How Temperature Affects the Performance of Solar Panels

When most people think of solar panels, they imagine sunshine — and the more of it, the better. But while sunlight is essential for energy production, too much heat is not. In fact, elevated temperatures can significantly degrade the performance of photovoltaic (PV) modules. This post explores how and why solar panels lose efficiency as temperatures rise, how this effect is measured, and what can be done to mitigate it.

The Basics: Voltage Falls as Temperature Rises

Solar panels convert sunlight into electricity using semiconductor materials, typically silicon. As light strikes the panel, photons knock electrons loose, generating direct current (DC) electricity.

However, as temperature increases, the voltage output of the cells decreases. The current rises slightly, but not enough to compensate for the voltage drop — and so the overall power output declines.

Temperature Coefficient: The Key Metric

Every PV module has a temperature coefficient — usually expressed as a percentage loss per °C above 25°C (the industry standard testing condition).

For example, a panel with a temperature coefficient of -0.35%/°C will lose:

• 0.35% of its rated power for each degree Celsius over 25°C.
• At 60°C (a realistic module temperature on a sunny day), that's 35°C × 0.35% = 12.25% less power.

And remember: panel temperatures can reach 60–70°C even in moderate ambient conditions if the airflow is poor or the roof is dark.

What Happens to the “Missing” 80%?

Most standard solar panels today have efficiencies around 20–22%, which means:

• Only 20–22% of the incident solar energy is converted into electricity
• The remaining 78–80% becomes heat

This unused energy doesn't disappear — it is absorbed by the panel’s materials and eventually converted into heat, raising the cell temperature significantly above ambient levels.

Energy Balance Example:

Let’s take a real-world scenario with 1,000 W/m² of solar irradiance:

| Component | Approximate Energy Use | |------------------------|------------------------| | Electrical output (20%) | 200 W/m² | | Heat absorbed (80%) | 800 W/m² |

That 800 W per square meter is thermal load — heating the panel's glass, encapsulant, and semiconductor layers. Over time, this heat:

• Reduces efficiency due to temperature sensitivity
• Accelerates aging (e.g. EVA yellowing, solder fatigue)
• Can push panels well beyond 60°C or even 75°C in some climates

High panel temperatures are not just a side effect — they are inherent to the physics of photovoltaics. Unless reflected or ventilated away, most of the sun's energy becomes heat.

Real-World Consequences

In hot climates — or even during heatwaves in temperate regions — this temperature effect can be significant:

• A 10 kW array could easily lose 600–800 W of power output on a hot afternoon.
• Systems in regions like the North Africa, the Middle East, or southern Spain often experience annual average efficiency losses of 5–10% due to temperature alone.

This is why some countries with the most sun aren't necessarily those with the highest PV yield per installed watt.

Different Technologies, Different Losses

Not all solar panels react to heat in the same way. Here’s how some technologies compare:

| Technology | Typical Temp. Coefficient (Pmax) | |--------------------|-------------------------------| | Monocrystalline Silicon | -0.35% / °C | | Polycrystalline Silicon | -0.40% / °C | | Thin-Film (CdTe) | -0.25% / °C | | Heterojunction (HJT) | -0.26% / °C | | TOPCon / IBC | -0.29% / °C |

Technologies like thin-film and HJT perform better under heat, making them attractive for desert or tropical regions — although they may be less efficient or costlier in other ways.

Ambient ≠ Module Temperature

It’s important to distinguish between ambient temperature and cell temperature. Panels heat up in the sun due to absorption of infrared radiation, poor ventilation, and mounting surface characteristics.

Typical temperature rise above ambient: - 30–40°C in rooftop systems with limited airflow - 15–25°C in ground-mounted systems with good ventilation

That’s why a 30°C day might mean 60°C panel temperature, and thus a 10% performance drop.

Mitigation Strategies

While we can’t control the weather, there are smart ways to reduce the impact of heat on PV performance:

1. Select low temperature coefficient panels (e.g. HJT, TOPCon)
2. Optimize airflow beneath the panels — especially for rooftop installs
3. Use light-colored mounting surfaces (white membranes reflect heat)
4. Install at a slight angle even on flat roofs, to allow convection
5. Consider bifacial panels, which typically run cooler due to higher albedo usage
6. Use performance modeling tools that factor in temperature (like PVsyst or SAM)

When Heat Meets Other Factors

Temperature doesn’t act alone. Its effects compound with: - Soiling losses (hot panels attract more dust) - Inverter clipping (hot panels produce lower voltages, sometimes dropping out of optimal inverter range) - Degradation over time (heat accelerates aging and delamination)

Conclusion

Heat hurts solar efficiency — and it’s one of the most underestimated, least intuitive factors in real-world PV performance. While sunlight is what powers solar energy, heat is the cost that comes with it. And the tradeoff isn’t linear: every additional degree affects system output more than most homeowners or even installers expect.

As climate change drives more frequent and intense heatwaves, PV systems in all regions — even temperate ones — are being pushed to their thermal limits. This isn’t just a design consideration; it’s an operational and economic one. Oversizing inverters, choosing thermally stable panel types, and designing for airflow are no longer “nice to have” — they’re critical for long-term yield stability.

If we want solar energy to fulfill its promise in a warming world, we need to stop seeing temperature as an afterthought — and start treating it as a key design constraint.

So the next time the sun blazes overhead and the forecast calls for 35°C, remember: Your panels are working hard — maybe too hard. And smart system design is what helps them keep going.