Do Solar Panels Work on Cloudy Days?
The short answer is yes, solar panels do work when it's cloudy, but they don't make as much power. The output of most panels drops by 10 to 25 percent when clouds block the sun. Even though this is a big drop, it doesn't mean that cloudy days are useless for solar cells. If solar is a good investment for your house, you should look at how much sunlight your area gets overall, not just on cloudy days.
How Solar Panels Work in Different Weather Conditions
The Solar Cell Conversion Process
Photovoltaic cells, which are mostly made of silicon, turn sunlight into power in solar panels. When sunshine hits these cells, it makes electrons move around, which makes an electric current. Any light that hits the panels will make some electricity, so the process doesn't need bright, direct sunlight to work. Each panel has a circuit with cells that are attached to each other. Several panels are linked together to make your home's solar system.
Sunlight Penetration Through Cloud Layers
Clouds don't completely block the sun; instead, they work as filters. Up to 80% of the sun's rays can still reach the Earth's surface, depending on how thick the clouds are. Some thin, high clouds may only block a small amount of light, but thick storm clouds block more light. Interestingly, sometimes cloudy weather can increase solar output. This happens because of something called the "edge effect," which means that sunlight bounces off the edges of clouds and briefly increases the amount of radiation that reaches your panels.
Two Types of Light That Power Your Solar Panels
Solar panels work with two types of solar radiation:
Direct radiation comes straight from the sun without interference. This provides maximum energy for your panels and dominates on clear days.
Diffuse radiation occurs when sunlight scatters through clouds, dust, or the atmosphere. While less powerful than direct sunlight, modern solar panels effectively capture this scattered light. On cloudy days, nearly all the energy that reaches your panels is diffuse radiation.
The solar technology we have now can change both types of light, but not all of it is as efficient as others. Most of the time, high-efficiency panels work better with scattered light, which makes them good choices for places where clouds are common. This ability to do two things at once is why solar systems work even in places that don't get a lot of sun.
Solar Panel Efficiency: Sunny vs. Cloudy Performance
Measured Output Drops on Cloudy Days
Solar panels produce significantly less electricity when clouds block the sun. According to a study conducted at the University of Port Harcourt, Nigeria (tropical climate region), there was a 23.80% loss in power output of a 250W monocrystalline solar module due to light cloud cover and a 66.75% loss in power output due to heavy cloud cover, when compared to the fully illuminated solar module. With light cloud cover, the solar module maintained 76.20% of its normal output, while during heavy cloud cover, the module generated only 33.25% of its rated capacity.
Why Efficiency Varies Under Different Conditions
Several factors directly cause performance differences between sunny and cloudy days:
Panel technology affects light absorption: Monocrystalline panels capture 15-20% more energy from diffuse light than polycrystalline panels because their cell structure better converts indirect sunlight.
Light quality changes: Clouds filter out certain light wavelengths while allowing others to pass through, changing the available light spectrum. Panels can convert to electricity.
Inverter efficiency drops with low input: When clouds reduce panel output below certain thresholds, inverters operate less efficiently, further decreasing overall system performance.
Weather-Specific Performance Data
A typical 6kW residential system generates approximately:
30 kWh on a clear, sunny summer day
15-21 kWh during partial cloud cover (50-70% optimal)
3-7 kWh during heavily overcast conditions (10-25% of optimal)
The impact varies by cloud type: thin, high clouds might reduce output by only 20-30%, while dark storm clouds can drop production by over 90%. These figures represent general estimates, and actual output may vary depending on various factors.
Solar Panel Performance in Different Geographical Regions
Annual Solar Production Across Major Climate Zones
While daily weather patterns affect short-term production, annual regional differences tell the complete story. A 10kW system installed in different locations produces dramatically different yearly totals:
16,500 kWh in Phoenix (desert climate)
13,400 kWh in Denver (high-altitude continental climate)
11,000 kWh in Chicago (continental climate)
9,500 kWh in Portland, Maine (humid continental climate)
8,900 kWh in Seattle (marine west coast climate)
Despite these variations, solar remains viable across all these regions when systems are properly sized for local conditions.
Geographical Factors Beyond Cloud Cover
Several geographical elements affect solar performance beyond just cloud frequency:
Latitude: Higher latitudes generally receive longer summer days but less intense sunlight compared to lower latitudes, impacting solar performance in complex ways.
Elevation: Solar radiation typically increases with elevation, but the exact effect varies depending on atmospheric conditions.
Regional humidity levels: Dry climates often allow more sunlight to reach panels even on partly cloudy days compared to humid regions, but the difference is hard to quantify universally.
Local terrain reflectivity: Snow cover, water bodies, or light-colored surroundings can provide additional reflected light to panels, potentially boosting production, especially in snowy northern regions during winter.
The influence of these factors on solar performance is complex and location-specific, requiring careful assessment based on local conditions.
How to Assess Your Location's Solar Potential
When evaluating whether solar makes sense in your region despite cloud frequency:
Check local production data: Look at actual generation from existing systems in your area rather than relying on general climate assumptions.
Understand cloud patterns: Some regions have predictable cloudy seasons followed by clearer periods, allowing for effective annual production planning.
Calculate sun hours accurately: Many cloudy regions still receive 4-5 hours of effective sunshine daily when averaged across the year.
Consider electricity rates: Higher local electricity costs often make solar viable even in cloudier regions with somewhat lower production.
This regional perspective explains why solar successfully operates in places often considered too cloudy, as total annual production, not daily weather fluctuations, determines overall system viability.
Are Solar Panels Worth It in Cloudy Regions?
Yes, Solar Can Still Pay Off
Even in cloudy locations, solar panels are profitable. In overcast areas, systems pay for themselves in 8-12 years, versus 5-8 in sunny areas. Solar panels last 25 years, so you'll have free electricity for years after breaking even.
Cloudy regions in the Northeast and Northwest have higher electricity prices, offsetting reduced production. Solar electricity saves money when you pay more per kilowatt-hour.
Cloud coverage can be improved by adding a larger system. To match sunny places, cloudier homeowners need 20-30% more panels. This is more expensive initially but valuable long-term.
What Helps Make Solar Affordable?
No matter the weather, several things boost solar economics. The 30% federal tax credit cuts costs equally in sunny Arizona and dreary Michigan. It essentially covers the expense of more panels in less sunny areas.
Net metering allows you to utilize excess energy on overcast days and receive credit on sunny days. In locations with seasonal weather, this is helpful.
Many states with less sunshine give local incentives to boost solar adoption, knowing that these areas need more money to make solar attractive.
FAQs About Solar Panels on Cloudy Days
Do solar panels work with moonlight?
Solar panels detect moonlight but generate little electricity. Reflected sunlight at 1/400,000th the intensity of direct sunlight is moonlight. The light registered by solar cells is too little for practical application, usually less than 0.1% of the panel's daytime capacity. This can't fully charge batteries or power household devices.
How much will a 100-watt solar panel output on a cloudy day?
Under heavy clouds, a 100-watt solar panel produces 10-25 watts. The same panel may generate 30-70 watts under partial cloud cover. Cloud density, time of day, and panel technology determine output. Standard panels may produce less than high-efficiency monocrystalline or PERC panels.
Do solar panels work with room lights?
Indoor lighting can be converted to power by solar panels, although at poor efficiency. Panels capture natural sunlight's intensity and spectrum, unlike standard home lighting. Under room lighting, a solar panel may yield less than 5% of its rated power, which is insufficient for practical use. Indoor solar cells for low-power devices differ from home solar panels.
Check Your Home's Solar Panel Potential!
Solar panels can still work on dark days, but they only work 10 to 25 percent as well. Even though the output has gone down, solar systems can still work in many cloudy areas thanks to advanced panel technologies, low energy costs in those areas, and tax breaks. The most important thing is not just the weather where you live, but also your unique situation, such as the shape of your roof and how much energy you need. For an accurate assessment, talk to solar pros in your area. They can look at your specific situation and figure out your potential returns based on the sun, clouds, and incentives that are available in your area.