Why Solar Panel Temperature Really Matters

here is a common misconception that hot locations are best suited for solar installations. The cause is easy to trace: hot climates are rightly associated with abundant sunshine, which is the main requirement for the efficient operation of solar panels. However, things are a little more complicated.

Is hot weather better for solar?

While this may seem surprising, photovoltaic panels perform worse in heat. This means finding the optimal location for solar is all about striking a balance between the amount of sunlight (the largest possible) and the air temperature (fairly moderate). Below, we’ll look into why solar panels temperature matters and how much it affects their performance.

Why is high solar panels temperature inadvisable?

To answer this question, we’ll have to quickly run through some of the very basic operating principles of PV panels. As you might already know, the panels we regularly see on the rooftops consist of smaller devices called solar cells. In most cases, they are made of two layers of silicon: p-type (positively charged) and n-type (negatively charged). The p-type layer is made by including atoms with one less electron than silicon, such as boron or gallium. Meanwhile, the n-type layer is made by doping silicon with atoms that have one more electron, most commonly phosphorus. This difference in charges creates an internal electric field.

As soon as the light reaches the surface of the solar cell, it energizes electrons within it. Then the electric field forces them to flow around the circuit, generating an electric current. This phenomenon is known as the “photovoltaic effect.”

So what happens if PV panels heat up? When solar cell temperature goes beyond a certain level, it reduces the bandgap -  the minimum energy needed to knock the electrons out of their regular positions. Therefore, the energy of the electrons rises, and less energy is required in order to set them in motion. The number of electrons in the excited state increases, thus reducing the voltage that the cell can generate.

How much worse do solar systems perform in heat?

You don’t need to worry that high solar panels temperature will lead to permanent damage. They are usually designed to withstand extreme weather conditions, including heat up to 85 degrees Celsius. However, during the hot days, the efficiency will inevitably drop.

Before entering the market, most PV modules are tested under Standard Test Conditions (STC), which include solar panels temperature of 25 degrees Celsius or 77 degrees Fahrenheit. When the temperature rises above this level, the performance of the panels starts decreasing. Depending on location and panel type, their efficiency can drop by 10% to 25%.  

What is the ‘temperature coefficient” of solar modules?

Suppose you live in a hot location where the air temperature is often higher than 25 degrees Celsius. In that case, you will likely want to choose the most heat-tolerant solar panels available.

The key parameter showing solar panel temperature efficiency can be easily found in a specification sheet; it is called the temperature coefficient of the maximum output power (Pmax). It is the percentage decrease in electricity output for each increase in degree over 25 °C. However, keep in mind that we're talking about the solar panels temperature, not the air temperature.

For example, the temperature coefficient of a solar panel is -0.5% / °C per 1 degree Celsius. This means every one-degree increase in solar panels temperature above 25°C will result in a half-percent decrease in efficiency.  

Generally, monocrystalline panels are known for performing better in heat; the temperature coefficient of conventional mono-Si PERC modules typically ranges between -0.35 and -0.40 % /°C. Meanwhile, the panels based on newer monocrystalline technologies do even better: IBC modules have a Pmax of -0.28 to -0.31 % /°C, and HJT options boast a coefficient of 0.25 to 0.27 % /°C.

In contrast, polycrystalline solar panels are slightly less heat-tolerant, with a temperature coefficient ranging from -0.39 to -0.43 % /°C. But that said, the gap between the two types of crystalline panels in terms of resistance to heat narrows as photovoltaic technologies develop.

Of all residential PV options, thin-film panels offer the lowest temperature coefficient on the market. For example, Cadmium telluride (CdTe) modules have an average Pmax of -0.21 %/ °C, while amorphous silicon (a-Si) alternatives reach -0.13 %/°C. Therefore, thin-film panels can be considered the best solar choice for hot climates.

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How to avoid solar panel overheating?

Unfortunately, your PV system will inevitably lose some efficiency if the temperature rises above standard levels. However, there are a few ways to maximize solar panel temperature efficiency. Following are a few tips on how to keep solar panels cooler.

• If you live in a hot climate, you should go for solar panels with white backsheets. All-black panels are definitely more aesthetically pleasing, but their black backing absorbs more light and converts it into heat, thus increasing solar panels temperature.
• Install panels a few inches above the roof not to restrict the cooling airflow between the roof surface and the panel system.
• Explore some new PV panel cooling technologies coming to the market. For example, researchers have recently developed a spraying water system that reduces solar panels temperature. They claim the system is suitable for residential use and can increase the maximum output by up to 1%.

Wrap-up: heat is bad for solar panels, but premium models are less affected

Ultimately, hot weather wouldn't do any good for solar. Quite the opposite, the power output of solar panels will drop with every degree above 25°C.

The metric indicating the magnitude of the decline is called the temperature coefficient – make sure to check the solar panel spec sheet for it. If your location often experiences intense heat, opt for monocrystalline PV modules with a lower coefficient to minimize power losses.

Sources:

https://www.greentechrenewables.com/article/how-does-heat-affect-solar-panel-efficiencies

https://www.pv-magazine.com/2022/01/18/spraying-water-system-for-solar-module-cooling/