When the atmospheric conditions are too hot, solar panels do not generate as much power as when the weather is cooler. It is therefore quite normal for solar systems to generate less electricity on a hot day, and more on a cool or windy day.
Solar panels with wattage ratings that were tested at a temperature of 25°C (77°F) against a light source of 1,000 watts/m 2 were found to generate more electricity at cooler temperatures than at warmer temperatures. This effect could be due to the panels over heating from their exposure to the sun’s infrared radiation. In cooler temperatures, the solar panels are more shaded and consequently can heat up more efficiently; sometimes to as high as 80 to 90°C (160 to 175°F).
Information on the temperature’s effects on solar panels is provided by many solar panel manufacturers in terms of the temperature coefficient of power rating. This is a total power reduction percentage for every degree Celsius of temperature increase.
A typical figure is 0.5 percent, which means that every degree of temperature increase (Celsius) will cause your solar array to lose 0.5 percent efficiency. Conversely, every degree of temperature decrease will improve efficiency by 0.5 percent.
Northern Europe and Canada do not have a problem with high temperatures when it comes to designing solar systems, since their temperatures remain relatively cool. A stand-alone solar electric system is usually not a problem even when there is plenty of electricity generated during hot summers. But in South America, India, Africa or the Middle East, the ambient temperature is an important factor for a solar system design. High temperatures above 25°C are experienced for most of the year in these places.
One way to reduce solar panel temperature is by choosing the right mount for the panels. A roof mount should allow a 7-10cm gap (3 - 4 inches) below the solar panels for air flow in between and all around. Alternatively, pole mounts are also a good way to encourage air flow around the solar panels, allowing them to cool on hot days.
For a roof-top installation, if the air temperature is 25°C (77°F) or above, multiply this temperature by 1.5 in order to get a likely solar panel temperature. For a pole-mounted installation, multiply your air temperature by 1.2, then increase your wattage requirements by the percentage loss in order to work out the wattage you need for your solar panels to generate sufficient energy.