How Hot Do Solar Panels Get? Effect of Temperature on PV Panel Efficiency
Imagine one of those searing hot days when all you can do is to sip a margarita somewhere in the shade. How would you perform on a day like that if you were asked to run a marathon? Not that well, right? Our body functions the best when the temperature is within our optimum range. Beyond this range we have to work much harder to maintain our performance level.
As surprising as it may sound, the same principle applies even to photovoltaic solar panels and their capacity to generate electricity!
The effect of temperature on PV solar panel efficiency
Most of us would assume that stronger and hotter the sun is, the more electricity our solar panels will produce. But that’s not the case. One of the key factors affecting the amount of power we get from a solar system is the temperature. Although the temperature doesn’t affect the amount of sunlight a solar cell receives, it does affect how much power is produced.
Solar cells are made of semiconductor materials, like the most used crystalline silicon. Semiconductors are sensitive to temperature changes. Temperatures above the optimum levels decrease the open circuit voltage of solar cells and their power output, while colder temperatures increase the voltage of solar cells.
The output of most solar panels is measured under Standard Test Conditions (STC) – this means a temperature of 25 degrees Celsius or 77 degrees Fahrenheit. The test temperature represents the average temperature during the solar peak hours of the spring and autumn in the continental United States .
According to the manufacture standards, 25 °C or 77 °F temperature indicates the peak of the optimum temperature range of photovoltaic solar panels. It is when solar photovoltaic cells are able to absorb sunlight with maximum efficiency and when we can expect them to perform the best.
The solar panel output fluctuates in real life conditions. It is because the intensity of sunlight and temperature of solar panels changes throughout the day. What interests us in this case is how does the temperature affect solar panel efficiency in real life. Let’s break it down.
What happens when the temperature of solar panels increases?
If you have photovoltaic solar panels installed at home or plan to get some in the near future, it’s useful to have a good understanding about the difference between the energy of electrons at a low energy state and electrons in the excited state, because this difference accounts for the power output produced by solar panels.
In a solar cell, you can find electrons bound at a low energy state. When these electrons receive extra energy, they enter a new state – known as the excited state – which allows them to break the bond and move. Electrons in the excited state can participate in conduction. The extra energy that elevates them to the excited state comes from two different sources – from light (sunlight) or from heat.
How much power is produced by a solar cell depends on how big is the energy difference (voltage) between these two states. Increase in temperature affects the semiconductor material parameters by increasing the energy of bound electrons. This means that the energy difference to achieve the exited state is smaller, which results in reduced power output and efficiency of solar panels .
When solar panels absorb sunlight, their temperature rises because of the sun’s heat. The common material used in solar cells, crystalline silicon, does not help to prevent them from getting hot either. As a great conductor of heat, silicon actually speeds up the heat building in solar cells on hot sunny days.
In a nutshell: Hotter solar panels produce less energy from the same amount of sunlight.
Luckily, the effect of temperature on solar panel output can be calculated and this can help us determine how our solar system will perform on summer days. The resulting number is known as the temperature coefficient.
Solar panel temperature coefficient
The temperature coefficient tells us the rate of how much will solar panel efficiency drop when the temperature will rise by one degree Celsius (1.8 °F).
For example, when the temperature coefficient is minus 0.5 percent, it means that efficiency decreases by 0.5 percent for every degree above 25 °C (or every 1.8 degrees above 77 °F).
Solar panels from different manufacturers will vary in their temperature coefficients. That is why all solar panel manufacturers provide a temperature coefficient value (Pmax) along with their product information.
In general, most solar panel coefficients range between minus 0.20 to minus 0.50 percent per degree Celsius. The closer this number is to zero, the less affected the solar panel is by the temperature rise.
If you want to find out which solar panels have the best temperature coefficient available today, we recommend checking out our recent report on the best solar panels for home use.
How hot do solar panels get? Can they overheat?
The maximum temperature solar panels can reach depends on a combination of factors such as solar irradiance, outside air temperature, position of panels and the type of installation, so it is difficult to say the exact number.
Generally, solar panels are made of dark-colored silicon cells (black or dark blue), covered by a sheet of glass and framed in metal.
Silicon and metal are good conductors of heat, contributing to faster buildup of heat inside solar cells. Even though, solar panel manufacturers and installers apply mechanisms to prevent solar panel overheating, in extremely hot conditions, the energy output of solar panels might decline significantly.
In summer 2017, The Times published an article discussing the problem of Qatar being too hot for photovoltaic solar panels. According to the article, the combination of temperatures rising up to 50 °C (122 °F) with dust reduced solar panel power output down to less than 40 percent.
What can you do to stop your panels from getting too hot?
Being aware of the effect higher temperature has on the energy output, most certified installers take steps to support natural cooling of solar systems.
A good practice for maximum efficiency is leaving at least a six-inch space between roof and panels to allow air circulation from both sides. But attaching your panels too far from the roof is not always a good idea. If the gap is too big, debris of leaves and twigs could accumulate underneath the array and cause damage to your roof or panels.
If you live in a hot climate, you should consider ground-mounted solar panels, because this way they get the most airflow to keep their temperature lower.
According to estimates, the temperature difference between the ground-mounted and roof attached solar panels can make up to 10 °C (50 °F) at the same location .
The best option is to get solar panels with temperature coefficient as close to zero as possible. The difference in total power output throughout the year can be significant.
For example, if your solar panels have a coefficient of minus 0.4 percent, their output on hot days will drop nearly twice that much compared to the output of a panel with a coefficient of only minus 0.2 percent per one degree Celsius.
White or light-colored roofing also helps to lower the temperature around your panels, since these colors reflect sunlight more and do not get heated up like dark roofing.
While above mentioned points involve passive cooling methods, some people opt even for active cooling systems.
For example, fans that blow air over panels, or circulating cold water which absorbs the heat from the panels and is then utilized in the household for showering or heating the building .
A side note: Be cautious about hosing down your panels during the hottest part of the day! It could make the glass crack and irreversibly damage your solar panels. The systems with water cooling do not expose solar panels to such a sudden temperature shock like you hosing them down would.
How does cold temperature affect solar panel output?
You may have heard people doubting solar panel performance in cold weather. Some may even think that solar panels stop working when it’s freezing outside. None of these statements is true.
Solar panels actually love colder temperatures on sunny days. The open circuit voltage produced by solar cells on cold days increases and may rise even 20 percent above the values obtained during the standard testing at 25 degrees Celsius. This means that solar panels will produce more power in an hour during the cold and sunny weather. The problem comes with the monthly production.
On average, photovoltaic solar panels still produce up to 80 percent more energy during the summer months than in winter. The main reasons are (as you may have guessed) shorter periods of sunlight per day and more days with heavy clouds in winter. It is the sunlight energy that is limited in winter, not temperature.
The angle of solar panels affects how well will solar cells utilize the sunlight. In winter, the sun is lower in the sky and sunlight is diffused over a larger area, whereas in summer, the sunlight hitting your solar panels is more concentrated. In order to get the best energy output in winter, the angle may need some adjustments to capture more light. In general, solar installers recommend 45 degrees angle. This angle also helps to prevent snow buildup on the panels.
Additional negative factors, reducing efficiency of solar panels in winter, are snow and ice. Solar panels are resistant. They do not get easily damaged by ice. It just takes some time for solar cells to defrost after a freezing night. During the time when the first sun rays shine on your solar panels, their efficiency is reduced, as the ice or snow blocks some of the sunlight that hits them. The time of unobstructed sunlight is then shorter, and you will get overall less power in winter months.
Before you decide on a solution that would work the best for you, do your research well. As you can see, there are already options to perform under different conditions and some help you to save money – even on production of warm water.
If none of them look appealing to you at the moment, do not despair. We live in the era of an amazing development in the solar energy industry.
Just as we speak many scientists are working on tackling issues of solar panel efficiency and performance optimization.
Scientists from the Stanford University have already pioneered a concept of “self-cooling” solar cells, which will be able to re-direct the heat from the cell’s surface. This design might be just one of many future solutions to tackle the problem of solar cell overheating.
So, let’s enjoy this solar revolution.