What Happens to Solar Panels on Cloudy or Rainy Days

If you’re considering solar for a home in a region that doesn’t see sunshine year-round, this is probably one of your first questions: do solar panels even work when it’s cloudy or raining? The short answer is yes, they keep producing electricity, just less of it. Here’s a closer look at exactly how weather affects solar output, and what that means for your overall system planning.

Solar Panels Don’t Need Direct Sunlight to Work

A common misconception is that solar panels only work under clear, direct sunlight. In reality, panels generate electricity from any daylight, including the diffused sunlight that passes through clouds. This is the same reason you can still get sunburned on an overcast day — UV rays and visible light still reach the ground even when the sun itself is hidden.

That said, cloud cover does reduce output, sometimes significantly, because it scatters and absorbs a portion of the sunlight before it reaches your panels.

How Much Output Drops on a Cloudy Day

The reduction in output depends heavily on how thick and dense the cloud cover is:

• Light or thin clouds: Output might drop by roughly 10-25% compared to a clear day.
• Moderate, overcast conditions: Output can drop by 40-60%.
• Heavy, dark storm clouds: Output can drop by 70-90%, though panels are still generating some electricity even under the darkest conditions short of nightfall.

Interestingly, there’s a well-documented phenomenon where certain types of partial cloud cover, specifically when bright sunlight reflects off the edges of nearby clouds, can briefly cause output to spike slightly above what you’d see on a completely clear day. These moments are short-lived and don’t meaningfully change overall daily production, but they illustrate that cloud effects on solar aren’t always a simple, linear reduction.

What Happens During Rain

Rain itself doesn’t damage solar panels or stop them from working; panels are designed and tested to handle rain, and are typically rated for a wide range of weather conditions. In fact, rain can provide a modest side benefit: it helps rinse dust, pollen, and debris off the panel surface, which can slightly improve performance in the days that follow compared to a long dry spell where dust has built up.

The main effect of rain on output comes from the cloud cover that typically accompanies it, not the rain itself. A light rain shower with thin cloud cover will have a much smaller impact on production than a dense, dark storm system.

Snow, Fog, and Other Weather Considerations

Since we’re talking about weather’s effect on solar, it’s worth quickly covering a few related conditions homeowners often ask about:

Snow can temporarily cover panels and block production entirely until it melts or slides off. Most panels are installed at an angle that helps snow slide off relatively quickly, and the panels’ own slight warmth from any sunlight hitting them often accelerates melting. In snowier climates, this is a normal seasonal factor that installers account for when projecting annual output.

Fog behaves somewhat like thin cloud cover, scattering light and reducing output, though usually less severely than dense storm clouds.

Extreme heat, somewhat counterintuitively, can actually reduce panel efficiency slightly. Panels are tested and rated at a standard temperature, and very high heat can cause a small dip in output, which is one reason the sunniest, hottest regions don’t always produce proportionally more energy than moderately warm, sunny regions.

Why This Doesn’t Break the Math on Solar Savings

If your region gets a fair amount of cloudy or rainy weather, it’s natural to wonder whether solar still makes financial sense. The good news is that solar installers don’t calculate your projected savings based on clear-sky days alone. Professional system sizing and production estimates already factor in your location’s actual historical weather patterns, using data collected over many years to model realistic annual output, cloudy days included.

This is why a home in a place like Seattle or Portland, which sees considerably more cloud cover than Phoenix, can still generate meaningful solar savings. The system is simply designed with local weather patterns in mind, whether that means a slightly larger system to compensate for lower average production, or realistic savings projections that already account for a certain number of low-production days throughout the year.

Cloudy-Day Production Still Counts Toward Your Bill

It’s worth remembering that even a cloudy day producing, say, 30% of a clear day’s output is still contributing real savings. Over the course of a year, your system’s total production reflects a mix of very sunny days, moderately cloudy days, and the occasional heavy storm, averaging out to the annual output your installer projected. A stretch of rainy days doesn’t erase your solar savings; it simply means those specific days contribute less than a sunny stretch would.

What This Means for System Sizing

If you live somewhere with significant cloud cover for part of the year, this is exactly the kind of detail a good installer should already be factoring into your system design. This might mean:

• A system sized somewhat larger than it would be in a consistently sunny climate, to make up for lower average daily output.
• Realistic month-by-month production projections rather than a single flat annual average, since cloudier seasons will show noticeably lower expected output than sunnier ones.
• For homeowners especially concerned about outages during storms (when cloud cover and bad weather often coincide), this is also a relevant consideration for whether a battery makes sense.

The Bottom Line

Solar panels keep producing electricity on cloudy and rainy days, just at a reduced rate depending on how thick the cloud cover is. Rain itself doesn’t harm panels and can even help keep them clean. Because professional solar installers already factor local weather patterns, including cloudy and rainy days, into their production estimates, cloudy weather is far less of a dealbreaker for solar viability than many homeowners initially assume. What matters most is getting a realistic, location-specific production estimate rather than assuming your region’s weather rules out solar altogether.