The Importance of Cooling Solar Panels For Improved Performance

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Executive Summary

This covers the necessity of cooling solar panels.

Introduction

One little covered area of solar is the efficiency of solar panels under higher temperatures.

Background on the Relationship Between Heat and Solar Panel Efficiency

This issue is covered well in the following quotations.

The Issue of Performance and Lifespan

Cheap and simple radiative cooling technologies can significantly increase the performance and lifespan of concentrated photovoltaic systems, according to researchers in the US. They found that a simple radiative cooling structure can increase the voltage produced by the solar cells by around 25%. It also reduced operating temperatures by as much as 36 °C and the scientists claim this could dramatically extend the lifetime of photovoltaic systems.

This is a particular issue for concentrated photovoltaic systems. While using mirrors or lenses to focus sunlight on solar cells can boost efficiency, it also increases heating. This can offset efficiency improvements and damage the photovoltaic cells, reducing their lifespan. – Physics World

As can be seen, the issue of solar panel cooling is about more than performance, but also about how long they last.

How Much Efficiency is Lost in Heat?

Commercial silicon-based photovoltaic cells convert around 20% of solar irradiation that falls on them into electricity. Much of the rest is turned into heat, which must be effectively managed. “Photovoltaic efficiency and lifetimes both decrease as temperature goes up – especially in humid environments,” explains Peter Bermel, an engineer at Purdue University. “The loss in efficiency is fundamental to how photovoltaics work.” – Physics World

This explains why it is important to cool solar panels. The cooler the solar panels, the more efficient and the higher output of the panels.

This is also expressed in the following quotation.

Despite many advances in recent decades, solar cells suffer from efficiency problems. Only a small amount of the energy from sunlight that falls on solar cells is converted to electricity, peaking at below 20 percent for most cells on the market today. Overheating is a constant problem because the sunlight used to generate electricity routinely heats up the panels to 130⁰ F (55⁰ C) or higher. – Self Cooling Solar Cells

How High Does The Temperature Have to Get to Reduce Panel Efficiency?

Generally, solar panels drop in efficiency after 77 degrees. However one should remember that this is not 77 degrees in the shade, which is how temperature is measured for weather reporting, so when you check the temperature on your weather app on your phone or computer. That is 77 degrees at the panels.

What this tells us is that in many cases solar panels are running below their efficiency.

Furthermore, while strong sunlight is normally thought to produce more power, as the temperature at the panels increases, this counteracts this power generation.

This is explained in the following quotation.

The reason why this is important is that most solar systems are not actually operating at these temperatures, especially in the hotter months. In fact, it is typical for a rooftop installation to rise 90-degrees above the outside temperature. This increase means that on a hot, 90-degree summer day your solar panels are sitting at closer to 180-degrees. – Understand Solar

That is shocking to learn that there can be such a heat difference and it also explains why panels reduce in efficiency that I have observed with my panels.

Testing The Sensitivity to Temperature

When the temperature was 53 degrees, which is a temperature I normally do not keep the campervan, I found my lithium batteries were floating between 14.5 and 14.6. However, that number is unheard of really. Later in the day, the temperature rose to 61 degrees, and the battery float level went down.

What this tells me is that the optimal temperature for the panels is the temperature of places where I don’t normally keep the campervan.

This means that solar panels are greatly underoptimized due to overheating. I am very surprised that there are no cooling systems that I c could find for portable solar panels. There are some new panels that pull moisture out of the air, but for the existing panels that does nothing. I think a full-time mister with a fan is the best solution.

The Sunbooster System

This explains one solution that has been developed recently (in 2020) but for large solar installations.

French PV system installer Sunbooster has developed a cooling technology for solar panels based on water. It claims its solution can ramp up the power generation of a PV installation by between 8% and 12% per year.

The solution consists of a set of pipes that can surround a rooftop PV system or ground-mounted plant. The pipes are used to spray a thin film of water onto the glass surface of the modules.

The company’s solution is a patented pipe with a number of very small holes, so special installation skills are required. Stored rainwater is pushed into a ramp at the edge of the panels. Water then flows onto the surface of the modules and immediately lowers the temperature.

The system is set in motion by a temperature sensor which triggers the water spread when ambient temperatures exceed 25 C. Although the water may have some influence on the modules’ light absorption, this is fully compensated by the increase in power yield that can be achieved by preventing temperatures from surpassing 30 C, Boutteau said. – PV Magazine

The Standard “Cooling System” Of Solar Panels

Solar panels do not have an active cooling system. However, what they do have can be considered to be passive air cooling. If there is a good wind, this will substantially reduce the temperature of the panels.

What is obviously more desirable is employing water, as water cooling is far more effective than air. Notice that nearly all cars are water-cooled. This improved ability of water to cool versus air is explained in the following quotation.

Water is the liquid that have the highest specific heat (heat capacity) among all common liquids which means that it needs much more energy than other liquids for its temperature to rise by one degree

That’s why its being used in almost all waste heat recovery systems industrially as well as being the most common cooling media industrially plus that it is used to generate power by heating the water into steam that eventually turns the steam turbines and generates electricity.

If you were asking about a number, the specific heat of water is 4.18 KJoule/Kg C which means you need 4.18 Kilo Joules to cause a temperature rise of one degree celcius for a kilo gram of water, to put things in perspective you only need 3.58 Kilo Joules to cause a temperature rise of one degree celcius for a kilogram of copper. – New Atlas

The Issue to Be Overcome to Provide a Solution

There are a number of engineering challenges, and cost challenges that would be necessary to provide a solution to solar panel overheating. However, the power generation lost to overheating is substantial, except in the winter months in the US. But fundamentally, any solution would need to consume substantially less power that it increases the efficiency of the panels and be low maintenance.

Conclusion

It is somewhat amazing how little discussion there has been over the importance of cooling solar panels. Not many people that use solar panels are aware of this issue or the magnitude of the issue.

Solar panels are tested, have their ratings assigned under air-conditioned conditions, and use low heat lights to measure the performance of the panels. These conditions have nothing to do with real-world conditions.