How Does Solar Work On Overcast Days?

March 11, 2021

Our company is based in the Northeast, which many people would say is “gloomy” and grey all winter. Does this climate negatively affect the performance of solar panels? The quick answer is: solar panels work great in overcast weather. The efficiency rating of your panel is really what matters when it comes to cloudy weather performance.

What are some cloudy day solar myths?

Before we get into the efficiency of your panels and solar system, let’s dispel some common myths about solar panels and cloudy days.

  • Solar DOES work in overcast areas and during the winter months. Solar works great in locations known to be cloudy such as Connecticut, New York, Seattle or San Francisco. We help customers save money every day by going solar. Your electric bill savings are not determined by the number of cloudy days but by the local cost of electricity.
  • Solar works well even when it is cooler outside. Solar actually works best in cool environments, with their optimum operating temperature below 77 degrees.
  • If one panel is shaded, the whole system still operates normally. In conventional DC systems, partial shade does decrease the amount of energy that will be produced and all panels act shaded together. The entire array is “strung” together and acts as one giant panel. In a SunPower AC system, each panel works independently from the rest through SunPower microinverters. If one panel is shaded, the rest of the panels in your array operate and produce energy normally.

So, what is the effect of clouds on my system?

Solar panels use solar radiation produced by the sun to generate energy. However, anyone who has ever been sunburned on a cloudy day knows that solar radiation is still strong regardless of clouds! Typically the average reduction of solar panel performance during non-sunny days is between 10 and 15 percent.

Is this significant enough to have New Englander’s worried?

Conventional panels are around 16 percent efficient: this means that if they drop 10-15 percent, you could be in big trouble in the winter! Generally, conventional solar companies will combat this by filling your roof with more panels to ensure that your electricity is covered in the winter. However, even if you fill your roof with panels there is no guarantee that they will produce during a cloudy forecast – if one panel is shaded in a DC system, the entire array will act shaded and under-produce.

Here’s where SunPower panels shine: SunPower panels have an efficiency of 22 percent, the highest performing panels on the market. The Maxeon cells used on SunPower panels are able to capture a broader range of the sun’s wavelengths. The cells have a backside mirror that bounces light photons not absorbed the first time around back through the cell to ensure that even on overcast days, your panels capture as much light as possible.

At SAVKAT we build out every system in-house to cover your electric needs year-round, and we take into account the local and regional statistics as well as shading from a 12-month period. We guarantee our estimated production and are usually spot on with our numbers.

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