The most obvious factor is that panels are usually placed where they can absorb direct sunlight for maximum energy capture, which naturally raises their temperature. Also, the materials used in the construction of solar panels, such as metal frames and silicon cells, are excellent conductors of heat.
It is important to remember that is only the light energy from the sun that solar panels use. The temperature does not change the amount of energy generated by a solar panel, so it doesn't matter if it is a hot or cold day, It is only the strength of sunlight that makes a difference.
Solar panels are vulnerable to heat because of their operating environment and construction materials. The most obvious factor is that panels are usually placed where they can absorb direct sunlight for maximum energy capture, which naturally raises their temperature.
While it’s correct that solar panels can be less efficient in hot temperatures, this reduction is relatively small. According to Solar Energy UK, solar panel performance falls by 0.34 percentage points for every degree that the temperature rises above 25°C.
While extreme heat can reduce a solar panel’s efficiency, they continue to function effectively, even in high temperatures. In the UK, around 40% of a solar panel system's energy is generated in the summer, showing its strong performance in warmer months.
Even if the summer temperatures were to creep towards boiling point, the reduction in power output would be only around 20% (assuming other conditions remain constant), according to Solar Energy UK. Solar panels become slightly less efficient with every degree they heat up beyond 25°C.