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Why Is the Temperature Coefficient Becoming a Key Factor in PV Module Selection?

Why Is the Temperature Coefficient Becoming a Key Factor in PV Module Selection?

In real-world PV system operation, modules often run for long periods under complex conditions such as high solar irradiation, limited ventilation, and heat accumulation on rooftops. To describe how temperature variations affect module performance, solar panel manufacturers typically specify a temperature coefficient in the technical datasheet. In specific application scenarios, this parameter has become a key factor influencing energy yield, overall system efficiency, and the long-term financial performance of PV projects.

Table of Contents

What Is the Temperature Coefficient and Which Operating Characteristics of PV Modules Does It Reflect?

In the technical specifications of PV modules, the temperature coefficient is often regarded as a “secondary parameter”. However, under real operating conditions, it actually reflects a module’s ability to adapt to high-temperature environments and maintain stable power generation.

From a technical definition perspective, the temperature coefficient describes how the electrical performance of a PV module changes when its operating temperature rises above Standard Test Conditions (STC, 25 °C). It is usually expressed in %/°C. This means that for every 1 °C increase in module temperature, the corresponding voltage, current, or output power changes by a defined proportion.

In practical projects, however, the significance of the temperature coefficient goes beyond the parameter change itself. Its real value lies in revealing the actual operating behaviour of PV modules under non-ideal conditions. Unlike laboratory environments, PV modules installed outdoors typically operate for long periods at temperatures well above 25 °C—especially during high-irradiance summer periods or on rooftops with limited heat dissipation.

From an application-oriented perspective, the temperature coefficient has several key characteristics:

  • Module temperature is influenced by multiple factors, including solar irradiance, ventilation conditions, mounting configuration, and roof structure, and is usually higher than the ambient air temperature at the same time;

  • It reflects the trend of performance variation with temperature, rather than the absolute efficiency level of PV modules;

  • Its value lies in assessing performance deviation under real operating conditions;

  • It cannot be considered in isolation from the application scenario and must be evaluated together with the operating temperature range, system design, and project objectives.

Only after clarifying this fundamental concept is it possible to further distinguish the performance implications of different types of temperature coefficients and understand their respective priorities in practical PV applications.

Schematic illustration of PV module I–V curve variations at different cell temperatures (25 °C, 50 °C, 75 °C), showing the impact of temperature increase on voltage and power output.

The Most Common Types of Temperature Coefficients and Their Impact on Energy Yield (Pmax, Isc and Voc)

In PV module datasheets, three temperature-related parameters are typically specified: open-circuit voltage (Voc), short-circuit current (Isc), and maximum power output (Pmax). Although all three are expressed as temperature coefficients, their influence on real-world energy yield is not the same. Understanding the differences between these coefficients helps avoid overinterpreting certain parameters during the module selection process.

2.1 Voc Temperature Coefficient: Primarily Affects System Limits, Not Energy Yield

As module temperature increases, the open-circuit voltage (Voc) generally decreases. In practical projects, this change mainly affects system-level design considerations, such as the number of modules per string, inverter voltage windows, and overall safety margins.

Because PV modules operate close to the maximum power point under normal grid-connected conditions, Voc does not directly determine actual energy production. As a result, the Voc temperature coefficient is better regarded as a constraint for system design and electrical matching, rather than a core indicator of power generation performance.

2.2 Isc Temperature Coefficient: Observable Variation, Limited Impact on Generation

Short-circuit current (Isc) typically increases slightly as temperature rises, which is why its temperature coefficient is usually a small positive value or close to zero.

However, under normal operating conditions, PV modules do not operate in a short-circuit state. The output current is governed by the maximum power point. Therefore, even though Isc varies with temperature, the Isc temperature coefficient has only a limited effect on actual energy yield. It is mainly used for electrical safety verification rather than as a primary metric for evaluating generation efficiency.

2.3 Pmax Temperature Coefficient: The Most Direct Indicator of High-Temperature Performance

By contrast, the temperature coefficient of maximum power output (Pmax) has the most direct relationship with power generation performance. As module temperature increases, changes in Pmax can almost be directly interpreted as changes in usable energy output.

In projects where high-temperature operation is the norm, differences in Pmax temperature coefficients between PV modules often translate into noticeable differences in energy yield. This is particularly relevant for commercial and industrial rooftops, carports, and high-temperature environments such as Southern Europe. In these scenarios, modules with a lower (less negative) Pmax temperature coefficient are generally able to maintain more stable output levels, thereby reducing the impact of high temperatures on annual energy production. Typical ranges of temperature-related parameters for common PV modules are shown in the table below.

Parameter type Typical range (indicative)
NOCT 42–48 °C
Pmax temperature coefficient −0.24% ～ −0.34% /°C
Voc temperature coefficient −0.22% ～ −0.30% /°C
Isc temperature coefficient +0.03% ～ +0.06% /°C
Note: The values above represent typical ranges for mainstream commercial PV modules, compiled based on IEC test methodologies and publicly available research data from authoritative institutions such as Fraunhofer ISE and NREL. They are intended to illustrate the general impact of temperature variations on PV module performance.

From an energy yield perspective, Pmax is the most practically relevant temperature coefficient, while Voc and Isc are primarily used for system design considerations and electrical safety checks.

How Does the Temperature Coefficient Affect the Actual Performance of PV Modules in Different Application Scenarios?

3.1 Why Does the Temperature Coefficient Directly Affect PV Project Returns in Southern Europe?

If your project is located in Southern Europe (such as southern Italy or southern France) and its main revenues come from summer power generation, the temperature coefficient is not an “optional parameter” but a variable that directly affects annual returns.

In regions such as southern Italy and southern France, PV projects typically share two key characteristics:

  • Summer solar irradiation is at its highest, with annual energy yield peaks concentrated between June and August;

  • During the same period, module operating temperatures also reach their highest levels of the year.

This means that high temperatures do not occur during low-yield periods but instead coincide with the most critical generation window. In engineering assessments, the industry often uses a simplified model based on IEC principles to evaluate power variations under high-temperature conditions:

P ≈ Pₛₜ𝒸 × [1 + Pmax × (Tcell − 25 °C)]

This formula is used to assess whether high-temperature operation will be amplified into a sustained power difference during the main energy-producing periods of the year.

Assumed operating conditions:

  • Module operating temperature: 80 °C

  • Temperature difference relative to STC: 80 °C − 25 °C = 55 °C

Examples:

  • TOPCon modules (Pmax temperature coefficient −0.32%/°C): power reduction of around 17.6%, resulting in an actual output of approximately 82% of rated power;

  • IBC modules (Pmax temperature coefficient −0.29%/°C): power reduction of around 15.95%, resulting in an actual output of approximately 84% of rated power;

  • HJT modules (Pmax temperature coefficient −0.243%/°C): power reduction of around 13.4%, resulting in an actual output of approximately 86%–87% of rated power.

For Southern European projects where summer generation dominates, the temperature coefficient is often directly linked to long-term revenue stability and should be considered an important comparison metric in PV module selection.

3.2 In Which Application Scenarios Should the Temperature Coefficient Be Given Priority?

Whether the temperature coefficient truly affects project returns depends not only on the country or latitude, but even more on the specific application scenario. In real projects, the following scenarios are those where the temperature coefficient is most likely to translate into noticeable differences in energy yield:

  • Commercial and industrial rooftop projects
    Rooftops typically offer limited ventilation, with restricted heat dissipation at the rear of the modules. In summer, modules are more likely to operate continuously at high temperatures. In such projects, the temperature coefficient often has a direct impact on output during peak generation periods and therefore has high reference value.

  • Carports and elevated structures
    Modules are usually exposed to direct sunlight, with combined effects of ground reflection and ambient temperature, leading to prolonged high-temperature operation. When project revenues rely heavily on summer generation, the temperature coefficient is again a key comparison factor.

  • Agrivoltaic and low-clearance installations
    With limited clearance from the ground, thermal radiation from the surface is more pronounced, and systems often aim for long-term stable operation. In these projects, the influence of the temperature coefficient on generation stability is more likely to become evident over multiple years of operation.

Therefore, when evaluating temperature coefficients, the decisive factor is not the geographic label itself, but whether PV modules operate for long periods under conditions combining high temperatures and high generation weighting. In the scenarios above, the temperature coefficient deserves particular attention as a key comparison criterion in PV module selection.

Illustration showing how low mounting height and ventilation conditions affect module operating temperature and the relevance of temperature coefficients.

How to Use the Temperature Coefficient Correctly in PV Module Selection

In PV module selection, the temperature coefficient is not a parameter that needs to be “optimised in isolation”. However, under specific project conditions, it should not be overlooked.

In practice, the temperature coefficient is mainly used to compare PV modules in the following types of projects:

  • Projects where revenues are largely concentrated in high-temperature generation periods, such as summer

    HJT modules feature a relatively low temperature coefficient, making them suitable for projects that place high value on generation stability under high temperatures and long-term returns, and where budgets are relatively flexible. IBC modules offer a well-balanced compromise between temperature coefficient performance and power output per unit area, making them suitable for commercial and industrial applications that aim to combine efficiency and stability in high-temperature environments.

  • Projects where high temperatures are present but do not dominate year-round operation

    In these scenarios, the impact of high temperatures on energy yield is more seasonal in nature. TOPCon modules provide a strong overall balance between efficiency, cost, and temperature coefficient, making them suitable for projects that prioritise cost-effectiveness, supply stability, and well-rounded performance. They are particularly well suited to long-term operation on rooftops, carports, and other structures with relatively limited heat dissipation.

  • Projects with low sensitivity to the temperature coefficient

    In such cases, module operating temperatures are relatively controllable, and the weighting of high-temperature effects on energy yield is low. During module selection, the temperature coefficient is usually not a primary differentiating factor and can be assessed alongside other performance parameters.

In summary, the temperature coefficient does not determine the outcome of every PV module selection decision. However, in applications where high-temperature operation is the norm, it should be included as an important comparison criterion and evaluated together with the specific PV technology route to assess its impact on actual energy yield and long-term project returns.

Filter suitable modules by operating conditions

Maysun Solar operates across the European market, supplying solar panels based on IBC technology, TOPCon technology, and HJT technology to wholesale and distribution partners. We focus on high-temperature generation stability, power density, and system compatibility to support reliable deployment and long-term project returns under real operating conditions.

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3 Comments

  3. Tom Hargreaves
    January 15, 2026,

    Nice to see the emphasis on real operating temperature, not just STC numbers. On poorly ventilated rooftops, temperature coefficient quickly becomes a differentiator. Well explained.

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