An increase in hot temperatures can mean a decrease in solar panel efficiency.

Because solar energy comes from the sun, you may be under the impression that heat would be great for your solar panels. The truth is, too much heat can actually lower your panels’ efficiency. The solar panels are getting blasted by so much energy, they cannot take it all in. On top of that, when electronics heat up, they don’t work as well as though should. This is because more of that electricity gets lost as heat. The optimal temperature for solar to operate under is 77 degrees Fahrenheit or 25 degrees Celsius. When you move 10 or 15 degrees away from that optimal temperature, either hotter or colder, the efficiency starts to drop. They are still efficient enough to completely power a home on the hottest day, they just aren’t as efficient.

Testing panels for the heat.

Home solar panels are tested at 25 degrees C or 77 degrees F, and thus the temperature of your solar panels will generally range between 15 degrees C and 35 degrees C during which solar cells will produce at maximum efficiency. However, solar panels can get as hot as 65 degrees C, and if they do, solar cell efficiency will be hindered. Factors such as how close the panels are installed to the roof can impact the average heat of your solar system.

The majority of solar panels are composed of silicon photovoltaic cells, that’s shielded by the glass and held with a metal frame. Those materials are comparable to the materials that make up the windows and frame of a car. When you want to understand how hot solar panels can get, think about a car that’s been sitting in a hot parking lot on a summer day. While the outside of the car will be hot if you touch it, you won’t be at risk of getting any serious burns or injuries from the hot windows. The actual temperature of your solar panels at different times during the day varies significantly depending on air temperature, how close you are to the equator, level of direct sunlight, and roof material.

Increased heat causes a decrease in the output of power.

The rules of hot electronics apply the same way to a hot solar panel, which is that an increase in heat decreases the output of power. This is because of those tricky laws of thermodynamics. Thus, warmer temperatures will always mean less output for solar cells, and this loss is quantified in a “temperature coefficient" by panel manufacturers, which varies from model to model.

Manufacturers rate their products’ susceptibility to a temperature in the form of the temperature coefficient, which is expressed as a percentage per degree Celsius. It is standard practice to test solar panels for power output at 25 degrees C. So, if a panel is rated to have a temperature coefficient of -0.50 percent per degree of Celcius, that panel’s output power will decrease by a half of a percent for every degree the temperature rises about 25 degrees C (77 °F). Although that number sounds small, the surface temperature of a dark-colored roof in the summer can be significantly higher than 25 degrees C.

While the loss of efficiency may seem small when just looking at it based on a percentage, when you consider how it compounds, it’s a lot more than it seems like. Here’s an example: if you have solar panels with an efficiency rating of 17 percent and a temperature coefficient of -0.45, they will lose 0.45 percent of their efficiency for every degree above 25 degrees C. If the surface temperature of your roof increases to 30 degrees C (86 degrees F), your solar panel’s efficiency will fall to 16.7 percent. If it increases to 35 degrees C (95 degrees F), efficiency falls to 16.3 percent.

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