Can Solar Panels Overheat?
It is a common assumption to relate really hot climates with excellent conditions for solar panels, however, the truth is that under extremely high ambient temperature conditions, solar panels can indeed overheat. This problem can become one of the major causes of a potential drop in performance and can reduce energy yields drastically if not considered properly.
In order to accurately describe how solar panels can overheat, we must first understand some basic theory behind solar PV system designs.
Solar Panels and Test Conditions
New solar panel models must pass through a set of lab tests known as Standard Test Conditions (STC) and Nominal Operating Cell Temperature (NOCT) which are related to the performance and power output of the module under specific environmental conditions. This post is useful to learn more about how solar panels are rated.
STC are referred to the following lab conditions:
Irradiance = 1kW/m2
Temperature = 25°C
Air Mass = 1.5 AM.
On the other hand, NOCT conditions test solar panels under the following parameters:
Irradiance = 800 W/m2
Wind Speed = 1 m/s
Ambient Temperature= 20°C
Surface Temperature = 45°C
As you can see, there are important differences between STC and NOCT. NOCT conditions represent a more realistic approach than STC because they consider irradiance values of 800 W/m2 and operation temperatures of 45°C in the solar cell.
However, STC is considered as the main reference for sizing PV systems. Power outputs, efficiencies, voltages, and current values are generally referred to STC conditions. The problem lies in the fact that real-world conditions can be very different from STC, therefore solar designers must use technical mathematical expressions to estimate the new values according to real-world conditions.
The Influence of Temperature in Solar Panel’s Performance
Temperature is an environmental parameter that deeply affects the voltage of the PV module. The effect in the power output is also important since the voltage is deeply affected. On the other hand, the effect of temperature in current values is technically negligible.
Low-temperature values rise the voltage in the module, while high-temperature values reduce the voltage of the solar panel. Since power is equal to current multiplied by voltage (P= V*I), low-temperature conditions improve the performance and efficiency of the module, while high temperatures reduce the power output and lead to other thermal losses.
Operation temperatures values of the PV cell change according to ambient temperatures and irradiance values. To estimate the new operating temperature values of the module, solar designers use the expression below, where Ic represents the estimated irradiance on the module.
Then, using this new operation temperature (Tcell), another important parameter must be considered and can be found in any datasheet of any solar panel: the temperature coefficient of voltage. This coefficient indicates the rate at which the solar panel will change its voltage output according to an increase of 1°C in the operating temperature of the module.
Using another expression and this coefficient, it is possible to estimate the new open circuit and maximum power point voltages. This expression can be found below, where is the temperature coefficient of open circuit voltage.
Solar panels under cool temperature conditions are similar to the NOCT temperature value (45°C), however, under hot temperature conditions, operating cell temperatures can reach values as high as 70°C.
How Do Solar Panels Work in Hot Climates?
We have learned that solar panels use solar radiation to generate electricity, but this source of energy has two components: light and heat. Solar panels use the incoming particles of light as the main source of energy to be transformed into electricity, however, the heat component is not used to generate electricity.
Heat is generally associated with high temperatures and high relative humidity. As we discussed above, high temperatures have a negative effect on the performance of the solar panels. Elevated relative humidity values are not good either for PV systems because they can lead to other problems like the presence of moisture, delamination, leakage currents, module degradation, and reduction in current values.
Moreover, if we are installing solar panels in a sloped roof, then another problem arises as well in hot climates. Air circulation behind the module is necessary to keep the module cool and to reduce thermal losses as well.
If the module is too close to the roof, then there is not enough airflow behind it, which also leads to higher temperature values, further losses in power, and reductions in voltage values as well. Ground mounting systems do not have that problem because air flows freely behind the module.
In other words, solar panels can indeed overheat. If your solar panel is overheating, then it will mean a reduction in the efficiency and performance of the module. That being said, it won’t mean that the module will be damaged by the excess of heat.
Solar panels are tested under damp heat tests, which submit the module to 1,000 hours of elevated temperature values such as 85°C with 85% relative humidity. In order for a module to be commercially available, it must pass this test and the thermal cycling test as well, which includes 200 cycles of temperature variations between -40°C and 85°C. As you can imagine, if the solar panel could pass that, then it is unlikely that it will get damaged by the temperature values available in your location.
What to Do if Your Location is Hot
The first thing that you need know is that if your location can reach to ambient temperature values as high as 40°C – 50°C during the summer season, then your solar panels will not perform at high efficiency, and unfortunately, there is nothing you can do about it.
However, there are a few details that you might want to think about when installing the PV system to minimize those losses.
We discussed the influence of temperature coefficients in the solar panel’s voltage. Choosing a solar panel with a high-temperature coefficient in an extremely hot location is an extremely bad idea. Here, it is a duty of the solar designer to pay attention to temperature coefficient values and choose the solar panels that have the lowest coefficients in order to minimize the effect of temperature in the module.
If you are wondering which is the solar panel with the lowest temperature coefficient of the industry, then check the HIT modules from Panasonic (the temperature coefficient is -0.258 % / °C – the lowest of the industry).
Moreover, forget about a rooftop mounting system. In a hot climate environment, you must maximize air cooling, therefore you must install a ground mounting system to allow the module to cool itself as much as possible.
Finally, hot locations are generally attributed with deserts or areas with a lot of dust. Considering the presence of dust, sandstorms, and the impact that soiling factors could have in the energy yields of the PV system, is also important the solar designer of your array takes that into account.