Summer is usually the peak season for solar power generation, but that does not mean solar panels operate more efficiently in high temperatures. On the contrary, rising temperatures lead to additional power loss. For HJT, TOPCon and IBC, the real difference lies not only in nominal efficiency, but in how much output each technology can retain under heat.
If heat resistance is the main priority, HJT usually has the edge. If the focus is on balancing cost and return, TOPCon is better suited to most standard projects. If the project also values appearance and architectural integration, IBC is still worth considering. For businesses, the differences between solar panels in summer heat will ultimately show up in generation stability, self-consumption rates and return on investment.
Table of Contents
Why Does Summer Heat Reduce Solar Panel Efficiency?
Solar panels are sensitive to temperature. As cell temperature rises, output voltage falls, which leads to power loss. In other words, although summer usually brings stronger sunlight and higher overall generation, heat itself does not improve solar panel efficiency. Instead, it weakens output during periods of strong irradiance.
To assess this effect, the key figure is the panel’s temperature coefficient. The lower the temperature coefficient, the smaller the power loss under high temperatures. The original calculation logic can be kept as follows:
Power loss = temperature coefficient × (panel operating temperature – 25°C)
Taking an N-TOPCon solar panel as an example, if the temperature coefficient is estimated at -0.32%/°C, and the operating temperature rises from 25°C to 65°C, the power loss is approximately:
-0.32%/°C × (65 – 25) = 12.8%
This is why, in many projects, solar panel output does not continue to rise in step with irradiance at midday in summer. What really affects performance is not just how strong the sun is, but how much effective output the solar panel can still retain under high-temperature conditions.
1.1 High temperatures affect more than efficiency alone
The impact of heat is not limited to lower output at a given moment. It can also amplify longer-term operating risks, mainly in three areas:
- More visible power loss
Under strong midday irradiance combined with high temperatures, solar panels are more likely to enter a high-temperature operating range, so output losses tend to be more pronounced than in spring or autumn.
- Greater risk of localised hotspots
When part of a solar panel is shaded, dusty or contaminated, local temperatures rise more quickly and hotspot risk increases. The earlier warning about hotspots can be retained, as this remains a very practical issue in summer operation.
- Greater long-term degradation pressure in hot and humid conditions
When heat and humidity act together, degradation risks such as PID deserve closer attention. Even though most modern solar panels are designed with PID resistance, these issues still cannot be ignored if system design or installation is not properly managed.
1.2 Why are commercial and industrial projects more exposed to high temperatures?
For commercial and industrial projects, the effect of heat should not be judged only by average generation levels. More importantly, it should be assessed in terms of output stability during key daytime load periods. Many businesses see peak electricity demand in summer daytime hours. If solar panels lose more output during high-temperature periods, the system’s ability to cover on-site demand will also decline, increasing reliance on grid electricity. As a result, high temperatures affect not only panel performance itself, but also wider system performance and technology selection.
What Are the High-Temperature Differences Between HJT, TOPCon and IBC?
The differences between these three technologies under high temperatures mainly come down to temperature coefficient, output stability and the applications they are best suited to. The temperature coefficient shows how quickly a solar panel loses power as heat rises, while cell structure and application scenario determine whether those differences become more pronounced in real projects.
2.1 HJT Solar Panels: Stronger Power Retention in High Temperatures
- Lowest temperature coefficient: HJT solar panels typically have a temperature coefficient of around -0.243%/°C, meaning power output drops by about 0.243% for every 1°C increase. If panel temperature rises from 25°C to 65°C, power loss is only around 9.72%, giving HJT a clearer advantage in high-temperature conditions.
- Advantage of a specialised cell structure: HJT uses heterojunction technology, combining crystalline silicon and amorphous silicon to absorb a broader light spectrum more effectively and improve overall generation efficiency. This makes it particularly suitable for high-irradiance regions such as southern Europe.
- Higher reliability: Low-temperature manufacturing processes and a more flexible cell structure help reduce the risk of microcracks during transport and installation, improving long-term operating stability.
2.2 TOPCon Solar Panels: Balanced Performance in Hot Conditions
- Moderate temperature coefficient: TOPCon solar panels generally have a temperature coefficient of around -0.32%/°C, with power loss of about 12.8% in high-temperature operation (25°C to 65°C). While this is slightly weaker than HJT, it still outperforms conventional technologies such as PERC.
- Clear structural advantages: TOPCon uses passivated contact technology and a rear reflective layer to improve carrier transport efficiency, reduce thermal damage and extend panel service life.
- Strong cost-performance balance: Compared with HJT, TOPCon solar panels are more cost-effective, making them well suited to business projects with tighter budgets but still meaningful requirements for heat resistance.
2.3 IBC Solar Panels: Better Suited to Projects with Higher Aesthetic Requirements
- Competitive high-temperature performance: IBC solar panels typically have a temperature coefficient of around -0.29%/°C. With panel temperature rising from 25°C to 65°C, power loss is about 11.6%. From a data perspective, IBC remains competitive, but on heat resistance alone it does not usually rank ahead of HJT.
- Better suited to specialised applications: Thanks to their structural design and visual appeal, IBC solar panels are better suited to commercial buildings with stricter aesthetic requirements, as well as building-integrated photovoltaics (BIPV). This is also where IBC stands apart most clearly from HJT and N-TOPCon.
High-Temperature Performance Comparison of Three Solar Panel Technologies
| Panel type | Temperature coefficient (%/°C) | Power loss (25→65°C) | Best suited to |
|---|---|---|---|
| HJT | -0.243% | 9.72% | High heat, strong sunlight, stable output |
| TOPCon | -0.32% | 12.8% | Standard commercial and industrial rooftops, balanced performance |
| IBC | -0.29% | 11.6% | Projects with higher aesthetic demands and building integration |
Note: Power loss is calculated based on the temperature coefficient, assuming the panel operating temperature rises from the standard test condition of 25°C to 65°C.
How Should Businesses Choose the Right Solar Panel for High Summer Temperatures?
When choosing solar panels for hot conditions, the key is not simply which technology has the strongest specification on paper, but which capability the project needs most. In regions with intense heat and strong sunlight, stable output under high temperatures should come first. For most standard commercial and industrial rooftops, the priority is a balance between performance, cost and practical implementation. If the project also places strong emphasis on roof appearance and architectural integration, IBC is often the more targeted option.
3.1 Prioritise thermal stability in hot regions
If the project is located in southern Italy, central and southern Spain, southern France or other high-temperature, high-irradiance regions, solar panels will often operate under prolonged heat in summer. In this case, temperature coefficient and power retention under high temperatures should be compared first. For projects like these, HJT is more likely to show a clear advantage.
If the project is in a milder climate, high temperatures will still affect generation, but may not be the deciding factor. In that case, N-TOPCon is often the more practical choice.
3.2 Prioritise output per square metre when roof space is limited
For projects with tighter roof space, such as factories and warehouse sites, how much effective capacity can be installed per square metre will directly affect system size and overall performance. In these cases, HJT or IBC is often better suited to projects with higher output requirements per unit area.
If roof space is more generous and the project is more focused on overall cost control, TOPCon will usually provide a more balanced solution.
3.3 Different project priorities lead to different technology choices
If the project places greater emphasis on stable output during peak summer heat, HJT is usually the first technology worth comparing. If the project is more focused on overall investment and ease of execution, TOPCon is often better suited to most standard rooftops. If the project also requires stronger visual appeal, architectural consistency and display value, IBC is the more targeted option.
In practice, businesses choosing solar panels for hot conditions should usually start by clarifying three questions:
- Will the project site face prolonged high-temperature operating conditions in summer?
- Is the project more focused on stable output during hot periods, or on overall system balance?
- Does the roof also require a higher level of appearance or building integration?
3.4 Long-life projects should place more weight on consistency
For long-lifecycle projects that demand stronger generation consistency and operational stability, such as centrally managed multi-site systems, long-term degradation control and operating consistency should also be prioritised. In these cases, HJT or IBC is often better placed to show its stability advantage over time, while TOPCon is more suitable for projects that place greater value on overall balance and implementation efficiency.
How Can Power Loss Be Reduced and Overall System Performance Improved?
For systems already in operation, reducing high-temperature losses can usually be approached in three steps: first identify where the loss is coming from, then improve cleaning and shading management, and finally optimise system conditions during the hottest hours.
4.1 Identify the Source of the Loss First
A drop in summer generation does not necessarily mean there is a problem with the solar panels themselves. In many cases, what gets amplified is poor ventilation, local shading, uneven soiling, wiring faults or excessive local temperature rise. For completed projects, the first step is not to rush into replacing panels, but to determine whether the loss comes from the panels themselves or from system conditions.
Initial checks can focus on the following areas:
- Compare output changes during peak midday heat with output in the morning and early evening
- Compare performance differences between different roof areas and different strings on the same roof
- Compare this summer’s generation curve and temperature rise with the same period last year
Only once the real source of the loss is clear can later optimisation be properly targeted.
4.2 Improve Cleaning and Shading Management
In high-temperature conditions, issues such as dust build-up, bird droppings, tree shade, parapet shading and equipment shadowing are more likely to turn into real generation losses. Since the solar panels are already operating at elevated temperatures, any local contamination or shading will usually cause local heating to rise faster and output to fall more sharply.
If the goal is to improve performance quickly on an existing system, the most worthwhile priorities usually include:
- Add a focused cleaning and inspection round before the start of summer
- Reassess shading points that occur at fixed times of day
- Increase inspection frequency in areas with heavier soiling or faster temperature rise
- Deal promptly with abnormal local heating and hotspot risks
These measures are not complex, but they often improve summer performance more directly than staying at the level of parameter analysis alone.
4.3 Optimise System Conditions During Peak Heat
If the investigation shows that losses are concentrated mainly during the hottest midday hours, the next step is to assess whether system conditions are making the problem worse. Poor rear-side ventilation, overly dense layout and strong roof heat build-up can all raise the actual operating temperature of the solar panels, increasing summer power loss.
For that reason, the focus of the third step is not large-scale system redesign, but prioritising the conditions that directly affect performance in high-temperature periods, including:
- Check heat dissipation and ventilation conditions in key areas
- Assess whether the layout is too dense or whether certain zones are prone to heat build-up
- Carry out targeted local corrections or zone-based optimisation in the worst-affected areas
- Focus optimisation on the key periods around midday and early afternoon in summer
For commercial and industrial projects, effective output during high-temperature periods matters more than average generation over the whole day. Once these key points are handled properly, summer operating performance is usually far more stable.
Frequently Asked Questions About Choosing Solar Panels for High-Temperature Conditions
1. Shouldn’t solar panels generate more electricity in summer because the weather is hotter?
Not exactly. Total generation is usually higher in summer mainly because solar irradiance is stronger and daylight hours are longer. But from the panel’s perspective, higher temperatures bring additional power loss. What really matters is how much effective output the solar panel can still retain during hot periods.
2. If the air temperature reaches 35°C, how hot will the solar panel actually get?
It is usually much hotter. Especially under strong midday sunlight, low wind speeds and average ventilation conditions, panel temperatures reaching 60°C or even higher are not unusual. So when assessing the impact of heat, it is not enough to look only at air temperature. The panel’s actual operating temperature, installation method and roof conditions must also be considered.
3. In high-temperature conditions, is HJT always a better choice than TOPCon?
Not necessarily. If the project places greater importance on power retention during hot periods, HJT usually has the advantage. If the priority is cost, supply-chain maturity and overall balance, TOPCon remains highly competitive, especially when using optimised designs such as 1/3-cut cell structures. The key is not simply which technology is better, but which is better suited to the project.
4. Are IBC solar panels still competitive in hot regions?
Yes. IBC offers more than just solid high-temperature performance. Its advantages also include an unobstructed front surface, cleaner aesthetics and stronger compatibility with building integration. If the project also values efficiency, visual appeal and roof design, IBC is still well worth considering.
5. When choosing solar panels for summer, is the temperature coefficient alone enough?
No. The temperature coefficient is important, but it is not the only factor that should guide summer panel selection. In real projects, installation method, ventilation conditions, roof environment, panel consistency and later operation and maintenance all affect actual performance during hot periods. The temperature coefficient only shows the panel’s power loss under heat; it cannot by itself determine the best choice for the project.
Maysun Solar is committed to providing European customers with solar panel solutions better suited to high-temperature conditions and complex rooftop scenarios. Across mainstream technologies such as IBC technology, TOPCon technology, and HJT technology, we continue to optimise temperature performance, output stability and application suitability, helping residential and commercial and industrial projects achieve a more balanced result across performance, cost and long-term operation.
Reference
European Commission Joint Research Centre (JRC) — Photovoltaic Geographical Information System (PVGIS) https://joint-research-centre.ec.europa.eu/photovoltaic-geographical-information-system-pvgis_en
Fraunhofer Institute for Solar Energy Systems ISE — Photovoltaic Module Performance Testing and Temperature Coefficients https://www.ise.fraunhofer.de/en/business-areas/pv-systems.html
World Bank Group — Global Solar Atlas https://globalsolaratlas.info/
European Commission — Renewable Energy Directive and Member States Incentives https://energy.ec.europa.eu/topics/renewable-energy/renewable-energy-directive_en
International Renewable Energy Agency (IRENA) — Solar PV Technology and Cost Trends https://www.irena.org/publications/2020/Jun/Solar-PV
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A lot of summer PV discussions still focus on irradiance, but in real operation the bigger issue is often how much output can actually be retained once module temperature rises. The distinction made here between nominal efficiency and heat-time power retention is important, especially for commercial rooftops where midday output has a direct effect on self-consumption.
What becomes clear in high-temperature conditions is that the technology choice starts to show up in system behaviour, not just in the datasheet. HJT, TOPCon and IBC are not serving exactly the same project logic, so comparing them only by headline efficiency misses the real question of where stability, cost balance or architectural fit matters more.