for the energy production simulation, how much ventilation is expected, how temperature losses are being evaluated, and whether the results might be overestimated. If you know how to interpret the wind conditions, when reading PVSyst reports you can assess the validity of the results more deeply, not just the size of the energy output.