How Do Solar Panels Work on Cloudy or Rainy Days?

One of the most common concerns about installing solar power on a home from people is the thought that they live in an area that is too cloudy or receives too much precipitation for solar panels to be effective. This is particularly a concern for homeowners in colder areas or areas of high rainfall. 

The myth that solar panels don’t work unless the sky is sunny and blue is a fairly common one. However, the reality is that solar panels work quite well even on cloudy and rainy days. While knowing this is useful, it can still be confusing. After all, it makes sense that solar panels would operate best in direct sunlight, right? Let’s take a look at how solar panels function even when it's cloudy and why cloudy weather isn’t necessarily a deterrent to the value of solar panels. 

Solar Panels in Cloudy or Rainy Weather

We’ve noted that cloudy weather seems as if it would not be ideal for solar panels. The reality is that cloudy or rainy weather does reduce the effectiveness of solar panels; however, they are still able to generate power. This requires thinking a bit about how solar panels function to generate power. 

Solar panels take in sunlight and convert it to direct electrical current (DC electricity). An inverter is then used to take the direct current and transition it into alternating current (AC electricity), which is what homes run on. When solar panels generate more power than can be used, the excess power can be stored in a battery or transferred to the electric grid via a process called net metering. 

Thus, in times when solar panels do not produce power (like night), power is used either from the batter (if a home has one) or from the standard electrical grid. For homes with net metering, which has rules that vary by state and power company, excess solar power supplied to the grid is calculated and used as a credit against your actual utility usage. 

Additionally, it is important to realize that solar panel design has improved dramatically in the past few decades with technological improvements. They have been specifically designed in ways to prevent the effects of shading from causing all energy production to cease. 

What does all this have to do with the functioning of panels in cloudy or rainy weather? The process that solar panels use to generate electricity still functions even during these days, just at a less efficient rate. It is estimated that solar panels produce approximately 25% of their typical output on cloudy or rainy days. Thus, if you use a lot of power, you may pull a bit from your electrical grid during these days. If you use less power, your panels may produce plenty. 

This is because even if it isn’t sunny, sunlight is still getting through, albeit in lower amounts and a less direct manner. After all, look around on a cloudy day. It may be cloudy and dreary, but you can still see fairly well. That’s because sunlight is still penetrating the clouds. In fact, have you ever been outside for a long time on a cloudy day and gotten a sunburn? Again, the sunlight is coming through even if it isn’t as bright. 

Solar panels function differently in a lot of different climates. However, they are also effective in nearly all climates. For example, it often surprises people to learn that solar panels are most efficient in sunny cold climates, outperforming even sunny warm climates. When encountering rainy days, there is also a bit of benefit for solar panels. The rain serves as a natural cleanser, washing away particles and dirt that may have accumulated on the surface of the panels. This keeps panels functioning at optimal efficiency and reduces the frequency that they need to be manually cleaned. 

Will Solar Panels be a Good Investment in a Cloudy Climate?

This is an important question. After all, one of the great things about solar panels is that they are environmentally friendly. However, the major driver for most people adding them to their homes is that they save money. Even though solar panels work on cloudy days, they are most effective when in direct sunlight. What if you live in a climate that gets fewer hours of annual direct sunlight? Does this mean solar panels are not a good investment? 

In reality, the factor that most influences the efficiency of solar panels is the hours of annual direct sunlight while the factor that most influences the value of solar panels is the cost of electricity. For example, let’s take a look at New York City versus Phoenix. New York City gets an average of 2,656 hours of sunlight per year compared to 3,870 hours in Phoenix. In other words, Phoenix gets 45.7% more sunlight than New York City. 

Now, let’s look at the cost of electricity. In New York City, the cost of electricity is approximately $0.18 per kilowatt-hour. By contrast, the cost of electricity in Phoenix is $0.09 per kilowatt-hour. This means that electricity costs 100% more in New York City than in Phoenix.  Thus, even though Phoenix has 46% more sunlight, solar power actually yields greater financial benefits in New York City than it does in Phoenix. 

In fact, more evidence for this reality can be gleaned by taking a look at the top cities for solar power in terms of annual savings on electricity. Among the top ten cities are places like New York, Philadelphia, and Denver, three areas that see a lot of cloudy days. Not far out of the top ten are Boston, Omaha, and Detroit, all places that get a lot of snow each winter. 

Furthermore, when looking at solar power around the globe, it is interesting to learn that Germany produces 25% of the world’s solar energy despite having a climate known for having extremely cloudy winters. Thus, while cloudy days limit the effectiveness of solar power, they don’t necessarily limit the financial benefits.