Five checks when handling high-temperature regions in the PVSyst manual

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Table of Contents

• The significance of reading the PVSyst manual in high-temperature regions

• Checklist item 1: Do not underestimate temperatures in meteorological data

• Confirmation item 2: Verify the module's temperature coefficient

• Confirmation item 3: Match the heat loss model and U-value to the installation conditions

• Confirmation Item 4: Consider wind speed and ventilation as on-site conditions.

• Checklist item 5: Link the report results to power output and design decisions.

• Common configuration mistakes in high-temperature regions

• On-the-job verification procedures

• Summary

The Importance of Reading the PVSyst Manual in High-Temperature Regions

Solar energy yield simulations make regions with higher solar irradiance look more favorable. However, in practice, if you assess energy yield based only on irradiance, you can encounter problems such as generating less than expected, large output drops in summer, and being unable to explain loss factors in reports. In high-temperature regions in particular, module temperature increases reduce output, so when reading the PVSyst manual it is important not merely to follow the procedural steps but to examine meteorological data, module specifications, thermal losses, wind speed, and the result reports as an integrated whole.

In PVSyst, cell temperature is a basic input to the single-diode model, and the evaluation of array temperature is carried out based on the energy balance of inputs and outputs. In other words, when assessing high-temperature regions, you need not only the intuitive understanding that “losses increase because the ambient temperature is high,” but also a clear grasp of which input values affect the temperature calculation and in which result items they are reflected.

A "hot region" does not refer only to areas with a high annual average temperature. You should also consider areas where ambient temperatures rise significantly during daytime in summer, rooftop projects with poor ventilation, development sites with strong radiant heat from the ground surface, dry regions close to desert climates, and projects where the roof surface itself tends to become hot, such as factory or warehouse roofs. When reading the PVSyst manual for practical work, you need to treat not only climate-classified high temperatures but also the installation surface, surrounding environment, mounting structure, ventilation, and module specifications as factors that make a project prone to high temperatures.

This article summarizes five points to check in the PVSyst manual when dealing with high-temperature regions, organized for practitioners. Rather than just covering screen operations, it explains how to interpret simulation results and focuses on where underestimation or overestimation is likely to occur.

Checklist item 1: Do not underestimate the air temperature in meteorological data

The first thing to check is the ambient temperature in the meteorological data you are using. In PVSyst, meteorological data are described as the starting point for project assessment and also as a primary source of uncertainty. Irradiance has the greatest impact on energy production, but in high-temperature regions the treatment of ambient temperature is just as important. Even if irradiance is high, if module temperature rises during hot periods the power generation efficiency will decrease.

A common mistake in projects in high-temperature regions is to check only the validity of solar irradiance and not adequately assess the representativeness of the temperature data. For example, when using regional meteorological data, the actual installation site—if it is in a basin, inland area, industrial zone, arid region, or far from the coast—can be hotter than nearby representative stations. Conversely, sites at higher elevation or influenced by sea breezes may experience milder temperature conditions than the regional data suggest. When reading the PVSyst manual, it is important not only to follow the procedure for importing meteorological data but also to verify that those data represent the local temperature environment.

One point to pay special attention to is not to judge based solely on monthly averages. Even if no major problems are apparent from the annual mean temperature or monthly mean temperatures, temperature-induced losses cannot be ignored if high temperatures are concentrated during periods of high power generation. In solar power generation, the impact of losses is greater during hours with higher generation. When solar irradiance is strong around solar noon and, on top of that, conditions are nearly windless, module temperatures can become considerably higher than the ambient air temperature. Therefore, in high-temperature regions it is important to look at the temporal combination of solar irradiance, ambient temperature, and wind speed.

Also, if the source of meteorological data differs, results can change even for the same location. Satellite-based, ground-observation-based, reanalysis, and private meteorological data differ not only in solar radiation but also in temperature and wind speed trends. When progressing a project using the PVSyst manual, it is reassuring to be able to explain in design memos and internal reviews which meteorological data were adopted and why you judged that data to be representative of the local conditions.

When evaluating high-temperature regions, if the temperatures in the meteorological data are biased low, power output may be overestimated. Conversely, using excessively high-temperature data results in an overly conservative simulation and can be disadvantageous in project feasibility assessments. What matters is not simply erring on the side of safety, but selecting meteorological data that match the local conditions.

Checklist item 2: Verify the module's temperature coefficient

Next, what we want to check is the module's temperature coefficients. In hot regions, module temperature tends to rise more easily even under the same irradiance, so differences in temperature coefficients are more likely to appear as differences in energy yield. In PVSyst's module settings, temperature characteristics for power, open-circuit voltage, short-circuit current, and so on are handled. The official documentation also explains that the temperature behavior of Pmpp, Voc, and Isc is normally specified in the manufacturer's datasheet.

What you should pay particular attention to in practice is the temperature coefficient of maximum power. In general, when the temperature of a photovoltaic module rises, its voltage falls, and as a result its power output also decreases. The temperature coefficient differs depending on the type of module, and in high-temperature regions this difference affects annual energy yield and summer peak output. When configuring settings with reference to the PVSyst manual, you must verify that the values registered in the database match the datasheet of the module you plan to use before using them as-is.

One thing to watch out for is that even if module model numbers are similar, the registered data may not be exactly the same. If you choose based only on similar manufacturer or series names, assumptions about temperature coefficients, rated output, electrical characteristics, dimensions, and NOCT or NMOT may differ. In high-temperature regions small differences can easily accumulate, so when consulting the PVSyst manual it is important to check not only that you entered data on the correct screen, but also that the input values match the specifications of the equipment being used.

PVSyst explains that, for crystalline modules, the modeled values of the maximum power temperature coefficient tend to be within a range close to the manufacturer's specified values. The official documentation states that the muPmpp for crystalline modules is usually close to the specified value, with a representative range shown as approximately -0.42 to -0.45 %/°C.

However, in practice you should not apply this range mechanically; you should prioritize checking the specification sheet of the selected module. In recent years, due to differences in cell technology and module structure, there are products with relatively good temperature coefficients. In high-temperature regions, choosing modules with smaller temperature coefficients may help suppress reductions in power generation during the summer. On the other hand, it is risky to select equipment based solely on the temperature coefficient. You need to make a comprehensive judgment that includes price, supply availability, warranty, output degradation, installation conditions, and the combination with the inverter.

When addressing high-temperature regions in the PVSyst manual, it is better to treat the module temperature coefficient not merely as one input parameter but as a precondition that can determine project viability under high-temperature conditions. In particular, for projects comparing multiple modules, it is effective to run simulations using the same meteorological data, identical installation conditions, and the same inverter settings, and to compare differences in temperature losses and annual energy yield.

Checklist item 3: Align the heat loss model and U-value with installation conditions

One of the most important things to check in hot regions is the heat-loss model and the U-value. In PVSyst, it is explained that the steady-state array temperature is calculated by a thermal balance model, and then the actual transient array temperature is obtained using a thermal inertia model. The calculation of the steady-state temperature requires the heat transfer coefficient called the U-value.

PVSyst's U-value is an important parameter that indicates how much heat a module can dissipate to the surrounding environment. Because the rear ventilation of a module varies greatly depending on the installation configuration, thermal losses change even in the same location, with the same module and the same solar irradiance: roof-mounted, ground-mounted, on racking under high-ventilation conditions, and low-ventilation conditions similar to roof-integrated installations all produce different temperature losses. In hot regions these differences tend to be larger, so it is essential to consider whether it is acceptable to use the standard U-value.

For example, in ground-mounted installations where there is sufficient airflow behind the modules, heat can dissipate easily and the rise in module temperature is somewhat suppressed. Conversely, in projects where modules are installed close to the roof surface or where the roofing material itself tends to become hot, heat on the module rear is more likely to become trapped. On factory roofs, profiled metal roofs, low-slope roofs, or rooftops enclosed by parapets, ventilation can vary greatly depending on site conditions. When reading the PVSyst manual, it is important not to treat the thermal loss settings as mere default inputs, but to verify the reproducibility of the mounting structure.

The official documentation shows that the U-values Uc and Uv are the primary inputs defining the thermal behavior of a PV array, and that the heat exchange is divided into a constant component and a wind-speed-proportional component. It also explains that these values must be determined empirically by fitting the equations to measured data.

This point is very important in practice. The thermal loss coefficient entered into PVSyst is not something with a single absolute correct value, but rather a parameter whose validity should be judged based on installation conditions and measured data. Especially in high-temperature regions, the choice of U-value affects module temperature in summer, temperature-related losses, and annual energy yield. While it is possible to estimate using standard settings in the early stages of a project, for final design, evaluations for financial institutions, EPC proposals, or uses close to performance guarantees, the rationale for the chosen settings should be clearly documented.

When checking the U-value, we look at the mounting structure type, the space behind the module, the distance to the roof surface, surrounding obstructions, wind ventilation, and the installation angle. In high-temperature regions, rather than simply thinking "strong solar irradiation means higher power output," confirming whether the structure allows heat to escape contributes to improved simulation accuracy.

Confirmation Item 4: Treat wind speed and ventilation conditions as on-site conditions

In high-temperature regions, the way wind speed is handled is also important. Even if the ambient air temperature is high, sufficient wind makes it easier for heat to dissipate from the module’s rear and front surfaces. Conversely, even if the ambient air temperature isn’t that high, if the wind is weak and heat becomes trapped by roof or ground surfaces, module temperatures are likely to rise. When reviewing the PVSyst manual, wind speed should be considered not merely as a meteorological data point but together with the thermal loss settings.

In PVSyst’s thermal model, Uv is treated as the component proportional to wind speed. However, the input wind speed can differ from the actual wind near the module depending on the measurement height, the environment, and the data source. The official documentation also notes that meteorological-quality wind speeds are generally measured in a free environment at a height of 10 m (32.8 ft) and do not necessarily represent array-level wind speeds directly.

Therefore, for projects in high-temperature areas, it is important not to place too much trust in wind speed data. For example, even if meteorological data show a certain wind speed, the actual installation site may be surrounded by buildings, windbreak forests, adjacent structures, parapets, equipment, or affected by terrain, which can weaken the wind around the modules. Conversely, in locations where wind can flow freely, such as coastal areas or elevated sites, conditions may allow heat to dissipate more easily.

On rooftop projects, ventilation conditions should be examined particularly carefully. If the gap between the roof surface and the modules is small, air warmed during the day will have difficulty escaping. Wind flow also changes depending on the racking height, spacing between rows, roof pitch, orientation, surrounding upstands, and the placement of outdoor air-conditioning units and equipment foundations. If you only look at the input fields in the PVSyst manual, the simulation can proceed without reflecting these on-site conditions.

Even for ground-mounted projects you cannot be complacent. A large development site may appear to have good airflow, but wind protection measures, fences, surrounding topography, grass height, racking height, and row spacing all change the airflow around the modules. In high-temperature regions, ground surface temperature also has an effect, so it is important not to simply assume that "because it is ground-mounted, ventilation is good."

When dealing with hot regions in the PVSyst manual, it is easier to understand if wind speed and ventilation conditions are considered separately. Wind speed is an external condition provided as meteorological data, while ventilation conditions are project-specific factors determined by the design and the site environment. The combination of these two determines how easily the modules are cooled.

Checklist Item 5: Link report results to power generation and design decisions

What you should check last are the post-simulation report results. Even if you proceed with the inputs while referring to the PVSyst manual, if you cannot read the result report correctly you will not be able to judge whether the settings are good or bad. In high-temperature regions, it is important to check not only the annual energy production but also temperature losses, monthly energy production, performance ratio, summer output decline, and the interaction with the inverter.

PVSyst explains that while the nominal performance of PV modules is specified at 25°C, in actual operation they often run at higher temperatures, and temperature rise causes thermal losses. The official documentation indicates that temperature-related losses are on the order of approximately −0.2 to −0.4%/°C.

When reviewing reports for high-temperature regions, first check not only the annual energy production but also how much temperature-related loss is occurring. Next, look at the monthly trends in generation and losses. By confirming whether generation also increases in months with high solar irradiance or is being dampened by high-temperature losses, you can identify design challenges. In particular, if generation growth is small despite strong summer irradiance, check the temperature conditions, ventilation (airflow) conditions, the module temperature coefficient, inverter capacity, and whether clipping is occurring.

Also, in high-temperature regions it is necessary to check the inverter-side behavior. Because module temperature increases cause voltage to drop, it is important to verify the string voltage, the MPPT range, the low-side voltage margin, and the operating point during hot summer conditions. While maximum voltage tends to be an issue in cold winter conditions, in hot regions during summer the impact of voltage reduction on the operating range and efficiency is easy to overlook. You should make judgments by cross-checking not only PVSyst results but also the design documents and equipment specifications.

If a report shows large temperature losses, don't immediately assume "the settings are wrong"; instead, verify whether they are reasonable given the site conditions. In hot regions, close to the roof surface, with weak wind and using modules with a high temperature coefficient, large temperature losses are natural. Conversely, if the installation is ground-mounted and should have good ventilation but the temperature losses appear excessive, check whether the U-value, the wind speed in the meteorological data, or the mounting configuration settings are stricter than actual conditions.

Simulation results are not merely figures of generated power, but a basis for decision-making to improve designs. In high-temperature regions, temperature conditions affect multiple design decisions such as module selection, racking height, clearance from the roof surface, inter-row spacing, inverter capacity, maintenance access routes, weed management, and measures against surrounding obstacles. The purpose of using the PVSyst manual is not to learn screen operations, but to be able to explain these decisions with numbers.

Common configuration mistakes in high-temperature regions

One common mistake in PVSyst settings for high-temperature regions is adopting standard meteorological data as-is without verifying the site's high-temperature characteristics. In particular, if the installation site is in an urban area, inland area, industrial zone, or on a rooftop, conditions can be harsher than the representative station's temperature. While this may be acceptable during preliminary studies, in the detailed design and contracting stages you need to be able to explain the rationale for your selection of meteorological data.

The second mistake is using values from the module database without verification. The PVSyst database is convenient, but that does not mean it exactly matches the datasheet of the module adopted for the project. In high-temperature regions differences in temperature coefficients have a greater impact, so it is necessary to check the model number, rated power, temperature coefficient, voltage, current, module dimensions, and so on.

The third mistake is failing to link the thermal loss settings to the installation type. On-roof, ground-mounted, agrivoltaic, pitched roof, flat roof, carport, and factory roofs all have very different ventilation conditions. If you only follow the PVSyst manual’s procedures, you can easily overlook what the settings actually mean. In hot regions, treating structures that impede heat dissipation lightly can lead to overestimating power generation.

The fourth mistake is to treat wind speed data directly as the on-site cooling effect. Wind speed data are useful as broad meteorological information, but they differ from the actual wind at the back of the module. Especially on rooftops or in densely built-up areas, even when meteorological data indicate wind speed, the wind around the array can be weak. It is important to distinguish between wind speed and ventilation conditions.

The fifth mistake is looking only at annual energy production in the results report. In high-temperature regions, the total annual production alone can make problems difficult to detect. You need to check monthly energy production, temperature losses, system losses, inverter losses, and the performance ratio together to determine which conditions are suppressing energy output.

Practical Verification Procedures

In practice, when using the PVSyst manual to handle projects in high-temperature regions, start by organizing the local site conditions. Check the installation site's climate, elevation, surrounding environment, roof or ground conditions, wind flow/ventilation, the space behind the modules, and the type of mounting structure. Identifying factors that are likely to cause high temperatures at this stage makes it easier to verify settings later.

Next, we review the meteorological data. We examine not only solar irradiance but also trends in ambient temperature and wind speed. When there are multiple candidate meteorological datasets, we do not compare them based solely on annual energy production; we also compare temperature losses and monthly trends. In high-temperature regions, datasets with higher solar irradiance are not necessarily more conservative, because differences in temperature and wind speed can alter the results.

Next, we check the module settings. We compare the specification sheet intended for adoption with the module data in PVSyst to confirm that the main items, including the temperature coefficient, match. If there are multiple candidate modules in the early stages of a project, we compare them under the same conditions and check differences in power output and temperature-induced losses at high temperatures. Modules with better temperature coefficients may have an advantage in hot regions, but the final decision also considers cost and supply availability.

Next, check the thermal loss settings. Depending on the installation configuration, determine whether the module can dissipate heat easily or is prone to heat buildup. For rooftop cases with weak rear ventilation, roof surfaces that tend to become hot, or sites with surrounding upstands, treating them with assumptions like a standard open racking system can be overly optimistic. Even for ground-mounted installations, caution is required if there are effects from wind protection or the surrounding terrain.

Finally, review the results report. While examining annual generation, monthly generation, temperature losses, performance ratio, and inverter losses, verify the consistency between the input conditions and the results. In high-temperature regions, it is important to be able to explain why summer generation does not increase as much as expected. If you cannot explain it, there may have been an oversight in checking the meteorological data, temperature coefficient, U-value, wind speed, or installation conditions.

Standardizing this process can reduce variability between personnel. Rather than reading the PVSyst manual as a one-off, incorporating it into internal design checklists and review procedures will stabilize the simulation quality for projects in high-temperature regions.

Summary

When dealing with high-temperature regions in the PVSyst manual, it is important not to focus solely on high irradiance but to read simulations assuming output reductions due to temperature. Points to check include the air temperature in the meteorological data, the module temperature coefficient, the thermal loss model and U-value, wind speed and ventilation conditions, and how to read the result report. Understanding these not as separate items but as a single temperature-assessment workflow makes it easier to avoid overestimating energy production and overlooking design judgments.

In high-temperature regions, factors that make energy production appear large and factors that suppress it exist simultaneously. Abundant solar irradiance is advantageous, but if the ambient air temperature is high, heat is trapped on the back of the modules, wind is weak, and modules with a large temperature coefficient are used, temperature losses will be significant. When reading PVSyst results, it is important not only to look at the annual energy yield but also to be able to explain why that figure was obtained.

Reading the PVSyst manual merely as an operational guide is insufficient. Especially in high-temperature regions, it is necessary to understand the meaning of input values, cross-check them with local conditions, and adopt an approach of using the results report to drive design improvements. Check the meteorological data, verify module specifications, set thermal loss parameters to match installation conditions, review wind speed and ventilation in light of local conditions, and tie the report results to design decisions. By addressing these five points, PV simulations for solar power generation in high-temperature regions become decision-making material that is closer to practical use.