The Impact of Temperature on Solar Panels: How to Optimize Your Production Despite Heat

Understanding the impact of temperature on your solar panels

Contrary to popular belief, photovoltaic panels don't particularly like heat. While sunshine is essential to produce electricity, high temperatures can paradoxically significantly reduce the performance of your installation. With more and more regions experiencing heatwaves, it's essential to understand this phenomenon in order to optimize the energy production of your solar system.

In this article, we'll take a closer look at the impact of temperature on the performance of photovoltaic panels, explain the STC (Standard Test Conditions) used as a reference in the industry, and suggest concrete solutions for limiting these losses and maximizing your electricity production, even during the hottest periods.

"Solar panels are like athletes: they need sun to perform, but too high a temperature is detrimental to their performance."

STC conditions: the benchmark for measuring power ratings

When you buy a solar panel, its power is always indicated in Watt-peak (Wp), such as the Shinson N3-TOPCon 450 Wp Bifacial panels available on our site. This power represents the panel's maximum production capacity under standard test conditions (STC), which are :

• Sunshine of 1000 W/m²
• Cell temperature of 25°C
• Solar spectrum AM 1.5 (Air Mass)

These ideal conditions serve as a benchmark for comparing the different panel models on the market. However, they rarely correspond to the reality in the field, particularly where temperature is concerned.

NOCT: a measurement closer to reality

To get a more realistic idea of panel performance under normal conditions of use, manufacturers sometimes also indicate the NOCT (Nominal Operating Cell Temperature) value, which represents the temperature the cell would reach under the following conditions:

• Sunshine of 800 W/m²
• Ambient temperature of 20°C
• Wind speed of 1 m/s

For most photovoltaic panels, the NOCT is generally between 45°C and 48°C, which means that even with a moderate ambient temperature of 20°C, the cell temperature is already well above the STC reference temperature of 25°C.

Temperature coefficient: the key loss indicator

To quantify the impact of temperature on solar panel performance, manufacturers specify an essential parameter: the power temperature coefficient. This coefficient, generally expressed as a percentage per degree Celsius (%/°C), indicates the power loss for each degree above 25°C.

For example, if a solar panel has a temperature coefficient of -0.35%/°C (a typical value for many panels), this means that for every degree above 25°C, the panel will lose 0.35% of its rated power.

How do I calculate yield losses?

The formula for calculating power loss is as follows:

Power loss = (Cell temperature - 25°C) × Temperature coefficient

Let's take a concrete example with a 450 Wp panel (like the Shinson N3-TOPCon) having a temperature coefficient of -0.30%/°C :

• If the cell temperature reaches 60°C (which is common on a sunny summer's day)
• The deviation from the STC reference temperature is :
• 60°C - 25°C = 35°C
• The power loss will therefore be :
• 35°C × (-0.30%/°C) = -10.5%
• The panel's real power will be only : 450 Wp - 10.5% = 402.75 Wp

This represents a significant loss of over 47 Wp for a single panel. For a complete installation with 10 panels, this represents a loss of almost 500 Wp!

-

-6

423

-9

-12

396

It's important to note that during hot summer months, cell temperatures can easily exceed 70°C, resulting in even greater losses.

How temperature affects different electrical parameters

Temperature does not uniformly affect all the electrical parameters of a solar panel. Here's how it affects the main parameters:

Voltage (Voc and Vmp)

Open-circuit voltage (Voc) and voltage at maximum power point (Vmp) are the most sensitive to temperature. They decrease significantly as temperature rises, with typical temperature coefficients of -0.30% to -0.40%/°C.

For example, a panel with a Voc of 40.20V at 25°C (like the Shinson N3-TOPCon) could see its voltage drop to around 36.18V at 60°C, a drop of 10%.

Current (Isc and Imp)

Short-circuit current (Isc) and current at point of maximum power (Imp) are less affected by temperature. They increase slightly with temperature, with positive coefficients typically of the order of +0.04% to +0.07%/°C.

However, this slight increase in current does not compensate for the significant drop in voltage, which explains the overall power loss.

Impact on overall efficiency

Voltage drop has important implications for photovoltaic system design, particularly for inverter sizing. If the voltage drops too low in summer, the inverter may no longer be able to operate in its optimum range, or even shut down completely if the voltage falls below its minimum operating threshold.

This is why it's crucial to take these temperature variations into account when designing a solar installation, especially in regions prone to high summer temperatures.

Panel technologies and their sensitivity to temperature

Not all solar panel technologies are equal when it comes to temperature. Some are more resistant than others to the negative effects of heat.

Comparison of temperature coefficients by technology

Heterojunction

N-type solar panels such as the Shinson N3-TOPCon and Leapton N-Type TOPCon panels available on our site therefore offer a significant advantage over older technologies in terms of temperature resistance.

Bifacial panels: an additional advantage

Bifacial panels like the Shinson N3-TOPCon 450 Wp Bifacial offer an additional advantage. By capturing light from both sides, they can partially compensate for temperature-related losses by increasing overall output through reflected light. What's more, their design often allows for better heat dissipation, thus reducing the operating temperature of the cells.

"Opting for bifacial panels with N-Type TOPCon technology means choosing an installation that performs better all year round, including during periods of high heat."

Practical solutions to limit the impact of temperature

Now that we understand why and how temperature affects solar panel performance, let's see what solutions can be implemented to limit these losses.

Solutions when designing the installation

1. Choose panels with a low temperature coefficient: As we've seen, certain technologies like N-type TOPCon are less sensitive to heat.
2. Choose the latest-generation panels available on our website.
3. Ensure good rear ventilation: Leave sufficient space between the roof and the panels (minimum 10 cm) to allow air to circulate and dissipate heat.
4. Orient the panels optimally: An east/west orientation can sometimes be preferable to a full-south orientation in very hot regions, as it distributes production better over the day and avoids midday temperature peaks.
5. Slightly oversize the installation: Plan for a slightly higher installed power than you need to compensate for summer losses.
6. Correctly size strings: Calculate panel strings taking into account temperature-related voltage variations to prevent the inverter from operating outside its optimal range.

Solutions for existing installations

• Improve ventilation: If possible, increase the space between the roof and the panels to facilitate air circulation.
• Use supports that promote air circulation: Some mounting systems allow for better air circulation.
• Clean panels regularly: Dust and debris can increase panel temperature by preventing heat dissipation.

For large-scale installations or in particularly hot climates, more advanced solutions may be considered:

• Active cooling systems: devices that spray a fine mist of water over the panels during the hottest periods.
• Reflective materials: Installing reflective surfaces near bifacial panels can increase efficiency while reducing temperature.

Important note: Manual watering of panels is generally not recommended, as thermal shock can damage glass and cells, and tap water can leave traces of limescale that will reduce panel efficiency.

The special case of green roofs

An ecological and effective solution for reducing panel temperatures is to install a green roof under or around the solar panels. The plants absorb some of the sun's energy and evaporate water, naturally cooling the environment around the panels.

This solution offers a number of advantages:

• Reduced ambient temperature around the panels
• Improved building insulation
• Rainwater retention
• Increased biodiversity
• Improved air quality

If you are interested in this solution, contact our experts who will be able to advise you on the possibilities of integrating it with your solar installation.

Do we really need to worry about temperature-related losses?

It's important to put these losses into perspective. Although hot summer days lead to a drop in yield, it's also during this period that sunshine is at its peak, which partly offsets temperature-related losses.

On the other hand, the summer months are generally the most productive for a photovoltaic installation, despite the negative effect of temperature. The annual electricity production of a well-designed installation will therefore always be satisfactory, even if it doesn't reach the theoretical values calculated under STC conditions.

Finally, it should be remembered that manufacturers already take these factors into account in their long-term production calculations, and that performance guarantees generally include these seasonal variations.

Conclusion

The impact of temperature on photovoltaic panels is an inescapable physical phenomenon that can temporarily reduce the performance of your solar installation, particularly during hot periods. However, thanks to recent technological advances such as the N-type TOPCon and bifacial panels available from Wattuneed, and to an adapted design of your installation, these losses can be significantly limited.

By choosing quality equipment and following good installation practices, you can optimize the performance of your photovoltaic system all year round and maximize your return on investment.

To benefit from personalized support for your solar project and select the panels best suited to your geographical location and energy needs, don't hesitate to contact our experts. They'll help you design a high-performance, long-lasting installation that minimizes the impact of high temperatures on your electricity production.

FAQ

At what temperature do solar panels work best?

Solar panels work best at a cell temperature of 25°C, which corresponds to STC conditions. However, in real-life conditions, they generally operate at much higher temperatures, which reduces their efficiency.

Is it advisable to water solar panels during heatwaves?

No, manual watering of panels is generally not recommended, as thermal shock can damage cells and glass. What's more, tap water can leave traces of limescale, reducing the panels' efficiency. Professional cooling systems are available for large-scale installations.

Which type of solar panel is the least sensitive to heat?

Panels using heterojunction technology (HJT) are generally the least sensitive to heat, with temperature coefficients of around -0.25% to -0.30%/°C. N-type TOPCon panels like those offered by Wattuneed also offer excellent temperature resistance, with coefficients around -0.30% to -0.35%/°C.

How do I calculate the actual temperature of a solar panel?

A simplified formula for estimating panel temperature is: T(cell) = T(ambient) + (NOCT-20)/800 × Sunshine. For example, with an ambient temperature of 30°C, sunshine of 1000 W/m² and an NOCT of 45°C, the cell temperature would be around 61.25°C.

Are bifacial panels better in hot weather?

Bifacial panels can actually perform better in hot weather for two reasons: they allow better heat dissipation thanks to their design, and their ability to capture reflected light can partially compensate for temperature-related losses.

Company details

Wattuneed
Rue Henripré 12
4821 Andrimont
Belgium
+32 87 45 00 34
info@wattuneed.com